1. Evaluation of a Novel Low Complexity Smart Antenna for Wireless LAN Systems T.J. Harrold*, D.C. Kemp†, M.A. Beach*, C. Williams*, M. Philippakis† and M.W. Shelley† *University of Bristol, †ERA Technology Limited Contact –
Aim : Simulation of the performance of a novel smart antenna array that can offer an increase in throughput for b/g WLAN systems.
Research Challenges
Smart antennas can offer an increase in throughput by permitting multiple transmissions to exist in the same environment.
However, the distributed nature of the channel access mechanisms in WLAN systems normally prevents smart antenna benefits from being realised.
e.g. in a CSMA based MAC, transmitters “A” and “C” would normally detect each others’ presence. The MAC would then arrange that throughput is shared fairly between the two links.
A directional antenna for must offer a combination of patterns that can isolate the nodes from each other to “deafen” the MAC processes and allow data transfer without mutual interference.
This is more challenging in a multipath environment.
Antenna Array
Antenna requirements:
Low complexity
Sufficient peak and null steering capability to permit operation in multipath environments
Able to work with off-the-shelf b/g units
One active element
8 surrounding passive elements
Passive elements may be open or shorted to ground
256 switch states A D B C
CSMA Example
Array fitted to Access Point
256 possible radiation patterns
Operation at 2.4GHz and 5.2GHz
Max beam peak of 5.75dBi
10dB peak to null ratio
3 Example Radiation Patterns
Evaluation Approach
OPNET for MAC and traffic models
A specific radio channel model using 3D ray tracing
Transmit and receive antenna gains for multiple rays ensure accurate received powers
Results
Simulation scenario comprises two individual 24Mbps transmissions
Success measured by the aggregate throughput; 48Mbps would be ideal
Various configurations of transmit power and smart antenna usage at AP and STA were considered
AP1→STA2 AP2→STA1
More challenging scenario
1mW power gives no throughput
AP1→STA1 AP2→STA2
“Fully smart” configuration gives best results
Environment Simulated
Conclusions
A novel smart antenna has been assessed using MAC models and 3D propagation predications.
Two simultaneous high data-rate links can be supported in certain cases.
Best configuration is where all nodes in the network are equipped with smart antennas; only modest gains are achievable otherwise.
The authors would like to thank the ERA Foundation for their financial support.