IFI and ISI premitigation for block-code-modulated noncoherent UWB impulse radio: A code optimization approach

Abstract

Codeword matching and signal aggregation (CMSA) is a recently proposed low-complexity noncoherent receiver for block code modulated UWB Impulse Radio (UWB-IR) systems. As the frame/symbol duration is shortened to boost data rate, inter-frame interference (IFI) or inter-symbol interference (ISI) occurs and degrades detection performance of CMSA. In this paper, an effective IFI/ISI pre-mitigation scheme is proposed for CMSA by means of a code optimization approach. By employing a tailored interference model that highlights the codeword properties, the system performance in the presence of moderate IFI/ISI is evaluated and an average collected channel gain (CCG) is introduced as the metric for code optimization. With the primary focus on binary modulation, two IFI/ISI-robust code properties are generalized as Shifted-Orthogonality and Shifted-Repetition. Based on these properties, the optimal code is constructed. It is observed that, when the optimal code occurs, the leaked signal energy or the interference can be partially used to enhance the detection performance of CMSA in the presence of IFI/ISI. Unlike most of the existing IFI/ISI mitigation schemes for noncoherent UWB-IR that focus mainly on signal processing after the nonlinear detector, the optimized code is exploited to aggregate leaked signal energy along with the linear pre-detection operation already involved in CMSA receiver. Both analysis and simulation show that a distinct performance improvement is achieved.

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