Priority-Based Max Link Selection for Double Differential Modulation-Based Buffer-Aided Relaying With Offsets

In this paper, we consider a decode-and-forward (DF) buffer-aided (BA) multi-relay system using double differential (DD) encoding and decoding for the transmission and reception of data packets. The proposed system does not require carrier frequency offset (CFO) information and channel state information (CSI) at any communicating node. A priority-based max link selection protocol has been adopted to select links based on the buffer status and channel quality. The Markov-chain approach is used for developing the state transition matrix, using which the steady state probability of the system is obtained. The outage probability and average bit error rate (ABER) expressions are derived using the steady-state probability. The proposed setup performance is then compared with the conventional coherent BA system. It is established that the considered setup is affected by a signal-to-noise ratio (SNR) penalty of $\approx 3$ dB, which is considerably lower than the well-known 6 dB SNR penalty existing for DD modulation compared to coherent modulation. Also, the proposed setup outcompetes the coherent max-link approach in the presence of a CFO.