Digital Signal Processing Reference
In-Depth Information
Chapter 1
Introduction
1.1 Interference Cancellation and Detection for Multiple Access
Channel with Perfect Feedback
Multi-user detection schemes with simple receiver structures have received a lot of
attention lately. Multiple transmit and receive antennas have been used to increase
rate and improve the reliability of wireless systems. In this chapter, we consider a
multiple-antenna multi-access scenario where receive antennas are utilized to cancel
the interference. When there is channel information at the transmitter, in [
1
], multiple
antennas have been used to suppress the interference from other users. They show
that one can decode each user separately by using enough number of receive anten-
nas. More specifically, for
J
users equipped with
N
transmit antennas, they show
how to cancel the interference using
NJ
receive antennas. To reduce the number of
required receive antennas, [
2
] provides an interference cancellation method for users
with 2 transmit antennas. The method is based on the properties of orthogonal space-
time block codes (OSTBCs) [
3
] and requires less number of receive antennas, i.e. as
many as the number of users. The work was extended to a higher number of transmit
antennas but only for
J
2usersin[
4
]. The common theme of the work in [
2
,
4
]
is the utilization of the properties of the orthogonal designs [
3
] at the transmitter to
cancel the interference at the receiver. Unfortunately, the method does not work for
a general case of complex constellations,
N
=
2users
[
5
]. In fact, [
5
] proves that such an extension using orthogonal designs is impos-
sible. Instead, [
5
] suggests a method based on quasi-orthogonal space-time block
codes (QOSTBCs) [
6
]. The main complexity tradeoff between OSTBCs and QOST-
BCs is the symbol-by-symbol decoding versus pairwise decoding. Therefore, by a
moderate increase of decoding complexity, [
5
] extends the abovemulti-user detection
schemes to any constellation, any number of users, and any number of transmit anten-
nas. Performance analysis of these systems in terms of signal-to-noise ratio (SNR)
is available in [
7
,
8
]. Further, it is shown in [
9
] that for
M
>
2 transmit antennas, and
J
>
J
receive antennas,
the diversity of each user is equal to
NM
using maximum-likelihood detection and
N
≥
(
−
+
)
M
J
1
using low-complexity array-processing schemes. Note that the
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