%% LTE Downlink Channel Estimation and Equalization %% Cell-Wide Settings clear SNR_values_db=linspace(0,30,8); Nrealizations=1; preEVM = zeros(length(SNR_values_db),Nrealizations); postEVM_mmse = zeros(length(SNR_values_db),Nrealizations); postEVM_mmse_lin = zeros(length(SNR_values_db),Nrealizations); postEVM_liblte = zeros(length(SNR_values_db),Nrealizations); enb.NDLRB = 6; % Number of resource blocks enb.CellRefP = 2; % One transmit antenna port enb.NCellID = 0; % Cell ID enb.CyclicPrefix = 'Normal'; % Normal cyclic prefix enb.DuplexMode = 'FDD'; % FDD %% Channel Model Configuration rng(1); % Configure random number generators cfg.Seed = 2; % Random channel seed cfg.NRxAnts = 2; % 1 receive antenna cfg.DelayProfile = 'EVA'; % EVA delay spread cfg.DopplerFreq = 5; % 120Hz Doppler frequency cfg.MIMOCorrelation = 'Low'; % Low (no) MIMO correlation cfg.InitTime = 0; % Initialize at time zero cfg.NTerms = 16; % Oscillators used in fading model cfg.ModelType = 'GMEDS'; % Rayleigh fading model type cfg.InitPhase = 'Random'; % Random initial phases cfg.NormalizePathGains = 'On'; % Normalize delay profile power cfg.NormalizeTxAnts = 'On'; % Normalize for transmit antennas %% Channel Estimator Configuration cec = struct; % Channel estimation config structure cec.PilotAverage = 'UserDefined'; % Type of pilot symbol averaging cec.FreqWindow = 9; % Frequency window size cec.TimeWindow = 9; % Time window size cec.InterpType = 'Linear'; % 2D interpolation type cec.InterpWindow = 'Centered'; % Interpolation window type cec.InterpWinSize = 1; % Interpolation window size %% Subframe Resource Grid Size gridsize = lteDLResourceGridSize(enb); K = gridsize(1); % Number of subcarriers L = gridsize(2); % Number of OFDM symbols in one subframe P = gridsize(3); % Number of transmit antenna ports for nreal=1:Nrealizations %% Transmit Resource Grid txGrid = []; %% Payload Data Generation % Number of bits needed is size of resource grid (K*L*P) * number of bits % per symbol (2 for QPSK) numberOfBits = K*L*P*2; % Create random bit stream inputBits = randi([0 1], numberOfBits, 1); % Modulate input bits inputSym = lteSymbolModulate(inputBits,'QPSK'); %% Frame Generation % For all subframes within the frame for sf = 0:10 % Set subframe number enb.NSubframe = mod(sf,10); % Generate empty subframe subframe = lteDLResourceGrid(enb); % Map input symbols to grid subframe(:) = inputSym; % Generate synchronizing signals pssSym = ltePSS(enb); sssSym = lteSSS(enb); pssInd = ltePSSIndices(enb); sssInd = lteSSSIndices(enb); % Map synchronizing signals to the grid subframe(pssInd) = pssSym; subframe(sssInd) = sssSym; % Generate cell specific reference signal symbols and indices cellRsSym = lteCellRS(enb); cellRsInd = lteCellRSIndices(enb); % Map cell specific reference signal to grid subframe(cellRsInd) = cellRsSym; % Append subframe to grid to be transmitted txGrid = [txGrid subframe]; %#ok end %% OFDM Modulation [txWaveform,info] = lteOFDMModulate(enb,txGrid); txGrid = txGrid(:,1:140); %% SNR Configuration for snr_idx=1:length(SNR_values_db) SNRdB = SNR_values_db(snr_idx); % Desired SNR in dB SNR = 10^(SNRdB/20); % Linear SNR %% Fading Channel cfg.SamplingRate = info.SamplingRate; % Pass data through the fading channel model rxWaveform = lteFadingChannel(cfg,txWaveform); rxWaveform = txWaveform; %% Additive Noise channel_gain = mean(rxWaveform(:).*conj(rxWaveform(:)))/mean(txWaveform(:).*conj(txWaveform(:))); % Calculate noise gain N0 = 1/(sqrt(2.0*enb.CellRefP*double(info.Nfft))*SNR); % Create additive white Gaussian noise noise = N0*complex(randn(size(rxWaveform)),randn(size(rxWaveform))); noiseTx(snr_idx) = N0; % Add noise to the received time domain waveform rxWaveform = rxWaveform + noise; %% Synchronization offset = lteDLFrameOffset(enb,rxWaveform); rxWaveform = rxWaveform(1+offset:end,:); %% OFDM Demodulation rxGrid = lteOFDMDemodulate(enb,rxWaveform); addpath('../../debug/lte/phy/lib/ch_estimation/test') %% Channel Estimation [estChannel, noiseEst(snr_idx)] = lteDLChannelEstimate(enb,cec,rxGrid); output=[]; snrest = zeros(10,1); for i=0:9 % if (SNR_values_db(snr_idx) < 25) [d, a, out, snrest(i+1)] = liblte_chest(enb.NCellID,enb.CellRefP,rxGrid(:,i*14+1:(i+1)*14),[0.15 0.7 0.15],[],i); % else % [d, a, out, snrest(i+1)] = liblte_chest(enb.NCellID,enb.CellRefP,rxGrid(:,i*14+1:(i+1)*14),[0.05 0.9 0.05],[],i); % end output = [output out]; end SNRest(snr_idx)=mean(snrest); disp(10*log10(SNRest(snr_idx))) %% MMSE Equalization % eqGrid_mmse = lteEqualizeMMSE(rxGrid, estChannel, noiseEst(snr_idx)); % % eqGrid_liblte = reshape(output,size(eqGrid_mmse)); % % % Analysis % % %Compute EVM across all input values EVM of pre-equalized receive signal % preEqualisedEVM = lteEVM(txGrid,rxGrid); % fprintf('%d-%d: Pre-EQ: %0.3f%%\n', ... % snr_idx,nreal,preEqualisedEVM.RMS*100); % % % %EVM of post-equalized receive signal % postEqualisedEVM_mmse = lteEVM(txGrid,reshape(eqGrid_mmse,size(txGrid))); % fprintf('%d-%d: MMSE: %0.3f%%\n', ... % snr_idx,nreal,postEqualisedEVM_mmse.RMS*100); % % postEqualisedEVM_liblte = lteEVM(txGrid,reshape(eqGrid_liblte,size(txGrid))); % fprintf('%d-%d: liblte: %0.3f%%\n', ... % snr_idx,nreal,postEqualisedEVM_liblte.RMS*100); % % preEVM(snr_idx,nreal) = preEqualisedEVM.RMS; % postEVM_mmse(snr_idx,nreal) = mean([postEqualisedEVM_mmse.RMS]); % postEVM_liblte(snr_idx,nreal) = mean([postEqualisedEVM_liblte.RMS]); end end % subplot(1,2,1) % plot(SNR_values_db, mean(preEVM,2), ... % SNR_values_db, mean(postEVM_mmse,2), ... % SNR_values_db, mean(postEVM_liblte,2)) % legend('No Eq','MMSE-lin','MMSE-liblte') % grid on % % subplot(1,2,2) %SNR_liblte = 1./(SNRest*sqrt(2.0*enb.CellRefP*double(info.Nfft))); SNR_liblte = SNRest; SNR_matlab = 1./(noiseEst*sqrt(2.0*enb.CellRefP*double(info.Nfft))); plot(SNR_values_db, SNR_values_db, SNR_values_db, 10*log10(SNR_liblte),SNR_values_db, 10*log10(SNR_matlab)) %plot(SNR_values_db, 10*log10(noiseTx), SNR_values_db, 10*log10(SNRest),SNR_values_db, 10*log10(noiseEst)) legend('Theory','libLTE','Matlab')