We investigate the relay selection problem for a decode and forward collaborative network. Users are able to collaborate; decode messages of each other, re-encode and forward along with their own messages. We study the performance obtained from collaboration in terms of 1) increasing the achievable rate, 2) saving the transmit energy and 3) reducing the resource requirement (resource means time-bandwidth). To ensure fairness, we fix the transmit-energy-to-rate ratio among all users. We allocate resource optimally for the collaborative protocol (CP), and compare the result with the non-collaborative protocol (NCP) where users transmits their messages directly. The collaboration gain is a function of the channel gain and available energies and allows us 1) to decide to collaborate or not, 2) to select one relay among the possible relay users, and 3) to determine the involved gain and loss of possible collaboration. A considerable gain can be obtained if the direct source-destination channel gain is significantly smaller than those of alternative involved links. We demonstrate that a rate and energy improvement of up to $(1+\sqrt[η]{\frac{k}{k+1}})^η$ can be obtained, where $η$ is the environment path loss exponent and $k$ is the ratio of the rates of involved users. The gain is maximum for low transmit-energy-to-received-noise-ratio (TERN) and in a high TERN environment the NCP is preferred.
Relay Assisted F/TDMA Ad Hoc Networks: Node Classification, Power Allocation and Relaying Strategies
本文考虑了中继辅助的F/TDMA ad hoc网络的设计与多个中继节点,其中每个节点协助传输的一个预定义的子集的源节点到各自的目的地。考虑总容量作为性能指标,我们解决了最优分配的问题,每个中继节点的总功率之间的传输,它是协助。我们考虑四种不同的中继传输策略,即再生解码转发(RDF)、非再生解码转发(NDF)、放大转发(AF)和压缩转发(CF)。我们首先获得的中继节点,采用统一的中继策略的最佳功率分配政策的所有节点。我们发现,最佳的RDF和NDF的情况下的功率分配修改注水解决方案。我们观察到,对于一个给定的中继传输功率,NDF总是优于RDF,而CF总是提供更高的总和容量比AF。当CF和NDF进行比较,它是观察到,CF或NDF可能优于其他在不同的情况下。这一观察表明,总容量可以进一步提高每个中继采用中继策略,帮助不同的源节点。我们接下来研究这个问题,并确定中继节点协助的每个源节点的最佳功率分配和中继策略。我们观察到,最佳功率分配的中继节点与混合中继策略提供了更高的总容量比纯RDF,NDF,AF或CF中继策略。
Considering two-hop cooperative communication with buffered half-duplex relays, this work jointly optimizes relay selection and transmit power at the relay to maximize the sum-throughput of the network subject to a minimum throughput requirement of each hop and transmit power constraint. The optimization problem is solved and two new buffer aware selection schemes, namely joint relay power allocation and selection scheme (JPASS) and ratio selection scheme (RSS) are proposed. Numerical results show that the average sum-throughput of both the proposed schemes is up to 40% higher compared to the …
In this paper, we study relay selection and power allocation in two-way relaying networks consisting of a source, a destination and multiply half-duplex decode-and-forward (DF) relays. A transmission model with three time subslots is purposely introduced. In the first subslot, selected relay applies time-switching protocol to harvest radio frequency energy radiated by source and destination; in the remaining subslots, selected relay facilitates source and destination to exchange information. Due to finite-size data buffer and finite-size battery of relay, an optimal relay selection and power a…
Unmanned aerial vehicle (UAV) networks have grown rapidly in recent years and become attractive for various emergence communications scenarios. In this paper, we consider a UAV acting as a relay node to assist wireless transmissions from a base station (BS) to a ground user (GUs). A closed-form expression of outage probability for the BS-GUs transmission via UAV relaying is derived over Rician fading channels. We then formulate an optimization problem to minimize the outage probability of UAV relay communications with a constraint on the total transit power of the BS and GUs. It is proved that…
Joint resource allocation involving optimization of subcarrier allocation, subcarrier pairing (SCP), and power allocation in a cooperative secure orthogonal frequency division multiple access (OFDMA) communication system with untrusted users is considered. Both amplify and forward (AF), and decode and forward (DF) modes of operations are considered with individual power budget constraints for source and relay. After finding optimal subcarrier allocation for an AF relayed system, we prove the joint power allocation as a generalized convex problem, and solve it optimally. Compared to the convent…
In this letter, we propose a power allocation scheme for relayed orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems. The proposed power allocation scheme replies on artificial neural network (ANN) and deep learning to allocate transmit power among various subcarriers at the source and relay nodes. The objective of the power allocation scheme is to minimize the overall transmit power under a set of constraints. Without loss of generality, we assume all subcarriers at source and relay nodes are independently distributed with different statistical distribution para…
Intelligent reflecting surface (IRS) has recently emerged as a new solution to enhance wireless communication performance via passive signal reflection. In this letter, we unlock the potential of IRS controller in relaying information and propose a novel IRS-assisted communication system with both IRS passive reflection and active relaying. Specifically, we jointly optimize the time allocations for decode-and-forward (DF) relaying by the IRS controller and the IRS passive beamforming to maximize the achievable rate of the proposed system. We also compare the rate performance of the proposed sy…
In this paper, we study the physical layer security (PLS) problem in the dual hop orthogonal frequency division multiplexing (OFDM) based wireless communication system. First, we consider a single user single relay system and study a joint power optimization problem at the source and relay subject to individual power constraint at the two nodes. The aim is to maximize the end to end secrecy rate with optimal power allocation over different sub-carriers. Later, we consider a more general multi-user multi-relay scenario. Under high SNR approximation for end to end secrecy rate, an optimization p…