Semester

Fall

Date of Graduation

2011

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Daryl Reynolds

Committee Co-Chair

Vinod Kulathumani

Committee Member

Matthew C Valenti

Abstract

The multiple-input multiple-output (MIMO) antenna systems are well known for achieving the higher spectral efficiencies and improving the link reliability in wireless communications. But the use of multiple antennas in a cellular uplink is impractical due to the size constraints of the mobile device. The potential solution which was used is to exploit the user cooperation to create a virtual antenna array. In this paper we investigate the cooperative diversity in an asynchronous code-division multiple-access (CDMA) uplink by taking inter-user non-orthogonality (allocation of non-orthogonal channels to multiple users) into consideration.;Most the previous research work assumes the use of the inter-user orthogonality and the synchronism between the signals transmitted from different users. Both of these assumptions might bring in extra complexities in the network as they both will need the users to be accurately coordinated. If we consider the inter-user nonorthogonality and the asynchronous communication between transmitter and the receiver, we will need a way to combat the multiple access interference (MAI) and the inter-symbol interference (ISI). In this thesis try to eliminate those effects by using the MMSE detector and Successive Interference Cancellation (SIC) receivers. These techniques help will enhance total network performance and can exploit maximum diversity. We will be assuming a CDMA cellular uplink model with a multi-user decode-and-forward (DF) cooperative diversity protocol wherein each user first transmits its own message and other users overhear that message and can relay it to base station. So each user here acts as a relay and also has its own information to transmit. The channel spans a single spreading code, sk(t) for two orthogonal time-phases. In the first time phase every user broadcasts its own spread message and in the second time phase, the users in the decoding set relays the re-encoded and re-spreaded messages. The relays which doesn't belong in the decoding set, continue to transmit their own information. But throughout the paper we consider that all of the users are cooperating and hence the decoding relays transmit asynchronously over the subchannel. And the use of non-orthogonal spreading codes leads to non-orthogonality across the subchannels.

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