Distributed Space-time Coding Research Articles

Survey on DSTC and PA-PSO Algorithmthrough Cross Layer Designin MANET

MANETs are used to economically extend coverage & capacity of existing GSM,UMTS & Wi-Fi networks.Performance of MANET protocol AODV is studied by using cross -layer interaction between different layers e.g. among physical,MAC & network layer using Received Signal Strength as cross layer interaction parameter.Here we study different algorithms such as DSTC(Distributed Space Time Coding) and PA-PSO(Power Allocation-Part icle Swarm Optimisation).We get improvised throughput and effective capacity maximisation in the output.

Differential Distributed Space-Time Coding With Imperfect Synchronization in Frequency-Selective Channels

Differential distributed space-time coding (D-DSTC) is a cooperative transmission technique that can improve diversity in wireless relay networks in the absence of channel information. Conventionally, it is assumed that channels are flat-fading and relays are perfectly synchronized at the symbol level. However, due to the delay spread in broadband systems and the distributed nature of relay networks, these assumptions may be violated. Hence, inter-symbol interference (ISI) may appear. This paper proposes a new differential encoding and decoding process for D-DSTC systems with multiple relays over slow frequency-selective fading channels with imperfect synchronization. The proposed method overcomes the ISI caused by frequency-selectivity and is robust against synchronization errors while not requiring any channel information at the relays and destination. Moreover, the maximum possible diversity with a decoding complexity similar to that of the conventional D-DSTC is attained. Simulation results are provided to show the performance of the proposed method in various scenarios.

Iterative Network-Channel Decoding with Cooperative Space-Time Transmission

One of the most efficient methods of exploiting space diversity for portable wireless devices is cooperative communication utilizing space-time block codes. In cooperative communication, users besides communicating their own information, also relay the information of other users. In this paper we investigate a scheme where cooperation is achieved using two methods, namely, distributed space-time coding and network coding. Two cooperating users utilize Alamouti space time code for inter-user cooperation and in addition utilize a third relay which performs network coding. The third relay does not have any of its information to be sent. In this paper we propose a scheme utilizing convolutional code based network coding, instead of conventional XOR based network code and utilize iterative joint network-channel decoder for efficient decoding. Extrinsic information transfer (EXIT) chart analysis is performed to investigate the convergence property of the proposed decoder.

Delay–Interleaved Cooperative Relay Networks

In this letter, we propose a novel system design for implementing distributed space-time codes (DSTCs) in order to improve the performance of the codes. The proposed method called delay and interleaved cooperative relay networks manages to force transmitted signals to experience different channel fading coefficients as much as possible, which increases the coding gain or even, in some cases, the diversity order of the codes. The only degradation to the conventional system is a small delay that is negligible in many communication applications. There are no extra computational complexities burdened to the relays, and only a simple permutation is performed at the relays and the destination. Simulation results also confirm the performance superiority of this innovative method over the conventional DSTC system.

Improved maximum a posteriori signal detection for amplify‐and‐forward relay networks with imperfect channel state information

In amplify-and-forward wireless relay networks, channel state information is required at the destination for signal detection when coherent distributed space-time coding is performed at the relays. The authors consider in this study signal detection in the case of imperfect partial channel knowledge at the destination. For the case of maximum a posteriori signal detection, they propose a modified detector formulation that takes the variance of channel estimation errors into account, and reduces the impact of channel uncertainty on the receiver performance. They show that the proposed modification permits a significant performance improvement, while increasing only slightly the receiver's complexity. It is of special interest for non-constant modulus signal constellations of relatively large size, as well as for relatively low pilot powers.

Bounded Delay-Tolerant Space-Time Codes for Distributed Antenna Systems

Distributed space-time codes (STCs) can achieve cooperative diversity in distributed antenna systems. But the path delay difference may cause diversity loss. In this paper, a family of asynchronous STC is proposed to achieve full diversity, given that the path delay difference is within a tolerance bound. The proposed code structure allows the overall decoding process to be decomposed into several independent sub-processes, which can be tackled by low-complexity maximum-likelihood decoders. Two code designs based on the Alamouti code and the Golden code are given for a system with two distributed antennas. Moreover, two designs based on orthogonal STC and fast group decodable STC are introduced for a system with four distributed antennas, with each transmitter having two antennas. Full diversity gain is proved for all code designs and their associated decoding complexities are analyzed. Simulations of the proposed codes confirm our theoretical results on full diversity gain.

Space-Time Network Coding With Overhearing Relays

Space time network coding (STNC) is a recently proposed time-division multiple-access (TDMA)-based cooperative relaying scheme for multi-relay wireless systems, which can achieve full diversity order with low transmission delay by taking advantage of the concepts of network coding and distributed space time coding. However, STNC does not fully exploit the benefit of the broadcast nature of wireless channels, since it only allows relays to receive signals from the sources. To explore the potential capacity of STNC-based systems, in this paper, we propose a new cooperative relaying scheme, termed space-time network coding with overhearing relays (STNC-OR), by allowing each relay to collect the signals transmitted from not only the sources but also its previous relays. Then, we derive some explicit expressions for the outage probability and symbol error rate (SER) for STNC-OR with decode-and-forward relaying over independent non-identically distributed (i.n.i.d) Rayleigh fading channels. For comparison, we also derive the explicit expression of the outage probability for STNC. To further improve the performance of STNC-OR, we investigate the effect of relay ordering on the performance of STNC-OR and then present the optimal relay ordering algorithm. Further, a suboptimal relay ordering is also designed to reduce the complexity. Extensive simulation and numerical results are presented finally to validate our theoretical analysis. It is shown that the proposed STNC-OR achieves much lower outage probability and SER than STNC and traditional pure TDMA relaying schemes.

Static hybrid multihop relaying and two hops hybrid relaying using DSTC

In this paper, we propose a static hybrid multihop relaying protocol where some relays amplify the received signal whereas the remaining ones use decode and forward (DF) relaying. The relaying mode in each relay is set using the distance between the different nodes and the average SNR. The exact and asymptotic bit error probabilities, the block error probability and the throughput of hybrid automatic repeat request (HARQ) protocols are derived. Simulation results are provided in different contexts to compare the performance of hybrid relaying to conventional AF and DF relaying. In the second part of the paper, we propose a static hybrid amplify and forward (AF) and DF relaying using distributed space-time coding (DSTC). Relays close to the source amplify the received signal, and the remaining relays transmit only if they correctly decoded. All AF relays and DF relays that have correctly decoded transmit using DSTC in order to benefit from spatial diversity. The proposed protocol offers better performance than AF relaying using DSTC and similar performance to DF relaying using DSTC. However, the complexity and transmission delays of the proposed static hybrid AF-DF relaying is lower than that of DF relaying since decoding is not performed at AF relays.

Effective Capacity Maximization in Multirelay Networks With a Novel Cross-Layer Transmission Framework and Power-Allocation Scheme

Effective capacity (EC) is a valuable metric in investigating the impact of the physical-layer infrastructure on the quality of service (QoS) of the data link layer. By means of the EC, this paper provides a link-layer look at the concept of multirelaying transmission. A closed-form expression for the EC of a multirelay network is derived to simplify the computation of this quantity. It is shown that increasing the number of relays leads to an unavoidable reduction in EC. Some techniques such as best relay selection (BRS) and distributed space-time coding (DSTC) are used to solve this problem. It is found that the EC performance of BRS, DSTC, and direct transmission schemes extremely depends on the amount of QoS exponent θ. Inspired by this dependence, a novel interesting cross-layer relaying transmission framework is introduced, in which the best scheme of transmission is selected for maximizing the EC, according to the amount of θ and the channel gain. Then, by the goal of EC maximization under a given θ, a cross-layer fixed power-allocation (PA) algorithm is proposed based on the particle swarm optimization (PSO) algorithm. The numerical results validate our analytical outcomes and evaluate our proposed algorithms. The complexity of the proposed algorithms is analyzed at the end of this paper.

Adaptive power allocation strategies for distributed space‐time coding in cooperative MIMO networks

Adaptive power allocation (PA) algorithms with different criteria for a cooperative multiple-input multiple-output network equipped with distributed space-time coding are proposed and evaluated. Joint constrained optimisation algorithms to determine the PA parameters and the receive filter are proposed for each transmitted symbol in each link, as well as the channel coefficients matrix. Linear receive filter and maximum-likelihood detection are considered with amplify-and-forward and decode-and-forward cooperation strategies. In these proposed algorithms, the elements in the PA matrices are optimised at the destination node and then transmitted back to the relay nodes via a feedback channel. The effects of the feedback errors are considered. Linear minimum mean square error expressions and the PA matrices depend on each other and are updated iteratively. Stochastic gradient algorithms are developed with reduced computational complexity. Simulation results show that the proposed algorithms obtain significant performance gains as compared with existing PA schemes.

Performance Analysis and Optimization of the Relay Multicast System with Space-Time Coding

In a sector of a single cell, due to the fading characteristic of wireless channels, several decode-and-forward relay stations are deployed to form a two-hop relay-assisted multicast system. We propose two schemes for the system, the first scheme combines the use of space-time code and distributed space-time code (DSTC), and the second one combines the use of DSTC and maximum ratio combining. We give an outage probability analysis for both of them. Based on this analysis, we manage to maximize the spectral efficiency under a preset outage probability confinement by finding out the optimal power allocation and relay location strategies. We use genetic algorithms to verify our analysis and numerical results show that the schemes proposed by us significantly outperform the scheme in previous work. We also show the effect of path loss exponent on the optimal strategy.

Distributed Space-Time Code with Mutual Information Based Soft Information Relaying

In this letter, we investigate a distributed space-time coded soft information relaying. In particular, we focus on mutual information based soft forwarding (MIF) scheme with Alamouti space-time block code. In order to achieve a full diversity order, we propose a weighted amplifying factor based on average soft noise variance instead of instantaneous one. The exact analytical expression for average soft noise variance is first derived. A tight upper bound of the average soft noise variance is also derived in closed-form. It is shown that the proposed distributed MIF Alamouti scheme can achieve a full diversity order, and outperforms various distributed Alamouti schemes reported in the literature.

A Fully Distributed Geo-Routing Scheme for Wireless Sensor Networks

When marrying randomized distributed space-time coding (RDSTC) to beaconless geo-routing, new performance horizons can be created. In order to reach those horizons, however, beaconless geo-routing protocols must evolve to operate in a fully distributed fashion. In this letter, we expose a technique to construct a fully distributed geo-routing scheme in conjunction with RDSTC. We then demonstrate the performance gains of this novel scheme by comparing it to one of the prominent classical schemes.

On the performance of distributed space-time coded cooperative relay networks based on inter-relay communications

A new protocol, called fully distributed space-time coded (FDSTC) protocol having information exchange between relays, is proposed and compared with the conventional distributed space-time coded (DSTC) protocol using non-regenerative relays (NR-relays) and regenerative relays (R-relays). Closed-form error probabilities are derived to verify the simulations. In terms of error performance, the FDSTC protocol gets significant average signal-to-noise ratio (SNR) gains (3.7 dB for NR-relays and 18.1 dB for R-relays). In addition, the impact of the relative distance of relays on the required SNR is reduced up to 70%. The system diversity order using the FDSTC protocol is higher than that using the DSTC protocol (especially, the FDSTC protocol obtains full diversity with NR-relays). As a result, at the same spectral efficiency, FDSTC has better performance in terms of outage probability in high SNR regions. In terms of energy efficiency, the FDSTC protocol is shown to outperform DSTC for long-range transmissions.

An Inter Symbol Interference Estimation and Cancellation Scheme for Asynchronous Distributed Differential Space-Time Code

In cooperative communication systems, as poor synchronization of different relays may induce inter symbol interference (ISI) and lead to substantial performance degradation, it is necessary to cancel ISI. In this letter, a simple ISI estimation and cancellation scheme is proposed for asynchronous distributed differential space-time code, where the destination node does not need to know the channel state information (CSI) from the source node to different relays or the CSI from the relays to the destination node. Simulation results show that the proposed scheme can cancel ISI effectively and obtain good bit error rate performance.

Soft decode-and-forward cooperative communication with distributed space-time coding

In existing soft decode-and-forward (SDF) cooperative communication systems, the source node is idling in the second time phase while the relay transmits the soft information. In fact, the source can transmit the hard information that cooperates with the relay's soft information using distributed space-time block codes (DSTBC). In this paper, we theoretically derive the detection performance in the second time phase by either using or not using the DSTBC based on the assumption that the soft information can be approximated by Gaussian distribution. This result also enables the optimal power allocation between the source and the relay in the second time phase. Finally, we show via simulation that the advantage of using DSTBC in the second time phase leads to the overall performance improvement of the coded cooperative system.

Diversity Analysis of Randomized Linear Dispersion Codes in a Half-Duplex Amplify-and-Forward Multiple-Relay System

A point-to-point multiple-relay communication system with half-duplex constraints is considered. The relays operate under the amplify-and-forward paradigm and implement a linear dispersion distributed space-time code with randomized dispersion matrices of independent and identically distributed entries. The large-signal-to-noise-ratio behavior of the asymptotically large deterministic system is studied for both the optimum (maximum likelihood) receiver and the linear minimum mean squared error (LMMSE) receiver. The diversity order of the system is shown to have a strong dependence on the aspect ratio of the linear dispersion matrices. More specifically, when the linear dispersion matrices are sufficiently tall, both receivers achieve the maximum diversity order, i.e., the total number of relays plus one. Conversely, when the linear dispersion matrices are fat (in the sense that relays linearly compress the information received from the source), the optimum receiver is shown to achieve an asymptotic diversity order of two, whereas the LMMSE receiver is totally unable to exploit the available spatial diversity.

Adaptive Distributed Space-Time Coding Based on Adjustable Code Matrices for Cooperative MIMO Relaying Systems

An adaptive distributed space-time coding (DSTC) scheme is proposed for two-hop cooperative MIMO networks. Linear minimum mean square error (MMSE) receive filters and adjustable code matrices are considered subject to a power constraint with an amplify-and-forward (AF) cooperation strategy. In the proposed adaptive DSTC scheme, an adjustable code matrix obtained by a feedback channel is employed to transform the space-time coded matrix at the relay node. The effects of the limited feedback and the feedback errors are assessed. Linear MMSE expressions are devised to compute the parameters of the adjustable code matrix and the linear receive filters. Stochastic gradient (SG) and least-squares (LS) algorithms are also developed with reduced computational complexity. An upper bound on the pairwise error probability analysis is derived and indicates the advantage of employing the adjustable code matrices at the relay nodes. An alternative optimization algorithm for the adaptive DSTC scheme is also derived in order to eliminate the need for the feedback. The algorithm provides a fully distributed scheme for the adaptive DSTC at the relay node based on the minimization of the error probability. Simulation results show that the proposed algorithms obtain significant performance gains as compared to existing DSTC schemes.

Distributed space‐time coding with decode‐and‐forward–amplify‐and‐forward selection relaying protocol in cooperative wireless sensor networks

Distributed space-time coding (DSTC) with an efficient relaying protocol, referred to as amplify-and-forward and decode-and-forward (DF-AF) selection relaying, has not received much attention yet. In the DF-AF selection relaying-aided DSTC transmissions, each relay could adaptively process the received signal according to its decoding state to improve the performance. In this study, the authors analyse the pairwise error probability (PEP) performance, the diversity order and the union bound on the error probability of the DSTC with DF-AF selection relaying in cooperative wireless sensor networks. More specifically, by introducing a random variable vector to denote the decoding state of the relays, the upper bounds of PEP are derived first for the DSTC with DF-AF selection relaying based on the Chernoff bound. Then, the diversity order and the union bound on the error probability are obtained based on the upper bounds of PEP. Finally, simulation results verify the theoretical analysis and demonstrate that the DSTC with DF-AF selection relaying has better error performance than the DSTC with DF protocol and the DSTC based on AF protocol.

Cooperative Relaying in Next-Generation Mobile WiMAX Networks

Distributed space-time coding (DSTC) is a key physical (PHY) layer technique to enable cooperative relaying in wireless networks. Compared with direct transmission and single-relay cooperation, DSTC exploits spatial diversity gain and achieves a higher end-to-end throughput performance. In particular, a novel variation of DSTC, which is called randomized DSTC (R-DSTC), further enhances the performance of conventional DSTC in a mobile environment due to its decentralized relay recruitment. This paper presents a medium access control (MAC) protocol, which is called CoopMAX, for Worldwide Interoperability for Microwave Access (WiMAX) systems to provide cooperative relaying with DSTC and R-DSTC techniques by the use of fixed and mobile relays. CoopMAX explores a joint PHY layer and MAC layer optimization for rate adaptation. The efficiency of CoopMAX is investigated, showing pronounced advantages, such as a doubling of throughput as compared with conventional WiMAX protocols in some typical scenarios.