Full Cooperative Diversity Research Articles

Mitigating interference and reducing detection complexity in asynchronous cooperative relay network utilising new distributed space time block coding

The synchronisation in wireless cooperative relay networks is impossible to achieve in real environment utilising orthogonal space time block coding. There have been several approaches proposed to mitigate the effect of synchronisation among the relay nodes at the receiver. All have managed to reduce the inter-symbol interference at the expense of low data rate with high detection complexity. Others achieved full data rate and high cooperative diversity using high decoding complexity that requires a feedback link. In this paper, a new approach is presented that reduces inter-symbol interference, achieves full data rate and full cooperative diversity with low complexity. This uses a new efficient distributed orthogonal space time block coding design with a sub-optimum detection scheme utilising dual relay nodes. This reduces the number of timing misalignments among the relay nodes and minimises the detection complexity. Furthermore, the new proposed method uses linear decoding process to achieve full data rate and full cooperative diversity without the need for any a feedback link. The analytical analysis and simulation results confirmed that sub-optimum approach with the new efficient design are very effective at reducing the lack of synchronisation among the relay nodes at the destination node with low encoding and decoding complexities.

Distributed Space-Time Coding Based on the Self-Coding of RLI for Full-Duplex Two-Way Relay Cooperative Networks

In this paper, we consider full-duplex two-way relay cooperative networks, which allow the relaying of communications in both directions simultaneously and over the same frequency band. We propose a self-coded distributed space-time coding (SC-DSTC) scheme, in which the relay node performs a self-convolutional encoding and forms a distributed linear convolutional space-time code together with the direct link. The self-convolutional code at the relay is realized by using the stronger part of residual loop interference. The encoding process is implemented for both directions simultaneously through the local loop channel by a single amplifying factor, which is optimized when the loop channel information is imperfect. The simulation results show that the proposed SC-DSTC scheme can achieve asynchronous full cooperative diversity and is robust to the loop channel state information error at the relay when it is dominant among the interference and noise.

A reliable relay selection scheme for SSK modulation in cooperative communication systems

Space shift keying (SSK) modulation is a scheme in which the indices of active transmit antennas play an essential role in carrying information bits. In SSK modulation, the communication channel acts as modulating unit. Therefore, using the conventional relay selection schemes based on channel coefficients are impossible in cooperative systems using SSK modulation. In this paper, we propose a novel relay selection scheme that is applicable in cooperative systems using SSK modulation. The proposed scheme is based on calculating and measuring the Euclidean distances between received signal and all active or inactive channel coefficients. The proposed relay selection scheme is applied for a cooperative communication system with multiple relay nodes and a direct link between source and destination. The analytical expressions are derived to calculate the average bit error rate over Rayleigh fading channels. The analytical and simulation results show that this relay selection scheme can provide a full cooperative diversity order, for SSK modulation. In addition, we show that this scheme can be used at destination as a signal selection method, to select the best received signal from different paths. The analytical results are validated using Monte Carlo simulation studies.

Full Diversity Uncoordinated Cooperative Transmission for Asynchronous Relay Networks

Due to the distributed nature of cooperative communications systems, the cooperative signals arriving at the destination may not be perfectly aligned, i.e., the system is inherently asynchronous, and signal coordination among multiple relay nodes is imperative. In this paper, we propose a distributed space–time transmission scheme for a general asynchronous cooperative relay network. The scheme provides asymptotic full cooperative diversity, even when the signals arrive at the receiver asynchronously, which can be achieved by a low-complexity minimum-mean-square-error (MMSE) decision feedback equalizer (DFE) instead of the maximum-likelihood (ML) detector. Furthermore, signal coordination is no longer required, which avoids extra coordinating overhead. The proposed scheme applies for both general amplify-and-forward (AF) and decode-and-forward (DF) cooperative communications networks, such as coordinated multipoint/networked multiple-input–multiple-output (MIMO) systems, distributed antenna systems, and relay architecture for cellular systems. Simulation results confirm our analytical results.

Error Performance of Physical-Layer Network Coding in Multiple-Antenna Two-Way Relay Systems With Outdated CSI

In this paper, we study the impact of outdated channel state information (CSI) on the error rate performance in multiple-antenna two-way decode-and-forward (DF) relay systems, where physical-layer network coding (PNC) is adopted. We consider two variations of relay selection, namely, single best relay selection (S-RS) and multiple successfully-participated relay selection (MSP-RS). Under perfect and outdated CSI assumptions, closed-form expressions for the end-to-end system symbol error probability (SEP) are derived for the S-RS scheme, along with the asymptotic SEP expressions in high SNR regions for the MSP-RS scheme. By both analytical and simulation results, it is clearly shown that a full cooperative diversity gain can be achieved with perfect CSI. The results also manifest that the S-RS scheme can achieve only the transmit diversity gain with outdated CSI. On the other hand, the MSP-RS scheme can achieve a full cooperative diversity gain even if the CSI is outdated at the expense of high complexity.

A full-cooperative diversity beamformingscheme in two-way amplify-and-forward relay systems

Consider a simple two-way relaying channel in which two single-antenna sources exchange information via a multiple-antenna relay. For such a scenario, all the existing approaches that can achieve full cooperative diversity order are based on antenna/relay selection, for which the difficulty in designing the beamforming lies in the fact that a single beamformer needs to serve two destinations. In this paper, a new full-cooperative diversity beamforming scheme that ensures that the relay signals are coherently combined at both destinations is proposed, and analytical results are provided to demonstrate the performance gains. Moreover, the impact of channel estimation error is also evaluated. Finally, numerical results are provided to verify the accuracy of the provided analytical results, and also to show that this proposed scheme can outperform existing schemes based on antenna selection.

Multi-band Strategy for Cooperative Communication Networking with Unmatched Carrier Frequencies

In this paper, we consider the cooperative networking with the presence of multiple carrier frequency offsets at different relays, which is difficult to be handled. Such an imperfect networking is inevitable due to the distributed nature of the relay system and unmatched central frequencies at different relays. We propose a multi-band scheme for cooperative communications and provide theoretical analysis of the proposed cooperative networking based on the analytical upper bound of the channel orthogonality deficiency. Theoretical analysis and simulation results show that the proposed scheme achieves the full cooperative diversity and improves the system capacity, only adopting linear equalizers such as zero-forcing and minimum mean square error equalizers. Such advatange is normlly only enjoyed by a non-linear equalizers like maximum-likelihood equalizer, whose huge complexity is however usually unacceptable.

Near‐optimum detection scheme with relay selection technique for asynchronous cooperative relay networks

A new near-optimum detection scheme for asynchronous wireless relay networks is proposed to cancel the interference component at the destination node caused by timing misalignment from the relay nodes. The detection complexity at the destination node as compared with a previous sub-optimum detection scheme is reduced. Closed-loop extended orthogonal space time block coding and outer convolutive coding are utilised to maximise end-to-end performance. A relay selection technique is also proposed in this study for two dual-antenna relay nodes to enhance the system performance by selecting the best links and the smallest time delay error among the relay nodes. Simulation results confirm that the proposed near-optimum detection scheme with relay selection is very effective at removing intersymbol interference at the destination node and achieving full cooperative diversity with unity data transmission rate between the relay nodes and the destination node.

Algebraic Number Precoded OFDM Transmission for Asynchronous Cooperative Multirelay Networks

This paper proposes a space-time block coding (STBC) transmission scheme for asynchronous cooperative systems. By combination of rotated complex constellations and Hadamard transform, these constructed codes are capable of achieving full cooperative diversity with the analysis of the pairwise error probability (PEP). Due to the asynchronous characteristic of cooperative systems, orthogonal frequency division multiplexing (OFDM) technique with cyclic prefix (CP) is adopted for combating timing delays from relay nodes. The total transmit power across the entire network is fixed and appropriate power allocation can be implemented to optimize the network performance. The relay nodes do not require decoding and demodulation operation, resulting in a low complexity. Besides, there is no delay for forwarding the OFDM symbols to the destination node. At the destination node the received signals have the corresponding STBC structure on each subcarrier. In order to reduce the decoding complexity, the sphere decoder is implemented for fast data decoding. Bit error rate (BER) performance demonstrates the effectiveness of the proposed scheme.

Distributed Linear Convolutional Space-Time Coding for Two-Relay Full-Duplex Asynchronous Cooperative Networks

In this paper, a two-relay full-duplex asynchronous cooperative network with the amplify-and-forward (AF) protocol is considered. We propose two distributed space-time coding schemes for the cases with and without cross-talks, respectively. In the first case, each relay can receive the signal sent by the other through the cross-talk link. We first study the feasibility of cross-talk cancellation in this network and show that the cross-talk interference cannot be removed well. For this reason, we design space-time codes by utilizing the cross-talk signals instead of removing them. In the other case, the self-coding is realized individually through the loop channel at each relay node and the signals from the two relay nodes form a space-time code. The achievable cooperative diversity of both cases is investigated and the conditions to achieve full cooperative diversity are presented. Simulation results verify the theoretical analysis.

Precoding and Symbol Grouping for NAF Relaying in BICM Systems

This paper considers the precoder design for a bandwidth-efficient bit-interleaved coded modulation (BICM) system over nonorthogonal amplify-and-forward (NAF) single-relay channels with an arbitrary length of cooperative frame 2N. Based on the tight union bound to the bit error probability (BEP), we first derive an asymptotic design criterion with regard to a general 2N × 2N rotation matrix. This expression allows us to develop a class of precoders that not only achieves full cooperative diversity but optimizes the asymptotic error performance as well. Interestingly, the developed class of optimal precoders indicates that the source should keep silent in the cooperative phase. In the broadcasting phase, it is shown that power is equally distributed to 2N information symbols at the source. By further examining the structure of the optimal class of 2N × 2N precoders, it is then revealed that precoding over a group of at least two information symbols is sufficient to fully exploit diversity and coding advantages. Such a precoding technique, which is referred to as symbol grouping, therefore significantly reduces the system complexity without sacrificing the error performance. Among the pool of optimal precoders with respect to the asymptotic performance, the design of a precoder that provides a good convergence property is also discussed. Numerical examples show that the proposed precoder greatly improves the error performance of the cooperative system with low complexity.

Round-Robin Relaying With Diversity in Amplify-and-Forward Multisource Cooperative Communications

In this paper, a round-robin-based relay protocol dubbed round-robin relaying with source selection protocol (R3SSP) is proposed to achieve full cooperative diversity in multisource cooperative communication networks. In R3SSP, all the sources transmit their individual information in turn. The relays then forward the messages of some specific sources in a fixed order according to the limited feedback information. Compared with traditional relay selection-based protocols, R3SSP is based on round-robin relaying, thus avoiding relay selection and requiring no specific channel state information feedback. R3SSP can therefore be implemented with lower complexity. Furthermore, the exact and asymptotic expressions of the outage probability are derived. The diversity-multiplexing tradeoff (DMT) performance is also analyzed. Theoretical analysis shows that R3SSP achieves full cooperative diversity and provides better DMT performance than relay selection-based protocols in a system where the number of sources is higher than that of the relays. Based on the DMT analysis, we further propose an adaptive relay activation scheme that is capable of achieving higher DMT by dynamically selecting the number of relays to be activated in the entire network. Simulation results also verify the validity and superiority of R3SSP.

Cooperative Performance and Diversity Gain of Wireless Relay Networks

In this paper, the error rate performance and diversity gain of amplify-and-forward (AF) wireless relay networks are studied. The distributed space-time block code (DSTBC) in a synchronous relay network with multiple relay nodes is considered. The distributed linear dispersion code is used at the relays. The symbol (or codeword) error rate is studied in terms of upper and lower bounds through rigorous derivations, and the diversity gain of the DSTBC is derived, for any number of relay nodes. As a corollary, a necessary and sufficient condition is obtained for achieving full cooperative diversity. Arbitrary coding matrices at the relays, path loss and general linear power allocation are considered. Finally, the orthogonal frequency division multiplexing (OFDM)-based space-time transmission scheme in asynchronous cooperative networks is also discussed.

Distributed Space-Time Coding for Full-Duplex Asynchronous Cooperative Communications

In this paper, we propose two distributed linear convolutional space-time coding (DLC-STC) schemes for full-duplex (FD) asynchronous cooperative communications. The DLC-STC Scheme 1 is for the case of the complete loop channel cancellation, which achieves the full asynchronous cooperative diversity. The DLC-STC Scheme 2 is for the case of the partial loop channel cancellation and amplifying, where some loop signals are used as the self-coding instead of treated as interference to be directly cancelled. We show this scheme can achieve full asynchronous cooperative diversity. We then evaluate the performance of the two schemes when loop channel information is not accurate and present an amplifying factor control method for the DLC-STC Scheme 2 to improve its performance with inaccurate loop channel information. Simulation results show that the DLC-STC Scheme 1 outperforms the DLC-STC Scheme 2 and the delay diversity scheme if perfect or high quality loop channel information is available at the relay, while the DLC-STC Scheme 2 achieves better performance if the loop channel information is imperfect.

Designing Peak Power Constrained Amplify-and-Forward Relay Networks with Cooperative Diversity

Relay networks with amplify-and-forward (AF) protocol have attracted attention due to its high performance and low implementation complexity at the relay. To collect full cooperative diversity, the AF relay networks are facing two main issues. One is that the channel state information (CSI) of the source to relay link (i.e., two-hop information) is needed at the destination. The other concern is that the power scaling factor (PSF) and output signals at the relay are unbounded. These two issues make AF less practical in resource constrained networks, e.g., blind and peak power constrained relays. In this paper, we reveal the sufficient and necessary conditions on the PSF for the maximum ratio combining (MRC) receiver with two-hop CSI to achieve full cooperative diversity. Furthermore, we also provide necessary conditions on the PSF design so that MRC with one-hop CSI still collects full cooperative diversity. Based on these design criteria, we show a practical peak power constrained AF strategy so that neither the relay nor the destination node needs the source-relay CSI, yet full cooperative diversity can still be achieved.

A Unified Matching Framework for Multi-Flow Decode-and-Forward Cooperative Networks

Recent works have shown that cooperative diversity can be achieved by using relay selection (RS), distributed space-time coding (DSTC), and distributed beam-forming (DBF) in narrow-band decode-and-forward (DF) cooperative networks with one source-and-destination (s-d) pair. However, the joint resource allocation for broadband DF cooperative networks with multiple s-d flows has not received much attention yet. In this paper, a random hypergraph based unified matching framework is proposed, under which five feasible types of multi-flow DF cooperative networks will be considered. In each type, the maximum matching method will be applied to RS, DSTC, and DBF schemes so as to achieve the optimal channel allocation and relay selection with fairness assurance. By analyzing the properties of maximum matching, the outage probability of each s-d pair after resource allocation will be obtained. The results of diversity-multiplexing tradeoff will show that the proposed framework is capable of achieving the full frequency diversity and cooperative diversity for each s-d pair simultaneously, while the frequency multiplexing is equally shared. Based on the unified framework, the random rotation based parallel Hopcroft-Karp (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PHK) algorithm will then be designed, which can work in each destination node independently, and shall enjoy a poly-logarithmic complexity O(log <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2l</sup> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> N), where N is the number of channels and l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> is a constant.

A game‐theoretic approach for relay assignment over distributed wireless networks

ABSTRACTFor full cooperative diversity gains to be achieved while still maintaining spectral and energy efficiency, relay assignment schemes for cooperative communications have been extensively studied in recent research. These schemes select only the best relay from multiple relaying candidates to cooperate with a communication link. However, it is challenging to find the optimal relay in distributed wireless networks because of the dynamic nature of such networks. In this paper, we first formulate the problem of relay assignment as a noncooperative, mixed‐strategy, repeated game, where relaying candidates are modeled as rational players. We then propose a game‐theory‐based relay assignment scheme GTRA, in which each player plays against all the other players and determines whether to cooperate with a communication link on a packet‐by‐packet basis in a distributed manner. To adapt to dynamic environments, players utilized an adaptive learning algorithm, that is, modified‐regret‐matching algorithm, to learn optimal strategies of relay assignment, as well as to orient the game to converge to a set of correlated equilibriums, which is often more system efficient than a Nash equilibrium. To evaluate the performance of GTRA, we compare it with BR, a fictitious two‐player game‐based approach. Simulation results have shown that GTRA outperforms BR in terms of network throughput, especially in environments where the channel fading becomes severe. It is also shown that GTRA can converge to a correlated equilibrium in a short period that enables the GTRA to work well in dynamic environments. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Collocated and Distributed STBCs with Partial Interference Cancellation Decoding, Part I: Full-Diversity Criterion

Low complexity decoders called Partial Interference Cancellation (PIC) and PIC with Successive Interference Cancellation (PIC-SIC), which include the Zero Forcing (ZF) and ZF-SIC receivers as special cases, were given by Guo and Xia along with sufficient conditions for a Space-Time Block Code (STBC) to achieve full diversity with PIC/PIC-SIC decoding for point-to-point MIMO channels. In Part-I of this two part series of papers, we give new conditions for an STBC to achieve full diversity with PIC and PIC-SIC decoders, which are equivalent to Guo and Xia's conditions, but are much easier to check. We then show that PIC and PIC-SIC decoders are capable of achieving the full cooperative diversity available in wireless relay networks and give sufficient conditions for a Distributed Space-Time Block Code (DSTBC) to achieve full diversity with PIC and PIC-SIC decoders. In Part-II, we construct new low complexity full-diversity PIC/PIC-SIC decodable STBCs and DSTBCs that achieve higher rates than the known full-diversity low complexity ML decodable STBCs and DSTBCs.

Asynchronous cooperative communication systems: A survey on signal designs

Cooperative communications is a promising technique for future high speed wireless communications. These systems may be formulated as virtual multi-input multi-output (MIMO) systems where spatial/cooperetive diversity is a key advantage. However, different from MIMO systems, one of the major challenges for cooperative communications systems is that the cooperative transmissions in cooperative systems may be neither time nor frequency synchronized, since the transmissions are from multiple cooperative nodes at different locations. The existing signal designs for co-located MIMO systems may not be able to collect the cooperative diversity in cooperative communications systems. This paper gives an overview of recent research efforts on combating the time and frequency asynchronism of the cooperative communication network. We focus on the signal designs (or space-time codings/modulations) to achieve full cooperative diversity, and summarize some of the resent distributed space-timing coding and space-frequency coding techniques to combat timing errors and frequency offsets, and in the meantime to achieve full cooperative diversity, in both one-way and two-way cooperative networks.

Bandwidth-Efficient Bit-Interleaved Coded Modulation Over NAF Relay Channels: Error Performance and Precoder Design

This paper investigates the error performance and precoder design for a bandwidth-efficient bit-interleaved coded modulation (BICM) system over a nonorthogonal amplify-and-forward (NAF) half-duplex single-relay channel. A tight union bound on the asymptotic bit error probability (BEP) is first derived for an arbitrary block length of 2 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> , which corresponds to the case of using a 2 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> × 2 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> precoder. This bound provides a useful tool for predicting the error performance. Attention is then paid to the coded NAF system that uses a 2 × 2 precoder, where a closed-form expression of the bound is obtained. Based on this expression, an optimal class of 2 × 2 precoders with respect to the asymptotic performance is then developed. Unlike the optimal precoders that are designed for uncoded systems, the derived precoder indicates that the source only needs to send the superposition of the first symbol and the rotated version of the second symbol in the first time slot while being silent in the remaining slot to achieve the best asymptotic performance. For good convergence property, it is further shown that a rotation angle that maximizes the minimum Euclidean distance of the superposition constellation should be used. An optimal rotation angle is then analytically determined for various modulation schemes. Both analytical and simulation results show that the proposed precoders not only exploit full cooperative diversity but offer a significant coding gain over the optimal precoders for uncoded NAF systems as well.