Systems and methods for enhanced rf mimo system performance

Description of equivalent WO 2013181219 A2

SYSTEMS AND METHODS FOR ENHANCED RF MIMO SYSTEM PERFORMANCE

FIELD OF THE INVENTION

The present invention relates generally to the field of radio frequency (RF) multiple-input- multiple- output (MIMO) systems and in particular to systems and methods for enhanced performance of RF MIMO systems using RF beamforming and/or digital signal processing.

BACKGROUND OF THE INVENTION

Prior to setting forth a short discussion of the related art, it may be helpful to set forth definitions of certain terms that will be used hereinafter. The term "MIMO" as used herein, is defined as the use of multiple antennas at both the transmitter and receiver to improve communication performance. MIMO offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. It achieves this goal by spreading the same total transmit power over the antennas to achieve spectral multiplexing that improves the spectral efficiency (more bits per second per Hz of bandwidth) or to achieve a diversity gain that improves the link reliability (reduced fading), or increased antenna directivity.

The term "beamforming" sometimes referred to as "spatial filtering" as used herein, is a signal processing technique used in antenna arrays for directional signal transmission or reception. This is achieved by combining elements in the array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity.

The term "beamformer" as used herein refers to RF circuitry that implements beamforming and may include a combiner, switches controllable phase shifters, and in some cases amplifiers.

The term "Receiving Radio Distribution Network" or "Rx RDN" or simply "RDN" as used herein is defined as a group of beamformers as set forth above.

The term "Spatial Multiplexing" as used herein applies to the technique where different MIMO signals streams are transmitted from multiple antennas. Each of these signals is from a set of data streams that is transmitted in a manner (e.g., different pre-coding) to ensure low channel correlation among data streams at the receiver Spatial Multiplexing may be employed in conjunction with beamforming.

The term "autonomous" as used herein describes a process that is performed by one side alone (e.g., the transmit side or the receive side of a communication system), without supporting signaling or feedback from the other side.

The term "collaborative" as used herein describes a process that uses cooperation between both sides of a communication link to assist each other, (e.g., in a communication system, the base station and the user equipment exchange information to assist each other in improving the link). The term "blind phase scan" as used herein, is an autonomous signal quality enhancing technique, according to which the phase of the receiving antennas is methodically changed while simultaneously monitoring one or more preselected quality indicators such as power control, SINR, Signal to noise ratio (SNR), or some cases a data rate measurement. The phase parameters are periodically tuned and updated so as to optimize the preselected one or more quality indie ators .

The term "Maximal Ratio Combining" or "MRC" as used herein, is an autonomous signal quality enhancing technique based on Diversity combining, in which the signals from each channel are added together, and the gain of each channel is made proportionally to the RMS signal level and inversely proportional to the Mean Square noise level. The term "Optimal Combining" or "OC" as used herein, is an autonomous signal quality enhancing technique based on Diversity combining, in which the signals from each channel are combined together to maximize Signal to Interference plus Noise Ratio (SINR).

The term "Least Mean Squares" or "LMS" as used herein, is an autonomous signal quality enhancing technique in which an equalizer filter processes a signal derived from signals received by a plurality of antennas. In some cases, a filter coefficient correction used by the equalizer filter may be generated by a tap coefficients generator using a least mean square (LMS) algorithm.

The term "interference cancellation" as used herein, is an autonomous signal quality enhancing technique based on selectively removing or reducing undesired interference, in such a way that improves SINR of the desired signal. The term "downlink transmit beamforming" as used herein, is a collaborative signal quality enhancing technique based on signaling between user equipment (UE) and base transmitter station (BTS), in which the BTS is provided with information received by the UE, regarding the desired tuning of its DL beamforming weights, e.g., using pilot signals coming from the BTS, and the UE sends feedback informing the BTS of desired corrections to be applied to its DL antennas' weights. This MIMO scheme is also referred to as Closed Loop BF.

The term "minimum mean-squared error" or "MMSE" as used herein, is a process for cases where a digital radio-communications systems operating on a jammed frequency-selective fading channel: The receiver performance can be improved by using the joint antenna diversity and equalization techniques to combat both time- and frequency- selective fades and jammers effects. In this process, the optimum, in the sense of MMSE, the structure of the linear equalizer (LE), and the decision feedback equalizer (DFE) for coherent receiver antenna diversity are all being derived for an un-jammed environment.

The term "Transmit Diversity" as used herein, sometimes called "Alamouti Tx Div" refers to a collaborative signal quality enhancing technique, where L transmitting antennas simultaneously emit up to L consecutive symbols, in up to L combinations, so that each given symbol is repeated up to L times, yielding time diversity without sacrificing bandwidth.

Many techniques are known in the art for enhancing signal quality in RF MIMO communication systems. The aforementioned techniques are a mere few and other techniques, currently the RF MIMO signal quality enhancement methods are implemented in the baseband domain, by a baseband DSP module.

Figure 1 is a high level schematic block diagram illustrating a MIMO receiver system 10 in accordance with the prior art. A baseband DSP processor 20 is fed by two or more radio circuits 30-1 to 30-N, each of which is in turn fed by its respective antenna 40-1 to 40-N. In operation, baseband DSP processor 20 may apply one or more signal quality-based enhancement techniques, including autonomous or collaborative techniques, or both, that may include, but are not limited to, the techniques discussed above.

There are several issues associated with the aforementioned architecture: firstly, 3rd Generation Partnership Project 3GPP standardization supports several canonical MIMO configurations, e.g., 2x2, 4x4, or 8x8, and consequently, protocols, base stations' software, and UE DSP software products do not currently support a flexible number of UE antennas. Second, the more complex standard configurations (e.g., 8x8) are going to take a while before they are brought to market. Third, the more complex standard configurations would be expensive, since advanced UEs need to support many RF bands (e.g., 7) and when the number of antennas is increased by a factor (e.g., by 1:5), then the RF chains supporting it must grow by such a factor, e.g., from 14 (i.e., 2x7) to 70 (i.e., 10x7), which becomes exceedingly expensive.

SUMMARY

Embodiments of the present invention address some or all of the aforementioned issues associated with the prior art. A first aspect of embodiments of the invention enables the addition of antennas to existing standards-compliant solutions via a minor addition of hardware and software. A second aspect of embodiments of the invention endows non- complex configurations (e.g., 2x2) that are already commercially available with some of the features that will only become available in years to come. According to a third aspect of embodiments of the invention, due to the wideband nature of some of the invention's versions, there may be less need to extensively duplicate front end RF circuit, for example, two RF beamformers may be able to support all 7 bands, thereby promoting affordability.

Some embodiments of the invention include a hybrid system comprising a legacy MIMO Receiving system including of baseband, radios and antennas (where the number of antennas is equal to the number of radios); a Rx RDN (comprised of an array of beamformers) and a larger number of antennas (larger than the number of radios); and a control module that derives its metrics from the MIMO system and tunes the RDN accordingly.

According to one embodiment of the present invention, there is provided a performance enhancement system for enhancing the performance of a multiple-input-multiple-output (MIMO) receiving system. The performance enhancement system may include a MIMO receiving system having N branches and configured to operate in accordance with one or more legacy MIMO receiving schemes; and a radio distribution network (RDN) connected to the MIMO receiving system. The RDN may comprise one or more beamformers, wherein at least one of the beamformers is fed by or receives input from two or more antennas. The total number of antennas in the system may be an integer M=K₁+K₂+ ... K_N, where K; is the integer number of antennas used by Beamformer i. It will be recognized that since a beamformer typically involves more than one antenna, M (an integer) will typically be larger than N (an integer). A control module is required to tune the one or more beamformers based on legacy MIMO Signals derived from the MIMO receiving system' s DSP, so that the

RDN adds gain and/or antenna directivity to the MIMO receiving system.

According to another aspect of the present invention, there is provided a method of enhancing the performance of a radio frequency (RF) of a legacy MIMO communication. The method includes deriving legacy MIMO signals from a MIMO receiving system's DSP, where the receiving system includes N branches and is configured to operate in accordance with one or more legacy MIMO receiving schemes; generating beamforming weights for a radio distribution network (RDN) connected to the MIMO receiving system comprised of one or more beamformers, wherein at least one of the beamformers is fed by two or more antennas, so that a total number of the antennas in the system is M>N, and tuning the one or more beamformers' input signal weights, so that the RDN adds gain and/or antenna directivity to the MIMO receiving system.

Some embodiments of the present invention are beneficial when antennas at the user equipment (UE) do not receive a uniform wave-front. The non-uniform wave-front yields unpredictable beam shapes when the antenna elements are combined with phases and amplitude as they are received. Therefore individual tuning of the RDN for each antenna may be beneficial, as will be further explained below.

According to some embodiments of the present invention, each of the beamformers has antenna distinguishing circuitry capable of distinguishing between the signals coming from the antennas which feed or provide signals to the respective beamformer, the beamformers also including a combiner configured to combine signals coming from the antennas which feed or provide signals to the respective beamformer into a single signal

According to another aspect of the present invention, there is provided a module and a method of distinguishing between the contribution of each individual antenna to the total received power of a given beamformer, per each layer; such distinguishing is achieved by applying RF manipulation during periodical "look-through" time intervals. According to some embodiments of the present invention, means for optimizing and selecting the best phases with which the antennas are tuned is provided herein. The optimizing means are required due to challenges in aligning the phases in the receive antennas coupled to the beamformers in the hybrid MIMO RDN architecture, in order to mitigate the combiners losses caused by misaligned phases. Embodiments of the present invention are based on seeking maximization of the total power received from all transmitted layers as measured by the MIMO's baseband; the summation includes all transmitting antennas signals, as viewed by all receiving RDN antennas, which are equipped with phase shifters. The received powers may be measured via channel estimation of individual antennas thru their respective beamformers, radios and baseband circuitry.

Different metrics are provided to quantify the said total received power:

= y ·.^·.; y s

It would be therefore advantageous to find a way to use a single degree of freedom i.e. the need to choose or select one phase in aligning a beamformer that serves 2, 4, or more different phase setting, stemming from the fact that multiple incoming signals have each a specific possible phase alignment for the beamformer.

The requirement for optimal alignment of phases for all transmitted layers appears also in higher MIMO ranks and in various RDN configurations. A general optimization process is addressed in embodiments of the invention described herein.

While standard MIMO receivers are capable of accumulating energy from all available antennas for each layer, without interdependency, additional antennas that are RF combined may need to rely on one weights setting that fits all layers, which may adversely affect performance; the source of the issue comes from the random or loosely correlated nature of the various layers' signals, as viewed by the various participant antennas in the RF beamforming; specifically, phases setting that optimizes a group of RF combined antennas' output for a given layer, may be suboptimal or even detrimental to others; it is therefore imperative to set a weight in such a way that will consider all layers.

It is therefore helpful to increases the set of antennas to be chosen, beyond the number of available inputs in the given RF combiners; it thus takes advantage of the very same randomness that characterizes the various layers' signals seen by each receiving antenna, picking best combinations and providing reduction of the performance loss; to achieve that, the invention offers a categorization where each candidate antenna to be combined with others is declared "good" if it can see all layers in non-conflicting phases, and "bad" if it cannot; by taking advantage of possible existence of several RF beamformers in the MIMO receiving system, each required to solve the same issue, by swapping antennas amongst the various beamformers, and thus using all or most available antenna resources.

These additional, and/or other aspects and/or advantages of the present invention are set forth in the detailed description which follows. BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and in order to show how it may be implemented, references are made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections. In the accompanying drawings:

Figure 1 is a high level schematic block diagram illustrating a MIMO receiver according to the prior art;

Figure 2A is a high level schematic block diagram illustrating a system according to some embodiments of the present invention;

Figure 2B is a detailed example block diagram of a controllable group of beamformers illustrating an aspect according to some embodiments of the present invention; Figure 3A is a high level flowchart diagram illustrating an aspect of a method according to some embodiments of the present invention;

Figure 3B is a high level flowchart diagram illustrating another aspect of a method according to some embodiments of the present invention;

Figure 4 is a high level block diagram illustrating an aspect related to one case of MIMO mode of downlink beamforming, treated in some embodiments of the present invention;

Figure 5 is a high level block diagram and flow chart illustrating aspects of the MIMO mode illustrated in Figure 4, according some embodiments of the present invention;

Figure 6 is a high level block diagram illustrating different possible processing levels used to derive RDN's tuning according to some embodiments of the present invention; and Figure 7A is a high level block diagram illustrating general block diagram of a combination of a Rx RDN and legacy MIMO according some embodiments of the present invention;

Figure 7B is a high level flowchart illustrating a method according to some embodiments of the present invention. Figure 8 is a high level block diagram illustrating a system according to embodiments of the present invention;

Figure 9 is a high level block diagram illustrating one aspect of a system according to embodiments of the present invention; Figure 10 is a high level block diagram illustrating another aspect of a system according to embodiments of the present invention;

Figure 11 is a high level block diagram illustrating yet another aspect of a system according to embodiments of the present invention;

Figure 12 is a signal diagram illustrating an aspect of a method according to some embodiments of the present invention;

Figure 13 is a signal diagram illustrating another aspect of a method according to some embodiments of the present invention;

Figure 14 is a high level block diagram illustrating yet another aspect of a system according to embodiments of the present invention; Figures 15 A and 15B are signal diagrams illustrating yet another aspect of a method according to some embodiments of the present invention;

Figure 16 is a high level flowchart illustrating a method in accordance with some embodiments of the present invention;

Figure 17 is a high level block diagram illustrating a system according to some embodiments of the prior art;

Figure 18 is a high level block diagram illustrating a system according to some embodiments of the present invention;

Figures 19A and 19B are signal diagrams illustrating an aspect according to embodiments of the present invention;

Figure 20 is a table with signal diagrams illustrating an aspect according to embodiments of the present invention;

Figure 21 is a signal diagram illustrating yet another aspect according to embodiments of the present invention; Figure 22 is an example of the 2x2 MIMO system augmented by a Radio Distribution

Network (RDN) according to the present invention;

Figure 23 is a schematic high level illustration of a simple MIMO receiving system with the

RDN and antenna routing module, according to some embodiments of the invention;

Figure 24 is an implementation for antenna routing module using switch matrix for the case illustrated in Figure 23, according to some embodiments of the invention;

Figure 25 is a schematic high level illustration of a more complex MIMO receiving system with the RDN and antenna routing module, according to some embodiments of the invention;

Figures 26 and 27 are signal phase diagrams illustrating the phase relationship of signals received by antennas according to embodiment of the present invention;

Figure 28 is a schematic high level illustration of a MIMO receiving system having a ten antenna array with the RDN and antenna routing module pooling 4 antennas, according to some embodiments of the invention;

Figure 29 is a schematic high level illustration of the switch matrix, as implemented for the system of Figure 28, according to some embodiments of the invention;

Figure 30 is a schematic high level illustration of the switch matrix, as implemented for the system of Figure 31, according to some embodiments of the invention;

Figure 31 is a schematic high level illustration of another MIMO receiving system having a ten antenna array with the RDN and antenna routing module pooling 2 sets of 4 antennas, according to some embodiments of the invention; and

Figure 32 is a high level flowchart illustrating a method in accordance with some embodiments of the present invention.

DETAILED DESCRIPTION With specific reference now to the drawings in detail, it is stressed that the particulars shown are for the purpose of example and solely for discussing the preferred embodiments of the present invention, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The description taken with the drawings makes apparent to those skilled in the art how the several forms of the invention may be embodied in practice. Before explaining the embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following descriptions or illustrated in the drawings. The invention is applicable to other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

Figure 2A depicts a hybrid of a MIMO receiver system comprising a number of radios, baseband DSP modems and an array of RF beamformers, in accordance with some embodiments of the present invention. Baseband processor 110, possibly in the form of an integrated circuit (IC), may include one or more legacy receiving DSP modems 112. Additionally, the baseband processor 110 may further include an RF signal processing control module 114. Baseband processor 110 is fed by two or more radio circuits 20-1 to 20- N, the outputs of which are input to the respective one or more legacy DSP receiving modems 112. Each one of radio circuits 20-1 to 20-N is fed in turn by a corresponding RF beamforming module (or RF beamformer) 120-1 to 120-N, which together form a receiving radio distribution network (Rx RDN) 130. Additionally, each one of RF beamforming modules 120-1 to 120-N is fed by a plurality of antennas 50-1 to 50-K and may be further tunable by RF signal processing control module 114. In some embodiments, RF signal processing control module 114 and DSP modems 112 are incorporated within a single integrated circuit.

In operation, the Baseband DSP modems 112 and radios 20 may be configured to enhance the communication link via the addition of the Rx RDN and additional antennas. The enhancement may be accomplished by adding RF signal processing control module (or RF Control Module) 114. RF control module 114 may generate beamforming weights (e.g., amplitude and phase) based on various possible processing levels applied to signals obtained from DSP modems 112, and tunes the one or more RF beamforming modules 120-1 to 120- N.

By the aforementioned architecture, RF MIMO receiver systems can be retrofitted and augmented with additional antennas while preserving the legacy signal processing implementation, and reusing existing signals with additional processing, in order to tune additional RF circuitry, i.e., Rx RDN 130, thus enhancing performance. Figure 2B is a block diagram illustrating a non-limiting exemplary implementation of a hybrid digital and RF MIMO system 200 according to embodiments of the present invention.

Hybrid system 200 includes a legacy UE MIMO system 210 which includes two or more radio circuits 232 and 234 which feed or provide signals to baseband processor 240. Hybrid system 200 further includes an RDN which includes RDN sub-modules 222 and 224 which include RF circuitry such as RF combiners, filters, phase shifters, amplifiers, and switches.

Each one of the RDN sub-modules may be fed in turn, by an array of antennas 262, and 264.

Hybrid digital and RF MIMO system 200 may further include an RF control module 250 configured to derive legacy MIMO metrics from legacy UE MIMO system 210 and tune the RDN which includes RDN sub-modules 222 and 224 accordingly. The legacy MIMO metrics relate to the qualitative parameters that are used in the classic MIMO configuration such as channel estimation, blind scan/search, MRC, OC, LSE, and MMSE.

Figures 3A and 3B illustrate embodiments of possible methods of tuning the beamformer array, based on signals derived from the various MIMO receiver modems, and in some cases on further processing.

Figure 3A shows an embodiment of an iterative method that applies blind weights by employing various specified techniques, for example, those known in the art. The quality indicators that result from each iteration may be used determine the best weights. Referring to Figure 3A in more detail, the high level flow chart illustrates the iterative tuning process 300A which is initiated by selecting some beamforming weight (for example, at random) and then modifying it according to some method. Step 310A describes the DSP function that generates a new beamforming weight. Step 320A describes applying the new beamforming weight to the RDN. Step 330A describes monitoring the resultant quality indicator as reported from a given section of the DSP. Step 340A compares the new quality indicator with the previous one. Step 350A grades the weight, and determines if the quality indicator was made better or worse. Step 360A performs an algorithmic function that stores results of the previous and recent iterations and determines the weights.

Figure 3B describes an embodiment of a method of tuning a RDN beamformer based on channel estimation, i.e. gauging the difference between a given antenna's measured weight (measured phase and amplitude), and its desired weight, where the desired weight is some reference, and modifying that antenna's current setting so as to reduce or minimize that difference. Referring now to Figure 3B in more detail, a high level flow chart illustrates channel estimation based tuning process 300B.The method systematically and periodically selects antennas and measures their phase and amplitude as described in 310B. Step 320B compares that measurement with a reference. According to an embodiment of the invention, the measurement from one of the antennas may be used as a reference, and measurements from other antennas may be compared against it. According to another embodiment of the invention, a combined signal of more the one antenna may be used as a reference. The comparison may result in a gap, e.g., a non-zero phase difference. Step 320B then reviews the set of possible beamformers' weights, and selects one that reduces or minimizes the difference. Step 330B applies the above determined weight by the control algorithm residing in the baseband, and sets the beamformer that is fed by or provided signals by that antenna accordingly. Step 340B transfers the channel estimation process to the next antenna, and if all antennas have been tuned (Step 350B) the first antenna is revisited, and so on (Step 360B). According to some embodiments of the invention, various classes/types of legacy MIMO receiving systems may be used, such as Maximal Ratio Combining, Optimal Combining, Minimum Mean Square Error, Alamouti Tx Diversity, Interference Cancellation, DL Transmit Beam Forming, Spatial Multiplexing, and others. When tuning the RF beamformers, two basic tuning methods may be practiced. In the first method (hereinafter "Method A"), demodulated signals of a given DSP modems are used to tune the specific corresponding Beamformer that feeds or provides signals to its radio, and in the second method (hereinafter: "Method B"), multiple demodulated signals of the multiple DSP modems are used to tune multiple beamforming in conjunction. Method A is typically easier to implement, requiring smaller added processing to the legacy MIMO modem processors, but provides in general less performance. However, that loss of performance is not the same for each one of the above mentioned MIMO classes/types, as will be described below.

Figure 4 is a high level block diagram illustrating a non limiting exemplary aspect according some embodiments of the present invention. When a base station (BTS) 410 is operating in a Downlink Transmit Beamforming mode, and user equipment (UE) 420 is operating in Receive RF beamforming mode according to an embodiment of the invention, it may be beneficial to tune each one of the beamforming sides in such a way that will not compromise or adversely affect either of both the process of tuning the UE antennas and the process of tuning the BTS antenna. That is, the UE measures the channel, and then performs two parallel processes: one is done by the legacy Closed Loop DL beamforming MIMO, the other is done by the RF control module. Since the two different mechanisms operate in parallel, unaware of each other, with different goals - one trying to satisfy the BTS 410 and the other trying to satisfy UE 420 - there is a potential risk of instability. This issue is illustrated by the geometric example of beams 422A-422C of UE 420 shown in Figure 4, where both the

BTS' beams 410 and the UE's beams 420 move back and forth trying to point at each other, resulting in instability of both beams.

According to some embodiments of the present invention, whenever downlink (DL) beamforming is being applied by UE 420, the metrics that are obtained from the baseband DSP modules of UE 420 may be measured, by way of example, every frame (or any other specified time unit), however the tuning of the one or more beamformer in UE 420 may be carried out at a lower rate than one command per frame (e.g., multiplied by a factor of 2 or 3). In this embodiment, the corresponding base station beamforming mechanism of BTS 410 may perform both channel estimation and codebook instructions to change the weights at BTS 410 every frame. Such a reduced rate of change at the UE results in a more robust BTS beamforming algorithm, due to reduction of the number of simultaneous changes. Alternatively, the UE may from time to time refrain from advising the BTS how to alter its weights (e.g., hold off making changes to the codebook it sends). In this way, the UE can make weight changes to its own RDN without impacting the BTS performance and thus improve the robustness of the UE and BTS beamforming algorithms.

Figure 5 is an embodiment of a high level timing diagram further illustrating and providing further insight to the aforementioned aspect of changing antenna settings of the UE and the BTS. Timing diagram 500 illustrates channel estimation implemented by a collaborative signal enhancement scheme between BTS 510, the UE closed loop mechanism 520, and the UE beamforming mechanism 530. In operation time slot i, the UE's MIMO assesses the required correction of the BTS weights i+1, while the RF Control Module assesses the required correction for the RDN i+1, and forwards these instructions simultaneously to both. This causes both UE and BTS to modify the signal at both ends, causing the next cycle i+2 to assess a correction that was partly caused by an unrelated mechanism.

Since any antenna setting change at one side generates a channel change for the other side, an undesirable oscillation effect may occur. One solution, as explained above, is to use a reduced change rate. Another solution is that UE beamforming mechanism 530 may learn over time the BTS 510 antenna change pattern (in a static environment), and predict the impact of the beamforming setting change on its own feedback to BTS 510, and selectively correct that feedback. More specifically, the control module of UE closed loop mechanism 520 may keep logbooks or otherwise store or keep records (e.g., in a memory or database) that store recent beamforming weight updates for the one or more beamforming circuits at the UE beamforming mechanism 530 and the BTS 510 beamforming. The logbooks may be used by the control module of UE 520 to estimate a mutual impact of the two processes on each other, and implement a correction. For example, the UE may perform correlation calculations between both logbooks, and if any correlation coefficient exceeds a certain threshold, then the UE may choose to use an alternative RF control module algorithm, and verify that the modified correlation has been properly reduced. Data structures other than logbooks may be used to store weights.

According to some embodiments of the present invention, whenever a tuning of a specified beamformer is carried out while temporarily degrading its performance, the control module may tune the beamformers one at a time, so that when the specified beamformer is engaged in tuning, the other beamformers are not being tuned. Figure 6 is an embodiment of a high level block diagram illustrating yet another aspect of a system according to some embodiments of the present invention. RF MIMO receiving system 600 includes a baseband processor 610 that includes a plurality of baseband processors 612-1 to 612-N fed by or receiving signals from radio circuits 620-1 to 620-N. Baseband processors 612-1 to 612-N have individual outputs Ai to A respectively which are fed into a multiple input processing/merging module 614 which generates a combined output B. MIMO receiving system 600 further includes an RF control module 615 fed by or receiving signals from individual outputs Ai - A and combined output B, which in turn generates control outputs ΑΊ - A'N when the aforementioned Method A is used, or alternatively control outputs ΒΊ - B'N when Method B is used. Depending on the actual MIMO class/type, the baseband signals may be used to tune beamforming circuitries 630-1 to 630-N may be tuned by the A'l to A'N outputs via a first set of controls lines, or tuned by B'l to B'N outputs via another set of control lines.

As stated above, the tuning of an individual RF beamformer based on its DSP modems signals can be implemented for all types of MIMO classes /types mentioned above, and is the preferable method when cross-correlation of the noise/interference between the channels is zero or below a predefined threshold. In other cases, when such cross-correlation between interference is significant or above a predefined threshold, then the RDN assembly of beamformers' tuning may yield better performance when the tuning algorithm takes into account multiple DSP Modems' signals derived from the multiple Radios fed by their multiple beamformers. For these cases it would be advantageous to tune the multiple beamformers as a group, thus implementing a better selection of RDN weights based on more accurate knowledge of the channel.

As stated above, the extra processing required for Method B is not always justified, depending on the particular MIMO class/type as described below.

Where a given UE MIMO receiving systems implements MRC, and when one may assume that this UE choice was made based on preference of simplicity, i.e., relating to interference as less significant, then RDN tuning may use similar assumptions, and thus tunes each individual beamformer based on each individual corresponding DSP modem as described by Method A.

Where a given UE MIMO receiving systems implements OC, and when one may assume that this UE choice is made based on preference, i.e., relating to interference as significant, then RDN tuning may use similar assumptions, and thus tunes multiple beamformers based on multiple DSP modems' signals as described by Method B.

Where a given UE MIMO receiving system implements MMSE, and when one may assume that this UE choice is made based on preference, i.e. relating to interference as significant, then RDN tuning may use similar assumptions, and thus tunes multiple beamformers based on multiple DSP modems' signals as described by Method B.

Where a given UE MIMO receiving systems implements Alamouti Tx Diversity, then Method A is practically possible but less preferable, due to the nature of the Alamouti transmission, rendering the individual DSP modems' signals jamming each other prior to modulation, as well as the need to perform individual deciphering for each one which increase complexity-defeating the purpose of reduced complexity; although possible, Method A for this class is inferior on most respects and so Method B preferably should be used in this class.

Where a given UE MIMO receiving systems implements Interference cancellation, and when the assumption is that the legacy MIMO significantly reduces the interferer impact on each one of the individual DSP's, and when the SINR declared by the legacy MIMO quality indicator is not marginal (Point B), i.e. above a certain level, then Method A for RDN tuning is implemented for this class/type of MIMO receiver system; otherwise, Method B is implemented.

Where a given UE MIMO receiving systems implements DL transmit beamformning, and when SINR declared by the MIMO quality indicator (Point B) is higher than a certain level, Method A will be used to individually tune beamformers via their corresponding DSP modems' signals; where marginal SINR is declared by the MIMO quality indicator, Method B is used.

Where a given UE MIMO receiving systems implements Spatial Multiplexing, RDN tuning is suboptimal due to the need to optimize for multiple uncorrected transmissions (e.g. via SVD techniques); when reviewing multiple suboptimal solutions together, is sometimes possible to modify some or all of them so that the combined effect has higher performance; hence, Method B is used for this class of MIMO system.

According to some embodiments of the present invention RF control module is configured to tune the beamformers based on individual outputs of the baseband DSP modems, whenever a signal to interference-plus-noise ratio (SINR) is higher than a specified threshold.

Figure 7A is a high level schematic block diagram illustrating yet another aspect according some embodiments of the present invention. Figure 7A shows an RF MIMO receiver configuration including baseband processor 710 being input by radio bank circuits 720 which are in turn being input by beamforming circuits 730 which may include an RF combiner 750 wherein beamforming circuits 730 are tunable via control by baseband processor 710.

Figure 7B is a high level flowchart diagram illustrating a method 700b according some embodiments of the present invention. The method may include the following stages: deriving legacy multiple-input-multiple-output (MIMO) metrics from a MIMO receiving system having N branches and configured to operate in accordance with one or more legacy MIMO receiving schemes 710b; generating beamforming weights for a radio distribution network (RDN) connected to the MIMO receiving system, the RDN comprising one or more beamformers, wherein at least one of the beamformers is fed by two or more antennas, so that a total number of antennas in the system is M, wherein M is greater than N 720b; and tuning the one or more beamformers using the beamforming weights 730b. The aforementioned architecture of Figure 7A may be beneficial to remedy a situation where antennas at the UE do not yield an approximately uniform wave front. The non-uniform wave-front yields unpredictable beam shapes when the antenna elements are combined with prescribed phases (and amplitude). One possible solution to produce more predictable beam shapes may be by using channel estimation of the signals by baseband 710 to better align the phases using phase shifter 740.

In some embodiments, a method implementing the aforementioned systems may include the following stages: deriving legacy multiple-input-multiple-output (MIMO) metrics from a MIMO receiving system having N branches and configured to operate in accordance with one or more legacy MIMO receiving schemes; generating beamforming weights for a radio distribution network (RDN) connected to the MIMO receiving system, the RDN comprising one or more beamformers, wherein at least one of the beamformers is fed by two or more antennas, so that a total number of antennas in the system is-M, wherein M is greater than N; and tuning the one or more beamformers using the beamforming weights. In some embodiments, the generating stage may be carried out based on radio links quality indicators. In other embodiments, the deriving stage may be carried out at individual outputs of digital signal processing (DSP) modems of the MIMO receiving system or at a combined output thereof.

In some embodiments, the aforementioned method may further include the stage of selecting either the individual outputs of the DSP modems or the combined outputs thereof, based on a type of the legacy MIMO receiving schemes operated by the MIMO receiving system. As discussed above, the different types of the legacy MIMO receiving schemes may include Maximal Ratio Combining, Optimal Combining, Minimum Mean Square Error, Alamouti Tx Diversity, Interference Cancellation, DL Transmit Beam Forming, and Spatial Multiplexing. In some embodiments, the one or more legacy MIMO receiving schemes may be downlink (DL) beamforming, wherein the MIMO receiving system may be implemented within a user equipment (UE), wherein the legacy MIMO metrics are measured every specified time unit, and wherein the tuning of the one or more beamformers of the UE is carried out every more than one specified time unit, and wherein a corresponding base station beamforming mechanism guided by the UE performs both channel estimation and code book instructions that change setting, at the base station every specified time unit. In some embodiments, the one or more legacy MIMO receiving schemes may be downlink

(DL) beamforming, wherein the MIMO receiving system may be implemented within a user equipment (UE), wherein the control module keeps a logbook or otherwise stores information storing recent beamforming tuning for the one or more beamformers of the UE, and beamforming tuning of a base station, and wherein the control module is further configured to use the logbook to estimate an undesirable impact or effect of a weights setting by one side on the other, so that the tuning of the one or more beamformers of the UE takes into account the estimated impact of UE weights setting.

In some embodiments, the one or more MIMO receiving schemes may be based on an interference cancellation receiver, wherein the legacy MIMO metrics may be measured at the individual outputs of the baseband DSP modems, whenever a signal to interference-plus- noise ratio (SINR) of at least one of the radio circuitries is higher than a specified threshold.

In some embodiments, the one or more receiving schemes is based on an interference cancellation receiver, wherein the legacy MIMO metrics may be measured at the combined output of the baseband DSP modems, so as to use a filtered quality indicators, as opposed to pre-filtered quality indicators.

In some embodiments, the aforementioned method may further include the stage of performing a linear combination of various MIMO inputs of the MIMO receiving system, wherein the tuning may be carried out based on respective individual DSP modems outputs, or on a combined output of the DSP modems, subject to performance superiority.

Distinguishing between individual antenna signals

As explained above, in order to properly assess the contribution of each individual antennas signal to the overall receive power at the combined (beamformed) signal, it would be advantageous to be able to distinguish between the different individual antenna signals looking at the combined signal at the DSP. While several ways are available, some of the solutions are detailed hereinafter by way of example.

Figure 8 is a high level block diagram illustrating a system according to embodiments of the present invention. System 800 includes a multiple-input-multiple-output (MIMO) receiving system baseband module 820 having N branches and configured to operate, on the baseband level, in accordance with a channel estimation MIMO receiving scheme. System 800 may further include a radio distribution network 810 (RDN) connected to baseband module 820 via radio circuits 82-1 to 82-N. RDN 810 includes at least one beamformer with antenna distinguishing circuitries such as 840-1, being fed by two or more antennas such as 80-1 to

80-Kj, so that a total number of antennas in system 800 is M = + K2 + ....+ K| |, wherein M is greater than N. Additionally, each one of the beamformers includes a combiner (not shown here) configured to combine signals coming from the antennas into a single combined signal converted to baseband by radio module 82-1 to 82-N. Baseband module 820 further includes an RF control module being configured to tune RDN 810, for example by adjusting phase shifters located within beamformers 8401 to 840-N.

As shown above system 800 includes one beamformer with antenna distinguishing circuitries for each group of antennas that is being combined into a single radio circuit. In operation, the beamformer is configured to distinguish between the signals coming from the antennas which feed or provide signals to the respective radio circuits. As will be explained below, there are many embodiments that may be used in order to implement the signal distinguishing operation which is crucial for derivation of phase and/or amplitude of each signal. These distinguishing schemes may further be controlled via control module 830. As will be described below the beamformer with antenna distinguishing circuitries may include radio frequency (RF) elements such as phase shifters, switches, terminators, and amplifiers.

Figure 9 is a high level block diagram illustrating one aspect of a system according to embodiments of the present invention. System 900 is an exemplary non-limiting embodiment of 5 antennas 90-1 to 90-5 wherein the beamformer includes a selectable bypass 92-1 to 92-5 for each antenna 90-1 to 90-5 configured to bypass combiner 910 in the respective beamformer and convey the signal from each one of antennas 90-1 to 90-5 to an output selector 920, and wherein the output selector is configured to deliver to the MIMO receiving system only the signal from one antenna at a time. In some embodiments, it would be advantageous to provide a calibration element (not shown) for each one of the selectable bypass units, wherein the calibration element is configured to identify and take into account phase and amplitude difference between the combiner and the selectable bypass unit. The calibration process may be carried out at the factory and may be either on the RF level or the baseband level or a combination thereof. Figure 10 is a high level block diagram illustrating another aspect of a system according to embodiments of the present invention. In exemplary system 1000 the beamformer is configured to selectively disconnect and terminate all but one of the antennas so that only one signal coming from the antennas is conveyed to the output of the combiner, at a time.

The disconnecting may be implemented, for example, by a set of switches 102-1 to 102-5 each switching a terminator for antennas 100-1 to 100-5. Each time, a different antenna signal is conveyed alone via combiner 1010. Figure 11 is a high level block diagram illustrating yet another aspect of a system according to embodiments of the present invention. In this exemplary embodiment, in system 1100, the beamformer is configured to selectively shift the phase of one antenna signal at a time and then resume original phase. The combined signal is compared after the phase is shifted and immediately after the phase has been restored so that phase and amplitude of the shifted phase shifter for each antenna can be derived. This can be implemented by controllable phase shifters 112-1 to 112-5 configured to shift the phase of only one signal coming from the antennas 110-1 to 110-5 at a time, so that the MIMO receiving system may derive phase and/or amplitude of the signal coming from the antenna with the shifted phase by comparing the combined signals at two different phases. It should be noted that controllable phase shifters 112-1 to 112-5 may also be used, when not used to assist in the antenna distinguishing operation, to tune the antennas as a part of the process of applying weights to the RDN as a part of the channel estimation MIMO receiving scheme.

Figure 12 is a signal diagram illustrating an aspect of a method according to some embodiments of the present invention. In this example, the phase of antenna 1202i is changed in going from time instance n-1 to n and becomes 1204i as seen in 1202 and 1204 respectively. When looking at the combined signal at the respective times n-1 and n, it is apparent that combined signal 1222 is longer than combined signal 1228. This way both phase and amplitude of 1202i may be derived by applying a differential approach.

Figure 13 is a signal diagram illustrating another aspect of a method according to some embodiments of the present invention. In this example the signal's phase of 1302i is not aligned with the rest of the signals coming from the rest of the antennas in 1302 and so the combined signals 1322 and 1324 illustrate that the phase Φι is different from Φ2 and so again, both phase and amplitude of the single antenna may be derived by way of comparison.

Figure 14 is a high level block diagram illustrating yet another aspect of a system according to embodiments of the present invention. In this exemplary embodiment, in system 1400, the beamformer includes a controllable amplifier 144-1 to 144-5 for each antenna wherein the controlling is achieved by switched 142-1 to 142-5 and 146-1 to 146-5. The amplifiers are configured to amplify only one signal coming from the antenna at a time, and wherein the MIMO receiving system is configured to derive phase and/or amplitude of the signal coming from the amplified antenna by comparing the combined signals combined by combiner 1410 at two different amplifications stages.. Figure 15A shows a signal diagram illustrating yet another aspect of a method according to some embodiments of the present invention. In this example, a signal 1502i is amplified at time n-1 and resumed at time n as shown in 1502 and 1512. The combined signal shown in 1506 and 1516 shows that the difference between them is apparent and both phase and amplitude of the amplified antenna can be derived. Figure 15B illustrates this embodiment for a case in which signal 1522i is not aligned with the rest of the signals. Another embodiment may be by using controllable attenuators instead of amplifiers and the effect of amplifying a single antenna (or its signal) may be achieved by attenuating the gain of all antennas but one, being the antenna that needs distinguishing at a specified point of time. It should be understood that many more implementations of antenna distinguishing may be used, some of which may include any combination of phase shifters, amplifiers, and attenuators.

Whenever the antenna distinguishing procedure is carried out with all antennas of a beamformer connected to the combiner, such as in the embodiments shown in Figures 11- 15B above, a differential approach is used to derive channel information for the individual antennas. Let ^Si^ ^ be the external channel from the transmitter antenna to receiver antenna

¹ at time instant , ^ai W _ancj Ψ ^η} ^₆ respectively the amplitude and phase of the internal path through the beamformer from receive antenna ¹ to the output of the combiner at time instant ^" , and ^" -^; be the estimation measurement provided by the receiver baseband at time instant . It should be noted that the amplitudes and phases of the internal paths through the beamformer are known quantities. The estimation ^{"! ; ι}· ' of channel ^' V -^' v' is derived from two separate baseband measurements, for example two consecutive measurements, e(n— I) e(n)

and , and is defined as: <img file="WO2013181219A2_D0001.tif" /> It should be noted that the estimation is perceived to be most efficient when ^ -'¹^^— 1) ^! ioO pig_ure [_{s a} high level flowchart illustrating an exemplary antenna signals distinguishing method in accordance with embodiments of the present invention. Method 1600 may include the following stages: receiving radio frequency (RF) multiple-input- multiple-output (MIMO) transmission via M antennas coupled to a MIMO receiving system having N branches and configured to operate in accordance with a channel estimation MIMO receiving scheme, wherein M is greater than N 1610; beamforming groups of two or more of the M antennas into each one of the N channels by combining signals coming from the antennas into a combined signal 1620; and applying a distinguishing procedure to the signals coming from the antennas in each one of the groups by applying RF manipulation during the beamforming 1630.

In some embodiments of distinguishing method 1600, the antenna distinguishing is carried out in accordance with a specified antenna distinguishing scheme being controlled at a baseband domain. In some embodiments, distinguishing method 1600 may further include the stage of deriving at least one of: phase and amplitude of each one of the distinguished signals; and tuning the beamformer accordingly.

In some embodiments of the distinguishing method 1600, the antenna distinguishing comprises selectively applying bypasses for each antenna for bypassing the combining so as to deliver to the MIMO receiving system only the signal from one antenna at a time.

In some embodiments, distinguishing method 1600 may further include the stage of identifying and taking into account phase and amplitude difference between the combining and the bypassing.

In some embodiments of distinguishing method 1600, the antenna distinguishing may be carried out by selectively disconnecting and terminating all but one of the antennas so that only one signal coming the antennas is conveyed to the MIMO receiving system, at a time.

In some embodiments of distinguishing method 1600, the antenna distinguishing may be carried out by selectively changing the phase of only one signal coming from the antennas at a time, and wherein the method further comprises deriving phase and/or amplitude of the signal coming from the antenna with the shifted phase by comparing the combined signals at two different phases. In some embodiments of distinguishing method 1600, the antenna distinguishing may be carried out by changing the gain of only one signal coming from the antenna at a time, and wherein the method further comprises deriving phase and/or amplitude of the signal coming from the amplified antenna by comparing the combined signals at two different amplifications.

Optimizing total receive power by selecting best phases

According to some embodiments of the present invention, means for optimizing and selecting the best phases with which the antennas are tuned may be provided herein. The use of optimizing means is advantageous due to challenges in aligning the phases in the receive antennas coupled to the beamformers in the hybrid MEVIO RDN architecture. The optimization is carried out in order to mitigate the combiners' losses caused by misaligned phases. An exemplary optimization process and algorithm is illustrated hereinafter. It is understood that the optimization process for selecting best phase may be used in embodiments with or without the aforementioned distinguishing circuitries and methods. Figure 17 is a block diagram showing a MIMO system according to the prior art having a base station 1710 and a UE 1720, both having two antennas and two MEVIO channels. Figure 18 shows an example of a 2x2 MEVIO RDN architecture with base station 1810 in which each receive antenna of UE 1820 as shown in Figure 17 such as Al, and Bl are enhanced by adding another antenna, A2 and B2 respectively, thus providing reception by four antennas instead of two. The hybrid MIMO RDN architecture further includes phase shifters 1840-1 and 1840-2 and combiners 1830-1 and 1830-2 feeding or providing signals to radio 1820.

Without losing generality, and for the sake of simplified explanation, it is assumed herein that the base station transmits each layer over one Tx antenna. The Hybrid MIMO RDN can provide an additional gain however, as the combiners 1830-1 and 1830-2 are serving two different Tx antennas with only one phase shifter, it is possible that the diversity parameters (e.g., phase) that are used to optimize the reception of Txl are not the same as those needed for receiving Tx2. This is especially true if the antennas are not correlated from one to another. As seen in Figure 18, if the phase shift introduced in the path from antenna radiating Txl

(1LA1-1LA2) is compensated by the phase shifter, that phase shifter setting will only be correct it the paths from the antenna radiating Tx2 are the same. That is, the phase setting will only be correct if (2LA1-2LA2) is the same or a multiple wavelength from (1LA1- 1LA2). A similar outcome holds for the Txl and Tx2 signals received by Antennas Bl and

B2.

If the case using four 90° phase shifts is compared to align the signals from Txl, it is apparent that there are three possible outcomes for the Tx2 signal: The first outcome is that the signals arrive at the antennas Al and A2 with a similar phase differences as for the Txl transmission so the same phase setting used to enhance the reception of Txl will also enhance Tx2. (25%)

The second outcome is that the resulting Tx2 signals to Al and A2 are +/-90⁰ from each other and will produce zero diversity gain for this process. (50%) The third outcome is that the resulting Tx2 signals are 180° from each other and can cancel each other or produce a negative diversity gain depending on their relative amplitudes. (25%).

When the result is the aforementioned third outcome, the system must choose to sacrifice diversity gain for Txl in order to avoid the total loss of the Tx2 signal. This would result in low diversity gain (~0 dB) for both Txl and Tx2.

The algorithm offered by embodiments of the invention results in phase optimization based on seeking maximization of the total power received from all transmitted layers as measured by the MIMO's baseband; the summation includes all transmitting antennas signals, as viewed by all receiving RDN antennas, which are equipped with phase shifters. The aforementioned received powers are measured via channel estimation of individual antennas thru their respective beamforaiers, radios and baseband circuitry.

In accordance with some embodiments of the present invention, a multiple inputs multiple outputs (MIMO) receiving system having number N channels is provided. The MIMO receiving system may include a radio distributed network (RDN) having number N beamforaiers, each having number K_N antennas. The MIMO system may further include at least one phase shifter associated with one or more of the N beamforaiers. Additionally, the MIMO receiving system is configured to: (a) select one phase that optimizes performance of multiple layers, via channel estimation of each layer as seen (e.g., taking into account the gain and phase affected by the physical location) by each receiving antenna, and (b) maximize a total received power from all transmitted signals.

Figures 19 and 20 are signal diagrams illustrating an aspect according to embodiments of the present invention. In the following non-limiting example, a case of N plurality of uncorrelated transmit signals projected from a base station, where N=2 , is received by a 2x2

MIMO UE which is augmented by an RDN with 2 beamformers, each beamformer has three receive antennas. It is assumed, for the sake of the following example that the beamformers can select one of 4 possible phases: 0°, 90°, 180°, and 270°. When selecting the beamformers' phases is such a way that will maximize the received signal coming from Txl, the Tx 2 phases may or may not be constructively combined, but rather, may have 1*4*4 = 16 phase combinations.

For the sake of simplicity, it is assumed that each receive antenna provides the same amplitude and a randomly selected phase out of 4 alternatives. It is also assumed that the amplitudes power is 0.33 (for the sake of the example).

As the signals are fed into an RF combiner, the translation into voltage of each signal provides a combined result as described herein below:

In Figure 19A, a signal diagram 1900A depicts 3 aligned vectors, each of 1/3 of a Watt are depicted so that the combined voltage equals 3x SQRT (0.333) = 1.732 V = &gt;3W. Since the gain is the output divided by the input, the gain here equals 3W/1W = 3, hence 4.77 dB. Figure 19B a signal diagram 1900B depicts two aligned vectors each of 1/3 of a Watt and a single 1/3 Watt perpendicular vector so that the combined voltage equals SQRT (0.33) + j SQRT (0.33) =&gt; Effective voltage combining = SQRT [(2x0.577) ²+0.577 ²]= &gt; 1.67W. For a similar reason, the gain equals 1.67W/1W= 1.67 hence 2.2 dB. Similar calculation for Figures 19A -C, D, E, F, G generates the gains of 2.2 for each one. Applying similar calculation for Figures 19B - H, I, J, K, L, M, N, O, P generates the gains of -4.77 dB for each one.

As can be seen, the seven combinations described in Figure 19A - A through G— provide positive gains for both layers, while the nine combinations described by Figure 19B - H through P— provide positive gain for one layer and negative gain for the other.

Figure 20 demonstrates in form of a table and a corresponding signal diagram how theses conclusion have been reached. Specifically, table 2000 illustrates the aforementioned calculations with specific configurations 2001-2005.

It can be easily seen that while configuration 2001 yields 4.77dB gain, configuration 2002 yields a lesser yet still positive gain of 2.22dB. Configurations 2003-2005 on the other hand, yield a negative gain of -4.77dB. As can seen above in Figures 19A and 19B when aligning one transmit signal to best gain, the second transmit signal is left for random combination of phases, and may become exceedingly adverse at many of the cases.

Figure 21 illustrates improvements that can be achieved by embodiments of the present invention in overall gain terms. The upper part illustrates cases where the selection of a maximal gain for Tx 1, where all antennas are aligned, undermines the gain for Tx 2. The lower part of Figure 21 demonstrates that replacing +4.77 dB gain for layer 1 and -4.77 dB for layer 2 provides gains of +2.22 dB for both layers at 9 out of 16 of the cases. (It is noted that in other 6 cases, the corresponding gains are +4.77 dB and 2.22 dB, and in one other case both are +4.77 dB.)

Similar approaches can be applied to more complex MIMO hybrid RDN configurations, where there are more layers and or more antennas are combined by RF beamformers.

One embodiment of metrics and a procedure for the selection of optimal phase settings to all participating beamformers is described below: Consider a beamformer with K receive antennas, each of them receiving signals from M transmit antennas. The channel functions from transmit antenna h = 1,2 to receive antenna i t = 1.2— at frequency ¾ ¾ = 1.2„.i (it is assumed the general case of frequency selective channels) are obtained through channel estimation done by the baseband. Each receive antenna is equipped with a set A of κ phase shifters,}, for phase adjustment. The set A of phase shifters could be, for example, {p^,misc,2?e} degrees. The algorithm needs to select the optimal phase Φ&lt;- ^A to be applied to receive antenna:

After phase adjusting the receive antennas, the overall channel functions seen by the receiver under consideration are: &lt;-ι , / = 1-2 ¾ = 1.2... 1

A power ¾* is associated with each one of them: ¾_* - i^s¾s(¾*3I , / = 1.2— mt&gt; ¾· = h z . i In one embodiment the algorithm selects phases ,· ^{E l} = ^{2 &lt;} , so as to maximize the total power defined as: *-* *-* In another embodiment, a procedure and metrics is provided wherein the antennas, e.g., antenna phases, are adjusted one by one recursively. As before, Φι may be set to zero. To calculate the contributions from only ^¾ ¾ and are considered. The combined channel and channel power P-z.i. for the first two antennas are defined as: s-&gt; _k = h_{t k}e* * 4 i , i = 1,_: 2„ N_t k = t.2 ... L <img file="WO2013181219A2_D0002.tif" />

The algorithm selects or chooses * ^e ^ that maximizes =ι ¾=ι

Continuing in a similar fashion for all antennas, once ¾-i has been calculated or

determined, 4^s; is calculated. Define: <img file="WO2013181219A2_D0003.tif" />

Pij* = Μ¾ )] _* J = 1, 2 ~ Af, fc = 1, 2 Then, similarly, the algorithm selects or chooses : ^E ^ that maximizes

N i i=i ¾=i

The total number of possible antenna phase combinations for the recursive algorithm is R (¾-l).

Since the order in which the antennas are optimized may affect the outcome, some criterion may be used for numbering of the antennas. For example, in some embodiments the antennas may be sorted or ordered in ascending/descending order based on the total power ^^'"*. of each antenna: <img file="WO2013181219A2_D0004.tif" /> According to some embodiments, the aforementioned stages of calculating selecting are repeated for each one of the N beamformers.

Antenna pooling in MIMO RDN architecture

Embodiments of the present invention offer a categorization where each candidate antenna to be combined with others is declared "good" if it can see all layers in non-conflicting phases, and "bad" if it cannot. It would be therefore advantageous to leverage possible existence of several RF beamformers in the MIMO receiving system, by swapping antennas amongst the various beamformers, and thus using all or most available antenna resources. The antenna pooling embodiment depicted below may be used on its own or in combination with the aforementioned antennas distinguishing and/or best phase optimization process.

Figure 22 shows an example of the MIMO receiver augmented by two additional antennas: if the phase shift introduced between the two antennas by phase shifters 2242 and 2244 optimizes the 1st layer, that phase shifter setting will only be correct for the 2^nd layer if multipath experienced by the two layers are similar. That is unlikely as multi-layer MIMO design is based on low correlation of the various streams; consequently, the relations between those phases that optimize both layers tend to be random.

In a simplified example case, where the said two layers are each transmitted from one Tx antenna (so that Txl radiates one stream and Tx2 the other) In comparing the case using four 90 degree phase shifts to align the signals from Txl, it can be seen that there are three possible outcomes for the Tx2 signal:

1. The signals arrive at the antennas Al and A2 with a similar phase differences as for the Txl transmission so the same phase setting used to enhance the reception of Txl will also enhance Tx2. (25%)

2. The resulting Tx2 signals to Al and A2 are +/-90 degrees from each other and will produce zero diversity gain for this process. (50%)

3. The resulting Tx2 signals are 180 degrees from each other and can cancel each other and produce a negative diversity gain depending on their relative amplitudes. (25%)

When the result is the outcome 3, the system could choose to sacrifice diversity gain for Txl in order to avoid the total loss of the Tx2 signal. This may result in low diversity gain (~0 dB) for both Txl and Tx2.

The issue at hand is the need to use a single degree of freedom i.e. the need to choose one phase in aligning a beamformer that serves 2, 4, or more different phase setting, stemming from the fact that multiple incoming signals have each a specific possible phase alignment for the beamformer. This invention presents an alternate approach to sacrificing gain as described above. The need to sacrifice diversity gain may be averted by providing a choice of additional antenna combinations.

Embodiments of he present invention disclose a system comprising: (i) a multiple-input- multiple- output (MEMO) receiving system comprising a MIMO baseband module having N branches; (ii) a radio distribution network (RDN) connected to the MIMO receiving system, the RDN comprising at least two beamformers, wherein each of the beamformers is fed by two or more antennas, so that a total number of antennas in the system (e.g., the MIMO receiving system) is M, wherein M is greater than N, wherein each of the beamformers includes at least one combiner configured to combine signals coming from the antennas feeding the respective beamformer into a combined signal; and (iii) an antenna routing module configured to swap at least one pair of antennas (e.g., for two antennas, to switch the association or assignment with a beamformer such that each antenna is associated with the beamformer previously associated with the other), each of the antennas in the at least one pair being associated with a different beamformer, wherein the antenna routing module is configured to swap said at least one pair of antennas.

These additional, and/or other aspects and/or advantages of the present invention are set forth in the detailed description which follows.

When using a phase optimization process like the antennas selection application, the enhancement achieved, is based on suboptimal setting for TX1 in order to eliminate destructive combining in other Tx signals.

This invention is yet another enhancement which increases the range of antenna selection beyond the set of antennas available for each beamformer, thus increasing the probability of grouping antennas that have lower conflicts between best phases of different Tx signals. The present invention can be used with or without phase selection process.

The system, as illustrated in Figures 23-25 and 28-31 that are explained in detail herein, may include a multiple-input-multiple-output (MIMO) receiving system comprising a MIMO baseband module having N branches and a radio distribution network (RDN) connected to the MIMO receiving system.

The RDN comprising at least two beamformers, each fed by two or more antennas, so that a total number of antennas in the system is M, wherein M is greater than N.

Each beamformer includes at least one combiner configured to combine signals coming from the antennas feeding the respective beamformer into a combined signal.

The system further comprises an antenna routing module configured to swap at least one pair of antennas, each of the antennas in the at least one pair being associated with a different beamformer. The antenna routing module is configured to swap said at least one pair of antennas

In some embodiments, the antenna routing module may be configured to route a subset of the antennas with respect to corresponding beamformers according to a switching matrix that is dynamically adjusted according to the qualitative indicators. Examples for matrices are presented in Figures 23 (matrix 2370), Figure 28 (matrix 2832) and Figure 31 (matrix 3132and 3134), as well as in Figures 25 29 and 30 as implemented the switches (see below) The swapped pair of antennas may be selected to increase a diversity gain of the MIMO receiving system.

The swapped pair of antennas may be selected with respect to at least one of signal phases and signal amplitudes.

The swapped pair of antennas may be selected according to a specified antenna signal weighting.

The qualitative indicators comprise a combined power of all beamformers, PWR_{TOTAL ;} defined as (see explanation below): <img file="WO2013181219A2_D0005.tif" />

where NBF is the total number of beamformers in RDN and BFpw_Rr is output power of the beamformer "r".

and at least one swapped pair of antennas may be selected to maximize TOTAL .

The present invention further comprises a method of improving reception by a multiple- input-multiple-output (MIMO) receiving system comprising a MIMO baseband module having N branches and a radio distribution network (RDN) connected to the MIMO receiving system.

The method comprises associating at least two beamformers with the RDN, each of the beamformers including at least one corresponding combiner; feeding each of the beamformers by two or more antennas, so that a total number of antennas in the system is M, wherein M is greater than N; configuring each combiner to combine signals coming from the antennas feeding the corresponding beamformer into a combined signal; and swapping at least one pair of antennas, each of the antennas in the at least one pair being associated with a different beamformer, based on qualitative indicators derived from the baseband module.

In some embodiments, the method further comprises routing a subset of the antennas with respect to corresponding beamformers by a switching matrix that is dynamically adjusted according to the qualitative indicators. In embodiments, the method further comprises selecting the at least one swapped pair of antennas according to the above specified criteria. Figure 23 is a schematic high level illustration of a simple MIMO receiving system with the

RDN and antenna routing module, according to some embodiments of the invention. One beamformer in the RDN comprises phase modulator 2362 and combiner 2352, another beamformer comprises phase modulator 2364 and combiner 2354. Antenna routing module comprises switching according to matrix 2370, as explained below. It shows that the antennas A2, B2 are placed in an "Antenna Pool" and selected under processor control through a matrix switch 2370 to be combined. In this example, antenna Al may be paired with either A2 or B2 to improve chances of non-conflicting phase setting for both layers.

Figure 24 is an implementation for switch matrix 2370 for the case illustrated in Figure 23 according to some embodiments of the invention. In this simple case switch matrix 2370 is implemented as a transfer switch.

Figure 25 is a schematic illustration of a more complex MIMO receiving system with the RDN and antenna routing module, according to some embodiments of the invention. One beamformer in the RDN is associated with antennas Al, A2 and A3 and comprises combiner 2512, another beamformer is associated with antennas Bl, B2 and B3 and comprises combiner 2514. The antenna routing module is or is implemented in switches 2522, 2532, 2524, 2534 and switches 2526, 2536, 2528, 2538 corresponding to the beamformers, as explained below.

When the signals from the three antennas are perfectly aligned in phase, this configuration offers up to 4.77 dB gain over the single antenna. If the signals are aligned in phase for Txl, there are 16 possible outcomes for receiving Tx2 when each of the two diversity antennas has four possible phases 0, 90, 180 270 degrees.

Figure 26 and Figure 27 are signal phase diagrams illustrating the dependency of the signals received from each antenna as they are combined in combiners 2512 or 2514 as described by Figure 25,. Figure 26 shows the cases where alignment of Txl signals result in positive gains for Tx 2 reception, while Figure 27 shows the cases where Tx2 signals result in negative gains. For every one of these relationships, the signal from one antenna is cancelled by one of the others, leaving a -4.77 dB result.

There are nine phase relationships designated H-P in Figure 27 that produce negative diversity gain and seven phase relationships shown in Figure 26 that produce positive gain. This means there is a 7/16 or 43.75% probability that the random combination of signals will produce positive diversity gain for one beamformer and about 43.75% squared (19%) chance both beamformers will produce a positive gain. 81% of the time at least one beamformer will experience negative gain. One strategy to increase the possibility to show positive gain in both beamformers is to substitute a different antenna for one of the antennas in the beamformer that produces the negative gain. If an antenna from each beamformer is swapped with the other the probability the new combination of antennas experiences negative gain is also 81%. This means for the two configurations the probability of negative gain is approximately 81% squared or 65%. This means the probability that the two beamformers both create positive gain is increased from 19% to 35% by trying a second antenna combination. Clearly, testing more antenna combinations improves the chance that a single combination that produces positive gain in both beamformers can be found.

Figure 25 illustrates a means to assign each of the four diversity antennas (A2, A3, B2 and B3) to either beamformer (A or B). The improvement in diversity gain can be evaluated for this capability by considering the pairing possibilities for antenna Al. It can be used with any two from the set of the four antennas A2, A3, B2 and B3 in combiner 2512. Because the antenna pairing for Antenna Bl is determined by the antennas not used for antenna Al, the number of choices is given by the combination probability equation for "n, choose k" in formula (1) as follows <img file="WO2013181219A2_D0006.tif" />

(1)

For this case n=4 and k=2 and the equation shows there are six unique combinations for antenna selection. It can be shown that by choosing from the best of the six antenna combinations reduces the probability no combination produces positive gain in both beamformers from 81% to approximately 28%. This means 72% of the time we should find a combination that produces positive gain.

In the previous embodiment all of the diversity antennas were pooled to produce the maximum number of combinations to choose from. It is possible to use the circuit of Figure 25 to allow six antenna combinations within a larger antenna array.

Figure 27 is a schematic illustration of possible switching configurations in Figure 25 that result in no diversity gain, according to some embodiments of the invention.

Figure 28 is a schematic illustration of a MEVIO receiving system having a ten antenna array with the RDN and antenna routing module embodied as device 2800, according to some embodiments of the invention. One beamformer in the RDN is associated with a main antenna A and four of the diversity antennas Al ... A4 and comprises LNA assemblies 2802, 2804, 2806, phase modulators 2830, 2824 and combiner 2836, another beamformer is associated with a main antenna B and another four of the diversity antennas B1...B4 and comprises LNA assemblies 2808, 2810, 2812, phase modulators 2826, 2828 and combiner 2838. The diversity antennas B1...B4 are modulated by the corresponding LNA assemblies and phase modulators. The antenna routing module is implemented by a switch matrix assembly 2832. Combiners 2836 and 2838 are connected to radio unit 2850, which is also connected to controller 2840 that controls the setting of the switch matrix 2832 according to qualitative indicators that are derived from the baseband module.

Figure 29 is a schematic illustration antenna routing module implementation using a switch matrix, used in the system of Figure 28 according to some embodiments of the invention. One beamformer in the RDN is associated with antennas A, Al... A4 and comprises combiner 2932, another beamformer is associated with antennas B, B1...B4 and comprises combiner 2934. The antenna routing module implementation in the form of a switch matrix is comprised of switches 2910, 2922, 2912, 2924 and switches 2914, 2926, 2916, 2928 corresponding to the beamformers, as explained below.

For this configuration, antennas A3 and A4 are pooled with antennas B3 and B4 using the circuit of Figure 29 to provide for the six possible configurations as in the previous discussion.

As shown in Figure 28, the circuit of Figure 29 must be duplicated to route the "bypass" signals from the antennas. Additional switch matrices may be added to pool other antennas. A following paragraph described later on in Figure 30 shows how a second switch matrix could be used with antennas Al, A2, Bl and B2. The application in the system is shown in Figure 31.

Figure 31 is a schematic high illustration of another MIMO receiving system 3101 having a ten antenna array with the RDN and antenna routing module embodied as device 3100, according to some embodiments of the invention. One beamformer in the RDN is associated with a main antenna A and four diversity antennas Al... A4 and comprises LNA assemblies 3112, 3114, 3116, phase modulators 3130, 3124 and combiner 3136, another beamformer is associated with a main antenna B and four diversity antennas BL. B4 and comprises LNA assemblies 3118, 3120, 3122, phase modulators 3126, 3128 and combiner 3138. The diversity antennas Al... A4 and BL. B4 are modulated by the corresponding LNA assemblies and phase modulators. The antenna routing module is implemented by switch matrix assemblies 3132 and 3134. Combiners 3136 and 3138 are connected to radio unit 3150, which is also connected to controller 1140 that manages the setting of matrices 1132, 1134 according to qualitative indicators that are derived from the baseband module.

Figure 30 is a schematic illustration of the second switch matrix, as implemented for the system of Figure 31 according to some embodiments of the invention. One beamformer in the RDN is associated with antennas A, Al ... A4 and comprises combiner 3032, another beamformer is associated with antennas B, Bl... B4 and comprises combiner 1034. The antenna routing module is implemented in switches 3012, 3022, 3014, 3024 and switches 3016, 3026, 3018, 3028 to be used with antennas Al, A2, B l and B2, offering a total of 36 unique antenna configurations rather than the 6 configurations provided by only one matrix, described in Figure 28 above.

The following is a procedure that applies optimal pooling based on desired signal' s power maximization with definitions set forth below.

NBFi number of beamformers sharing the same pool.

number of Rx antennas in each beamformer (it could vary).

NPooh number of Rx antennas in the pool ( Pool≥ NBF * N NPool≤ NBF * (N - 1) ).

Ι^&lt;ίΤ^χ : number of Tx antennas.

NFreq ; number of frequencies.

hu._r : channel transfer function from Tx antenna h J = 2 -■ NTx_* to Rx antenna i, i - 2 -NP&amp;el. at frequency k.

Φ_Ε:^: phase shift applied to Rx antenna * .

The Rx antennas are numbered from 1 to NPooL The indexes of all antennas assigned to a beamformer form a set. These sets are denoted by SET._rtr = 1..2 -. NBF. For example, for two beamformers of five antennas each, the sets could be S£T i =€L¾ 4, 7_f ioi and SET_a = f2,$_F 6&amp;9}.

For each beamformer, phases Φ; are optimized for example using the algorithm described in a previous disclosure.

After optimizing the delta phase of all Rx antennas in use, the combined channel transfer functions seen b the receivers are: <img file="WO2013181219A2_D0007.tif" /> r = 1. 2... NBF, k = % 2 .... NFreq

The power associated with ^sr,j,k is defined as:

For each beamformer, a beamformer power Bfpwst® is defined as: <img file="WO2013181219A2_D0008.tif" /> The combined power of all beamformers, W -TGTAL , is defined as: WRTOTM, = £ BF_PWRR

&gt;-= 1

In the aforementioned embodiment, the optimal pooling is the one that maximizes P^ B TOTAL-

Following in table (1) below is a non limiting example illustrating the benefit of pooling based on the aforementioned power maximization procedure.

Table (1)

In table (1) above, various number of transmitted layers (Tx ANT), as well as various number of receiving antennas per RF beamformers (Rx Ant) are compared with and without pooling.

In addition, table (1) presents how the received power changes when several variants are introduced, such as fading models (constant amplitude and Rayleigh ), as well as different Tx ANT correlations (0, 0.3 are shown).

Throughout table (1) the performance metric used is gain achieved by a MIMO augmented by an RDN, over legacy MIMO (i.e., not augmented architecture) with the same number of layers, is expressed in dB. As the table shows, an increase in dB is achieved for all pooling cases, both for correlated and uncorrelated antennas and for various number of receive and transmit antennas alike.

Figure 32 is a high level flowchart illustrating an aspect of a method according to some embodiments of the present invention. Method 3200 is a method of improving reception by a multiple-input-multiple-output (MIMO) receiving system comprising a MIMO baseband module having N branches and a radio distribution network (RDN) connected to the MIMO receiving system. Method 3200 may include the following stages: associating at least two beamformers with the RDN, each of the beamformers including at least one corresponding combiner; feeding each of the beamformers by two or more antennas, so that a total number of antennas in the system is M, wherein M is greater than N, configuring each combiner to combine signals coming from the antennas feeding the corresponding beamformer into a combined signal; and swapping at least one pair of antennas, each of the antennas in the at least one pair being associated with a different beamformer, based on at least one qualitative indicator derived from the baseband module.

As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or an apparatus. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit," "module" or "system."

The aforementioned flowchart and block diagrams illustrate the architecture, functionality, and operation of possible implementations of systems and methods according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

In the above description, an embodiment is an example or implementation of the inventions. The various appearances of "one embodiment," "an embodiment" or "some embodiments" do not necessarily all refer to the same embodiments.

Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination.

Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. Reference in the specification to "some embodiments", "an embodiment", "one embodiment" or "other embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the inventions. It is to be understood that the phraseology and terminology employed herein is not to be construed as limiting and are for descriptive purpose only.

The principles and uses of the teachings of the present invention may be better understood with reference to the accompanying description, figures and examples.

It is to be understood that the details set forth herein do not construe a limitation to an application of the invention.

Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in embodiments other than the ones outlined in the description above.

It is to be understood that the terms "including", "comprising", "consisting" and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps or integers.

If the specification or claims refer to "an additional" element, that does not preclude there being more than one of the additional element. It is to be understood that where the claims or specification refer to "a" or "an" element, such reference is not be construed that there is only one of that element.

It is to be understood that where the specification states that a component, feature, structure, or characteristic "may", "might", "can" or "could" be included, that particular component, feature, structure, or characteristic is not required to be included. Where applicable, although state diagrams, flow diagrams or both may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described. Methods of the present invention may be implemented by performing or completing manually, automatically, or a combination thereof, selected steps or tasks.

The term "method" may refer to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the art to which the invention belongs.

The descriptions, examples, methods and materials presented in the claims and the specification are not to be construed as limiting but rather as illustrative only.

Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined.

The present invention may be implemented in the testing or practice with methods and materials equivalent or similar to those described herein.

While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention.