Ce code M simule modulation DBPSK et Barker code d'�talement sur
une parfaite synchronisation 802.11b lien.
Il calcule le taux de REC � chaque Es / Non
et placettes du r�sultat.
**********************************************
EsNoRange = 0:2:10; % Range of noice levels to calculate BER
NumPackets = 2;
PacketSizeBytes = 1024;
PacketSizeBits = PacketSizeBytes*8; % Ignore preamble and sync bits
clear BERResults;
clear ErrorResults;
% Spreading parameters
Barker = [1 -1 1 1 -1 1 1 1 -1 -1 -1]'; % Barker sequence
SpreadingRate = length(Barker); % Spreading rate
% Upsampling rate
SamplesPerChip=8;
% Filter order and coefficients - root raised cosine
FilterOrder = 40; % Set to multiple of SamplesPerChip to make delay calculation easy
h = firrcos(FilterOrder,7e6,.7,88e6,'rolloff','sqrt',FilterOrder/2,kaiser(FilterOrder+1,1));
BitDelay = 1;
ChipDelayAdd = 6;
NumEsNos = length(EsNoRange);
ErrorResults = zeros(1,NumEsNos);
disp(' ');disp('Start Simulation');
for EsNoIndex = 1:NumEsNos
EsNo = EsNoRange(EsNoIndex);
disp(['Simulating: Es/No=' num2str(EsNo) 'dB']);
SNR = EsNo+10*log10(1/SpreadingRate)+10*log10(1/SamplesPerChip);
% Initialize system and simulation measurements state
% Bits
TotalBits = false; % Bit count for BER calculation
ErrorBits = false; % Error count for BER calculation
LastTxSymbol = 1; % Set DBPSK Modulator state
LastRxSymbol = 1; % Set DBPSK Demodulator state
% Filters
Rx_chips_delayed_store = zeros(ChipDelayAdd,1);
Tx_bits_delayed_store = false(BitDelay,1);
Tx_Filter_State = h(1:end-1); % Fill filter with a +1 symbol
Rx_Filter_State = h(1:end-1); % Fill filter with a +1 symbol
% Main simulation loop
% Each packet is transmitted, and the recieved bits compared with the
% transmitted bits to calculate the BER.
for Packet = 1:NumPackets
% Construct frame of bits
rand('state', 0);
Tx_bits = rand(PacketSizeBits,1)>.5; % Random bits
% Modulate
Tx_bits_bp = (1-2*Tx_bits); % Convert to bipolar 0,1 --> 1, -1
Tx_symbols = LastTxSymbol*cumprod(Tx_bits_bp); % New DBPSK symbol = previous * 1 or -1
LastTxSymbol = Tx_symbols(end); % Store modulator state (last symbol)
% Spread symbols with Barker code, upsampling by spreading rate
Tx_chips = reshape(Barker*Tx_symbols',[],1); % Multiply by barker and reshape to a columm
Tx_chips = complex(Tx_chips); % Make complex to ensure correct baseband transmission
% Upsample chips by SamplesPerChip factor
Tx_samples = zeros(length(Tx_chips)*SamplesPerChip,1); % Create empty Tx_samples
Tx_samples(1:SamplesPerChip:end,1) = sqrt(SamplesPerChip)*Tx_chips; % Normalize power due to upsampling
% Tx Filter
[Tx_samples_filtered,Tx_Filter_State] = filter(h,1,Tx_samples,Tx_Filter_State); % Filter
Tx_samples_filtered = Tx_samples_filtered*2.495; % Set output power to 1W
var(Tx_samples_filtered); % Calculate Tx signal power, view by removing ';'
% Transmit though AWGN Channel assuming 0dBW input power (check
% with line above)
Rx_samples_unfiltered = awgn(Tx_samples_filtered,SNR,0,0);
% Rx Filter
[Rx_samples_filtered,Rx_Filter_State] = filter(h,1,Rx_samples_unfiltered,Rx_Filter_State);
% Downsample - sample chips
Rx_chips = Rx_samples_filtered(1:SamplesPerChip:end);
% Add 1 chip delay to move signal to 11 chip boundary
Rx_chips_delayed = [Rx_chips_delayed_store; Rx_chips(1:end-ChipDelayAdd)];
Rx_chips_delayed_store = Rx_chips((end-ChipDelayAdd+1):end); % Store delayed chips
% Despread - sample symbol
Rx_symbols = Barker'*reshape(Rx_chips_delayed,SpreadingRate,PacketSizeBits); % Multiply by Barker
Rx_symbols = Rx_symbols(:)/SpreadingRate; % Make a column and normalize
% Demodulate
Rx_symbols_plus_last = [LastRxSymbol; Rx_symbols];
Rx_symbols_plus_last_mult = Rx_symbols_plus_last(1:end-1).*conj(Rx_symbols_plus_last(2:end));
Rx_bits = Rx_symbols_plus_last_mult < 0;
LastRxSymbol = Rx_symbols(end); % Demodulator state
% Calculate BER
% Add BitDelay to Tx signal to align with Rx signal
Tx_bits_delayed = [Tx_bits_delayed_store; Tx_bits(1:end-BitDelay)];
Tx_bits_delayed_store = Tx_bits(end-BitDelay+1:end); % Store delayed symbol
if Packet==1 % Ignore delayed bits on first packet
TotalBits = TotalBits+length(Rx_bits)-BitDelay;
ErrorBits = ErrorBits+sum(Tx_bits_delayed(BitDelay+1:end)~=Rx_bits(BitDelay+1:end));
else
TotalBits = TotalBits+length(Rx_bits); % Calculate total bits
ErrorBits = ErrorBits+sum(Tx_bits_delayed~=Rx_bits); % Compare Tx and Rx bits
end
end
ErrorResults(EsNoIndex) = ErrorBits; %error bits
end
BERResults = ErrorResults/TotalBits; % Calculate BER
semilogy(EsNoRange,BERResults,'*-');
grid;
title('802.11b 1Mbps DBPSK BER');
ylabel('BER')
xlabel('Es/No (dB)');
