Bhuvan Modi

Tight bounds on the ergodic capacity of cooperative analog relaying with adaptive source transmission techniques

Tight bounds for the Shannon capacity of amplify-and-forward cooperative diversity networks are derived for three different adaptive source transmission policies in a myriad of fading environments: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). Our unified framework based on the moment-generating function (MGF) approach allows us to gain insights as to how fade distributions and dissimilar fading statistics across the distinct communication links will affect the Shannon capacity, without imposing any restrictions on the fading parameters.

Improving the Spectral Efficiency of Adaptive Modulation in Amplify-and-Forward Cooperative Relay Networks with an Adaptive ARQ Protocol

This paper investigates the effectiveness of a cross-layer design that combines adaptive modulation (AM) at the physical layer with an adaptive truncated automatic repeat request (ARQ) protocol at the data link layer to maximize the throughput of cooperative amplify-and-forward (CAF) relay networks under prescribed delay and/or error performance constraints. A by-product of our proposed analytical framework, that involves evaluation of the marginal moment generating function (MGF) of the end-to-end signal-to-noise ratio (SNR), for computing the average throughput and average packet error rate performance metrics is the unification and generalization of existing studies on cross-layer combining of AM and truncated ARQ for non-cooperative diversity systems to generalized fading channels. Our analytical methodology is motivated by the fact that the MGF of end-to-end SNR for multi-relay CAF networks is either available in the research literature (for certain fading environments) or it can be computed much more conveniently than its PDF, while the desired marginal MGF can be evaluated efficiently using a multi-precision Laplace inversion formula of an auxiliary MGF function. The efficacy of an adaptive Rmax (maximum retransmission limit) strategy over the classical fixed Rmax scheme is also examined.

Ergodic capacity analysis of cooperative amplify-and-forward relay networks over generalized fading channels

This paper presents two new methods for evaluating the ergodic channel capacities of cooperative non-regenerative multirelay networks in a myriad of fading environments and under three distinct source-adaptive transmission policies: i optimal rate adaptation with a fixed transmit power; ii optimal joint power-and-rate adaptation; and iii truncated channel inversion with fixed rate. In contrast to the previous related works, our proposed unified analytical frameworks that are based on the moment generating function and/or the cumulative distribution function of end-to-end signal-to-noise ratio allow us to gain insights into how power assignment during different transmission phases, relay node placement, fade distributions, and dissimilar fading statistics across the distinct communication links impact the ergodic capacity, without imposing any restrictions on the channel fading parameters. Copyright

Analysis of amplify-and-forward cooperative relaying with adaptive modulation in Nakagami-m fading channels

This article investigates the efficacy of a constant-power, rate-adaptive M-QAM transmission technique in amplify-and-forward cooperative wireless networks. Tight upper and lower bounds are derived for the mean achievable spectral efficiency, outage probability, and error probability performance of non-regenerative cooperative relay networks in Nakagami-m fading environments. We observe that the spectral efficiency of a practical discrete-rate MQAM comes within a constant gap of the theoretical ergodic capacity of that channel, although this gap is smaller for an adaptive continuous-rate M-QAM.

Joint-design of adaptive modulation and coding with adaptive ARQ for cooperative relay networks

This article investigates the efficacy of a joint-design of adaptive modulation and coding (AMC) at the physical (PHY) layer with an adaptive Rmax-truncated selective-repeat automatic repeat request (ARQ) protocol at the medium access control (MAC) layer to maximize the throughput of cooperative amplify-and-forward (CAF) relay networks under prescribed delay and/or error performance constraints. Specifically, we generalize the existing design/results for cross-layer combining of AMC with truncated ARQ in non-cooperative diversity systems in three-folds: (i) extension of the cross-layer PHY/MAC design or optimization to cooperative diversity systems; (ii) generalization/unification of analytical expressions for various network performance metrics to generalized block fading channels with independent but non-identically distributed (i.n.d) fading statistics among the spatially distributed nodes; (iii) investigation of the effectiveness of joint-adaptation of the maximum retransmission limit Rmax in ARQ protocol and cooperative diversity order N for delay-insensitive applications. Our numerical results reveal that the average throughput can be increased considerably by judiciously combining two additional degrees of freedom (N and Rmax) that are available in CAF relay networks besides employing AMC at the PHY layer, especially in the most challenging low signal-to-noise ratio (SNR) regime.

On ergodic capacity of cooperative non-regenerative relay networks in Rice fading environments

In this article, we have derived closed form moment generating function (MGF) of upper and lower bounds of the harmonic mean signal-to-noise ratio (SNR) of the two-hop cooperative amplify-and-forward (CAF) relay networks over Rice fading environments. The derived MGF formulas are then applied to the computation of ergodic capacity of optimal rate adaptation with constant power (ORA) and optimal joint power and rate adaptation (OPRA) source adaptive transmission policies over Rice fading channels. The above mathematical framework for the ergodic capacity allows us to investigate how the power assignment during different transmission phases, node placement (i.e., position of relay with respect to source and destination), fade distributions and dissimilar fading statistics across the distinct communication links affect the ergodic capacity, without imposing any restrictions on the fading parameters. Moreover, the ergodic capacity of ORA and OPRA source adaptive transmission policies have also been computed using new closed-form approximate MGF expression of two-hop CAF relay networks in our further attempt to reduce the computational complexity of the mean achievable rates for CAF relay networks. The proposed analytical frameworks have been validated by Monte Carlo simulations and are in good agreement.

Analysis of cooperative non-regenerative relay networks with adaptive modulation in generalized fading channels

This article analyzes the performance of CSI-assisted cooperative amplify-and-forward (CAF) relay networks that employ both the optimal power allocation strategy among collaborating nodes and adaptive M-ary quadrature amplitude modulation (M-QAM) technique in Nakagami-m wireless fading environments. In particular, we advocate a simple yet unified numerical approach based on the marginal moment generating function (MGF) of the total received SNR to derive tight approximations or upper and lower bounds for the average bit error rate (ABER), mean achievable spectral efficiency, and outage probability performance metrics. The proposed analytical framework is sufficiently general to characterize the performance of adaptive-link CAF relay networks over a wide range of fading distributions (i.e., not restricted to Rayleigh fading) with independent but non-identically distributed (i.n.d) fading statistics across the spatially distributed diversity paths. Numerical results reveal that the optimal transmit power allocation among cooperative nodes in a practical CAF relay topologies could lead to a further substantial increase in the mean spectral efficiency compared to the equal power assignment case but at the expense of higher network overhead. The accuracies of our analytical results have been validated via Monte Carlo simulations.

An MGF approach for performance evaluation of non-regenerative cooperative relay networks with adaptive modulation and optimum power allocation in nakagami-m fading environments

This article analyzes the performance of CSI-assisted cooperative amplify-and-forward (CAF) relay networks that employ both the optimal power allocation strategy among collaborating nodes and adaptive M-ary quadrature amplitude modulation (MQAM) technique in Nakagami-m wireless fading environments. In particular, we advocate a simple yet unified numerical approach based on the marginal moment generating function (MGF) of the total received SNR to derive tight approximations or upper and lower bounds for the average bit error rate (ABER), mean achievable spectral efficiency, and outage probability performance metrics. The proposed analytical framework is sufficiently general to characterize the performance of adaptive-link CAF relay networks over a wide range of fading distributions (i.e., not restricted to Rayleigh fading) with independent but non-identically distributed (i.n.d) fading statistics across the spatially distributed diversity paths. Numerical results reveal that the optimal transmit power allocation among cooperative nodes in a practical CAF relay topologies could lead to a further substantial increase in the mean spectral efficiency compared to the equal power assignment case but at the expense of higher network overhead. The accuracies of our analytical results have been validated via Monte Carlo simulations.

On the ergodic capacity of cooperative analog relaying with source adaptive transmission policies

Tight bounds for the mean achievable rates of amplify-and-forward cooperative relay networks are derived for three distinct source adaptive transmission policies in a myriad of fading environments: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). Our unified framework based on the moment-generating function (MGF) technique allows us to gain insights as to how power assignment during different transmission phases, fade distributions and dissimilar fading statistics across the distinct communication links affect the ergodic capacity, without imposing any restrictions on the fading parameters.

Unified analysis of ergodic capacity of cooperative non-regenerative relaying with adaptive source transmission policies

Tight bounds for the ergodic capacity of amplify-and-forward cooperative diversity networks are derived for three different adaptive source transmission policies in a myriad of fading environments: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). Our unified framework based on the moment-generating function (MGF) approach allows us to gain insights as to how fade distributions and dissimilar fading statistics across the distinct communication links will affect the mean achievable rates, without imposing any restrictions on the fading parameters.