ETTC'2003 - SEE

detector, synchronous decorrelation multiuser detector and conventional detector. It is seen from
it that the output SNR of conventional detector (without cancellation of MAI) degrades quickly
along with the active users increase. When the system has few users, the conventional detector has
better performance than the Quasi-synchronous multiuser detector because the new noise vector of
R -1. N is introduction. When the number of users increase, the DF of the conventional detector
increase significantly, the DF of the Quasi-synchronous multiuser detector and the synchronous
decorrelation multiuser detector almost keep a constant. It’s shown that the output SNR
degradation of the Quasi-synchronous multiuser detector is larger 0.8dB and 1.7dB than the
synchronous decorrelation multiuser detector for relative time delay tk=10Tc and tk=20Tc
respectively, this is the cost of correlation time truncation.
Fig.4 shows the output SNR as a
function
of relative time delay. Where
the input SNR is 20 dB, the number of
users is 20. We can know from Fig.4
that the relative time delay varied
from 10Tc to 20Tc, resulting the DF
of the Quasi-synchronous multiuser
detector is 0.8dB~1.7dB larger than
that of the synchronous decorrelation
multiuser detector, and the DF of
conventional detector is 7 dB larger
than that of the synchronous
decorrelation multiuser detector.
Conclusion:
In the asynchronous
DS/CDMA data transmission system, signal is transmitted
synchronously
and arrived to the reception station asynchronously. The Quasi-synchronous
References:
Fig.4 Output SNR vs. relative time delay
multiuser detector can be used to reduce the computation complexity. It has good near-far
resistance performance because it needn’t amplitude information of users. So in some telemetry
System applications, The Quasi-synchronous multiuser detector is a good approach for multiuser
detection.
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