This example measures the Acknowledgment (ACK) missed detection probability using the LTE Toolbox™ under the single user Physical Uplink Control Channel (PUCCH1a) conformance test conditions as defined in TS 36.104 Section 220.127.116.11 [ 1 ].
This example uses a simulation length of 10 subframes. This value has been chosen to speed up the simulation. A higher value should be chosen to obtain more accurate results. The probability of erroneous ACK detection is calculated for a number of SNR point. The target defined in TS36.104 Section 18.104.22.168 [ 1 ] for 1.4 MHz bandwidth (6 RBs) and a single transmit antenna is an ACK missed detection probability not exceeding 1% at an SNR of -4.2 dB. The test is defined for 1 transmit antenna.
NSubframes = 10; % Number of subframes SNRIn = [-10.2 -8.2 -6.2 -4.2 -2.2]; % SNR range in dB NTxAnts = 1; % Number of transmit antennas
ue = struct; % UE config structure ue.NULRB = 6; % 6 resource blocks (1.4 MHz) ue.CyclicPrefixUL = 'Extended'; % Extended cyclic prefix ue.Hopping = 'Off'; % No frequency hopping ue.NCellID = 9; ue.Shortened = 0; % No SRS transmission ue.NTxAnts = NTxAnts;
% Hybrid ARQ indicator bit set to one. Only one bit is required for PUCCH % 1a ACK = 1; pucch = struct; % PUCCH config structure % Set the size of resources allocated to PUCCH format 2. This affects the % location of PUCCH 1 transmission pucch.ResourceSize = 0; pucch.DeltaShift = 1; % Delta shift PUCCH parameter % Number of cyclic shifts used for PUCCH format 1 in resource blocks with a % mixture of formats 1 and 2. This is the N1cs parameter pucch.CyclicShifts = 0; % Vector of PUCCH resource indices, one per transmission antenna. This is % the n2pucch parameter pucch.ResourceIdx = 0:ue.NTxAnts-1;
Configure the channel model with the parameters specified in the tests described in TS36.104 Section 22.214.171.124 [ 1 ].
channel = struct; % Channel config structure channel.NRxAnts = 2; % Number of receive antennas channel.DelayProfile = 'ETU'; % Channel delay profile channel.DopplerFreq = 70.0; % Doppler frequency in Hz channel.MIMOCorrelation = 'Low'; % Low MIMO correlation channel.NTerms = 16; % Oscillators used in fading model channel.ModelType = 'GMEDS'; % Rayleigh fading model type channel.Seed = 13; % Channel seed channel.InitPhase = 'Random'; % Random initial phases channel.NormalizePathGains = 'On'; % Normalize delay profile power channel.NormalizeTxAnts = 'On'; % Normalize for transmit antennas % SC-FDMA modulation information: required to get the sampling rate scfdmaInfo = lteSCFDMAInfo(ue); channel.SamplingRate = scfdmaInfo.SamplingRate; % Channel sampling rate
The channel estimator is configured using a structure
cec. Here cubic interpolation will be used with an averaging window of 12-by-1 Resource Elements (REs). This configures the channel estimator to use a special mode which ensures the ability to despread and orthogonalize the different overlapping PUCCH transmissions.
cec = struct; % Channel estimation config structure cec.PilotAverage = 'UserDefined'; % Type of pilot averaging cec.FreqWindow = 12; % Frequency averaging window in REs (special mode) cec.TimeWindow = 1; % Time averaging window in REs (Special mode) cec.InterpType = 'cubic'; % Cubic interpolation
For each SNR point the loop below calculates the probability of successful ACK detection using information obtained from
NSubframes consecutive subframes. The following operations are performed for each subframe and SNR values:
Create an empty resource grid
Generate and map PUCCH 1 and its Demodulation Reference Signal (DRS) to the resource grid
Apply SC-FDMA modulation
Send the modulated signal through the channel
Minimum Mean Squared Error (MMSE) equalization
PUCCH 1 demodulation/decoding
Measure missing or incorrect Hybrid Automatic Repeat Request (HARQ)-ACK
% Preallocate memory for probability of detection vector PMISS = zeros(size(SNRIn)); for nSNR = 1:length(SNRIn) % Missed or incorrect ACK detection counter missCount = 0; % Noise configuration SNR = 10^(SNRIn(nSNR)/20); % Convert dB to linear % The noise added before SC-FDMA demodulation will be amplified by the % IFFT. The amplification is the square root of the size of the IFFT. % To achieve the desired SNR after demodulation the noise power is % normalized by this value. In addition, because real and imaginary % parts of the noise are created separately before being combined into % complex additive white Gaussian noise, the noise amplitude must be % scaled by 1/sqrt(2*ue.NTxAnts) so the generated noise power is 1 N = 1/(SNR*sqrt(double(scfdmaInfo.Nfft)))/sqrt(2.0*ue.NTxAnts); % Set the type of random number generator and its seed to the default % value rng('default') % Loop for subframes offsetused = 0; for nsf = 1:NSubframes % Create resource grid ue.NSubframe = mod(nsf-1,10); reGrid = lteULResourceGrid(ue); % Create PUCCH 1 and its DRS pucch1Sym = ltePUCCH1(ue,pucch,ACK); pucch1DRSSym = ltePUCCH1DRS(ue,pucch); % Generate indices for PUCCH 1 and its DRS pucch1Indices = ltePUCCH1Indices(ue,pucch); pucch1DRSIndices = ltePUCCH1DRSIndices(ue,pucch); % Map PUCCH 1 and PUCCH 1 DRS to the resource grid reGrid(pucch1Indices) = pucch1Sym; reGrid(pucch1DRSIndices) = pucch1DRSSym; % SC-FDMA modulation txwave = lteSCFDMAModulate(ue,reGrid); % Channel state information: set the init time to the correct value % to guarantee continuity of the fading waveform channel.InitTime = (nsf-1)/1000; % Channel modeling % The additional 25 samples added to the end of the waveform are to % cover the range of delays expected from the channel modeling (a % combination of implementation delay and channel delay spread) rxwave = lteFadingChannel(channel,[txwave; zeros(25,ue.NTxAnts)]); % Add noise at receiver noise = N * complex(randn(size(rxwave)),randn(size(rxwave))); rxwave = rxwave + noise; % Receiver % Synchronization % An offset within the range of delays expected from the channel % modeling (a combination of implementation delay and channel % delay spread) indicates success offset = lteULFrameOffsetPUCCH1(ue,pucch,rxwave); if (offset < 25) offsetused = offset; end % SC-FDMA demodulation rxgrid = lteSCFDMADemodulate(ue,rxwave(1+offsetused:end,:)); % Channel estimation [H,n0] = lteULChannelEstimatePUCCH1(ue,pucch,cec,rxgrid); % Extract REs corresponding to the PUCCH 1 from the given subframe % across all receive antennas and channel estimates [pucch1Rx,pucch1H] = lteExtractResources(pucch1Indices,rxgrid,H); % MMSE equalization eqgrid = lteULResourceGrid(ue); eqgrid(pucch1Indices) = lteEqualizeMMSE(pucch1Rx,pucch1H,n0); % PUCCH 1 demodulation/decoding rxACK = ltePUCCH1Decode(ue,pucch,length(ACK),eqgrid(pucch1Indices)); % Detect missed (empty rxACK) or incorrect HARQ-ACK (compare % against transmitted ACK if (isempty(rxACK) || any(rxACK ~= ACK)) missCount = missCount + 1; end end PMISS(nSNR) = (missCount/NSubframes); end
The graph shows the simulation result for ACK missed detection test
plot(SNRIn,PMISS,'b-o','LineWidth',2,'MarkerSize',7); hold on; plot(-4.2,0.01,'rx','LineWidth',2,'MarkerSize',7); xlabel('SNR (dB)'); ylabel('Probability of missed ACK detection'); title('ACK missed detection test (TS36.104 Section 126.96.36.199)'); axis([SNRIn(1)-0.1 SNRIn(end)+0.1 -0.05 .35]); legend('simulated performance','target');
3GPP TS 36.104 "Base Station (BS) radio transmission and reception"