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Quasi-synchronous multiuser detection technique
used in telemetry System
Jin shubo
Electronics Engineering Institute of China Academy of Engineering Physics.
P.O Box 919-517 Mianyan,Sichuan 621900,P.R.China, E-mail: jsb_caep@21cn.com.
Abstract: The performance of a DS/CDMA system degrades due to Multiple Access Interference
(MAI), when the asynchronous multiuser detection technique is used to remove the MAI, its
matrix order is larger than the number of users, resulting in larger computational intensive. In
some specific asynchronous DS/CDMA system, the quasi-synchronous multiuser detection
algorithm, whose matrix order is equal to the number of users, needn’t estimate MAI power levels,
thereby resulting in lower computational complexity and high “near-far” resistance. In this paper
the performance of quasi-synchronous multiuser detection algorithm is analysized theoretically,
and the numerical results are presented.
Keywords: Quasi-synchronous, Multiuser Detection, DS/CDMA, MAI, Telemetry System.
1. Introduction
DS/CDMA system is used in many communication systems because it has the capability of
anti-jamming. Some results indicate that the CDMA system has larger system capacity than the
TDMA system, but this result is based the hypothesis that the PN sequences are orthogonal with
each other. If the DS/CDMA receiver use traditional single-user detector ( correlator or matched
filter), the performance of a DS/CDMA system degrades due to Multiple Access Interference
(MAI).
In order to increase the system capacity of DS/CDMA system, Some researchers proposed the
use of smart antenna or the power control in the DS/CDMA system to abate the effect of MAI,
Others resort to the suboptimal multiuser detection such as linear decorrelation, successive
interference cancellation and parallel interference cancellation.
Most communication systems are asynchronous system. The DS/CDMA system in some
telemetry System is a special asynchronous system. It has following specialties: 1) the mobile
users have the inner timer, 2) the distance from the mobile users to base station are almost equal, 3)
the mobile users in the system are fixedness, 4) the system work in simplex system. Considering
these specialty and based the theory of synchronous decorrelation multiuser detection,
Quasi-synchronous multiuser detection was used in the system to reduce the computation
complexity. This paper analysis the performance of the quasi-synchronous multiuser detector
theoretically, and compare with the synchronous decorrelation multiuser detection and the
conventional detection. The numerical results are present.
2. Quasi-synchronous DS/CDMA system
S.Verdu proposed the optimal multiuser detector that is too complex for practical
implementation. R.Lupas put forward the decorrelation multiuser detection, for synchronous case,