On Coherent and Non-coherent Receiver Structures for Impulse Radio UWB Systems

University dissertation from Karlskrona : Blekinge Institute of Technology

Abstract: The demand and growth of short-range wireless communications has been tremendous in the past few years for a diverse range of applications. There is significant interest in ultra wideband (UWB) as a physical layer technology for both high-data-rate (HDR), and low power, low-data-rate (LDR) short-range communications. The unique qualities of UWB such as large bandwidth, very low power spectral density (PSD) and fine time-resolution provide higher channel capacity, reduced fading effects and position location capability in a UWB system. The extremely wide bandwidth of UWB systems also poses many system design challenges to achieve low cost and low-complexity UWB devices. The UWB systems have difficulties in using digital signal processing (DSP) technology, require high sampling frequencies and also face frequency dependent signal distortion. The propagation characteristics of UWB signals also require consideration as it differs significantly from traditional narrowband systems. In this thesis, the issue of design and performance evaluation of coherent and non-coherent receivers for detection of impulse radio (IR) UWB signals is addressed. The coherent RAKE and non-coherent transmitted reference (TR) receiver structures are investigated for low power and low-data-rate wireless sensor network applications. First, the performance of coherent RAKE receivers for a single-user system operating in non-line-of-sight (NLOS) scenarios in an industrial environment is evaluated. The results and performance comparison is presented for partial RAKE (PRake) and selective RAKE (SRake) using maximal ratio combining (MRC) and equal gain combining (EGC). Secondly, the recursive structures of conventional TR and averaged TR schemes are presented to decrease the performance loss associated with the low-complexity TR scheme for IR-UWB systems. Further, a doublet-shift TR (DSTR) signaling and detection scheme is presented for IR-UWB systems. The simulation results validate that the doublet-shift TR signaling scheme improves the performance over conventional TR signaling scheme. Finally, dual-doublet TR (DDTR) signaling and detection schemes are proposed. The proposed dual-doublet TR schemes recover 25 to 50% energy/rate loss of conventional TR scheme. The performance of receiver structures is evaluated in terms of uncoded bit-error-rate (BER) over the channels measured in a medium-sized industrial environment and standard IEEE 802.15.4a multipath channels.