Two-path amplify-and-forward relaying method for bandwidth efficient cognitive radios

摘要

The two-path amplify-and-forward relaying method for bandwidth efficient cognitive radios utilizes a primary user (PU) transmitter cooperating with a secondary user (SU) transmitter and receiver to relay PU data to the PU receiver. The present algorithm makes use of the inter-relay interference (IRI) between the two relay nodes to transmit SU data and cancel this IRI at the PU receiver node. The SU transmission power and the relaying amplifying factors are optimized to minimize the probability of error. Lagrangian multiplier method is used to obtain the optimal solution for the problem. Simulation results show that the present algorithm outperforms the single data transmission and gets closer to the performance of multiple input multiple output (MIMO) system of diversity 3 for PU network and 2 for SU network when a maximum likelihood decoder (MLD) is used.

主权项

1. A two-path amplify-and-forward relaying method for a bandwidth efficient cognitive radio, comprising the steps of:
transmitting PU data from a primary user (PU) transmitter S to a primary user (PU) receiver D in cooperation with a first secondary user (SU) relay RA (SU receiver) and a second secondary user relay RB (SU transmitter), the PU data transmission being divided into first, second, and third timeslots; in the first timeslot transmitting the algebraic subtraction of two successive modulated signals, s1 and s2 with total power Ps from S to the first secondary user relay RA and the PU receiver D; in the first timeslot transmitting data b1 with power PB from RB to RA and the PU receiver D, the data b1 interfering with PU data at RA and D, the received signal at D and RA in the 1st time slot being characterized by the relations,yD(1)=Ps2⁢hSD⁡(s1-s2)+PB⁢hBD⁢b1+wD(1),andyA(1)=Ps2⁢hSA⁡(s1-s2)+PB⁢hBA⁢b1+wA(1); in the second timeslot transmitting the second symbol only s2 with total power Ps to RB and D from S, while RA transmits the previous received data after applying amplify-and-forward (AF) protocol, the second time slot received signals at D and at RB being characterized by the relations,
yD(2)=√{square root over (Ps)}hSDs2+hADxA(2)+wD(2)and
yB(2)=√{square root over (Ps)}hSBs2+hABxA(2)+wB(2),where wB and wA are AWGN samples with zero mean and variance σ2 and xA(2) is the amplified received signal at RA such that xA(2)=βAyA(1);
in the third timeslot transmitting from RB to RA and D the received signal after removing the interfered SU data b1 and adding a new fresh version of it but with negative sign −b1 with power PB, the received signal at D and RA in the third time slot being characterized by the relations,
yD(3)=hBDxB(3)−√{square root over (PB)}hBDb1+wD(3),and
yA(3)=hBAxB(3)−√{square root over (PB)}hBAb1+wA(3),where xB(3) is the amplified received signal at RB after the subtraction of the SU data such that xB(3)=βB(yB(2)−b′1), where b′1 is the modified image of SU data b1 such that b′1=βAhABhBAb1;
using a maximum likelihood detector (MLD) in the PU and SU to detect the PU and SU data, wherein the MLD estimates a symbol vector {circumflex over (x)}s that gives the minimum Euclidean distance metric at D and RA, independently, the Euclidean distance metric for D and RA being characterized by the relations,μD=yD=HD⁢xS2=∑l=1L=3⁢yD(l)-hD(l)⁢xS2,andμA=yA=HA⁢xS2=∑l=1L=2⁢yA(l)-hA(l)⁢xS2,where hD(l) and hA(l) denote the l-th row of HD and HA, respectively, a pairwise-error probability being defined as the probability that the MLD chooses the erroneous data vector ci=(ci1, ci2, ci3) instead of the transmitted data vector cj=(cj1, cj2, cj3), where the data symbols cim and cjm are for the m-th user; and
controlling SU transmission power and amplifying factors of the two relays RA and RB based on the pairwise-error probability.