Distributed space-time coding is a cooperative transmission scheme proposed for wireless relay networks. With this scheme, antennas of the distributive relays work as transmit antennas of the sender and generate a space-time code at the receiver. When the transmit power is infinitely large, it achieves the maximum diversity. Although the scheme needs no channel information at relays, it requires full channel information at the receiver. In this paper, based on distributed space-time coding, we propose a differential transmission scheme, which requires channel information at neither relays nor the receiver. As distributed space-time coding can be seen as the counterpart of space-time coding in the network setting, this scheme is the counterpart of differential space-time coding. Compared to distributed coherent space-time coding, the differential scheme is 3dB worse. In addition, we show that Alamouti, square real orthogonal, and Sp(2) codes, which are originally proposed for multiple-antenna systems, can be used differentially in networks with corresponding numbers of relays.

The idea of space-time coding devised for multiple-antenna systems is applied to the problem of communication over a wireless relay network, a strategy called distributed space-time coding, to achieve the cooperative diversity provided by antennas of the relay nodes. In this paper, we extend the idea of distributed space-time coding to wireless relay networks with multiple-antenna nodes and fading channels. We show that for a wireless relay network with M antennas at the transmit node, N antennas at the receive node, and a total of R antennas at all the relay nodes, provided that the coherence interval is long enough, the high SNR pairwise error probability (PEP) behaves as (1/P) min {M,N}R if M /=N and (log 1/M P/P) MR if M = N, where P is the total power consumed by the network. Therefore, for the case of M /=N, distributed space-time coding achieves the maximal diversity. For the case of M = N, the penalty is a factor of log 1/M P which, compared to P, becomes negligible when P is very high.

Abstract—This paper proposes and analyzes differential modulation schemes for two cooperation protocols in multinode cooperative wireless networks; namely, multinode differential amplify-and-forward scheme (DiffAF) and multinode differential decode-and-forward scheme (DiffDF). In the DiffAF scheme, with knowledge of long-term average of received signals from all communication links, the destination efficiently combines signals from direct and all multiple-relay links to improve communication reliability. In the DiffDF scheme, by utilizing a decision threshold at each relay-destination link, the destination efficiently combines signals from the direct link and each relay link whose signal amplitude is larger than the threshold. For the DiffAF scheme, an exact bit error rate (BER) formulation based on optimum combining is provided for differential-ary phase shift keying (DMPSK) modulation, and it serves as a performance benchmark of the proposed DiffAF scheme. In addition, BER upper bounds, BER lower bounds, and simple BER approximations are derived. Then, optimum power allocation is provided to further improve performance of the DiffAF scheme. Based on the tight BER approximation, the optimum power allocation can be simply obtained through a single dimensional search. In case of the DiffDF scheme, the performance of DMPSK modulation is analyzed. First, a BER formulation for DMPSK modulation is derived. Next, an approximate BER formulation of the DiffDF scheme is obtained, and a tractable BER lower bound is derived to provide further insights. Then, the performance of the DiffDF scheme is enhanced by jointly optimizing power allocation and decision thresholds with an aim to minimize the BER. Finally, simulation results under the two proposed cooperation protocols are given to validate their merit and support the theoretical analysis. Index Terms—Bit error rate (BER), cooperative communications, differential modulation, multinode wireless networks, virtual multiple-input–multiple-output (MIMO). I.

Abstract—This paper proposes a simple non-coherent amplifyand-forward receiver for the relay channel and evaluates its diversity performance for Rayleigh fading channels. We use the generalized likelihood ratio test to obtain the decision rule in closed form, independent of the fading distribution. The receiver is developed for M-ary orthogonal signals and multiple relays. The only side information required is the average noise energy at the receiver; no statistical knowledge of the channel gains is needed. We develop closed-form upper and lower bounds on the probability of error of this receiver for the case of binary signaling with a single relay and show that this receiver achieves near-full diversity, with the probability of error decreasing with increasing signal-to-noise ratio (SNR) as log 2 (SNR) /SNR 2 for large SNR. Additional results obtained by simulation demonstrate increasing diversity gain with additional relays. I.

Abstract — In this paper, we develop a protocol for the construction of cooperative networks when the channel state information is not available at the transmitters and the receivers. In the proposed protocol, differential space-time codewords are generated at the source terminal. In the broadcast phase, each row of the differential space-time codeword is transmitted to a different relay, whereas in the relay phase, the relaying terminals retransmit the codeword through simple amplify-and-forward algorithm. The performance of the cooperative diversity system is analyzed for a two-user case for different channel environments in terms of the diversity gain and the diversity product. The optimization of the power allocation between source and relay terminals is considered for the maximization of the diversity product. When the same modulation scheme is used, the performance of differential detection is degraded by 3 dB noise enhancement compared with coherent detection. Index Terms — Cooperative diversity, MIMO, space-time cod-ing, differential coding.

Abstract — Cooperative diversiy is a promising technology for future wireless networks. In this paper, based on the moment generating function (MGF), we derive exact closed-form expressions for the average bit error rate (BER), the amount of fading (AF), and outage probability (Pout) for cooperative diversity networks with amplify-and-forward relaying over Rayleigh-fading channel using differentiallynon-coherent equal gain combining (EGC) technique. We show that this scheme (differentially-non-coherent EGC) achieves a diversity order of 2 at high SNR. The main advantage of this scheme is that it does not need channel state information of the transmission links at the relay and destination nodes. This feature reduces the design and implementation complexity. Furthermore, we study in this paper the impact of the relay location on the system performance. Index Terms — Cooperative diversity, single relay networks, Rayleigh fading, error performance, outage probabilities. I.

In this paper, we propose double-differential (DD) modulation for the amplify-and-forward protocol over Nakagami-m 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. I.

Abstract—Two-way cooperative communications are consid-ered to improve the throughput of conventional one-way coop-erative communications. For fast Rayleigh fading channels, we propose optimal and suboptimal non-coherent detectors for on-off keying (OOK) and frequency-shift keying (FSK) modulated two-way amplify-and-forward (AF) cooperative communications in this paper. In the proposed system, the relaying node combines the received signals from two nodes, amplifies them and retrans-mits the conjugate of the combined and amplified signals to the above-mentioned nodes. At the receivers of above-mentioned nodes, the optimal non-coherent detection is employed which is based on maximum likelihood rule. Since it involves integration operation, the optimal detector is simplified to a suboptimal detector which omits the real component of the relayed signal over the frequency which includes interference. The simulation results have shown that compared with the optimal detector, the proposed suboptimal detector reduces the receiver com-plexity at the expense of acceptable performance degradation. Furthermore, we have analytically studied the bit-error-rate performance upper and lower bounds of proposed non-coherent FSK modulated two-way AF cooperative communications. Index Terms—Non-coherent detection, cooperative communi-cation, amplify-and-forward (AF), two-way, Rayleigh fading. I.

Abstract — In this paper, distributed double-differential coding is proposed to avoid the problem of carrier offsets in amplify and forward protocol based cooperative network with two relays. A double-differential orthogonal-space-time block code is trans-mitted by the relays in a distributed manner without channel knowledge. We derive a low complexity linear decoder which does not require the channel and carrier offset knowledge. A pairwise error probability (PEP) analysis is also conducted and we found an upper bound of the PEP for the proposed system. In addition, an optimized power allocation is proposed to improve the SER performance of the system. I.

Among various diversity techniques to combat fading in wireless channels, spatial diversity through MIMO coding scheme is an effective way to increase link capacity and system reliability without sacrificing bandwidth efficiency. Recently, cooperative diversity has been introduced as an efficient alternative to improve system performance without the requirement of additional antennas. However, most of existing works on MIMO and cooperative communications are based on an assumption that the destination has perfect knowledge of channel state information of all transmission links and hence introduces high complexity to the receiver. To overcome such problems, this thesis proposes differential modulation schemes for space-time coded MIMO and cooperative communications. By exploiting spatial/cooperative diversity without the requirement of channel state information, the proposed schemes provide an excellent tradeoff between receiver complexity and system performance. First, a matrix rotation based signal design for differential space-time modulation is investigated to minimize the union bound on block error probability. Next, a robust differential scheme for MIMO-OFDM systems is proposed by which the signal transmission of each differentially encoded signal