Single Carrier Block Transmission With Frequency Domain Equalization Research Articles

Design and Analysis of Timing Synchronization in Block Transmission UWB Systems

In this paper, timing synchronization in high-rate ultra-wideband (UWB) block transmission systems is investigated. A new joint timing and channel estimation scheme is proposed for orthogonal frequency division multiplexing (OFDM) and single carrier block transmission with frequency domain equalization (SC-FDE) UWB systems. The scheme is based on a newly designed preamble for both coarse timing and the subsequent channel estimation. Despite of the presence of coarse timing error, the estimated channel impulse response (CIR) is simply the cyclic shifted version of the real CIR, thanks to the unique structure of the preamble. The coarse timing error (CTE) is then determined from the CIR estimation and used to fine tune the timing position and the frequency domain equalization coefficients. The proposed scheme saves preamble overhead by performing joint synchronization and channel estimation, and outperforms existing timing acquisition methods in the literature in dense multipath UWB channels. In addition, the impact of timing error on channel estimation and the performance of SC-FDE UWB systems are analyzed, and the bit-error-rate (BER) degradation with respect to a certain timing error is derived.

Comparison of Frequency Offset and Timing Offset Effects on the Performance of SC-FDE and OFDM Over UWB Channels

In this paper, the effects of carrier frequency offset (CFO) and sampling time offset (STO) on the performance of single-carrier block transmission with frequency-domain equalization (SC-FDE) and orthogonal frequency-division multiplexing (OFDM) over ultrawideband (UWB) channels are investigated. The signal-to-interference-plus-noise ratio (SINR) of SC-FDE in the presence of CFO is derived and compared with that of OFDM. The effects of CFO on the bit error rate (BER) performance of both systems are also simulated and compared. Two forms of STO are considered, i.e., a constant timing shift from its optimum sampling timing instant and a random timing jitter. We show through analysis that although SC-FDE is reasonably robust to a constant timing offset, it is fairly sensitive to random timing jitter. The BER performances of SC-FDE in the presence of a constant STO and random timing jitter are simulated and compared with OFDM.

Performance of SC-FDE system in UWB communications with imperfect channel estimation

Single carrier block transmission with frequency domain equalization (SC-FDE) has been shown to be a promising candidate in ultra-wideband (UWB) communications. In this paper, we analyze the performance of SC-FDE over UWB communications with channel estimation error. The probability density functions of the frequency domain minimum mean-squared error (MMSE) equalizer taps are derived in closed form. The error probabilities of single carrier block transmission with frequency domain MMSE equalization under imperfect channel estimation are presented and evaluated numerically. Compared with the simulation results, our semi-analytical analysis yields fairly accurate bit error rate performance, thus validating the use of the Gaussian approximation method in the performance analysis of the SC-FDE system with channel estimation error.

Spectrum Shaping and NBI Suppression in UWB Communications

This paper investigates spectrum shaping in ultra-wideband (UWB) communications in order to introduce spectral nulls to limit interference with narrowband signals. Each transmitted symbol is represented by a "coded Gaussian monocycle pulse" in which Gaussian monocycles are weighted, delayed and summed in accordance with a designed codeword. The use of the Gaussian monocycle ensures that the UWB spectrum mask established by the Federal Communications Commission (FCC) is met, and the codeword is designed to generate a spectral null at the frequency or frequencies being used by existing narrowband devices. Signals obtained with different spectrum shapings (e.g., Butterworth, Chebyshev, elliptical) and by introducing nulls at multiple interference frequency bands are discussed. This approach can be used in various systems; as one application, we simulate the performance of a coded monocycle UWB system with a spectral null in the presence of narrowband interference (NBI) using single carrier block transmission with frequency domain equalization (SC-FDE), and compare its performance with that of an uncoded SC-FDE UWB system using a single Gaussian monocycle. Our results show that NBI can be effectively suppressed by transmitting and matched filtering the pulse with a spectral null at the interference frequency, therefore improving the robustness of UWB systems to NBI

Frequency-Domain Channel Estimation for SC-FDE in UWB Communications

Recently, single-carrier block transmission with frequency-domain equalization (SC-FDE) has been shown to be a promising candidate for ultra-wideband (UWB) communications. In this paper, we address the channel estimation problem for SC-FDE transmission over UWB channels. A mean-square error (MSE) lower bound for the frequency-domain linear minimum mean-squared error (LMMSE) channel estimator is derived, and the optimal pilot sequence that achieves this lower bound is obtained. Further simplification leads to a frequency-domain channel estimator with reduced computational complexity. The performance of the simplified estimator for SC-FDE over UWB channels is evaluated and compared with that with perfect channel state information. The effects of nonoptimal and optimal pilot symbols are also investigated. Our results show that the proposed frequency-domain channel estimator performs well over UWB channels with only small performance degradation, compared with that with perfect channel estimation

A time-division multiple-access SC-FDE system with IBI suppression for UWB communications

We propose a time-division multiple-access (TDMA) scheme for the binary phase-shift keying (BPSK) modulated single carrier block transmission with frequency domain equalization (SC-FDE) over ultra-wideband (UWB) channels. The transmitter and receiver matrices for the proposed TDMA SC-FDE system are derived to achieve the multiple-access interference (MAI) free and interblock-interference (IBI) free transmission without the insertion of cyclic prefix (CP) between blocks, avoiding long CP and large fast Fourier transform (FFT) size in high-speed UWB communications. The performance of the proposed TDMA SC-FDE system over UWB channels is investigated and compared with that of the block spread code-division multiple-access (CDMA) scheme. The impact of oversampling diversity and imperfect channel estimation on the performance of the proposed system are also investigated. Results show that the proposed TDMA scheme can effectively eliminate the error floor in CDMA due to insufficient CP, and it is more efficient to accommodate larger number of users than CDMA in high data rate transmission.