Evaluation of a Novel Low Complexity Smart Antenna for Wireless LAN Systems T'J' Harrold, D'C' Kemp,

1
Evaluation of a Novel Low Complexity
SmartAntenna for Wireless LAN SystemsT.J.
Harrold, D.C. Kemp, M.A. Beach, C. Williams,
M. Philippakis and M.W. ShelleyUniversity of
Bristol, ERA Technology LimitedContact
Tim.Harrold_at_bris.ac.uk
Aim Simulation of the performance of a novel
smart antenna array that can offer an increase in
throughput for 802.11b/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 802.11 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 802.11
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 802.11b/g units

• One active element
• 8 surrounding passive elements
• Passive elements may be open or shorted to ground
• 256 switch states

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

• 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

• Evaluation Approach
• OPNET for 802.11 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

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 802.11 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.