Directional radio beam information in a mobile communications system

0001The present invention relates to the provision of radio beam information for one or more radio beams in a mobile communications system.

0002With the evolution of cellular technology from existing 3.9G and 4G systems (such as 3GPP's LTE and LTE-Advanced radio access technologies) to 5G, higher frequencies are likely to be required. For example, the next generation radio access technology to be specified by 3GPP as a submission into the IMT 2020 process triggered by ITU-R is expected to operate in "legacy" frequency bands of up to 6 GHz and in some new frequency bands well beyond this point. Future base stations may therefore use wireless technology based on millimetre wavelengths (e.g., in frequency bands ranging from 20 to 300 GHz) to communicate with mobile devices within their coverage areas.

0003In order to achieve greater reach using a given power budget or to make use of the good spatial re-use properties radio links operated on higher frequencies offer, deployed base stations may utilize directional transmission and reception techniques to communicate with mobile devices.

0004This invention deals with directional antennas and beam steering methods, which are particularly useful for deployment in future communication systems operating in higher frequency bands. In principle, beam forming techniques can also be utilized in current cellular communication systems operating in "legacy" frequency bands below 6 GHz.

0005As opposed to omnidirectional antennas, directional antennas allow concentration of radio signals towards a certain spot or area. Concentration of radio waves into a certain direction can be achieved for instance with antenna arrays (also known as "phased arrays"). Usually, concentrated transmissions come along with a reduction of the respective radio beam's width.

0006An antenna array is an antenna system that encompasses a certain number of distinct antenna elements in a geometrical arrangement. The geometrical arrangement of these single antenna elements may vary significantly and determines the beam forming characteristics as follows: arranging multiple antenna elements in a row (e.g., in a 1x8 formation) would allow for two-dimensional beam forming within a (pre-defined) dissemination plane. An arrangement in matrix format (e.g., in an 8x8 formation) would allow for three-dimensional beam forming in a (pre-defined) dissemination space.

0007The relative phases of the respective signals feeding the distinct antenna elements forming an antenna array are set in such a way that the effective radiation pattern of the entire array is reinforced in a desired direction and - at the same time - suppressed in undesired directions. The phase relationship among the single antenna elements may be fixed or it may be adjustable (as for beam steering). The present invention is concerned with the latter.

0008A directed antenna beam (e.g., generated by means of a one dimensional antenna array, such as the 1x8 phased array mentioned above) usually consists of a strong main lobe pointing in the desired direction of signal reinforcement and at least one side lobe with much less intensity.

0009While the directional transmission and reception techniques may provide a given base station with greater reach, a trade-off may be that at any point in time, they may provide coverage to only part of that base station's coverage area. In order to provide coverage to its entire coverage area over time, a base station may (e.g. continuously or occasionally) modify its directional transmission and reception orientations. From the perspective of a given mobile device in the base station's coverage area, this may mean that data can be exchanged only at certain times, namely times at which the base station's directional transmission and reception orientation is approximately in the direction of the mobile device.

0010With a two dimensional antenna array, two beam forming operations may be performed. A radio beam can be tilted vertically and laterally. By placing the antenna array at a suitable height above the ground, a base station is able to concentrate a main lobe towards a particular region on the ground which may be considered as a sub-section within a base station's coverage area.

0011Beam steering within mobile communications systems is known. <patcit id="pcit0001" dnum="US2014235254A1"><text>US 2014/235254 A1</text></patcit>, for example, describes a set of femto access points (FAPs) utilized to localize, predict, and/or weight potential wireless communication traffic within and between areas. Moreover, attachment data can be indicative of user equipment (UE) density/traffic within coverage areas of respective femtocells. The attachment data can be consolidated and analysed to identify location and motion of a UE "swarm". Moreover an automatic cell planning (ACP) component can be employed to utilize the attachment data for determining an optimal macro site and optimal antenna setting(s) that facilitate steering/tuning the macro antenna beam to focus upon the swarm area. In addition, the ACP component can facilitate reconfiguration of the macro antenna beam as reported swarm concentrations shift between the FAPs.

0012<patcit id="pcit0002" dnum="US2013336176A1"><text>US 2013/336176 A1</text></patcit> describes an LTE base station employing scanning beam forming techniques. The base station is arranged to locate users within sub-areas of an overall coverage area. A coordination system is provided to enable data transmission where a scanning beam is employed. <patcit id="pcit0003" dnum="US2013337822A1"><text>US 2013/337822 A1</text></patcit> describes a further LTE system employing an agile beam forming antenna system. To determine a position of a user, a channel quality indicator measurement and a sounding reference signal are used.

0013<patcit id="pcit0004" dnum="US20150351135A1"><text>US 2015/0351135 A1</text></patcit> describes an earlier invention of the present inventors relating to beam forming and in particular the exchange of beam forming information for a dual connection to a user equipment. A beam activation response message including a beam identifier is received by a UE. It is indicated that the beam identifier is transmitted as part of the beam adjustment data and therefore encoded in the data link layer of the OSI layer model. The beam activation response message is a dedicated downlink message exchanged at the RRC layer and is a response to a request coming from the UE (i.e. a preceding uplink message, also sent at the RRC layer). The network tells the UE in the message what beam it is supposed to listen to, and in what direction it is expected to turn its transmission and reception orientation.

0014<patcit id="pcit0005" dnum="US20130223251A1"><text>US 2013/0223251 A1</text></patcit> describes a beam forming system in which identifiers of beams are transmitted in downlink control channels and the steered beams carry these identifiers.

0015The present invention provides a method performed by a user equipment of providing information to a first base station relating to directional beam signals received by the user equipment from one or more other base stations and optionally the first base station, the method comprising receiving with signals transmitted from a base station via a directional beam an identifier, the identifier having a property of distinguishing the directional beam from other directional beams; and transmitting to the first base station a report including information about the received identifier of the directional beam and in a further aspect a user equipment adapted to perform such a method, wherein the received identifier is encoded in the signals transmitted by the base station at a physical layer, the physical layer being the lowest layer for communication between the base station and the user equipment according to a multi-layer model known as the open systems interconnection, OSI, model. The other base stations are referred to as second base stations in the following.

0016In a further aspect, the invention provides a radio communication transmission and reception point arranged to transmit a plurality of directional beams with each directional beam covering a sub-section of a total coverage area, and wherein the transmission and reception point periodically changes which sub-sections are receiving directional beams, wherein the transmission and reception point is arranged to transmit a beam identifier with each directional beam, the beam identifier being capable of distinguishing one directional beam from other directional beams, wherein the transmission and reception point is arranged to transmit the beam identifier by encoding the beam identifier in the directional beams at a physical layer, the physical layer being the lowest layer for communication between the base station and the user equipment according to a multi-layer model known as the open systems interconnection, OSI, model..

0017Embodiments of the present invention may include information about a current beam forming and/or hopping configuration of a transmission and reception point (TRP) in a radio signal. In other words, a form of lobe direction indicator (LDI) or a beam identifier or a target area itemization code is included on a downlink signal that differs from sub section to sub section.

0018According to a first embodiment of the present invention, a mobile device may receive this signal or identifier and may report it in an uplink direction to its serving base station (e.g., as part of the neighbouring cell measurements reporting procedure). On the infrastructure side a lookup table may be provided. It enables derivation of the appropriate beam forming settings from the LDI for usage by the transmission and reception point (TRP) to serve the UE right at the spot where it picked up the reported signal strength.

0019The network may use this new LDI to quickly steer a beam to the indicated direction to enable a permanent link towards this UE instead of using a hopping pattern. A new resource is provided for the LDI, rather than occupying an already available resource in a downlink direction.

0020By means of the invention, the UE does not have to wait for the beam to complete a full hopping cycle before it returns to the area of interest. Instead, the base station's transmission and reception orientation (i.e. the lobe) can be directed by the transmission and reception point (TRP) right away to the respective sub section where the mobile device of interest is currently residing.

0021Thus, the mobile device's handover to a cell offered by the second base station or the addition/activation of further carriers in the scope of carrier aggregation (CA) or dual connectivity (DC) may be faster.

0022According to a second embodiment of the present invention, a mobile device may receive the signal or identifier and may report it in an uplink direction to its serving base station (e.g., as part of positioning activities). On the infrastructure side the LDI may be used to assist in determining the mobile device's position. In order to enhance accuracy, it may be beneficial to let the mobile device report multiple LDIs received from multiple second base stations.

0023In the context of the present invention a directional beam signal shall be understood as a directed radio transmission in general, i.e. a directional beam signal may be made up of one or multiple stationary and/or (partially) moving transmission lobe(s), whereby the kind of movement may be anything from hopping in coarse granularity to continuous sweeping in fine granularity.

0024Preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: <dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>shows a coverage area of a transmission and reception point;</dd><dt>Fig. 2</dt><dd>shows a schematic representation of a heterogeneous network;</dd><dt>Fig. 3</dt><dd>illustrates a downlink resource grid for FDD-LTE;</dd><dt>Fig. 4</dt><dd>is a schematic representation of a UE within a heterogeneous network;</dd><dt>Fig. 5</dt><dd>is a schematic representation of a UE within a heterogeneous network implementing the present invention;</dd><dt>Fig. 6</dt><dd>illustrates the transmission of a beam identifier using spare sub-carriers;</dd><dt>Fig. 7</dt><dd>illustrates the transmission of a beam identifier using phase shift keying of synchronization signals;</dd><dt>Fig. 8</dt><dd>illustrates the transmission of a beam identifier using phase shift keying of synchronization signals across multiple frames;</dd><dt>Fig. 9</dt><dd>illustrates phase shift keying of synchronization signals in an I/Q diagram;</dd><dt>Fig. 10</dt><dd>shows an example of a message sequence chart implementing the first embodiment of the present invention; and</dd><dt>Fig. 11</dt><dd>shows an example of a message sequence chart implementing the second embodiment of the present invention.</dd></dl>

0025Referring to <figref idref="f0001">Fig. 1</figref>, there is shown an example of a coverage area of a transmission and reception point TRP that supports beam forming. The coverage area is shown schematically to illustrate the principles of the present invention. The coverage area shown may be an excerpt of a bigger coverage area. In this example it is subdivided into eight sub sections A through H. In detail, a vertical tilt of -2° plus a horizontal rotation of -2° (to the left) would enable the base station to service sub section G, i.e. to provide a wireless connection to UE1. Similarly, a vertical tilt of -3° plus a horizontal rotation of +2° (to the right) would enable the base station to provide its service offerings to UE2 residing in sub section F. The sub-sections represent areas which would be illuminated by a beam generated when the antenna elements at the TRP are subject to the appropriate beam forming characteristics.

0026As the end points of beams are concentrated on relatively small spots (i.e. the base station's directional transmission and reception orientation is at any point in time directed to exactly one of the sub sections A through H of the base station's coverage area according to <figref idref="f0001">Fig. 1</figref>), the base station may control the orientation of lobes from the TRP in such a way that all (or at least all relevant) sub sections are served successively. This solution is reasonable e.g. if the location of the receiving UE is unknown. The hopping pattern doesn't have to be in strict order from A to H; it may be any order. Even skipping one area or another from time to time and/or serving an area multiple times during one cycle would be possible (e.g., depending on population of mobile devices and/or their traffic demands). A deployment scenario like this (with sequential hopping from one sub section to the next one) will be referred to as Example Configuration #1 in the following description.

0027It is also possible for a TRP to simultaneously create multiple lobes pointing into different or roughly the same direction. For example, in the scenario of <figref idref="f0001">Fig. 1</figref>, a lobe structure of four main beams could be created offering equally good coverage at the same time instance to sub sections C, D, E, and F - provided that the antenna array is composed of a number of antenna elements adequate to create such complex lobe structures. A deployment scenario like this (with multiple lobes serving more than one sub section at the same time) will be referred to as Example Configuration #2 in the following description.

0028Furthermore, it is possible for a TRP to combine the two example TRP configurations #1 and #2 discussed above, i.e. to create complex lobe structures consisting of multiple radio beams that are (partially or entirely) hopping through a coverage area. Within such a complex lobe structure, new lobes may be created and existing lobes may be deactivated on a per need basis or based on some algorithms. Lobes may also partially overlap in the time and/or space domain(s). For example, in reference to <figref idref="f0001">Fig. 1</figref>, the TRP could be configured at a first time instance to form a lobe structure made up of four main beams offering equally good coverage to sub sections A, B, C, and D, then (at a second time instance) a lobe structure made up of four main beams offering equally good coverage to sub sections C, D, E, and F, and so on. In another example, again with reference to <figref idref="f0001">Fig. 1</figref>, the TRP could be configured at a third time instance to form a lobe structure made up of five main beams offering equally good coverage to sub sections A, C, E, G, and H, then (at a fourth time instance) a lobe structure made up of three main beams offering equally good coverage to sub sections F, G, and H, and so on.

0029Referring to <figref idref="f0001">Fig. 2</figref>, there is shown a schematic example of a communications network. In order to provide optimum network coverage many deployment scenarios in today's cellular communication networks combine a macro cell layer (base stations operating on a first, often lower, frequency layer covering a big service area) and a small cell layer to increase data throughput (base stations operating as "booster cells" on a second, often higher, frequency layer deployed to service certain hot spots). The example network architecture in <figref idref="f0001">Fig. 2</figref> shows base station A operating on the macro cell layer and base station B operating as a "booster cell" on the small cell layer. Such a deployment is referred to as a heterogeneous network or HetNet. Some types of mobile devices can connect to both types of frequency layers simultaneously for example in the context of Carrier Aggregation (CA) or Dual Connectivity (DC).

0030To enable seamless connectivity, mobile devices are constantly required to perform neighbour cell measurements (NCM) on neighbouring cells.

0031In RRC_IDLE mode of operation NCM are needed to allow a terminal to always camp on the best cell. If a terminal detects a stronger cell, it initiates the cell re-selection procedure (which may, in some cases, trigger a tracking area update). In idle mode, mobility is always UE controlled and most of the measurement criteria is determined by SIB messages.

0032In RRC_CONNECTED mode of operation NCM are needed, so that a terminal can inform the base station during an ongoing connection about the detection of stronger cells. Based on the measurement reports received from the terminal, the base station may then prepare the switch of an ongoing connection from the current source cell into a new target cell by triggering the handover procedure. In connected mode mobility is network controlled and most of the measurement criteria is determined by specific RRC Messages dedicated for a particular mobile device.

0033In LTE, the downlink is based on orthogonal frequency division multiplexing, OFDM. In <figref idref="f0002">Fig. 3</figref> an exemplary LTE downlink resource grid of a 20 MHz carrier in a FDD system is given. On the y-axis the frequency domain is shown with the various OFDM sub carriers. A carrier with a nominal bandwidth of 20 MHz consists of 100 Resource Blocks (RBs). As there are twelve sub carriers per RB and the sub carrier spacing is 15 kHz (in subframes not configured for MBMS), the useable bandwidth is 18 MHz in total (which is 90% of the nominal 20 MHz bandwidth). The edges of the LTE channel bandwidth are guard bands (1 MHz on each side). In the centre, the so-called DC-carrier is shown in the middle between RBs 49 and 50.

0034The x-axis represents the time domain. In the present exemplary downlink configuration ("normal cyclic prefix"), there are 7 OFDM symbols per slot. Two slots make up a subframe of 1 ms duration. There are ten subframes per frame.

0035In every downlink resource lattice, regardless of the configured bandwidth, primary (P-SS) and secondary (S-SS) synchronization symbols are located in the last two symbols of slots #0 and #10. These are not spread over the entire bandwidth of the carrier. Instead they only stretch over the six inner RBs, i.e. from RB#47 to RB#52. This RB numbering is valid only for a system bandwidth of 20 MHz. In case of a smaller system bandwidth, the numbering differs. But in any case, the synchronization symbols are located around the DC carrier.

0036The smallest time-frequency unit for downlink transmission is denoted a resource element (as described in section 6.2.2 of 3GPP TS 36.211). A downlink physical channel corresponds to a set of resource elements carrying information originating from higher layers. A downlink physical signal corresponds to a set of resource elements used by the physical layer but does not carry information originating from higher layers. Downlink physical signals may be reference signals or synchronization signals.

0037As indicated, primary synchronization signals (P-SS) are located in the six innermost RBs centred around the DC-carrier in symbol #6 of slot #0 (in subframe #0) and slot #10 (in subframe #5). They are built from a Zadoff-Chu sequence of length 62 with three different sequences being defined, selected based on the Physical Cell ID. Out of 72 sub carriers only 62 are carrying the P-SS data; the remaining 10 subcarriers (five on each side) are zero padded. The P-SS signals are used for downlink frame synchronization and to determine the Physical Cell ID (together with S-SS). In an LTE TDD system, the P-SS are mapped to the third symbol of the first slot in subframes #1 and #6.

0038Secondary synchronization signal (S-SS) are located in the six innermost RBs centred around the DC-carrier in symbol #5 in slot #0 (Subframe #0) and in slot #10 (Subframe #5). The S-SS sequence used in subframe #0 is different from the one used in subframe #5. 168 different sequences are defined, selected based on the Physical Cell ID. They are made up of 62 scrambling sequences (based on m-sequence calculation). The values in odd indexed resource elements and the ones in even indexed resource elements are generated from different equations. The S-SS signals are used for downlink frame synchronization and are used to determine the Physical Cell ID (together with P-SS). In an LTE TDD system, the S-SS are mapped to the last symbol of the second slot of subframes #0 and #5.

0039The symbol location of P-SS/S-SS in time domain is different between a FDD and a TDD system as this helps the UE to identify, if this is a FDD or a TDD system.

0040Since the location of P-SS/S-SS is always fixed in frequency domain, the UE can easily do a correlation at the expected band to get the P-SS/S-SS, from which the UE can acquire many parameters such as the physical cell ID (PCID), the duplexing mode FDD vs. TDD (from the location of P-SS/S-SS in the time domain), the subframe number (from the S-SS sequence), and also the slot boundary.

0041P-SS and S-SS together define the physical cell ID (PCID) of a radio cell. A UE detects the physical layer identity from the P-SS and the physical layer cell identity group from the S-SS. As discussed above, there are three different P-SS (= Layer_ID) and 168 different S-SS (= Group_ID), limiting the maximum number of PCIDs to 504. The PCID is composed according to the following formula: <maths id="math0001"><math display="block"><mrow><mi>PCID</mi><mo>=</mo><mn>3</mn><mo>*</mo><mi>Group_ID</mi><mo>+</mo><mi>Layer_ID</mi></mrow></math><img file="EP3849100A1_D0001.tif" /></maths>

0042<figref idref="f0002">Fig. 4</figref> shows a HetNet scenario in which a mobile device (UE) has an ongoing connection to base station A. Hence, base station A has configured the mobile device for collection and reporting of NCM. Within the coverage area of base station A which is providing macro cell layer coverage another base station (base station B) is operating on the small cell layer using beam forming techniques. It is assumed that TRP B is configured to use a beam hopping pattern (according to Example Configuration #1).

0043When the first base station (base station A) receives NCM results from a UE containing measurements that have been collected on the small cell layer of a second base station (base station B) where beam hopping has been activated, the infrastructure side has currently no means to identify the sub section of the cell in which the respective set of measurements has been collected. That means information about the TRP's beam forming configuration at the time of measurement collection is not known, or -to put it another way- it is not possible either for the first or for the second base station to provide and/or derive any TRP control information from the NCM results that would be helpful for quick beam forming on the small cell layer in order to target the respective UE specifically (for example, when a second radio link in scope of CA or DC is supposed to be set up).

0044Accordingly, the HetNet of <figref idref="f0002">Fig. 4</figref> is modified as shown in <figref idref="f0003">Fig. 5</figref>.

0045Base station A is providing macro cell layer coverage and base station B is operating on the small cell layer using beam forming techniques. In detail, TRP B assigned to base station B is configured to apply a beam hopping sequence, such as the pattern according to Example Configuration #1 discussed above in context with <figref idref="f0001">Fig. 1</figref>.

0046At a first time instance t_x the beam disseminated by TRP B is directed to sub-section G (as shown in <figref idref="f0003">Fig. 5</figref>), while at a second time instance t_y the beam is directed to another sub-section of the coverage area, namely sub section H. At a further time instance the beam may jump back to serve sub-section A (not shown), so that a new hopping cycle can begin. In this example we assume that the dwell time of the beam in each sub-section has a constant value of N seconds. That means an entire cycle with M sub-sections to be served would have a duration of N * M seconds.

0047As discussed above, according to Example Configuration #2 with multiple lobes serving more than one sub section at the same time, a downlink signal D_z (not shown) may have a complex lobe structure with individual lobes directed at sub-section G and sub-section H at the same time.

0048A lobe direction indicator (LDI) or a "beam identifier" or a "target area itemization code" is included in the respective TRP's downlink signal (i.e. in the various beams disseminated by TRP B in the <figref idref="f0003">Fig. 5</figref>). The value of this parameter uniquely identifies (at least from a base station's perspective) a lobe direction (or a beam or a target area). It changes from sub-section to sub-section.

0049With respect to Example Configuration #2, a base station may control the simultaneous dissemination of multiple lobes from a TRP in such a way that individual beams (or at least certain sub sets of beams) are carrying different LDIs. For this, a form of LDI multiplexing would be required, to enable proper reception of different simultaneously transmitted LDIs. Details on different LDI multiplexing options according to this invention are provided below.

0050The LDI signal is provided with or within the physical layer rather than in any of the higher protocol layers of the cellular communication system. The following describes different encoding options to achieve this.

0051In a first encoding option, the spare sub-carriers at the edges of RBs #47 and #52 (in the 20 MHz example of <figref idref="f0002">Fig. 3</figref>, for other nominal bandwidths the RB numbers differ) are used to transmit the LDI in the downlink direction thereby spreading the LDI information in the frequency domain.

0052On each side, five sub carriers are currently left unused offering an opportunity to encode at least 10 bits (per symbol length) when we use a simple On/Off Keying (OOK) or, for example, 20 bits per symbol length when we use Quadrature Phase Shift Keying (QPSK). In case of QPSK the number of supported beam identifiers is in the range of up to 2²⁰ (per symbol length). As synchronization signals appear four times per frame (namely, twice in each of the slots #0 and #5) there is enough flexibility to encode the LDIs even with some redundancy to enhance the reliability of the LDI. Well known methods for error detection and/or correction could also be applied. Furthermore, these spare sub-carriers may be used with reduced transmission power (at least lower than the carriers carrying the P-SS and S-SS information) in order not to disturb the synchronization process. <figref idref="f0003">Fig. 6</figref> gives an example configuration. The five spare sub carriers at the edges of the six inner most RBs in symbols carrying the S-SS and P-SS are used to transmit the LDI in the downlink direction.

0053In another variant, only some of the 10 unused subcarriers, e.g. only 4 so that some (6 in this example) subcarriers remain unused to offer a guard interval.

0054Some UEs might encounter difficulties in finding the sync signals quickly, so the synchronization process might take a little longer, but this drawback can be mitigated when the transmission power applied to the sub carriers for the LDI signal is reduced (compared to the transmission power of the sub carriers used for P-SS and S-SS).

0055Complex lobe structures according to Example Configuration #2 of the present invention might require identification of individual lobes if multiples lobes were received simultaneously. This can be achieved by assigning different LDIs to distinct lobes by applying multiplexing techniques on the resources available. Here, multiple LDIs could for instance be multiplexed in the frequency domain (e.g., different LDIs in different sets of sub carriers) or in the time domain (e.g., different LDI from frame to frame) on the available spare sub carriers and/or CDMA techniques could be used to spread individual LDIs with different codes (bearing suitable auto- and cross-correlation properties).

0056In a second encoding option, instead of using the spare sub carriers space for our purposes, the P-SS and/or S-SS are themselves used for indicating the LDI value of a beam by using phase shift keying (PSK) that alters the phase of all 62 synchronization symbols by a single phase shift value, thereby spreading the LDI information over time.

0057For example, in any given frame the phases of the respective set of synchronization symbols of P-SS and S-SS in slot #0 as well as P-SS and S-SS of slot #10 are shifted. In principle, this phase shifting method is not restricted to slots within a single frame; in order to enhance the amount of LDIs it may continue across multiple frames, too.

0058However, it is deemed advantageous to use the phases of one synchronization signal per frame (in the example of <figref idref="f0004">Fig. 7</figref>, the first S-SS in slot #0) as a reference for the upcoming three phase shifts in the same frame, i.e. not to perform phase shifting on this synchronisation signal. As there are in total four occurrences of P-SS/S-SS symbols per frame (namely, two in each of the slots #0 and #10), this method would allow encoding of three bits per frame (assuming that the first occurrence of the S-SS in slot #0 serves as a phase reference and assuming encoding of one bit per synchronization sequence). If the phase shifting is not restricted to within a single frame, more than three bits could be encoded.

0059Other ways to enhance the number of LDIs are for instance: using all four synchronisation sequences per frame (in this case the phase reference cannot be indicated), or spreading the coding over more than one frame (e.g. coding over two frames without phase reference sequence would allow for an eight bit LDI, as shown in <figref idref="f0004">Fig. 8</figref>), or using more coding symbols (e.g. using four different phases instead of two would provide two bits per synchronisation sequence). All these methods could be combined to obtain the desired amount of LDIs.

0060<figref idref="f0004">Fig. 7</figref> shows the variant of deploying phase shift keying within a single frame. In this case the S-SS symbol residing in slot #0 is serving as a phase reference. <figref idref="f0004">Fig. 8</figref> depicts the variant of deploying phase shift keying across multiple frames (perpetual encoding).

0061Theoretically, it would be possible to shift the phases of the respective set of synchronization symbols by any value between ± 180°, but we propose to only use a maximum phase shift value of ± 90° for the selected sub carriers, in order to allow receiving legacy UEs, which may not be aware of this new modulation, to easily filter out the LDI information (which is solely contained in the ± 90° phase rotation) over time.

0062As theoretically more coding symbols per synchronization symbol could be used (e.g. using four different phases) a ± 45° phase rotation and a ± 135° phase rotation could be combined.

0063The encoding variants of <figref idref="f0004">Figs. 7 and 8</figref> can also be combined by grouping several consecutive frames to a block of frames, thereby using only one (e.g., the very first) S-SS in the block as a phase reference (i.e. not shifting it) while all the other S-SS occurrences in the block may be shifted as needed.

0064<figref idref="f0005">Fig. 9</figref> shows two example constellation diagrams for (the first 32 values of) a P-SS sequence: On the left, the values of the P-SS sequence are not shifted (state-of-the-art). On the right, they are shifted by +90° according to the PSK encoding concept. The first value n₀ of the P-SS sequence is highlighted for better readability in both constellation diagrams. The ± 90° phase shifting of the other synchronization symbols is performed similarly (not shown here for sake of brevity).

0065As discussed above, complex lobe structures according to Example Configuration #2 of the present invention might require identification of individual lobes if multiples lobes were received simultaneously. This can be achieved by assigning different LDIs to distinct lobes by applying multiplexing techniques on the resources available. For the second encoding option (especially in case several consecutive frames are grouped to a block of frames), multiple LDIs could for instance be multiplexed over time and/or CDMA techniques could be used to spread individual LDIs with different codes (bearing suitable auto- and cross-correlation properties).

0066A third encoding option is a combination of options 1 and 2, i.e. coding the LDI in the spare sub-carriers and onto the synchronization signals (not shown).

0067In a fourth encoding option, special resource elements (REs) or resource blocks (RBs) in the LTE downlink lattice, i.e. others than those reserved for P-SS and S-SS, are defined to carry the LDI in the downlink direction. For example, the LDI information could be transmitted in REs or RBs (collectively resource regions) formerly allocated to the PDSCH (physical downlink shared channel) region of the grid, and legacy UEs could be configured to ignore this information e.g., by appropriate scheduling. This can be seen as a definition of a new physical signal in the time frequency lattice of an LTE communication system for providing information related to beam forming and beam tracking (in addition to the two already existing physical signals defined for downlink reference and synchronization).

0068A possible drawback with this option is it eats into the resources originally destined for the PDSCH.

0069In the fourth encoding option multiple lobes as they may appear in complex lobe structures according to Example Configuration #2 of the present invention can be assigned distinct LDIs by applying all kinds multiplexing techniques on the resources available. For instance, in the fourth option different LDI values can be multiplexed in the frequency domain and/or in the time domain and/or by means of CDMA techniques.

0070A fifth encoding option is to put the information into the master information block (MIB) or one of the subordinate system information blocks (SIB) designed for system information broadcast in the mobile communications system. This requires that the respective information (i.e. the LDI) is changed if the beam is directed to the next subsector. As system information was not designed to allow broadcast of quickly changing information elements, this option is suitable when the formation and/or hopping of beams is a rather slow procedure.

0071Having obtained the LDI by means of one of the above options, or otherwise, the LDI receipt is reported to the network. For example, this reporting may be done either during the course of its regular NCM reporting (according to the first embodiment of the present invention), or during the course of its regular positioning activities (according to the second embodiment of the present invention), or otherwise.

0072If the UE reports the (at least one) detected LDI value(s) in the course of its regular NCM reporting, some RRC information elements need to be enhanced as follows.

0073In the MeasConfig information element (IE) that is contained in the RRC Message "connection reconfiguration" (as described in 3GPP TS 36.331) a new IE could optionally be added for the configuration of measurement thresholds (incl. dwell time) and reporting events particularly tailored to measurements collected on directive antenna beams.

0074UEs in RRC_CONNECTED report their measurement results in the MeasResults IE contained in the RRC Message "measurement report" (as described in 3GPP TS 36.331). For the present invention, a new object may be included in the MeasResults IE enabling the UE to report details related to detected directive antenna beams, such as the LDI, the signal strength, and the dwell time in coverage of the respective beam. There can be multiple (up to maxBeamReport) MeasResultBeam instances for example in a SEQUENCE structure - one for each beam detected. Such an IE may have the following form: <img file="EP3849100A1_D0002.tif" />

0075Alternatively, a new IE MeasResultBestBeam object containing the important attributes of the best beam detected, such LDI, signal strength, and dwell time in coverage of the respective beam may be defined and included with the following form: <img file="EP3849100A1_D0003.tif" />

0076Further lEs that may be reported by a UE per beam are, for instance: reference signal time difference (RSTD) and Rx-Tx-time-difference. These are not shown in the above IE representations for the sake of brevity. However, they shall not be excluded from the scope of the present invention.

0077Once one or more LDIs have been received by the infrastructure side (for example, by macro cell Base Station A of <figref idref="f0003">Fig. 5</figref> receiving a "measurement report" RRC Message modified according to this invention), the beam specific measurements may be processed and lobe control parameters may be derived for TRP B to enable steering of a directed radio beam to a particular spot (i.e. a beam specific for one or more UEs residing at a certain location instead of hopping beams), so that handover and/or cell addition/activation (e.g., in a CA or DC environment) can be initiated right away. For this it is advantageous to provide a look-up table on the infrastructure side. This look-up table may for example reside in one of the involved macro cell layer or small cell layer base stations or in another logical entity in the radio access network (RAN) or core network (CN) of the cellular communication system. Table 1 shows an example look-up table according to this invention. If the UE of <figref idref="f0003">Fig. 5</figref> in the multi-lobe beam arrangement Example Configuration #2 reports a beam Beam_G received from TRP B as the strongest lobe received at its current location for a reasonable dwell time (e.g., the dwell time of UE in Beam_G is above the threshold received previously in the MeasConfig IE). Let's further assume the LDI value was set to "7" on Beam_G. In addition to this the UE of <figref idref="f0003">Fig. 5</figref> might also report other beams with their respective LDIs (in a further embodiment, these other beams might be transmitted by the same or by other transmission and reception points) as being beams with an acceptable signal strength, but with a much shorter dwell time, and beams with an acceptable dwell time but a much lower signal strength. The infrastructure side can now quickly determine all parameters (from the the look-up table) needed for TRP B to form an optimal beam to serve the UE in question. The originally configured beam hopping pattern can be altered (if required). The UE doesn't have to wait for TRP B to complete a full hopping cycle. <tables id="tabl0001" num="0001"><table frame="all"><title>TABLE 1</title><tgroup cols="7"><colspec colnum="1" colname="col1" colwidth="19mm" /><colspec colnum="2" colname="col2" colwidth="28mm" /><colspec colnum="3" colname="col3" colwidth="32mm" /><colspec colnum="4" colname="col4" colwidth="21mm" /><colspec colnum="5" colname="col5" colwidth="26mm" /><colspec colnum="6" colname="col6" colwidth="15mm" /><colspec colnum="7" colname="col7" colwidth="28mm" /><thead><row><entry morerows="1" align="center" valign="middle">Reported Value</entry><entry namest="col2" nameend="col6" align="center" valign="middle">Transmission and Reception Point (TRP) Parameters</entry><entry morerows="1" align="center" valign="middle">Targeted Sub Section</entry></row><row><entry align="center" valign="middle">Horizontal Rotation</entry><entry align="center" valign="middle">Horizontal Beam Width</entry><entry align="center" valign="middle">Vertical Tilting</entry><entry align="center" valign="middle">Vertical Beam Width</entry><entry align="center" valign="middle">TX Power</entry></row></thead><tbody><row><entry align="center" valign="middle">LDI = 1</entry><entry align="center" valign="middle">-2° left</entry><entry align="center" valign="middle">60°</entry><entry align="center" valign="middle">-5°</entry><entry align="center" valign="middle">10°</entry><entry align="center" valign="middle">81%</entry><entry align="center" valign="middle">A</entry></row><row><entry align="center" valign="middle">LDI = 2</entry><entry align="center" valign="middle">+2° right</entry><entry align="center" valign="middle">60°</entry><entry align="center" valign="middle">-5°</entry><entry align="center" valign="middle">10°</entry><entry align="center" valign="middle">82%</entry><entry align="center" valign="middle">B</entry></row><row><entry align="center" valign="middle">LDI = 3</entry><entry align="center" valign="middle">-2° left</entry><entry align="center" valign="middle">60°</entry><entry align="center" valign="middle">-4°</entry><entry align="center" valign="middle">10°</entry><entry align="center" valign="middle">86%</entry><entry align="center" valign="middle">C</entry></row><row><entry align="center" valign="middle">⋮</entry><entry align="center" valign="middle">⋮</entry><entry align="center" valign="middle">⋮</entry><entry align="center" valign="middle">⋮</entry><entry align="center" valign="middle">⋮</entry><entry align="center" valign="middle">⋮</entry><entry align="center" valign="middle">⋮</entry></row><row><entry align="center" valign="middle">LDI = 7</entry><entry align="center" valign="middle">-2° left</entry><entry align="center" valign="middle">30°</entry><entry align="center" valign="middle">-2°</entry><entry align="center" valign="middle">15°</entry><entry align="center" valign="middle">95%</entry><entry align="center" valign="middle">G</entry></row><row><entry align="center" valign="middle">LDI = 8</entry><entry align="center" valign="middle">-2° right</entry><entry align="center" valign="middle">30°</entry><entry align="center" valign="middle">-2°</entry><entry align="center" valign="middle">30°</entry><entry align="center" valign="middle">98%</entry><entry align="center" valign="middle">H</entry></row></tbody></tgroup></table></tables>

0078In the present example, the UE of <figref idref="f0003">Fig. 5</figref> residing in sub-section G will be provisioned by TRP B with an optimal radio beam orientation to set-up a new or additional communication link on the small cell layer. The lobe's optimal orientation has a rotation of -2° to the left, and a vertical tilt of -2°. The TX power previously used in this direction can also be read from the look-up table. In this example, it was 95% of the maximum TX power.

0079<figref idref="f0006">Fig. 10</figref> shows a flow chart with messages exchanged in the course of the procedure of the first embodiment of the present invention relating to beam steering. A first base station (Base Station A offering a macro cell layer) through TRP A configures the UE with NCM. TRP B is the transmission and reception point associated with a second base station (Base Station B offering a small cell layer) and capable of supporting beam forming and tracking methods. According to the NCM configuration the UE may perform measurements on various beams and report the results back to the first base station including the inventive LDI. For reporting the UE may also take various thresholds related to the received signal strength and/or the dwell time of each detected beam into account, thereby reducing the overall number of measurement values to the most relevant lobes. On the infrastructure side the measurement report(s) is (are) evaluated. If on the infrastructure side it is decided to establish an additional connection between the UE and the second base station e.g., in course of Carrier Aggregation (CA) or Dual Connectivity (DC) operation, or to hand off the UE from the first base station to the second base station then information (including the LDI) may be exchanges between the first base station and a second base station so that the second base station may derive a set of TRP parameters from a memory (data repository) based on at least the LDI information. Said TRP parameters may then be used to direct TRP B's transmission and reception orientation to target the respective UE right away. This may mean, that TRP B's current beam hopping pattern (cf. Example Configuration #1) and/or the currently configured multiple lobe structure (cf. Example Configuration #2) need(s) to be altered. Once the lobe's transmission and reception orientation has been adjusted to meet the UE's position, a further carrier can be activated/added or a handover procedure can be initiated.

0080If the UE reports the (at least one) detected LDI value(s) in course of its regular reporting activities for positioning, some RRC information elements could be enhanced in a similar manner.

0081In the second embodiment of the present invention relating to providing positioning information, the content of Table 1 doesn't have to be as comprehensive as in the example shown above. In some cases, it may be sufficient to only provide a mapping of LDI values to horizontal rotation angles. In cases, where the vertical position is important, the vertical tilting could be used in addition to the horizontal rotation angles. In order to increase the accuracy for determining a mobile device's position, it is beneficial to take (at least one of) the following measures: <ol id="ol0001" compact="compact"><li>a) Configure the TRP to generate relatively narrow lobes;</li><li>b) Use a fine granularity for the horizontal rotation angle;</li><li>c) Configure the mobile device to report multiple LDIs from different TRPs;</li><li>d) Configure the mobile device to report the reception level (i.e. signal strength) of each reported LDI, and</li><li>e) Use multiple reported LDIs in the position determination process. This might involve derivation of TRP configuration settings from more than one look-up table.</li></ol>

0082<figref idref="f0007">Fig. 11</figref> shows a flow chart for the second embodiment with messages exchanged in the course of the procedure of the invention. A first base station (base station A, for instance offering a macro cell layer) through TRP A configures the UE for LDI collection and reporting. According to this configuration the UE may try to pick up from surrounding base stations (e.g., second base stations, such as base stations B and C offering a small cell layer) as many LDI values as possible. The detected LDIs may be compared against thresholds received as part of the configuration and stored if appropriate (i.e. if certain criteria are met). Once a reporting event is detected (for example, when the mobile device has collected a sufficient number of LDI values from surrounding base stations, or upon receiving an appropriate request from the infrastructure side), the mobile device may choose to generate an LDI report for submission in an uplink direction to the first base station. With knowledge of the various TRP's geolocations and the various beam's horizontal rotation angles and probably the vertical tiltings (both can be derived from look-up tables by means of the reported LDI values) the mobile device's position can be calculated on the infrastructure side.

0083One possible criteria for LDI storage and/or reporting could be the time difference between two arbitrary LDI values on UE side (for instance, LDI values received via DL Signal B_x and DL Signal C_y of <figref idref="f0007">Fig. 11</figref>). If the time difference t_d = t_y - t_x is above a certain threshold this indicates that the derived position would be inaccurate due to the mobile device's movement between two reception occasions of the different LDIs. The mobile device may then choose to delete a (series of) previously received LDI value(s) (e.g., the one received via DL Signal B_x) and begin a new LDI collection cycle (e.g., using the LDI received via DL Signal C_y as a new start value). If the time difference t_d = t_y - t_x is below a configured threshold the mobile device may choose to report the (at least one) previously received LDI value(s) (e.g., the ones received via DL Signal B_x and DL Signal B_y).

0084The term Transmission and Reception Point (TRP) used throughout the text shall explicitly include transmission and reception capabilities. Thus, a directed orientation for radio communication may include a transmission orientation (in downlink direction, i.e. from the tower to the mobile device) and/or a reception orientation (in uplink direction, i.e. from the mobile device to the tower).

0085A further abstraction of the described method leads to a very general method to impress information on synchronization symbols of an LTE or LTE-Advanced communication system. The information stamped on the synchronization symbols according to this invention does not have to be related to beam forming and/or beam hopping patterns and may be used for communicating further pieces of information.

Preferred aspects of the invention

0086<ol id="ol0002"><li>1. A method performed by a user equipment of providing information to a first base station relating to directional beam signals received by the user equipment from one or more other base stations and optionally the first base station, the method comprising: <ul id="ul0001" list-style="none" compact="compact"><li>receiving with signals transmitted from a base station via a directional beam an identifier, the identifier having a property of distinguishing the directional beam from other directional beams; and</li><li>transmitting to the first base station a report including information about the received identifier of the directional beam,</li></ul> characterized in that the received identifier is encoded in the signals transmitted by the base station at a physical layer, the physical layer being the lowest layer for communication between the base station and the user equipment according to a multi-layer model known as the open systems interconnection, OSI, model.</li><li>2. The method according to aspect 1, wherein the received identifier is encoded within a radio transmission sub-carrier.</li><li>3. The method according to aspect 1 or aspect 2, wherein the received identifier is encoded by phase shift keying of one or more synchronization signals per transmission frame.</li><li>4. The method according to aspect 1, wherein the received identifier is transmitted in a dedicated resource element or resource block.</li><li>5. The method according to aspect 1, wherein the identifier is encoded in the signals transmitted by the base station by at least one of transmitting the signals in a predetermined combination of resource block sub-carriers, phase shift keying of synchronization symbols of the transmitted signals, and transmitting signals in particular resource regions of a resource grid.</li><li>6. The method according to any preceding aspect, wherein one or more reception characteristics of the directional beam are measured for inclusion in the report, the one or more reception characteristic being selected from a list comprising signal strength, dwell time, reference signal time difference and receive-transmit time difference.</li><li>7. The method according to any preceding aspect, wherein the report includes multiple information elements relating to identifiers received in respect of multiple directional beams disseminated from a plurality of base stations.</li><li>8. The method according to any preceding aspect, wherein the transmitting of the report is performed as part of a procedure for performing neighbour cell measurement reporting.</li><li>9. The method according to aspect 8, wherein the report enables the first base station to derive position information about the user equipment.</li><li>10. The method according to aspect 8, wherein the report provides information enabling a dedicated directional beam to be directed to the user equipment.</li><li>11. A radio communication transmission and reception point arranged to transmit a plurality of directional beams with each directional beam covering a sub-section of a total coverage area, and wherein the transmission and reception point periodically changes which sub-sections are receiving directional beams, wherein the transmission and reception point is arranged to transmit a beam identifier with each directional beam, the beam identifier being capable of distinguishing one directional beam from other directional beams, characterized in that the transmission and reception point is arranged to transmit the beam identifier by encoding the beam identifier in the directional beams at a physical layer, the physical layer being the lowest layer for communication between the base station and the user equipment according to a multi-layer model known as the open systems interconnection, OSI, model.</li><li>12. The transmission and reception point according to aspect 11, wherein the identifier is encoded within a radio transmission sub-carrier.</li><li>13. The transmission and reception point according to aspect 11 or aspect 12, wherein the identifier is encoded by phase shift keying of one or more synchronization signals per transmission frame.</li><li>14. A user equipment adapted to provide information to a first base station relating to directional beam signals received by the user equipment from one or more other base stations and optionally the first base station, the user equipment being arranged to: <ul id="ul0002" list-style="none" compact="compact"><li>receive with signals transmitted by a base station via a directional beam an identifier, the identifier having a property of distinguishing the directional beam from other directional beams; and</li><li>transmit to the first base station a report including information about the received identifier of the directional beam,</li></ul> characterized in that the received identifier is encoded in the directional beam signals at a physical layer, the physical layer being the lowest layer for communication between the base station and the user equipment according to a multi-layer model known as the open systems interconnection, OSI, model.</li></ol>