Yun-Ming Siu

PAPR reduction of an OFDM signal by use of PTS with low computational complexity

One of the major drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the transmitted OFDM signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of an OFDM signal. However optimum PTS (OPTS) technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of sub-blocks. By combining sub-optimal PTS with a preset threshold, a novel reduced complexity PTS (RC-PTS) technique is presented to decrease the computational complexity. Numerical results show that the proposed approach can achieve better performance with lower computational complexity when compared to that of other PTS approaches.

Particle-Swarm-Optimization-Based Multiuser Detector for CDMA Communications

In a code-division multiple-access system, multiuser detection (MUD) can exploit the information of signals from other interfering users to increase system capacity. However, the optimum MUD can be characterized as an NP-hard combinatorial optimization problem such that the computational complexity increases exponentially with the number of users. In this paper, we apply a new evolutionary algorithm, called particle swarm optimization (PSO), to develop a suboptimal MUD strategy. The decorrelating detector (DD) or linear minimum mean square error (LMMSE) detector is used as the first stage to initialize the PSO-based MUD. Then, the PSO algorithm is applied to detect the received data bit by optimizing an objective function incorporating the linear system of the DD or LMMSE detector. Simulation results show that the performance of our proposed decorrelating PSO and LMMSE-PSO MUD are promising and outperform the decorrelating and LMMSE MUD with a slight increase in computation.

A Low Complexity Selected Mapping Scheme by Use of Time Domain Sequence Superposition Technique for PAPR Reduction in OFDM System

By using the time domain sequence superposition (TDSS) technique, in this paper, we propose a low complexity selected mapping (LC-SLM) scheme for the peak-to-average power ratio (PAPR) reduction of the orthogonal frequency division multiplexing (OFDM) system. Unlike the conventional selected mapping (SLM) scheme which needs several inverse fast Fourier transform (IFFT) operations for an OFDM signal, the proposed scheme requires to implement two IFFT operations only. Thus, it can remarkably reduce the computational complexity. Simulation results show that the proposed scheme can achieve similar PAPR performance as the conventional SLM scheme.

PAPR Reduction Using Low Complexity PTS to Construct of OFDM Signals Without Side Information

Partial transmit sequence (PTS) is one of the most well-known peak-to-average power ratio (PAPR) reduction techniques proposed for orthogonal frequency-division multiplexing (OFDM) systems. The main drawbacks of the conventional PTS (C-PTS) are high computational complexity and transmission of several side information bits. A new PTS with simple detector is proposed in this paper to deal with these drawbacks of C-PTS. The candidates can be generated through cyclically shifting each sub-block sequence in time domain and combining them in a recursive manner. At the receiver, by utilizing the natural diversity of phase constellation for different candidates, the detector can successfully recover the original signal without side information. Numerical simulation shows that the proposed scheme performs very well in terms of PAPR. The probability of detection failure of the side information demonstrates that the detector could work without any side information with high reliability. The proposed scheme achieves almost the same bit error rate (BER) performance as the C-PTS with perfect side information, under both additive white Gaussian noise (AWGN) channel and Rayleigh fading channel.

Single-Layer Microstrip High-Directivity Coupled-Line Coupler With Tight Coupling

A novel symmetrical coupled-line circuit structure without patterned ground plane is proposed to design tight-coupling high-directivity couplers, which would be found in numerous applications in a microstrip RF front end because of its simple structure and inherent excellent compatibility. Based on a traditional even- and odd-mode technique, closed-form mathematical equations for both circuit electrical parameters and scattering parameters are obtained. Due to the use of two coupled-line sections placed in the vertical direction, the directivity of this novel coupler without any other compensation techniques can be enhanced while maintaining tight-coupling performance of almost 3 dB. For demonstrative purposes, three typical full-wave simulation examples with realized physical dimensions in microstrip technology are presented, indicating high directivity and tight coupling coefficient. Finally, a practical microstrip coupled-line coupler is designed and fabricated to operate at approximately 2 GHz. The measured results show good return loss, quadrature phase characteristics, high directivity, and strong coupling performances.

A fuzzy approach to signal integration

A new fuzzy concept for postdetection signal integration is presented. The fuzzy integrator is developed as a simple extension of the classic binary integrator by replacing the crisp binary threshold, which quantizes the observed data, with a fuzzy threshold. The performance of the fuzzy integrator is illustrated for detection of a simple nonfluctuating signal in Gaussian noise and is shown to exceed that of the binary integrator, approaching that of the optimal detector with Neyman-Pearson decision rule. Furthermore, the fuzzy integrator has the characteristic that the false alarm rate can be tuned using a single threshold, more easily than that of the dual-threshold binary integrator.

A SFH spread spectrum synchronization algorithm for data broadcasting

In this paper, a practical slow frequency hopping (SFH) spread spectrum discrete synchronization algorithm suitable for data broadcasting is proposed. This algorithm uses additional sync bits in the binary stream of the slow frequency hopping signals for both initial synchronization and tracking purposes. A complete hop period or a complete time slot in every frame is used to carry these additional sync bits. These sync bits are changed at each frame and are used to control the startup condition of the pseudo-random number (PN) generator. As a result, a robust algorithm with fast synchronization time is obtained. The security measure is enhanced while at the same time using simpler hardware, requiring only one detector. It can also be used in systems with any number of hop channels, whether large or small, and may operate with several broadcasters simultaneously in a cell to improve the spectra usage.

Effect of internal patch antenna ground plane on SAR

This paper investigates the effect of different ground plane configurations of a typical internal planar inverted-F patch antenna (PIFA) on specific absorption rate (SAR). The effect of the size and the addition of vertical sidewall of the ground plane are investigated; it is found that by varying the ground plane locations and configurations, SAR value can be reduced by 15%

SSOR preconditioned CG method for the linear interference cancellation of asynchronous CDMA systems

An ideal computation of the decorrelating or the linear minimum mean-squared-error (LMMSE) detector requires computational complexity of order K 3 when there K is the number of users. To alleviate the computational complexity, iterative decorrelating and LMMSE detectors are proposed for solving a set of linear equations corresponding to linear interference cancellation structures. Iterative conjugate gradient (CG) method has been used for the linear interference cancellation detectors. Its main advantages are to reduce the order of computation complexity and their suitability to highly parallel implementations. In this paper, the symmetric successive overrelaxation (SSOR) preconditioning scheme is applied to the CG method. The performance of the detectors is investigated and it is found that the SSOR preconditioned CG method can provide significantly faster convergence than CG method.

SLM with non-unit magnitude phase factors for PAPR reduction in OFDM

Selected mapping (SLM) scheme with non-unit magnitude phase factor is developed for the peak-to-average power ratio (PAPR) reduction of the orthogonal frequency division multiplexing (OFDM) system. A new low-complexity version of SLM is introduced, which employs the shifting time-domain signal combination technique to generate new candidates. Unlike the conventional SLM scheme, which needs several inverse fast Fourier transform (IFFT) operations for an OFDM signal, the proposed scheme requires to implement one IFFT operation only. Thus, it can significantly decrease the computational complexity. The simulation results show that the proposed scheme can obtain slightly poorer PAPR reduction performance than the conventional SLM scheme with the same number of candidates.