ETTC'2003 - SEE

quasi-synchronous multiuser detector is :
−1 −1
b ′ = R ⋅ Z = E ⋅b
+ R ⋅ n = E ⋅b
+ n′
−1
where n ′ = R ⋅ n is new noise vector, define ri
k is element value of R -1 . So the noise
2
power in the quasi-synchronous multiuser detector decision statistic is: σ ⋅∑
rik
.
i=
1
The output SNR of Quasi-synchronous multiuser detector is:
SNR
( k )
can
⎛ Tb
−τ
k ⎞ ⎛ Tb
−τ
k ⎞
⎜
⎟ ⋅ E
⎜
⎟
k
⋅ SNR
=
⎝ Tb
⎠
=
⎝ Tb
⎠
N
N
2
2
2
σ ⋅ r
r
∑
i=
1
ik
∑
i=
1
ik
( k )
in
N
2
(3)
(k )
where SNR is the input SNR of kth user of Quasi-synchronous multiuser detector.
in
Fig.2~Fig.4 compare the
performance of Quasi-synchronous
multiuser detector, synchronous
decorrelation multiuser detector and
conventional detector. Fig.4 shows
the near-far resistance performance,
where the number of active users is
20, the length of PN sequence is 63,
the SNR of desire user is 10 dB.
Other users have equal power, the
power ratio between it to that of
desired user varied in the range:
η = 10 lg( ( Eb / N o ) i, i≠
k /( Eb
/ N o ) k )
=-5~20dB 。 It shows the
Quasi-synchronous multiuser detector
near-far resistance performance is as
good as that of synchronous
decorrelation multiuser detector.
The performance of a multiuser
detector can be evaluated by output
SNR degradation factor (DF) of
detector as well as BER. According to
the definition of output SNR
degradation factor by C.L.Weber,
Fig.3 shows output SNR degradation
factor as a function of active users
Fig.2 Near-far resistance performance
for Quasi-synchronous multiuser Fig.3 Output SNR Degradation factor