Relay-destination Channels Research Articles

Performance analysis of the dual-hop asymmetric fading channel

In real wireless communication environments, it is highly likely that different channels associated with a relay network could experience different fading phenomena. In this paper, we investigate the end-to-end performance of a dual-hop fixed gain relaying system when the source-relay and the relay-destination channels experience Rayleigh/Rician and Rician/Rayleigh fading scenarios respectively. Analytical expressions for the cumulative distribution function of the end-to-end signal-to-noise ratio are derived and used to evaluate the outage probability and the average bit error probability of M-QAM modulations. Numerical and simulation results are presented to illustrate the impact of the Rician factor on the end-to-end performance. Furthermore, these results confirm that the system exhibits an improved performance in a Rician/Rayleigh (source-relay link/relay-destination link) environment compared to a Rayleigh/Rician environment.

Bandwidth-efficient cooperative MIMO relaying schemes

Coded cooperative MIMO relaying schemes in which all successfully decoded signals from multiple sources are simultaneously forwarded by a multi-antenna relay to a common multi-antenna destination to increase bandwidth efficiency are proposed in this paper. These schemes facilitate the various retransmission strategies at relay and single-user and multi-user iterative decoding techniques at destination, suitable for trade-offs between performance, latency, and complexity. When channel state information (CSI) is available, pre-coding and power allocation at the relay can be exploited to enhance the information transmission reliability over the relay-destination channel, thus improving the overall system performance. Simulation result shows their superiority to direct transmission under the same transmit power and bandwidth efficiency.

Two hop amplify-and-forward transmission in mixed rayleigh and rician fading channels

The performance of a two hop amplify-and-forward relay system, where the source-relay and the relay-destination channels experience Rayleigh and Rician fading respectively, is investigated. We derive exact and lower bound expressions for the outage probability and average bit error probability, where the bounds become tight at high signal-to-noise ratios (SNR). Our results are verified through comparison with Monte Carlo simulations, where we also illustrate the positive impact of the Rician factor on the system performance.

Performance of Decode-and-Forward Cooperative Communications Over Nakagami- $m$ Fading Channels

In this paper, we analyze the symbol error rate (SER) performance of decode-and-forward (DF) cooperative communications over Nakagami-m fading channels. For the classical three-node cooperation model, the exact SER expressions for both M phase shift keying (PSK) and M quadrature amplitude modulation (QAM) are derived. For easy usage, we also provide asymptotic approximations for the SER. In the analysis, we first consider the cooperation scenario in which all the channels are uncorrelated. In practice, it may happen that a correlation exists between the source-destination and relay-destination channels, e.g., for user cooperation in the uplink of a cellular network. We then examine the SER in this scenario. In addition, by varying the parameters of the Nakagami-m fading channels in the analytical results, we obtain some perceptions of choosing a good relay for enhancing the cooperation and make clear about how the included Nakagami fading figures and channel variances affect the SER performance. In addition, the optimal power allocation is investigated based on the derived asymptotic SER expressions. Simulations are finally provided to verify the correctness of our analysis.

Orthogonal decode and forward relaying with improved spectral efficiency

Cooperative relay communications can significantly improve the reliability of data transmission over wireless fading channels by implementing spatial diversity in a distributed fashion. Orthogonal decode and forward (ODF) relaying achieves maximum diversity provided by the source-destination and relay destination channels, but suffers from low spectral efficiency. We propose a novel ODF protocol having higher spectral efficiency without sacrificing the diversity gain. We analyze the symbol error probability of the proposed protocol and also present simulation results.

Performance Analysis and Power Allocation for Amplify-and-Forward Cooperative Networks over Nakagami-m Fading Channels

In this paper, we consider a dual-hop wireless cooperative network with amplify-and-forward (AF) relaying. The output signal-to-noise ratio (SNR) at the destination of the AF cooperative networks is in the form of the sum of harmonic mean of the source-relay channel SNR and the relay-destination channel SNR. Instead of deriving the exact probability density function (PDF) of the output SNR, we study the series expansion of this PDF around zero. This result is then applied to evaluate the performance of the AF cooperative systems over Nakagami-m fading channels, and closed-form high-SNR approximations of the average symbol error rate (SER) and the outage probability are derived. Next, we investigate the optimal power allocation (OPA) among the source node and the relays to minimize the approximate SER as well as the outage probability. It is shown that the optimal power allocation depends on the channel mparameters and the ratio of the source-relay channel gain to the relay-destination gain. In addition to the optimal power allocation, we also propose a low complexity sub-optimal power allocation (SubOPA) scheme. The performance improvement with optimal and sub-optimal power allocation is analyzed and validated by numeric results. It is shown that equal power allocation is near optimal when the relays are close to the source, while significant performance improvement is observed by both the optimal and sub-optimal power allocation schemes when the relays are close to the destination.

Outage-based Decision Strategies for Coded Cooperative Relaying Schemes

Two cooperation decision strategies based on the instantaneous signal-to-noise ratio (SNR) differences between source-destination, source-relay, and relay-destination channels are considered for coded cooperative relaying systems. Upper bounds on outage probability at the destination for the coded cooperative relaying schemes are first derived and exhaustive search is then used for SNR difference values and partitioning to minimize the outage probability for a given range of the SNR differences. Numerical results confirm the performance enhancement offered by the proposed schemes.

Beamforming Algorithms for Information Relaying in Wireless Sensor Networks

We develop beamforming algorithms for information relaying over shared slowly nonselective fading channels in wireless sensor networks. We assume that, prior to beamforming their received data to a destination, the relays preprocess them by either data amplifying or decoding. The beamforming weights are broadcasted by the destination to the relays and are formed based on the individual relay-destination channel coefficients and an m-bit description of the quality of each source-relay channel. For both relay data-preprocessing models, we present methods for optimizing the m-bit quantizer employed at each relay for encoding its source-relay channel quality level, and for choosing the beamforming weights at the destination, so as optimize the destination uncoded bit error rates. As our simulations and analysis reveal, a coarse single-bit description of each source-relay channel coefficient at the destination may suffice, as it results in only a small increase in uncoded bit error rates with respect to the case where full knowledge of the source-relay channel coefficients are exploited at the destination.

On the Performance of Multiple Relay Zero-Forcing Precoding Based on Limited Feedback

Recently, it has been shown in the literature that in a relaying network utilizing multiple relay precoding techniques, the signal-to-noise ratio (SNR) at each destination node will scale linearly with the number of relays K, which is referred to as the distributed array gain (DAG) K. In this paper, we focus on the performance of multiple relay precoding based on limited channel state information (CSI) feedback, which is different from the prior studies that assume perfect CSI at each of the relay nodes. Our analysis shows that the conventional limited feedback scheme fails to obtain the DAG K, which is a consequence of the phase ambiguity introduced by the channel quantization function. Based on the theoretical analysis, we propose a novel feedback and precoding procedure, and prove that the proposed procedure can obtain the DAG K with only one additional feedback bit for quantizing each relay-destination channel compared with the conventional scheme. Simulation results verify that with the proposed procedure, the SNR performance is effectively improved when the number of relays K is small, and scales linearly with K in relatively large K regime.

Cooperative communications with relay-selection: when to cooperate and whom to cooperate with?

In this paper; we propose a new cooperative communication protocol, which achieves higher bandwidth efficiency while guaranteeing the same diversity order as that of the conventional cooperative schemes. The proposed scheme considers <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">relay</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">selection</i> via the available partial channel state information (CSI) at the source and the relays. In particular, we discuss the multi-node decode-and-forward cooperative scenarios, where arbitrary N relays are available. The source determines when it needs to cooperate with one relay only, and which relay to cooperate with in case of cooperation, i.e., " <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">When</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">to</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cooperate?</i> " and " <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Whom</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">to</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cooperate</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">with?</i> ". An optimal relay is the one which has the maximum instantaneous scaled harmonic mean functionof its source-relay and relay-destination channel gains. For the symmetric scenario, we derive an approximate expression of the bandwidth efficiency and obtain an upper bound on the symbol error rate (SER) performance. We show that full diversity is guaranteed and that a significant increase of the bandwidth efficiency is achieved. Moreover, we present the tradeoff between the achievable bandwidth efficiency and the corresponding SER. Finally, the obtained analytical results are verified through computer simulations.

Practical Quantize-and-Forward Schemes for the Frequency Division Relay Channel

We consider relay channels in which the source-destination and relay-destination signals are assumed to be orthogonal and thus have to be recombined at the destination. Assuming memoryless signals at the destination and relay, we propose a low-complexity quantize-and-forward (QF) relaying scheme, which exploits the knowledge of the SNRs of the source-relay and relay-destination channels. Both in static and quasistatic channels, the quantization noise introduced by the relay is shown to be significant in certain scenarios. We therefore propose amaximum likelihood (ML) combiner at the destination, which is shown to compensate for these degradations and to provide significant performance gains. The proposed association, which comprises the QF protocol and ML detector, can be seen, in particular, as a solution for implementing a simple relaying protocol in a digital relay in contrast with the amplify-and-forward protocol which is an analog solution.

Combining Coded Signals with Arbitrary Modulations in Orthogonal Relay Channels

We consider a relay channel for which the following assumptions are made. (1) The source-destination and relay-destination channels are orthogonal (frequency division relay channel). (2) The relay implements the decode-and-forward protocol. (3) The source and relay implement the same channel encoder, namely, a convolutional encoder. (4) They can use arbitrary and possibly different modulations. In this framework, we derive the best combiner in the sense of the maximum likelihood (ML) at the destination and the branch metrics of the trellis associated with its channel decoder for the ML combiner and also for the maximum ratio combiner (MRC), cooperative-MRC (C-MRC), and the minimum mean-square error (MMSE) combiner.

Efficient ARQ protocols for exploiting cooperative relaying in wireless sensor networks

Cooperative relaying is an efficient technique to provide diversity in wireless sensor networks. In this paper, we exploit the limited feedback from the destination and propose a novel cooperative ARQ protocol, which combines the incremental relaying and selection relaying schemes. A relay node is requested to repeat the erroneously received packet, instead of the source node. Both simple and hybrid type I ARQ schemes are studied. An analysis model is established to analyze and compare the data link layer performances of different ARQ protocols in slow fading wireless channel. We prove two SNR thresholds of the relay–destination channel, above which the cooperative ARQ protocols have better performances than the traditional counterparts. In addition, the diversity performances of the various protocols are investigated and it is demonstrated that full order diversity (second-order in this case) can be exploited by the proposed cooperative ARQ protocol. Simulation results are given, which verify the theoretical analysis and comparison.

Cooperative ARQ protocol for correlated wireless channels

A novel Automatic repeat ReQuest (ARQ) protocol called cooperative ARQ is presented in this letter, where a relay terminal is requested to retransmit an erroneously received packet, instead of the source terminal. The data link layer Packet Error Rate (PER) performance of cooperative ARQ is derived in correlated wireless channel. The results show that even though the relay-destination channel is worse than the source-destination channel, the new protocol outperforms the traditional one as long as the average SNR of the relay-destination channel is better than a certain threshold. It is also demonstrated that a second order diversity gain can be achieved with the cooperative ARQ protocol.

Dual-Hop System Analysis in Nakagami-m Environment

In this paper, performance analysis of dual-hop transmission system is presented. The source-relay (S-R) and relay-destination (RD) channels experience Nakagami-m fading. The generalized case in which desired signal and cochannel interference (CCI) experience mutually different amount of fading is considered. Furthermore, analysis includes the case in which fading severity in S-R and R-D links can be unequal which is real scenario in practice. Outage probability, as an important performance measure, is considered. As an illustration of mathematical formalism, numerical results are presented to show the effects of system and channel parameters on overall performance. Ill. 5, bibl. 5 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.108.2.143