Cooperative retransmission protocols in fading channels : issues, solutions and applications

Future wireless systems are expected to extensively rely on cooperation between terminals, mimicking MIMO scenarios when terminal dimensions limit implementation of multiple antenna technology. On this line, cooperative retransmission protocols are considered as particularly promising technology due to their opportunistic and flexible exploitation of both spatial and time diversity. In this dissertation, some of the major issues that hinder the practical implementation of this technology are identified and pertaining solutions are proposed and analyzed. Potentials of cooperative and cooperative retransmission protocols for a practical implementation of dynamic spectrum access paradigm are also recognized and investigated. Detailed contributions follow. While conventionally regarded as energy efficient communications paradigms, both cooperative and retransmission concepts increase circuitry energy and may lead to energy overconsumption as in, e.g., sensor networks. In this context, advantages of cooperative retransmission protocols are reexamined in this dissertation and their limitation for short transmission ranges observed. An optimization effort is provided for extending an energy- efficient applicability of these protocols. Underlying assumption of altruistic relaying has always been a major stumbling block for implementation of cooperative technologies. In this dissertation, provision is made to alleviate this assumption and opportunistic mechanisms are designed that incentivize relaying via a spectrum leasing approach. Mechanisms are provided for both cooperative and cooperative retransmission protocols, obtaining a meaningful upsurge of spectral efficiency for all involved nodes (source-destination link and the relays). It is further recognized in this dissertation that the proposed relaying-incentivizing schemes have an additional and certainly not less important application, that is in dynamic spectrum access for property-rights cognitive-radio implementation. Provided solutions avoid commons-model cognitive-radio strict sensing requirements and regulatory and taxonomy issues of a property-rights model

Analysis of Outage Probability and Throughput for Half-Duplex Hybrid-ARQ Relay Channels

International audienceWe consider a half-duplex wireless relay network with hybrid-automatic retransmission request (HARQ) and Rayleigh fading channels. In this paper, we analyze the average throughput and outage probability of the multirelay delay-limited (DL) HARQ system with an opportunistic relaying scheme in decode-and-forward (DF) mode, in which the best relay is selected to transmit the source's regenerated signal. A simple and distributed relay selection strategy is considered for multirelay HARQ channels. Then, we utilize the nonorthogonal cooperative transmission between the source and selected relay for retransmission of source data toward the destination, if needed, using space-time codes. We analyze the performance of the system. We first derive the cumulative density function (cdf) and probability density function (pdf) of the selected relay HARQ channels. Then, the cdf and pdf are used to determine the exact outage probability in the lth round of HARQ. The outage probability is required to compute the throughput-delay performance of this half-dublex opportunistic relaying protocol. The packet delay constraint is represented by L, which is maximum number of HARQ rounds. Furthermore, simple closed-form upper bounds on outage probability are derived. Based on the derived upper bound expressions, it is shown that the proposed schemes achieve the full spatial diversity order of N+1, where N is the number of potential relays. In addition, simulation shows that our proposed scheme can achieve higher average throughput, compared with direct transmission and conventional tho-phase relay networks

Outage Probability Analysis of Multi-Relay Delay-Limited Hybrid-ARQ Channels

We consider a wireless relay network with with hybrid-automatic retransmission request (HARQ) and Rayleigh fading channels. In this paper, we analyze the outage probability of the multi-relay delay-limited HARQ system with opportunistic relaying scheme in decode-and-forward mode. A simple and distributed relay selection strategy is proposed for multi-relay HARQ channels. Then, we analyze the performance of the system. We first derive the cumulative density function (CDF) and probability density function (PDF) of the selected relay channels. Then, the CDF and PDF are used to determine the outage probability in the l-th round of HARQ. The packet delay constraint is represented by L, the maximum number of HARQ rounds. Furthermore, closed-form upper-bounds on outage probability are derived, which are used to investigate the diversity order of the system. Based on the derived upper-bound expressions, it is shown that the proposed schemes achieve the full spatial diversity order of N + 1, where N is the number of potential relays. Our analytical results are confirmed by simulation results

Stochastic Geometry Analysis of a Class of Cooperative Relaying Protocols

This thesis examines wireless relay networks that use hybrid-ARQ protocols. Relays networks efficiently combat fading and exploit the spatial diversity present in the channel. Hybrid-ARQ involves retransmitting the signal if it is not decoded correctly. In conventional HARQ, the retransmission comes from the source, but in cooperative HARQ the retransmission could come from a relay that has successfully decoded the message, thus attaining transmit diversity.;A Markov chain model is conceived and used to compute the effective throughput and outage probability in the presence of Rayleigh fading. The analytical results are validated with simulations. The spatial configuration of the network plays an important role in the performance of the network. The behavior of the protocols for fixed network topologies and random topologies is examined. The impact of parameters such as path loss exponent, number of relays, and Signal to Noise Ratio are determined.;Spatial averaging is helpful in capturing the spatial variations present in the system. When network topology is random, the analysis proceeds by first assuming the number of relays is fixed, in which case they are drawn from a Binomial Point Process (BPP). For each network realization, the outage probability, throughput and effective throughput are found, and the spatial average of these quantities are found by averaging over a large number of network realizations. Moreover, the maximum throughput is found for each network realization, leading to a characterization of the distribution of throughputs achievable in a random network. Finally, networks with a random number of relays are considered, including the important case that the number of relays in a given area is Poisson distributed, in which case they are drawn from a Poisson Point Process (PPP)

Resource Allocation for Network-Integrated Device-to-Device Communications Using Smart Relays

With increasing number of autonomous heterogeneous devices in future mobile networks, an efficient resource allocation scheme is required to maximize network throughput and achieve higher spectral efficiency. In this paper, performance of network-integrated device-to-device (D2D) communication is investigated where D2D traffic is carried through relay nodes. An optimization problem is formulated for allocating radio resources to maximize end-to-end rate as well as conversing QoS requirements for cellular and D2D user equipment under total power constraint. Numerical results show that there is a distance threshold beyond which relay-assisted D2D communication significantly improves network performance when compared to direct communication between D2D peers