UWB system provides very high bit rates services, low power consumption and accuracy position capability. A significant difference between traditional radio

transmissions and UWB radio transmissions is that traditional systems transmit information by varying the power level, frequency, and/or phase of a sinusoidal wave. UWB transmissions transmit information by generating narrow pulses of width of nanosecond at specific time instants and occupying large bandwidth thus enabling a pulse-position or time-modulation. As system occupies very large bandwidth the same bandwidth is also used by other existing communication systems. UWB signal must be transmited without affecting the performance of other systems operating in its coexistence and viceversa. Implantation of UWB transmitter and receiver do not require expensive and large components, such as modulators, demodulators, and IF stages. This fact can reduce cost, size, weight, and power consumption of UWB systems in comparison with conventional narrowband communication systems.

The performance of Victim receiver is obtained by finding the signal to noise ratio with and without UWB interference. So, the interference issue is on the proximity.

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FCC has mandated that UWB transmissions can legally operate in the range 3.1 GHz up to 10.6 GHz, at a limited transmit power of -41dBm/MHz.

At such low power level does interference from WiMaX and WLAN is any issue ?

After the authorization by FCC,IEEE has incorporated UWB into technical standard for high rate WPANS ,Low rate WPAN and Body Area Network, so interference from wimax and wlan it is not an issue.

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Then why notch generation in UWB antennas is a major research area?

Actually, a perfect approach to solve the interference problem is the Cognitive UWB Radio, which could not only avoid the interference due to the spectrum overlay between UWB and NB communication systems but improve the spectrum

efficiency remarkably as well. Nevertheless, the dynamic control for the spectra of the UWB signals, which is the key for implementing the dynamic spectrum access in the cognitive radio (CR), is still a challenge because of the limited processing speed of the analog-to-digital (A/D) and digital-toanalog (D/A) converters.

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Where ever the overlap portion of a spectrum used exists at the same time and same space, interference can not be avoided. The other signal act as a noise and especially, in a digital system, it will create jitters which may kill synchronization. This will have prominent effect in case of narrow pulse signal. 

Kindly validate your answer with numeric data (of power levels) for both UWB antennas and narrowband systems like WiMax and WLan.

It is expected, (looking to the today available receiver capability) that the difference between wanted signal and unwanted signal should be 10 dB down for good detection of own signal. _41 dBm/MHz you referred could be small for strong signal reaching to receiver which could be nearby the receiver and could be huge for the signal which weak due to distant transmitter