Cooperative Diversity Scheme Research Articles

A low complexity distributed differential scheme based on orthogonal space time block coding for decode-and-forward wireless relay networks

<span lang="EN-US">This work proposes a new differential cooperative diversity scheme with high data rate and low decoding complexity using the decode-and-forward protocol. The proposed model does not require either differential encoding or channel state information at the source node, relay nodes, or destination node where the data sequence is directly transmitted and the differential detection method is applied at the relay nodes and the destination node. The proposed technique enjoys a low encoding and decoding complexity at the source node, the relay nodes, and the destination node. Furthermore, the performance of the proposed strategy is analyzed by computer simulations in quasi-static Rayleigh fading channel and using the decode-and-forward protocol. The simulation results show that the proposed differential technique outperforms the corresponding reference strategies.</span>

Distributed Spatial Modulation based Cooperative Diversity Scheme

In this paper, a distributed spatial modulation based cooperative diversity scheme for relay wireless networks is proposed. Where, the space-time block code is exploited to integrate with distributed spatial modulation. Therefore, the interested transmission scheme achieves high diversity gain. By using Monte-Carlo simulation based on computer, we showed that our proposed transmission scheme outperforms state-of-the-art cooperative relaying schemes in terms bit error rate (BER) performance.

Cooperation Diversity for Secrecy Enhancement in Cognitive Relay Wiretap Network Over Correlated Fading Channels

In this paper, we investigate the secrecy performance of dual-hop randomize-and-forward (RaF) cognitive relay multi-channel wiretap networks over correlated fading channels, in which the eavesdropper can wiretap the information from source and relays simultaneously. Specifically, in order to enhance the secrecy performance, we introduce two cooperation diversity schemes: 1) traditional partial relay selection (TPRS), where an optimal relay is selected to receive-and-forward the information based on the channel quality between the source and relays and 2) decoding threshold-aided optimal relay selection (DTaORS), where an optimal relay is selected from the threshold-based relay set based on the channel quality between the relays and destination. For these criteria, we analyze the secrecy performance of two cooperation diversity schemes by deriving the exact and asymptotic expressions for the secrecy outage probability of cognitive relay wiretap networks over correlated fading channels. From the results, we conclude that: 1) even though the channel correlation does not influence the secrecy diversity order, it is beneficial to the secrecy coding gain in high main-to-eavesdropper ratio regime; 2) DTaORS with an appropriate decoding rate can achieve better secrecy performance than TPRS. However, affected by the multi-channel wiretap, both of DTaORS and TPRS can not increase the secrecy diversity order any more, which is always equal to 1; and 3) the secrecy performance with a RaF scheme is better than that with a decode-and-forward scheme in multi-channel wiretap scenario.

Overlapping Coalition Formation Game for Resource Allocation in Network Coding Aided D2D Communications

Due to spectrum sharing, device-to-device (D2D) communications underlaying cellular networks enhance system capacity significantly that benefits services of local area. On the other hand, network coding enables highly efficient cooperation, which increases the system capacity through code-and-forward mechanism. It is a challenging problem that how to allocate resource in the network coding aided cooperative D2D communications. In this paper, we first design a network coding aided cooperative diversity scheme for D2D communication, and derive the system transmission rate with the consideration of interference. Then, we formulate the problem of joint spectrum resource allocation and relay selection as an overlapping coalition formation game, where one relay is able to serve multiple coalitions to increase the system capacity. For each coalition, maximum bipartite graph matching model is established to select the optimal relay to achieve the maximum transmission rate. Finally, to solve the formulated game problem, we propose a distributed algorithm based on switch operations with low computation complexity. Extensive numerical results demonstrate that our solution increases the system transmission rate by about 30-40 percent without bringing extra computation complexity, compared with other state-of-the-art schemes.

Transceiver Grouping: A Novel Diversity Method for Collaborative Multiuser FSO Communications

In this paper, we propose a novel multipoint-to-multipoint cooperative diversity scheme for multiuser free-space optical (FSO) communications. This scheme is motivated by the inherit immobility and directivity of FSO communications where several transceivers mounted on a given building can be easily interconnected for achieving enhanced diversity levels through joint encoding/decoding. In this case, the $N$ users are clustered in a number of groups depending on the state of the FSO network. Users of a given group transmit the same encoded symbol comprising the information of all these users while maximum-ratio combining is implemented at the receive apertures. We present an asymptotic analysis of the bit error rate and derive the achievable diversity orders over the gamma–gamma turbulence-induced fading channels affected by pointing errors. Results show that while grouping all users in one group achieves the highest diversity order, this partitioning is suboptimal for practical ranges of the signal-to-noise ratio. In this context, the partitioning of the $N$ users turns out to be of crucial importance where the optimal grouping outperforms the all-user grouping by several orders of magnitude.

Incremental relaying cooperative networks with dual transmit diversity

This paper studies the performance of cooperative wireless networks using incremental-relaying and dual transmit diversity with the simple orthogonal space time block coding (OSTBC) scheme. The proposed model is studied by utilizing different relaying schemes including decode and forward (DF), amplify and forward (AF), and adaptive incremental-relaying (i.e., best relay selection) with DF relaying. In particular, upper-bounded expressions are derived for the averagebit error rate (BER), signal to noise ratio (SNR) outage probability, average achievable rate, and normalized throughput. Detailed results show that the dual transmit diversity approach outperforms the regular incremental relaying cooperative diversity scheme in terms of transmission power and channel efficiency for the same transmit power. Moreover, best relay selection with multiple relaying nodes outperforms fixed incremental DF relaying, especially for lower transmitted SNR values.

Low-Latency Multi-Flow Cooperative Broadcast in Fading Wireless Networks

Though a cooperative broadcast scheme has been proposed for fading environments, it has two defects: First, it only handles a packet flow from a single source node in the network, but does not consider the scenario of multiple packet flows simultaneously broadcasted from different source nodes. Second, it only allows a single relay node to forward a packet in each time slot, though multiple relay nodes forwarding in a time slot can significantly reduce broadcast latency. In this paper, we aim achieve low-latency multi-flow broadcast in wireless multi-hop networks with fading channels. To describe the interference among the transmission in different flows, we incorporate the Rayleigh fading model to the signal to noise ratio (SNR) model. Then, we introduce a cooperative diversity scheme which allows multiple relays forwarding in a time slot to reduce broadcast latency. We then formulate an interesting problem: In a fading environment, what is the optimal relay allocation schedule to minimize the broadcast latency? We propose a warm up heuristic algorithm for single-flow cooperative broadcast, based on which, we further propose a heuristic algorithm for multi-flow cooperative broadcast. Simulation results demonstrate that the two algorithms achieve lower broadcast latency than a previous method.

Joint design of physical and MAC layer by applying the constellation rearrangement technique in cooperative multi-hop networks

Cooperative diversity schemes can be seen as an extension of spatial diversity systems, where distributed antennas are placed in relay nodes distributed in space as compared to a single multi-antenna source or receiver in conventional spatial diversity systems. Such cooperative communication systems improve the diversity gain significantly. In this paper a cross layer optimization scheme, based on cooperative diversity along with constellation rearrangement, is proposed for minimizing energy toll and enhancing the network longevity. By utilizing a cross-layer cooperative strategy, distributive algorithms are proposed for the dependability restriction multi-hop networks. We demonstrate through simulations that the proposed cross-layer cooperative strategies along with constellation rearrangement achieve considerable energy savings and extend the network longevity significantly. Finally the proposed scheme is evaluated through NS2 simulations in terms of throughput and delay.

An Improved Transmission Scheme in Cooperative Communication System

Abstract—Recently developed cooperative diversity scheme enables a terminal to get transmit diversity through the support of other terminals. However, most of the introduced cooperative schemes have a common fault of decreased transmission rate because the destination should receive the decodable compositions of symbols from the source and the relay. In order to achieve high data rate, we propose a cooperative scheme that employs hierarchical modulation. This scheme is free from the rate loss and allows seamless cooperative communication.

Performance analysis of DCSK-SR systems based on best relay selection in multiple MIMO relay environment

A relay selection based differential chaos shift keying (DCSK) cooperative diversity scheme is proposed, namely DCSK selection relaying (DCSK-SR). Multiple multiple-input multiple-output (Multiple MIMO) relays are used to cooperate with the source node. The relays and the destination employ multiple antennas to exploit the benefit of diversity combining. The relay which maximizes the total received signal-to-noise ratio (SNR) at the destination is selected for cooperation, where all the relays adopt decode-and-forward (DF) protocol. Probability density function (PDF) of the SNR of the received signal at each hop is derived. The bit-error-rate (BER) of the proposed scheme is evaluated in Nakagami-m fading channels. Results show that the proposed scheme performs better compared to the single MIMO relay cooperation scheme. Numerical and simulation results are obtained and plotted for the parameters of interest.

Cooperative diversity scheme using SPC in MIMO‐OFDMA system

A method to obtain high diversity gain is proposed by spatial phase coding (SPC) in the cooperative multiple input multiple output-orthogonal frequency division multiple access (MIMO-OFDMA) system. SPC provides improved diversity gain dramatically in proportion to the number of received paths although the one-bit feedback information is used. Moreover, the cooperative MIMO-OFDMA system has received paths without additional antennas more than the conventional MIMO-OFDMA system. Therefore, SPC can improve reliability in the cooperative MIMO-OFDMA system effectively.

Decode-and-forward relaying based on orthogonalcomplementary codes

In this note, we propose a full-duplex decode-and-forward cooperative diversity scheme based on code division with orthogonal complementary codes. We consider a simple case in which a single user is assisted by a single relay to achieve cooperative diversity. When the cooperation is full-duplex, the operational delay of the relay makes the channel asynchronous and this may cause multiple-access interference (MAI) between the user and relay. The orthogonal complementary codes have perfect autocorrelation and cross-correlation properties that provide MAI-free operation in asynchronous channels. In the proposed scheme, the user and relay terminals spread their messages with complementary codes and the spread messages can reach the destination without interfering with each other. The numerical results reveal that the proposed scheme reaches the same bit-error-rate performance in both synchronous and asynchronous channels. The results are also compared with the conventional orthogonal code sets, such as Hadamard sets, which fail to provide diversity.

General switch‐and‐examine relaying for demodulate‐and‐forward cooperative diversity

SummaryTwo new demodulate‐and‐forward schemes of multi‐relay cooperative diversity with switch‐and‐examine relaying (SER) are analyzed. To reduce relay usage and enhance bandwidth efficiency, the two new cooperative diversity schemes employ a switch‐based relay selection. The proposed schemes consume less communication resource than regular relaying schemes, such as the selection combining (SC) or maximal ratio combining (MRC) schemes that always use all relays, and also achieve better performance than distributed switch‐and‐stay schemes. In the first scheme, the decision statistic for relay usage and selection is based on the signal‐to‐noise ratio (SNR). In the second scheme, the log‐likelihood ratio (LLR) of received signals is used for the decision of relay usage and selection. With the two SER schemes, the bit error probability (BEP) of binary phase shift keying (BPSK) and the average number of used paths are derived and expressed in closed‐form for the independent and identically distributed (i.i.d.) Rayleigh fading channels. Numerical and simulation results are presented for performance illustrations. According to the numerical results, the LLR‐based SER not only achieves a lower BEP but also consumes less relay resource than the SNR‐based SER. Furthermore, the LLR‐based SER scheme even outperforms the corresponding SNR‐based SC scheme for a range of average SNR. Copyright © 2014 John Wiley & Sons, Ltd.

An Optimization Framework for XOR-Assisted Cooperative Relaying in Cellular Networks

This work seeks to address two questions in cooperative OFDMA networks: First, how network coding based cooperative diversity can be exploited effectively when overhearing is not readily available. Second, how to realize various forms of gains available, including multi-user diversity, cooperative diversity, and network coding. The main contribution of this paper is an unifying network utility maximization framework that jointly considers relay assignment, relay strategy selection, channel assignment and power allocation. We formulate the optimization problem both with and without XOR-CD, a simple XOR-assisted cooperative diversity scheme. We show that the optimization of physical layer resource allocation with XOR-CD is equivalent to a weighted 3-set packing problem, which is NP-complete, and can be efficiently solved with provably the best approximation factor. Without XOR-CD, the problem reduces to a weighted bipartite matching problem which can be optimally solved.

Performance Analysis of Relaying Strategies in Cooperative Diversity Scheme

Wireless network nowadays demands high service quality, high data rates, network coverage, and minimum processing time. The 2G/3G are not sufficient to fulfill the demands for high data rates due to limited availability of bandwidth and energy. Future wireless broadband applications are required to have data rates that are hundreds of megabits per second. A new 4G standard provides high data rate transmission and long range communication, it will give full broadband service for fixed and mobile users and it uses a new technology called multiple-input multiple-output system (MIMO) because it increases the spectrum efficiency also. Cooperative diversity is a virtual MIMO and is introduced due to practical constraints on the number of antennas at the base station. Cooperative diversity scheme comprises of source, relay and destination nodes. In this paper, we are comparing two relaying strategies (amplify-and-forward and decode-and-forward) with BPSK and QPSK modulation at source and different combining techniques at destination.

Large-Scale Site and Frequency Diversity in Urban Peer-to-Peer Channels for Six Public-Safety Frequency Bands

We report on peer-to-peer large-scale wireless channel characteristics for an urban environment in six public-safety bands, for five simultaneous receiving sites. Results are based upon measurements taken in Denver in July 2009 with stationary receivers and a pedestrian transmitter. The six frequencies at which we measured are (in MHz) 430, 750, 905, 1834, 2400, and 4860. We quantify both site and frequency diversity, and show that 5-site selection yields minimum average gains of 15 dB in mean received power levels; 5-site selection diversity also reduces received power variation by 17-29 dB, depending on frequency. Frequency diversity yields similar gains. By approximating received powers as lognormal, we describe an analytical method to approximate the cdf of the per-site, or per-frequency (or both) maximum received power. These data and diversity models should be useful for public-safety and ad hoc communication system designers, and for cooperative diversity schemes, wherein multiple users act as a virtual array.

Cooperative multicasting based on superposition and layered coding

Cooperative diversity plays an important role in combating channel fading and increasing reliability of wireless communication links. The main purpose of cooperative diversity is to transmit the same data from multiple sources. Hence, there is no inherent capability in the cooperative diversity schemes to deal with scalable types of data, for example, scalable video coded signals. The authors introduce a two-phase cooperative multicast scheme based on superposition coding to transmit scalable video signals. The new scheme mixes the superposition with cooperative diversity, and chooses the right parameters in both schemes to enhance the system's multicast capability. This study also derives an exact closed-form expression of the average multicast group throughput in case of Rayleigh flat fading channel. The closed-form expression allows system designers to choose the correct cooperation and superposition parameters to satisfy the network operator needs. Simulations show that, in addition to the additional degrees of freedom resulting from using cooperation with superposition, the proposed scheme outperforms the conservative scheme and schemes solely exploiting cooperative relaying or superposition. Simulations show that the new scheme can increase the average network throughput more than four times compared to the conservative scheme.

Design and Analysis of Transceiver for Combating Turbulence Induced Fading over Fso Links

In this paper, we investigate the cooperative diversity technique as a candidate solution for combating turbulence induced fading over Free-Space Optical (FSO) links. In particular, a one-relay cooperative diversity scheme is proposed and analyzed for non-coherent FSO communications with intensity modulation and direct detection (IM/DD). The error performance is derived in semi-analytical and closed-form expressions in the presence and absence of background radiation, respectively. Results show the enhanced diversity orders that can be achieved over both Rayleigh and lognormal fading models. In this transceiver design coherent transmitter and receiver design is carried out with the reference to q-ary PPM(pulse position modulation).performance analysis is carried out in all possible strategy.

Multi-Relay Turbo-Coded Cooperative Diversity Networks Over Nakagami- <formula formulatype="inline"><tex Notation="TeX">$m$</tex></formula> Fading Channels

This paper studies a multi-relay adaptive turbo-coded cooperative diversity scheme over Nakagami- m fading channels. In the underlying scheme, after receiving a fraction of the codeword determined by a tradeoff parameter denoted by f, all the relays decode, and only the reliable relays forward the rest of the codeword to the destination. We assume binary phase-shift keying modulation and analyze the scheme under study in terms of bit error rate (BER) and outage probability. Union bounds on the BER are derived using the transfer function bounding and the limit-before-average techniques. Furthermore, we examine the asymptotic behavior of the system in the high-signal-to-noise-ratio (SNR) regime using the derived pairwise error probability (PEP). We also derive a closed-form expression for the outage probability of the system and its high-SNR approximation to evaluate the achievable diversity order. Simulations are provided to assess the accuracy of our analytical work.

Diversity and Delay Analysis of Buffer-Aided BICM-OFDM Relaying

In this paper, we study a cooperative diversity scheme for wireless systems where the relay is equipped with a buffer. We consider practical frequency—selective channels and adopt the combination of bit interleaved coded modulation and orthogonal frequency division multiplexing (BICM—OFDM). We propose a novel link selection protocol for BICM—OFDM systems where the relay either transmits or receives in a given time slot depending on the quality of the links. We derive a closed—form upper bound for the asymptotic worst—case pairwise error probability (PEP) and the diversity gain of the considered buffer—aided relaying scheme for both infinite and finite buffer size. We show that significant diversity gains can be achieved with buffer—aided relaying compared to conventional relaying at the expense of larger packet delays. In fact, for buffers of infinite (or very large) size, the diversity gain is doubled for links with identical frequency diversity, and an even higher diversity gain advantage is possible for links with non—identical frequency diversities. Furthermore, we perform an exact closed—form average delay analysis for buffers of both finite and infinite size which provides important insight into the achieved delay—performance tradeoff. The derived analytical results and performance gains are corroborated by extensive simulation results.