need help about the variance

[aniket18]

hello i am doing project on Power allocation in cooperative communication..

i am using source, relay and destination

so channel(1) from source to destnation
channel(2) from source to relay
channel(3) from relay to destnation

i want to set the variance of channel link between source to relay and relay to destination for optimum power allocation

like by using variance we can decide quality of link

for example

δ^2s,r=1

δ^2r,d=10

how could i implement this in matlab

this channel model

Channel gains
channel_BS1_RS1=(1/sqrt(2)).*[randn(1,N2)+1i*randn(1,N2)];% Channel coefficients for Soure-Relay Link
a11=sum((abs(channel_BS1_RS1)))/N2; %Average channel gain for Soure-Relay Link Channel

channel_RS1_MS1=10.*[randn(1,N2)+1i*randn(1,N2)];% Channel coefficients for Relay-Desination Link
b11=sum((abs(channel_RS1_MS1)))/N2; %Average channel gain for Relay-Desination Link Channel

channel_BS1_MS1=(1/sqrt(2))*[randn(1,N2)+1i*randn(1,N2)];% Channel coefficients for Soure-Desination Direct Link
c11=sum((abs(channel_BS1_MS1)))/N2; %Average channel gain for Soure-Desination Link Channel
%% AWGN
nbr=(1/sqrt(2)).*(randn(1,N2)+1i*randn(1,N2));%AWGN for at Relay for Soure-Relay Link
nrm=(3.16/sqrt(2)).*(randn(1,N2)+1i*randn(1,N2));%AWGN for at Desination for Relay-Desination Link
nbm=(1/sqrt(2)).*(randn(1,N2)+1i*randn(1,N2));%AWGN for at Desination for source-Desination Link