No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
A New Insight Towards Buffer-Aided Relaying in Cooperative Wireless Networks
Abstract
This piece of work presents a novel design for buffer-aided relaying to increase the diversity gain. In this design, we used random buffer access method and associate each buffer location with its own antenna resource. Thus, each buffer location acts as an independent entity known as the virtual relay. The relay selection is based on the instantaneous strength of wireless link and the status of buffers. Markov chain is used to illustrate the growth of buffer status and to derive the closed-form expressions for the outage probability and diversity gain. The proposed design achieves the diversity gain of KL as compared to current buffer-aided max-link and max-max schemes having the diversity gain of 2K and K, respectively. Moreover, the proposed design achieves less delay at low SNR and 1+KL at high SNR. Analytical results are validated via simulation results.
... Other schemes outperforming the traditional max-link [7] in terms of OP are the Buffer-Threshold-Based Relay Selection (BTRS) scheme [30] and the virtual-max-link relay selection (V-MLRS) [31]. BTRS [30] introduces a buffer-threshold that manipulates the selection probability of source-relay or relay-destination links. ...
... V-MLRS attains similar diversity order to MLRS, but with fewer relays and a trivial buffer size. Diversity gains are improved while maintaining the same delay [31]. [34] tackles a different virtual FD relaying scheme for BA HD multi-hop DF cooperative network, which is the centre-partition max-link relaying. ...
... However, for larger buffer size, the OP of the conventional max-link scheme is better, while the APD of the proposed scheme is better [34]. The V-MLRS in [31] is aspired by the proposed scheme in [35], where the authors utilize the idea of inverse channel packet matching to choose the best packet in the buffer, by allowing the packet that suffers bad channel condition in the S-R hop to go through good channel condition in the R-D hop to enhance the outage probability. ...
Ever since the idea of buffers was incorporated in wireless communications, buffer-aided relaying has become an emerging breakthrough in the world of transmitting and receiving signals. Equipping the relays with buffers adds a new degree of freedom capable of enhancing numerous quality-of-service (QoS) metrics including throughput, outage probability, power efficiency and physical-layer security. The QoS enhancement is achieved by compromising the end-to-end delay that is inflicted by storing the packets in the relays' buffers until a suitable source-relay or relay-destination link is selected. In this context, the selection of a relay for transmission/reception is important since it governs the QoS-delay trade-off that can be contemplated. In this survey, the authors review and analyse various link selection protocols in buffer-aided relaying systems. These relaying strategies are categorised and contrasted according to their performance levels, limitations, applications, system model assumptions and complexity. Finally, they discuss current challenges, and highlight future research directions.
... We evaluate the proposed scheme for the symmetric and asymmetric buer size and channel conditions and provide a comprehensive set of results for four cases: 1) symmetric buer and symmetric channel, 2) symmetric buer and asymmetric channel, 3) asymmetric buer and symmetric channel and 4) asymmetric buer and asymmetric channel. The initial work is in [86] and the extended version is given in [87]. ...
In this thesis, a suite of schemes is presented to enhance the performance of cooperative communication networks. In particular, techniques to improve the outage probability, end-to-end delay and throughput performances are presented. Firstly, a buffer-aided cooperative communication is studied and analyzed for packet selection and relay selection. A three-node network is considered in the beginning and the phenomenon of packet diversity is taken into consideration to overcome bad channel conditions of the
source to relay (SR) and relay to destination (RD) links. The closed-form expressions for the computation of the outage probability along with the delay, throughput and diversity gain are derived. Then, packet selection is studied along with relay selection for buffer-aided amplify and forward (AF) cooperative relaying networks. The proposed protocol is analyzed for both symmetric and asymmetric channel conditions and buffer size using multiple antennas at relays and compared against the existing buffer-aided schemes.
Markov chain (MC) is used to derive the closed-form expressions for outage probability, diversity gain, delay and throughput.
Next, the performance of SNR based hybrid decode-amplify-forward relaying protocol is observed. When SR link is the strongest, data is transmitted to the selected relay and checked against the predefined threshold at the relay. If it is greater than the threshold, data is decoded and stored in the corresponding buffer. Otherwise, it is amplified and stored in the respective buffer. When RD link is the strongest, data is transmitted to the destination. MC based theoretical framework is used to derive an expression for the outage probability, the average end-to-end delay and throughput. Then, relay selection schemes considering the instantaneous link quality along with buffer status in the relay selection are proposed. A scheme is proposed that simultaneously considers buffer status and link quality. Then, we discuss multiple links with equal weights using a general relay selection factor. It includes the weight of the link as the first metric and the link quality, or priority, as the second metric for different cases of the same weight. The proposed scheme is evaluated for symmetric and asymmetric channel conditions.
Moreover, we propose a specific parameter, termed as the bu�er-limit, which controls the selection of SR or RD links and also have its impact on the average delay and throughput. In this scheme, the outage probability is traded with the average end-to-end queuing delay or the average throughput by adjusting the values of the buffer-limit. The MC based framework is employed to derive the closed-form expressions for the outage probability, average end-to-end queuing delay and the average throughput. The suggested schemes are compared to the existing bufferaided relay selection schemes.
Lastly, we consider the energy constraint cooperative network and propose a generalized approach to study the performance of energy harvesting relaying schemes.
The unified modeling of generalized energy harvesting relaying (GEHR) scheme covers the non-energy harvesting schemes and the well-known energy harvesting schemes, i.e., time switching based relaying (TSR) and power splitting based relaying (PSR). Moreover, the scheme also caters the hybrid of both TSR and PSR schemes. The closed-form expressions for the outage probability and ergodic capacity and average throughput are formulated for non-mixed Rayleigh fading and mixed Rayleigh-Rician fading channels. Each case is analyzed for AF and decode and forward relaying models. Comprehensive Monte-Carlo simulations confirm all theoretical results.
This paper presents an incremental cooperative
communication scheme for a buffer-aided three node relay
network consisting of a source, an Amplify and Forward (AF)
relay and a destination. We consider the presence of direct link
and propose a scheme which is based on the concept of packet
diversity rather than link diversity. The scheme is designed in
such a way that packets that experienced bad channel conditions
in source-relay link experience good channel conditions in the
relay-destination link and vice versa. Source multi-casts all
packets to both relay and destination. If direct transmission is not
successful, source needs assistance from the relay. Based on the
quality of relay-destination link, a packet is picked from buffer at
the relay to be transmitted to the destination. Further, direct and
relayed signals are combined at the destination using Maximal
Ratio Combining (MRC) technique. The closed-form expressions
for outage and error probabilities are derived, further, the
delay and the diversity orders for the proposed scheme are also
investigated.
Applying data buffers at relay nodes significantly improves the outage performance in relay networks, but the performance gain is often at the price of long packet delays. In this paper, a novel relay selection scheme with significantly reduced packet delay is proposed. The outage probability and average packet delay of the proposed scheme under different channel scenarios are analyzed. Simulation results are also given to verify the analysis. The analytical and simulation results show that, compared with non-buffer-aided relay selection schemes, the proposed scheme has not only significant gain in outage performance but also similar average packet delay when the channel SNR is high enough, making it an attractive scheme in practice.
This paper investigates the buffer-aided relay selection problem for a decode-and-forward cooperative wireless network with K relays. We propose a new relay selection scheme, that incorporates the status of the relay buffers and the instantaneous strength of the wireless links. Specifically, each link is assigned with a weight related to the buffer status, then the best relay is selected with the largest weight among all the qualified source-relay and relay-destination links. We derive the closed-form expression for the outage probability as well as the diversity gain by introducing several Markov chains to model the evolution of the buffer status. The analysis shows that the proposed scheme can achieve the optimal diversity gain, 2K, for a small L (i.e., L 3), an improvement in comparison with the existing max-link scheme that achieves the optimal diversity gain only when L is sufficiently large, where L denotes the buffer size of each relay. The provided theoretical and numerical results confirm the performance gain of the proposed relay selection scheme over the existing max-link scheme.
We consider a wireless relay network that consists of a source, half-duplex decode-and-forward buffer-aided relays and a destination. While the majority of previous works on relay selection assume no direct transmission between source and destination in such a setting, we lift this assumption and propose a link selection policy that exploits both the buffering ability and the opportunity for successful reception of a packet directly from the source. The proposed relay selection scheme incorporates the instantaneous strength of the wireless links and adapts the relay selection decision based on the strongest available link. The evolution of the network as a whole is modeled by means of a Markov chain and thus, the outage probability is associated with the steady state of the Markov chain. It is deduced that even if the link between the source and the destination is in principle a very unreliable link, it is always beneficial for the source to multicast a packet to both the relay with the strongest available link and the destination.
This paper investigates the outage performance of an amplify-and-forward (AF) relay system that exploits buffer-aided max-link relay selection. Both asymmetric and symmetric source-to-relay and relay-to-destination channel configurations are considered. We derive the closed-form expressions for the outage probability and analyze the average packet delays. We prove that the diversity order is between N and 2N (where N is the relay number), corresponding to a relay buffer size between 1 and infinity, respectively. We also analytically show the coding gain. Numerical results are given to verify the theoretical analyses.
Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However, most of the proposed solutions require distributed space-time coding algorithms, the careful design of which is left for future investigation if there is more than one cooperative relay. We propose a novel scheme that alleviates these problems and provides diversity gains on the order of the number of relays in the network. Our scheme first selects the best relay from a set of M available relays and then uses this "best" relay for cooperation between the source and the destination. We develop and analyze a distributed method to select the best relay that requires no topology information and is based on local measurements of the instantaneous channel conditions. This method also requires no explicit communication among the relays. The success (or failure) to select the best available path depends on the statistics of the wireless channel, and a methodology to evaluate performance for any kind of wireless channel statistics, is provided. Information theoretic analysis of outage probability shows that our scheme achieves the same diversity-multiplexing tradeoff as achieved by more complex protocols, where coordination and distributed space-time coding for M relay nodes is required, such as those proposed by Laneman and Wornell (2003). The simplicity of the technique allows for immediate implementation in existing radio hardware and its adoption could provide for improved flexibility, reliability, and efficiency in future 4G wireless systems.
In this letter, we discuss multiple links with equal weights, in buffer size based relay selection schemes in cooperative wireless networks. A general relay selection factor is defined, which includes the weight of the link as the first metric and the link quality, or priority, as the second metric for different cases of the same weight. The Markov chain based theoretical framework is employed to evaluate the outage probability, delay and throughput of the system. The proposed scheme is evaluated for symmetric and asymmetric channel conditions. The link quality based second selection metric achieves lower outage probability, while the link priority based selection shows significant improvements in terms of delay and throughput. Theoretical results are validated through extensive Monte carlo simulations.
Relay selection in cooperative communication is an
efficient approach to mitigate the spectral efficiency loss faced
in cooperative diversity systems. In this paper, we propose a
relay selection scheme for buffer-aided cooperative systems. It
simultaneously considers the instantaneous link quality and the
buffer status of relay nodes in the relay selection decision. The
normalized and weighted sum of these parameters results into
the overall score of each link, and a link with maximum score
is selected. First, the concept of equivalent outage of a link
corresponding to a buffer-aided relay is explained, and then
Markov chain (MC) modeling is used for the evaluation of states
of buffer. We provide the specific examples with fixed values of
number of relays and buffer size. The system achieves the full
diversity gain of 2K for the smaller buffer sizes.
Motivated by the recent max-link protocol and the max-max protocol, both of which were developed for a simple dual-hop buffer-aided cooperative network, we present a novel hybrid buffer-aided cooperative protocol that attains the benefits of high reliability and reduced packet delay. More specifically, we incorporate a two-stage relay selection strategy, which is capable of attaining a low outage probability comparable to the max-link protocol. In addition, the proposed protocol maintains a beneficial end-to-end packet delay, which is lower than that of the max-link protocol in the realistic scenario supporting finite source-packet transmissions. Furthermore, by introducing a periodic Markov chain model, we derive the theoretical outage probability of our hybrid buffer-aided scheme under the realistic assumption of finite-buffer relays. Our analytical and simulation results demonstrate that the proposed protocol benefits from the aforementioned high-diversity reliable performance and the reduced end-to-end packet delay.
A new packet-selection based transmission scheme is proposed on a dual-hop link with buffer aided amplify-and-forward relay, where the relay with a buffer can record the channel information of source-relay hop and store the received packets. In order to satisfy the constraint of equivalent end-to-end SNR, the relay may pick up a packet in the buffer to transmit, with consideration of the channel statuses of both the source-relay hop and the relay-destination hop. Therefore, by adjusting the packet transmission order in the relay, the outage probability can be decreased in the proposed transmission scheme. Both theoretical analyses and simulation results show that the proposed scheme outperforms traditional ones by a significant margin of 2-4 dB gain in terms of outage probability.
In this paper, we propose a buffer state based relay selection scheme for a finite buffer-aided cooperative relaying system. Our proposed relay selection scheme selects a relay node based on both the channel quality and the buffer state of the relay nodes. The Markov chain model is adopted to analyze the buffer state transition properties and the outage probability of the proposed relay selection scheme is obtained in a closed-form expression. Our analytical results show that if the buffer size of each relay node is greater than 2, the proposed relay selection scheme can achieve full diversity. Furthermore, it is shown that our proposed relay selection scheme has lower average packet delay compared with the max-link relay selection scheme. In addition, the average packet delay of the proposed relay selection scheme does not increase as the buffer size increases.
Cooperative communication technology exploiting distributed spatial diversity is a promising solution for the future high data-rate cellular and ad-hoc wireless communications. To characterize the performance of a cooperative network, the cooperative diversity is commonly used. In this paper, we revisit the concept of diversity and look into the essence of cooperative diversity. We analyze the diversity performance of a general cooperative relaying system with multiple branches. Moreover, each branch consists of one or more hops. Unlike in other analyses, the assumptions that each node being only equipped with a single antenna and that all channel characteristics belonging to the same family are NOT required in our study. Using the decode-and-forward (DF) relaying protocol as an illustration, we provide analytical results on the diversity gain and the coding gain. The results also encompass most of the existing results as special cases. We further show the relationship between the diversity order of a branch and those of the constituent links; and the relationship between the diversity order of the network and those of the constituent branches. In particular, we show that for the uncoded DF protocol, the full diversity order can be achieved by using simple hard-decision detection at the destination. The requirement is to set appropriate signal-to-noise-ratio (SNR) thresholds for the multi-hop branches. To improve the bandwidth efficiency, we also randomly select one branch, among those branches satisfying the SNR-threshold requirement, for the transmission. We show that such a scheme accomplishes the full diversity order and produces a good error performance.
In this paper, we study the relay selection problem for a finite buffer-aided decode-and-forward cooperative wireless network. A relay selection policy that fully exploits the flexibility offered by the buffering ability of the relay nodes in order to maximize the achieved diversity gain is investigated. This new scheme incorporates the instantaneous strength of the wireless links as well as the status of the finite relay buffers and adapts the relay selection decision on the strongest available link by dynamically switching between relay reception and transmission. In order to analyse the new relay selection policy in terms of outage probability and diversity gain, a theoretical framework that models the evolution of the relay buffers as a Markov chain (MC) is introduced. The construction of the state transition matrix and the related steady state of the MC are studied and their impact on the derivation of the outage probability is investigated. We show that the proposed relay selection scheme significantly outperforms conventional relay selection policies for all cases and ensures a diversity gain equal to two times the number of relays for large buffer sizes.
In this paper, we propose a new relay selection scheme for half-duplex relays with buffers. The proposed scheme is referred to as max-max relay selection (MMRS) since the relays with the best source-relay and the best relay-destination channels are selected for reception and transmission, respectively, which is only possible without data loss if the relays have buffers of infinite size. To relax this idealized assumption, we propose hybrid relay selection (HRS) for relays with buffers of finite size. HRS is a combination of conventional best relay selection (BRS) and MMRS and takes into account both the channel state and the buffer state for relay selection. We provide a comprehensive analysis of the outage and symbol error probabilities of both MMRS and HRS for a decode-and-forward protocol in Rayleigh fading. This analysis reveals that BRS, HRS, and MMRS achieve the same diversity gain. However, for N relays, MMRS achieves a signal-to-noise ratio (SNR) gain of 3(1-1/N) dB compared to BRS, and HRS closely approaches the SNR gain of MMRS for moderate buffer sizes (e.g. 30 transmission intervals).