| Coding Techniques for Multicasting (2006) | |||||||||||
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| Coding Techniques for Multicasting Ashish Khisti Engineering Science University Toronto Submitted the Department Electrical Engineering and Computer Science partial fulfillment the requirements for the degree Master Science the MASSACHUSETTS INSTITUTE TECHNOLOGY May Massachusetts Institute Technology All rights reserved Author Department Electrical Engineering and Computer Science May Certified Gregory Wornell Professor Thesis Supervisor Certified Uri Erez Post Doctoral Scholar Thesis Supervisor Accepted Arthur Smith Chairman Department Committee Graduate Students Coding Techniques for Multicasting Ashish Khisti Engineering Science University Toronto Submitted the Department Electrical Engineering and Computer Science May partial fulfillment the requirements for the degree Master Science Abstract study some fundamental limits multicasting wireless systems and propose practical architectures that perform close these limits Chapter study the scenario which one transmitter with multiple antennas distributes common message large number users For system with fixed number transmit antennas show that the number users becomes large the rate the worst user decreases Thus having multiple antennas provides significant gains the performance multicasting system with slow fading propose robust architecture for multicasting over block fading channels using rateless erasure codes the application layer This architecture provides new insights into the cross layer interaction between the physic. We study some fundamental limits of multicasting in wireless systems and propose practical architectures that perform close to these limits. In Chapter 2, we study the scenario in which one transmitter with multiple antennas distributes a common message to a large number of users. For a system with a fixed number (L) of transmit antennas, we show that, as the number of users (K) becomes large, the rate of the worst user decreases as O(Kâ 1 L ). Thus having multiple antennas provides significant gains in the performance of multicasting system with slow fading. We propose a robust architecture for multicasting over block fading channels, using rateless erasure codes at the application layer. This architecture provides new insights into the cross layer interaction between the physical layer and the application layer. For systems with rich time diversity, we observe that it is better to exploit the time diversity using erasure codes at the application layer rather than be conservative and aim for high reliability at the physical layer. It is known that the spatial diversity gains are not significantly high in systems with rich time diversity. We take a step further and show that to realize these marginal gains one has to operate very close to the optimal operating point. Next, we study the problem of multicasting to multiple groups with a multiple antenna transmitter. The solution to this problem motivates us to study a multiuser generalization of the dirty paper coding problem. This generalization is interesting in its own right and is studied in detail in Chapter 3. The scenario we study is that of one sender and many receivers, all interested in a common message. There is additive interference on the channel of each receiver, which is known only to the sender. The sender has to encode the message in such the way that it is simultaneously âgood’ to all the receivers. This scenario is a non-trivial generalization of the dirty paper coding result, since it requires that the sender deal with multiple interferences simultaneously. We prove a capacity theorem for the special case of two user binary channel and derive achievable rates for many other channel modes including the Gaussian channel and the memory with defects model. Our results are rather pessimistic since the value of side information diminishes as the number of users increase. | |||||||||||
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Cited publications (10) | |||||||||||