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An ultrawideband (UWB) format that jointly utilizes direct-sequence (DS) and time-hopping (TH) spreading, which is called direct-sequence impulse radio (DS-IR), is analyzed. A simple and widely applicable expression for the symbol error rate (SER) of a multiuser DS-IR system that operates over a frequency-selective channel with RAKE reception and quadrature phase-shift keying (QPSK) modulation is presented, based on the well-known simplified improved Gaussian approximation. The SER expression is next used in conjunction with a quasianalytical SER estimation to analyze the performance of DS-IR over the IEEE 802.15.4a channel, focusing on the impact of the TH and the system duty cycle on the SER. It is shown that the duty cycle can be varied with a minor effect on the SER if TH is exploited. On the other hand, when TH is suppressed, low-duty systems suffer an increase in SER, which, depending on the system parameters, can range from dramatic to negligible.
Date of Publication: March 2011