Delay Minimization by Optimizing Antenna
Allocation in SIMO System
Tao Huang
∗
, Baoliu Ye
∗
, Song Guo
†
, Sanglu Lu
∗
, Toshiaki Miyazaki
†
∗
National Key Laboratory for Novel Software Technology, Nanjing University, China
Email: schrodinger.huang@gmail.com, yebl, sanglu@nju.edu.cn
†
The University of Aizu, Aizu-Wakamastu, Japan
Email: {sguo, miyazaki}@u-aizu.ac.jp
Abstract—In this paper, we investigate the minimization prob-
lem of average delay of multi-antenna AP based SIMO (single-
input and multiple-output) system by optimizing the antenna
allocation. We first obtain the upper bound of transmission
bandwidth by deriving the expected error probability of coherent
detection for SIMO under Rayleigh fading, and then develop the
expression of average delay of terminals sharing the same channel
via contention by applying CTMC (continuous-time Markov
chains). Upon the above results, we formulate the optimization of
antenna allocation as a non-linear integer programming problem
and present a polynomial time algorithm based on integer
partition and minimum matching to support optimized allocation.
We prove the correctness of our theoretical derived results by
extensive simulations. The performance comparison results show
that the proposed antenna allocation algorithm outperforms
other heuristic based algorithms under different traffic models.
I. INTRODUCTION
Wireless terminals always suffer from severe signal fading
arising from multipath propagation and shadowing, which
can result in much higher transmission error probability. An
intuitive approach to address fading problem is to let the
terminal choose the channel (channel here refers to frequency
band) with least fading and interference. Actually, most of
modern wireless access points (AP) are equipped with multiple
antennas that can work with different channels. The multi-
antenna based AP is in essence a kind of MIMO (multiple-
input multiple-output) system where the antennas can be
classified into disjoint subsets according to their allocated
channels. The antennas within each subset can cooperate
as an antenna-array by exploiting spatial diversity [1], thus
being shared by terminals working at the same channel. Such
features not only enable the channel selection for wireless
terminal in real wireless networks, but also provide the venue
to improve the transmission reliability.
Fig. 1 illustrates an example of multi-antenna AP where
there are seven terminals denoted as t
0
, . . . , t
6
, and an AP
equipped with five antennas labelled as a
0
, . . . , a
4
. These
antennas are grouped into three subsets {a
0
, a
1
, a
2
}, {a
3
},
{a
4
} according to their allocated channels, i.e. c
0
, c
1
and c
2
,
respectively. From Fig. 1 we can see that terminal t
0
, t
1
, t
2
,
and t
3
share the first subset of antennas on channel c
0
, t
4
and
t
5
share the second subset of antennas on channel c
1
, while
t
6
is served by antenna a
4
on c
2
. W
0
, . . . , W
6
represent the
transmission bandwidth of these terminals accordingly.
AP
t
0
W
0
W
1
W
2
W
3
W
4
W
5
W
6
a
0
a
1
a
2
a
3
a
4
t
1
t
2
t
3
t
4
t
5
t
6
c
0
c
1
c
2
F
ig. 1: Example of multi-antenna AP based SIMO system
Prior research efforts have made significant progress on
optimizing the transmission reliability and efficiency of MIMO
system by exploring the cooperation of antennas. To increase
the data transmission rate as well as coding gain, [2] inves-
tigates the tradeoff between the diversity and multiplexing in
multiple-antenna channels. [3] studies the transmission quality
issue and theoretically derived the closed-form expressions for
the outage probability and ergodic Shannon capacity of SIMO
system. [4] further focuses on the reliability and capacity
optimization problem under power control and presents a
power allocation for amplify-and-forward MIMO-OFDM relay
links.
Different from previous work, in this paper we are interested
in the minimization of average delay of multi-antenna AP.
For simplicity, we assume the terminal is equipped with
single antenna. In this case, the multi-antenna AP forms
a SIMO system (a special case of MIMO). Intuitively the
achievable transmission bandwidth (equivalent with data rate)
and reliability can be improved with the increased number of
antennas cooperating in the same channel. However, there is a
trade-off between the transmission bandwidth and reliability
since the higher data transmission rate of wireless termi-
nal will introduce higher outage probability, thus decreasing
the reliability. To balance the trade-off, we investigate the
optimization problem of antenna allocation with guaranteed
reliability, aiming to minimize the average delay of terminals.
We first theoretically obtain the upper bound of transmission
bandwidth constrained by the coherent detection error prob-
ability of SIMO, and then give the expression of average
delay of terminals sharing the same channel via contention
according to their traffic model. Based on the above obtained
results, we formulate the optimization of antenna allocation
as a non-linear integer programming problem and present
a polynomial time algorithm based on integer partition and
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