Relay Selection Rule Research Articles

Energy‐Harvesting Cooperative NOMA in IOT Networks

Buffer‐aided cooperative nonorthogonal multiple access (NOMA) improves the effectiveness of the spectral by allowing more than one user to share the same resources to realize massive connectivity. This is notably attractive in the fifth generation (5G) and beyond systems, where a massive number of connections are essential such as the Internet of Things (IoT). Wireless‐powered communication through energy harvesting is another 5G promising solution for the future massively dense networks. To sufficiently utilize energy harvesting in a buffer‐aided cooperative NOMA network, the relay selection rule must consider the energy level of the selected relay in addition to its data content to avoid an outage. This paper proposes a relay selection rule for energy‐harvesting buffer‐aided cooperative NOMA networks. The proposed relay selection scheme considers the state of both the data buffer and the energy buffer. The simulations show that the proposed selection rule has improved the network outage probability and throughput as well. This enhancement is kept with changing the number of relays. The results also show that the impact of changing the energy buffer size is crucial, and the larger, the better. Furthermore, making the source transmitting power larger than the relay transmitting power is beneficial, especially with large enough energy buffer sizes.

Robust backbone network based on hybrid selection of relays for multi-hop data dissemination in VANETs

Relay nodes selection as a key word to ensure efficient multi-hop data dissemination in VANETs has received tremendous attention for many years. However, previous literature often fails to address two critical topics. Firstly, the conception of a reliable relay distribution model to ensure information coverage without generating additional overheads. Secondly, the simultaneous exploit of both existing sender-oriented and receiver-oriented relay selection mechanisms to avoid the trade-off among them and improve the overall dissemination efficiency. In this paper, we propose a Robust BACKbone NETwork based on Hybrid Selection of Relays for multi-hop data dissemination in VANETs (BACKNET-HSR). Its novelty lies in adequately addressing the aforementioned topics. To avoid the chaotic distribution of relays and enhance information coverage, we adjust the relay selection and inhibition rules according to a novel concept of message propagation pattern. The goal is to realize a synergy among the potential relay candidates to build an on-the-fly backbone network parallel to the road lines topology in a distributed manner. With the aim of enhancing the relay selection robustness, we propose a tight coupling of both investigated relay selection mechanisms in one hybrid scheme. The objective is to leverage the low latency feature of the sender-oriented mechanism, and the high reachability feature of the receiver-oriented mechanism. Simulation results show that the proposed scheme disseminates data with low delay and high information coverage, outperforming the existing dissemination protocols in different scenarios and under varying vehicular densities.

BER-based relay selection strategy for cooperative communication

In this paper, a bit error ratio (BER)-based relay selection strategy is investigated under opportunistic relay selection. The challenging problem is to design the relay selection rule so that the relay is able to measure the performance of the cooperative system at the destination exactly with low computation costs. This paper derives a closed-form expression of the end-to-end bit error rate firstly. Then, an approximate BER expression based on the relationship between the instantaneous signal-to-noise ratio (SNR) of the relay-to-destination link and the probability of error propagation is derived. Finally, a simplified relay selection formula is proposed. Simulation results prove that the proposed relay selection rule can reflect the BER of each relay properly as well.

Auction-Based Relay Selection and Power Allocation in Green Relay-Assisted Cellular Networks

Nowadays, wireless communication has become a fabric of our daily life, and it has been a universal demand for higher capacity and longer battery lifetime. For the sake of solving these problems, this paper considers taking the advantage of cooperative communication with the assistance of green relays. So, in this paper, we design an auction market that is composed of one base station (acts as the auctioneer), multiple green relays (act as sellers), and multiple mobile terminals (act as buyers). The terminals need to pay for the cooperative service, and the relays sell it for revenue. In addition, the terminals can raise their bid according to their residual energy; thus the terminals that lack energy have more opportunities to get cooperative service to avoid energy exhaustion. At the same time, the relays can reduce the price based on their instantaneous energy harvesting amount, and, hence, the relays can serve more terminals when they can harvest more energy from the environment. This paper also proposes three different auction rules to show the effect of relay selection. Furthermore, power allocation among relays and terminals is adopted to minimize the power consumption of terminals under the SNR requirement. Simulation results show that the three relay selection rules perform diversely and have their own advantages and disadvantages, but all of them can improve system capacity and prolong the lifetime of the mobile terminals effectively. And, with power allocation, the terminal can utilize the least energy to achieve its SNR requirement.

Incentive Mechanisms and Impacts of Negotiation Power and Information Availability in Multi-Relay Cooperative Wireless Networks

Cooperative relaying is highly affected by the way that the source and relays are incentivized. However, the existing studies have not paid enough attention to the impacts of negotiation power and information availability of the players on the network performance. In this paper, two incentive mechanisms for cooperative relaying are first proposed to explore the influence of negotiation power, wherein the source holds either strong or weak negotiation power. In these two cases, the source posts take-it-or-leave-it offers for the relays and has to negotiate possible deals with the relays, respectively. The relay selection rules and the optimal amounts of relaying service and rewards are derived for each mechanism, respectively. Another two incentive mechanisms are also proposed to explore the influence of information availability, wherein the source has either weakly or strongly incomplete information about the relays. In these two cases, the source acquires the number of relays belonging to each type and the probability of each relay belonging to a certain type, respectively. The relay selection rules and the optimal contract offers are derived for the two mechanisms, respectively. The numerical results are provided to verify the theoretical analyses and demonstrate the effectiveness of the proposed mechanisms.

Rate-Optimal Relay Selection for Average Interference-Constrained Underlay CR

Cooperative relaying combined with selection exploits spatial diversity to improve the performance of interference-constrained secondary users in an underlay cognitive radio (CR) network. While a relay improves the signal-to-interference-plus-noise ratio (SINR) of the secondary network, it requires two hops and also generates interference to the primary network. We present a novel, optimal relay selection rule that maximizes the fading-averaged transmission rate of an average interference-constrained underlay secondary network. It differs from the several ad hoc incremental relaying schemes proposed in the literature, while requiring a feedback overhead that is comparable to them. We then analyze the average rate of the optimal rule. We also present insightful high and low SINR asymptotic analyses, which bring out the extent to which the use of the relays improves the average rate as a function of the system parameters. Our numerical results show that the proposed rule outperforms several known relay selection schemes for CR, and also characterize the regimes in which some of these schemes are near-optimal.

Novel Relay Selection Rules for Average Interference-Constrained Cognitive AF Relay Networks

Cooperative relaying combined with selection exploits spatial diversity to significantly improve the performance of interference-constrained secondary users in an underlay cognitive radio (CR) network. However, unlike conventional relaying, the state of the links between the relay and the primary receiver affects the choice of the relay. Further, while the optimal amplify-and-forward (AF) relay selection rule for underlay CR is well understood for the peak interference-constraint, this is not so for the less conservative average interference constraint. For the latter, we present three novel AF relay selection (RS) rules, namely, symbol error probability (SEP)-optimal, inverse-of-affine (IOA), and linear rules. We analyze the SEPs of the IOA and linear rules and also develop a novel, accurate approximation technique for analyzing the performance of AF relays. Extensive numerical results show that all the three rules outperform several RS rules proposed in the literature and generalize the conventional AF RS rule.

Direct Link-Aware Optimal Relay Selection and a Low Feedback Variant for Underlay CR

Cooperative relaying combined with selection has been extensively studied in the literature to improve the performance of interference-constrained secondary users in underlay cognitive radio (CR). We present a novel symbol error probability (SEP)-optimal amplify-and-forward relay selection rule for an average interference-constrained underlay CR system. A fundamental principle, which is unique to average interference-constrained underlay CR, that the proposed rule brings out is that the choice of the optimal relay is affected not just by the source-to-relay, relay-to-destination, and relay-to-primary receiver links, which are local to the relay, but also by the direct source-to-destination (SD) link, even though it is not local to any relay. We also propose a simpler, practically amenable variant of the optimal rule called the 1-bit rule, which requires just one bit of feedback about the SD link gain to the relays, and incurs a marginal performance loss relative to the optimal rule. We analyze its SEP and develop an insightful asymptotic SEP analysis. The proposed rules markedly outperform several ad hoc SD link-unaware rules proposed in the literature. They also generalize the interference-unconstrained and SD link-unaware optimal rules considered in the literature.

Energy-Efficient Relay Selection for Cooperative Relaying in Wireless Multimedia Networks

In existing wireless networks, supporting multimedia services are becoming more popular and important. In general, wireless multimedia networks should require energy efficiency and reliable transmission while keeping satisfactory quality of services. In this respect, cooperative communications have been considered as an efficient approach to address these demands by offering significant diversity gains over single-antenna systems without increasing requirements on radio resources. In this paper, we propose a power-allocation method to optimize the decode-and-forward (DF) cooperative transmission for source and relay nodes as a means to reduce the total power consumption, while maintaining the required quality of services, and investigate fundamental characteristics of cooperative transmission in terms of power efficiency. Moreover, for a network with multiple cooperative nodes, we also propose an energy-efficient relay selection rule to offer fairness at each node and implement it into a practical routing protocol. Our performance analysis is supplemented by simulation results to illustrate significant energy savings of the proposed methods.

Power Efficient Decode-and-Forward Cooperative Relaying

Cooperative communications have been proven to be effective in enhancing performance of wireless networks. In this letter, we introduce and propose adaptive relay-selection rules to offer a tradeoff between fairness and energy consumption at each node for a network with multiple, mutually cooperative nodes. Our performance analysis is supplemented by simulation results to illustrate the significant energy savings of the proposed optimal power allocation and the relay-selection rules.

Single Relay Selection for Bidirectional Cooperative Networks with Physical-Layer Network Coding

To serve the growing demand of the bidirectional information exchange, we propose a single relay selection (RS) scheme for physical-layer network coding (PNC) in a bidirectional cooperative network consisting of two sources and multiple relays. This RS scheme selects a single best relay by maximizing the bottleneck of the capacity region of both information flows in the bidirectional network. We show that the proposed RS rule minimizes the outage probability and that it can be used as a performance benchmark for any RS rules with PNC. We derive a closed-form exact expression of the outage probability for the proposed RS rule and show that it achieves full diversity gain. Finally, numerical results demonstrate the validity of our analysis.

Single Relay Selection for Bidirectional Cooperative Networks with Physical-Layer Network Coding

To serve the growing demand of the bidirectional information exchange, we propose a single relay selection (RS) scheme for physical-layer network coding (PNC) in a bidirectional cooperative network consisting of two sources and multiple relays. This RS scheme selects a single best relay by maximizing the bottleneck of the capacity region of both information flows in the bidirectional network. We show that the proposed RS rule minimizes the outage probability and that it can be used as a performance benchmark for any RS rules with PNC. We derive a closed-form exact expression of the outage probability for the proposed RS rule and show that it achieves full diversity gain. Finally, numerical results demonstrate the validity of our analysis.

A Simulation Study of Underwater Acoustic Communications in the North Field of Qatar

Abstract Qatar is a leading natural gas producer and exporter in the world. Most of the natural gas (and oil) of Qatar is extracted from offshore wells, and then it is transferred to onshore for processing. In addition, Qatar is connected to UAE by one of the world's longest underwater pipelines (managed by Dolphin Energy), to transfer processed gas from the offshore north field to the UAE. Security of such critical offshore infrastucture against threats along with the environmental and preventive maintenance monitoring (e.g., pollution, leakage) are of utmost importance. A wireless underwater sensor network can be deployed for the security and safety of underwater pipelines. However, underwater acoustic communication brings its own challenges such as limited transmission range, low data rates and link unreliability. In this paper, we propose “cooperative communication” as an enabling technology to meet the challenging demands in underwater acoustic communication (UWAC). Specifically, we consider a multi-carrier and multi-relay UWAC system and investigate relay (partner) selection rules in a cooperation scenario. For relay selection, we consider different selection criteria, which rely either on the maximization of signal-to-noise ratio (SNR) or the minimization of probability of error (PoE). These are used in conjunction with so-called per-subcarrier, allsubcarriers, or subcarrier grouping approaches in which one or more relays are selected. In our simulation study, we choose an offshore area in the North Eastern side of Qatar (which coincides with the North Field) and conduct an extensive Monte Carlo simulation study for the chosen location to demonstrate the performance of the proposed UWAC system. Our channel model builds on an aggregation of both large-scale path loss and small-scale fading. For acoustic path loss modeling, we use the ray-tracing algorithm Bellhop software to precisely reflect the characteristics of the simulation location such as the sound speed profile, sound frequency, bathymetry, type of bottom sediments, depths of nodes, etc (See Fig.1 ). Our simulation results for the error rate performance have demonstrated significant performance improvements over direct transmission schemes and highlighted the enhanced link reliability made possible by cooperative communications (See Fig.2 ).

Design of optimal relay location in two-hop cellular systems

Relay stations are usually used to enhance the signal strength for the users near cell boundary, thereby extending the cell coverage. However, transmission through a relay station needs two transmission phases. The first phase is from base station to relay station, and the second one is from relay station to mobile station. Thus, using relay station may decrease system capacity due to two-phase transmission time. As a result, whether or not data are transmitted by one-hop or two-hop phases should be determined according to both signal strength and throughput. In this paper, we investigate the optimal relay location aiming to maximize system capacity. We consider two relay selection rules for determining whether two-hop transmission will be used: signal strength-oriented and throughput-oriented selection rules. We find that the signal strength-oriented two-hop transmission may yield even lower system capacity than the one-hop transmission. In the throughput-oriented scheme, the two-hop transmission can achieve higher system capacity than the one-hop transmission. By simulations, we determine the optimal relay location and show the coverage enhancement by the relaying network. Extensive simulations are performed to investigate the impacts of relay transmission power and the number of relay stations on system capacity and optimal relay location. The simulation results reveal important insights into designing a relaying network with high system capacity.

Energy-Efficient Cooperative Relaying over Fading Channels with Simple Relay Selection

We consider a cooperative wireless network where a set of nodes cooperate to relay in parallel the information from a source to a destination using a decode-and-forward approach. The source broadcasts the data to the relays, some or all of which cooperatively beamform to forward the data to the destination. We generalize the standard approaches for cooperative communications in two key respects: (i) we explicitly model and factor in the cost of acquiring channel state information (CSI), and (ii) we consider more general selection rules for the relays and compute the optimal one among them. In particular, we consider simple relay selection and outage criteria that exploit the inherent diversity of relay networks and satisfy a mandated outage constraint. These criteria include as special cases several relay selection criteria proposed in the literature. We obtain expressions for the total energy consumption for general relay selection and outage criteria for the non-homogeneous case, in which different relay links have different mean channel power gains, and the homogeneous case, in which the relay links statistics are identical. We characterize the structure of the optimal transmission scheme. Numerical results show that the cost of training and feedback of CSI is significant. The optimal strategy is to use a varying subset (and number) of relay nodes to cooperatively beamform at any given time. Depending on the relative location of the relays, the source, and the destination, numerical computations show energy savings of about 16% when an optimal relay selection rule is used. We also study the impact of shadowing correlation on the energy consumption for a cooperative relay network.