Round Robin, Centralized and Distributed Relay Selection for Free Space Optical Communications

Concerning the problem between the optimality and efficiency of the relay selection algorithm,an algorithm of the relay selection based on fast symbol error probability was proposed in Amplify-and-Forward(AF) cooperative networks.First,with the equal power allocation,and based on the statistic channel information and symbol error probability of the system,an equivalent channel gain was brought in.The parameter described the compositive channel character of two phases that were the source node to relay node as well as relay node to the destination in the cooperative process.Then with the descending order of the parameter,the Signal-to-Noise Ratio(SNR) could be taken as the threshold,and different relay node set was chosen to minimize the symbol error probability in case of equal power allocation.And combined with the near optimal power allocation,the proposed scheme further reduced the symbol error probability.As shown in the simulation results,the error probability performance of this relay selection scheme is similar to the optimal full-search scheme but the complexity is reduced to at least 1/20 of the latter one.And it also shows that the error probability of the proposed scheme is lower than the other schemes such as all participating amplify-and-forward(AP-AF) relay selection and pre-select single relay amplify-and-forward(S-AF) relay selection.

In this study, a two‐stage decode‐and‐forward cooperative network is investigated consisting of a source, a corresponding destination, an eavesdropper and several intermediate nodes. In this study, the authors present an analysis of overall secrecy rate considering both distributed relay selection and secure beamforming problems. The achievable rate constraint is newly included into the system model. This modelling framework offers a more reliable approximation of the practical wireless channel. The relay selection is formulated as a coalitional game with transferable utility, which decreases the computation complexity in solving the distributed relay selection problem. A new ‘Max–Pareto order’ is constructed, which not only considers the player value, but also reflects the dominated weight of coalition value. Moreover, a distributed merge‐and‐split coalition formation algorithm is presented in this study. This algorithm achieves the system performance close to the theoretical upper limit, but it requires much less computation consumption.

For cooperative wireless networks, we propose a medium access control (MAC) protocol with distributed relay selection using group-based probabilistic contention and reparticipation. The relay with the minimum outage probability is selected in a distributed way. Based on the achievable outage probability, relay candidates are divided into multiple groups, and each relay candidate in a group uses a probability to send the acknowledgement (ACK) packet back to the source to contend for being selected. Each group is defined by a specified range of the outage probability. Relays in a group with lower outage probability range contend earlier. In addition, the relay candidate that does not send the ACK packet in the current time slot is assigned with a higher probability to contend in the next time slot. Once a relay candidate survives, the contention process is terminated. Thus, transmitting the unnecessary ACK packets for contention is avoided. Simulation results show that compared to the conventional scheme, the proposed one has a better performance in terms of the outage probability, shortens the contention period, and reduces the number of ACK packets for contention.

In cluster-based multihop networks, the Ad Hoc Routing (AHR) scheme has been proposed to reduce the implementation complexity of the optimal routing scheme. However, this complexity reduction also causes performance loss. In addition, when the practical distributed relay selection is considered, further performance loss occurs due to the relay selection error. In this paper, we exploit cooperative diversity to compensate these performance losses, address the problem of the conventional distributed relay selection scheme, and then propose a novel Distributed Ad Hoc Cooperative Routing (DAHCR) scheme. In the proposed approach, the sender selects not only the receiver but also one relay to form a cooperative communication to reduce the power consumption. Simulation results reveal that the performance improvements achieved by the cooperative diversity and the proposed DAHCR scheme are the trade-offs of increased complexity.

The key question need to be answered about relay selection in a large‐scale randomly distributed wireless network is that how to select a relay energy efficiently under a throughput (i.e., effective data rate) constraint with a reasonable complexity. It is not practical to collect instantaneous channel state information of all relays for relay selection because of excessive control packet transmission and useless energy consumption because to hold a relay in active mode to participate relay selection process needs significantly more power consumption than to hold in sleep mode. In this paper we propose a new energy‐efficient relay selection technique for large‐scale randomly distributed wireless networks for which an active relay region is introduced where only the relays in the region are taken into consideration for relay selection. Then, we propose a simple relay selection technique, which is only based on the channel state information of source‐relay channels of the relay subset to reduce the complexity and signaling overhead. The proposed relay selection technique increases energy efficiency at an acceptable complexity level without jeopardizing the effective data rate. We investigate the optimum size of the active relay region for energy efficient in which relays perform decode‐and‐forward technique. A detailed and realistic power consumption model is studied by taking all possible sources of power consumption into consideration, i.e., data transmission, signaling packets transmission, and circuit power consumption during all phases of the communication. We show that the proposed technique is more energy efficient and provides better effective data rate in comparison to the reference techniques.

This paper analyzes the performance of multicarrier index modulation (MCIM) with greedy detection (GD) in a dual hop, multiple decode and forward (DF) relay network. We propose a novel partial relay selection (PRS) technique combined with index modulation and its energy detection. For performance analysis, we derive novel closed form solutions for both the average pairwise error probability (PEP) and the average symbol error probability (SEP) at the relays and destination over Nakagami-m fading channels. Unlike the information theoretical works, with presence of positive detection error in the relays, the derived expressions provide a useful insight into the error performance of PRS based MCIM in a multiple DF relay network under various fading conditions. Also, we address the impacts of both relays and different rates of sub-carrier index activation.

Application relays can be used to reduce end-to-end latency to provide shorter paths than IP default paths. To fit the large-scale and distributed features of Internet, the nodes can cooperate to form a latency-reducing routing overlay by acting as relays for each other in peer-to-peer paradigms. In this paper, we utilize the triangle inequality violations (TIV) in delay space to model the relays and analyze their properties to help relay selections. We find that the utility of relays approximate the power law distribution, which inspires us to propose a distributed power law relay selection algorithm, which tries to locate super candidates which has large relay utility to act as good relays. It is simulated to show its performance and efficiency.

The presence of restrictive network address translators (NATs) and firewalls prevent nodes from directly exchanging packets and thereby pose a problem for peer-to-peer (p2p) communication systems. Skype, a popular p2p VoIP application, addresses this problem by using another Skype client (relay) with unrestricted connectivity to relay the signaling and media traffic between session endpoints. This distributed technique for addressing connectivity issues raises challenging questions about the reliability and latency of relayed calls, relay selection techniques, and the interference of relayed calls with the applications running on relays -- a phenomena we refer to as user annoyance.We devise a framework to analyze reliability in peer-to-peer communication systems and present a simple model to estimate the number of relays needed for maintaining the desired reliability for the media sessions. We then analyze two techniques for improving the reliability of relayed calls. We present a distributed relay selection technique that leverages a two level hierarchical p2p network to find a relay in O(1) hop. We augment our distributed relay selection technique to find a relay that minimizes call latency and user annoyance. Our results indicate that for Skype node lifetimes, at least three relays are needed to achieve a 99.9% success rate for call duration of 60 mins (95th percentile of Skype call durations).

In this paper, we compare the performance in terms of symbol error probability, data rate and power consumption of the use of fixed transmit power (FTP) and adaptive transmit power (ATP) in underlay cognitive radio networks. The use of FTP alleviates the signaling requirements of underlay cognitive radio networks compared to the ATP. Nevertheless, the use of FTP influences the performances of the underlay cognitive radio networks. To study this influence, we consider three relay selection schemes using FTP: opportunistic decode and forward with FTP (O-DF with FTP), opportunistic amplify and forward with FTP (O-AF with FTP) and partial relay selection with FTP (PR with FTP). We compare the performances of these schemes in terms of symbol error probability, data rate and power consumption with three relay selection schemes using ATP: opportunistic decode and forward with ATP (O-DF with ATP), opportunistic amplify and forward with ATP (O-AF with ATP) and partial relay selection with ATP (PR with ATP). We provide exact and/or lower bound expressions of the symbol error probabilities of O-DF, O-AF and PR with FTP. The analytical study for the data rate and the power consumption is also provided. Our comparison study shows that FTP has a positive impact on the data rate and power consumption performance while it deteriorates the symbol error probability performance.

This paper presents a new cooperative ARQ protocol for a hybrid mobile wireless sensor network. The mobile relay nodes decode the signal from the source sensor using cyclic redundancy check (CRC) and forward it to the destination sink. A distributed relay selection that exploits overhearing of inter-relay node transmission is employed to achieve higher selection diversity gain during retransmissions. Upon reception from the source sensor, the number of relay nodes available to contend for transmission depends on the conditions of source-relay channels. When source-relay channels are instantaneously poor, achievable selection diversity gain decreases. Such relay availability dependency over source-relay channels can be reduced if erroneous relays exploit inter-relay channels to opportunistically listen ( OL ) to the transmission of the error-free selected relay. By combining the initially received erroneous signals with the signal overheard from the selected relay and decoding again, erroneous relays may be able to decode the signals successfully thanks to the spatial diversity. This results in an increase in relay availability for distributed selection in subsequent retransmissions. It is also shown that the selection protocol based on end to end channel quality approach cannot make full use of the increased relay availability. The proposed cooperative ARQ protocol ensures to make full use of the increased relay availability. The numerical results show that the proposed cooperative ARQ significantly improves the successful packet arrival rate.

We consider a spectrum-sharing network where n secondary relays are used to increase secondary rate and also mitigate interference on the primary by reducing the required overall secondary emitted power. We propose a distributed relay selection and clustering framework, obtain closed-form expressions for the secondary rate, and show that secondary rate increases proportionally to log n. Remarkably, this is on the same order as the growth rate obtained in the absence of a primary system and its imposed constraints. Our results show that to maximize the rate, the secondary relays must transmit with power proportional to n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> (thus the sum of relay powers is bounded) and also that the secondary source may not operate at its maximum allowable power. The tradeoff between the secondary rate and the interference on the primary is also characterized, showing that the primary interference can be reduced asymptotically to zero as n increases, while still maintaining a secondary rate that grows proportionally to log n. Finally, to address the rate loss due to half-duplex relaying in the secondary, we propose an alternating relay protocol and investigate its performance.

In this paper, we newly analyze the effect of phase noise in the frequency synthesizer on the performance of fast frequency-hopping (FFH)/M-ary noncoherent frequency-shift keying (M-NCFSK) system. The symbol-error probability (SER) of the frequency-hopping spread-spectrum (FHSS) system is derived when the noncoherent FSK demodulation with the square-law detector is considered. Also, the effect of phase noise on the performance of the FFH/M-NCFSK system is analyzed in terms of phase noise power spectrum and frequency-hopping spacing, as well as the diversity level. The required signal-to-noise ratio (SNR) to meet P/sub s/=10/sup -3/ is about 11.8 dB when the standard frequency deviation is about 31.623 kHz and the frequency-hopping spacing in the FFH/2-NCFSK system is 400 kHz. So, it is found that there is about 0.8-dB power penalty than the phase noise-free system. Similarly, there is about 0.7-dB power penalty in the FFH/4-NCFSK system. SER performance is changed with the standard frequency deviation, but SER is nearly independent of the modulation level. As the diversity level is increased from 1 to 4, frequency diversity effect is trivial in the lower SNR below 6 dB, but is considerably improved in the higher SNR.

We consider relay selection technique in a cooperative cellular network where user terminals act as mobile relays to help the communications between base station (BS) and mobile station (MS). A novel relay selection scheme, called Joint Uplink and Downlink Relay Selection (JUDRS), is proposed in this paper. Specifically, we generalize JUDRS in two key aspects: (i) relay is selected jointly for uplink and downlink, so that the relay selection overhead can be reduced, and (ii) we consider to minimize the weighted total energy consumption of MS, relay and BS by taking into account channel quality and traffic load condition of uplink and downlink. Information theoretic analysis of the diversity-multiplexing tradeoff demonstrates that the proposed scheme achieves full spatial diversity in the quantity of cooperating terminals in this network. And numerical results are provided to further confirm a significant energy efficiency gain of the proposed algorithm comparing to the previous best worse channel selection and best harmonic mean selection algorithms.

In this paper, we analyze the performance of cooperative wireless networks with multiple-relays with single-relay selection using limited feed back, exploiting the concepts of Alamouti space-time coding. A two-stage protocol is used with the relay terminals operating in the amplify-and-forward mode (AF). The analysis uses the Rayleigh fading model to reduce the complexity in handling versatile Nakagami fading channels. Taking these effects into account, symbol error probability (SEP) for single relay selection in a multiple-relay environment is derived . The selection is based on the gain of the source-relay (SR) channel and we claim that this is the best achievable SEP for transmission of the Alamouti code using the described protocol, under the given selection criteria. Numerical results are provided to verify the accuracy of the formulation.

As large energy consumers, base stations need energy-efficient wireless access networks. An advanced energy efficiency measure was developed in this paper, considering throughput, the number of served users, and actual coverage area. The actual coverage area considered in the proposed measure is also in harmony with the measured network coverage area proposed by ETSI ES 203 228 V1.1.1 standard [1] which has been published by 3GPP. It is emphasized by 3GPP that to evaluate the actual coverage area, coverage probability should be taken into account in relation to the quality of service (QoS) definitions. However, coverage probability is not considered in all of the existing measurement methods. Hence, the developed measure turns out to be more effective than them as shown from the analysis and simulation results. Based on the developed measure, energy efficiency of Round Robin (RR) and Maximum SINR (MSINR) scheduling strategies for fractional frequency reuse (FFR) Schemes in orthogonal frequency division multiple access (OFDMA) Cellular Networks was investigated through closed-form expressions. The optimal power threshold of a base station (BS) and the optimal distance threshold of a cell were obtained from the results and the optimal distance threshold of MSINR is higher than that of RR while the optimal power threshold is not affected by scheduling strategies. Simulation also demonstrates that energy efficiency increases and the optimal distance threshold decreases with the number of users. However, the number of users has little impact on the optimal power threshold.