Author_Institution :
Discipline of Electr. Eng., Indian Inst. of Technol. Indore, Indore, India
Abstract :
In this paper, we investigate the impact of outdated channel estimates on the overall performance of a two-way multirelay system that employs a three-phase (3P) analog network coding (ANC)-based opportunistic relay selection (ORS) scheme under Rayleigh fading. Specifically, considering the imperfect estimation and the time variation of the fading channels, we formulate the 3P ANC-based ORS strategy for the best relay among multiple relays in terms of both outdated and imperfect channel state information (CSI). With such a practical CSI modeling, we derive a tight lower bound expression for the overall outage probability (OOP) and an upper bound expression for the ergodic sum-rate (ESR) of the considered scheme. In addition, by deriving an asymptotic outage behavior in the high signal-to-noise ratio (SNR) regime, we highlight the impact of outdated and imperfect CSI on the achievable diversity order. Moreover, based on the asymptotic analysis, we investigate three optimization problems, namely, optimal relay power allocation for fixed relay location, optimal relay location for fixed power allocation, and jointly optimal relay power allocation and location to minimize the OOP and to maximize the ESR of the considered system. Our results reveal that the optimal relay power allocation has a more significant impact on the performance when the CSI is imperfect, whereas the optimal relay location has a more noticeable impact when the CSI is outdated and unbalanced over the two hops. Furthermore, we show that the imperfect CSI can degrade system performance more severely than the outdated CSI, and it can even reduce the system diversity order to zero. The numerical and simulation results corroborate our theoretical analysis and findings and demonstrate that the 3P ANC-based ORS scheme can achieve better performance than its two-phase counterpart, depending upon the quality of the direct link, particularly in the medium-to-high-SNR regime.
Keywords :
Rayleigh channels; channel coding; channel estimation; network coding; numerical analysis; optimisation; probability; radio links; relay networks (telecommunication); telecommunication network reliability; 3P ANC-based ORS strategy; Rayleigh fading channel time variation; asymptotic analysis; direct link quality; ergodic sum-rate; fixed relay location; high signal-to-noise ratio regime; imperfect channel state information; medium-to-high-SNR regime; numerical simulation; opportunistic relay selection scheme; opportunistic two-way ANC-based relaying; optimal relay location; optimal relay power allocation; optimization problem; outdated channel estimation impact; outdated channel state information; overall outage probability; three-phase analog network coding; three-phase transmission; two-way multirelay system performance; upper bound expression; Channel estimation; Channel state information; Data communication; Fading; Network coding; Relays; Resource management; Signal to noise ratio; Analog network coding; Analog network coding (ANC); Rayleigh fading; channel estimation errors; ergodic sum-rate; ergodic sum-rate (ESR); outage probability; outdated CSI; outdated channel state information (CSI); power allocation; relay location; two-way relaying;
