Interference Cancellation for Short-code DS-CDMA in the Presence of Channel Fading
Interference Cancellation for Short-code DS-CDMA in the Presence of Channel Fading

Author: Amit K. Dutta

Publisher:

Published: 1997

Total Pages: 238

ISBN-13:

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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.

Estimation of Fading Channel in DS-Cdma Multiuser Communications Systems
Estimation of Fading Channel in DS-Cdma Multiuser Communications Systems

Author: Chun-Yu Fung

Publisher: Open Dissertation Press

Published: 2017-01-27

Total Pages:

ISBN-13: 9781374709430

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This dissertation, "Estimation of Fading Channel in DS-CDMA Multiuser Communications Systems" by Chun-yu, Fung, 馮震宇, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of the Thesis Entitled Estimation of Fading Channel in DS-CDMA Multiuser Communications Systems submitted by Fung Chun Yu for the degree of Master of Philosophy at the University of Hong Kong in December 2002 Multipath fading and multiuser access interference are two major impairments in direct-sequence code-division multiple-access (DS-CDMA) systems. Efficient channel estimation and multiuser detection techniques play important roles in overcoming these deficiencies. This thesis is concerned with the design of a space-time (ST) blind adaptive receiver for DS-CDMA systems and the accompanied channel estimation algorithm. A new space-time decorrelating RAKE (ST-DRAKE) receiver is developed for blind reception of CDMA signals in frequency-selective fading channels. It has the advantage that only the knowledge of the desired user's signature waveform is required and therefore no transmission of training sequence is needed. The ST-DRAKE receiver consists of two parts. The first part is a set of constrained adaptive filters that are designed to suppress interference based on the minimum output energy criterion. These filters are implemented in a structure analogous to the general sidelobe canceller in array processing, which is implemented by a multistage Weiner filter is employed to reduce the complexity of the receiver. The second part of the ST-DRAKE receiver coherently combines the outputs of the constrained adaptive filters and gives an estimate of the transmitted signal. Simulation results show that the ST- DRAKE delivers significant performance improvement by exploiting the spatial diversity of the antenna array. The problem of estimating fast fading channels in the proposed receiver is also addressed. The time-varying channel is modeled as an autoregressive process and the Kalman filter is employed to estimate the time-varying channel coefficients. A robust Kalman filter based on the M-estimate cost function is also developed to suppress impulsive noise present in the received signals. Simulation results show that the Kalman filter provides more accurate channel estimate to the ST-DRAKE than using the decomposition method. Simulation results also show that the coupled receiver has a performance comparable to the optimum minimum mean-squared error receiver with known channel information. DOI: 10.5353/th_b2750902 Subjects: Code division multiple access Wireless communication systems

Adaptive WCDMA
Adaptive WCDMA

Author: Savo G. Glisic

Publisher: John Wiley & Sons

Published: 2003-07-25

Total Pages: 628

ISBN-13: 0470859253

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CDMA (Code Division Multiple Access) is one type of multiple access system used in radio communication. Other multiple access methods include TDMA, FDMA, etc. WCDMA (Wideband Code Division Multiple Access) is the main air interface used for third generation mobile communication systems - UMTS (Universal Mobile Telecommunication System) and is characterised by a wider band than CDMA. WCDMA uses a wider radio band than CDMA, which was used for 2G systems, and has a high transfer rate and increased system capacity and communication quality by statistical multiplexing, etc. WCDMA efficiently utilises the radio spectrum to provide a maximum data rate of 2 Mbit/s. Third generation mobile communication systems are scheduled for operational startup in Japan and Europe in 2001-2002. Applying high-speed data transfer and state-of-the-art radio terminal technology, third generations systems enable multimedia and are currently in the process of being standardised under 3GPP. Among the three types of system to be standardised (i.e. WCDMA, MC-CDMA, UTRA TDD), Japan and Europe will adopt WCDMA in a strategy to take the lead through superior service. This volume will cover the latest theoretical principles of WCDMA and explain why these principles are used in the standards. Starting with a general overview, the more advanced material is then gradually introduced providing an excellent roadmap for the reader. * Presents comprehensive coverage of the theoretical and practical aspects of WCDMA * Provides a detailed roadmap by presenting the material step-by-step for readers from differing backgrounds * Systematically presents the latest results in the field Ideal for Engineers, academics and postgraduate students involved in research and development, engineers involved in management and administration.