Error Correction and Opportunistic Scheduling Protocols in Random Wireless Networks

Retransmission with error correction capability and opportunistic user scheduling are two of the cross layer protocols that hold promise to substantially improve the performance of wireless networks. In this thesis, we do a performance analysis of Hybrid Automatic Repeat reQuest (HARQ), a joint error correction and retransmission protocol, and downlink multiuser diversity opportunistic scheduling in both single hop and multihop wireless adhoc networks (WANETs).;In the first part of the thesis, we study the performance of rateless codes employed in the physical layer of a WANET. The nodes of the WANET are modeled by a homogeneous space time Poisson point process with Rayleigh fading, constant transmission power per node and pure ALOHA as the channel access protocol. The thesis considers 2 types of receivers, an ideal matched receiver and a practical nonmatched receiver. For such a WANET, the thesis quantifies the rate density and the dynamic variations of packet transmission time by deriving an upper bound to the CCDF of the packet transmission time. The thesis presents a WANET system model in which a packet transmission spans a single coherence time and it is shown that the rate density can be upto 70% of the ergodic rate density. This is good news, because the presented network does not require diversity, and transmits each message within one coherence time. Thus, the presented network nearly achieves the ERD, while requiring significantly shorter delays. From a rate density perspective, the thesis illustrates the advantage of power control in the form of channel thresholding. For both the rate density and the dynamic variations of packet transmission time, the analytical insights are supported by a very good match with the simulation results.;In the second part of the thesis, we do a performance analysis of the cooperative HARQ protocol in a wireless adhoc multihop network employing spatial ALOHA. We model the nodes in such a network by a homogeneous 2-D Poisson point process. We study the tradeoff between the transport capacity submetrics inherent in the network by optimizing the transport capacity w.r.t the network design parameters, HARQ coding rate and medium access probability. Using stochastic geometirc approximations, we obtain an analytic expression for the expected progress of opportunistic routing and optimize the capacity approximation by convex optimization. By way of numerical results, we show that the network design parameters obtained by optimizing the analytic approximation of transport capacity closely follows that of Monte Carlo based exact transport capacity optimization. As a result of the analysis, we argue that the optimal HARQ coding rate and medium access probability are independent of the node density in the network.;In the final part of the thesis, we do a cost-benefit analysis of multiuser diversity in single antenna broadcast channels. It is well known that the multiuser diversity can be beneficial but there is a significant cost in terms of system resources, bandwidth and power associated with acquiring instantaneous CSI. We work out a cost-benefit analysis of multiuser diversity for 2 types of CSI feedback methods, dedicated feedback and SNR dependent feedback, quantifying how many users should feedback CSI i.e the amount of available multiuser diversity that should be used from a net throughput perspective. Dedicated feedback, in which orthogonal resources are allocated to each user, has significant feedback cost and this limits the amount of available multiuser diversity that can be used. SNR dependent feedback method, in which only users with SNR above a threshold attempt to feedback, has relatively much smaller feedback cost and this allows for all of the available multiuser diversity to be used. Next, we study the effect of single user multiantenna techniques, which reduce the SNR variation, on the number of feedback users. It is seen that a broadcast channel using single user multiantenna techniques should reduce the number of feedback users with the spatial dimension.