Non-orthogonal Amplify-and-forward Protocol Research Articles

Perbandingan Kinerja Non-Orthogonal dan Orthogonal Amplify and Forward pada Two-Way Cooperative WLAN

Nowadays, the advancement of Wireless Local Area Network (WLAN) technology has developed very rapidly because it is very practical and has effective mobility level. In practice, there is a major problem in wireless communications systems, which is fading. Fading can cause information signal power decreasing. Fading can be overcome using a cooperative communication system, which is a method that utilizes antenna from other users (relays), using principle of diversity, hence the performance of wireless communication system is improved. A relay has several protocols on cooperative communication system, such as Amplify and Forward (AF), Decode and Forward (DF), and Compress and Forward (CF). The AF protocol is divided into two types: Non-Orthogonal Amplify and Forward (NAF) and Orthogonal Amplify and Forward (OAF). In this paper, the performance comparison of two-way NAF and OAF in terms of outage probability, throughput, and spectral efficiency is investigated. The method used is computer simulation with system modeling and performance analysis. The simulation results show that OAF protocol can minimize outage probability and increase throughput and spectral efficiency, compared to NAF protocol on two-way WLAN cooperative network.

Distributed Space-Time Codes for Full-Duplex IR-UWB Amplify-and-Forward Cooperation

In this paper, we consider the problem of full-duplex (FD) relaying in the context of impulse-radio ultra-wideband (IR-UWB) communications. In particular, we propose two novel distributed space-time block codes (STBCs) suitable for the amplify-and-forward (AF) cooperation protocol with one and two relays. Despite the fact that FD relaying results in significant levels of interference between the transmit and receive antennas of each relay, it introduces new concepts to the problem of distributed STBC design. Compared to half-duplex (HD) STBC, FD-STBC is subject to an additional constraint that imposes the structure of the codewords while it offers the predominant advantage that resides in the possibility of including a smaller number of information symbols per codeword for achieving a full rate. We take advantage of this potential for constructing fully-diverse, full-rate and totally-real IR-UWB FD-STBCs that outperform the existing HD-STBCs for all practical levels of the residual self loop interference. In fact, for the sake of transmitting at full rate, the best known distributed HD-STBCs for the non-orthogonal AF protocol require the joint encoding/decoding of $4N_{r}$ symbols where $N_{r} $ is the number of relays. On the other hand, the proposed FD-STBCs require embedding only $N_{r} +2$ symbols per codeword for transmitting at full rate. Following from this fact, not only the decoding complexity is reduced, but also the coding gains are improved resulting in enhanced performance levels.

Linear Transceiver Design for Nonorthogonal Amplify-and-Forward Protocol Using a Bit Error Rate Criterion

The ever growing demand of higher data rates can now be addressed by exploiting cooperative diversity. This form of diversity has become a fundamental technique for achieving spatial diversity by exploiting the presence of idle users in the network. This has led to new challenges in terms of designing new protocols and detectors for cooperative communications. Among various amplify-and-forward (AF) protocols, the half duplex non-orthogonal amplify-and-forward (NAF) protocol is superior to other AF schemes in terms of error performance and capacity. However, this superiority is achieved at the cost of higher receiver complexity. Furthermore, in order to exploit the full diversity of the system an optimal precoder is required. In this paper, an optimal joint linear transceiver is proposed for the NAF protocol. This transceiver operates on the principles of minimum bit error rate (BER), and is referred as joint bit error rate (JBER) detector. The BER performance of JBER detector is superior to all the proposed linear detectors such as channel inversion, the maximal ratio combining, the biased maximum likelihood detectors, and the minimum mean square error. The proposed transceiver also outperforms previous precoders designed for the NAF protocol.

Performance Comparison of Orthogonal and Non-orthogonal AF Protocols in Cooperative Relay Systems

For a single relay channel, we compare the capacity of two different amplify-and-forward (AF) protocols, which are orthogonal AF (OAF) and non-orthogonal AF (NAF). The NAF protocol has been proposed to overcome a significant loss of performance of OAF in the high spectral efficiency region, and it was also theoretically proved that NAF performs better than OAF in terms of the diversity-multiplexing tradeoff. However, existing results have been evaluated at the asymptotically high signal to noise ratio (SNR), thus the power allocation problem between the source and the relay was neglected. We examine which protocol has better performance in a practical system operating at a finite SNR. We also study where a relay should be located if we consider the power allocation problem. A notable conclusion is that the capacity performance depends on both SNR and power allocation ratio, which indicates OAF may perform better than NAF in a certain environment.

Coding for the Nonorthogonal Amplify-and-Forward Cooperative Channel

In this paper, we consider the problem of coding for the half-duplex nonorthogonal amplify-and-forward (NAF) cooperative channel where the transmitter to relay and the interrelay links are highly reliable. We derive bounds on the diversity order of the NAF protocol that are achieved by a distributed space-time bit-interleaved coded modulation (D-ST-BICM) scheme under iterative APP detection and decoding. These bounds lead to the design of space-time precoders that ensure maximum diversity order and high coding gains. The word error rate performance of D-ST-BICM are also compared to outage probability limits.

Linear detection for the nonorthogonal amplify and forward protocol

In this paper, we present three new detection schemes for the nonorthogonal amplify and forward (NAF) protocol in a cooperative diversity system based on a multiuser detection approach, namely, a channel inversion type detector, a maximal-ratio combining (MRC) type detector, and a biased maximum likelihood (ML) detector. The decision variables in these schemes are linear functionals of the transmitted symbol vector and therefore they are termed as ldquolinearrdquo detectors. A cooperative relay network using the NAF protocol with N - 1 relays is considered where the source transmits symbols in N - 1 blocks of two time slots in a Rayleigh fading environment. For the case of a general linear space-time block coding scheme using K symbols, we present the performance of this protocol in terms of the code symbol error probability when the symbols come from an M-ary phase-shift keying constellation. The approach is further extended to the transmission in N - 1 blocks of L time slots. Numerical results show that the performance of the MRC type detector is superior to that of the channel inversion type detector, while the biased ML detector has the best performance. However, the MRC type detector has the lowest complexity while the biased ML detector the highest.

Optimization Issues for Cooperative Amplify-and-Forward Systems Over Block-Fading Channels

In this paper, we deal with an amplify-and-forward (AF) cooperative strategy in slot-based, block-fading environments. In contrast with previous schemes, which assume a constant channel during the cooperative frame (several slots), here, we relax this constraint and assume a classical quasi-static block- fading channel (constant for one slot). This additional degree of freedom modifies the behavior of the conventional nonorthogonal AF (NAF) schemes and generates a new block-fading NAF (BFNAF) protocol, where the source can usefully retransmit the same data during the cooperative slot. This new protocol is interesting at low spectral efficiencies, where diversity against fading is more important. To overcome performance degradation, which characterizes cooperative schemes at low signal-to-noise ratios (SNRs), an adaptive version of the considered schemes is also proposed, where cooperation is activated according to the outage behavior of the direct link. Moreover, an optimal hybrid protocol that allows intelligent switching between noncooperation, NAF, and BFNAF protocols is also proposed. Another issue that is discussed throughout this paper is the optimal power allocation of the investigated schemes. The proposed power-allocation strategy uses as an optimization criterion the well-defined asymptotic expressions of the outage probabilities, which are averaged over the fading statistics. The minimization (and avoidance for the nonhybrid protocols) of the required data feedback makes it suitable for practical ad hoc networks with crucial power constraints. The enhancement of the proposed schemes and the efficiency of the power allocation policy are shown by theoretical analysis and simulation results.