Reduced complexity trellis-based multiuser detector for CDMA

Details Reduced complexity trellis-based multiuser detector for CDMA Reduced complexity trellis-based multiuser detector for CDMA

1999-02-24

2003-11-25

Marcelo, Melvin (Department: 2663)

Multiplex communications

Communication over free space

Combining or distributing information via code word channels...

C375S147000

Reexamination Certificate

active

06654365

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a maximum-likelihood (ML) multiuser detector for direct-sequence code division multiple access (CDMA) and, more particularly, to a reduced-complexity multiuser detector based on the trellis structure of the ML detector.
There is an ever increasing demand or communication of different types of information, such as voice, data and video. In telecommunications systems, use may be made of frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). CDMA has a number of advantages over the other forms of communication, these advantages having led to the IS-95 standard for direct-sequence CDMA (DS-CDMA) for mobile communications, and a similar standard for personal communication systems (PCS). In uplink transmission (mobile users to base stations) of a system based on the IS-95 standard, the users transmit asynchronously with resulting interference between users.
In many CDMA applications, the performance of the communication system is limited by the interference from other users of the communication system. This situation is made worse if one or more of the interfering user signals reaches a receiver with higher power than the power received from a desired user. This results in what is commonly referred to as the near-far problem, and causes unacceptably high bit-error rates if nothing is done to reduce the resulting interference. Therefore, in an interference-limited system, it is important to reduce the multiple user interference (MUI) There are circumstances in which the MUI has a known structure which can be exploited to develop multiuser detectors that improve the performance of both synchronous and asynchronous CDMA channels. However, a problem arises in that existing solutions for reduction of multiple user interference do not produce a desired level of performance.
SUMMARY OF THE INVENTION
The aforementioned problem is overcome and other advantages are provided by the ML detector providing improved performance in the presence of MUI. In accordance with the invention, the ML detector can be implemented using the Viterbi algorithm, this greatly reducing system sensitivity to MUI. This is accomplished in accordance with the invention, by using an approximation to be ML detector which does a sparse trellis search based on the structure of the ML detector. The resulting detector, which may be referred to as a reduced-complexity recursive detector (RCRD), has a dynamic structure that allows a trade-off between complexity and performance. The trellis structure of the RCRD is similar to the trellis structure found in other communication subsystems such as trellis codes, equalizers for the removal of inter-symbol interference, and the modulation of digitally phase modulated signals. The RCRD may be integrated with a decoder for the error-control code (ECC) in a coded CDMA system.
The invention provides a flexible trellis-based method for improving the performance of a multiuser receiver for asynchronous CDMA. The procedure consists of using a unique metric to define the trellis-structure and a unique algorithm to reduce the number of surviving paths. The metric calculation is then repeated at decision points to provide soft-decision information for further signal processing, soft-decision decoding of an error-correction code, or iterative reception of the multiuser signal. The invention provides a variable-complexity model for providing reliable multiple point-to-point communications in an asynchronous CDMA system. The invention allows the user to trade complexity for performance and demodulate a large number of user communications.


REFERENCES:
patent: 5905742 (1999-05-01), Chennakeshu et al.
patent: 6345073 (2002-02-01), Curry et al.
U. Fawer and B. Aazhang. Multiuser Receivers for Code-Division Multiple-Access Systems with Trellis-Based Modulation. IEEE Journal on Selected Areas in Communications, vol. 14, No. 8, Oct. 1996. pp. 1602-1609.*
U. Fawer and B. Aazhang. Multiuser Reception for Trellis-Based Code Division Multiple Access Communications. 1994 IEEE. pp. 977-981.*
M. Nasiri-Kenari, R. Sylvester, and C. Rushforth. An Efficient Soft -In-Soft-Out Multiuser Detector for Synchronous CDMA with Error-Control Coding. IEEE Transactions on Vehicular Technology, vol. 47, No. 3, Aug. 1998. pp. 947-953.*
Minimum Probability of Error for Asynchronous Gaussian Multiple-Access Channels, by Sergio Verdú, IEEE Transactions on Information Theory, vol. IT-32, No. 1, Jan. 1986, pp. 85-96.
Joint Signal Detection and Parameter Estimation in Multiuser Communications, by Zhenhua Xie, Craig K. Rushforth, Robert T. Short, and Todd K. Moon, IEEE Transactions on Communications, vol. 41, No. 7, August 1993, pp. 1208-1216.
On Channel Coding and Multiuser Detection for DS-CDMA, by Peter Hoeher, Institute for Communications Technology, German Aerospace Research Establishment (DLR), pp. 1-12.
An Efficient Soft-Decision Decoding Algorithm for Synchronous CDMA Communications woth Error-Control Coding, by M. Nasiri-Kenari, C.K. Rushforth, Department of Electrical Engineering, University of Utah, 1 page.
An Efficient Sof-In-Soft-Out Multiuser Detector for Synchronous CDMA with Error-Control Coding by Masoumeh Nasiri-Kenari, Randal R. Sylvester, and Craig K. Rushforth, IEEE Transactions on Vehicular Technology, vol. 47, No. 3, Aug. 1998, pp. 947-953.

Affiliated with

Also associated with

Rating

Reduced complexity trellis-based multiuser detector for CDMA does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Reduced complexity trellis-based multiuser detector for CDMA, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reduced complexity trellis-based multiuser detector for CDMA will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3147915