We consider the effective capacity performance measure of persistent- and truncated-retransmission schemes that can involve any combination of multiple transmissions per packet, multiple communication modes, or multiple packet communication. We present a structured unified analytical approach, based on a random walk model and recurrence relation formulation, and give exact effective capacity expressions for persistent hybrid automatic repeat request (HARQ) and for truncated-retransmission schemes. For the latter, effective capacity expressions are given for systems with finite (infinite) time horizon on an algebraic (spectral radius-based) form of a special block companion matrix. In contrast to prior HARQ models, assuming infinite time horizon, the proposed method does not involve a non-trivial per case modeling step. We give effective capacity expressions for several important cases that have not been addressed before, e.g., persistent-HARQ, truncated-HARQ, network-coded ARQ, two-mode-ARQ, and multilayer-ARQ. We propose an alternative quality-of-service-parameter (instead of the commonly used moment generating function parameter) that represents explicitly the target delay and the delay violation probability. This also enables the closed-form expressions for many of the studied systems. Moreover, we use the recently proposed matrix-exponential distributed modeling of wireless fading channels to provide the basis for numerous new effective capacity results for HARQ.

We propose a novel performance analysis framework for lossless- and truncated-hybrid automatic repeat request (HARQ) that enables neat, general, closed-form throughput expressions in a matrix exponential (ME) distribution form. This approach is applicable to all HARQ schemes for which the probability density function of the effective channel can be characterized by a rational Laplace transform, or equivalently, an ME-distribution. This includes, for example, repetition redundancy HARQ in ME distributed channels. Throughput expressions are also given for the K-truncated-HARQ N-fold diversity, ARQ N-fold diversity, and lossless-HARQ 2-fold diversity cases in the ME distributed channel. Schemes with effective channels of non-rational Laplace transforms, such as IR-HARQ, are explored using truncated continued fractions. A novel integration trick is developed for the integration of ME distributions with singular matrices and yields the simple throughput expression of lossless-HARQ. We also give general analytical expressions for the optimal throughput and optimal rate point that benefit from the compact ME-distribution form proposed.

In this paper, we consider throughput and rate optimized throughput for large-scale MIMO-(H)ARQ systems in i.i.d. complex Gaussian block fading channels. Exact analysis of large-scale MIMO is generally intractable, yet the field of random matrix theory has provided asymptotic expressions for the instantaneous channel capacity, which we propose for studying MIMO-(H)ARQ systems. Even with those expressions, closed-form results for the maximum throughput and optimal rate are not known. We therefore provide i) tight asymptotic lower and upper bounds, with a diminishing gap, for the optimal rate that is useful for the design of practical link adaptation algorithms, and ii) a tight asymptotic lower bound for the maximized throughput, suggesting the practical sufficiency of MIMO-ARQ, without any packet combining, over more complex MIMO-HARQ methods.

We consider the throughput performance of ARQ in interfering channels, where the signal of interest as well as the interferers are subject to independent distributed Nakagami-m block fading. The key contribution is the derivation of closed-form expressions for the rate-maximized throughput. For this purpose, we employ the powerful parameterization approach from [1], allowing the problem to be solved exactly in a closed-form. We also consider the scaled-power, and the interference-limited, case.

This paper examines throughput performance, and its optimization, for lossless and truncated automatic repeat request (ARQ) schemes in Gaussian block fading channels. Specifically, ARQ, repetition redundancy, and in part also incremental redundancy-hybrid ARQ, are considered with various diversity schemes. We propose a parameterization-based method that allows (semi-)closed-form expressions, linking optimized throughput, optimal rate, and mean SNR, to be derived for any ARQ and repetition redundancy-HARQ method even when a non-parameterized closed-form does not exist. We derive numerous throughput and optimal throughput expressions for various ARQ schemes and diversity scenarios, potentially useful for benchmarking purposes or as design guidelines.

In this paper, we consider network coded (NCed) Hybrid-ARQ (HARQ) for multiple unicast flows. The main contribution of the paper is the derivation of throughput expressions for NCed HARQ with arbitrary number of users in identical i.i.d. channels amid packets for all users. We apply the result to Rayleigh fading channels and two packet combining schemes: incremental redundancy (IR) and chase combining (CC). We verify the analytical results with simulations and observe substantial SNR improvements over NCed ARQ and HARQ. The SNR gains in the moderate/high and low throughput regimes are mainly due to network coding and packet combining, respectively. For low/moderate SNRs, NCed HARQ with IR surpasses the CC performance. In addition, we introduce a novel re-transmission strategy that makes the network coding more efficient at low SNR.

In this paper, we consider network coded (NCed) Hybrid-ARQ (HARQ) for multiple unicast flows. The main contribution of the paper is the derivation of a throughput expression for NCed HARQ with arbitrary number of users in i.i.d. channels. We apply the result to Rayleigh fading channels for incremental redundancy (IR) and chase combining (CC) based NCed HARQ. We verify the analytical approach with simulations and observe substantial SNR (or energy) improvements over regular ARQ with network coding as well as classical (H)ARQ. The SNR gains in the high and low throughput regimes are mainly due to the network coding and HARQ aspects, respectively. For low SNRs, NCed HARQ with IR surpass the CC performance.

A repeater is a device that improves the rate-coverage performance of a system by amplifying and forwarding its received signal. When multiple antennas are deployed on a repeater, spatial signal processing becomes possible for better performance. In this paper we propose a spatial filter for such a multi-antenna repeater. This filter is designed based on first-hop channel state information (CSI) and end-to-end signal-to-noise ratio (SNR). The optimal filter matrix is proved to be a product of a diagonal matrix and the conjugate transpose of the left singular matrix of the first-hop channel matrix. The diagonal matrix is obtained by maximizing an upper bound of the ergodic channel capacity. Simulation results indicate that the proposed filter outperforms that without filtering in end-to-end channel capacity, especially when the number of repeater antennas is greater than that of the source antennas. As the first-hop CSI and the end-to-end SNR can be obtained without any modification of the source or the destination, a repeater with the proposed spatial filter can be easily implemented in a current system.

In this paper, we consider the idea of a MIMO on- frequency repeater (OFR), with end-to-end MIMO channel rank preservation, MIMO aware repeater output-to-input self- interference cancellation, and a new repeater output-to-input beamforming based interference mitigation method for MIMO signals. The latter is used to increase the repeater output-to-input isolation and in turn increase the communication rate and range. The MIMO-OFR idea is compared via simulation to two 2-phase forwarding methods. Through simulation, we observe higher mean channel capacity and improved outage probability for the proposed idea. The viability of the interference feedback mitigation method is also discussed by considering a reflection channel and channel estimation errors for the output-to-input channel, indicating positive potential worth exploring further.

In this paper, a new and simple arithmetic operation for network coding (NC) in wireless communication is proposed. It is built on the assumption of constant modulus signals with phase conveyed information such as PSK and employs, in contrast to classical NC finite field additions, a multiplicative NC operation. The benefit of the method is that it decouples the NC operation from forward error correction (FEC) and modulation imposed joint constraints and thus permits for greater flexibility to adapt code and modulation rates to different user. It may further reduce hardware (HW) complexity and cost for NC enabled relays and it may operate directly on (potentially noisy) baseband signals. The performance of the proposed NC method is examined in a three phase NC bi-directional relaying scenario and compared to a traditional four phase non-NC scheme illustrating performance benefits in the high signal to noise (SNR) region and its viability for the former.

A joint adaptive power and adaptive rate (APAR) control algorithm for OFDM systems that aims at sum-rate maximization, subject to certain power and rate constraints, is presented in this paper. In the basic optimization framework, the overall system throughput is the main objective, but as such it lacks user fairness consideration. Two scheduling schemes that allow adjusting the trade-off between fairness and throughput are proposed and combined with the APAR scheme for fairness enhancement. Simulation results show that enhanced system performance and balanced efficiency-fairness trade-off can be achieved by the proposed schemes in downlink.

In this paper, multiuser ARQ is extended to multicasting. The core idea is that the sender, based on feedback from users regarding successfully received transmissions, adapts code weights for data packet linear combinations that are then sent. Each user exploits its previously received information in decoding the linearly combined packets. Specifically, a throughput optimal, low en-/decoding complexity enabling, low overhead and on-line multicast coding and scheduling algorithm is devised based on a per user rank increase criterion. For throughput optimality, a minimum field size criterion is derived. Relative previous work, which adaptively identifies sets of users suited to receive linearly combined packets and uses GF(2) and XOR coding, the proposed method adaptively select weights from a sufficient large finite field for optimality instead. Throughput is analyzed and simulated, and en-/decoding complexity, signaling overhead, and latency etc. are studied through realistic simulations. Overall, it is found that the throughput is significantly higher than multicast selective repeat ARQ, and that the optimal throughput for an erasure channel is attained.

A power and rate control scheme especially crafted for delay tolerant traffic under interfering link conditions is presented in this paper. Specifically, an iterative distributed algorithm, based on a sum-power constrained sum-rate maximization with upper (and lower) power and rate constraints, is developed. The feasibility and performance of the algorithm is demonstrated by simulation in a cellular system, where it is applied both for SISO and MIMO links. Simulations show significant improvement of the sum-rate vs. sum-power relation compared to both HSDPA-like "fixed power adaptive rate" and GSM-like "fixed rate adaptive power" radio resource management. Also, the method offers automatic re-use handling by silencing sub-optimal links. In a MIMO scenario, the sum-rate scales near linearly with the number of antenna elements.

This paper presents an analysis of multi-user ARQ for multiple unicast flows with arbitrary reception probabilities. The core idea of multi-user ARQ is to exploit knowledge of previously overheard packets by unintended users, and perform wise selection and joint encoding of any retransmitted information. Intended users may decode the jointly encoded packet by exploiting the previously overheard packets. In this paper, a scheduling approach that balances the traffic shares and maximizes the throughput is proposed and analyzed. It is found that identical reception probabilities among the users yield the best performance and that the sensitivity in throughput efficiency, with respect to changes in reception probabilities, is reduced when the number of user increases.

This paper presents a novel ARQ scheme for multiple unicast flows in a multi-user system, which enhances the aggregate throughput efficiency. The core idea is to exploit knowledge of previously overheard packets by unintended users, and perform wise selection and joint encoding of any retransmitted information. Intended users may decode the jointly encoded packet by exploiting the previously overheard packets. It is found that the throughput efficiency in a K-user system approaches, the fairly remarkable result of, unit value when K goes to infinity. Moreover, complexity and overhead of the scheme is studied and a link to (feedback free) network coding is established

In this paper, bi-directional traffic between two nodes communicating via a relay node is considered. A novel relaying method based on joint data packet encoding in conjunction with exploitation of a priori known information is presented. Moreover, a specially crafted method for combining of the direct and relayed radio signal is suggested. The proposed scheme enables a reduced number of transmissions, whereby enhancing aggregate throughput. Evaluation, where optimal power and rate settings are derived, shows that the proposed method enhances the throughput up to 33% as compared to a (traditional) four-phase bi-directional protocol under a system energy constraint, both with and without the proposed combining method

This paper investigates power allocation in cooperative relaying based on Alamouti diversity. The objective is to find channel capacity optimal ways to allocate power between two relays under aggregate relay power constraints. Both a nonregenerative and a regenerative case are evaluated. The analysis shows that the total power should be allocated to one of the two relays, provided the instantaneous channel state information of both the 1sthop and the 2ndhop are available at the relays, i.e. for both non-regenerative and regenerative relaying. For the scenario that the relays have the instantaneous channel state information of the 1sthop, but only the average channel state information of the 2ndhop, the efforts focus on the regenerative relays while assuming the relays could perform decoding perfectly. Several optimization schemes: maximization of the mean channel capacity, maximization of the mean signal-to-noise ratio (SNR) and minimization of SNR variance are investigated. The "minimization of the SNR variance" scheme results in significantly lower mean channel capacity than the other two schemes do. The "maximization of the mean SNR" scheme still leads to the conclusion that the total power should be allocated to one of the two relays. The "maximization of the mean channel capacity" scheme gives almost the same mean channel capacity compared to the "maximization of the mean SNR" scheme and the two schemes are equivalent to each other in most cases

Multihop packet radio networking promises increased data rates and enhanced coverage in wireless networks. In this paper, we propose a new high performing low complexity multihop forwarding scheme, denoted multiuser diversity forwarding (MDF), that efficiently exploits inherent radio channel characteristics. The scheme is founded on a cross-layer paradigm, which enables a transmitting node to perform instant rate adaptation as well as to select among relays and among flows, thereby taking full advantage of the inherent multiuser diversity. The relative performance of MDF is benchmarked against two reference schemes, nearest with forward progress (NFP) and selection diversity forwarding (SDF). The simulations indicate that the proposed scheme yields a substantial throughput increase.

Recent and increased interest of wireless mobile ad hoc networking motivates detailed examination of routing schemes specifically targeted for the demanding constraints that an unreliable, time varying and braodcast like wireless medium imposes. Incorporation and exploitation of radio characteristics are fundamental keys to successful and near optimal operation of routing schemes in a wireless environment. In this paper, for warding methods for wireless mobile multihop networking in Rayleigh fading and non-fading channels are examined. An adaptive forwarding scheme denoted Selection Diversity Forwarding (SDF) is introduced and compared with two classical forwarding methods. It is shown that SDF presents significant peformance improvements. In particular and in constrast to the reference methods NFP and MFR, the performance of SDF is enhanced under fading channel conditions. It is found that local path adaptation has potential to perform better than routing approaches along a single path