Xianfu Lei

Exact Performance of Two-Way AF Relaying in Nakagami-m Fading Environment

The performance of two-way amplify-and-forward (AF) relaying networks over independently but not necessarily identically distributed (i.n.i.d.) Nakagami-m fading channels, with integer and integer plus one-half values of fading parameter m, is studied. Closed-form expressions for the cumulative distribution function (CDF), probability density function (PDF), and moment generating function (MGF) of the end-to-end signal-to-noise ratio (SNR) are presented. Utilizing these results, we analyze the performance of two-way AF relaying system in terms of outage probability, average symbol error rate (SER), and average sum-rate. Simulations are performed to verify the correctness of our theoretical analysis.

Secure Multiple Amplify-and-Forward Relaying With Cochannel Interference

We investigate the impact of cochannel interference on the security performance of multiple amplify-and-forward (AF) relaying networks, where N intermediate AF relays assist the data transmission from the source to the destination. The relays are corrupted by multiple cochannel interferers, and the information transmitted from the relays to the destination can be overheard by the eavesdropper. In order to deal with the interference and wiretap, the best out of N relays is selected for security enhancement. To this end, we derive a novel lower bound on the secrecy outage probability (SOP), which is then utilized to present two best relay selection criteria, based on the instantaneous and statistical channel information of the interfering links. For these criteria and the conventional max-min criterion, we quantify the impact of cochannel interference and relay selection by deriving the lower bound on the SOP. Furthermore, we derive the asymptotic SOP for each criterion, to explicitly reveal the impact of transmit power allocation among interferers on the secrecy performance, which offers valuable insights into practical design. We demonstrate that the all selection criteria achieve full secrecy diversity order N, while the proposed two criteria in this paper outperform the conventional max-min scheme.

Secure Multiuser Communications in Multiple Amplify-and-Forward Relay Networks

This paper proposes relay selection to increase the physical layer security in multiuser cooperative relay networks with multiple amplify-and-forward relays, in the presence of multiple eavesdroppers. To strengthen the network security against eavesdropping attack, we present three criteria to select the best relay and user pair. Specifically, criteria I and II study the received signal-to-noise ratio (SNR) at the receivers, and perform the selection by maximizing the SNR ratio of the user to the eavesdroppers. To this end, criterion I relies on both the main and eavesdropper links, while criterion II relies on the main links only. Criterion III is the standard max-min selection criterion, which maximizes the minimum of the dual-hop channel gains of main links. For the three selection criteria, we examine the system secrecy performance by deriving the analytical expressions for the secrecy outage probability. We also derive the asymptotic analysis for the secrecy outage probability with high main-to-eavesdropper ratio. From the asymptotic analysis, an interesting observation is reached: for each criterion, the system diversity order is equivalent to the number of relays regardless of the number of users and eavesdroppers.

A Survey on Non-Orthogonal Multiple Access for 5G Networks: Research Challenges and Future Trends

Non-orthogonal multiple access (NOMA) is an essential enabling technology for the fifth-generation (5G) wireless networks to meet the heterogeneous demands on low latency, high reliability, massive connectivity, improved fairness, and high throughput. The key idea behind NOMA is to serve multiple users in the same resource block, such as a time slot, subcarrier, or spreading code. The NOMA principle is a general framework, and several recently proposed 5G multiple access schemes can be viewed as special cases. This survey provides an overview of the latest NOMA research and innovations as well as their applications. Thereby, the papers published in this special issue are put into the context of the existing literature. Future research challenges regarding NOMA in 5G and beyond are also discussed.

Multiuser Cognitive Relay Networks: Joint Impact of Direct and Relay Communications

In this paper, we propose a multiuser cognitive relay network, where multiple secondary sources communicate with a secondary destination through the assistance of a secondary relay in the presence of secondary direct links and multiple primary receivers. We consider the two relaying protocols of amplify-and-forward (AF) and decode-and-forward (DF), and take into account the availability of direct links from the secondary sources to the secondary destination. With this in mind, we propose an optimal solution for cognitive multiuser scheduling by selecting the optimal secondary source, which maximizes the received signal-to-noise ratio (SNR) at the secondary destination using maximal ratio combining. This is done by taking into account both the direct link and the relay link in the multiuser selection criterion. For both AF and DF relaying protocols, we first derive closed-form expressions for the outage probability and then provide the asymptotic outage probability, which determines the diversity behavior of the multiuser cognitive relay network. Finally, this paper is corroborated by representative numerical examples.

Outage Probability Analysis and Power Allocation for Two-Way Relay Networks with User Selection and Outdated Channel State Information

This paper considers a multiuser two-way relay network (TWRN) consisting of one base station (BS), one amplify-and-forward (AF) relay and K mobile stations (MSs) among which the Nth-best MS is selected to exchange information with the BS. Specifically, we study the impact of outdated channel state information (CSI) on the system over time-varying Rayleigh block-fading channels by deriving a tight closed-form lower bound for the outage probability. We also obtain an asymptotic outage probability expression for high signal-to-noise ratio (SNR). Moreover, by minimizing the asymptotic outage probability, we optimize the power allocation (PA) among the network nodes. Numerical and simulation results collaborate the proposed studies.

Exact Closed-Form Expression for Ergodic Capacity of Amplify-and-Forward Relaying in Channel-Noise-Assisted Cooperative Networks with Relay Selection

In this letter, an exact closed-form expression is derived for the ergodic capacity of dual-hop channel-noise-assisted amplify-and-forward cooperative networks with relay selection considered by Costa and Aïssa. Simulation results corroborate the theoretical analysis.

Exact symbol error probability of general order rectangular QAM with MRC diversity reception over nakagami-m fading channels

Exact average symbol error probability (SEP) of the general order rectangular quadrature amplitude modulation (QAM) with maximal ratio combining (MRC) diversity over L independent and identically distributed Nakagami-m fading channels with arbitrary fading index m is derived in this letter. The average SEP expression is given in terms of the Appell and Gauss hypergeometric functions and is then used to study the impact of diversity reception on the performance of general order rectangular QAM with different values of the quadrature-to-in-phase decision distance ratio. It is shown that the derived expression includes some existing results as special cases.

Cost Analysis of Movement-Based Location Management in PCS Networks: An Embedded Markov Chain Approach

In this paper, we develop an approach of embedded Markov chain to analyze the signaling cost of a movement-based location management (MBLM) scheme. This approach distinguishes itself from those developed in the literature in the following aspects. 1) It considers the location area (LA) architecture used by personal communication service (PCS) networks for location management. 2) It considers two different call handling models that determine after a call whether a location update should be performed. 3) It considers the effect of the call holding time on the call handling models. 4) It proposes to use a fluid flow model to describe the dependence between the cell and the LA residence time. We derive closed-form analytical formulas for the signaling cost, whose accuracy is manifested by a simulation. Based on the analytical formulas, we conduct a numerical study to evaluate the influence of various parameters on the signaling cost. The formulas can contribute to the implementation of the MBLM scheme in PCS networks including Fourth-Generation (4G) Long-Term Evolution. The modeling approach developed in this paper can be exploited to model other location management schemes.

Outage Probability of TDBC Protocol in Multiuser Two-Way Relay Systems with Nakagami-m Fading

This paper considers a multiuser two-way relay system with time division broadcast (TDBC) protocol, where multiple end-sources compete to exchange information with another end-source through the help of a single half-duplex amplify-and-forward (AF) relay. We derive a tight closed-form lower bound for the system outage probability over Nakagami-m fading channels with integer fading parameters. An asymptotic expression for the outage probability in high signal-to-noise ratio (SNR) regime is also obtained. Numerical results corroborate the theoretical analysis.