Effect Of Relay Location Research Articles

Cooperative Uplink NOMA for Frequency Selective Environment: Outage Analysis and Power Allocation

Non-Orthogonal Multiple Access (NOMA) is emerging as an efficient multiple access technique for the fifth-generation (5G) and beyond 5G (B5G) cellular networks in order to meet the increasing demands on low latency, high reliability, massive connectivity, improved fairness, and high throughput. On the other hand, cooperative relay networks have shown to improve significantly the throughput, the coverage, and the achievable rates of wireless networks, in which the relay nodes assist the communication between the source node and the destination node when the direct channel is low. In this paper, three users’ scenario that simultaneously send information to a base station with the help of a half-duplex relay applying a decode-and-forward (DF) scheme have been studied. Differently from all the existing works and in order to make the work more realistic, it has been assumed that (i) all the channels undergo frequency-selective multipath fading and (ii) the power allocation factors at the transmitting nodes are decided based on the statistical Channel State Information (CSI) not perfect CSI. Under Rayleigh fading channels, expressions of the outage probability are derived and an ad-hoc approach is proposed in order to determine the power allocation factors. Furthermore, the effect of relay location on the outage performance is investigated and the importance of choosing the power allocation factors carefully is demonstrated. Simulation results show that the proper selection of the power allocation factors and the relay location plays a decisive role in uplink NOMA’s performance jointly. Moreover, NOMA always performs better than the Orthogonal Multiple Access (OMA).

Relay selection schemes for Cooperative NOMA (C-NOMA) with simultaneous wireless information and power transfer (SWIPT)

Non-orthogonal multiple access (NOMA) is considered as an important technique to alleviate the spectral scarcity of wireless networks. Cooperative NOMA (C-NOMA) along with simultaneous wireless information and power transfer (SWIPT) pave paths towards energy and spectral efficient communication networks. This paper investigates SWIPT enabled multiple relay C-NOMA network, where dedicated intermediate relays are energy-constrained and harvest energy from the transmitted source signal. New two-stage relay selection (RS) schemes for C-NOMA with fixed power allocation and dynamic power allocation at relay node are proposed. Analytical expressions and asymptotic expressions of outage probability for proposed schemes and partial RS are derived to evaluate the system performance. Simulation results demonstrate that two stage RS provides the maximum performance gain at high SNR regime, while the partial RS is preferable at low SNR. Based on outage probability difference, a hybrid RS scheme which switches between partial and two-stage is introduced. The important insights of analytical results, such as comparative analysis of relay selection schemes, performance gain over SWITP OMA networks, effect of data rates, effect of relay location, and impact of using SWIPT on the outage performance of C-NOMA networks are discussed.

Resource Allocation of Two-relay Networks with Partially Differential Modulation

Relay networks enhance the system performance by creating cooperative diversity gain and extend communication range by relaying the received signal to other devices. In this paper, the performance of two-relay networks is analyzed by adopting decode-andforward (DF) relaying protocol. The signaling scheme uses partially differential modulation which applies coherent modulation in source-relays links and differential modulation in relay-destination links. We first analyze the effect of relay location in the system performance. Based on this, we find the optimum relay selection which minimizes the symbol error rate (SER). Then, we explores the effect of energy allocation for the given relay location.

부분차등변조 방식을 이용한 협력통신 전송기법

Cooperative communication, which transmit signal via arbitrary number of relays, enhances the overall communication performance by providing virtual Multi-Input Multi-Output (MIMO) gain without imposing multiple antennal limitation in physical system. There are two representative relaying protocols, i.e., Amplify-and-Forward (AF) and Decode-and-Forward (DF), where we analyze the performance of cooperative communication by adopting DF relaying protocol applying partially differential modulation. The performance is based on symbol error rate (SER), and the effect of relay location on the performance is analyzed. We also compare the performance of the proposed scheme with the system which uses differential modulation scheme.

Relay-Aided Amplify-and-Forward Powerline Communications

Powerline communications (PLC) is a favorable technique for many smart grid applications. By transmitting information over the existing powerline infrastructure, PLC has the benefit of low deployment cost. However, due to low transmit power, limited bandwidth, and harsh channel conditions, reliable long-distance and high-capacity PLC is challenging. Relay-aided (RA-) PLC is promising in addressing these issues. In this paper, we investigate the performance of the amplify-and-forward (AF) RA-PLC system from an information-theoretic perspective. The capacity of AF-based RA-PLC is analyzed for frequency-selective PLC channels. The capacity bounds are derived, and the optimal power allocation between the transmitting nodes and the optimal power distribution over the signal frequency band are obtained. The capacity benefits and features of AF-based RA-PLC are evaluated with two prevalent powerline channel models. Based on the signal attenuation model, the capacity of AF-based RA-PLC is compared with direct-link (DL-)PLC, and the effect of relay location is revealed. In addition, based on the transmission line (TL) model, the effects of branch density and load impedance on the capacity of AF-based RA-PLC are evaluated.

Outage Probability and Power Allocation for Cooperative Multicast Systems

This letter analyzes the group outage performance of cooperative multicast systems, in which the source multicasts its signal to multiple destinations by the aid of a single relay. In order to improve the system performance, both the transmit powers of the source and the relay are optimized based on the asymptotically tight group outage probability. The proposed optimized power allocation (OPA) scheme is compared with the traditional equal power allocation (EPA) scheme, and its performance enhancement and the effect of relay location on both schemes are provided through simulation results.

Resource allocation for orthogonal frequency division multiplexing (OFDM) underwater acoustic cooperative transmission with limited feedback

In this paper, we first compare the difference between the wave cooperative (WC) protocol (designed for acoustic propagation) and amplify-forward (AF) protocol. In WC protocol, the relay nodes will transmit the received signal from the transmitter to the destination immediately (one time slot), in order to overcome the low transmission data rate problem in acoustic communication systems. Then we will propose the closed-form expression of the WC protocol with single relay. We will adopt the underwater acoustic (UWA) Rayleigh fading channel model and ambient noise in this cooperative transmission system. We propose capacity criterion based power allocation for UWA cooperative transmission (WC model) with the total transmitted power constraint, achieved under different levels of quantized CSI feedback using Lloyd algorithm. Meanwhile, limited feedback general procedure and Lloyd algorithm based codebook design will be presented. Simulation results will compare the system capacity with different bits of feedback, perfect feedback and non-feedback. In addition, the effect of relay locations on the system performance and the convergence speed of the Lloyd algorithm will be explored in the results.

Performance of amplify-and-forward cooperative networks with differential unitary space time coding

In wireless communications, multi-input multi-output technology has been appreciated for its high transmission rate and diversity gain. These can also be exploited in cooperative networks by using network nodes as virtual antenna arrays. In this paper, we analyze the performance of cooperative networks with differential unitary space-time modulation under high signal-to-noise ratio. Relaying protocol is based on amplify-and-forward. The effect of relay location and energy allocation as well as the comparison with a conventional cooperative network is also addressed.