Yu-Hao Chang

Ultrawideband Transceiver Design Using Channel Phase Precoding

A novel transceiver design for ultrawideband (UWB) communication systems using the channel phase precoding (CPP) technique is proposed in this work. With the CPP-UWB transceiver, we encode data symbols using the reversed order of the channel phase. A simple phase estimation algorithm is presented for the CPP-UWB implementation. Owing to its ability to coherently combine the channel magnitude of every multipath, the CPP-UWB transceiver can achieve a higher data rate by shortening its symbol duration with a tolerable interference. The performance of the CPP-UWB can be further improved using an optimal code length and/or the MMSE receiver to suppress intersymbol interference.

Design and analysis of channel-phase-precoded ultra wideband (CPPUWB) systems

A new indoor data communication scheme called the channel phase preceded ultra wideband (CPPUWB) system is proposed in this work. The proposed CPPUWB system is efficient in computational power saving by encoding the transmit symbol with a channelized codeword. The channelized codeword is determined by the channel phase information that is estimated at the receiver and then fed back to the transmitter. A method to estimate the channel phase information using training symbols is presented. For a given number of training symbols, we derive a lower bound for the average output SNR, which can be used to evaluate the system performance. Finally, an MMSE receiver is proposed to suppress the residual intersymbol interference (ISI) for the high data rate scenario

Performance Enhancement of Channel-Phase Precoded Ultra-Wideband (CPP-UWB) Systems by Rake Receivers

We propose to use the Rake receiver to improve the system performance by collecting more signal power in an ultra-wideband (UWB) system precoded by the channel phase information, called the CPP-UWB system [1], in this work. The performance of the proposed system is determined by the selected channel taps and the corresponding combining schemes for those Rake fingers. Three combing schemes, Le., the maximum ratio combining (MRC), the minimized mean square error (MMSE) and the zero-forcing (ZF), are proposed. When the MRC scheme is applied to the Rake receiver with M fingers, M channel taps can be easily found to maximize the averaged signal power at the receiver output by exploiting the property of the channel- phase-precoded channel. It is shown by simulation results that the proposed scheme significantly outperforms the preceding system using one matched filter as proposed in [1].

Techniques for received signal focusing in DSUWB systems

Several techniques for received signal focusing based on multiple transmit antennas and time-reversal prefiltering (TRP) for direct-sequence ultra-wideband (DSUWB) systems are studied in this work. The use of multiple transmit antennas offers a higher spatial diversity gain for better signal focusing. To perform TRP, we need to feed the channel information back to the transmitter, which may contain hundreds of taps and could be expensive in transmission. The previously proposed partial-Pre-RAKE (PPR) scheme is analyzed and shown to provide the maximum average power concentration if a fixed number of consecutive taps avail- able from the feedback. To further enhance this algorithm, we propose a phase-assisted tap selection scheme. The performance of the proposed phase-assisted tap selection scheme is analyzed and verified by computer simulation.

Codeword Length Optimization for CPPUWB Systems

The optimal codeword length that generates the maximum output signal to interference ratio (SIR) for the channel-phase-precoded ultra-wideband (CPPUWB) system proposed in Y.H. Chang et al. (2006) is studied in this work to mitigate the interference in high data rate transmission. As compared with the proposed MMSE receiver in Y.H. Chang et al. (2006), this code length optimization technique demands no additional training symbols, which sacrifices the actual data rate, and maintains a simple receiver structure. This optimization problem is highly nonlinear in nature, and a fast search algorithm is developed to speed up the optimization process. The signal to interference plus noise ratio (SINR) performance of the proposed scheme degrades slightly when the input SNR is low, and it will converge to the maximum SINR as the input SNR becomes large

On Robustness of Ultra-Wideband (UWB) Precoding Against Timing Jitter

The channel phase precoding (CPP) technique was recently proposed for the ultra-wideband (UWB) communication system in [1] to save the feedback overhead and the computational complexity as compared with the time-reversal prefllter (TRP) technique [2]. Two ideal assumptions have been made in both systems; namely, the availability of accurate channel information and perfect synchronization of transmitted pulses. In this work, we examine the impact of timing jitter on the performance of TRP and CPP and show that the CPP-UWB system is more robust against the timing jitter than the TRP- UWB svstem.

SPCp1-11: Optimal Codeword Design for Precoded UWB (PUWB) Systems

A preceding technique applied to symbols transmitted in an ultra-wideband (UWB) system was proposed, which can concentrate the signal power at the receiver to facilitate data detection. The design of the optimal codeword for preceding is investigated in this work. After the problem is formulated, we examine its solution in the full-rank space as well as the reduced-rank subspace to get different tradeoff between detection performance and the amount of feedback messages. Furthermore, we propose two subspace selection schemes that are suitable for different channel conditions. The codeword obtained from this work improves the performance of the result significantly at the price of a larger amount of feedback messages.