Coherent and non-coherent ultrawideband communications

Short-range wireless communication has become an essential part of everyday life thanks to the enormous growth in the deployment of wireless local and personal area networks. However, traditional wireless technology cannot meet the requirements of upcoming wireless services that demand high-data rates to operate. This issue has motivated an unprecedented resurgence of ultra-wideband (UWB) technology, a transmission technique that is based on the emission of sub-nanosecond pulses with very low power spectral density. Because of the particular characteristics of UWB signals, very high data rates can be provided with multipath immunity and high penetration capabilities. Nevertheless, formidable challenges must be faced in order to fulfill the expectations of UWB technology. One of the most important challenges is to cope with the overwhelming distortion introduced by the intricate propagation physics of UWB signals. In addition to this, UWB antennas behave like direction-sensitive filters such that the signal driving the transmit antenna, the electric far field, and the signal across the receiver load, they all may differ considerably in wave shape. As a result, the well-known and popular concept of matched filter correlation cannot be implemented unless high computational complexity is available for perfect waveform estimation. The lack of knowledge about the received waveform leads UWB receivers to be implemented under a coherent or non-coherent approach depending on a tradeoff between waveform estimation complexity and system performance. On the one hand, coherent receivers provide the reference benchmark in the sense that they have ideally perfect knowledge of the end-to-end channel response and thus, optimal performance is achieved. On the other hand, non-coherent receivers appear as a low-cost and low-power consumption alternative since channel estimation is not considered and thus, suboptimal performance is expected.