Forward compatibility for demodulation reference signals (DMRS)

Abstract

FIELD: wireless communications.SUBSTANCE: invention relates to a method for ensuring forward compatibility for processing demodulation reference signals (DMRS) on the user equipment side in a wireless communications system, as well as to corresponding devices. The method comprises the steps of receiving first information at the user equipment from a base station of a wireless communication system, which comprise an indication of the possibility of using by the base station more than one length of an orthogonal covering code (OCC) in DMRS modulation for a physical downlink shared channel (PDSCH); receiving second information indicating at least one DMRS port that will be used for transmitting the PDSCH to the user equipment and one length of the OCC; receiving from the base station a DMRS corresponding to each of said at least one DMRS port, and processing the received DMRS based on the length of the OCC indicated by the second information. In this case, for at least some DMRS ports, OCC sequences corresponding to OCCs having a larger OCC length are obtained by correspondingly replicating OCC sequences corresponding to OCCs having a smaller OCC length. The implementation of the proposed method for the case of DMRS physical downlink control channel (PDCCH) is also provided.EFFECT: direct compatibility on the user equipment side with respect to DMRS extensions, without changing the DMRS sequences themselves, which makes it possible to avoid a decrease in the efficiency of expanding the use of the multi-user MIMO (MU-MIMO) mode in the communication system.31 cl, 20 dwg

Description

[0001] FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0002] The present invention relates generally to wireless communications and, more particularly, to a method for providing forward compatibility (FC) for processing demodulation reference signals (DMRS) on the user equipment (UE) side in a wireless communication system, as well as to corresponding devices.

[0003] PRIOR ART

[0004] At the present stage, there is an increasingly active deployment of wireless communication networks 5 го generation (5G) of the New Radio (NR) standard, the advantages and capabilities of which are widely known.

[0005] The 5G NR base stations (BS) use massive MIMO (mMIMO) antenna arrays containing multiple transmit / receive antenna elements to effectively implement multiple-input multiple-output (MIMO) technology, where data (e.g., physical downlink shared channel (PDSCH)) is transmitted to one or more user equipments using multiple spatial MIMO layers.Spatial multiplexing (SM) allows the same frequency and time resources to be used for downlink (DL) transmission of multiple MIMO layers to user equipment, while adaptive beamforming (BF) enables dynamic control of the transmitted signal in one or more spatial directions; orthogonal frequency division multiplexing (OFDM) modulation ensures efficient wideband signal transmission in a multipath channel. Single-user MIMO (SU-MIMO) can be supported, where, for example, all MIMO layers multiplexed in PDSCH are intended for a single user equipment, while multi-user MIMO (MU-MIMO) can be supported, where the MIMO layers transmitted in PDSCH are intended for multiple user equipment.

[0006] Although the deployment of 5G NR systems worldwide is only just beginning to gain momentum, active research is already underway in various areas to standardize next-generation wireless communication systems, the so-called 6G, which will have characteristics superior to 5G NR. Specifically, for the 6G operating range of 7-13 GHz (UPPER MID BAND), base stations are planned to support ultra-large antenna arrays (e.g., consisting of 3072 antenna elements) with hybrid analog and digital beamforming and a large number of antenna ports (≤256). Thus, with support for up to 64 simultaneously transmitted spatial MIMO layers in UPPER MID BAND communication systems, the concept of the ultra-large antenna array (xMIMO) air interface will be taken to a fundamentally new level.

[0007] The deployment of 6G communication systems is projected to begin by 2030. Fig. 1 illustrates an estimated diagram of the dynamics of the total traffic load for 6G systems, showing the growth in the share of network resources (NW) used by years.

[0008] As a rule, when a new wireless technology is introduced, the traffic load is not very high at the beginning of its deployment by telecom operators. This was true for both 4G and 5G NR, and is predicted for 6G (see Fig. 1). This is explained, among other things, by the fact that users need time to migrate to new mobile devices that fully support the corresponding new wireless technology. In other words, as a rule, at the beginning of the deployment of a new wireless technology, the overall network load is low relative to the capabilities provided by the new technology. However, as users upgrade their wireless devices, the penetration of the new technology becomes wider, and, as a result, the network traffic load increases over time.

[0009] Next, this aspect is considered from the perspective of MU-MIMO technology. MU-MIMO is generally effective when there are multiple user equipments in the network, but if the network load is not very high, using this mode becomes impractical. That is, at the initial stage of deploying a new wireless communication technology, a corresponding implementation of the SU-MIMO mode will most likely be used; however, as the number of subscribers and traffic increases, the use of the MU-MIMO mode becomes more feasible and more likely. Fig. 2 illustrates the expected, predicted evolution of the use of MU-MIMO in commercial communication systems for 6G, depending on the release (Rel) of the wireless communication standard. As can be seen from Fig. 2, when Rel-21 is deployed in real commercial networks, SU-MIMO will be predominantly used.Over time, MU-MIMO will increasingly be used, with a large number of user equipments being served simultaneously. Accordingly, the importance of proper support for MU-MIMO technology increases as 6G deployment and penetration becomes more widespread across the communications device ecosystem.

[0010] Starting with the first 5G NR release, Rel-15, forward compatibility (FC) was provided in terms of the physical resources used in DL for data transmission. More specifically, during the development of Rel-15 5G NR, reserved resources were introduced for the purposes of forward compatibility; these physical resources were reserved for future 5G NR releases, or even for the next-generation technology (6G). In other words, already at the development stage of the first 5G NR release, the idea was that Rel-15-compliant user equipment could be configured with special frequency and time resources that the user equipment should not use in any way, that is, with a clear understanding that no data transmitted in DL would be mapped to these reserved resources.

[0011] Reserved frequency-time resources are typically a set of subcarriers on one or more OFDM symbols (see Fig. 3). Accordingly, when processing data transmitted to user equipment in the DL, the user equipment does not make any assumptions regarding DL transmissions on reserved resources, but simply skips them. Support for such reserved frequency-time resources allows base stations of future releases to use these resources depending on needs. Thus, if any DL data transmissions are introduced in the future (for example, in the 6G system, which will use the same bands), the corresponding base station will be able to carry out such data transmissions on reserved resources without disrupting DL data transmissions to user equipment compliant with Rel-15.Hereinafter in the text of the description of the invention, user equipments corresponding to older releases of the wireless communication standard may, without limitation of generality, be referred to as 'legacy user equipments', and user equipments corresponding to the current release of the wireless communication standard may, without limitation of generality, be referred to as 'non-legacy user equipments'.

[0012] Two types of reserved resources have been introduced:

[0013] • at the resource element (RE) level, i.e. with the possibility of reservation at the level of certain subcarriers and OFDM symbols; this type is provided rather for backward compatibility with LTE; and

[0014] • at the resource block (RB) level, i.e. with a smaller granularity in the frequency domain; this option corresponds to the possibility of reserving certain resource blocks on certain OFDM symbols (see Fig. 3).

[0015] Thus, starting with Rel-15 5G NR, user equipment could skip certain rate-matching resources and receive data only on unreserved resources (shown in white on the grid in Fig. 3). That is, a mechanism was provided for future releases, according to which reserved subcarriers or resource blocks (highlighted in dark gray in Fig. 3) allow base stations to implement certain new DL transmissions according to these future releases without disrupting communications with legacy user equipment (e.g., Rel-15). At the same time, it should be emphasized that this forward compatibility mechanism is limited to DL data transmission, i.e., PDSCH, and does not cover DL transmission of reference signals.

[0016] Next we will specifically discuss demodulation reference signals (DMRS).

[0017] In general, a separate DMRS port is associated with each MIMO layer. When transmitting data in DL across multiple (N>1) MIMO layers in PDSCH, a DMRS (i.e., an orthogonal DMRS sequence) of the corresponding DMRS port is transmitted for each of the N MIMO layers in PDSCH. In SU-MIMO mode, the user equipment uses the N received DMRSs to independently estimate the DL channel in each of the corresponding N MIMO layers and, based on the channel estimate, demodulates / decodes the data of these corresponding MIMO layers. Similarly, in MU-MIMO mode, the user equipment uses at least one DMRS port to demodulate / decode the data of its corresponding at least one MIMO layer.

[0018] The 5G NR specification TS 38.211, which is incorporated by reference in its entirety into this application, defines, among other things, a Type 1 DMRS structure for PDSCH. As illustrated in Fig. 4, the Type 1 DMRS structure is defined by two code division multiplexing (CDM) groups, each of which defines subcarriers in the frequency domain (FD) on two OFDM symbols in the time domain (TD) on which the DMRS is to be transmitted, as well as two frequency domain orthogonal cover codes (FD-OCC) of length 2 and two time domain OCCs (TD-OCC) of length 2. Essentially, in the case under consideration, one of the two CDM groups corresponds to the use of an even comb in the frequency domain, and the other CDM group corresponds to the use of an odd comb. Each DMRS port can be said to have a unique set associated with it, consisting of a CDM group, FD-OCC, and TD-OCC, when using a DMRS configuration with two OFDM symbols.As a result, the Type 1 DMRS structure provides a maximum of eight orthogonal DMRS ports, i.e. eight orthogonal DMRS sequences.

[0019] The following describes the DMRS extension introduced in Rel-18 5G NR over Rel-15 DMRS Type 1 with reference to Fig. 5, which increases the maximum number of supported orthogonal DMRS ports to sixteen. In the table in Fig. 5, p is the DMRS port index; λ, Δ=0, 1 is the CDM group index; - FD-OCC sequence element, k'=0, 1, 2, 3 - DMRS subcarrier index in the CDM group; - TD-OCC sequence element, , 1 - the DMRS OFDM symbol index in the CDM group. In this table, the FD-OCC and TD-OCC, respectively, used for DMRS ports, are outlined in bold. =1000, …, 1007 Type 1 DMRS structures, i.e. Rel-15 5G NR.

[0020] As can be seen from the table in Fig. 5, the extended structure of Type 1 DMRS Rel-18 also uses two CDM groups and two TD-OCCs of length 2, but it provides the ability to use FD-OCCs of length 4 in each CDM group. For each of the DMRS ports =1000, ..., 1007, which were also used in Rel-15, the FD-OCC sequence of length 4 in the extended Type 1 DMRS structure is obtained by duplicating the corresponding FD-OCC sequence of length 2 from the Type 1 DMRS structure; that is, in fact, for a given DMRS port, its FD-OCC sequence itself has not changed in any way compared to Rel-15. Plus, in the extended Type 1 DMRS structure, eight new FD-OCC sequences of length 4 have been added, respectively, for DMRS ports =1008, …, 1015.

[0021] Below is the mathematical expression (1) describing the DMRS sequence for the corresponding DMRS port for PDSCH:

[0022]

[0023] where

[0024] - power offset for DMRS relative to PDSCH power; - the maximum number of k' (i.e. 2 for the Type 1 DMRS structure and 4 for the extended Type 1 DMRS structure); m=0, 1, … is the current index; k is the subcarrier index, where

[0025]

[0026] - the index of the OFDM symbol in the slot, and

[0027]

[0028] - the initial index of the OFDM symbol within the slot on which DMRS is transmitted; p z - DMRS port index, z=0,1,…, υ-1 - MIMO layer index, υ - total number of MIMO layers transmitted to user equipment; r(n) - QPSK sequence, where

[0029]

[0030] where j is the imaginary unit, c() is the binary Gold sequence of length 31, which is unique for each of the CDM groups and, accordingly, is initialized for each CDM group with its own cinit , moreover

[0031]

[0032] where - the number of OFDM symbols in a slot, - slot index in the frame, μ - interval index between subcarriers,

[0033]

[0034] n SCID - a scrambling parameter that can be dynamically specified in the downlink control information (DCI), - CDM group index, - a CDM group-specific initialization parameter, configured accordingly via radio resource control (RRC) layer signaling.

[0035] A more detailed explanation regarding equations (1)-(6) and the terms included in them is given in the specification TS 38.211.

[0036] Although the DMRS sequences provided by the mechanism described above with reference to Fig. 5 are generally orthogonal, grouping legacy Rel-15 user equipment and Rel-18 user equipment in MU-MIMO mode proves to be extremely difficult. As noted earlier, for each of the DMRS ports =1000, …, 1007 of the extended DMRS Type 1 structure (see Fig. 5), the FD-OCC sequence itself has not changed compared to Rel-15; however, there is a peculiarity that, when receiving data (PDSCH) by the user equipment, the user equipment correspondingly demodulates the DMRS sequence, and this demodulation is performed by the user equipment based on the assumption that the FD-OCC length is equal to 2 (according to Rel-15). This aspect may cause a number of complications if the base station decides to transmit data in MU-MIMO mode simultaneously for both Rel-15 and Rel-18 user equipment; this will be discussed in more detail below.

[0037] So, further with reference to Fig. 6, an example of grouping legacy and non-legacy user equipment - Rel-15 UE and Rel-18 UE - is given with simultaneous transmission of DMRS for PDSCH by the base station. It is assumed that Rel-15 UE should use DMRS port p=1000 of the DMRS Type 1 structure (see the upper left part of Fig. 6), and Rel-18 UE should use DMRS port =1008 of the extended DMRS Type 1 structure (see the lower left part of Fig. 6). For the example under consideration, it is emphasized that the DMRS multiplexing for UE Rel-15 and UE Rel-18 is implemented by the base station in one CDM group Δ=0 (see the right parts of Fig. 6, where the use of the same comb in the frequency domain is shown accordingly).

[0038] Although the FD-OCCs for the DMRS ports in question are generally orthogonal when viewed in terms of the FD-OCC length of 4, as stated earlier, there is a problem in that the legacy Rel-15 UE, when demodulating its DMRS sequence for the DMRS port, =1000 will assume that the FD-OCC length is 2 (see the upper left corner of Fig. 6: FD-OCC for a given port [+1 +1]), and, accordingly, in one of the possible implementations, will perform averaging in the frequency domain over an OCC length of 2, i.e., between two adjacent subcarriers within the comb. Operating in this way in the context of an FD-OCC of length 2, the Rel-15 UE will not be able to suppress interference from the DMRS port =1008 from the UE Rel-18 side, since on the two comb subcarriers that are used by the UE Rel-15 for averaging in the frequency domain to suppress interference during DMRS demodulation, for the DMRS port =1008 also uses FD-OCC [+1 +1] in the same comb (see the lower left part of Fig. 6). That is, with the described grouping, in fact, the orthogonality of some DMRS ports of the DMRS Type 1 structure and the extended DMRS Type 1 structure (as in the case of the ones considered here) =1000 and =1008) may be violated when the same CDM group is associated with such DMRS ports.

[0039] The above-described inability to suppress interference on the Rel-15 legacy UE side causes a number of limitations in 5G NR on the base station side in terms of grouping legacy and non-legacy UEs (e.g., Rel-15 and Rel-18) when scheduling DMRS transmission for PDSCH in MU-MIMO mode.

[0040] Figure 7, in a format similar to Figure 6, essentially illustrates an example of implementing such a restriction, which allows for the procedure of grouping Rel-15 UEs and Rel-18 UEs with simultaneous transmission of DMRS for PDSCH by the base station. As can be seen from the left side of Figure 7, in the example under consideration, it is assumed that the Rel-15 UE must use the DMRS port =1000 DMRS Type 1 structure, and UE Rel-18 - DMRS port =1010 of the extended DMRS Type 1 structure, so that the DMRS multiplexing for Rel-15 UE and Rel-18 UE is implemented by the base station in different CDM groups: Δ=0 for Rel-15 UE and Δ=1 for Rel-15 UE. The right parts of Fig. 7 show the respective use of different combs in the frequency domain.

[0041] In the example shown in Fig. 7, the DMRS ports under consideration remain orthogonal, since the Rel-15 UE and the Rel-18 UE use different subcarriers of different combs, respectively, when demodulating DMRS. Thus, each of the Rel-15 UE and the Rel-18 UE can demodulate its DMRS sequence and perform channel estimation; that is, in the case of the constraint of using DMRS ports with different CDM groups for PDSCH in the MU-MIMO mode, grouping the legacy Rel-15 UE and the Rel-18 UE becomes possible. Obviously, this may significantly limit the system's capabilities in terms of using orthogonal DMRS ports when scheduling DL transmission.

[0042] To summarize the above discussion on Figs. 6, 7, it should be noted that there is virtually no direct compatibility between the Rel-15 DMRS structure and future extensions of the PDSCH DMRS supporting longer FD-OCCs in a CDM group (in particular, Rel-18); as a consequence, in 5G NR, grouping of Rel-15 and Rel-18 UEs when transmitting DMRS for PDSCH in MU-MIMO mode may be, at the very least, very difficult.

[0043] Next, with reference to Fig. 8a, 8b, a similar forward compatibility problem is described for transmitting DMRS for the physical downlink control channel (PDCCH) in the MU-MIMO mode.

[0044] According to Rel-15 5G NR, one DMRS port for PDCCH is defined, namely =2000, with the DMRS sequence length equal to 1, i.e. the sequence [+1]; as illustrated accordingly in Fig. 8a, in the time domain such a DMRS for the PDCCH is simply repeated on the adjacent OFDM symbol.

[0045] Below is the mathematical expression (7) describing the DMRS sequence for PDCCH:

[0046]

[0047] where - power offset for DMRS relative to the PDCCH power; m=0, 1, … - current index; k'=0, 1, 2 - RE DMRS index in REG / PRB; - index of OFDM symbol in the slot; k is the subcarrier index, where

[0048]

[0049] - the number of subcarriers in the resource block. QPSK sequence is determined by equation (4), the binary Gold sequence is initialized as follows c init :

[0050]

[0051] where is the initialization parameter N ID configured via RRC signaling and is equal to the Cell ID by default.

[0052] A more detailed explanation regarding equations (7), (8), (9) and the terms included in them is given in the specification TS 38.211.

[0053] If a future Rel-X release requires the extension to introduce an orthogonal DMRS port for PDCCH using, for example, TD-OCC [+1 -1], i.e., a length of 2 (see Fig. 8b), then grouping of Rel-15 and Rel-X UEs during DMRS transmission for PDCCH in MU-MIMO mode will be impossible, since the Rel-15 UE is not aware of the possible presence of an orthogonal DMRS sequence of length 2 and, accordingly, will not perform the demodulation procedure with averaging over the OCC length in the time domain. In other words, the orthogonality of the DMRS port for PDCCH according to Rel-15 5G NR to the corresponding extended Rel-X DMRS port cannot be ensured.

[0054] Again, it should be noted that the Rel-15 DMRS structure for PDCCH is not directly compatible with future DMRS extensions supporting, for example, longer TD-OCC. Alternatively, in this context, the base station will have to serve Rel-X UEs in MU-MIMO mode, while serving legacy Rel-15 UEs in SU-MIMO mode.

[0055] A similar situation may occur for the case of DMRS transmission on non-adjacent OFDM symbols in a slot, which is illustrated in Fig. 9a; more specifically, a front-loaded DMRS (FL DMRS), which is transmitted closer to the beginning of the slot, and an additional DMRS (AD DMRS), which is transmitted closer to the end of the slot, are transmitted in the slot. The DMRS structure shown in Fig. 9a is supported in Rel-15 and Rel-18 5G NR and is widely used in commercial communication systems to track the channel in view of the mobility of user equipment. The TS 38.211 specification provides a table defining the possible positions of FL DMRS and AD DMRS on OFDM symbols in a slot.

[0056] According to the Rel-15 and Rel-18 5G NR specifications, no additional modulation using orthogonal codes is applied between FL DMRS and one or more AD DMRS within the same slot. This can be interpreted as using an OCC sequence of length 1 of the [+1] type on the corresponding OFDM symbols (see Fig. 9a).

[0057] If in some future Rel-Y release an extension is required to introduce a new orthogonal DMRS port using a TD-OCC [+1 -1] of length 2 between the FL DMRS and the AD DMRS (see Fig. 9b), then grouping of Rel-15 / Rel-18 UEs and Rel-Y UEs in such DMRS transmission for PDSCH in MU-MIMO mode will not be possible, since the Rel-15 UE is not aware of the possible presence of an orthogonal DMRS sequence of length 2 between the FL DMRS and the AD DMRS and, accordingly, will not perform the demodulation procedure with averaging over the length of the OCC in the time domain.

[0058] Again, it is stated that there is no direct compatibility between the Rel-15 / Rel-18 DMRS structure in the context under consideration with respect to future DMRS extensions, such as support for a longer TD-OCC between FL DMRS and AD DMRS.

[0059] Thus, in 5G NR, forward compatibility is properly supported only for PDSCH, but not for reference signals, in particular DMRS. Even the enhancement of 5G NR communication systems at the Rel-18 level turned out to be only partially backward compatible in this regard, since the grouping of Rel-18 and Rel-15 user equipment when transmitting DMRS for PDSCH in MU-MIMO mode is possible at best with strong transmission scheduling constraints (see the disclosure of Figs. 6 and 7).

[0060] The expected expansion of MU-MIMO capabilities in 6G (see Fig. 2) necessitates support for a larger number of orthogonal DMRS ports, with the corresponding development of enhanced DMRS structures that can utilize longer OCCs. At the same time, the aforementioned lack of forward compatibility may reduce the effectiveness of the wider deployment of MU-MIMO in networks due to the lack of awareness among legacy user equipment of the ability to utilize such enhanced DMRS.

[0061] SUMMARY OF THE INVENTION

[0062] The basic concept underlying the present invention, in view of the above-described shortcomings of the prior art due to the lack of forward compatibility for DMRS in 5G NR, is that in an earlier release of the communication standard (e.g., the first release of 6G), the user equipment should be provided with the ability to use longer corresponding DMRS sequences by the base station in future releases.

[0063] Accordingly, according to the first aspect of the present invention, a method for ensuring forward compatibility for processing DMRS at user equipment in a wireless communication system is proposed. The proposed method comprises the steps of, at the user equipment: receiving from a base station of the wireless communication system first information containing an indication of the possibility of using more than one OCC length by the base station when modulating DMRS for PDSCH; receiving from the base station second information indicating: at least one DMRS port that will be used by the base station for transmitting PDSCH to the user equipment, and one OCC length; and receiving from the base station a DMRS corresponding to each of said at least one DMRS port, and processing the received DMRS based on the OCC length indicated by the second information.For at least some DMRS ports, OCC sequences corresponding to OCCs with a longer OCC length are obtained by correspondingly replicating the OCC sequences corresponding to OCCs with a shorter OCC length. According to the proposed method, the user equipment is configured to avoid, during said DMRS processing, the assumption that the base station does not transmit DMRS sequences corresponding to other DMRS ports with an OCC length specified by the second information to other user equipment.

[0064] The first information is preferably transmitted by the base station via RRC signaling. The second information is preferably transmitted by the base station via DCI, wherein the second information is represented by at least one bit field in the DCI, wherein the value of each of the at least one bit field of the DCI is respectively selected by the base station from at least a portion of a corresponding predetermined set of bit values.

[0065] A DMRS port for PDSCH is generally associated with a set of at least a CDM group, an FD-OCC of a specified FD-OCC length, and a TD-OCC of a specified first TD-OCC length.

[0066] According to the first embodiment of the first aspect of the present invention, the OCCs are FD-OCCs. In the communication system, a first set of DMRS ports for the PDSCH is predefined, wherein the FD-OCCs associated with the DMRS ports of the first DMRS set have a basic FD-OCC length. In the communication system, one or more second sets of DMRS ports for the PDSCH are further predefined, wherein each of the one or more second sets of DMRS ports comprises at least a subset of DMRS ports, with each of which FD-OCCs of different FD-OCC lengths are associated, based on the basic FD-OCC length, wherein the number of CDM groups and the first TD-OCC length in said subsets of the one or more second sets of DMRS ports are respectively the same.

[0067] Preferably, the DMRS ports of the subset of DMRS ports of each of the N second sets of DMRS ports respectively correspond to the DMRS ports of the first set of DMRS ports and have the same DMRS port indices, where N≥1 is the number of pre-defined second sets of DMRS ports. With a DMRS port from a subset of DMRS ports of the i-th second set of DMRS ports, where i=1, …, N, are associated: FD-OCC of the corresponding DMRS port from the first set of DMRS ports and FD-OCC, the OCC sequence of which is obtained by 22-fold replication of the OCC sequence of FD-OCC of the corresponding DMRS port of the first set of DMRS ports, wherein with the said DMRS port from the subset of DMRS ports and with the said corresponding DMRS port, the same CDM group and the same OCC sequence TD-OCC are associated.

[0068] The first set of DMRS ports can use two CDM groups, two FD-OCCs of the basic FD-OCC length of 2, and two TD-OCCs of the first TD-OCC length of 1 or 2, where N is 1 or 2.

[0069] According to the first implementation of the first embodiment of the first aspect of the present invention, the first information comprises an indication of the used set of DMRS ports from said predetermined one or more second sets of DMRS ports, wherein the second information is represented by a single bit field in the DCI, which indicates said at least one DMRS port from a subset of DMRS ports of the used set of DMRS ports, wherein the OCC length indicated by the second information is the FD-OCC length of this at least one DMRS port. For DMRS ports with different FD-OCC lengths, different values ​​of the DCI bit field can be used accordingly.

[0070] According to the second implementation of the first embodiment, the second information is represented by two bit fields in the DCI, wherein the first bit field in the DCI indicates said at least one DMRS port among the first set of DMRS ports, and the second bit field in the DCI indicates the value of the FD-OCC basic length repetition parameter, wherein the OCC length indicated by the second information is determined as the product of the FD-OCC basic length by n t , where n t - a natural number greater than or equal to 1. The first information contains an indication of the presence of a second bit field in the DCI.

[0071] According to an embodiment, said DMRS processing comprises demodulating the DMRS with averaging in the frequency domain over the length of the OCC indicated by the second information.

[0072] According to the second embodiment of the first aspect of the present invention, the DMRS is transmitted twice in a time slot, wherein in the time domain, the first DMRS is transmitted in at least one OFDM symbol closer to the beginning of the slot, and the second DMRS is transmitted in at least one OFDM symbol closer to the end of the slot. Said set associated with the DMRS port further comprises an additional TD-OCC of a predetermined second TD-OCC length, wherein the additional TD-OCC is used between the first DMRS and the second DMRS in the slot.

[0073] According to the second embodiment, the OCCs are additional TD-OCCs. In the communication system, a first set of DMRS ports for the PDSCH is predefined, wherein the additional TD-OCCs associated with the DMRS ports of the first set of DMRS ports have a basic second TD-OCC length. In the communication system, a second set of DMRS ports for the PDSCH is further predefined, wherein additional TD-OCCs of different second TD-OCC lengths are associated with each DMRS port of the second set of DMRS ports, based on the basic second TD-OCC length, wherein the number of CDM groups, the FD-OCC length, and the first TD-OCC length in the second set of DMRS ports are the same as in the first set of DMRS ports.

[0074] Preferably, the DMRS ports of the second set of DMRS ports respectively correspond to the DMRS ports of the first set of DMRS ports and have the same DMRS port indices, and the CDM group, FD-OCC, and TD-OCC associated with the DMRS port of the second set of DMRS ports are the same as the CDM group, FD-OCC, and TD-OCC associated with the corresponding DMRS port of the first set of DMRS ports. In the first set of DMRS ports, two CDM groups are used, two FD-OCCs of the basic length FD-OCC equal to 2 and two TD-OCCs of the first length TD-OCC equal to 1 or 2, and the same additional TD-OCC of the basic second length TD-OCC equal to 1 is associated with the DMRS ports of the first set of DMRS ports. The following are associated with the DMRS ports of the second set of DMRS ports: the same additional TD-OCC of the first set of DMRS ports and the same additional TD-OCC of the second length TD-OCC equal to 2, the OCC sequence of which is obtained by duplicating the OCC sequence of the additional TD-OCC of the first set of DMRS ports.

[0075] According to the first implementation of the second embodiment, the first information contains an indication of using the second set of DMRS ports, wherein the second information is represented by a single bit field in the DCI, which indicates said at least one DMRS port among the second set of DMRS ports, wherein the OCC length indicated by the second information is the second TD-OCC length of this at least one DMRS port. For DMRS ports with different second TD-OCC lengths, different DCI bit field values ​​can be used accordingly.

[0076] According to the second implementation of the second embodiment, the second information is represented by two bit fields in the DCI, wherein the first bit field in the DCI indicates said at least one DMRS port among the first set of DMRS ports, and the second bit field in the DCI indicates the value of the parameter n trepetitions of the basic length TD-OCC, wherein the length of the OCC indicated by the second information is determined as the product of the basic second length TD-OCC by n t , where n t - a natural number greater than or equal to 1. The first information contains an indication of the presence of a second bit field in the DCI.

[0077] According to an embodiment, said DMRS processing comprises demodulating the DMRS with time-domain averaging over said OFDM symbols of the first DMRS and the second DMRS.

[0078] According to the second aspect of the present invention, a forward compatibility method for DMRS processing at user equipment in a wireless communication system is provided. The proposed method comprises the steps of, at the user equipment: receiving from a base station of the wireless communication system information containing an indication of the length of the OCC used by the base station for the DMRS of the PDCCH port; receiving from the base station a DMRS corresponding to the DMRS of the PDCCH port, and processing the received DMRS based on the OCC length indicated by said information. In the communication system, an OCC with an OCC sequence of the OCC base length is predetermined for the DMRS of the PDCCH port, wherein the OCC length indicated by said information is greater than the OCC base length, wherein the OCC sequence used by the user equipment in said DMRS processing is obtained by correspondingly replicating the OCC sequence of the OCC base length.According to the proposed method, the user equipment is configured to avoid, during said DMRS processing, the assumption that the base station has not transmitted DMRS to other user equipment corresponding to the DMRS port with the OCC length specified by said information. Said information is preferably transmitted by the base station via RRC signaling.

[0079] According to the first embodiment of the second aspect of the present invention, the OCC is a TD-OCC, and the basic length of the OCC is the basic length of the TD-OCC. Said information indicates the value of the parameter n t repetitions of the basic length of TD-OCC, wherein the length of the OCC indicated by said information is determined as the product of the basic length of TD-OCC by n t , where n t - a natural number greater than or equal to 1. Preferably, the base length of TD-OCC is 1, n t =2.

[0080] According to an embodiment, said DMRS processing comprises demodulating the DMRS with time-domain averaging over the length of the OCC indicated by said information.

[0081] According to the second embodiment of the second aspect, the OCC is an FD-OCC, and the base length of the OCC is the base length of the FD-OCC. Said information indicates the value of the parameter n t repetitions of the basic length of the FD-OCC, wherein the length of the OCC indicated by said information is determined as the product of the basic length of the FD-OCC by n t , where is a natural number greater than or equal to 1. Preferably, the base length of the FD-OCC is 1, n t =2.

[0082] According to an embodiment, said DMRS processing comprises demodulating the DMRS with averaging in the frequency domain over the length of the OCC indicated by said information.

[0083] According to a third aspect of the present invention, user equipment is provided in a wireless communication system, comprising at least: transmitting and receiving devices, data processing devices, and data storage devices. The data storage devices store computer-executable codes that, when executed by the data processing devices, ensure the implementation of the method according to any embodiment of the first or second aspect of the present invention.

[0084] According to a fourth aspect of the present invention, a machine-readable storage medium is provided, on which machine-executable codes are stored, which, when executed by at least one data processing device of a user equipment, cause the user equipment to perform a method according to any embodiment of the first or second aspect of the present invention.

[0085] The technical result achieved by the present invention consists, first of all, in ensuring direct compatibility on the user equipment side with respect to future DMRS extensions for both PDSCH and PDCCH, without additional restrictions regarding the grouping of legacy and non-legacy user equipments when planning the simultaneous transmission of DMRS on the base station side and without changing the DMRS sequences themselves for legacy user equipments, which, in turn, makes it possible to avoid a decrease in the efficiency of expanding the use of MU-MIMO in the communication system, with relatively low implementation costs.

[0086] BRIEF DESCRIPTION OF DRAWINGS

[0087] Fig. 1 - Estimated diagram of the dynamics of the total traffic load for 6G systems.

[0088] Fig. 2 - Illustration of the projected evolution of MU-MIMO deployment in commercial communication systems.

[0089] Fig. 3-Illustration of frequency-time resource reservation according to 5G NR.

[0090] Fig. 4 - Illustration of the time-frequency structure of Type 1 DMRS for PDSCH according to 5G NR.

[0091] Fig. 5 - Illustration of DMRS extension according to Rel-18 5G NR with respect to Rel-15 5G NR.

[0092] Fig. 6 is an illustration of one example of grouping Rel-15 and Rel-18 user equipment with the base station simultaneously transmitting DMRS for PDSCH to them.

[0093] Fig. 7 - illustration of another example of grouping Rel-15 and Rel-18 user equipment with simultaneous transmission of DMRS for PDSCH by the base station.

[0094] Fig. 8a is an illustration of DMRS transmission for PDCCH according to Rel-15 5G NR.

[0095] Fig. 8b is an illustration of possible DMRS transmission for PDCCH according to a future release of the communication standard.

[0096] Fig. 9a is an illustration of FL DMRS and AD DMRS transmission for PDSCH according to Rel-15 / Rel-18 5G NR.

[0097] Fig. 9b - illustration of possible transmission of FL DMRS and AD DMRS for PDSCH according to a future release of the communication standard.

[0098] Fig. 10 is an illustrative diagram of a wireless communication system in which embodiments of the present invention may be implemented.

[0099] Fig. 11 is an illustration of configuring legacy user equipment DMRS ports for PDSCH according to one implementation of the first embodiment of the first aspect of the present invention.

[0100] Fig. 12 is a flow chart of a method for processing DMRS for PDSCH at the user equipment side according to the first embodiment of the first aspect of the present invention.

[0101] Fig. 13 is an illustration of configuring legacy DMRS ports for a user equipment in the case of transmitting FL DMRS and AD DMRS for a PDSCH according to one implementation of the second embodiment of the first aspect of the present invention.

[0102] Fig. 14 is an illustration of configuring legacy user equipment DMRS ports in the case of transmitting FL DMRS and AD DMRS for PDSCH according to an alternative implementation of the second embodiment of the first aspect of the present invention.

[0103] Fig. 15 is a flow chart of a method for processing DMRS at the user equipment side in the case of transmitting FL DMRS and AD DMRS for PDSCH, according to a second embodiment of the first aspect of the present invention.

[0104] Fig. 16a, 16b are illustrations of configuring the length of the OCC for the DMRS port of the PDCCH for the legacy user equipment according to embodiments of the second aspect of the present invention.

[0105] Fig. 17 is a flow chart of a method for processing DMRS for PDCCH at the user equipment side according to the second aspect of the present invention.

[0106] DETAILED DESCRIPTION OF THE INVENTION

[0107] Reference is now made to exemplary embodiments of the present invention, which are illustrated in the accompanying drawings, wherein like reference numerals designate like elements. It is to be understood that the embodiments of the invention may take various forms and should not be considered as limited by the descriptions given herein. Accordingly, the exemplary embodiments

[0108] are described below with reference to the drawing figures to explain the essence of the aspects of the present invention.

[0109] Figure 10 generally illustrates a wireless communication system in which various aspects of the present invention can be implemented. As shown in Figure 10, user equipments (UEs) 1001 communicate with base stations (BSs) 1002 in a radio access network (RAN) 1000. The UEs 1001 (e.g., UEs 1001-1, 1001-2, 1001-3, ...) are distributed over the RAN 1000, and each of the UEs 1001 may be stationary or mobile. Well-known examples of UEs include smartphones, tablets, modems, and the like.

[0110] Base stations 1002 (e.g., BS 1002-A, 1002-B, 1002-C) can provide coverage for a specific geographic area, often referred to as a 'cell'. Base stations 1002 are generally of a fixed design, but may also be of a mobile design. In general, base stations may be macro base stations (as illustrated by BS 1002-A, 1002-B, 1002-C in Fig. 10), as well as pico base stations for pico cells or femto base stations for femto cells. Cells, in turn, can be divided into sectors.

[0111] Coordination and control of the operation of the base stations 1002 may be provided by a network controller in communication with them (for example, via a backhaul connection). RAN 1000 may be in communication with a core network (CN) (for example, via a network controller), which provides various network functions, such as, for example, access and mobility management, session management, an authentication server function, an application function, etc. In this case, the base stations 1002 in RAN 1000 may also be connected to each other, for example, via a direct physical connection, which is preferably a high-speed connection.

[0112] When user equipment moves within RAN 1000, it can be handed over from one base station to another. For example, UE 1001-3 can be handed over from BS 1002-B to BS 1002-A. This involves reconfiguring the relevant communication system parameters on the user equipment to operate with the new base station. Handover of user equipment can also occur between sectors of a single base station.

[0113] Each of the BS 1002 shown in Fig. 10 includes hardware and logical means for implementing the corresponding functions in the base station. The hardware includes, in particular, an antenna array consisting of the transmitting and receiving antenna elements discussed above, various specially configured processors, controllers, data storage devices, other circuit elements, as well as buses connecting them. The logical means include software stored in the corresponding memory devices and configuring the corresponding circuit elements. The software also includes firmware directly embedded in the processors and controllers.The specified hardware is configured, among other things, to perform various processing in relation to transmitted and received signals, including (de)modulation, (de)multiplexing, (de)coding, amplification, filtering, digitization, (de)interleaving, resource allocation, reception / transmission scheduling.

[0114] Similarly, each of the UEs 1001 shown in Fig. 10 includes hardware and logic means for implementing the corresponding functions in the user equipment. The hardware includes, in particular, transceivers with corresponding antenna elements, various specially configured processor(s), controllers, data storage devices, other circuit elements, as well as buses connecting them. The logic means include software stored in the corresponding memory devices and configuring the corresponding circuit elements. The software also includes firmware directly embedded in the controllers.The specified hardware is configured, among other things, to perform various processing on transmitted and received signals, including (de)modulation, (de)multiplexing, (de)coding, amplification, filtering, digitization, and (de)interleaving. In addition, the UE comprises means for interacting with the user, including a touch screen, speakers / microphone, buttons, and user applications stored in the user equipment's memory and executed by the user equipment's processor in the corresponding operating system.

[0115] Examples of the above-mentioned processors / controllers include microprocessors, microcontrollers, digital signal processing (DSP) devices, field programmable gate arrays (FPGA), discrete hardware chips, etc. The (micro)software executed by the processors / controllers should be broadly construed as meaning machine-executable instructions, instruction sets, program code, code segments, subroutines, program modules, objects, procedures, etc. The software is stored on corresponding machine-readable media, which can be implemented, for example, in the form of RAM, ROM, EEPROM, solid-state memory, magnetic memory, optical memory, etc., on which corresponding program codes and data structures can be recorded or stored and can be accessed by the corresponding processors / controllers.

[0116] The above-mentioned hardware and software elements of the base stations and user equipment are configured to ensure that the operations described below are performed in the base stations and user equipment according to this application. The implementation of the component hardware of the base stations and user equipment and their specialized configuration, including by means of corresponding logical means, are known in the technical field to which this application pertains. Moreover, various functions corresponding to this application may be performed in a plurality of individual elements or in one or more integrated elements, which is determined by the design structural characteristics.

[0117] As noted earlier, the present invention is based on the technical concept that, starting from an earlier release of the communication standard (for example, the first release of 6G), on the user equipment side, the possibility of using longer corresponding DMRS sequences by the base station in future releases is taken into account, even in the absence of a current need on the operator side to support a large number of orthogonal DMRS ports.Accordingly, in this application, it is generally proposed that if a communication system of a certain new release supports a certain number of DMRS ports for the corresponding physical DL channel, it should be possible to explicitly or implicitly communicate to the user equipment side the length of the OCC that was respectively used by the base station for modulating the DMRS for this physical DL channel, so that the legacy user equipment can make correct assumptions regarding the length of the OCC when demodulating the DMRS.

[0118] The approach according to the first aspect of the present invention provides forward compatibility for processing DMRS for PDSCH at the user equipment, in general, as follows. The user equipment receives first information from the base station, containing an indication of the possibility of the base station using more than one OCC length when modulating DMRS for PDSCH. The first information is transmitted by the base station via RRC signaling (L3 layer). The user equipment also receives second information from the base station, which indicates: at least one DMRS port that will be used by the base station for transmitting PDSCH to the user equipment, and one OCC length. The second information is transmitted by the base station via DCI (L1 layer). Then, the user equipment receives from the base station a DMRS corresponding to each of the indicated at least one DMRS port, and processes the received DMRS based on the indicated OCC length.Moreover, for at least some DMRS ports, the OCC sequences corresponding to OCCs with a longer OCC length are obtained by correspondingly replicating the OCC sequences corresponding to OCCs with a shorter OCC length. Unlike current 5G NR releases, during the aforementioned DMRS processing, including demodulation, the user equipment does not assume that the base station does not transmit DMRS sequences corresponding to other DMRS ports with the OCC length specified by the second information to other user equipment. In other words, when processing the received DMRS, the user equipment must assume the possibility of transmitting DMRS sequences from the base station to other user equipment with the OCC length specified by the second information.

[0119] Next, with reference to Fig. 11, which has a format similar to Fig. 5, an implementation of the first embodiment of this approach according to the present invention is illustrated using an example based on Rel-15 / Rel-18 5G NR. The upper left part of Fig. 11 shows a table of DMRS ports according to Rel-15, where FD-OCCs of length 2 are used, and this set of DMRS ports in the considered illustrative case is considered to be the original, 'native' for the legacy user equipment; the OCC length of the FD-OCC sequence of the original set of DMRS ports may, without loss of generality, be referred to in this application in the relevant context as the 'basic FD-OCC length'.

[0120] The lower left part of Fig. 11 shows a table of a subset of the DMRS port set for a later release of the communication standard (Rel-Z), similar to Rel-18, with the FD-OCC length equal to 4; accordingly, it is implied that there are more DMRS ports in the Rel-Z set than shown in Fig. 11. It should be emphasized that the DMRS port indices are shown in this table with a prime for clarity purposes only: preferably, the DMRS port indices in such a subset of DMRS ports with a longer FD-OCC sequence length respectively coincide with the DMRS port indices of the original Rel-15 DMRS port set, unlike Rel-18; in particular, the index '=1001' is in fact the same as =1001. It is also implied that with each DMRS port from the original set, in addition to the corresponding CDM group index and the OCC sequence FD-OCC, there is also associated an OCC sequence TD-OCC of length 2 (not shown in Fig. 11), as reflected in Fig. 5. Alternatively, a corresponding TD-OCC sequence of length 1 can be associated with the DMRS port. In this case, with each DMRS port from the considered subset of the set of DMRS ports Rel-Z, the same OCC sequence TD-OCC, as well as the same CDM group index, are associated as with the corresponding DMRS port from the set Rel-15. Let's say, if, according to Fig. 5, with the DMRS port =1001 the CDM group index 0 and the OCC sequence TD-OCC [+1 +1] are associated, then the same CDM group index and the same OCC sequence TD-OCC will be associated with the port '=1001'.

[0121] As can be seen from the left part of Fig. 11, the difference between the corresponding DMRS ports of the original set and the subset of DMRS ports of Rel-Z is only in the length of FD-OCC, while for the DMRS port of the Rel-Z subset, the OCC sequence FD-OCC is obtained by double replication (duplication) in the frequency domain of the OCC sequence FD-OCC of the corresponding DMRS port of the original set. For example, if the FD-OCC sequence of the DMRS port =1001 - [+1 -1], then the FD-OCC sequence of the DMRS port '=1001' represents [+1 -1 +1 -1].

[0122] As a result, in the case of using the considered subset of DMRS Rel-Z ports, the DMRS sequence of any port from this subset will not change for the user equipment compared to the DMRS sequence of the corresponding DMRS port of the original set.

[0123] The approach according to the discussed implementation of the present invention allows considering the subset of DMRS ports shown in the lower left part of Fig. 11 in such a way that with each of its DMRS ports there are associated FD-OCCs of different lengths, namely the OCC sequence of FD-OCC of basic length 2 (from the Rel-15 set) and the OCC sequence of FD-OCC of length 4, obtained by double replication of the corresponding OCC sequence of FD-OCC Rel-15. Let's say with a DMRS port '=1001' (or, what is the same, =1001) the OCC sequence [+1 -1] and the replicated OCC sequence [+1 -1 +1 -1] are associated. The subset of DMRS ports of Rel-Z considered in this way may, without loss of generality, be referred to throughout the text of this application as the set of DMRS ports with variable OCC length, as opposed to the original set of DMRS ports, which is characterized by a fixed FD-OCC length.

[0124] Accordingly, the base station may configure either a set of DMRS ports with a variable OCC length or an initial set of DMRS ports for the user equipment via RRC signaling. Such configuration may be accomplished by transmitting a special parameter via RRC that configures either an initial set of DMRS ports with a fixed FD-OCC length or a set of DMRS ports with a variable OCC length for the user equipment. The implementation of such RRC configuration should be clear to those skilled in the art and is not directly related to the subject matter of the present invention.

[0125] Then, the base station, via the DCI transmitted in the PDCCH, indicates to the user equipment one or more DMRS ports that will be used by the base station for transmitting the PDSCH to the user equipment. This indication is represented by a bit field in the DCI, and the value of this DCI bit field is accordingly selected by the base station from at least part of a corresponding predetermined set of bit values. An illustrative example of such a set of values ​​is shown in the right part of Fig. 11.

[0126] Therefore, if a set of DMRS ports with variable OCC length has been configured for the user equipment by the base station via RRC, then, for example, a value of 4 in the DCI indicates to the user equipment to use the DMRS port. =1001 with FD-OCC length equal to 2, and the value 13 indicates the use of the corresponding (essentially the same) DMRS port '=1001' with an FD-OCC length of 4. In both cases, the DMRS sequence for the user equipment will be the same, but in the case of a DCI value of 13, the user equipment will know that the FD-OCC length is 4 and will make the corresponding assumption when processing the received DMRS - in particular, when demodulating DMRS, the user equipment can perform frequency domain averaging over an FD-OCC length of 4. Thus, for a set of DMRS ports with variable OCC length, different FD-OCC lengths of the same DMRS port use correspondingly different DCI bit field values. In the right part of Fig. 11, DMRS ports with the same DMRS sequences but different FD-OCC lengths are outlined in bold frames. According to the above, a larger number of orthogonal DMRS ports and, accordingly, associated FD-OCCs with a longer OCC sequence can be used by the base station when MU-MIMO mode is enabled.

[0127] At the same time, as noted earlier, traffic in a cell or sector served by a base station can change dynamically over time; therefore, at one point in time, the base station may need to use MU-MIMO, but at another point in time, it may not. Furthermore, in some cases, there may be no need to use MU-MIMO with user equipment processing, assuming a longer FD-OCC, since the number of user equipment in MU-MIMO is limited under low network load, and there is no need to increase the number of DMRS ports.

[0128] The use of longer OCC sequences by legacy user equipment for averaging in the frequency domain during DMRS demodulation may lead to additional noise in the channel estimation, especially in the case of frequency-selective channels. Using the DCI-based mechanism described above, a base station, for example, in the case where the use of the MU-MIMO mode is impractical or the use of the MU-MIMO mode is possible with the original number of orthogonal DMRS ports, can accordingly dynamically indicate to the user equipment the DMRS port(s) with a shorter FD-OCC sequence in order to avoid the negative effects described above. Continuing with the example discussed with reference to Fig. 11, the base station can set the bit field value in DCI to 4, thereby indicating the DMRS port to the user equipment. =1001 with an FD-OCC length of 2; thus, when demodulating the corresponding DMRS, the user equipment can perform frequency domain averaging over a length of 2.

[0129] It should be clear to a person skilled in the art that in the predetermined set of bit values ​​illustrated in the right part of Fig. 11, for a subset of DMRS ports with a longer FD-OCC length (see the lower left part of Fig. 11), at least one value may be provided that simultaneously indicates more than one DMRS port from this subset, by analogy with values ​​7-11 for Rel-15.

[0130] In addition, using the above-mentioned slower, semi-static configuration mechanism based on RRC, the base station may initially configure an initial set of DMRS ports with the basic FD-OCC length (see the upper left part of Fig. 11) for the user equipment. In this case, the base station may use only a part of the set of values, namely, a subset of values ​​0-11 according to the right part of Fig. 11, to indicate the DMRS port(s) in the DCI. Using this approach may, in general, allow using fewer bits to convey such an indication in the DCI to the user equipment. Since in this case, any indication of a DMRS port in the DCI will indicate a DMRS port from the initial set, the user equipment will know that the length of the associated FD-OCC is 2.Subsequent configuration of a set of DMRS ports with variable OCC length for the user equipment can also be performed by the base station via the RRC mechanism.

[0131] An exemplary implementation was considered above, where FD-OCC lengths of 2 and 4 were used. It should be noted that the approach described above with reference to Fig. 11 is equally applicable to longer FD-OCC OCC sequences of length greater than 4. For example, if it is necessary to provide a greater number of orthogonal DMRS ports in a later release of the communication standard (Rel-W), a subset of the set of DMRS ports of Rel-W can be used, similar to that shown in the lower left part of Fig. 11, but with an FD-OCC length equal to 8. In this case, for a DMRS port of the Rel-W OCC subset, the FD-OCC sequence is obtained by fourfold replication in the frequency domain of the OCC of the FD-OCC sequence of the corresponding DMRS port of the original set. For example, using the symbols of Fig. 11, if the OCC sequence is FD-OCC DMRS port =1001 - [+1 -1], then the OCC sequence FD-OCC DMRS port '=1001' will represent [+1 -1 +1 -1 +1 -1 +1 -1].

[0132] The approach to configuring DMRS ports for PDSCH in user equipment with forward compatibility, which corresponds to the first embodiment of the present invention, may have another, alternative implementation with respect to that described with reference to Fig. 11.

[0133] In the alternative implementation under consideration, it is implied that in the communication system for the legacy user equipment, only its initial set of DMRS ports is explicitly specified (see, for example, the upper left part of Fig. 11). At the same time, in contrast to the implementation of Fig. 11, in this alternative implementation, two bit fields can be used in the DCI to implement the said dynamic indication to the user equipment. One of these bit fields, without loss of generality referred to in this application as the 'first bit field', is used to indicate one or more DMRS ports in their initial set that will be used by the base station for transmitting PDSCH to the user equipment, i.e., it is essentially used similarly to the DCI bit field in the implementation of Fig. 11. The other bit field in the DCI, without loss of generality referred to in this application as the 'second bit field', indicates the value of the parameter n trepetitions of the FD-OCC base length, so that the FD-OCC length assumed by the user equipment for frequency domain averaging during DMRS demodulation is calculated as the product of the FD-OCC base length and n t , where n t - a natural number. For the case n t >1, in the implementation under consideration it is implicitly assumed, similar to the implementation in Fig. 11, that the OCC sequence for FD-OCC is of greater length, determined by n t , is obtained through the corresponding replication of the OCC sequence of the DMRS base length of the port specified by the first DCI bit field. In other words, in this case, for the user equipment, there is again no change in the DMRS sequence itself when the FD-OCC length increases.

[0134] For example, if the first field in the DCI indicates the DMRS port p=1001 (for example, by the value 4, as shown in the right part of Fig. 11), and the value indicated by the second field of the DCI is 2, then, according to the above, the user equipment, when processing the corresponding DMRS, will assume the length of the FD-OCC to be 4, i.e., actually imply the port sequence for the FD-OCC OCC '=1001' (see the lower left part of Fig. 11). If the value of n t is equal to 4, then the user equipment, when processing DMRS, will assume the FD-OCC length to be 8, i.e., it will actually assume the OCC sequence [+1 -1 +1 -1 +1 -1 +1 -1], as indicated earlier.

[0135] The use of the DCI-based dynamic indication mechanism is essentially similar to that in the implementation of Fig. 11. Say, a base station, for example, in a case where the use of the MU-MIMO mode is not practical or the use of the MU-MIMO mode is possible using the original number of orthogonal DMRS ports, can accordingly dynamically indicate the DMRS port(s) with the basic length of the FD-OCC to the legacy user equipment by setting the value in the second DCI field to 1; thus, when demodulating the corresponding DMRS, the user equipment can perform averaging in the frequency domain on the basic length of 2.

[0136] In the alternative implementation under consideration, the base station indicates in advance via RRC signaling the presence or absence of the second bit field in the DCI. This indication can be performed, in general, similar to the implementation of Fig. 11, i.e., by transmitting a special parameter via RRC.

[0137] Similar to the implementation of Fig. 11, the base station, using the semi-static RRC configuration mechanism, may initially configure the user equipment to use only the initial set of DMRS ports with a fixed FD-OCC basic length by transmitting, via RRC, a corresponding parameter indicating the absence of the second bit field in the DCI.

[0138] Thus, the approach according to the first embodiment of the present invention makes it possible to ensure forward compatibility in the processing of DMRS for PDSCH for legacy user equipment by dynamically indicating to the user equipment the corresponding DMRS port(s) with an explicit or implicit indication of the length of the FD-OCC to be used by the user equipment when processing DMRS, and without changing the DMRS sequence itself.

[0139] Next, with reference to the flowchart of Fig. 12, a description will be given of a method 1200 for processing DMRS for PDSCH in legacy user equipment (for example, such as UE 1001-1, 1001-2, 1001-3, ... in the wireless communication system 1000 of Fig. 10) while ensuring forward compatibility, according to a preferred embodiment of the first embodiment of the present invention.

[0140] In step 1210, the user equipment receives first information from a base station (for example, such as BS 1002-A, 1002-B, 1002-C of the wireless communication system 1000 in Fig. 10). The first information is preferably transmitted by the base station via RRC signaling and, in general, contains an indication of the possibility of the base station using more than one FD-OCC length in DMRS modulation for the PDSCH.

[0141] According to the implementation described with reference to Fig. 11, this indication is carried out by transmitting, using RRC, a corresponding parameter by which a set of DMRS ports with a variable OCC length is configured for the user equipment; that is, in this implementation, the first information of step 1210 is represented by this RRC parameter.

[0142] In step 1220, the user equipment receives second information from the base station. The second information is preferably transmitted by the base station via DCI and generally indicates at least one DMRS port that will be used by the base station to transmit the PDSCH to the user equipment, as well as the FD-OCC length. As noted previously, the second information is represented in the DCI by at least one bit field, and the value of each of the at least one DCI bit field is respectively selected by the base station from at least a portion of a corresponding predetermined set of bit values.

[0143] According to the implementation described with reference to Fig. 11, the second information of step 1220 is represented in the DCI by one bit field that indicates at least one DMRS port among the set of DMRS ports with a variable OCC length configured for the user equipment in step 1210. The same user equipment is implicitly indicated the FD-OCC length: the indicated length is the FD-OCC length of this at least one DMRS port. For example, if in the considered implementation the value 13 was transmitted in the DCI (see the right part of Fig. 11), then the DMRS port will be indicated to the user equipment =1001 with the OCC sequence [+1 -1 +1 -1] and, accordingly, the FD-OCC length equal to 4.

[0144] According to an alternative implementation with respect to the implementation of Fig. 11, the second information of step 1220 is represented in the DCI by two bit fields, where the first field indicates at least one DMRS port among the original set of DMRS ports, and the second field indicates the value of the FD-OCC basic length repetition parameter.

[0145] According to the considered preferred option of the first embodiment of the present invention, in this alternative implementation, said indication of step 1210 is carried out by transmission using RRC

[0146] of the corresponding parameter, which indicates the presence of the second bit field in the DCI (i.e., in this alternative implementation, the first information in step 1210 is again represented by this parameter), and the value n t, indicated by the second field of the DCI received by the user equipment in step 1220, is greater than one. For example, if in the alternative implementation under consideration the value 4 is transmitted in the first bit field of the DCI (see the right part of Fig. 11), and the value n is indicated by the second field t equal to 2, then the user equipment is assigned a DMRS port as a result =1001 with the OCC sequence [+1 -1] of base length 2 and, accordingly, the FD-OCC length is indicated, defined as the product of the FD-OCC base length by n t , i.e. the length of FD-OCC is equal to 4.

[0147] In step 1230, the user equipment receives from the base station a DMRS corresponding to each of at least one DMRS port indicated by the second information received in step 1220. In step 1240, the user equipment processes the received DMRS based on the FD-OCC length indicated by the second information. The processing in step 1240 includes, in particular, demodulating the DMRS with possible averaging in the frequency domain over the indicated FD-OCC length. Other possible actions that can be performed by the user equipment when processing the received DMRS should be clear to those skilled in the art and are not directly related to the subject matter of the present invention.

[0148] In contrast to the 5G NR scenario illustrated previously with reference to Fig. 6, 7, the approach to ensuring forward compatibility for the reference signal according to the first embodiment of the present invention, described with reference to Fig. 11, 12, makes it possible to maintain the orthogonality of the DMRS for the PDSCH when grouping legacy and non-legacy user equipment in the MU-MIMO mode, without the above-described limitation with respect to CDM groups, which is achieved, in particular, by explicitly or implicitly indicating to the legacy user equipment the length of the FD-OCC that it should use when demodulating the corresponding DMRS, without changing the DMRS sequence itself.

[0149] Next, with reference to Fig. 13, an implementation of a second embodiment of the approach according to the first aspect of the present invention is illustrated, where the second embodiment relates to the FL DMRS and AD DMRS transmission context for PDSCH, illustrated previously with reference to Fig. 9a, 9b.

[0150] Similar to Fig. 11, for the considered implementation of the second embodiment, the DMRS port table according to Rel-15 / Rel-18 5G NR is shown in the upper part of Fig. 13. In the left column of this table, for each of the DMRS ports, the OCC sequence of the additional TD-OCC, which is used between the FL DMRS and AD DMRS in the slot, is given. As noted earlier, in Rel-15 / Rel-18, additional modulation using orthogonal codes is not applied for all DMRS ports, which can be interpreted as using an additional sequence of length 1 of the type [+1] on the corresponding OFDM symbols. As in the case of the first embodiment described above with reference to Figs. 11, 12, the set of DMRS ports shown in the upper part of Fig.13, in the second embodiment under consideration, is considered to be the initial length for the legacy user equipment; the length of the OCC sequence of the additional TD-OCC of the initial set of DMRS ports may, without loss of generality, be referred to in this application in the relevant context as the 'basic length of TD-OCC'.

[0151] Again similar to Fig. 11, the lower portion of Fig. 13 shows a table of a subset of the DMRS port set for a later release of the communication standard (Rel-Y), with an additional TD-OCC length of 2; accordingly, it is implied that there are more DMRS ports in the Rel-Y set than shown in Fig. 13. As in the case of the first embodiment, it is implied that the indices of the DMRS ports shown with a prime in such a subset of DMRS ports with a longer additional TD-OCC length are respectively the same as the indices of the DMRS ports of the original DMRS port set; It is also implied that each DMRS port from the considered subset of DMRS ports Rel-Y is associated with the same OCC sequence FD-OCC, the same OCC sequence TD-OCC and the same CDM group index as with the corresponding DMRS port from the original set of DMRS ports.

[0152] As can be seen from Fig. 13, the difference between the corresponding DMRS ports of the original set and the Rel-Y DMRS port subset is only in the length of the additional TD-OCC. It can be said that, as in the case of the first embodiment, for the Rel-Y subset, the additional TD-OCC sequence is obtained by double replication in the OCC time domain of the additional TD-OCC sequence of the original set of DMRS ports. In the case of using the considered Rel-Y DMRS port subset, the DMRS sequence of any port from this subset will not change for the user equipment compared to the DMRS sequence of the corresponding DMRS port of the original set.

[0153] Below is the mathematical expression (1') describing the DMRS sequence for the corresponding DMRS port for PDSCH in the FL / AD DMRS context under consideration:

[0154]

[0155] where - an element of the sequence of additional TD-OCC, while the other members of equation (1') have the same semantic content as the corresponding members of equation (1), as described above, while .

[0156] As in the case of the first embodiment, the approach according to the discussed implementation of the second embodiment of the present invention allows considering the subset of DMRS ports shown in the lower part of Fig. 13 in such a way that additional TD-OCCs of different lengths are associated with each of its DMRS ports, namely, the same OCC sequence of additional TD-OCC of basic length 1 (from the Rel-15 / Rel-18 set) and the same OCC sequence of additional TD-OCC of length 2. The subset of DMRS ports of Rel-Y considered in this way can, without limitation of generality, be referred to throughout the text of the present application in the corresponding context as a 'set of DMRS ports with variable OCC length'.

[0157] Similar to the first embodiment, the base station can configure either a set of DMRS ports with a variable OCC length or an initial set of DMRS ports with a fixed OCC length for the user equipment via RRC signaling, for example, using a special RRC parameter. Then, the base station, using an appropriately selected bit field value in the DCI, indicates to the user equipment one or more DMRS ports that the base station will use to transmit the PDSCH to the user equipment. For a set of DMRS ports with a variable OCC length, different DCI bit field values ​​are used for different additional TD-OCC lengths of the same DMRS port, while the corresponding DMRS sequence for the user equipment remains unchanged.

[0158] Therefore, if a base station has configured a set of DMRS ports with a variable OCC length for a user equipment via RRC and the DCI bit field value indicates to the user equipment the use of a DMRS port with a longer additional TD-OCC length, the user equipment will know that the additional TD-OCC length is 2 and will make the corresponding assumption. In particular, when demodulating DMRS, the user equipment can perform time-domain averaging over the FL DMRS and AD DMRS OFDM symbols. It should be recalled that such averaging is not performed in 5G NR (see the disclosure in Fig. 9a).

[0159] As noted earlier, an additional TD-OCC of longer length may be used by the base station when MU-MIMO mode is enabled, while, as shown in Fig. 9b, non-legacy user equipments that comply with the newer Rel-Y release may receive DMRS ports using the orthogonal sequence [+1 -1] of the additional TD-OCC of length 2.

[0160] By using the DCI-based mechanism described above, the base station, for example, in the case where the use of the MU-MIMO mode is not practical or the use of the MU-MIMO mode is possible with the original number of orthogonal DMRS ports, can accordingly dynamically switch the legacy user equipment to use the DMRS port(s) with an OCC sequence of an additional TD-OCC of the basic length of 1. In this way, the user equipment may not perform averaging in the time domain over the FL DMRS and AD DMRS OFDM symbols, which, in turn, can improve the efficiency of the channel estimation, since, as noted earlier, averaging over a longer OCC length may introduce additional noise, especially in the case of a channel with time selectivity.

[0161] In addition, using the RRC-based configuration mechanism, the base station can initially configure the initial set of DMRS ports with a basic length for the user equipment (see the upper part of Fig. 13). Since in this case, any indication of a DMRS port in the DCI will indicate a DMRS port from the initial set, the user equipment will know that the length of the additional TD-OCC is equal to 1. Subsequent configuration of the set of DMRS ports with a variable OCC length for the user equipment can also be performed by the base station using the RRC mechanism.

[0162] The approach to configuring DMRS ports for PDSCH in user equipment with forward compatibility, which corresponds to the considered second embodiment of the present invention, may have another, alternative implementation with respect to that described with reference to Fig. 13, as in the case of the first embodiment.

[0163] In the alternative implementation under consideration, it is implied that in the communication system for the legacy user equipment, only its initial set of DMRS ports is explicitly specified (see, for example, the upper part of Fig. 13). At the same time, in contrast to the implementation of Fig. 13, in this alternative implementation, two bit fields can be used in the DCI to implement the said dynamic indication of the user equipment. As in the first embodiment, the first bit field is used to indicate one or more DMRS ports in their initial set that will be used by the base station for transmitting PDSCH to the user equipment, i.e., it is essentially used similarly to the DCI bit field in the implementation of Fig. 13. The second bit field in the DCI indicates the value of the parameter n trepetitions of the basic TD-OCC length, so that the length of the additional TD-OCC assumed by the user equipment when demodulating DMRS is calculated as the product of the basic TD-OCC length and n t , where n t - a natural number. For the case n t >1, in the implementation under consideration it is implicitly assumed, similar to the implementation in Fig. 13, that the OCC sequence for the additional TD-OCC is of greater length, determined by n t , is obtained through the corresponding replication of the OCC sequence of the DMRS base length of the port specified by the first DCI bit field. In other words, in this case, for the user equipment, there is again no change in the DMRS sequence itself when the length of the additional TD-OCC increases.

[0164] The use of the DCI-based dynamic indication mechanism is essentially similar to that in the implementation of Fig. 13. Say, the base station, for example, in the case where the use of the MU-MIMO mode is not practical or the use of the MU-MIMO mode is possible with the original number of orthogonal DMRS ports, can accordingly dynamically indicate to the legacy user equipment the DMRS port(s) with the basic length of TD-OCC by setting the value of n t in the second DCI field equal to 1; thus, when demodulating the corresponding DMRS, the user equipment will not perform time domain averaging over the FL DMRS and AD DMRS OFDM symbols.

[0165] An alternative embodiment of the second embodiment of the present invention discussed above is illustrated in Fig. 14.

[0166] As in the case of the first embodiment, in the considered alternative implementation of the second embodiment, the base station indicates in advance via RRC signaling the presence or absence of the second bit field in the DCI.

[0167] Similar to the implementation of Fig. 13, the base station, using the RRC configuration mechanism, may initially configure the user equipment to use only the initial set of DMRS ports with a fixed TD-OCC length by transmitting, via RRC, a corresponding parameter indicating the absence of the second bit field in the DCI.

[0168] Thus, the approach according to the considered second embodiment of the present invention makes it possible to ensure forward compatibility in the processing of FL DMRS and AD DMRS for PDSCH with respect to legacy user equipment by dynamically indicating to the user equipment the corresponding DMRS port(s) with an explicit or implicit indication of the length of the additional TD-OCC to be used by the user equipment when processing DMRS, and without changing the DMRS sequence itself.

[0169] Next, with reference to the flowchart of Fig. 15, a description will be given of a method 1500 for processing DMRS for PDSCH in a legacy user equipment (for example, such as UE 1001-1, 1001-2, 1001-3, ... in the wireless communication system 1000 of Fig. 10) in the context of transmitting FL DMRS and AD DMRS in a slot, in accordance with a preferred option of the second embodiment of the present invention.

[0170] In step 1510, the user equipment receives first information from a base station (for example, such as BS 1002-A, 1002-B, 1002-C of the wireless communication system 1000 in Fig. 10). The first information is preferably transmitted by the base station via RRC signaling and, in general, contains an indication of the possibility of the base station using more than one length of an additional TD-OCC when modulating FL DMRS and AD DMRS for PDSCH. According to the implementation described with reference to Fig. 13, this indication is performed by transmitting a special parameter via RRC, which configures a set of DMRS ports with a variable OCC length to the user equipment.

[0171] In step 1520, the user equipment receives second information from the base station. The second information is preferably transmitted by the base station via DCI and generally indicates at least one DMRS port that will be used by the base station to transmit the PDSCH to the user equipment and one additional TD-OCC length.

[0172] According to the implementation described with reference to Fig. 13, the second information of step 1520 is represented in the DCI by a single bit field, the value of which is selected by the base station and indicates at least one DMRS port among the set of DMRS ports with a variable OCC length configured for the user equipment in step 1510. The length of the additional TD-OCC is also implicitly indicated to the user equipment: the indicated length is the length of the additional TD-OCC of this at least one DMRS port. For example, a value can be transmitted in the DCI that indicates the DMRS port to the user equipment =1001' (or, what is the same in terms of the port index, =1001: see Fig. 13) from a set of DMRS ports with variable OCC length, with OCC sequence [+1 +1] of additional TD-OCC and, accordingly, length equal to 2

[0173] According to the alternative implementation described with reference to Fig. 14, the second information of step 1520 is represented in the DCI by two bit fields, where the first field indicates at least one DMRS port among the initial set of DMRS ports with a fixed basic length of the TD-OCC, and the second field indicates the value of the parameter n t TD-OCC base length repetitions.

[0174] According to the considered preferred option of the second embodiment in this alternative implementation, said indication of step 1510 is carried out by transmitting by RRC a corresponding parameter that indicates the presence of the second bit field in the DCI, and the value n t , indicated by the second DCI field received by the user equipment in step 1520, is equal to 2. For example, if in the alternative implementation under consideration, the first DCI bit field conveys a value that indicates to the user equipment the DMRS port =1001 of the original set (see the top of Fig. 13), and the second field indicates the value of n t equal to 2, then the user equipment is assigned a DMRS port as a result =1001 with the OCC sequence [+1] of base length 1 and, accordingly, the length of the additional TD-OCC is indicated, defined as the product of the base length by n t , i.e. the length of the additional TD-OCC is equal to 2.

[0175] In step 1530, the user equipment receives from the base station a DMRS corresponding to each of at least one DMRS port indicated by the second information received in step 1520. In step 1540, the user equipment processes the received DMRS based on the length of the additional TD-OCC indicated by the second information. The processing in step 1540 includes, in particular, demodulating the DMRS with possible averaging in the time domain over two OFDM symbols of the FL DMRS and the AD DMRS, when the length of the additional TD-OCC indicated to the user equipment in step 1520 is equal to 2.

[0176] Unlike the 5G NR scenario illustrated previously with reference to Fig. 9a, 9b, the approach to ensuring forward compatibility for the reference signal according to the second embodiment of the present invention, described with reference to Fig. 13-15, allows, in the case of transmitting FL DMRS and AD DMRS in a slot, to group legacy and non-legacy user equipment in MU-MIMO mode.

[0177] Although the mentioned approach was illustrated above (see, in particular, Fig. 14) for the case of using one OFDM symbol for FL DMRS and for AD DMRS, it should be understood that it is, in general, also applicable for a correspondingly larger number of OFDM symbols.

[0178] The approach according to the second aspect of the present invention provides forward compatibility for processing DMRS for PDCCH at the user equipment, in general, as follows. The user equipment receives information from the base station containing an indication of the length of the OCC used by the base station for the DMRS port of the PDCCH. This information is transmitted by the base station via RRC signaling. As noted earlier, one DMRS port p=2000 is defined for the PDCCH, with an OCC sequence of the form [+1]; that is, in the terminology of the present application, it can be said that the OCC sequence of the basic OCC length equal to 1 is predetermined for the DMRS port of the PDCCH. Then, the user equipment receives the DMRS corresponding to the DMRS port of the PDCCH from the base station, and performs processing of the received DMRS based on the OCC length indicated by the said information.In this case, the specified OCC length is greater than the base OCC length, and the OCC sequence used by the user equipment when processing DMRS is obtained by correspondingly replicating the OCC sequence of the base OCC length. Again, unlike in existing 5G NR releases, when processing DMRS for PDCCH, the user equipment does not assume that the base station does not transmit DMRS with a longer OCC length to other user equipment, as indicated by the aforementioned information.

[0179] The approach according to the other aspect of the present invention is applicable in both the time domain and the frequency domain, and therefore the general term LOSS was used in the above general description thereof.

[0180] Next, with reference to Fig. 16a, one embodiment of this approach as applied to the time domain is illustrated.

[0181] As noted above in the disclosure of Fig. 8a, 8b, if a future release of the Rel-X communication standard requires the introduction of a DMRS port for PDCCH using a TD-OCC with an orthogonal OCC sequence [+1 -1] of length 2 (see Fig. 8b), then grouping of legacy user equipment (e.g., Rel-15 / 18) and non-legacy user equipment when transmitting DMRS for PDCCH in the MU-MIMO mode will not be possible, since the legacy user equipment is not aware of the possibility of the presence of an orthogonal DMRS sequence of length 2 (see Fig. 8a) and, accordingly, may not perform the demodulation procedure with averaging over the OCC length in the time domain.

[0182] In the present embodiment, the base station transmits the parameter n via RRC signaling trepetitions of the TD-OCC basic length, thereby indicating to the user equipment that the TD-OCC length to be assumed by the user equipment when demodulating DMRS for the PDCCH is calculated as the product of the TD-OCC basic length and n t This parameter can be transmitted as part of the RRC PDCCH configuration. For case n t >1 (more specifically, n t =2 in the example under consideration), in this embodiment, it is assumed, similarly to the embodiments of the first aspect of the present invention, that the OCC sequence for TD-OCC is of greater length, determined by n t , is obtained by duplicating the OCC sequence of the base length, which duplication is accordingly illustrated by the bold frame at the bottom of Fig. 16a. In other words, the DMRS sequence does not change with an increase in the TD-OCC length for the user equipment.

[0183] Therefore, if the base station, for example for the MU-MIMO mode, instructs the user equipment via RRC to use the DMRS port of the PDCCH with a longer TD-OCC length (see the bottom of Fig. 16a), then the user equipment will know that the TD-OCC length is 2 and will make the corresponding assumption - in particular, when demodulating DMRS, the user equipment can perform averaging in the time domain over the length of 2. It should be recalled that in the context under consideration, such averaging is not provided for in 5G NR (see the disclosure of Figs. 8a, 8b).

[0184] In the case where, for example, using the MU-MIMO mode is not practical, the base station may, using the semi-static RRC configuration mechanism, configure the base length for the user equipment by specifying n t =1. Thus, when demodulating DMRS for PDCCH, the user equipment may not perform time domain averaging.

[0185] The following is a mathematical expression (7') that generally describes the DMRS sequence for the PDCCH in the context of the one embodiment under consideration:

[0186]

[0187] where - an element of the TD-OCC sequence, while the other members of equation (7') have the same semantic content as the corresponding members of equation (7), as described above.

[0188] Below, with reference to Fig. 16b, another embodiment of the approach according to the second aspect of the present invention, as applied to the frequency domain, is illustrated. The implementation of this embodiment is generally similar to the implementation of the TD-OCC-based embodiment disclosed with reference to Fig. 16a, therefore, similar details are omitted below.

[0189] In another embodiment, the base station transmits the FD-OCC basic length repetition parameter n through RRC signaling, thereby indicating to the user equipment that the FD-OCC length to be assumed by the user equipment when demodulating the DMRS for the PDCCH is calculated as the product of the basic length and n t . For case n t =2 in this embodiment it is assumed that the OCC sequence for FD-OCC is of greater length, determined by n r , is obtained by duplicating the OSS sequence of the base length, which is accordingly illustrated by the bold frame at the bottom of Fig. 16b.

[0190] If the base station instructs the user equipment via RRC to use a DMRS port PDCCH with a longer FD-OCC length, the user equipment will know that the FD-OCC length is 2 and will make an assumption accordingly - in particular, when demodulating DMRS, the user equipment may perform frequency domain averaging over a length of 2.

[0191] Using the RRC configuration mechanism, the base station can configure the basic OCC length for the user equipment by specifying n t =1, and accordingly, when demodulating DMRS for PDCCH, the user equipment will not perform frequency domain averaging.

[0192] The following is a mathematical expression (7'') that generally describes the DMRS sequence for the PDCCH in the context of the other embodiment under consideration:

[0193]

[0194] where - an element of the FD-OCC sequence, while the other members of equation (7'') have the same semantic content as the corresponding members of equation (7).

[0195] Next, with reference to the flowchart of Fig. 17, a description will be given of a method 1700 for processing DMRS for a PDCCH in a legacy user equipment (for example, such as UE 1001-1, 1001-2, 1001-3, in the wireless communication system 1000 of Fig. 10) in accordance with a preferred embodiment of the second aspect of the present invention.

[0196] In step 1710, the user equipment receives information transmitted by RRC from a base station (for example, such as BS 1002-A, 1002-B, 1002-C of the wireless communication system 1000 in Fig. 10), which contains an indication of the length of the OCC used by the base station for the DMRS port of the PDCCH. In the case of using the TD-OCC (see the disclosure of the embodiment of Fig. 16a), this information indicates the value of the parameter n trepetitions of the TD-OCC base length, and the TD-OCC length it specifies is calculated as the product of the base length and n t In the case of using FD-OCC (see the disclosure of the embodiment of Fig. 16b), said information indicates the value of the parameter n t repetitions of the FD-OCC base length, and the FD-OCC length it specifies is calculated as the product of the base length and n t In the preferred embodiment under consideration, n t or n t accordingly, it is indicated by the base station at step 1710 as equal to 2 (see the lower parts of Figs. 16a, 16b).

[0197] In step 1720, the user equipment receives a DMRS for the PDCCH from the base station, and in step 1730, the user equipment performs DMRS processing based on the OCC length indicated by said information received in step 1710. The processing in step 1730 includes, in particular, demodulating the DMRS with possible averaging in the time or frequency domain, respectively, when the indicated OCC length is 2.

[0198] Thus, the approach according to the second aspect of the present invention, described with reference to Fig. 16a, 16b, 17, makes it possible to ensure forward compatibility with respect to legacy user equipment in processing DMRS for PDCCH by indicating to the user equipment the length of the OCC that should be used by the user equipment in processing DMRS, without changing the DMRS sequence itself, which, in turn, makes it possible to group legacy and non-legacy user equipment in MU-MIMO mode when transmitting DMRS PDCCH.

[0199] The present invention generally provides forward compatibility on the user equipment side with respect to future DMRS extensions for both PDSCH and PDCCH, without changing the DMRS sequences themselves for legacy user equipments, which in turn makes it possible to avoid reducing the efficiency of expanding the use of MU-MIMO in a communication system.

[0200] It should also be understood that the illustrated exemplary embodiments are merely preferred, and not the only possible embodiments of the present invention. Rather, the scope of the present invention is defined by the following claims and their equivalents.

Claims

1. A forward-compatible method for processing a demodulation reference signal (DMRS) at a user equipment (UE) in a wireless communication system, comprising the steps of: receiving from a base station (BS) of a wireless communication system first information comprising an indication of the possibility of the base station using more than one orthogonal cover code (OCC) length in DMRS modulation for a physical downlink shared channel (PDSCH); receive from the base station second information indicating: at least one DMRS port that will be used by the base station for transmitting PDSCH to the user equipment, and one length of OCC; and receiving from the base station a DMRS corresponding to each of said at least one DMRS port, and processing the received DMRS based on the OCC length indicated by the second information, wherein, for at least some DMRS ports, OCC sequences corresponding to OCCs having a larger OCC length are obtained by correspondingly replicating OCC sequences corresponding to OCCs having a smaller OCC length.

2. The method according to claim 1, in which the user equipment is configured to avoid, during said DMRS processing, assumptions about the absence of transmission by the base station to other user equipments of DMRS corresponding to other DMRS ports with the OCC length indicated by the second information.

3. The method according to paragraph 1 or 2, in which the first information is transmitted by the base station via radio resource control (RRC) layer signaling; the second information is transmitted by the base station via downlink control information (DCI), wherein the second information is represented by at least one bit field in the DCI, wherein the value of each of the at least one bit field of the DCI is respectively selected by the base station from at least a portion of a corresponding predetermined set of bit values.

4. The method according to claim 3, in which a set of at least a code division multiplexing (CDM) group, a frequency domain OCC (FD-OCC) of a given FD-OCC length, and a time domain OCC (TD-OCC) of a given first TD-OCC length is associated with the DMRS port for the PDSCH.

5. The method according to claim 4, wherein the OCCs are FD-OCCs; wherein a first set of DMRS ports for the PDSCH is predefined in the communication system, and the FD-OCCs associated with the DMRS ports of the first set of DMRS ports have a basic length of the FD-OCCs.

6. The method according to claim 5, wherein in the communication system one or more second sets of DMRS ports for the PDSCH are further predefined, wherein each of the one or more second sets of DMRS ports comprises at least a subset of DMRS ports, with each of which FD-OCCs of different FD-OCC lengths are associated, based on a basic FD-OCC length, wherein the number of CDM groups and the first TD-OCC length in said subsets of the one or more second sets of DMRS ports are respectively the same.

7. The method according to claim 6, in which the DMRS ports of the subset of DMRS ports of each of the N second sets of DMRS ports respectively correspond to the DMRS ports of the first set of DMRS ports and have the same DMRS port indices, where N≥1 is the number of predetermined second sets of DMRS ports, while with a DMRS port from the subset of DMRS ports of the i-th second set of DMRS ports, where i=1, …, N, are associated: FD-OCC of the corresponding DMRS port from the first set of DMRS ports and FD-OCC, the OCC sequence of which is obtained 2i - multiple replication of the OCC sequence FD-OCC of the corresponding DMRS port of the first set of DMRS ports, wherein the same CDM group and the same OCC sequence TD-OCC are associated with the said DMRS port from the subset of DMRS ports and with the said corresponding DMRS port.

8. The method according to claim 7, wherein the first set of DMRS ports uses two CDM groups, two FD-OCCs of a basic FD-OCC length equal to 2, and two TD-OCCs of a first TD-OCC length equal to 1 or 2, wherein N is equal to 1 or 2.

9. The method according to item 7 or 8, in which the first information contains an indication of the set of DMRS ports used from said predetermined one or more second sets of DMRS ports, wherein the second information is represented by one bit field in the DCI, which indicates the at least one DMRS port among the subset of DMRS ports of the used set of DMRS ports, wherein the OCC length indicated by the second information is the FD-OCC length of this at least one DMRS port.

10. The method according to claim 9, wherein for a DMRS port with different FD-OCC length, different values ​​of the DCI bit field are used accordingly.

11. The method according to paragraph 5, in which the second information is represented by two bit fields in the DCI, wherein the first bit field in the DCI indicates said at least one DMRS port among the first set of DMRS ports, and the second bit field in the DCI indicates the value of the parameter f repetitions of the basic length of the FD-OCC, wherein the length of the OCC indicated by the second information is determined as the product of the basic length of the FD-OCC and n f , where n f - a natural number greater than or equal to 1, while The first information contains an indication of the presence of a second bit field in the DCI.

12. The method according to any one of claims 4 to 11, wherein said DMRS processing comprises demodulating the DMRS with frequency domain averaging over the OCC length indicated by the second information.

13. The method according to claim 4, wherein the DMRS is transmitted twice in a time slot, wherein in the time domain the first DMRS is transmitted in at least one OFDM symbol closer to the beginning of the slot, and the second DMRS is transmitted in at least one OFDM symbol closer to the end of the slot, wherein said set associated with the DMRS port further comprises an additional TD-OCC of a given second TD-OCC length, wherein the additional TD-OCC is used between the first DMRS and the second DMRS in the slot.

14. The method according to claim 13, wherein the OCCs are additional TD-OCCs, and wherein a first set of DMRS ports for PDSCH is predefined in the communication system, and wherein the additional TD-OCCs associated with the DMRS ports of the first set of DMRS ports have a basic second TD-OCC length.

15. The method according to claim 14, wherein a second set of DMRS ports for the PDSCH is further predefined in the communication system, wherein additional TD-OCCs of different second TD-OCC lengths are associated with each DMRS port of the second set of DMRS ports, based on the basic second TD-OCC length, wherein the number of CDM groups, the FD-OCC length and the first TD-OCC length in the second set of DMRS ports are the same as in the first set of DMRS ports; wherein the DMRS ports of the second set of DMRS ports respectively correspond to the DMRS ports of the first set of DMRS ports and have the same DMRS port indices, wherein the CDM group, FD-OCC and TD-OCC associated with a DMRS port from the second set of DMRS ports are the same as the CDM group, FD-OCC and TD-OCC associated with the corresponding DMRS port from the first set of DMRS ports.

16. The method according to claim 15, wherein the first set of DMRS ports uses two CDM groups, two FD-OCCs of a basic FD-OCC length equal to 2, and two TD-OCCs of a first TD-OCC length equal to 1 or 2, and the same additional TD-OCC of a basic second TD-OCC length equal to 1 is associated with the DMRS ports of the first set of DMRS ports; wherein the following are associated with the DMRS ports of the second set of DMRS ports: the same additional TD-OCC of the first set of DMRS ports and the same additional TD-OCC of a second TD-OCC length equal to 2, the OCC sequence of which is obtained by duplicating the OCC sequence of the additional TD-OCC of the first set of DMRS ports.

17. The method according to claim 16, in which the first information contains an indication of the use of the second set of DMRS ports, while the second information is represented by one bit field in the DCI that indicates said at least one DMRS port among the second set of DMRS ports, wherein the OCC length indicated by the second information is the second TD-OCC length of this at least one DMRS port.

18. The method according to claim 17, wherein for a DMRS port with a different second TD-OCC length, different values ​​of the DCI bit field are used respectively.

19. The method according to claim 14, in which the second information is represented by two bit fields in the DCI, wherein the first bit field in the DCI indicates said at least one DMRS port among the first set of DMRS ports, and the second bit field in the DCI indicates the value of the parameter t repetitions of the basic length of TD-OCC, wherein the length of OCC indicated by the second information is determined as the product of the basic second length of TD-OCC by n t , where n t - a natural number greater than or equal to 1, while The first information contains an indication of the presence of a second bit field in the DCI.

20. The method according to any one of claims 13-19, wherein said DMRS processing comprises demodulating the DMRS with time-domain averaging over said OFDM symbols of the first DMRS and the second DMRS.

21. A forward-compatible method for processing a demodulation reference signal (DMRS) at a user equipment (UE) in a wireless communication system, comprising the steps of: receiving from a base station (BS) of a wireless communication system information containing an indication of the length of an orthogonal covering code (OCC) used by the base station for a DMRS port of a physical downlink control channel (PDCCH); receive from the base station a DMRS corresponding to the DMRS port of the PDCCH, and process the received DMRS based on the OCC length indicated by the said information, wherein in the communication system for the DMRS port of the PDCCH, an OCC is pre-set with an OCC sequence of the OCC base length, wherein the OCC length indicated by said information is greater than the OCC base length, wherein the OCC sequence used by the user equipment in said DMRS processing is obtained by correspondingly replicating the OCC sequence of the OCC base length.

22. The method according to claim 21, wherein the user equipment is configured to avoid, during said DMRS processing, assumptions about the absence of transmission of the base station to other DMRS user equipment corresponding to the DMRS port with the OCC length indicated by said information.

23. The method according to claim 21 or 22, wherein said information is transmitted by the base station via RRC signaling.

24. The method according to claim 23, wherein the OCC is a TD-OCC, and the base length of the OCC is the base length of the TD-OCC; and wherein said information indicates the value of the parameter n t repetitions of the basic length of TD-OCC, wherein the length of OCC indicated by said information is determined as the product of the basic length of TD-OCC and n t , where n t - a natural number greater than or equal to 1.

25. The method according to claim 24, wherein the base length of the TD-OCC is equal to 1.n t =2.

26. The method according to claim 24 or 25, wherein said DMRS processing comprises demodulating the DMRS with time-domain averaging over the OCC length indicated by said information.

27. The method of claim 23, wherein the OCC is an FD-OCC, wherein the base length of the OCC is the base length of the FD-OCC; wherein said information indicates the value of the parameter n frepetitions of the basic length of the FD-OCC, wherein the length of the OCC indicated by said information is determined as the product of the basic length of the FD-OCC by n f , where n f - a natural number greater than or equal to 1.

28. The method according to claim 27, wherein the base length of the FD-OCC is 1.n f =2.

29. The method according to claim 27 or 28, wherein said DMRS processing comprises demodulating the DMRS with averaging in the frequency domain over the OCC length indicated by said information.

30. User equipment (UE) in a wireless communication system, comprising at least: transmitting and receiving devices, data processing devices and data storage devices, wherein the data storage devices contain stored machine-executable codes which, when executed by the data processing devices, ensure the implementation of the method according to any one of paragraphs 1-29.

31. A machine-readable storage medium on which machine-executable codes are stored which, when executed by at least one data processing device of a user equipment (UE), instruct the user equipment to perform the method according to any one of paragraphs 1-29.

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