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Optimal Relay Location in Wireless Networks

Sharif Nassab, Arsalan | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44558 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Golestani, Jamaloddin; Nasiri-Kenari, Masoumeh
  7. Abstract:
  8. According to the wide range of applications and numerous implementations, wireless networks are considered as a prominent means of providing data services, and have attracted the attention of many researches in recent years. Performance enhancement of these networks can be very beneficial to industry and wireless data service providers. Manipulation of relays, have been always considered as a proper means for improvement of network performance measures throughput and outage probability.In order to design relay networks efficiently, one should address two following problems: 1- determining transmission policy, and 2- relay location. In this research work, having in mind the optimality of network design, we study performance enhancement of numerous network scenarios using relays. In the uplink direction, the performance measures are data rate of users and lifetime of wireless nodes , e.g. sensors in the sensor networks. We will show that optimal performance is achievable only when relay nodes cooperate in decoding the user messages. After characterizing optimal transmission and reception policies, we study the problem of relay location in different special cases and general case of the network. The first special case is placement of a single relay in a two dimensional network, for which the previous research works in the literature have led to sub optimum solutions and in some cases, wrong analytical results. For this network we show that a simple algorithm can find the optimal solution. In another special case, we study the problem of locating many relays in a one-dimensional network, propose an exact analytical approach based on numerically solving ordinary differential equations, and analyze its computational complexity. For the general case of locating many relays in two-dimensional network, we show that the problem is np-hard and present an intractable approach to find the optimal solution with desirably high precision. We also propose an approximate algorithm for solving this general case together with a lower bound for accuracy of approximation. In the downlink direction, first, we study multicast networks and show its close relation to relay placement in uplink. Next, for the broadcast networks we show that optimal communication policy doesn’t rely on cooperation between relays, and in special cases, the optimal relay location problem is transformed to well-known problems in clustering. For the general case which is also np-hard, we present an approximate algorithm with low complexity. For our last scenario, by take into consideration the effect of fading, we tackle networks with a more real model. Finally, the accuracy of the results of this thesis are verified through numerous numerical experiments
  9. Keywords:
  10. Optimization ; Fading ; Relay Location ; Facility Location Model ; Broadcost Services ; Multicast

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