Conventional quadrature mixer for impulse radio receivers- filter design issues

One of the distinguishing features of impulse radio or ultra-wideband (UWB) systems is by their broad bandwidth. The resulting power spectral density of UWB systems can become very small due to the very large bandwidth. With such low radiated power, it is important to design a receiver that maximises the signal-to-noise ratio (SNR). Conventionally, this is achieved by a pulse matched filter. Due to the high data rate of UWB, pulse matching may not be feasible. Therefore, a template matching approach is employed instead. A local-oscillator (LO) based UWB receiver scheme is presented, derived from the conventional down-converter for narrowband systems. Instead of carrier modulation, the LO in the proposed receiver is for sub-optimal template matching with the received signals, matched in time but not in amplitude. This sub-optimal matched template is made possible by certain properties of the received UWB signals. The output is then low-pass filtered, and sampled. The selection of suitable low pass filters (LPF) and sampling rate for maximum energy collection with favourable correlation properties is investigated in this paper.