Abstract
This paper presents performance and its simulation results of pseudonoise (PN) code acquisition scheme with MIMO scheme for an ultra-wideband time-hopping/code-division-multiple-access (UWB TH/CDMA) system. The transmission channel is modelled as a frequency selective lognormal fading channel. In almost practical PN code acquisition system, the existence of more than two synchronous cells in the uncertainty region of the search process is possible due to multipath effect. Therefore, based on deriving the detection probability, false alarm rate, miss detection probability, and mean acquisition time, the acquisition performance is analyzed under the hypothesis of multiple synchronous states (cells) in the uncertainty region of the PN code. And the code acquisition performance is evaluated when the correlator outputs are noncoherently combined by using equal gain combining (EGC) scheme. In this procedure, the closed form for the conditional probability of decision variable is derived using the Gauss-Hermite quadrature formula. The performance comparison of the scheme mentioned above shows that the code acquisition performance with the diversity combining technique, especially when increasing the number of antenna, is more robust than that using no diversity. And code acquisition performance comparison also shows that if the detection threshold is set inappropriately, the performance might be degraded, even if an antenna diversity method is applied. It is also shown that Tx diversity can improve the acquisition performance but not as much as Rx diversity does. And Rx diversity can be applied to the acquisition system for additional diversity gain if the complexity of the receiver can be accepted.
Highlights
UWB systems have been considered in several commercial and military communication applications due to several advantageous features such as low transmission power requirement, high data rate, robustness to severe multipath, low probability of intercept, and fine delay resolution property
Wireless Communications and Mobile Computing we focus on pseudo noise (PN) code acquisition of the UWB signals in the UWB TH/CDMA systems
We have proposed Tx and Rx diversity techniques for the PN code acquisition of the UWB TH/CDMA signal in the frequency selective lognormal fading channel
Summary
UWB (ultra-wideband) systems have been considered in several commercial and military communication applications due to several advantageous features such as low transmission power requirement, high data rate, robustness to severe multipath, low probability of intercept, and fine delay resolution property. Tx diversity schemes have received more and more attention to improve the acquisition performance and to reduce the receiver complexity in wireless communication systems [8]. We analyze a PN code acquisition performance for the UWB TH/CDMA system using Tx and Rx diversity schemes which improve the signal quality at the receiver. The proposed diversity technique is that the transmitter sends the UWB signals from multiple transmitting antennas using time delays. In order to analyze the performance, the statistics of the decision variables associated with the EGC scheme and the expressions for the detection probability, false alarm rate, miss detection probability, and mean acquisition time are derived in the lognormal fading channel.
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