Interference from other adjacent users in wireless applications is a major problem
in direct-sequence code-division multiple-access (DS-CDMA). This is also known as the
near-far problem where a strong signal from one user interferes with other users. The
current approach to deal with the near-far problem in DS-CDMA systems is to use strict
transmitter power control. An alternative approach is to use near-far resistant receivers.
The practical near-far resistance receiver structure is the adaptive decorrelating detectors
since it avoids complex matrix inversion.
The existing CDMA standard known as IS-95 uses a long signature code
sequence. However for simplicity, the adaptive multi-user receiver uses short signature
code sequence. The problem is that adaptive receivers lose near-far resistance as the
number of users increases in the system. This thesis describes a novel method of multistage
decision feedback cancellation (DFC) scheme immune from the near-far problem.
The performance of the new DFC structure is constructed using three different adaptive
algorithms: the least mean squared (LMS), the recursive least squared (RLS) and the
linearly constraint constant modulus (LCCM) adaptive algorithms. It is found that LMS
adaptive algorithm provides the best result considering its simple hardware complexity.
It is also found that the LMS adaptive receiver along with the DFC structure provides a
better bit synchronization capability to the over all system. Since the receiver is near-far
resistant, the LMS adaptive receiver along with the decision feedback cancellation
structure also performs better in the presence of Rayleigh fading. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33881 |
| Date | 21 August 1997 |
| Creators | Dutta, Amit K. |
| Contributors | Kiaei, Sayfe |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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