CDMA/HMD (Hierarchical Multiuser Diversity) Access Schemes for Multimedia Wireless Networks

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This project aims at developing a suite of multiuser diversity driven algorithms for packet scheduling and localized routing, and to obtain some overriding principles in multimedia wireless systems. In particular, the issues of hierarchical multiuser diversity (HMD) driven downlink and uplink access schemes for multimedia traffic will be studied. The objective related to HMD driven downlink access schemes is to devise efficient packet transmission schemes for the downlink, exploiting multiuser diversity gain in a multiuser wireless system. Specifically, the proposal addresses such an HMD scheme in which each user can choose either a direct transmission mode or a relay transmission mode. Treating delay tolerance as a network resource, the HMD-driven scheduling for both direct trans-mission and relay transmission is then explored for both single-cell setting and cellular networks. Also the localized routing algorithms will be developed for both slowly fading channels and fast fading channels, due to mobility. In the part of the project related to based on code division multiple access (CDMA/HMD) uplink access schemes, the pro-ject will include studies of access schemes taking into account explicitly the delay con-straints of different multimedia traffic, with particular focus on the uplink. Since the up-link is a multi-access channel, the multiuser diversity will be explored in the context of CDMA. In particular, the number of simultaneous transmissions will be optimized, based on the channel conditions across the users. The project will also address the critical issues related to the buffering, jitter, fairness and possible loss due to switching to a new relay. Finally, the trade-off between HMD and CDMA will be studied, with the aim at develop-ing a hybrid scheme that achieves multiuser diversity gain and guarantee the user's minimal throughput requirement as the same time.