ECE External Research Board Meeting Wireless Network and Communications

1. Tan F. Wong Wireless Information and Networking Group twong@ece.ufl.edu http://wireless.ece.ufl.edu/~twong Ph: 352-392-2665 Fax: 352-392-0044 ECE External Research Board Meeting Wireless Network and Communications

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 Wireless Information Networking Group (WING)

3. Collaborative Communications1 • Multiple antennas can be used to provide diversity against many impairments in radio networks: • Fading, Hostile Jamming, Collisions (especially for ad hoc networks) • However, multiple antennas are an unattractive choice in many systems because: • Antenna spacing needs to be several times the wavelength of the RF carrier • Array elements should be physically connected to a central combiner • Many systems, such as small handsets carried by infantry, cannot support these requirements 1Sponsored by the Office of Naval Research, National Science Foundation, and Harris Corporation. Joint work with Drs. Mike Fang and John Shea Wireless Information Networking Group (WING)

4. Collaboration: A Cross-Layer Approach • Collaboration uses Network-Based Approaches to Achieve (Physical-Layer) Diversity • Antenna arrays are inherently present in any wireless network! • Different nodes in the network can act like elements of an antenna array • Since the nodes are not physically connected we refer to this as a Distributed Array • Information to be combined must be exchanged over wireless links! • There is no inherent central combiner, so distributed processing may be used. Wireless Information Networking Group (WING)

5. Challenges • Traditional combining techniques (MRC, EGC) require a largeamount of information to be sent to the combining node new physical-layer approaches to achieve diversity are required • Collaborating nodes must coordinate information exchanges; information exchanges should depend on physical layer signals  new collaboration protocols are required • Phase coherence cannot usually be achieved between nodes because of the difficulty in synchronization new distributed signal processing techniques are required • In ad hoc networks, relay transmissions not only reduce spectral efficiency but also interfere with other transmissions  practical collaborative protocols are required for use in ad hoc networks Wireless Information Networking Group (WING)

6. Our Research • Cooperative communications is an active area of research in the Wireless Information Networking Group at the University of Florida • Our current research has three major thrusts • In Collaborative Reception/Distributed Decoding, we are developing efficient combining techniques and iterative, distributed decoding protocols • In Collaborative Jamming Mitigation, we are developing distributed signal processing techniques to detect jammed symbols and reduce the effect of the jamming before or during the decoding process. • In Network Diversity through Relaying in Ad Hoc Networks, we are developing efficient MAC protocols that use cross-layer information to enable efficient relaying in ad hoc networks Wireless Information Networking Group (WING)

7. Collaborative Reception • IDEA: • Nodes in the cluster form a virtual array • All nodes receive independent copies of the message from the transmitter Wireless Information Networking Group (WING) • 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 Wireless Information Networking Group (WING)

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! Wireless Information Networking Group (WING) • 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 Wireless Information Networking Group (WING) • 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. Wireless Information Networking Group (WING)

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 Wireless Information Networking Group (WING)

13. Network Diversity through Relaying • Extend simple ALOHA protocol to support relay forwarding • Significant gains in end-to-end throughput and delay Wireless Information Networking Group (WING)

14. FPGABoard FPGABoard A/D D/A A/D D/A ISM-Band RF Frontend ISM-Band RF Frontend DAQ (A/D-D/A) DAQ (A/D-D/A) Laptop Computer Laptop Computer 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 Wireless Information Networking Group (WING)

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 Wireless Information Networking Group (WING)

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 Wireless Information Networking Group (WING)