Channel estimation for systems with transmission diversity

Channel estimation for systems with transmit diversity

[001] Technical Field

[002] The present invention generally relates to communications, and more particularly to a novel and improved method and apparatus for transmitting diversity pilot processing.

[003] Background Technology

[004] Wireless communication systems are widely used to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation technique. CDMA systems provide certain advantages over other types of systems, such as increased system capacity.

[005] The CDMA system can be designed to support one or more CDMA standards, such as (1) "TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System" (IS-95 standard) , (2) The standards provided by the association named "3rd Generation Partnership Project" (3GPP) are included in a set of documents, including document numbers 3G TS 25.211, 3G TS 25.212, 3G TS 25.213 and 3G TS 25.214 ( W-CDMA standard), (3) standards provided by the association named "3rd Generation Partnership Project 2" (3GPP2), included in a set of documents, including "C.S0002-A PhysicalLayer Standard for cdma2000 Spread Spectrum Systems ", "C.S0005-A UpperLayer(Layer 3)Signaling Standard for cdma2000 Spread Spectrum Systems and "C.S0024 cdma2000 High Rate Packet Data Air Interface Specification (cdma2000 standard), and (4) some other standards.

[006] A technique for improving performance, including system capacity and data throughput, is to reduce the required transmit signal power by using transmit diversity. Transmit diversity includes transmitting data on two or more antennas, where the geographic separation between the antennas results in independent path loss characteristics between the antennas. In this way, the receiving station can coherently combine the signals from the transmit diversity antenna without coherently combining the noise introduced in the channel, thereby improving the received signal-to-noise ratio (SNR).

[007] In order to distinguish the transmitted signals, a different pilot sequence is used for each antenna. In the dual-antenna scheme, for example, the main antenna transmits a main pilot sequence, and the diversity antenna transmits a diversity pilot sequence. The diversity pilot sequence can be generated by multiplying the main pilot sequence and the orthogonalization sequence, so that the main and diversity pilots are orthogonal.

[008] In order to demodulate each transmit diversity signal in the mobile station, an estimate of the pilot signal related to them is made. A method of pilot estimation known in the art utilizes the relationship between primary and diversity pilots just described. The received samples are despread with the main pilot sequence and accumulated. The buffer stores the previously accumulated symbols. According to the relationship between the main and diversity pilots, the current and previous accumulated symbols can be added or subtracted at a specific symbol boundary to derive estimates of both the main and the diversity pilot symbols. For example, by using the pilot sequence defined in the W-CDMA specification, a pilot estimate is generated every few symbols. These symbols are used for data demodulation of each symbol, working under the following assumption: During other symbols, the pilot estimate is approximately equal to those received during the previous symbol. In this way, during every few symbols, the recently despread pilot symbol does not play a role in channel estimation, and therefore is not used in data demodulation. This process is described in further detail below.

[009] Under certain circumstances, the assumption that the sequential pilot symbols are approximately equal is valid, and therefore the demodulation estimated using the previous pilot symbols is sufficient. However, when the channel adjustment changes more quickly, such as when the mobile station is operating at high speed, this assumption may no longer be valid, and the demodulation performance may be degraded to a point where it is not sufficient for the desired communication performance level. Therefore, there is a need in the art for improved diversity pilot estimation in a rapidly changing channel environment.

[010] Summary of the Invention

[011] The embodiments described herein address the need for improved diversity pilot estimation in a rapidly changing channel environment. On the one hand, the difference estimate is updated when the currently received symbol includes the difference between the main and diversity channels, and the sum estimate is updated when the currently received symbol includes the sum of the main and diversity channels. The main channel and the diversity channel are estimated in response to the sum estimation and the difference estimation. On the other hand, the total sum estimate and the difference estimate are generated by filtering the received symbols. In yet another aspect, the received symbols are demodulated in response to the primary and diversity channel estimates. The benefits of these aspects are the combination of the latest received symbols, resulting in more accurate channel estimation, and therefore improved demodulation performance, increased system capacity, reduced required transmit power, and other benefits.

[012] The present invention provides methods and system elements for implementing various aspects, embodiments, and features of the present invention, as detailed below.

[013] Brief Description of the Drawings

[014] The features, properties and advantages of the present invention will become more apparent through the detailed descriptions provided below in conjunction with the accompanying drawings. The same elements in the accompanying drawings have the same labels, among which:

[015] FIG. 1 is a general block diagram of a wireless communication system capable of supporting multiple users;

[016] FIG. 2 depicts a part of a wireless communication system with base stations and mobile stations configured for transmit diversity;

[017] FIG. 3 shows an exemplary relationship between two pilot signals used for diversity transmission as defined by the W-CDMA standard;

[018] FIG. 4 depicts a part of a mobile station suitable for transmitting diversity pilot processing;

[019] FIG. 5 describes the prior art implementation of the pilot de-cover block;

[020] FIG. 6 describes an embodiment of an improved pilot de-covering block;

[021] FIG. 7 depicts an embodiment of an exemplary parameter estimation block; and

[022] FIG. 8 depicts a flowchart of an embodiment of a method for estimating channel parameters using newly received symbols.

[023] Specific embodiment

[024] FIG. 1 is a schematic diagram of a wireless communication system 100. The system 100 can be designed to support one or more CDMa standards and/or designs (eg, W-CDMA standard, IS-95 standard, cdma2000 standard, HDR standard). For the sake of brevity, the illustrated system 100 includes three base stations 104 that communicate with two mobile stations 106. The base station and its coverage area are usually collectively referred to as "cells." In the IS-95 system, a cell will include one or more sectors. In the W-CDMA specification, each sector of the base station and the coverage area of the sector is called a cell. As used herein, the term "base station" can be used interchangeably with the terms "access point" or "Node B". The term "mobile station" can be used interchangeably with the terms "user equipment (UE)", "subscriber unit", "subscriber station", "access terminal", "remote terminal" or other corresponding terms known in the art. The term "mobile station" encompasses fixed wireless applications.

[025] According to the implemented CDMA system, each mobile station 106 will communicate with one (or possibly more) base stations 104 on the forward link at any given moment, and will vary according to whether the mobile station is in soft handover or not. Communicate with one or more base stations on the reverse link. The forward link (ie, downlink) refers to the transmission from the base station to the mobile station, and the reverse link (ie, uplink) refers to the transmission from the mobile station to the base station.

[026] For the sake of clarity, the examples used to describe the present invention will assume the base station as the originator of the signal and the mobile station as the receiver and acquirer of the signal, which is the signal on the forward link. Those skilled in the art will understand that mobile stations and base stations can be configured to transmit data as described herein, and various aspects of the present invention can also be applied to those situations. The word "exemplary" used exclusively here means "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" need not be considered more preferred or advantageous than other embodiments.

[027] FIG. 2 shows an embodiment of the system 100, which details a transmit diversity scheme. The base station 104 is equipped with two antennas 210 and 220 for communicating with the mobile station 106. (Other embodiments may use more than two antennas.) The links between antennas 210 and 220 and mobile station 106 are labeled S1 and S2, respectively. There is sufficient geographic separation between the positions of the two antennas, so that the fading experienced on S1 is independent of the fading on S2, and the two signals arrive at the mobile station 106 substantially at the same time. Various techniques can be used to make the two signals structurally combined at the mobile station, which can resist the harmful effects that would be introduced when only a single antenna is used.

[028] One such scheme detailed in the W-CDMA standard cited above is closed loop transmit diversity. The signal S2 transmitted on the diversity antenna 220 is adjusted in phase relative to the signal S1 transmitted on the main antenna 210 so that the two signals S1 and S2 are received in the same phase at the mobile station 106 and combined to the maximum. The terms "main" and "diversity" applied to the antennas 210 and 220, respectively, are only used to distinguish the two antennas. Those skilled in the art will recognize that the phase adjustment can occur on any antenna (or on multiple antennas).

[029] In another scheme, such as space-time transmit diversity (STTD), different data is sent on each antenna. The data is sent in such a way that it can be reassembled when it is received at the mobile station. For example, imagine a two-antenna transmit diversity scheme in which the symbols transmitted on the main antenna (i.e. antenna 1) have a complex gain of α when received at the mobile station, and the symbols transmitted on the diversity antenna (i.e. antenna 2) are When the mobile station is received, the complex gain is β. The complex gain is a function of the channel through which the two signals propagate.

[030] Consider two adjacent complex data signals d1 and d2 waiting to be transmitted. The data to be sent is distributed between the two antennas as follows: within a symbol transmission period, d1 is sent on antenna 1, and -d2* is sent on antenna 2 (where * represents conjugate). In the next symbol transmission period, d2 is sent on antenna 1 and d1* is sent on antenna 2. The signal received at the mobile station in the first symbol transmission period is r1, where r1=αd1-βd2*. The signal received at the mobile station in the second symbol transmission period is r2, where r2=αd2+βd1*. If the channel gains α and β are known, the two formulas r1 and r2 are sufficient to recover the data d1 and d2.

[031] The pilot signal received at the mobile station is proportional to the channel gains α and β. By recovering the two pilot signals sent on the main and diversity antennas: pilot 1 and pilot 2, the channel gain can be estimated. The recovered pilot is used to demodulate the signal sent from the corresponding antenna, as detailed below. In an exemplary embodiment, the pilot signals transmitted on each of the plurality of diversity antennas are orthogonal to each other. This property facilitates the recovery of the pilot once it is received at the mobile station and minimizes interference.

[032] A technique for generating orthogonal pilots in a CDMA system is to multiply the first pseudorandom noise (PN) sequence used for the first pilot signal with an orthogonalized signal to generate the second pilot. Frequency signal. Figure 3 describes how to generate an exemplary set of pilot signals as described in the W-CDMA standard. In Figure 3, the primary and diversity pilots are generated by multiplying the base PN sequence by the value showing the corresponding symbol number. In this example, the primary pilot is generated by multiplying the base PN sequence by a constant amplitude A. Use A in symbols 0 and 3, and multiply the base PN sequence by -A in symbols 1 and 2 to generate diversity pilots. This pattern is repeated for each subsequent group of four symbols (as specified for the W-CDMA standard, except at frame boundaries). In an exemplary embodiment, each symbol includes 256 chips. It can be easily seen that the generated main and diversity pilot sequences are orthogonal to each other. Those skilled in the art will recognize various other orthogonalization sequences that can use a common basic sequence to generate orthogonal pilot sequences. Those skilled in the art also recognize that other orthogonalization sequences can be constructed to generate multiple orthogonal pilots for transmission on multiple diversity antennas.

[033] FIG. 4 depicts a part of a mobile station suitable for transmission diversity pilot processing. The signal is received at antenna 410 and transmitted for conversion to baseband in RF downconverter 415 using techniques known in the art. The baseband samples are transmitted to the timing offset 420, where the sampling streams of on-time, advanced and delayed are generated corresponding to the timing offsets within the incoming signal τ, τ-1/2, and τ+1/2, respectively. The advance sequence is sampled before the timing reference, and the lag sequence is sampled after the timing reference. The advance and lag sequences are usually sampled from one-half of a chip from the timing reference, but other differences can also be used.

[034] The advance and lag sequence are transmitted to the tracking loop 460. In order to maximize the received energy and minimize the error, timing tracking is performed to minimize the phase difference between the demodulated pilot signal and the demodulated signal. Various time tracking techniques are known in the art. Techniques for time tracking in a transmit diversity system include a method of independently tracking signals from multiple antennas, and a method of tracking a weighted average of signals from each antenna using a single tracking loop. These methods are described in the following U.S. patent applications: Pending U.S. Patent Application No. 09/964,589, filed on September 25, 2001, entitled "TIME TRACKING IN ANON-NEGLIGIBLE MULTIPATH SPACING ENVIRONMENT"; January 31, 2002 U.S. Patent Application No. 10/061,873 filed on Japan, entitled "TIME TRACKING LOOP FOR DIVERSITY PILOTS", both patent applications are assigned to the assignee of the present invention. One type of technique compares the energy in the advance and lag sequence, and adjusts the timing reference τ accordingly.

[035] The data demodulator 430 is used to demodulate the punctual sequence from the timing offset 420, the timing of which is indicated by the output of the tracking loop 460. Pilot de-coverer 440 also uses on-time sampling to generate estimates of the main and diversity pilots,

with

They are used to demodulate data in the data demodulator 430. The data demodulator 430 generates data corresponding to the data received from the main and diversity antennas. If necessary, a data demultiplexer 450 is used to demultiplex the two antenna data streams to generate output data symbols.

[036] The following discussion will use the main and diversity pilot sequences defined in the W-CDMA standard as an example. Those skilled in the art will apply these principles to other pilot sequences. Figure 3 shows the relationship between the main and diversity sequences, as described above. In W-CDMA, the downlink common pilot channel (CPICH) can be used as a channel condition reference in the demodulation process. When transmit diversity is not used, CPICH is a fixed rate (30 kbps, spreading factor = 256) downlink channel that transmits a predefined bit/symbol sequence. In particular, CPICH is the main scrambling code of a cell spread by an all-zero sequence. In this way, CPICH is the scrambling code multiplied by 1+j. In order to simplify the following formula, A=1+j.

[037] When using transmit diversity on the downlink channel, CPICH is sent from two antennas, as described with reference to the non-diversity case above. In addition, in order to distinguish between primary and diversity channels, the data transmitted on the diversity antenna is modulated by a specific pattern. The k-th symbol in a radio frame is given in formula 1, expressed as sk:

[038] <math> <mrow> <msub> <mi>s</mi> <mi>k</mi> </msub> <mo>=</mo> <msup> <mrow> <mo>( </mo> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <msub> <mi>f</mi> <mi>k</mi > </msub> </msup> <mo>·</mo> <mi>A</mi> </mrow> </math> Formula 1

[039] where fk is given by Equation 2:

[040]

Formula 2

[041] The sequences generated by Equations 1 and 2 are the diversity pilot sequences described in FIG. 3. Note that in the W-CDMA embodiment, each radio frame includes 150 symbols, so k is incremented in the range of 0...149, and then repeated. The principle of the present invention is applied to any number of symbols in a radio frame, and fk can be modified to generate any sequence sk. Generally, sk can be designed so that the main and diversity pilots are orthogonal over some number of symbols. In this example, the main and diversity pilots are orthogonal on two symbols. Those skilled in the art will recognize many combinations of primary and diversity pilot sequences, with the two pilots being orthogonal over many symbol lengths. All these combinations are within the scope of the present invention.

[042] Equation 3 gives the symbol rk received at the mobile station at time k:

[043] <math> <mrow> <msub> <mi>r</mi> <mi>k</mi> </msub> <mo>=</mo> <msub> <mi>α</ mi> <mi>k</mi> </msub> <mi>A</mi> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mo>-</ mo> <mn>1</mn> <mo>)</mo> </mrow> <msub> <mi>f</mi> <mi>k</mi> </msub> </msup> < msub> <mi>β</mi> <mi>k</mi> </msub> <mi>A</mi> <mo>+</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> </mrow> </math> Formula 3

[044] where αk and βk are the complex-valued channel gains from the main and diversity antennas, respectively, and nk is the additional noise. For use in the demodulation process, estimates of αk and βk are made. In other words, the calculated value in the pilot de-coverer 440 can be estimated from αk and βk

with

Those skilled in the art can recognize this technology.

[045] In order to understand the limitations of the prior art on estimating channel gain, first assume a case where there is no transmit diversity. In this case, the single complex-valued channel gain αk represents the transmission channel. Equation 4 gives the symbols received at the mobile station at time k:

[046] γk=αkA+nk Formula 4

[047] A reliable approximation of αk can be formed from the received symbols, an example of which is given in Equation 5:

[048] <math> <mrow> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> <mi>k</mi> </msub> <mo >=</mo> <msub> <mi>h</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>r</mi > <mi>k</mi> </msub> <mo>,</mo> <msub> <mi>r</mi> <mrow> <mi>k</mi> <mo>-</mo > <mn>1</mn> </mrow> </msub> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> < mo>)</mo> </mrow> </mrow> </math> Formula 5

[049] where h1 will be any filter.

[050] Approximately

It is formed with symbols received at time k and before, and can be used to demodulate data symbols arriving at time k. Doing so will need to buffer the data symbols, because it will need to be in the calculation

Previously received rk. Usually, this kind of buffering requires additional storage resources and introduces a delay in the demodulation process. To avoid buffering, the channel estimation at time k can be used to demodulate the symbols received at time k+1. The principle of the present invention is applied with equal force regardless of whether the cushioning is used. For the sake of clarity, the buffered demodulation case will be described in this discussion, that is, where the data received at time k is demodulated using channel estimates based on symbols received at time k and before.

[051] When using transmit diversity, the existing implementation relies on the following assumptions: αk is approximately equal to αk+1, and βk is approximately equal to βk+1. Therefore, the pilot estimation can be approximated as in Equations 6 and 7:

[052] <math> <mrow> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> <mrow> <mn>2</mn> <mi> l</mi> </mrow> </msub> <mo></mo> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> < mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo>=</mo> <msub> <mi>h</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mfrac> <mrow> <msub> <mi>r</mi > <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>2</mn> </mrow> </msub> <mo>+</ mo> <msub> <mi>r</mi> <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> </mrow> <mn>2</mn> </mfrac> <mo>,</mo> <mfrac> <mrow> <msub> <mi>r</mi> < mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>4</mn> </mrow> </msub> <mo>+</mo> <msub> <mi>r</mi> <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>3</mn> </mrow> </msub> </mrow> <mn>2</mn> </mfrac> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> mo> <mo>)</mo> </mrow> </mrow> </math> Formula 6

[053] <math> <mrow> <msub> <mover> <mi>β</mi> <mo>~</mo> </mover> <mrow> <mn>2</mn> <mi> l</mi> </mrow> </msub> <mo></mo> <msub> <mover> <mi>β</mi> <mo>~</mo> </mover> < mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo>=</mo> <msub> <mi>h</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mfrac> <mrow> <msup> <mrow> <mo>( </mo> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <msub> <mi>f</mi> <mrow> <mn>2 </mn> <mi>l</mi> <mo>-</mo> <mn>2</mn> </mrow> </msub> </msup> <msub> <mi>r</mi> <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>2</mn> </mrow> </msub > <mo>+</mo> <msup> <mrow> <mo>(</mo> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow > <msub> <mi>f</mi> <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>1</mn> </mrow > </msub> </msup> <msub> <mi>r</mi> <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn> 1</mn> </mrow> </msub> </mrow> <mn>2</mn> </mfrac> <mo>,</mo> <mfrac> <mrow> <msup> <mrow> < mo>(</mo> <mo>-</mo> <mn>1</mn><mo>)</mo> </mrow> <msub> <mi>f</mi> <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>4</mn> </mrow> </msub> </msup> <msub> <mi>r</mi> <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>4</mn> </mrow> </msub> <mo>+</mo> <msup> <mrow> <mo>( </mo> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <msub> <mi>f</mi> <mrow> <mn>2 </mn> <mi>l</mi> <mo>-</mo> <mn>3</mn> </mrow> </msub> </msup> <msub> <mi>r</mi > <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>3</mn> </mrow> </msub> </mrow> <mn >2</mn> </mfrac> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>)</mo> </mrow> </mrow> </math> Formula 7

[054] Where h2 can be any filter, and 1 is an integer. In this way, <math> <mrow> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> <mn>2</mn> </msub> <mo> </mo> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> <mn>1</mn> </msub> <mo>,< /mo> </mrow> </math> <math> <mrow> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> <mn>4</ mn> </msub> <mo></mo> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> <mn>3</mn> </msub> <mo>,</mo> </mrow> </math> <math> <mrow> <msub> <mover> <mi>α <mn>6</mn> </msub> <mo></mo> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> <mn >5</mn> </msub> <mo>,</mo> </mrow> </math> and so on. Similarly, <math> <mrow> <msub> <mover> <mi>β</mi> <mo>~</mo> </mover> <mn>2</mn> </msub> <mo> </mo> <msub> <mover> <mi>β</mi> <mo>~</mo> </mover> <mn>1</mn> </msub> <mo>,< /mo> </mrow> </math> <math> <mrow> <msub> <mover> <mi>β</mi> <mo>~</mo> </mover> <mn>4</ mn> </msub> <mo></mo> <msub> <mover> < </msub> <mo>,</mo> </mrow> </math> <math> <mrow> <msub> <mover> <mi>β</mi> <mo>~</mo> < /mover> <mn>6</mn> </msub> <mo></mo> <msub> <mover> <mi>β</mi> <mo>~</mo> </mover > <mn>5</mn> </msub> <mo>,</mo> </mrow> </math> and so on.

[055] Comparing Formula 5 with Formulas 6 and 7, it is noted that all other estimation groups do not act on the newly received symbol in the case of transmit diversity. especially,

with

The newly received symbol r21 is not used. Under certain circumstances, such as when the mobile station is moving at a high speed, ignoring the newly received symbols will lead to a large estimation error in the channel estimation, and thus the pilot estimation

with

The demodulation performance is significantly degraded.

[056] FIG. 5 depicts a prior art implementation of the pilot de-coverer 440. The incoming on-time symbols are despread with the main pilot sequence in the despreader 510, and are accumulated in the accumulator 520 to generate the symbol r1. The buffer 530 also stores the previously accumulated symbols, denoted as τ0.

[057] The current or previous symbols r0 and r1 can be added or subtracted to derive estimates of both the main and diversity pilot symbols. Note that during each symbol interval k, the mobile station receives a combination of signals transmitted from the main and diversity antennas, corresponding to the complex gains of the corresponding channels as αk and βk. In symbol 0, (αk+βk)A is received. In symbol 1, (αk-βk)A is received. In symbol 2, (αk-βk)A is received. In symbol 3, (αk+βk)A is received. These patterns repeat. Adding symbol 0 to symbol 1 leads to 2(αk)(A), which is proportional to αk and can be used for estimation

Subtracting symbol 1 from symbol 0 derives 2(βk)(A), which is proportional to βk and can be used for estimation

Add symbol 2 and symbol 3 and derive 2(αk)(A), which is proportional to αk and can be used for estimation

The difference between symbol 2 and symbol 3 is 2(βk)(A), which is proportional to βk and can be used for estimation

This process can be repeated, using the estimates used for data demodulation to calculate pilot estimates for all other symbols. This process is implemented in a parameter estimation block 540, which receives r0 and r1 and generates outputs (r0+r1)/2 and (r0-r1)/2. Switches 570 and 580 direct these two outputs to filters 550 and 560, respectively, every few symbols. The filters 550 and 560 can be used to achieve the average noise factor nk, and to generate estimates based on the previous symbols, as given in Equations 6 and 7 above. The outputs of filters 550 and 560 are estimates of αk and βk, respectively.

[058] For example, imagine filters 550 and 560 each using a single-pole infinite impulse response (IIR) filter. For the sake of brevity, only

The generation.

The generation is similar.

The estimate of is determined according to Equation 8:

[059] <math> <mrow> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> <mrow> <mn>2</mn> <mi> l</mi> </mrow> </msub> <mo></mo> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> < mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo>=</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>a</mi> <mo>)</mo> </mrow> <msub> <mover> <mi>α</mi> <mo>~</mo> </mover> <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo > <mn>3</mn> </mrow> </msub> <mo>+</mo> <mi>α</mi> <mrow> <mo>(</mo> <mfrac> <mrow> <msub> <mi>r</mi> <mrow> <mn>2</mn> <mi>l</mi> <mo>-</mo> <mn>1</ mn> </mrow> </msub> <mo>+</mo> <msub> <mi>r</mi> <mrow> <mn>2</mn> <mi>l</mi> <mo >-</mo> <mn>2</mn> </mrow> </msub> </mrow> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> </mrow> </math> Formula 8

[060] where a is the IRR coefficient and 1 is an integer. By using this example, we can see that when k is an even number,

The estimate of is the same as the previous estimate, so the most recent symbol is not included. This effect is summarized in Table 1.

[061] Table 1 k The average age of the symbols used by the symbols 1 r0, r1 1.0 0.5 2 r0, r1 2, 1 1.5 3 r2, r3 1, 0 0.5 4 r2, r3 2, 1 1.5 5 r4 , R5 1, 0 0.5 ... ... ... ...

[062] The first column in Table 1 shows the symbol index k. The second column indicates which two most recently received symbols are included in the filter calculation. The third column indicates the age of the two most recent symbols, expressed in symbol numbers. The fourth column shows the average age of the two most recent symbols. Those skilled in the art will recognize that as the average age of the symbols used in the estimation decreases, the accuracy of the estimation increases. These prior art age calculations will be compared with those of an embodiment of the present invention using similar IIR filters, as detailed below.

[063] Compared with the prior art above with reference to FIG. 5, the embodiments disclosed herein incorporate the most recently received symbols in each channel parameter estimation. The principle is that each symbol is proportional to the sum or difference of α and β. Estimated a difference term and a sum term, instead of waiting for consecutive symbols to arrive to find an estimate, the latter means the delay of one symbol in the W-CDMA system (other systems will use orthogonalized sequences that introduce additional delay requirements) . The difference or sum will be updated every symbol. The difference or sum terms can be filtered to provide a more stable estimate. Then estimate from the difference estimate and the sum estimate

with

Combines the information included in the most recently received symbol.

[064] FIG. 6 illustrates an embodiment of the pilot de-coverer 440, which alleviates the above-mentioned symbol age problem. As shown in FIG. 5, the on-time sampling is despread and accumulated in the despreader 510 and the accumulator 520. Then, the switch control 610 is used to control the switches 612 and 614 to introduce the symbols accumulated in the accumulator 520 into the α+β estimate 620 or the α-β estimate 630, respectively. The most recently accumulated symbol is always used to update one estimate or the other. The parameter estimation block 640 receives the estimates of α+β and α-β, and generates αk and βk, and

with

Estimate.

[065] The timing of the switches 612 and 614 controlled by the switch control 610 will change according to the relationship between the pilot signals on the primary and diversity antennas, and those skilled in the art will easily adapt the switch control 610 to any system. For the exemplary W-CDMA embodiment, switch 612 is activated whenever the received symbol is the sum of the main and diversity pilots, which occurs when fk is an even number. The switch 614 is activated whenever the switch 612 is not activated, or whenever fk is an odd number.

[066] FIG. 7 illustrates an embodiment of the parameter estimation block 640. The estimate of α+β is added to the estimate of α-β in the adder 710 to generate

Then divide by two in the divider 730 to produce

Those skilled in the art will recognize that a variety of techniques can be used to perform the divider 730, including simple shift operations. Moreover, those skilled in the art will recognize that in some embodiments, due to

versus

It is proportional and will compensate for the subsequent pilot processing by a factor of 2, so the division is not necessary. Similarly, α-β is subtracted from α+β in adder 720 to produce

It can be divided in the divider 740. For the above reasons, the divider 740 is optional, and can be used with any division technique, including shifting as known in the art.

[067] The implementation of the α+β estimation 620 or the α-β estimation 630 may include any type of filter. An example is an IIR filter similar to that described in Equation 8 above. In this example, filters 620 and 630 are given by Equations 9 and 10, respectively:

[068] (α+β)k=(1-a)(α+β)k-1+ark Equation 9

[069] (α-β)k=(1-a)(α-β)k-1+ark Equation 10, where rk is the input to the filters 620 and 630 according to the switch control 610.

[070] For the sake of brevity, consider an example in which the filter coefficient a is equal to 1, and the α+β estimate 620 and the α-β estimate 630 are just registers. According to this example, it can be seen that the most recently arrived symbol rk is always used to calculate the estimate

with

These effects are summarized in Table 2.

[071] The average age of the symbols used in table 2 k is 1 r0, r1 1.0 0.5 2 r0, r2 2, 0 1.0 3 r3, r2 0, 1 0.5 4 r4, r2 0, 2 1.0 5 r4 , R5 1, 0 0.5 ... ... ... ...

[072] In a manner similar to Table 1, the first column in Table 2 shows the symbol index k. The second column represents the two most recently received symbols included in the filter calculation. The third column indicates the age of those symbols, expressed in symbol numbers. The fourth column shows the average age of the two most recent symbols. As described above, those skilled in the art will recognize that as the average age of the symbols used in the estimation decreases, the accuracy of the estimation increases. Compared with the above age effect with reference to Table 1, Table 1 shows the average age of symbols between 0.5 and 1.5, and the average age of this embodiment is between 0.5 and 1.0. During the period when k is an odd number of symbols, the performance of the two embodiments is the same. During the period when k is an even number of symbols, this embodiment shows the benefit of using the most recently received symbol.

[073] FIG. 8 depicts a flowchart of an embodiment of a method for estimating channel parameters using recently received symbols. The process starts at step 810, where the symbols including the main and diversity pilot symbols are correlated and accumulated. Proceed to decision block 820. In decision block 820, if the symbol contains the difference between the main and diversity pilots, proceed to step 830 and update the difference estimate with the most recent symbol. In the exemplary embodiment shown in FIG. 6, the decision block 820 may be implemented with a switch control 610 and switches 612 and 614. The activation switch 614 updates the α-β estimate in the α-β estimate 630. In decision block 820, if the symbol does not contain the difference between the pilots, but the sum of the main and diversity pilots, then proceed to step 840 and update the sum estimate with the latest symbol. In the exemplary embodiment depicted in FIG. 6, the activation switch 614 updates the α+β estimate in the α+β estimate 620. Continue from either step 830 or 840 to step 850 and estimate the channel parameters from the difference estimation and the sum estimation. In the exemplary embodiment of FIG. 6, step 850 may be implemented by the parameter estimation block 640, an example of which is detailed in FIG. 7.

[074] Note that the above discussion uses the signals, codes, and parameters defined in the W-CDMA standard as some exemplary signals, codes, and parameters. This is just for the convenience of discussion and should not be regarded as limiting the scope of the present invention to the W-CDMA system. The principle of the present invention is applied to any conceivable system that uses an orthogonalized sequence to generate primary and diversity pilots with the attributes. Various combinations of pilot and data coding schemes for diversity transmission according to antenna authentication are anticipated, and they fall within the scope of the present invention. Those skilled in the art will recognize how to apply the various embodiments described to these other systems.

[075] It should be noted that in all the above embodiments, the method steps can be interchanged without departing from the scope of the present invention.

[076] Those skilled in the art can understand that information and signals can be represented by any of a variety of different technologies and processes. For example, the data, instructions, commands, information, signals, bits, symbols, and chips that may be involved in the above description can be represented by voltage, current, electromagnetic waves, magnetic fields or their particles, light fields or their particles, or any combination thereof. .

[077] Those skilled in the art can further understand that the various illustrative logical blocks, modules, circuits, and algorithm steps described in the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of both . In order to clearly illustrate the interchangeability between hardware and software, various illustrative components, block diagrams, modules, circuits, and steps are generally described according to their functionality. Whether these functions are implemented as hardware or software depends on the specific application and constraints on the overall system design. Skilled technicians may implement the functions in different ways for each specific application, but such implementation decisions should not be construed as departing from the scope of the present invention.

[078] The various illustrative logic blocks, modules, and algorithm steps described in conjunction with the embodiments described herein can be implemented or executed by: general-purpose processors, digital signal processors (DSP), and application-specific integrated circuits (ASIC) , Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented by a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration.

[079] The steps of the method or algorithm described in the embodiments disclosed herein may be directly included in the hardware, in the software module executed by the processor, or in both. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from the storage medium or write information to the storage medium. Alternatively, the storage medium may be integrated with the processor. The processor and storage medium may reside in the ASIC. The ASIC may reside in the user terminal. Alternatively, the processor and storage medium may reside as discrete components in the user terminal.

[080] The above description of the disclosed specific embodiments is provided to enable those skilled in the art to make or use the present invention. Various modifications of these embodiments are obvious to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the embodiments shown here, but should conform to the broadest scope consistent with the principles and novel features disclosed herein.