In this letter, we propose an effective preamble based on constant amplitude and zero auto-correlation (CAZAC) sequence for multi-input multi-output (MIMO) and cooperative WiMedia ultra-wideband (UWB) systems. The proposed preamble even provides better single-channel estimation performance than the preamble specified in the standard in severe UWB channel model. The effectiveness of the proposed design is confirmed through the mean square error (MSE) performance.

The code division multiplexing (CDM)-based MIMO channel sounder architecture is efficient at measuring fast fading MIMO channels. This paper examines loosely synchronous (LS), CAZAC, Kasami, and Chaotic sequences as probing signals in the CDM architecture. After comparing the performance of the channel measurement among the sequences, it is concluded that the LS sequences are the most appropriate codes for the probing signals. However, because LS sequences have a significant drawback in that the number of transmit antennas is limited to less than 4, we propose using a hybrid architecture combining CDM with TDM for supporting a greater number of transmit antennas. The simulation results show that the proposed scheme can improve the measurement performance when more than 4 transmit antennas are used.

The classical 4-phase constant-amplitude zero-autocorrelation (CAZAC) sequence with the length of 16 has been used for multifarious purposes such as channel estimation and frequency/timing synchronizations since it presents good performance even in low signal to noise ratio (SNR) conditions. However, as multiple transmit antennas are employed, its properties are easily destroyed by the effect of multipath. In this letter, we propose a technique which ensures that the conventional CAZAC sequence is reliable in a multi-antenna system by inserting nulls. The performance of the modified sequence is verified through the mean s quare error (MSE) performance with the least squares (LS) method.

In this letter, we evaluate the M-BOK based DS-UWB system that uses a space-time block code (STBC) with Rake receivers in the WPAN environment. The conventional DS-UWB system doesn't ensure receiver reliability for the WPAN envrionment due to multipath fading, while the proposed M-BOK based DS-UWB system employing a STBC can overcome multipath fading causing attenuation of receiver reliability in the WPAN environment. In addition, a simple diversity combining receiver, called PRake receiver, shows the performance similar to that of a ARake receiver using the ideal diversity combining and reduces the receiver complexity.

In this letter, the problem of attaining frequency synchronization for high rate WPANs is considered. An estimation of the frequency offset is essential step at the receiver because the frequency offset means that the phase of transmitted signal is corrupted. The proposed algorithm utilizes the difference in phase between received preamble and estimated preamble. It turns out that the proposed algorithm has low complexity and good performance. To enhance the capability, we use peak phase detector. The performance of the proposed algorithm is assessed by computer simulation, and the frequency offset variance is compared to Cramer Rao Bound.

This letter presents a timing synchronization method of high-rate wireless personal area network (WPAN) systems encountered with a multipath fading channel. Two-stage timing synchronization using constant amplitude zero auto-correlation (CAZAC) training symbols and correlation techniques is adopted. At the same time, a simple way of setting a reliable threshold used to estimate WPAN timing is provided.

This letter presents an investigation of channel estimation scheme for a high rate WPAN system using multiple transmit antennas over indoor wireless channel. A simple algorithm utilizing the autocorrelation property of a CAZAC preamble is proposed for channel estimation. Simulation and analytical results show the performance of the proposed algorithm in terms of mean square error (MSE) of channel estimation. At the same time, the effect of imperfect channel estimation introduced by relatively large RMS delay spread is highlighted.