Shu-Min Liao

Design of low peak-to-average power ratio transceiver with enhanced link quality for coded single-carrier frequency division multiple access system

A new low peak-to-average power ratio (PAPR) transceiver is proposed for the coded single-carrier frequency division multiple access (SC-FDMA) system over frequency selective fading channels. By exploiting the constant envelope of the Chu-sequence in both frequency and time domains, the parallel spreading scheme and M-ary cyclic shift mapping technique can support the coded SC-FDMA system with a low PAPR for transmission at a high data rate. Interleaved time and frequency domain orthogonal modulation can increase the frequency diversity gain through the frequency domain equaliser and the time domain despreader. Moreover, the maximum likelihood rule is designed to detect the M-ary mapping data, which can provide M-ary gain to improve system performance. Simulation results reveal that the proposed high-rate coded SC-FDMA system can provide a lower PAPR and a better bit error rate (BER) performance than the conventional interleaved SC-FDMA system.

A Low-PAPR Multiplexed MC-CDMA System with Enhanced Data Rate over Multipath Channels

Recently, a new multi-carrier CDMA (MC-CDMA) systems with cyclic-shift orthogonal keying (CSOK) has been proposed and shown to be more spectral and power efficient than conventional MC-CDMA systems. In this paper, a novel extension called the multiplexed CSOK (MCSOK) MC-CDMA system is proposed to further increase the data rate while maintaining a low peak-to-average power ratio (PAPR). First, the data stream is divided into multiple parallel substreams that are mapped into QPSK-CSOK symbols in terms of cyclic shifted Chu sequences. Second, these sequences are repeated, modulated, summed, and placed on IFFT subcarriers, resulting in a constant-modulus multiplexed signal that preserves the desired orthogonality among substreams. The receiver performs frequency-domain equalization, and uses an efficient demultiplexing, despreading, and demapping schemes to detect the modulation symbols. Simulation results show that the proposed MCSOK system attains lower PAPR and BER, as compared to conventional MC-CDMA system using Walsh codes.

An iterative receiver with intercarrier interference cancellation for ofdm communication systems with carrier-frequency and timing offsets over multipath fading channels

A joint estimation and compensation algorithm of the carrier frequency offset (CFO) and sampling clock offset (SCO) is proposed for orthogonal frequency division multiplexing (OFDM) systems under multipath fading channels. First, we propose the joint weighted least-squares (JWLS) algorithm with intercarrier interference (ICI) cancellation to enhance the accuracy of the CFO and SCO estimation. Next, the partial parallel interference cancellation (PPIC) algorithm with maximal ratio combining (MRC) method is proposed to recover the synchronization errors and reconstruct the ICI interference. Finally, the iterative JWLS and PPIC algorithms are designed to overcome the serious ICI effect and improve the performance of OFDM systems. With computation simulation, it is shown that the proposed receiver is reliable and provides nearly the performance of the ideal receiver as iterations proceed.

A Fuzzy MOE Receiver for Uplink MC-CDMA Systems with Carrier Frequency Offset over Multipath Fading Channels

A novel fuzzy minimum output energy (MOE) detector is proposed for uplink multicarrier CDMA (MC-CDMA) systems with carrier frequency offset (CFO) over multipath fading channels. The proposed receiver involves the following stages. First, the fuzzy CFO constrained MOE detector after coarse CFO estimation is proposed to suppress multiple access interference and combat the degradation problem of the conventional MOE detector caused by the CFO effect. Next, using the signal subspace projection technique, the proposed detector can further reduce the enhanced noise due to the fuzzy CFO constrained detector. Finally, the output data obtained from these detectors are coherently combined to offer multipath diversity gain in accordance with the maximum ratio combining criterion. Furthermore, the proposed single input single output (SISO) robust detector can be easily extended for a multiple input multiple output (MIMO) MC-CDMA system with a high rate of performance. Simulation results show that the proposed SISO detector, which offers a similar performance as the optimal detector, can provide robustness against CFO and outperform the conventional detectors. The proposed MIMO detector with spatial multiplexing gain also exhibits excellent performance.

A Low-PAPR Differential Frequency Shift Orthogonal Keying Transceiver for Multi-Carrier Spread Spectrum System over High Mobility Multipath Channels

A new differential transceiver with a frequency-shift orthogonal keying (FSOK) technique is proposed for the multi-carrier spread spectrum (MC-SS) system over high mobility multipath fading channels. The design of the transceiver involves the following stages. First, the data stream is mapped into MPSK-FSOK symbols and spreaded by the frequency-shift orthogonal sequences. Second, the differential block encoder is exploited to combat the mobile channels. The Chu sequence is adapted for initial differential encoding, making the post-IFFT transmit signals with a low peak-to-average power ratio. Next, for the receiver, the maximum ratio combining technique is used for the block-based differential frequency-domain equalizer, which can overcome the multipath fading channel effect without requiring channel estimation. Finally, an efficient maximum likelihood despreading and demapping scheme is used to detect the modulation symbols. Furthermore, the differential MC-SS transceiver can be easily re-configured for a MISO differential MC-SS system with high link quality. Simulation results show that, under high mobility multipath channels, the proposed SISO differential MC-SS system can outperform the conventional MC-SS system. The proposed MISO differential MC-SS system with space-time diversity gain and M-ary modulation gain also exhibits excellent performance.

Adaptive space-time beamforming technique for passive radar system with ultra low signal to interference ratio

The multiple constrained LCLMS algorithm for bistatic radar has been investiagted. The proposed space-time LCLMS beamformer can be adaptive to constrain the spatial and temporal weights to cancel multiple interferences simultaneously. From simulation results, it is shown that the multiple constraint LCLMS algorithm provides better OSINR performance with resistance to strong DPI interferences.

Robust carrier frequency offset and channel estimation for orthogonal frequency division multiple access downlink systems in the presence of severe adjacent-cell interference

This study investigates joint estimation carrier frequency offset (CFO) and channel impulse response (CIR) in the problematic orthogonal frequency division multiple access (OFDMA) downlink scenario at the cell boundary, where a maximum supposition of three adjacent base stations preambles can be received. A novel scheme is proposed for estimating the CFOs and CIRs of different cells. First, the highly efficient joint maximum-likelihood (JML) algorithm is used to enable robust CFO estimation by exploiting the idempotent property of the projection matrix. Next, in order to estimate the precise CIR, the composite CFO-based and circularly shifted preamble signatures are proposed by applying the constrained minimum variance (CMV) algorithm to suppress adjacent-cell interference. Finally, the CFO and CIR estimations are enhanced by an iterative cancellation scheme. To the best of the authors research, there is no publication study proposed joint JML-CFO and CMV-CIR estimators for OFDMA downlink systems with adjacent-cell interference. Simulation results show that the proposed algorithms provide better performance than the conventional estimators and approach the theoretical Cramer–Rao lower bound at the cell boundary over frequency-selective fading channels.

A Low-PAPR Differential Frequency Shift Orthogonal Keying Transceiver for Multi-Carrier Spread Spectrum Communication System over High Mobility Multipath Channels

A new differential transceiver with a frequency-shift orthogonal keying (FSOK) technique is proposed for the multi-carrier spread spectrum (MC-SS) system over high mobility multipath fading channels. The design of the transceiver involves the following stages. First, the data stream is mapped into MPSK-FSOK symbols and spreaded by the frequency-shift orthogonal sequences. Second, the differential block encoder is exploited to combat the mobile channels. The Chu sequence is adapted for initial differential encoding, making the post-IFFT transmit signals with a low peak-to-average power ratio. Next, for the receiver, the maximum ratio combining technique is used for the block-based differential frequency-domain equalizer, which can overcome the multipath fading channel effect without requiring channel estimation. Finally, an efficient maximum likelihood despreading and demapping scheme is used to detect the modulation symbols. Furthermore, the differential MC-SS transceiver can be easily re-configured for a MISO differential MC-SS system with high link quality. Simulation results show that, under high mobility multipath channels, the proposed SISO differential MC-SS system can outperform the conventional MC-SS system. The proposed MISO differential MC-SS system with space-time diversity gain and M-ary modulation gain also exhibits excellent performance.

A Multistage Decision-Feedback Receiver Design for LTE Uplink in Mobile Time-Variant Environments

Single-carrier-frequency division multiple access (SC-FDMA) has recently become the preferred uplink transmission scheme in long-term evolution (LTE) systems. Similar to orthogonal frequency division multiple access (OFDMA), SC-FDMA is highly sensitive to frequency offsets caused by oscillator inaccuracies and Doppler spread, which lead to intercarrier interference (ICI). This work proposes a multistage decision-feedback structure to mitigate the ICI effect and enhance system performance in time-variant environments. Based on the block-type pilot arrangement of the LTE uplink type 1 frame structure, the time-domain least squares (TDLS) method and polynomial-based curve-fitting algorithm are employed for channel estimation. Instead of using a conventional equalizer, this work uses a group frequency-domain equalizer (GFDE) to reduce computational complexity. Furthermore, this work utilizes a dual iterative structure of group parallel interference cancellation (GPIC) and frequency-domain group parallel interference cancellation (FPIC) to mitigate the ICI effect. Finally, to optimize system performance, this work applies a novel error-correction scheme. Simulation results demonstrate the bit error rate (BER) performance is markedly superior to that of the conventional full-size receiver based on minimum mean square error (MMSE). This structure performs well and is a flexible choice in mobile environments using the SC-FDMA scheme.

Fuzzy MIMO detector for MC-CDMA systems with carrier frequency offset over multipath fading channels

A multistage fuzzy minimum output energy (MOE) detector is proposed for multiple input multiple output (MIMO) multi-carrier code-division-multiple access (MC-CDMA) uplink systems with carrier frequency offset (CFO) over multipath fading channels. The first stage of the receiver uses a novel MIMO receiver model with offset symbols to achieve a fuzzy CFO-constrained MOE detector that suppresses multiple access interference (MAI) and minimizes cancellation of the desired signal. To suppress noise and to enhance signal reception after the fuzzy MOE detector, a signal subspace projection and minimum mean square error weight combiner is proposed to enhance signal-to-interference-plus-noise ratio and bit error rate performances. Simulation results show that the proposed MIMO detector outperforms conventional MOE detectors and achieves the ideal receiver performance against MAI and CFO effects.