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Performance analysis of IEEE 802.15.4a BPSK/BPPM UWB transmission Ahmadian, Zahra

Abstract

The ultra-wideband (UWB) technology has recently attracted considerable attention in industry and academia. This is due to the great potentials of the license exempt operation with UWB signals. These include high data. rate, low power consumption, robustness to multipath propagation, good penetration properties and the ability for accurate localization and ranging. The IEEE working group 802.15 set up two task groups (TGs) for the standardization of UWB physical layers for short-range communication: the IEEE T G 802.15.3a for high data-rate transmission which was officially formed in December 2007 and the IEEE TG 802.154a for low data-rate that became an official task group in March 2004. While the TG 802.15.3a did not succeed and was finally disbanded in January 2006; the TG 802.15.4a approved a draft standard in March 2007. This standard prescribes a rather unique coding and modulation scheme, namely the concatenation of an outer Reed-Solomon and an inner convolutional encoder with a mixed binary phase-shift keying and pulse position modulation (BPSK/BPPM) and time-varying spreading and position hopping. The decoding for and performance analysis of this coding and modulation scheme are the subjects of this thesis. First, we study the inner convolutional coded BPSK/BPPM in isolation. We suggest an optimal symbol-wise decoding metric, which replaces the sub-optimal bit-wise metric previously suggested in standardization documents, and we define semi-analytical ex- pressions for the bit-error rate (BER) performance with both optimal and sub-optimal decoding metrics. It is shown through analytical and simulated results that, using the optimal symbol-wise metric results in significant performance gains, of e.g. 2 dB at BER of 10‾³. while decoding complexity is identical to that with bit-wise decoding metric. Based on our semi-analytical results, we also quantify the performance loss due to RAKE combining with a limited number of fingers as opposed to ideal combining. Next, we investigate the entire concatenated coded BPSK/BPPM scheme, including the outer RS code and the inner convolutional code, and we suggest an improved decoding scheme by introducing reliability information generated by the inner decoder. More specifically, two different soft output Viterbi algorithms (SOVA) are considered and compared for generation of reliability information. For the conventional setup of inner Viterbi and outer RS decoder, we define semi-analytical expressions for the frame-error rate (FER) of the overall system, these expressions are highly valuable for quick performance assessment, since simulating the system's performance is extremely time consuming. In addition to decoding assuming perfect channel state information at the receiver (coherent receiver) considered so far, we also study the performance of decoding without channel state information (non-coherent receiver) to detect the BPPM data bit. This decoding mode is explicitly envisioned by the standard. Again, analytical expressions for BER. and FER are obtained, and the performance of non-coherent and coherent receivers are compared.

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