ioannis broustis srikanth krishnamurthy mart molle whynet ucla november 2004 l.
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Ioannis Broustis, Srikanth Krishnamurthy Mart Molle WHYNET - UCLA, November 2004. U ltra B and Wireless Ad Hoc Networks. Motivation. Current wireless solutions (IEEE 802.11, Bluetooth…) face many problems: Limited channel capacity High power consumption

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Current wireless solutions (IEEE 802.11, Bluetooth…) face many problems:

Limited channel capacity

High power consumption

UWB is an excellent solution for short-range communications. However, it is not intended to replace the above technologies, but coexist with them.

170+ companies have already jumped on the UWB wagon

why uwb
Why UWB?


Low-power operation.

Low cost.

Low probability of detection and low probability of jamming capabilities.

Low interference levels to existing services.

Ability to penetrate walls, etc.

Availability of precise location information.

uwb what is it
UWB: What is it?
  • Available bandwidth
    • FCC allocates 7,500 MHz in the 3.1 to 10.6 GHz band.
  • Any signal that:
    • Occupies at least 500MHz of BW, or
    • More than 25% of a center frequency:
uwb applications
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..)
phy single band and multi band
PHY: Single-Band and Multi-Band

Single-Band Implementation

One pulse occupies the whole BW at a time.

Multi-Band Implementation

The 7.5GHz are divided into multiple bands.

Information is independently encoded in the different bands.

The lower limit of 500MHz, as well as the transmission power restrictions, must be maintained.

Other possibilities OFDM, MC-CDMA (for future).

why prefer multi band
Why prefer Multi-Band ?

The delay spread of the wireless channel, unless combated, restricts the achievable rate.

Adaptive band selection Avoids interference

Low complexity Small transceiver cost

Simultaneous transmissions in the different bands




Time Hopping

  • Time Hopping has been mostly proposed so far, to alleviate pulse collisions.
    • Pulses are transmitted according to a Time Hopping Sequence (THS)
    • The THS is known by both the transmitter and the receiver
    • Receiver-based: The receiver's THS is followed
    • Transmitter-based: The transmitter's THS is followed

THS1: 0, 3, 2, 6

0 12 3 4 5 6 7

0 12 3 4 5 6 7

0 12 3 4 5 6 7

0 12 3 4 5 6 7

THS2: 4, 6, 3, 3


Our current MAC scheme

  • Advantages
    • Increased channel capacity
    • No need for Time Hopping
    • All the multi-band advantages, discussed earlier, over a potential single-band implementation
  • Ad hoc communications are enabled

Tc frame



Pulse width


Our current MAC scheme

  • Increased channel capacity
    • Each band is capable of achieving the same capacity as that of a single-band system, due to the delay spread effect
  • No need for Time Hopping
    • A band is exclusively dedicated to a pair of nodes
    • Pulses are now being transmitted consecutively

Data 7


Data 6

Data 5

Data 4

Data 3

Data 2

Control 1

Control 0



Availability frame


Our current MAC scheme








Preliminary results

  • Simulations
    • Average throughput of correct bits

Preliminary results

  • Simulations
    • Frequency of collisions

Preliminary results

  • Simulations
    • Average delay for resource occupancy

Future Work

  • MAC Layer
    • Dealing with the expensive preamble period with UWB.
    • Improving on contention resolution.
    • Investigating the possibility of using OFDM/ MC-CDMA.
    • Integration with better coding schemes.
  • Higher Layer Artifacts
    • How does the MAC layer fit in with the routing layer?
    • Transport layer feedback.
questions references available upon request
Questions?(References available upon request)

General Atomics Multi-Band Transceiver Prototype