Jyh-Horng Wen

A suboptimal PTS algorithm based on particle swarm optimization technique for PAPR reduction in OFDM systems

A suboptimal partial transmit sequence (PTS) based on particle swarm optimization (PSO) algorithm is presented for the low computation complexity and the reduction of the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) system. In general, PTS technique can improve the PAPR statistics of an OFDM system. However, it will come with an exhaustive search over all combinations of allowed phase weighting factors and the search complexity increasing exponentially with the number of subblocks. In this paper, we work around potentially computational intractability; the proposed PSO scheme exploits heuristics to search the optimal combination of phase factors with low complexity. Simulation results show that the new technique can effectively reduce the computation complexity and PAPR reduction.

Performance Analysis of a New ICI-Self-Cancellation-Scheme in OFDM Systems

In orthogonal frequency division multiplexing communication systems, the system performance may be degraded by the effect of inter-carrier interference. In this paper, a new scheme is proposed to cancel the effect of ICI. The system performances are evaluated based on carrier-to-interference ratio and bit error rate. The simulation results show that the effect of phase error with the proposed scheme is lighter than that with Zhaos scheme. Hence, the BER performance of proposed scheme is better than that of Zhaos scheme even in a large frequency offset.

An adaptive robust LMS employing fuzzy step size and partial update

We propose a fuzzy step size least-mean-square (LMS) algorithm, in which an appropriate step size is selected by a fuzzy inference system (FIS) to achieve faster convergence rate and lower steady-state fluctuation. An adaptive fuzzy sequential partial update scheme is developed to reduce system complexity without trading off bit-error rate (BER) and convergence/tracking performance. Simulations of a DS-CDMA interference suppression receiver illustrate the robust convergence and tracking behavior of the proposed LMS-based approaches with various fuzzy input vectors and fuzzy sets. The performance advantages of the proposed algorithms over other LMS algorithms in multipath Rayleigh-fading channels are investigated as well.

Performance evaluation of a joint CDMA/NC-PRMA protocol for wireless multimedia communications

A joint code division multiple access and noncollision packet reservation multiple access (CDMA/NC-PRMA) technique is proposed and investigated as an uplink protocol for the third-generation (3G) mobile systems. Being the underlying time division multiple access (TDMA) architecture of the CDMA transmissions, NC-PRMA enables the base station (BS) to have a centralized control over the slot allocation policy. In order to reduce the multiple access interference (MAI) variation in a CDMA transmission, two different slot assignment schemes, referred to as load-balancing (LB) and power-grouping (PG) schemes, are proposed and evaluated. Simulation results show that considerable improvement can be achieved over the joint CDMA/PRMA scheme, in which the MAI variation is reduced by way of a dynamic permission probability for contending terminals. Especially when an imperfect power control mechanism is considered, the proposed PG assignment scheme achieves significant performance advantages.

OFDM Channel Prediction Using Fuzzy Update LMS Algorithm in Time-Variant Mobile Channel

Channel predictor implemented by discrete Fourier transform (DFT) is considered, which predict the channel gain of each receiving path by adaptive filters. A fuzzy logic controlled step size could overcome the drawback of conventional least-mean-square error (LMS) algorithm. In this paper, LMS algorithm with fuzzy updated step size is proposed to realize the adaptive channel prediction in orthogonal frequency division multiplexing (OFDM) systems. Simulation results show that as compared to conventional LMS algorithm, the proposed algorithm can achieve a faster convergence rate and lower steady-state mean square error. The proposed algorithm can also achieve more robust tracking ability in the various channel environments.

A Generalized Temporal and Spatial Role-Based Access Control Model

Securing access to data, applied to mobile service applications with temporal and spatial controlling, requires constructing innovative definitions with temporal and spatial limitations for an access-control system. To cope with the temporal and spatial requirements, we propose a generalized Temporal and Spatial RBAC (TSRBAC) model. In the TSRBAC model, temporal-period and spatial-location based entities are used to constrain the permissions of objects, user positions, and geographically bounded roles. Furthermore, we also present temporal and spatial relations of Temporal and Spatial Separation of Duties (TSSSD), Temporal and Spatial Dynamic Separation of Duties (TSDSD) constraints in the TSRBAC model.

Performance analysis of PSO-based parallel interference canceller for MC-CDMA communication systems

This work analyses the performance of particle swarm optimisation (PSO) algorithm-based parallel interference cancellation (PIC) multiuser detectors exploited in multicarrier direct-sequence code-division multiple-access (MC-DS-CDMA) communication systems over frequency-selective fading channels. The PSO, which attempts to reduce the complexity in optimal detection caused by the greedy exhausted searching, achieves adequate sub-optimal multiuser detection in CDMA systems. Simulation results reveal that with a lower generation of Gn = 5, 10, the constant weight PIC (CWPIC) scheme outperform the conventional PIC (CPIC) particularly at heavy load. However, with higher generation Gn = 20 in PSO, the CPIC schemes contrarily outperform the CWPIC for all system loads. Copyright

Adaptive fuzzy-based rate management and power control in multimedia CDMA cellular systems

In the literature, a number of fuzzy-based power control schemes have been proposed for systems with a single rate. However, emerging CDMA cellular systems are expected to include multimedia services. In such systems, different services have different quality of service (QoS) requirements, such as minimum transmission rates and tolerable delays. This paper introduces an adaptive fuzzy-based controller to integrate power control and transmission rate management for multimedia services in CDMA cellular systems. Simulation results show that the novel scheme is superior to other fuzzy-based or balanced power control schemes proposed for single rate. We also compare our scheme to a multi-rate scheme called the selective power control (SPC) scheme. Results show that our scheme can achieve better performance in several measurements, such as outage probability, average transmission rates, probability of unsuccessful transmissions, and probability of changes in transmission rates.

The effect of multipath interference on the performance of packet radios

The effect of multipath interference on the performance of packet radios is investigated. The protocols considered include pure ALOHA and slotted ALOHA. Signal reception with and without capture effect is considered in the analysis. Mathematical expressions of system throughput and packet delay have been successfully obtained for each protocol. Numerical calculations are used to demonstrate when the multipath interference can be ignored and when it can be disastrous. >

Timing and delay spread estimation scheme in OFDM systems

In this paper, a scheme for symbol timing estimation and delay spread estimation using subblock correlation is proposed in the OFDM systems. The subblock correlation between the cyclic prefix and data symbol is applied to estimate symbol timing and the length of delay spread. Under a multipath fading channel referred to the OFDM multipath channel model in the standard of IEEE 802.11a/g WLAN, the results show that performance with the proposed scheme is better than that with Beeks scheme. In addition, the length of the delay spread could be estimated in the proposed scheme. Hence, in order to increase the bandwidth efficiency, the length of cyclic prefix could be adaptively assigned in the OFDM system.