Thursday, October 26, 2006

Transmitted-reference methods

TR modulation technique has the advantage of sending the same pulse twice through an unknown channel where both pulses experience the same type of channel distortion and detection becomes easier with a correlation receiver. Therefore, instead of correlating the distorted received pulse with a “clean” template pulse as in PPM, both the data pulse and so called template ("reference pulse") are distorted and show high correlation at the TR receiver. Therefore, there is no need for channel estimation in TR receivers.

Furthermore, a TR receiver is self-synchronized and eliminates the need for individual pulse synchronization with locally generated templates that exists in PPM scheme. The reason is that each "reference pulse" acts as a preamble for its "data pulse" and has the advantage of providing rapid synchronization. Moreover, synchronization in TR receivers occurs after correlation between the "data pulses" and "reference pulses," thus the sampling requirements are relaxed to baseband signals. This way, the need for synchronization of the received short duration RF pulses and very fast ADCs are eliminated.

Another advantage of TR modulation to the other UWB modulation schemes is its high performance in multipath environments. TR receivers exploit multipath phenomenon to improve their performance in dense multipath and indoor channels. This is because the reference and data pulses are correlated with each other, and the multipath channel introduces a longer duration in the signal component of the received signal, thus increasing the overall signal energy at detection stage

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