A RAKE Combining Scheme for an Energy Detection Based Noncoherent OOK Receiver in UWB Impulse Radio Systems

Ultra-wideband (UWB) impulse radio systems based on non-coherent on-off keying (OOK) energy detection are relatively simpler to implement than their coherent counterparts, because the strict synchronization requirements are relaxed. However, the design challenge is to set a hard decision threshold value after energy detection because the detected energy may vary due to multipath fading and inter-pulse interference (IPI). Moreover, to find and track the starting point of the integration for energy detection, a timing recovery block is needed. This block requires a fairly accurate phase-locked loop (PLL) circuit, the cost of which is prohibitive for a low cost and low power UWB device. In this paper, we propose an orthogonal code sequence with RAKE combining for an energy detection based noncoherent OOK receiver. It uses a RAKE combiner with soft despreading to combat the severe IPI. With this structure, threshold setting for conventional energy detector can be avoided and a larger integration timing offset can be tolerated. Simulation results show that the energy detection based OOK receiver using the proposed orthogonal code sequence and the RAKE combining scheme can improve packet error rate performance significantly in a dense multipath fading channel