In odd slot, source S transmits its symbol to D and to both relays A and B. The received signal at D is given by
Where n is the time slot, and are the data symbols of PU and SU. the amplification factor satisfying the power constraint expressed as below
The received signal at relays A and B during nth slot is
Similarly in even time slot, the received signal at D is
The received signal at relays A and B during (n-1) th slot is
IRI mitigation – ZF SIC
In this section, we propose ZF-SIC for interference cancellation at D. The extraction of PU symbols considering the received signal at D in time slot t1 and t2 is given by
Extracting one of the symbols with better channel gain from received signal , we obtain the other symbol S2 by iteratively subtracting with . So, we have
Finally, S2 is obtained after equalization by zero forcing method as given below
where the equalized symbol
Optimum power allocation
In this section, power is allocated to secondary relays appropriately to satisfy the interference constraint on PU destination and also for guaranteed QOS for PU.
For optimum power allocation in t2 and t3, the sum of individual powers of PU (Ps) and SU (PA and PB) should be equal to the total power constraint Ptotal. In t2 and t3, optimal power constraint is as follows
The individual powers of the transmitters in the proposed model is found as below
Then, the individual powers of , and is obtained as PS=0.657W, PA=0.342W for t2 and PS=0.686W, PB =0.314W for t3.
The maximum achievable rate in bits/sec/hertz based on the proposed scheme SENT after MRC is given by
where is rate at D through direct link communication given by
is the SNR of direct link. and is the rate achieved through relay A and B at D and ,, are the MRC constants.
where is the SNR between source S to relay A and
is the SNR between A and destination D.
Similarly for SU, the rate is expressed as
where is the SNR between A and B.
Relay based routing performance
Fig.6 Number of SU nodes Vs PDR
Computed rates are used for SU data transmission and it is inferred from Fig.6 that as number of relay nodes increases, PDR performance is improved by 24% when compared to CAODV.