Browsing by Author "Shieh, KJ"

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On the performance of using multiple transmit and receive antennas in pulse-based ultrawideband systems
(2005-11-01)
Wang, LC
;
Liu, WC
;
Shieh, KJ
;
電信工程研究所
;
Institute of Communications Engineering
This paper presents an analytical expression for the signal-to-noise ratio (SNR) of the pulse position modulated (PPM) signal in an ultrawideband (UWB) channel with multiple transmit and receive antennas. A generalized fading channel model that can capture the cluster property and the highly dense multipath effect of the UWB channel is considered. Through simulations, it is demonstrated that the derived analytical model can accurately estimate the mean and variance properties of the pulse-based UWB signals in a frequency-selective fading channel. Furthermore, the authors investigate to what extent the performance of the PPM-based UWB system can be further enhanced by exploiting the advantage of multiple transmit antennas or receive antennas. Numerical results show that using multiple transmit antennas in the UWB channel can improve the system performance in the manner of reducing signal variations. However, because of already possessing rich diversity inherently in the UWB channel, using multiple transmit antennas does not provide diversity gain in the strict sense [i.e., improving the slope of bit error rate (BER) versus SNR] but can possibly reduce the required fingers of the RAKE receiver for the UWB channel. Furthermore, because multiple receive antennas can provide higher antenna array combining gain, the multiple receive antennas technique can be used to improve the coverage performance for the UWB system, which is crucial for a UWB system due to the low transmission power operation.
Spectrum sharing for frequency hopped CDMA systems with overlaying cellular structures
(2003)
Wang, LC
;
Shieh, KJ
;
電信工程研究所
;
Institute of Communications Engineering
This paper analyzes the uplink capacity of a frequency hopped CDMA system with spectrum sharing between a hot spot microcell embedded in an overlaying macrocell. We investigate how frequency hopping can function together with power control in order to allow the same frequency spectrum to be shared between the two tiers in the CDMA hierarchical cellular system. We consider random frequency hopping (RFH) and dynamic frequency hopping (DFH) combined with three power management methods: 1) signal strength based dynamic power control (PC), 2) static power setting with different maximum transmit power constraints (SPS), and 3) no power control (NPC). Through analysis and simulation, we demonstrate that when employing either the SPS or the PC methods, frequency sharing with DFH outperforms frequency sharing with RFH in terms of system capacity. Both frequency sharing schemes provide larger capacity than splitting frequency band between. macrocells and microcells. However, without using any power management methods, only frequency sharing with DFH can still perform better than the frequency splitting approach. In some cases frequency sharing with RFH may even have lower capacity than frequency splitting.