Design and Experimental Evaluation of Multi-User Beamforming in Wireless LANs
∗Hua Yen Tseng
Department of Computer Science and Information
Engineering
[email protected]
Brian Chen
Department of Computer Science and Information Engineering[email protected]
Chang Ning Tsai
Department of Computer Science and Information
Engineering
[email protected] Harry Chang
Department of Computer Science and Information
Engineering
[email protected]
Lynda Lin
Department of Computer Science and Information
Engineering
[email protected] ABSTRACT
In this final project, we will use USRP to implement Zeros- Forcing Beamforming which allow mutli-antenna AP to send packets to multiple single-antenna client simultaneously. Multi- User MIMO promise to increase the spectral efficient of cur- rent wireless system. We will experiment whether Zeros- Forcing Beamforming can increase throughput in multiple user environment than TDMA technique.
Categories and Subject Descriptors
C.2.1 [Computer-Communication Networks]: Network Architecture and Design—Wireless Communication
General Terms
Measurement, Performance, Reliability, Experimentation, De- sign
Keywords
Multi-User MIMO, Beamforming, Wireless LAN, Channel Information, Mobility, Interference Suppression
1. INTRODUCTION
Most of APs have multi-antenna to increase throughput.
Currently, most wireless system implement Multiple-Input Multiple-Output(MIMO) for this purpose. Based on this concept, we want to experiment whether the throughput for MIMO system can imporve or not. In tradition single user systems, one user is servered at a time. we using s time
∗(Does NOT produce the permission block, copyright in- formation nor page numbering). For use with ACM PROC
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division multiple access (TDMA) to solve multiple user in the environment. Therefore, TDMA has low throughout for multiple users’ environments. We do not like such thing, because there are a lot of scenarios show that a great number of people in some place which is servered for some APs. We would not like to see that people go on internet slow.
In class,Kate Ching-Ju Lin introduce Zero Forcing Beam- forming technique in current MIMO system. We are inter- esting in this technique. In our final project, we will use USRP to experiment the MIMO multiple-users system. we will evaluate the technique how much throughout does this system increase and what benefit for the MIMO system. Our implement is based on [1] and class lecture note.
1.1 mathematical model
We know that channel matrix is y = Hx + n and
y =
y1
y2
... yn
H =
h11 h12 . . . h1n
...
hm1 hm2 . . . hmn
x =
x1
x2
...
xm
We using Zero-Forcing to solve the equation. Assume that we have only two antenna for transmitter y1, y2 and reciver x1, x2, and we compute x1
y1h22− y2h21= (h11h22− h12h21)x1
then
x1=y1h22− y2− h21
h11h22− h12h21
Finally, we using successive interference cancellation to solve rest of variable xk. Since our secnario have multi-users, we want interference nulling between antennas. Therefore, we solve the below equation
y = HW P x + n Let
W = H∗(HH∗)−1 Then
y = P x + n
2. ADDITIONAL AUTHORS 3. REFERENCES
[1] E. Aryafar, N. Anand, T. Salonidis, and E. W.
Knightly. Design and experimental evaluation of multi-user beamforming in wireless lans. In Proceedings of the sixteenth annual international conference on Mobile computing and networking, pages 197–208.
ACM, 2010.
