Juinn-Horng Deng

Fast FPGA prototyping of a multipath fading channel emulator via high-level design

A baseband multipath fading channel emulator is implemented on Xilinx XtremeDSP FPGA platform through high-level design. Without any RTL coding, fast prototyping of important modules can be done in the form of high-level Simulink models and Xilinx System Generator IP blocks. These modules include the white Gaussian noise generator (WGNG), Doppler filter, direct digital frequency synthesizer (DDFS), multi-rate interpolators, and multipath signal generator. Since all modules are designed in high level, the system parameters and configuration can be easily changed as desired. The FPGA emulator have been tested at a sampling rate of 30 Msps, and all the measured signals are well coincides with the simulation results, thus verifying the correctness of the design.

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.

Novel low-PAPR parallel FSOK transceiver design for MC-CDMA system over multipath fading channels

A low peak-to-average power ratio (PAPR) transceiver using a new parallel frequency-shift orthogonal keying (FSOK) technique is proposed for the multiuser uplink multi-carrier CDMA (MC-CDMA) system over multipath fading channels. By employing the frequency modulated and multiplexed FSOK techniques to combat the multiuser and parallel substream interferences, respectively, the system retains a low-PAPR transmitted signal and a low-complexity equalizer without any matrix inversion. At the basestation, a multiuser receiver is derived, which involves parallel FSOK despreading, demapping, and maximum likelihood decision rule to acquire M-ary modulation gain and frequency diversity gain. For higher link quality, a multiple input single output FSOK uplink system can flexibly be configured. Simulation results are included to demonstrate that the proposed system achieves the low-PAPR property, space-frequency diversity, and M-ary modulation gain. Compared to the existing MC-CDMA and SC-FDMA systems, the proposed system exhibits significant performance superiority.

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.

Novel multiuser MIMO relay precoder design for cognitive radio systems with primary interference cancellation

A novel multiuser MIMO cognitive radio (CR) system with enhanced interference suppression from primary system is proposed in the presence of multiple CR users and parallel streams communication. Moreover, in the overlay system with the unlicensed CR user (CU) and the licensed primary user (PU), PU performance will be degraded by interferences. Similarly, CU transmission efficiency will be reduced by PU interferences. For the traditional multiuser MIMO system, the precoding schemes are utilized to limit the CU transmission power, which can reach the no interference to PU. However, the PU signal will induce the interference to CU. For the traditional CR system, the PU interference signals are considered as white noise to study the CR performance. In this paper, we proposed a cooperative multiuser MIMO CR relay system and use the relay station to cancel the PU interference within two time slots, which can enhance the transmission quality of CR system. Note that the relay station exhibits the multiuser MIMO precoding capability to convey the negative multiple PU data for CU user to cancel PU interference. Simulation results demonstrate that the proposed CR relay system outperforms the traditional CR system and shows the linear growth of sum rate over the strong PU interference and multiple CUs and streams interference. The robust CR relay system can be extended to use in the future 5G overlay system.

Time-frequency multiplex estimator design of joint Tx IQ imbalance, CFO, channel estimation, and compensation for OFDM systems

A low complexity time-frequency multiplex estimator and low complexity equalizer transceiver design is proposed to combat the RF impairment problems for the zero-IF transceiver of orthogonal frequency-division multiplexing (OFDM) systems. Moreover, the proposed preamble can estimate and compensate the transmitter (Tx) in-phase and quadrature-phase (IQ) imbalance, carrier frequency offset (CFO) and channel impulse response parameters. There are two parts in the proposed system. Firstly, all parameters of impairments are estimated by the proposed time-frequency multiplex estimator design. Secondly, the estimated parameters are used to equalize the above problems and detect the transmitted signal with low complexity advantage. Simulation results confirm that the proposed estimator can provide reliable performance over the severe IQ imbalance, CFO, and multipath fading channel environment.

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.