ECE External Research Board Meeting Wireless Network and Communications

1
ECE External Research Board Meeting Wireless
Network and Communications

• Tan F. Wong
• Wireless Information and Networking Group
• twong_at_ece.ufl.edu
• http//wireless.ece.ufl.edu/twong
• Ph 352-392-2665
• Fax [phone]

2
Current Research Interests

• Communication and signal processing techniques to
  support wireless ad hoc and sensor networks
• Channel and timing estimation in MIMO systems
• Bit-interleaved space-frequency coded modulation
  for OFDM
• Collaborative communications coding, processing,
  and protocols
• Interference detection resource allocation for
  cognitive radios
• Physics-based source localization using binary
  observations
• Spread spectrum and ultra-wideband research
• Interference avoidance cancellation in spread
  spectrum
• Joint power control and sequence optimization in
  CDMA
• Power-efficient ARQ protocols for CDMA links
• Acquisition and MAC protocols for UWB

3
1Sponsored by the Office of Naval Research,
National Science Foundation, and Harris
Corporation. Joint work with Drs. Mike Fang and
John Shea
4
(No Transcript)
5
(No Transcript)
6
(No Transcript)
7
Collaborative Reception

• IDEA
• Nodes in the cluster form a virtual array
• All nodes receive independent copies of the
  message from the transmitter

• Collaborative Decoding (Iterating between a
  process of information exchange and decoding)
  yields receive diversity

8
Collaborative Reception

• Each node individually decodes received signal
  and estimates reliabilities of data bits using
  soft-input soft-output (SISO) decoders
• The nodes use the reliability information in a
  process of smart information exchange
• The nodes perform decoding at the end of
  information exchange
• Collaborative Decoding (Iterating between a
  process of information exchange and decoding)
  yields receive diversity

9
Reliability Filling

• Idea more information needs to be combined for
  unreliable parts of a codeword than for reliable
  parts of the codeword
• Technique combine just the right amount of
  information such that the combined bit
  reliabilities exceed a pre-determined threshold T
• Water filling in the reliability domain!

• Reliability filling combines fewer symbols!

10
Collaborative Jamming Mitigation

• Hostile jamming can severely disrupt
  communications networks
• If multiple receive antennas with a coherent
  phase reference are available, jamming can
  be mitigated by beamforming
• When multiple nodes collaborate in the presence
  of a jamming signal, phase coherence between
  nodes is not possible
• Furthermore, in the presence of fading, each
  node receives the information and jamming
  signals at different amplitudes and phases

• Both techniques have been shown effective
  against jamming in nonfading channels

11
Collaborative Jamming Mitigation

• In Collaborative Jamming Mitigation, we
  develop distributed detection and estimation
  techniques to improve performance in the presence
  of hostile jammer
• Nodes exchange received information to estimate
  and reject jammer
• Jammer must use more power or transmit more of
  the time.

12
Network Diversity through Relaying

• Employ relay forwarding to achieve diversity or
  increase capacity in ad hoc networks
• Example (see figure below)
• The message has final destination H but
  intermediate destination B
• Nodes B and D suffer deep fades
• Node C can act as a relay for the message
  rather than relay it to B, node C sends it to F
  to move it on toward the destination H

13
Network Diversity through Relaying

• Extend simple ALOHA protocol to support relay
  forwarding
• Significant gains in end-to-end throughput and
  delay

14
Reconfigurable Multi-node Wireless Communication
Testbed

• Conduct physical and network layers experiments
• Six-node cluster
• Software processing baseband unit (A/D-D/A board
  PC)
• Maximum reconfigurability, off-line processing
• Hardware processing baseband unit (FPGA board)
• Real-time implementation
• 250MHz Arbitrary waveform generator, 1GHz digital
  oscilloscope, spectrum analyzer

15
MIMO Processing and Coding

• Employ physical antenna arrays to improve comm.
  performance
• Interference mitigation using receive antenna
  array
• Blind adaptive space-time interference rejection
  and multipath diversity combining algorithm for
  DS-SS

16
MIMO Processing and Coding

• Interference avoidance by selecting optimal
  spreading codes for users in presence of jammers
  and MUI
• More robust against jammers
• Higher user capacity with QoS control
• Lower Tx power ? better LPI/LPD
• Spreading codes depend on channel ? natural PHY
  security

17
MIMO Processing and Coding

• Spatial multiplexing with multiple transmit
  antennas to increase data rate
• Bit-Interleaved Space-Time Coded-Modulation with
  Iterative Decoding
• Channel and timing estimation in MIMO systems
  with jammers and interference