Praise for Fundamentals of WiMAX

144 Chapter 4 • Orthogonal Frequency Division Multiplexing4.7 Simulating OFDM SystemsIn this section, we provide some resources for getting started on simulating an OFDM system.The popular LabVIEW simulation package from National Instruments can be used to developvirtual instruments (VI’s) that implement OFDM in a graphical user interface. See also [1].Other communication system building blocks and multicarrier modulation tools are available inthe National Instruments Modulation Toolkit.OFDM functions can also be developed in Matlab. 6 Here, we provide Matlab code for abaseband OFDM transmitter and receiver for QPSK symbols. These functions can be modifiedto transmit and receive M-QAM symbols or passband—complex baseband—signals.function x=OFDMTx(N, bits, num, nu)%==========================================================% x=OFDMTx( N, bits, num, nu,zero_tones)%% APSK transmitter for OFDM%% N is the FFT size% bits is a {1,-1} stream of length (N/2-1)*2*num (baseband, zero DC)% num is the number of OFDM symbols to produce% nu is the cyclic prefix length%==========================================================if length(bits) ~= (N/2-1)*2*numerror('bits vector of improper length -- Aborting');end x=[];real_index = -1; %initial valuesimag_index = 0;for a=1:numreal_index = max(real_index)+2:2:max(real_index)+N-1;imag_index = max(imag_index)+2:2:max(imag_index)+N-1;X = (bits(real_index) + j*bits(imag_index))/2;X=[0 X 0]; % zero nyquist and DCx_hold=sqrt(N)*ifft([X,conj(fliplr(X(2:length(X)-1)))]); %Baseband so symmeteicx_hold=[x_hold(length(x_hold)-nu+1:length(x_hold)),x_hold]; %Add CPx=[x,x_hold];endx=real(x);function bits_out = OFDMRx(N,y,h,num_symbols,nu)%=========================================================% bits_out = OFDMRx(M,N,y,num_symbols,nu,zero_tones)%% N is the FFT size% y is received channel output for all symbols (excess delay spread removed)% h is the (estimated) channel impulse response6. These functions also can be used in MathScript for LabVIEW.