Adaptive Decode-and-forward Research Articles

Analysis of Variable Bit Rate SOFDM Transmission Scheme Over Multi-Relay Hybrid Satellite-Terrestrial System in the Presence of CFO and Phase Noise

In this paper, the exact closed-form signal-to-interference-noise ratio (SINR) expression, for the joint impact of carrier frequency offset (CFO) and phase noise (PHN), is derived for each channel link in a multi-relay hybrid satellite-terrestrial broadcast system, employing the Walsh Hadamard (WH) based spread-orthogonal frequency multiplexing (S-OFDM) and OFDM transmission scheme at satellite terminal and terrestrial repeaters (relays) respectively. Additionally, bit error rate and spectral efficiency are analyzed for such hybrid system with $M$ -relay, based on the obtained SINR expressions. To examine that, an adaptive decode and forward (ADF) strategy is employed at relay terminals. Also, three-state Fontan Land Mobile Satellite and six-path typical urban terrestrial channel models are considered. This analysis is performed to support variable bit rate (VBR) quality of service at the physical layer of Digital Video Broadcast Satellite Handheld (DVB-SH)-A architecture, the provision of which is absent in the DVB-SH standard. VBRs are assumed for S-OFDM. The results illustrate that both single-relay and three-relay ADF-based VBR WH-SOFDM yield an identical performance in the presence of the combined effect of CFO and PHN, under both performance measures. However, the improvement in performance for the three-relay strategy is observed in the presence of CFO only. Further, a pilot-based channel estimation technique is performed at the receiver, and the estimated error variance is evaluated for every channel link. Later, the block-by-block system computational complexity of single-relay and $M$ -relay ADF-based VBR WH-SOFDM is evaluated. It is shown that the complexity of the $M$ -relay ADF strategy is rate dependent and almost $M-1$ times the single-relay strategy. Hence, an increase in the number of relays would not yield any significant performance gain, but would enhance the system computational complexity considerably. Therefore, for high data rate transmission, the single-relay ADF-based WH-SOFDM scheme could be a suitable candidate for hybrid satellite-terrestrial communication systems in future.

TAS-Based Incremental Hybrid Decode–Amplify–Forward Relaying for Physical Layer Security Enhancement

In this paper, a transmit antenna selection (TAS)-based incremental hybrid decode–amplify–forward (IHDAF) scheme is proposed to enhance physical layer security in cooperative relay networks. Specifically, TAS is adopted at the source in order to reduce the feedback overhead. In the proposed TAS-based IHDAF scheme, the network transmits signals to the destination adaptive select direction transmission (DT) mode, AF mode, or DF mode depending on the capacity of the source-relay link and source-relay link. In order to fully examine the benefits of the proposed TAS-based IHDAF scheme, we first derive its secrecy outage probability (SOP) in a closed-form expression. We then conduct asymptotic analysis on the SOP, which reveals the secrecy performance floor of the proposed TAS-based IHDAF scheme when no channel state information is available at the source. Theoretical analysis and simulation results demonstrate that the proposed TAS-based IHDAF scheme outperforms the selective decode-and-forward, the incremental decode-and-forward, and the noncooperative DT schemes in terms of the SOP and effective secrecy throughout, especially when the relay is close to the destination. Furthermore, the proposed TAS-based IHDAF scheme offer a good tradeoff between complexity and performance compared with using all antennas at the source.

Performance comparison of dual‐hop hybrid decode‐or‐amplify‐forward relay schemes for M‐ary quadrature amplitude modulation burst transmission over Rayleigh fading channels

SummaryThis paper shows the analytical performance expressions of M‐ary quadrature amplitude modulation burst symbol transmission for hybrid decode‐or‐amplify‐forward (HDAF) relay schemes over quasi‐static Rayleigh‐fading channels. First, we derive the probability density function of the received instantaneous signal‐to‐noise ratio as the simplified form, which is related to all the possible occurrence probabilities of error‐events for M‐ary quadrature amplitude modulation burst transmission. On the basis of the derived probability density function, we express average bit error probability, average symbol error probability, and average burst error rate as closed forms, which can be also applied to both amplify‐and‐forward and adaptive decode‐and‐forward (ADF) schemes. The analysis and simulation results show that HDAF scheme for burst transmission can achieve the performance of ADF scheme with symbol‐by‐symbol transmission, which is the achievable lower bound. Furthermore, the outage probability, the normalized channel capacity, and the goodput performance are also derived as closed forms. The analysis shows the superiority of HDAF scheme to ADF scheme. Comparison with simulations confirms that the derived analytical expressions are accurate over all signal‐to‐noise ratio regions and for different numbers of relays and modulation orders.

Fading Correlations for Wireless Cooperative Communications: Diversity and Coding Gains

We theoretically analyze outage probabilities of the lossy-forward (LF), decode-andforward (DF), and adaptive decode-and-forward (ADF) relaying techniques, with the aim of characterizing the impact of the spatial and temporal correlations of the fading variations. First, the exact outage probability expressions are analytically obtained for LF, DF, and ADF relaying assuming each link suffers from statistically independent Rayleigh fading. Then, approximated, yet accurate closed-form expressions of the outage probabilities for the relaying schemes are derived. Based on the expressions, diversity and coding gains are found. The mathematical methodology for the derivation of the explicit outage probability is further extended to the case, where the account is taken of the spatial and temporal correlations of the fading variations. The diversity gains with LF, DF, and ADF are then derived in the presence of the correlations. It is found out that the three techniques can achieve full diversity, as long as the fading variations are not fully correlated. We then investigate the optimal relay location and the optimal power allocation for the three relaying techniques. It is shown that the optimal solutions can be obtained under the framework of convex optimization. It is revealed that in correlated fading, the relay should move close to the destination or allocate more transmit power to the relay for achieving lower outage probabilities, compared with the case in independent fading.

A Comparative Study on the Performance of LLR- and SNR-Based Hybrid Relaying Schemes

A comparative study on the theoretical bit error rate (BER) is presented for hybrid relaying schemes that toggle between adaptive decode-and-forward (ADF) and amplify-and-forward (AF) protocols, for a typical three-node wireless network. Toggling between the two forwarding protocols is based on the log-likelihood ratio (LLR) or the signal-to-noise ratio (SNR) of the received signal at the relay node. Closed-form expressions for the probability of error are presented, as well as the expressions of the proposed schemes’ gains over classical ADF and AF protocols. Comparisons are carried out among the two schemes and other hybrid schemes found in the literature. Moreover, the impact of relay location on the probability of error is investigated.

OFDM based link adaptive one-way DF relaying

OFDM based one-way DF relaying has recently received significant attention to improve the reliability and performance of wireless communication systems. In this paper, link adaptive relaying (LAR) approach which combats performance degradation due to error propagation in digital relaying has been applied to the OFDM based one-way DF relaying. It is shown that the power of sub-carriers can be scaled to reduce the error propagation to the destination which improves the BER performance of system. The power scaling is obtained from source-relay and relay-destination channel knowledge. The proposed system has the advantage of low complexity and it can help the relay use the power more efficiently. The error performance analysis of proposed system over frequency selective Nakagami-m fading channel is investigated. The results show that the proposed system outperforms the non-link adaptive based system. BER derivation is given for Rayleigh fading channel (m=1) under high signal to noise ratio (SNR). Monte-Carlo simulation results are provided in order to confirm the obtained numerical results by considering various position of relay.

On the Spectral Efficiency of Selective Decode-and-Forward Relaying

Multirelay cooperative relaying enables spatial diversity, often at the expense of spectral efficiency. To alleviate the loss in spectral efficiency due to half-duplex relaying and transmission over orthogonal channels, we propose a novel transmission scheme for selective decode-and-forward (DF) networks. In this scheme, we assume that destination may receive signals from transmitting nodes with different modulation levels. Particularly, we obtain a closed-form expression for both end-to-end (E2E) average error probability and spectral efficiency in such a scheme. Subsequently, using these closed-form expressions and average channel statistics, we perform joint optimization of power allocation and modulation level selection to maximize the E2E spectral efficiency while maintaining a target E2E average error probability and a set of transmit power constraints. Simulation results demonstrate that the transmission scheme proposed herein improves the E2E spectral efficiency significantly, in comparison with the conventional adaptive DF transmission scheme.

Impact of M-ary Data Symbol Burst Transmission on Averaged Channel Capacity for ADF Relay Systems

In this paper, we consider M-ary phase shifting keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) data symbol burst transmission for adaptive decode-andforward (ADF) relay systems over quasi-static Rayleigh fading channels. A burst has pilot symbols and data symbols. From pilot symbols, we can estimate the channel gain and detect each relay node’s transmission mode for ADF schemes. At first, we focus on the derivation of the received signal to noise ratio’s (SNR’s) probability density function (PDF) for ADF relay systems, in which error events at relay nodes and channel estimation errors are considered. Then, we derived the averaged channel capacity as an approximated closed-form for an arbitrary link signal-to-noise ratio (SNR) for different modulation orders. We verified its accuracy by comparison with simulation results.

Approximated Outage Probability for ADF Relay Systems with Burst MPSK and MQAM Symbol Transmission

In this paper, we derive the outage probability for M-ary phase shifting keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) burst transmission (BT) of adaptive decode-and-forward (ADF) cooperative relay systems over quasi-static Rayleigh fading channels. Within a burst, there are pilot symbols and data symbols. Pilot symbols are used for channel estimation schemes and each relay node’s transmission mode selection schemes. At first, we focus on ADF relay systems in which the probability density function (PDF) is derived on the basis of error events at relay nodes corresponding to channel estimation errors. Next, the average outage probability is derived as an approximate expression for an arbitrary link signal-to-noise ratio (SNR) for different modulation orders. Its accuracy is demonstrated by comparison with simulation results. Further, it is confirmed that BT-ADF relay systems with pilot symbol based channel estimation schemes enables to select correctly decoded relay nodes without additional signaling between relay nodes and the destination node, and it is verified that the ideal performance is achieved with small SNR loss.

Impact of relay placement on diversity order in adaptive selective DF relay-assisted FSO communications.

The impact of relay placement on diversity order in adaptive selective decode-and-forward (DF) cooperative strategies is here investigated in the context of free-space optical (FSO) communications over atmospheric turbulence channels with pointing errors when line of sight is available. The irradiance of the transmitted optical beam here considered is susceptible to moderate-to-strong turbulence conditions, following a gamma-gamma (GG) distribution together with a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Novel closed-form approximate bit error-rate (BER) expressions are obtained for a cooperative FSO communication setup with N relays, assuming that these relays are located in an area similar to an annulus around source or destination node. An analytical expression is here found that determines the best selection criterion based on the knowledge of the channel state information (CSI) of source-relay or relay-destination links in order to significantly increase the diversity order corresponding to the cooperative strategy under study. It is concluded that the highest diversity order is achieved when the relation β(SR(min)) > β(SD) + β(R(min)D) is satisfied, wherein β(SR(min)), β(R(min)D) and β(SD) are parameters corresponding to the atmospheric turbulence conditions of source-relay and relay-destination link with the greatest scintillation index, and source-destination link, respectively.

Burst-by-Burst Adaptive DF Relay Systems with PSA-CE Methods over Quasi-Static Rayleigh Fading Channels

In this paper, we propose an analytical approach for adaptive decode-and-forward (ADF) relaying schemes consisting of burst data transmission based on pilot symbol assisted-channel estimation (PSA-CE) methods over quasi-static Rayleigh fading channels. At first, we focus on the error-event at relay nodes in which the transmission mode switching is carried out burst by burst, whereas previous studies assumed the transmission mode switching symbol-by-symbol, thus showing lower error rate bound. Under consideration of burst transmission for ADF relay systems, we derive exact error rate expressions which better estimate the performance of actual systems. Then, the average bit and burst error rates are derived in approximated expressions for an arbitrary link signal-to-noise ratio (SNR) related with channel estimation errors. Their accuracy is confirmed by comparison with simulation results. Furthermore, ADF relay systems with PSA-CE schemes are confirmed to select correctly decoded relay nodes without additional signaling between relay nodes and the destination node and it is verified to achieve the performance at a cost of negligible SNR loss.

Upper Bound for Average Outage Probability of BT-ADF relay networks Over Quasi-Static Rayleigh Fading channels

In this paper, we propose the analytical approach for burst transmission (BT) adaptive decode-and-forward (ADF) relaying schemes consisting of burst transmission over quasistatic Rayleigh fading channels. At first, we focus on the error-event at relay nodes for symbol burst transmission, whereas previous researches considered one data symbol transmission so that they showed the best performance bounds. By considering symbol burst for ADF relay systems, we derive an exact outage probability expression which can be the performance of practical systems. Furthermore, the average outage probability is derived in approximated closed-form upper bound for an arbitrary link SNR. The derived analytical approach is verified based on the number of relays and burst symbols. Its accuracy is confirmed by comparison with simulation results.

Cooperative mobile-to-mobile communications over double Nakagami- m fading channels

Double Nakagami-m fading model can be used to provide a realistic description of the mobile-to-mobile (M2M) channel. The moment generating function (MGF)-based approach is used to derive the symbol error probability (SEP) expressions for the multiple-mobile-relay-based M2M system. Under the consideration of better performance and lower complexity, both decode-and-forward (DF) and amplify-and-forward (AF) protocols are addressed in this study. For adaptive DF (ADF) relaying, the asymptotic SEP at high signal-to-noise ratio regime in addition to the exact SEP formulations are derived. Furthermore, the impacts of channel estimation error for the insight of non-ideal channel estimation are analysed. For fixed-gain AF (FAF) relaying, the authors present approximate SEP and asymptotic SEP to indicate the cooperative gain. For L mobile relays and under the assumption of independent and identically distributed (i.i.d) source- relay channels and i.i.d relay-destination channels, it is shown in this paper that asymptotic diversity orders of L × min(mRD,1, mRD,2) + min(mSD,1, mSD,2) and L × min(mSR,1, mSR,2, mRD,1, mRD,2) + min(mSD,1, mSD,2) can be achieved for ADF-M2M and FAF-M2M schemes, respectively. Simulations are performed to verify the analytical results.

네트워크 코딩 기반의 협력통신에서 Hybrid AF and DF 방식의 아웃티지 성능 분석 및 최적 파워 할당 기법

네트워크 코딩은 멀티캐스트 네트워크에서 전송량을 증가시키기 위해 제안된 기법으로 최근에는 다수의 사용자가 성능 향상을 위해서로의 자원을 공유하는 협력통신에 네트워크 코딩을 적용하는 연구가 활발히 진행 중이다. 네트워크 코딩 기반의 협력통신에서 사용자는 자기 자신의 데이터와 다른 사용자의 데이터를 네트워크 코딩 연산을 통해 결합하여 전송한다. 기존의 연구에서는 네트워크 코딩을 기반으로 한 적응형 복호 후 전송(Network-Coding-based Adaptive Decode-and-Forward, NC-ADF) 방식이 다이버시티(diversity) 이득과 추가적인 전송량 증대를 가져올 수 있음을 보였다. 본 논문에서는 기존 프로토콜의 성능 증대와 네트워크 코딩의 이득을 극대화 하기 위해 사용자간 채널의 상태에 따라 증폭 후 전송(Amplify-and-Forward, AF) 방식과 복호 후 전송(Decode-and-Forward, DF) 방식을 적응적으로 적용한 새로운 네트워크 코딩 기반의 협력통신 기법을 제안하였다. 또한 제안한 기법의 아웃티지 확률을 구하고 높은 SNR 영역에서 최대 다이버시티 차수(full diversity order)를 가짐을 보였다. 나아가 추가적인 성능 향상을 위해 본 논문에서 제안된 기법에 의한 아웃티지 확률을 기반으로 최적의 전송 파워 비율을 구하였다. Network coding was proposed to increase the achievable throughput of multicast in a network. Recently, combining network coding into user cooperation has attracted research attention. For cooperative transmission schemes with network coding, users combine their own and their partners messages by network coding. In previous works, it was shown that adaptive DF with network coding can achieve diversity gain and additional throughput gain. In this paper, to improve performance of conventional protocols and maximize advantage of using network coding, we propose a new network coding based user cooperation scheme which uses adaptively amplify-and-forward and decode-and-forward according to interuser channel status. We derive outage probability bound of proposed scheme and prove that it has full diversity order in the high SNR regime. Moreover, based on the outage bound, we compute optimal power allocation for the proposed scheme.

Cooperative multiple relay system for frequency selective environment: outage analysis and power allocation

AbstractIn this paper, we propose a novel cooperative relaying scheme with multiple relays for frequency selective wireless environment. In our proposed scheme, the frequency selective wireless channel is divided into flat fading sub‐channels. Cooperative relaying is then employed over each sub‐channel to improve the system diversity order. We then investigate the asymptotic behavior of the outage probability and show that the proposed scheme achieves full diversity order in both amplify and forward (AF) and adaptive decode and forward (ADF) relaying scenarios. Furthermore, we propose a power allocation strategy to minimize the system outage probability. Simulation results confirm our analysis and show that the proposed power allocation method outperforms uniform power allocation. Copyright © 2010 John Wiley & Sons, Ltd.

Performance Analysis of Adaptive Decode-and-Forward Cooperative Single-Carrier Systems

A cyclic prefixed single-carrier (CP-SC) relay network incorporating an adaptive decode-and-forward (ADF) protocol is proposed in this paper. For a two-hop ADF protocol, a general expression for the effective end-to-end signal-to-noise ratio (ESNR) is examined for multiple relays. With the help of a derived probability density function (pdf) for the ESNR, closed-form expressions for the outage probability and an asymptotic average symbol error rate (AASER) are obtained. An asymptotic analysis revealing the diversity gain is also performed. Monte Carlo simulations verify these derived analytical results.

불완전한 채널정보를 사용하는 다중안테나 적응형 복호 후 전송 중계 프로토콜의 Diversity-Multiplexing Tradeoff 분석

본 논문에서는 적응형 복호 후 전송 (decode-and-forward) 중계 프로토콜이 송신을 위해 불완전한 채널정보를 사용할 때, 목적지 노드에서만 다중 안테나를 사용하는 경우, 릴레이 노드에서만 다중안테나를 사용하는 경우, 그리고 소스 노드에서만 다중 안테나를 사용하는 경우에 대한 diversity-multiplexing tradeoff (DMT) 상계 함수들을 유도하여 그 결과를 제시한다. 또한 소스 노드와 목적지 노드, 소스 노드와 릴레이 노드, 릴레이 노드와 목적지 노드 사이의 불완전한 채널정보들이 점근적 조건하에 있을 경우, 적응형 복호 후 전송 중계 프로토콜이 얻을 수 있는 다이버시티 이득을 조사한다. In this paper, assuming that the transmitter can exploit imperfect channel state information (CSI), the diversity-multiplexing tradeoff (DMT) functions of three adaptive decode-and-forward (DF) relay protocols, each of which uses multiple-antennas at the destination node, at the relay node, or at the source node are derived. When the imperfect CSI qualities for the source-relay link, the relay-destination link, and the source-destination link are subject to asymptotic conditions, the additional diversity gains attainable by exploiting the imperfect CSI at the transmitter for those three adaptive DF relay protocols are investigated.

Multi-branch decode-and-forward cooperative diversity networks performance analysis over Nakagami- m fading channels

In this study, the performances analysis of cooperative-diversity networks using adaptive decode-and-forward (DF) relaying over independent non-identical flat Nakagami-m fading channels is investigated. The authors derive exact and approximate closed-form expressions for the error probability, outage probability and average channel capacity, and analyse their dependence on the channel parameters. In adaptive DF relaying, among M relays that can participate, only C relays (C≤M), with good channels to the source, DF (retransmit) the source information to the destination. Then, the destination combines the direct and the indirect signals using maximum ratio combining technique. The authors derive a closed-form expression for the the moment generating function of the total signal-to-noise ratio (SNR) at the destination node. Then, the authors find an exact closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the exact closed-form expressions of the performance metrics. Such closed-form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. Since exact expressions are complicated, the authors have introduced simple approximate expressions for the error and outage probabilities where these expressions explicitly show the diversity order. Computer simulations are used to validate our analytical results. Results show the significant performance improvement because of the use of the adaptive DF cooperative diversity. Also, results indicate that increasing the number of relays will not always decrease the outage probability.

Exact & Closed-Form BER Expressions Based on Error-Events at Relay Nodes for DF Relay Systems over Rayleigh Fading Channels

In this letter, we derive another exact bit error rate (BER) for decode-and-forward (DF) relay systems over Rayleigh fading channels. At first, our focus is on fixed-DF (FDF) relay schemes in which the probability density function (PDF) is derived based on error-events at relay nodes. Some insight into how erroneous detection and transmission at relay nodes affect both the combined signal-to-noise ratio (SNR) and the averaged BER is obtained, and cooperative diversity is observed from the closed-form BER expression. In addition, the developed analytical method is extended to adaptive-DF (ADF) schemes and the exact BER expressions are derived. Simulation results are finally presented to validate the analysis.

Adaptive DF Relaying Scheme Based on CDD for Multi-Hop Networks with Multiple Relay Terminals

In multi-hop wireless networks, the transmitted signal is generally forwarded over several relay terminals. So, the quality of communications is degraded due to these re-transmissions over fading channels in relay terminals. Basically, the conventional cooperative relaying scheme based on cyclic delay diversity (CDD) reduces this degradation because this scheme could have numerous relay terminals which simultaneously transmit the signals. However, we cannot obtain the maximum diversity gain because of the re-transmission without considering relay channel environments. In this letter, to overcome the decreased performance, we propose an adaptive decode-and-forward (DF) relaying scheme based on CDD which uses cyclic redundancy check (CRC) code. Simulation results show that the proposed scheme provides more improvement in error performance than the conventional schemes in multi-hop networks.