Bit Error Rate and Power Allocation of Soft-Decision-and-Forward Cooperative Networks

Abstract

In this paper, the performance of the soft-decision-andforward (SDF) protocol in the cooperative communication network with one source, one relay, and one destination, where each node has two transmit and receive antennas, is analyzed in terms of the bit error rate (BER) obtained from the pairwise error probability (PEP). Using the moment generating function and Q-function approximation, the PEP of SDF protocol is calculated and we confirm that the SDF with two antennas achieves the full diversity order. For the slow-varying Rayleigh fading channel, the optimal power allocation ratio can be determined so as to minimize the average PEP (or BER). Due to the difficulty of deriving the optimal value analytically, an alternative strategy of maximizing the product signal-to-noise ratio (SNR) of direct and relay links, which we call the suboptimal power allocation, is considered. Through a numerical analysis, we show that the performance gap between the suboptimal and optimal power allocation strategies is negligible in the high SNR region. key words: cooperative diversity, harmonic mean, power allocation, product signal-to-noise ratio (SNR), soft-decision-and-forward (SDF) from Seoul

Analysis on Soft-Decision-and-Forward Cooperative Networks with Multiple Relays

“…It is shown in [12] that the PEP depends on the instantaneous end-to-end SNR, γ eq , which is the sum of two SNRs, i.e.,…”

“…Then, we can bound the PEP by averaging the conditional PEP in (6) over H using the Q-function inequality in (7). It gives the upper and lower bounds of the average PEP for the SDF protocol [12] as…”

“…For the sake of tractability, let us assume that the uniform power allocation is used between the source and relays, i.e., P 1 = P 2 = P/(M + 1). Using the results in [12], the MGFs of γ 0 and γ m are expressed as…”

“…Since the relay nodes can separate the signals in SDF protocol while they simply amplify the received signals according to the power constraint in AF protocol, SDF becomes substantially different from AF in the case of multiple antennas. In [12], performance on SDF with single relay where each node is equipped with two antennas was analyzed in terms of bit error rate (BER). Furthermore, power allocation scheme between source and relay nodes was proposed so as to maximize the instantaneous end-to-end signal-to-noise ratio (SNR).…”

“…This paper is organized as follows. Section 2 describes the SDF protocol and reviews the results in [12]. Sections 3 and 4 address the conventional multiple-relay transmission and the 'best relay selection' schemes, respectively.…”