SOUNDING REFERENCE SIGNALS (SRS) IN NEW RADIO (NR) COMMUNICATION SYSTEMS

Abstract

A New Radio (NR) system and a method for transmitting sounding reference signals in a new radio communications system is provided that enables mutual orthogonality to be maintained between SRS resources of different UEs. The system an eNodeB and a plurality of UEs, and the method includes: generating, at a UE, a base sequence based upon a sequence number received from the eNodeB; generating a plurality of blocks from the base sequence by applying cyclic-shifts to the base sequence; and generating a sounding reference signal by concatenating the cyclically shifted blocks. The sounding reference signal is then transmitted to the eNodeB. By using the same Zadoff-Chu base sequence with different cyclic shifts among overlapped UEs, mutual orthogonality of the SRS of each UE is maintained.

Claims

1. A method for transmitting sounding reference signals in a new radio (NR) communications system including an eNodeB and a plurality of UEs, the method including: generating, at a UE, a base sequence based upon a sequence number received from the eNodeB; generating a plurality of blocks from the base sequence by applying cyclic-shifts to the base sequence on a plurality of subcarrier groups; generating a sounding reference signal by concatenating the cyclically shifted blocks; and transmitting the sounding reference signal to the eNodeB; wherein the plurality of blocks comprises 48 orthogonal blocks, and each of the plurality of blocks is 4 Physical Resource Blocks (PRBs) long.

2. The method of claim 1, wherein the base sequence r.sub.u ,v is determined according to:
r.sub.u,v(n)=x.sub.q(nmodN.sub.ZC.sup.RS), 0n<M.sub.SC.sup.RS, where the q.sup.th root Zadoff-Chu sequence is defined by $x_q\left(m\right)=e^{-j.Math.\frac{.Math..Math.\mathrm{qm}\left(m+1\right)}{N_{\mathrm{ZC}}^{\mathrm{RS}}}},0m{N}_{\mathrm{ZC}}^{\mathrm{RS}}-1,$ with q given by
q=q++v.Math.(1).sup.2q
q=N.sub.ZC.sup.RS.Math.(u+1)/31 where the length N.sub.ZC.sup.RS of the Zadoff-Chu sequence is given by the largest prime number such that N.sub.ZC.sup.RS<M.sub.SC.sup.RS.

3. The method of claim 1, wherein the cyclically-shifted base sequence r.sub.u,v.sup.({tilde over (p)}) (n) is determined according to:
r.sub.u,v.sup.({tilde over (p)})(n)=e.sup.j{tilde over (p)}nr.sub.u,v(n), 0n<M.sub.SC.sup.RS, where .sub.{tilde over (p)} is the cyclic shift, and wherein the cyclic shift o is determined according to: ${}_{\tilde{p}}=2.Math..Math.\frac{n_{\mathrm{SRS}}^{\mathrm{cs},\tilde{p}}}{n_{\mathrm{SRS}}^{\mathrm{cs},\max }}$ $n_{\mathrm{SRS}}^{\mathrm{cs},\tilde{p}}=\left(n_{\mathrm{SRS}}^{\mathrm{cs}}+\frac{n_{\mathrm{SRS}}^{\mathrm{cs},\max }.Math.\tilde{p}}{N_{\mathrm{ap}}}\right).Math.\mathrm{mod}.Math..Math.n_{\mathrm{SRS}}^{\mathrm{cs},\max },.Math.\tilde{p}\left\{0,1,\mathrm{.Math.}.Math.,N_{\mathrm{ap}}-1\right\}$ where n.sub.SRS.sup.cs {0, 1, . . . , n.sub.SRS.sup.cs,max} and N.sub.ap is the number of antenna ports used for sounding reference signal transmission.

4. The method of claim 1, wherein the sounding reference signal is transmitted such that blocks thereof are aligned with blocks of sounding reference signals of other UEs.

5. The method of claim 1, wherein the cyclic shift used by each UE at each block is signalled by the eNodeB to the UEs.

6. The method of claim 1, wherein different cyclic shifts are used by different UEs in corresponding blocks.

7. The method of claim 1, wherein the same base sequence is used by the UEs in corresponding blocks.

8. The method of claim 1, wherein the eNodeB is configured to schedule SRS resources at each of the UEs such that mutual orthogonality is maintained between the SRS resources of the different UEs.

9. A new radio communications system including an eNodeB and a plurality of UEs, wherein each UE is configured to: generate, a base sequence based upon a sequence number received from the eNodeB; generate a plurality of blocks from the base sequence by applying cyclic-shifts to the base sequence; generate a sounding reference signal by concatenating the cyclically shifted blocks; and transmit to the sounding reference signal to the eNodeB.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] Various embodiments of the invention will be described with reference to the following drawings.

[0035] FIG. 1 illustrates a MU-MIMO system, according to an embodiment of the present invention.

[0036] FIG. 2 illustrates a method of generating an Sounding Reference Signal (SRS) sequence at a UE, for transmission to the eNodeB 105, according to an embodiment of the present invention.

[0037] FIG. 3 illustrates an exemplary SRS sequence transmission diagram 300, according to an embodiment of the present invention.

[0038] Preferred features, embodiments and variations of the invention may be discerned from the following Description of Embodiments which provides sufficient information for those skilled in the art to perform the invention. The Description of Embodiments is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way.

DESCRIPTION OF EMBODIMENTS

[0039] FIG. 1 illustrates a MU-MIMO system 100, according to an embodiment of the present invention. The MU-MIMO system 100 includes an eNodeB 105 including a plurality of antennas 110. The eNodeB 105 is configured to communicate with a plurality of different UEs 120, each equipped with multiple antennas 125.

[0040] As outlined in further detail below, the UEs 120 transmit sounding reference signals (SRS) to the eNodeB 105 to enable the eNodeB 105 to estimate the UL channel quality. In short, the SRS comprise sequences known to the eNodeB 105, transmitted from the UEs 120 in the UL direction, enabling the eNodeB 105 to estimate UL channel quality based upon reception thereof.

[0041] The eNodeB 105 schedules SRS resources, and can schedule SRS resources to multiple UEs 120 such that the resources comprise fully and/or partially overlapping in SRS time-frequency resource elements (REs). The SRS are Zadoff Chu (ZC) based, and multiple SRS resources can share the same root sequence values in the overlapping REs, which allows for low or zero mutual cross-correlation.

[0042] FIG. 2 illustrates a method 200 of generating an SRS sequence at a UE 120, for transmission to the eNodeB 105, according to an embodiment of the present invention.

[0043] Initially, and at step 205, a base sequence r.sub.u,v is generated based upon a base sequence number u {0,1, . . . ,29} received from the eNodeB 105.

[0044] In particular, the base sequence r.sub.u,v(0), . . . , r.sub.u,v (M.sub.SC.sup.RS1) is given by

r.sub.u,v(n)=x.sub.q(nmodN.sub.ZC.sup.RS), 0n<M.sub.SC.sup.RS

where the q.sup.th root ZC sequence is defined by

[00003]$x_q\left(m\right)=e^{-j.Math.\frac{.Math..Math.\mathrm{qm}\left(m+1\right)}{N_{\mathrm{ZC}}^{\mathrm{RS}}}},0m{N}_{\mathrm{ZC}}^{\mathrm{RS}}-1$

with q given by

q=q++v.Math.(1).sup.2q

q=N.sub.ZC.sup.RS.Math.(u+1)/31

[0045] Here M.sub.sc.sup.RS=4N.sub.sc.sup.RB=48, N.sub.ZC.sup.RS=47 and v=0 (due to M.sub.sc.sup.RS<6N.sub.sc.sup.RB).

[0046] At step 210, a plurality of blocks are generated from the base sequence. In particular, cyclic-shifts n.sub.SRS.sup.cs {0,1, . . . ,n.sub.SRS.sup.cs,max} which are received from the eNodeB 105, are applied to the base sequence r.sub.u,v as follows:

[0047] The cyclic shift sequence r.sub.u,v.sup.({tilde over (p)})(n) is defined by a cyclic shift .sub.{tilde over (p)} of a base sequence r.sub.u,v (n) according to:

r.sub.u,v.sup.({tilde over (p)})(n)=e.sup.j{tilde over (p)}nr.sub.u,v(n), 0n<M.sub.sc.sup.RS

[0048] The cyclic shift .sub.{tilde over (p)} of the sounding reference signal is given as:

[00004]${}_{\tilde{p}}=2.Math..Math.\frac{n_{\mathrm{SRS}}^{\mathrm{cs},\tilde{p}}}{n_{\mathrm{SRS}}^{\mathrm{cs},\max }}$$n_{\mathrm{SRS}}^{\mathrm{cs},\tilde{p}}=\left(n_{\mathrm{SRS}}^{\mathrm{cs}}+\frac{n_{\mathrm{SRS}}^{\mathrm{cs},\max }.Math.\tilde{p}}{N_{\mathrm{ap}}}\right).Math.\mathrm{mod}.Math..Math.n_{\mathrm{SRS}}^{\mathrm{cs},\max },.Math.\tilde{p}\left\{0,1,\mathrm{.Math.}.Math.,N_{\mathrm{ap}}-1\right\}$

where n.sub.SRS.sup.cs{0,1, . . . , n.sub.SRS.sup.cs,max} and N.sub.ap is the number of antenna ports used for sounding reference signal transmission.

[0049] For n.sub.SRS.sup.CS,max=48, there are up to 48 orthogonal blocks.

[0050] At step 215, the SRS sequence is constructed by concatenation of the cyclically shifted blocks. In particular, the blocks are concatenated according to an instruction received from the eNodeB 105.

[0051] Advantageously, the method has Cubic Metric (CM), peak-to-power average ratio (PAPR), and cross-correlation properties, amongst overlapping SRS resources that are similar to in LTE.

[0052] FIG. 3 illustrates an exemplary SRS sequence transmission diagram 300, according to an embodiment of the present invention.

[0053] The sequence transmission diagram illustrates transmission from four UEs 305 (UE1, UE2, UE3, UE4), each of which transmits an SRS sequence 310 comprising a plurality of cyclically shifted blocks 315 which are concatenated.

[0054] Each of the blocks 315 are aligned in the frequency domain, and each block 315 is orthogonal to the blocks 315 of the other UEs 305 at that frequency band.

[0055] The base sequence and the cyclic shift used by each UE at each block is signalled by the eNodeB 105 to the UEs 120. As such, the eNodeB 105 is able to ensure, through appropriate scheduling of SRS resources, that mutual orthogonality is maintained between the SRS resources of the different UEs. This is possible, as the same base sequence may be used by all UEs in a particular frequency band, but with a different cyclic shift.

[0056] Advantageously, the methods and systems described above enable mutual orthogonality to be maintained between SRS resources of the different UEs, which in turn enables more accurate uplink channel quality estimation. Furthermore, the method is aligned with existing LTE-based methods.

[0057] In the present specification and claims (if any), the word comprising and its derivatives including comprises and comprise include each of the stated integers but does not exclude the inclusion of one or more further integers.

[0058] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases in one embodiment or in an embodiment in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[0059] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

[0060] This application is based upon and claims the benefit of priority from Australian provisional patent application No. 2017902832, filed on Jul. 19, 2017, the disclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

[0061] 100 MU-MIMO system [0062] 105 eNodeB [0063] 110, 125 antennas [0064] 120 UE