Abstract
Wireless body area networks (WBAN) emerge as one of the main research streams for future wireless communications. One of the candidates for the WBAN physical layer is multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) technology. However, despite its high data rate feature, it performs poorly in the very dispersive WBAN channel. To improve its performance, this paper proposes two novel mechanisms. First, the space-time-frequency coding (STFC) is introduced into MB-OFDM UWB system in order to enhance the diversity order, resulting in a substantial improvement in the average error performance compared to the conventional MB-OFDM UWB system. Nevertheless, the performance is very sensitive to the body orientation towards the transmitter due to the body shadowing effect. Secondly, to improve further the performance of the proposed STFC MB-OFDM UWB system in all body directions, we propose an adaptive scheme that changes the modulation, STFC coding rate, and constellation power. Simulations confirm that an additional improvement in the order of 1 to 3 dB is achieved by the adaptive system. This improvement practically means a possible 12.5% to 50% reduction of the power consumption, which may also result in smaller size of WBAN devices.
Highlights
There have been active engagements in the wireless body area network (WBAN) research in recent years
In [18], we proposed the combination of space-time-frequency coding (STFC) and MB-OFDM UWB, referred to as the STFC MB-OFDM UWB, as an improved physical layer for WBAN
Comparing to the BER of the best link (0° direction, cross-marked curves in Figure 6) of the non-adaptive system in both multiple-input multiple-output (MIMO) configurations, as expected, the averaged BER of the adaptive scheme is slightly worse. This is because the adaptive system selects the highest STFC coding rate (3/2) for the 0° direction in order to maximize the capacity, with a price of minor performance degradation compared to the best performance scenario in the non-adaptive case
Summary
There have been active engagements in the wireless body area network (WBAN) research in recent years. Γ varies significantly for different body directions with respect to the transmitter in the case of CM4 over the UWB WBAN channel. In [18] as previously mentioned, we present the performance analysis of STFC MB-OFDM UWB in CM3 and CM4 WBAN channels using the Alamouti code. This paper proposes for the first time a body directionbased adaptive algorithm for STFC MB-OFDM UWB WBAN, in order to improve the average BER performance and/or reduce the power consumption of the body-toexternal link for WBAN applications [32]. This might possibly be due to the different surrounding environments of the 90° and 270° directions during the measurement.
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