Time-Hopping  -Walsh UWB Transmission Scheme for a One-Bit Non-Coherent Receiver Nuan Song, Mike Wolf, and Martin Haardt Communications Research Laboratory, Ilmenau University of Technology P.O. Box 100565, D-98693 Ilmenau, Germany {nuan.song, mike.wolf, martin.haardt }@tu-ilmenau.de Abstract—We propose a Time-Hopping (TH) -ary Walsh transmission scheme using a one-bit non-coherent receiver for power efficient and low complexity low data rate Ultra Wideband (UWB) communications. The analytical Bit Error Rate (BER) bounds of the -Walsh modulation and the widely used -ary Pulse Position Modulation (-PPM) are derived and validated in the multipath scenario. We compare both schemes in terms of the receiver implementation and complexity, the quantization loss due to the one-bit receiver, and the multiple access performance. Taking into account the perfect/imperfect power control, the Multi-User Interference (MUI) resistance is evaluated via Monte Carlo simulations. According to the performance comparison and analysis, we show the suitability of the proposed TH -Walsh scheme using a one-bit non-coherent UWB receiver to achieve a high power efficiency. I. I NTRODUCTION The promising Impulse Radio Ultra Wide Band (IR-UWB) technology is based on discontinuous transmission of very narrow pulses with durations of sub-nanoseconds. The large bandwidth of the UWB signal results in a lot of resolvable multipath components at the receiver. Fully exploiting the rich multipath diversity, e.g., by means of a channel matched filter or its correlator equivalent, promises a high robustness to the fading. However, due to the complicated structure and unaffordable cost of such receivers, non-coherent detection has become an attractive candidate for low-complexity and low- power UWB communication systems. Pulse Position Modulation (PPM) is one of the most com- monly used orthogonal modulation schemes that enable non- coherent detection. To support multiple access communica- tions, Time-Hopping (TH) techniques are suggested [1] due to their sparse feature and accordingly the reduced receiver complexity (compared to the direct sequence spread spectrum approach). However, for non-coherent detection, the power efficiency is always lower than the coherent case due to the non-coherent combining loss [2]. In order to reduce this loss, in [3] we propose a Digital Code Matched Filter (DCMF)- based non-coherent receiver for a TH binary PPM UWB system. The DCMF follows after a high-speed and low- resolution Analog-to-Digital Converter (ADC) [4], [5] and restricts the non-coherent combining only to the multipath ar- rivals. One big advantage is that applying such digital solutions will facilitate the development of various techniques, such as non-coherent multipath combiners, multi-user detection, differential receivers. It is shown that the proposed digital non-coherent receiver is robust to the Multi-User Interference (MUI), even with a one-bit ADC. If the modulation order increases, the power efficiency of the system will be further improved. Thus, it calls for utilizing  -ary orthogonal modulation for non-coherent UWB communications. There are some  -ary modulation schemes proposed for TH-IR-UWB systems, such as  -PPM [6], [7],  -Walsh [8], On-Off Keying (OOK) combined with  -ary Pulse Shape Modulation (PSM) [9]. Increasing  of such orthogonal schemes will also provide a higher robustness to the MUI than the binary case. Most of the discussions and performance evaluations for those proposed  -ary schemes focus on the coherent detection. When  is large, the PSM requires a greater number of different pulse matched filters in parallel, imposing an even higher complexity on the receiver. Therefore, in order to achieve a higher power efficiency, we propose a TH  -ary Walsh transmission scheme based on a one-bit non-coherent receiver for low data rates and low complexity UWB communications. The performance of the proposed scheme is evaluated and compared to  -PPM by considering the impact from the receiver implementation, the one-bit quantization, and the multiple access. Thereby, we will show the suitability and the superior performance of the proposed TH  -Walsh scheme using a digital non-coherent receiver. II. SYSTEM DESCRIPTIONS The block diagram of the TH  -Walsh system is shown in Fig. 1. The sequential input bits are first converted in parallel and then mapped onto Walsh symbols. After each Walsh symbol is encoded by a TH sequence, the pulse shaping () is applied to generate the transmitted signal (). At the receiver, the received signal () goes through a pulse matched filter   ()= () to obtain a filtered signal (). The DCMF matched to the TH code follows after an ADC. The resulting signal samples will be fed to parallel block delays and the Fast Walsh Hadamard Transformation (FWHT) is carried out. A set of correlators can also be realized but has a higher computational complexity of order O (  2  compared to the FWHT with complexity of order O ( ⋅ log 2  ) [10]. In each branch, a square-law device and a digital accumulator are applied in order to collect the multipath energy for each 978-1-4244-6317-6/10/$26.00  2010 IEEE ISWCS 2010 516