SRS资源映射

SRS（Sounding Reference Signal）是一种关键的上行链路信号，用于无线资源管理、质量测量和调度，以确保5G网络的高性能和高效率运行。它允许基站了解终端设备的信道状况，从而更好地满足不同应用和服务的需求。
  1. 上行链路质量测量：SRS信道主要用于终端设备（如手机）向基站报告上行链路的质量。终端设备周期性地发送SRS信号，基站通过分析这些信号可以了解信道的状况，包括信号功率、多径衰落情况等。
  2. 频域位置：SRS信道在频域上占用一定的带宽，通常与用户数据信号不同。这有助于基站区分SRS信号和用户数据信号，并有效地进行资源分配和调度。
  3. 调度和资源分配：基站可以根据SRS信号的信息来决定如何最优地分配资源给不同的终端设备。这有助于提高网络的性能和效率。
  4. SRS配置：5G系统允许配置SRS的参数，如周期性发送的时间间隔、频率偏移等，以适应不同的网络和业务需求。
  5. 用于MIMO系统：多输入多输出（MIMO）技术在5G中得到广泛应用，SRS信道也可以用于MIMO系统中，帮助基站确定适当的波束形成和天线选择。

1 载波配置

clear;
clc;
close all;
 
% Carrier configuration
carrier = nrCarrierConfig;
carrier.NCellID = 2; % Cell identity
carrier.SubcarrierSpacing = 30; % Carrier/BWP Subcarrier spacing
carrier.CyclicPrefix = 'normal'; % Cyclic prefix
carrier.NSlot = 0; % Slot counter
carrier.NFrame = 0; % Frame counter
carrier.NStartGrid = 0; % Carrier offset
carrier.NSizeGrid = 273; % Size of carrier in RB

2 SRS资源配置

时域：时域符号数和时域重复
频域：
梳分：梳分数和梳分偏移
码域：CyclicShift
% SRS configuration
srs = nrSRSConfig;
srs.NumSRSPorts = 2; % Number of SRS antenna ports (1/2/4)
srs.NumSRSSymbols = 1; % Number of OFDM symbols (1/2/4)
srs.SymbolStart = 13; % 0-based index of first OFDM symbol (8...13)
srs.KTC = 4; % 梳分数 (2/4)
srs.KBarTC = 0; % 梳分偏移 (0...KTC-1)
srs.CyclicShift = 0; % 梳分循环移位 (KTC=2 0...7; KTC=4 0...11)
srs.FrequencyStart = 0; % Frequency-domain offset (0...271)
srs.NRRC = 0; % Additional circular frequency-domain offset (0...67)
srs.CSRS = 63; % Bandwidth configuration C_SRS (0...63)
srs.BSRS = 1; % Bandwidth configuration B_SRS (0...3)
srs.BHop = 0; % Frequency hopping index (0...3)
srs.Repetition = 1; % Repetition factor of OFDM symbols (Repetition ≤ NumSRSSymbols)
srs.SRSPeriod = 'on'; % 'on' (default) | 'off' | [TSRS Toffset]
srs.ResourceType = 'periodic';
srs.GroupSeqHopping = 'neither';
srs.NSRSID = 0; % SRS scrambling identity
srs.SRSPositioning = false;
 
% 计算SRS子带带宽和数目
srs_band_config = srs.BandwidthConfigurationTable(srs.CSRS+1,:);
N_values = [srs_band_config.N_0, srs_band_config.N_1, srs_band_config.N_2, srs_band_config.N_3];
num_srs_subband = prod(N_values(1:srs.BSRS+1));
info = table([srs.NRB; srs.NRBPerTransmission;num_srs_subband],'RowNames', {'Freq-Hopping bandwidth (RB)','Instantaneous bandwidth (RB)','SRS subband num'},'VariableNames',"info");
disp(info)
info ____ Freq-Hopping bandwidth (RB) 272 Instantaneous bandwidth (RB) 16 SRS subband num 17

3 资源映射

srsSym = nrSRS(carrier,srs);
srsInd = nrSRSIndices(carrier,srs);
 
carrierGrid = nrResourceGrid(carrier,srs.NumSRSPorts);
carrierGrid(srsInd) = srsSym;
 
slot_duration = num_srs_subband;
hSRSGrid(carrier,srs,slot_duration,true);
title('SRS Resource Grid');
hSRSAnnotations(carrier,srs);

4 附录

（1）SRS资源信元

SRS-Resource ::= SEQUENCE {
srs-ResourceId SRS-ResourceId,
nrofSRS-Ports ENUMERATED {port1, ports2, ports4},
ptrs-PortIndex ENUMERATED {n0, n1 } OPTIONAL, -- Need R
transmissionComb CHOICE {
n2 SEQUENCE {
combOffset-n2 INTEGER (0..1),
cyclicShift-n2 INTEGER (0..7)
},
n4 SEQUENCE {
combOffset-n4 INTEGER (0..3),
cyclicShift-n4 INTEGER (0..11)
}
},
resourceMapping SEQUENCE {
startPosition INTEGER (0..5),
nrofSymbols ENUMERATED {n1, n2, n4},
repetitionFactor ENUMERATED {n1, n2, n4}
},
freqDomainPosition INTEGER (0..67),
freqDomainShift INTEGER (0..268),
freqHopping SEQUENCE {
c-SRS INTEGER (0..63),
b-SRS INTEGER (0..3),
b-hop INTEGER (0..3)
},
groupOrSequenceHopping ENUMERATED { neither, groupHopping, sequenceHopping },
resourceType CHOICE {
aperiodic SEQUENCE {
...
},
semi-persistent SEQUENCE {
periodicityAndOffset-sp SRS-PeriodicityAndOffset,
...
},
periodic SEQUENCE {
periodicityAndOffset-p SRS-PeriodicityAndOffset,
...
}
},
sequenceId INTEGER (0..1023),
spatialRelationInfo SRS-SpatialRelationInfo OPTIONAL, -- Need R
...,
[[
resourceMapping-r16 SEQUENCE {
startPosition-r16 INTEGER (0..13),
nrofSymbols-r16 ENUMERATED {n1, n2, n4},
repetitionFactor-r16 ENUMERATED {n1, n2, n4}
} OPTIONAL -- Need R
]]
}

（2）SRS bandwidth configuration（38211 Table 6.4.1.4.3-1:）

BSRS = 0 BSRS = 1 BSRS = 2 BSRS = 3
C_SRS m_SRS_0 N_0 m_SRS_1 N_1 m_SRS_2 N_2 m_SRS_3 N_3
_____ _______ ___ _______ ___ _______ ___ _______ ___
 
0 4 1 4 1 4 1 4 1
1 8 1 4 2 4 1 4 1
2 12 1 4 3 4 1 4 1
3 16 1 4 4 4 1 4 1
4 16 1 8 2 4 2 4 1
5 20 1 4 5 4 1 4 1
6 24 1 4 6 4 1 4 1
7 24 1 12 2 4 3 4 1
8 28 1 4 7 4 1 4 1
9 32 1 16 2 8 2 4 2
10 36 1 12 3 4 3 4 1
11 40 1 20 2 4 5 4 1
12 48 1 16 3 8 2 4 2
13 48 1 24 2 12 2 4 3
14 52 1 4 13 4 1 4 1
15 56 1 28 2 4 7 4 1
16 60 1 20 3 4 5 4 1
17 64 1 32 2 16 2 4 4
18 72 1 24 3 12 2 4 3
19 72 1 36 2 12 3 4 3
20 76 1 4 19 4 1 4 1
21 80 1 40 2 20 2 4 5
22 88 1 44 2 4 11 4 1
23 96 1 32 3 16 2 4 4
24 96 1 48 2 24 2 4 6
25 104 1 52 2 4 13 4 1
26 112 1 56 2 28 2 4 7
27 120 1 60 2 20 3 4 5
28 120 1 40 3 8 5 4 2
29 120 1 24 5 12 2 4 3
30 128 1 64 2 32 2 4 8
31 128 1 64 2 16 4 4 4
32 128 1 16 8 8 2 4 2
33 132 1 44 3 4 11 4 1
34 136 1 68 2 4 17 4 1
35 144 1 72 2 36 2 4 9
36 144 1 48 3 24 2 12 2
37 144 1 48 3 16 3 4 4
38 144 1 16 9 8 2 4 2
39 152 1 76 2 4 19 4 1
40 160 1 80 2 40 2 4 10
41 160 1 80 2 20 4 4 5
42 160 1 32 5 16 2 4 4
43 168 1 84 2 28 3 4 7
44 176 1 88 2 44 2 4 11
45 184 1 92 2 4 23 4 1
46 192 1 96 2 48 2 4 12
47 192 1 96 2 24 4 4 6
48 192 1 64 3 16 4 4 4
49 192 1 24 8 8 3 4 2
50 208 1 104 2 52 2 4 13
51 216 1 108 2 36 3 4 9
52 224 1 112 2 56 2 4 14
53 240 1 120 2 60 2 4 15
54 240 1 80 3 20 4 4 5
55 240 1 48 5 16 3 8 2
56 240 1 24 10 12 2 4 3
57 256 1 128 2 64 2 4 16
58 256 1 128 2 32 4 4 8
59 256 1 16 16 8 2 4 2
60 264 1 132 2 44 3 4 11
61 272 1 136 2 68 2 4 17
62 272 1 68 4 4 17 4 1
63 272 1 16 17 8 2 4 2
function [csrs,bsrs] = hSRSBandwidthConfiguration(srs, NRB)
% [CSRS,BSRS] = hBandwidthConfiguration(SRS, NRB) returns the SRS
% bandwidth configuration parameters CSRS and BSRS required to transmit an
% SRS in a bandwidth specified by NRB. The function calculates CSRS and
% BSRS considering the SRS properties FrequencyStart and NRRC, so the
% available bandwidth NRB is reduced by the frequency origin of the SRS.
% For frequency hopping cases, the value of BSRS returned is equal to that
% of the BSRS property in the input SRS configuration object.
 
f0 = hSRSFrequencyOrigin(srs);
NRB = NRB - f0;
if NRB < 4
error('The available bandwidth is not sufficient to allocate an SRS transmission. Increase the carrier bandwidth or configure the SRS in a lower frequency.' )
end
% For frequency hopping configurations
if srs.BHop >= srs.BSRS && nargout == 2 % No frequency hopping and BSRS is requested
BSRS = 0:3;
else
BSRS = 0;
end
% Initialize gap between SRS frequency allocation and carrier bandwidth
NRBGap = NRB;
% Find the appropriate CSRS for each BSRS that minimizes the gap only
% in non-hopping cases. For freq. hopping, find the value of CSRS only.
for b = BSRS
% NRB allocated to the SRS for BSRS = b and all CSRS
srsNRBb = srs.BandwidthConfigurationTable{:,2*(b+1)};
mSRSbMax = max( srsNRBb( srsNRBb <= NRB ));
% Calculate gap between SRS allocation and carrier bandwidth
gap = NRB - mSRSbMax;
if gap < NRBGap
csrs = srs.BandwidthConfigurationTable{ srsNRBb == mSRSbMax ,1};
bsrs = b;
NRBGap = gap;
end
end
csrs = csrs(1);
if srs.BHop < bsrs
bsrs = srs.BSRS;
end
end
 
function out = hSRSNumberOfSubbandsOrHoppingPatterns(srs)
% N = hSRSNumberOfSubbandsOrHoppingPatterns(SRS) returns the number of
% unique SRS subbands or frequency-hopping patterns N configurable by the
% SRS property NRRC. An SRS subband is the frequency band allocated for SRS
% in a given OFDM symbol (See SRS property NRBPerTransmission). N is
% calculated using TS 38.211 Table 6.4.1.4.3-1 for the bandwidth
% configuration parameters CSRS, BSRS, and BHop specified in the SRS
% configuration object SRS.
 
bwct = nrSRSConfig.BandwidthConfigurationTable{:,:};
if srs.BHop < srs.BSRS % Number of unique frequency-hopping patterns
b0 = srs.BHop+1;
else % Number of unique SRS subbands
b0 = 0;
end
out = prod(bwct(srs.CSRS+1,2*(b0:srs.BSRS)+3));
end
 
function [Grid,dispGrid] = hSRSGrid(carrier,srs,Duration,displayGrid,chplevels)
% [GRID,DISPGRID] = hSRSGrid(CARRIER,SRS,DURATION,DISPLAYGRID,CHPLEVELS)
% returns a multi-slot OFDM resource grid GRID containing a set of sounding
% reference signals in a carrier, as specified by the configuration objects
% CARRIER and SRS. This function also returns a scaled version of the grid
% used for display purposes. The optional input DURATION (Default 1)
% specifies the number of slots of the generated grid. The resource grid
% can be displayed using the optional input DISPLAYGRID (Default false).
% CHPLEVELS specifies the channel power levels for display purposes only
% and it must be of the same size as SRS.
 
numSRS = length(srs);
if nargin < 5
chplevels = 1:-1/numSRS:1/numSRS;
if nargin < 4
displayGrid = false;
if nargin < 3
Duration = 1;
end
end
end
SymbolsPerSlot = carrier.SymbolsPerSlot;
emptySlotGrid = nrResourceGrid(carrier,max([srs(:).NumSRSPorts])); % Initialize slot grid
% Create the SRS symbols and indices and populate the grid with the SRS symbols
Grid = repmat(emptySlotGrid,1,Duration);
dispGrid = repmat(emptySlotGrid,1,Duration); % Frame-size grid for display
for ns = 0:Duration-1
slotGrid = emptySlotGrid;
dispSlotGrid = emptySlotGrid; % Slot-size grid for display
for ich = 1:numSRS
srsIndices = nrSRSIndices(carrier,srs(ich));
srsSymbols = nrSRS(carrier,srs(ich));
slotGrid(srsIndices) = srsSymbols;
dispSlotGrid(srsIndices) = chplevels(ich)*srsSymbols; % Scale the SRS for display only
end
OFDMSymIdx = ns*SymbolsPerSlot + (1:SymbolsPerSlot);
Grid(:,OFDMSymIdx,:) = slotGrid;
dispGrid(:,OFDMSymIdx,:) = dispSlotGrid;
carrier.NSlot = carrier.NSlot+1;
end
if displayGrid
plotGrid(dispGrid(:,:,1),chplevels,"SRS " + (1:numSRS)');
end
end
function varargout = plotGrid(Grid,chplevels,leg)
% plotGrid(GRID, CHPLEVEL,LEG) displays a resource grid GRID containing
% channels or signals at different power levels CHPLEVEL and create a
% legend for these using a cell array of character vector LEG
 
if nargin < 3
leg = {'SRS'};
if nargin < 2
chplevels = 1;
end
end
cmap = colormap(gcf);
chpscale = length(cmap); % Scaling factor
h = figure;
image(0:size(Grid,2)-1,(0:size(Grid,1)-1)/12,chpscale*abs(Grid(:,:,1))); % Multiplied with scaling factor for better visualization
axis xy;
title('Carrier Grid Containing SRS')
xlabel('OFDM Symbol'); ylabel('RB');
clevels = chpscale*chplevels(:);
N = length(clevels);
L = line(ones(N),ones(N),'LineWidth',8); % Generate lines
% Index the color map and associate the selected colors with the lines
set(L,{'color'},mat2cell(cmap( min(1+fix(clevels),length(cmap) ),:),ones(1,N),3)); % Set the colors according to cmap
% Create legend
legend(leg(:));
if nargout > 0
varargout = {h};
end
end
 
function hSRSAnnotations(carrier,srs)
% hSRSAnnotations(carrier,srs) adds annotation to the current figure
% indicating the frequency origin of the SRS and the number of RB used per
% OFDM symbol for the configuration objects CARRIER and SRS.
 
% Calculate the frequency origin of the first SRS symbol
f0 = hSRSFrequencyOrigin(srs);
hold on;
hfig = gcf;
set(hfig,'Units','Normalized');
Sym0 = srs.SymbolStart-0.5;
if isnumeric(srs.SRSPeriod)
Sym0 = srs.SRSPeriod(2)*carrier.SymbolsPerSlot + srs.SymbolStart-0.5;
end
IP = get(gca,'Position');
% Y-coordinate in the current axes of the SRS freq position f0
Yf0 = f0/carrier.NSizeGrid*IP(4)+IP(2);
Xc = Sym0/((carrier.NSlot+1)*carrier.SymbolsPerSlot)*IP(3)+IP(1);
% Add annotation to the figure including f0 in RB
if f0/carrier.NSizeGrid > 0.08 % Only plot f0 when there is enough space in the y-axis
% Create doublearrow for F0
YMin = IP(2);
annotation(hfig,'doublearrow',Xc*[1 1], [YMin Yf0],...
'Color',[1 0.4 0.15]);
% Text for F0
str = sprintf('$$F_0 = %d $$ RB', f0);
Ystr = f0/carrier.NSizeGrid/2;
text(gca,(Xc-IP(1))/IP(3)-0.25, Ystr,str,...
'Color',[1 0.4 0.15],'FontSize',14, ...
'Units','Normalized','Interpreter','latex');
end
% Create doublearrow from f0 and spanning the SRS bandwidth
Yf1 = Yf0 + srs.NRBPerTransmission/carrier.NSizeGrid*IP(4);
annotation(hfig,'doublearrow',Xc*[1 1], [Yf0 Yf1],...
'Color',[1 0.4 0.15]);
% Text for NRBt
str = sprintf('$$\\textrm{NRB}_T = %d $$ RB', srs.NRBPerTransmission);
Ystr = (f0 + 0.5*srs.NRBPerTransmission)/carrier.NSizeGrid;
text(gca,(Xc-IP(1))/IP(3)-0.32, Ystr ,str,...
'Color',[1 0.4 0.15],'FontSize',14, ...
'Units','Normalized','Interpreter','latex');
end
 
function f0 = hSRSFrequencyOrigin(srs)
% Calculate the frequency origin of the first SRS symbol in a slot
 
NSBTable = hSRSNumberOfSubbandsOrHoppingPatterns(srs);
NRBt = srs.NRBPerTransmission;
% Origin of the SRS in frequency in RB
f0 = srs.FrequencyStart + NRBt*mod(floor(4*srs.NRRC/NRBt),NSBTable);
end
 
function [NRRC,NRB] = hNRRCSet(srs)
% Calculate the values of NRRC that generate a unique set of orthogonal SRS in frequency
if srs.BHop < srs.BSRS % Frequency-hopping cases
NRB = srs(1).NRB; % Hopping bandwidth
else
NRB = nrSRSConfig.BandwidthConfigurationTable{srs(1).CSRS+1,2};
end
% Number of frequency-hopping patterns or SRS subbands depending on the values of BSRS and BHop
N = hSRSNumberOfSubbandsOrHoppingPatterns(srs);
NRRC = NRB/4*(0:N-1)/N;
end