Abstract
We propose double-differential (DD) modulation for the amplify-and-forward protocol over Nakagami- fading channels with carrier offsets. We propose an emulated maximum ratio combining (EMRC) decoder, which could be used by the double-differential receiver in the absence of exact channel knowledge. Approximate bit error rate (BER) analysis is performed for the proposed double-differential modulation-based cooperative communication system. The proposed double-differential system is immune to random carrier offsets, whereas the conventional single-differential modulation-based cooperative system breaks down. In addition, the proposed scheme is able to perform better than the same rate training-based cooperative system which utilizes training data for finding estimates of carrier offsets and channel gains.
Highlights
Cooperative communications has several promising features to become a main technology in future wireless communications systems
Where Γ(·) is the gamma function [16, Equation (8.310.1)], mp,q ≥ 1/2 is the Nakagami-m fading parameter, γp,q = Pp|hp,q|2/σ2 is the instantaneous signal to noise ratio (SNR), Pp ∈ {Ps, Pr} is the power transmitted by source or relay with Ps = P1 and Pr = P2, hp,q is a zero-mean Nakagamim channel coefficient, σ2 is the variance of the additive white Gaussian noise (AWGN), and γp,q = Ppσp2,q/σ2 is the average SNR over the link between p and q terminals in the cooperative system, where σ
The presence of carrier offsets makes all three block-fading channels behave as time-varying channels, which do not remain stationary over two consecutive time intervals
Summary
Cooperative communications has several promising features to become a main technology in future wireless communications systems. Several single-differential strategies for cooperative communications have been proposed so far to avoid the estimation of the channel coefficients at the receiver side [4,5,6,7] All of these conventional differential schemes assume that the channel is constant over at least two consecutive time intervals. A distributed double-differential modulation based on [12] with regenerative relays over cooperative Rayleigh channels is proposed and an upper bound of the pairwise error performance (PEP) is obtained in [13] It is assumed in [13] that the flat-fading part of the timevarying channel remains constant over 104 time intervals [13, Sections IV and VI]. (1) A double-differential modulation-based amplifyand-forward (AAF) cooperative wireless communication is proposed to improve the performance over flat-fading Nakagami-m channels with random carrier offsets. The article contains two appendices, which provide details of the derivations
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