The Energy Efficiency (EE) is usually measured in bits per joule (bits/J) and is calculated as follows:
Energy Efficiency (EE) = Capacity (C)/Energy Consumption (E)
Modifying the Code for Energy Efficiency
When considering energy efficiency, you need to model the energy consumption of the selected antennas. Let’s assume that each selected antenna consumes energy Ea (joules/bit), and there is a fixed energy consumption Ef (joules/bit) for the system.
The energy consumption E for a selection of Lr antennas can be modeled as:
E = Ef + Lr ⋅ Ea
Subsequently, the energy efficiency can be calculated as follows:
Energy Efficiency (EE) = Capacity (C)/ E
Here’s the modified MATLAB code to select the optimal sub-matrix from an energy efficiency point of view:
Ns=4;
Nr=16;
SNR=6; %dB
SNR= 10^(SNR/10);
simulation=10;
Ea = 0.1; % Energy consumption per antenna (joules/bit)
Ef = 1; % Fixed energy consumption (joules/bit)
energyEfficiencyAver=[];
for Lr=1:8
energyEfficiencySum=0;
antennaSubset=nchoosek([1:Nr],Lr);
for sim=1:simulation
H=sqrt(1/2)*(randn(Nr,Ns)+1j*randn(Nr,Ns));
energyEfficiencySubsetMax=0;
for k=1:nchoosek(Nr,Lr);
indexOfChannel=antennaSubset(k,:);
H_sel=H(indexOfChannel,:);
capacityOfSubset=log2(det(eye(Ns)+SNR/Ns*(H_sel'*H_sel)));
E = Ef + Lr * Ea; % Total Energy Consumption
energyEfficiency = capacityOfSubset / E; % Energy Efficiency Calculation
if(energyEfficiency > energyEfficiencySubsetMax)
energyEfficiencySubsetMax = energyEfficiency;
end
end
energyEfficiencySum = energyEfficiencySum + energyEfficiencySubsetMax;
end
energyEfficiencyAver=[energyEfficiencyAver, energyEfficiencySum/simulation];
end
% Plot
X=[0:8];
plot(X,[0,energyEfficiencyAver]);
xlabel('Lr');
ylabel('Energy Efficiency (bits/J)');
grid on;
hold on;
