Adding first version for multipath channel model support

Adding methods to generate rayleigh channel correlated in time domain
(Jake spectrum)
Adding method to emulate various multipath channel models
Adding example with minimal OFDM transceiver
Update documentation

Author: RGerzaguet

docs/src/base.md

@@ -24,7 +24,7 @@ Depth	= 1
 
 ```@autodocs
 Modules = [DigitalComm]
-Pages   = ["addNoise.jl"]
+Pages   = ["Channel/addNoise.jl","Channel/rayleighChan.jl","Channel/getChannel.jl"]
 Order   = [:function, :type]
 Depth	= 1
 ```

examples/example_multipathChannel.jl

@@ -0,0 +1,135 @@
+# --- testingChannelApplication.jl
+# ---
+# Description
+#    Testing how wo apply time varying channel model
+# ---
+# Syntax
+#    include("testingChannelApplication.jl");
+# ---
+# v 1.0 - Robin Gerzaguet.
+
+
+module example_multipathChannel 
+
+# ----------------------------------------------------
+# --- Modules
+# ----------------------------------------------------
+# --- External
+using Plots
+using Printf
+using DSP
+using FFTW
+# --- Custom
+using DigitalComm
+
+# ----------------------------------------------------
+## --- Functions
+# ----------------------------------------------------
+# --- Tx scheme
+function minimalPhy(nbSymb,mcs,ofdm)
+	# Minimal transmitter scheme
+	nbSubcarriers = length(ofdm.allocatedSubcarriers);		  # Subcarrier length
+	nbBits		  = Int(nbSymb * nbSubcarriers * log2(mcs));		  # nbBits
+	bitSeq	      = genBitSequence(nbBits);					  # Binary sequence
+	qamSeq		  = bitMappingQAM(mcs,bitSeq);				  # QAM generation
+	qamMat		  = reshape(qamSeq,nbSubcarriers,nbSymb);	  # QAM matrix
+	sigId		  = genSig(qamMat,ofdm);					  # OFDM signal
+	return sigId;
+end
+function zeroPad(x,n)
+	if n > length(x) 
+		out = [x;zeros(n-length(x))];
+	else 
+		out = x;
+	end
+	return out;
+end
+# --- Receiver equalizer
+function minimalEqualizer(qamRx,ofdm,strucChan)
+	# Simple ZF equalisation scheme:
+	qamEq	= zeros(Complex{Float64},size(qamRx));
+	firAll	= zeros(Complex{Float64},ofdm.nFFT,size(qamRx,2));
+	for iN = 1 : 1 : size(qamRx,2)
+		# --- Getting all channel samples in current symbol
+		# We get a nFFT x nbTaps matrix (all channel taps in current symbol)
+		# We will consider that channel is constant, and that channel of interest
+		# is at the middle of the OFDM symbol
+		if Bool(strucChan.timeVarying)
+			currChan  = strucChan.cir[(iN-1)*(ofdm.nFFT+ofdm.nCP) + ofdm.nCP + ofdm.nFFT÷2,:];
+		else
+			# COnstant FIR
+			currChan = strucChan.cir;
+		end
+		# Switch to frequency domain
+		firFreq   = fft(zeroPad(currChan,ofdm.nFFT));
+		qamEq[:,iN] = qamRx[:,iN] ./ firFreq[ofdm.allocatedSubcarriers];
+		firAll[:,iN] = firFreq;
+	end
+	return qamEq,firAll;
+end
+
+function plotFIR(fir,ofdm,samplingFreq) 
+	# --- Calculate freq axis 
+	freqAx	= (((0:1:ofdm.nFFT-1) ./ ofdm.nFFT) .- 0.5) .* samplingFreq;
+	firC	= circshift(10*log10.(abs2.(fir)), ofdm.nFFT ÷2);
+	pObj	= plot(freqAx,firC[:,1],label="First Channel");
+	plot!(pObj,freqAx,firC[:,end],label="Last Channel");
+	xlabel!("Frequency [Hz]");
+	ylabel!("Channel magnitude");
+	return pObj;
+end
+
+
+function main()
+	# ----------------------------------------------------
+	# --- Parameters
+	# ----------------------------------------------------
+	sizeFFT	  		= 1024;
+	carrierFreq		= 5.2e9;
+	speed	  		= 1300;
+	samplingFreq	= 15.36e6;
+	allocatedSubcarriers= getLTEAlloc(sizeFFT);
+
+	# ----------------------------------------------------
+	# --- Minimal Phy
+	# ----------------------------------------------------
+	# --- Init OFDM structure
+	ofdm  = initOFDM(
+								 sizeFFT,						    # --- nFFT                 : FFT size
+								 72,						        # --- nCP                  : CP size
+								 allocatedSubcarriers,		        # --- allocatedSubcarriers : Subcarrier allocation
+								 );
+	# --- Init parameters
+	sigId	  = minimalPhy(14,4,ofdm);
+	# ----------------------------------------------------
+	# --- Multipath Channel
+	# ----------------------------------------------------
+	# --- profile 
+	profile         = "etu";
+	# --- Channel object
+	channelObj      = initChannel(profile,carrierFreq,samplingFreq,speed);
+	# --- Channel instance
+	strucChan0       = getChannel(length(sigId),channelObj,-1);
+	# ---------------------------------------------------- 
+	# --- Channel application  
+	# ---------------------------------------------------- 
+	sigChan	  = applyChannel(sigId,strucChan0);
+	qamRx	  = ofdmSigDecode(sigChan,ofdm);
+	scatter(qamRx[:])
+	# ----------------------------------------------------
+	# --- Setting a minimal equalizer
+	# ----------------------------------------------------
+	# --- Assuming a perfect CSI
+	qamEq,firFreq	= minimalEqualizer(qamRx,ofdm,strucChan0)
+	#
+	pObj = scatter(qamRx[:],xlims=(-1,1),ylims=(-1,1),label="before eq.");
+	scatter!(pObj,qamEq[:],xlims=(-1,1),ylims=(-1,1),label="after eq.");
+	display(pObj);
+	# 
+	pObj2 = plotFIR(firFreq,ofdm,samplingFreq);
+	display(pObj2);
+
+
+end
+
+end