1. 1 Ultra Wide Band Wireless Communications Ioannis Broustis March 23rd, 2004 Department of Computer Science & Engineering University of California, Riverside

2. 2 Motivation Current wireless solutions (IEEE 802.11, Bluetooth…) face some of the following problems: Limited channel capacity High power consumption Multipath fading

3. 3 Why UWB? Advantages:  Low-power operation.  Low cost.  Low probability of detection and low probability of jamming capabilities.  Low interference levels to existing services.  Higher immunity to multi-path fading effects.  Ability to penetrate walls, etc.  Availability of precise location information.

4. 4 What are we trying to do… There are no sufficient solutions for the MAC layer. Limited previous work exists for UWB based ad hoc networks. We will address the problem of a suitable MAC protocol for UWB ad hoc wireless networks.

5. 5 Roadmap UWB definition and applications Possible PHY layer implementations MAC principles Previous Work on MAC layer Conclusions

6. 6 UWB: What is it? Any signal that:  Occupies at least 500MHz of BW, or  More than 25% of a center frequency: Wireless Personal Area Networks (WPANs)  FCC allocates 7,500 MHz in the 3.1 to 10.6 GHz band.

7. 7 UWB Applications Stream DVD content to HDTVs simultaneously. Wirelessly synchronize appliance clocks. Connect high-data rate peripherals. Move huge files between digital cameras, camcorders, and computers. Military applications (radars, penetrate walls, etc.)

8. 8 What makes UWB so interesting? Manufacturers are still jumping on the UWB band wagon even with the frequency and power restrictions. Why? Let an old friend explain: Shannon’s theorem:

9. 9 PHY: Single-Band and Multi-Band Single-Band Implementation  One pulse occupies the whole BW. Multi-Band Implementation  The 7.5GHz are divided into multiple bands.  Information is independently encoded in the different bands.  The lower limit of 500MHz must be maintained.

10. 10 Single-Band and Multi-Band

11. 11 Single-Band and Multi-Band Multi-band signals transmitted at different discrete times. The sequence repeats at each symbol. Center frequencies are shown in the vertical axis.

12. 12 Why prefer Multi-Band ? Adaptive band selection  Avoids interference. Low complexity  Smaller transceiver cost. Low circuit frequency  Power conservation. Sacrifice one band for co-existence

13. 13 IEEE 802.15.3a Requirements ParameterValue Bit rate110 and 200 Mb/s Range30 and 12 ft Power Consumption100 and 250 mW Bit error rate1e-5 Co-located piconets4 Interference capabilityRobust to IEEE systems Co-existence capabilityReduced interference to IEEE systems

14. 14 MAC Principles Two main aspects:  Intra-WPAN interference Polling schemes (master/slave) CSMA CDMA TDMA A new idea...  Inter-WPAN interference Time Hopping Spread Spectrum techniques.

15. 15 UWB ad-hoc MAC - Previous Work [1] Jin Ding, Li Zhao, Sirisha Medidi and K. M. Sivalingam, "MAC Protocols for Ultra-Wide-Band Wireless Networks: Impact of Channel Acquisition Time", in SPIE ITCOM Conf. 4869, Boston, July 2002. The channel acquisition time is large enough and prohibits CSMA or TDMA approaches: CSMA-CA TDMA

16. 16 UWB ad-hoc MAC - Previous Work [2] H. Yomo, P. Popovski, C. Wijting, I. Z. Kovacs, N. Deblauwe, A. F. Baena, and R. Prasad, "Medium Access Techniques in Ultra-wideband Ad Hoc Networks", the 6th national conference of ETAI, 2003 September, 2003, Ohrid, Skopia. They examine the Inter-WPAN interference approach of the MAC layer. “The only way to control this kind of interference is to determine appropriate values for some Time-Hopping pattern parameters”.

17. 17 UWB ad-hoc MAC - Previous Work [3] Jean-Yves Le Boudec, Ruben Merz, Bozidar Radunovic, Joerg Widmer, “A MAC protocol for UWB very low power mobile ad-hoc networks based on dynamic channel coding with interference mitigation”, EPFL Technical Report ID: IC/2004/02 It is the 1 st ad hoc MAC with Dynamic Channel Coding. Time-Hopping for Inter-WPAN interference. Schemes for:  Interference mitigation.  Synchronization between transmitter and receiver.  Dynamic channel coding with incremental redundancy. “Private MAC”: Enforce that several senders cannot communicate simultaneously with one destination. 

18. 18 UWB ad-hoc MAC - Previous Work PRIVATE MAC:  Request  Response  Data  Ack.  The request is sent to the receiver’s THS (Time-Hopping sequence).  Response, Data and Ack are transmitted using a common Sender- Receiver THS.  If no feedback is received, the sender will re-transmit after a random backoff.

19. 19 UWB ad-hoc MAC - Previous Work PRIVATE MAC (contd.)  Assume that B is transmitting to A.  An interfering node C will send a request to A and will wait listening to A’s THS.  After the end of a successful transmission, A & B issue a beacon to their THS to inform other nodes that they are idle.  If multiple nodes wait for A, they start counting a backoff timer as soon as they hear the beacon.  With a proper synchronization scheme, collisions are avoided.

20. 20 Conclusions UWB is an excellent solution for high-speed WPANs  Many times the maximum required data rate  Power efficiency and no multi-path fading.  The Multi-Band approach provides with even more advantages. A lot of work has been done in PHY. Upper layers must be examined in detail. Above MAC, nothing has been proposed.

21. 21 Questions? (References available upon request) General Atomics Multi-Band Transceiver Prototype