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Full-rate and full-diversity extended orthogonal space-time block coding in cooperative relay networks with imperfect synchronization
Abstract
In this paper we present a novel extended orthogonal space-time block coding (EO-STBC) scheme for three and four relay nodes to use in asynchronous cooperative relay networks. This approach attains full-rate and full-diversity in that each hop attains unity rate and all four uncorrelated paths are utilized. Robustness against the effects of random delays at the relay nodes is enhanced through the use of a low-rate feedback channel. A new low complexity phase feedback scheme has been proposed which can retain the advantage of the perfect feedback scheme with substantial reduction in the feedback overhead. Orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP) is used at the source node to combat the timing errors at the relay nodes, which operate in a simple amplify-and-forward (AF) mode. Simulations show that our new scheme outperforms the previous schemes and uses a very simple symbol-wise maximum-likelihood (ML) decoder.
... -Alotaibi and Chambers [49] proposes a novel transmission scheme for three and four relaying node asynchronous AF WRNs, using the same model as [29]. This transmission scheme employs the OFDM with a cyclic prefix, along with a low-rate feedback channel, to provide a robustness which can counter the time misalignment among the relaying nodes. ...
... It also provides an additional robustness in the form of fourth order spatial diversity, in addition to coding gain. Alotaibi and Chambers [49] examine the system under the assumption of frequency-selective fading channel. This scheme requires a feedback channel over two relaying nodes to maximize the received SNR, which may introduce some additional design complexity. ...
Deployment of Space-Time Block Code (STBC) over wireless relaying communication networks has been identified as one of the most promising techniques because of its potential to support high-performance and high data-rate for wireless communication technologies of the future. It is called Distributed-STBC (D-STBC) as it uses clients’ nodes as relaying nodes to form a virtual Multiple-Input Multiple-Output (MIMO) channel. However, this requires perfect synchronization among the relaying nodes. Unfortunately, as this is impossible to achieve in real world networks, the structure of the code matrix is compromised causing the channel to appear dispersive. This paper firstly derives a general model of D-STBC systems which will then be used to show the effects of imperfect synchronization on such schemes. Then, it highlights the majority of the schemes used to mitigate the performance degradation due to the asynchronism. In addition, it suggests some schemes that could be considered when conditions of imperfect synchronization exist.
This paper proposes a dual-hop amplify-and-forward (AF) relay system which employs a modified transmit antenna selection (TAS)/orthogonal space-time block coding (OS-TBC) scheme in both signaling links (i.e., Source→Relay and Relay→Destination) that provides reduced feedback-rate and robust error performance in the presence of feedback errors (FEs) when compared to the conventional TAS/OSTBC (C-TAS/OSTBC). The error probability performance of the proposed dual-hop AF relay scheme in Nakagami fading channels has been examined via Monte Carlo simulations.
Signal detection for an asynchronous 4-relay-node cooperative cellular system using Distributed Space-Time Coding (DSTBC) on the uplink is investigated in this paper, where co-channel interference (CCI) limits the system capacity more than thermal noise and inter-symbol-interference (ISI) caused by the imperfectly synchronized cooperating relays greatly degrades the system performance. Most research has so far focused on applying DSTBC with 2 relay nodes to cooperative communications on individual links rather than in a cellular environment, and assumed perfect synchronization among all the relays. This paper derives a signal detector based on parallel interference cancellation and successive interference cancellation to remove the CCI and ISI within an asynchronous cooperative cellular system. Simulation results demonstrate the effectiveness of the proposed scheme in suppressing the impact of co-channel interference and imperfect synchronization.
In this paper, we present a new robust scheme for use in asynchronous cooperative networks over frequency-selective channels through using three and four relay nodes. Based on extended orthogonal space-time block coding (EO-STBC), we have presented a direct quantized feedback approach that can achieve full cooperative diversity and array gain with unity code rate over each hop. In this scheme, we have employed orthogonal frequency division multiplexing (OFDM) type pre-coding at the source node to combat multipath fading and timing errors from relay nodes by using cyclic prefix insertion for the broadcasted and relayed signals. To reduce the feedback overhead significantly we have proposed a quantized group feedback approach which can enhance the system performance. Simulation results show that the proposed scheme yields a significant improvement in bit error rate performance over the previous scheme that has been implemented over two relays and uses a very simple symbol-wise maximum-likelihood decoder.
Cooperative relays have recently been proposed and studied for mobile ad hoc networks. It has been shown that under perfect symbol synchronization, parallel relays with space-time modulation can yield more than 10 dB power savings over conventional serial relays in a highly mobile environment. We analyze the effect of synchronization errors on the performance of parallel relays, and also study several effective methods to reduce the negative impact of synch errors. Our study shows that when the synch errors are much smaller than a symbol interval, the performance of parallel relays deteriorates gracefully. We have also found that well designed space-time coding techniques, such as TR-STC and ST-OFDM, can be highly effective in combating large synch errors with only marginal reduction of data rate.
We apply the idea of space-time coding devised for multiple-antenna systems to the problem of communications over a wireless relay network with Rayleigh fading channels. We use a two-stage protocol, where in one stage the transmitter sends information and in the other, the relays encode their received signals into a "distributed" linear dispersion (LD) code, and then transmit the coded signals to the receive node. We show that for high SNR, the pairwise error probability (PEP) behaves as (logP/P)<sup>min{TH}</sup>, with T the coherence interval, that is, the number of symbol periods during which the channels keep constant, R the number of relay nodes, and P the total transmit power. Thus, apart from the log P factor, the system has the same diversity as a multiple-antenna system with R transmit antennas, which is the same as assuming that the R relays can fully cooperate and have full knowledge of the transmitted signal. We further show that for a network with a large number of relays and a fixed total transmit power across the entire network, the optimal power allocation is for the transmitter to expend half the power and for the relays to collectively expend the other half. We also show that at low and high SNR, the coding gain is the same as that of a multiple-antenna system with R antennas. However, at intermediate SNR, it can be quite different, which has implications for the design of distributed space-time codes
In this paper we propose complex extended orthogonal space-time block codes (EO-STBCs) with feedback for wireless relay networks with the assumption of quasi-static flat fading channels. Full rate in each stage and full cooperative diversity for distributed EO-STBCs (D-EO-STBCs) are achieved by providing channel state information (CSI) at certain relay nodes. Two closed-loop schemes are proposed which make use of limited feedback from the destination node to a particular number of relay nodes, not exceeding half of the total number of such relay nodes. In our simulations, we use four relay nodes. Simulation results show that these two closed-loop D-EOSTBCs achieve full cooperative diversity in addition to array gain with linear processing. In particular, the proposed D-EO-STBCs designs preserve low decoding complexity and save both transmission power and total transmit time between source and destination.
Cooperative diversity, which employs multiple nodes for the simultaneous relaying of a given packet in wireless ad hoc networks, has been shown to be an effective means of improving diversity, and, hence, mitigating the detrimental effects of multipath fading. However, in previously proposed cooperative diversity schemes, it has been assumed that coordination among the relays allows for accurate symbol-level timing synchronization at the destination and orthogonal channel allocation, which can be quite costly in terms of signaling overhead in mobile ad hoc networks, which are often defined by their lack of a fixed infrastructure and the difficulty of centralized control. In this paper, cooperative diversity schemes are considered that do not require symbol-level timing synchronization or orthogonal channelization between the relays employed. In the process, a novel minimum mean-squared error (MMSE) receiver is designed for combining disparate inputs in the multiple-relay channel. Outage probability calculations and simulation results demonstrate the not unexpected significant performance gains of the proposed schemes over single-hop transmission, and, more importantly, demonstrate performance comparable to schemes requiring accurate symbol-level synchronization and orthogonal channelization
In this letter, we propose a simple orthogonal frequency-division multiplexing (OFDM) scheme for an asynchronous cooperative system, where OFDM is implemented at the source node, and time-reversion and complex conjugation are implemented at the relay nodes. The cyclic prefix (CP) at the source node is used for combating the timing errors from the relay nodes. In this scheme, the received signals at the destination node have the Alamouti code structure on each subcarrier, and thus, it has the fast symbol-wise ML decoding. It should be emphasized that the relay nodes only need to implement the time-reversion, some sign changes from plus to minus, and/or the complex conjugation to the received signals, and no IDFT or DFT operation is needed. It is shown that this simple scheme achieves second-order diversity gain without the synchronization requirement at the relay nodes.
For mobile users without antenna arrays, transmission diversity can be achieved with cooperative space-time encoded transmissions. However, a challenge is the lack of perfect synchronization on delay, timing and carrier frequency of distributed transmitters, which destroys the required space-time signal structure. In this letter, a new transmission scheme is proposed which employs distributed space-time block codes to achieve full diversity while tolerating imperfect synchronization. It is promising in distributed wireless networks such as sensor networks both to enhance transmission energy efficiency and to reduce synchronization cost.
This paper presents a simple two-branch transmit diversity scheme.
Using two transmit antennas and one receive antenna the scheme provides
the same diversity order as maximal-ratio receiver combining (MRRC) with
one transmit antenna, and two receive antennas. It is also shown that
the scheme may easily be generalized to two transmit antennas and M
receive antennas to provide a diversity order of 2M. The new scheme does
not require any bandwidth expansion or any feedback from the receiver to
the transmitter and its computation complexity is similar to MRRC
In current cooperative communication schemes, to achieve cooperative diversity, synchronization between terminals is usually assumed, which may not be practical since each terminal has its own local oscillator. In this paper, based on the stack construction proposed by Hammons and El Gamal, we first construct a family of space-time trellis codes for BPSK modulation scheme that is characterized to possess the full cooperative diversity order without the synchronization assumption. We then generalize this family of the space-time trellis codes from BPSK to higher order QAM and PSK modulation schemes based on the unified construction proposed by Lu and Kumar. Some diversity product properties of space-time trellis codes are studied and simplified decoding methods are discussed. Simulation results are given to illustrate the performance of the newly proposed codes
We develop and analyze space-time coded cooperative diversity protocols for combating multipath fading across multiple protocol layers in a wireless network. The protocols exploit spatial diversity available among a collection of distributed terminals that relay messages for one another in such a manner that the destination terminal can average the fading, even though it is unknown a priori which terminals will be involved. In particular, a source initiates transmission to its destination, and many relays potentially receive the transmission. Those terminals that can fully decode the transmission utilize a space-time code to cooperatively relay to the destination. We demonstrate that these protocols achieve full spatial diversity in the number of cooperating terminals, not just the number of decoding relays, and can be used effectively for higher spectral efficiencies than repetition-based schemes. We discuss issues related to space-time code design for these protocols, emphasizing codes that readily allow for appealing distributed versions.
A simple quasi-orthogonal space-time scheme for use in asynchronous virtual antenna array enabled cooperative networks
- M Hayes
- J A Chambers
- M D Macleod