Rong-Terng Juang

Mobile location estimation based on differences of signal attenuations for GSM systems

GSM system provides measurements regarding the signal attenuations from serving and neighboring base stations for managing radio resources. This paper proposes a mobile location estimation based on differences of downlink signal attenuations, which yield circles along which the mobile may lie. Then, the curves intersect at the estimated mobile position. The proposed method does not require a known and accurate path loss modeling, reduces the impact of shadowing on location, and is capable of being applied in existing systems without hardware development. Performance simulations include environments involving different standard deviation and cross-correlation of shadowings, and different abilities to detect base stations. Simulations demonstrate encouraging performance with only three base stations being available in severe shadowing environments. Additionally, the results of driving measurement show that the proposed method outperforms the cell-ID method in a real GSM in urban Taipei.

Interference management of femtocell in macro-cellular networks

This paper investigates the impact of femtocell interference on existing macrocells with fractional frequency reuse (FFR). Instead of using complicated transmission techniques by coordinating multiple base stations (BSs), this paper adaptively configures FFR pattern to avoids interference caused by femtocells, depending on density and locations of femtocells. Simulation results show that the proposed femtocell BS deployment can effectively reduce downlink interference to macro-cellular networks.

Hybrid SADOA/TDOA mobile positioning for cellular networks

A signal attenuation difference of arrival (SADOA) scheme is proposed to combine with the time difference of arrival (TDOA) method for mobile location estimation. On the basis of ratio of distances between the mobile and base stations derived from differences of signal attenuations, each SADOA measurement yields a circle on which the mobile may lie. Meanwhile, each TDOA measurement defines a hyperbola on which the mobile may reside. The proposed hybrid SADOA/TDOA scheme uses Taylor-series expansion to linearise the circles and hyperbolas and iteratively computes the mobile position based on least-squares estimation. Without perfect path loss modelling and hardware modification, the proposed scheme reduces location errors compared with either technique separately. Simulations demonstrate encouraging performance with 50% improvement over the conventional TDOA method in shadowing and non-line-of-sight propagation environments.

Mobile location estimation and tracking for GSM systems

This paper proposes a mobile location estimation and tracking technique for wireless communication systems. The location estimation is based on the differences of downlink signal attenuations, which are used to determine circles composed by possible mobile locations. Then the actual location is given by the intersection of the circles. The great advantages of this method are the non-necessity of a known and accurate path loss modelling and the reduction of shadowing effect. Furthermore, a mobile tracking technique via piecewise linear optimization using a simple genetic algorithm is applied to improve the locations estimation. As the results are shown, the estimation errors are much smaller than the errors from cell-ID method in a real GSM system.

Hybrid SADOA/TDOA Location Estimation Scheme for Wireless Communication Systems

This paper proposes SADOA scheme to combine with TDOA method for mobile location estimation. Based on the ratio of distances between the mobile and base stations derived from differences of signal attenuations, each SADOA measurement yields a circle on which the mobile may lie. Meanwhile, each TDOA measurement defines a hyperbola on which the mobile may reside. The proposed hybrid SADOA/TDOA scheme uses Taylor-series expansion to linearize the circles and hyperbolas and iteratively computes the mobile position based on least-squares estimation. Without perfect path loss modeling and hardware modification, the proposed scheme reduces location errors compared with either technique separately. Simulations demonstrate encouraging performance with 50% improvement over the conventional TDOA method in shadowing and non-line-of-sight propagation environments

Performance enhancement for microcell planning using simple genetic algorithm

Microcell planning is quite different from the cell planning used for macrocells. For achieving efficient cell planning, it is necessary to understand the propagation characteristics of microcell systems. In this paper, we present the propagation measurement results at the campus area located at urban Taipei city. We verify that the Walfisch-Ikegami model is an accurate model for predicting path loss in microcell systems. Based on the Walfisch-Ikegami model and digitized building information, cell planning using a simple genetic algorithm is presented. The optimum solution for base station numbers, locations, antenna heights, and transmitting power can be achieved. On other hand, due to capacity demand and coverage requirement, the existing system must be enhanced. We also present the simulation results for system enhancement using the simple genetic algorithm with the help of digitized building information and the Walfisch-Ikegami model.

Robust mobile location estimation based on signal attenuation for cellular communication systems

This paper proposes a mobile location scheme using weighted centroid method based on the ratios of distances between mobile and base stations derived from the differences of signal attenuations. The proposed method does not require perfect path loss and shadowing models, and is capable to be applied in existing systems without hardware modifications. Simulations demonstrate encouraging performance with only two base stations being available in shadowing environments. Additionally, the results of driving measurement show that the proposed method outperforms the cell-ID method in an existing GSM system

Enhanced hierarchical modulation with interference cancellation for OFDM systems

Hierarchical modulation provides layered transmission and is a very promising mechanism to reliably provide basic services to receivers with various reception conditions. Because the high priority layer is allocated with more power, the low priority layer is vulnerable to noise and interference. This paper applies a repetition coding to either of the layers of hierarchical modulation to cancel the inter-carrier-interference, and thus the inter-layer-interference. More importantly, the proposed scheme provides a finer granularity of modulation order, which makes it more flexible to support various radio resource allocation.

Link adaptation based on repetition coding for mobile worldwide interoperability for microwave access systems

Worldwide interoperability for microwave access (WiMAX) suffers from inter-carrier interference (ICI) since it adopts orthogonal frequency division multiplexing in physical layer. This study applies a repetition coding scheme, which encodes the same data on a subcarrier pair, to the hierarchical modulation to suppress the ICI and thus the inter-layer interference. Consequently, the proposed method mitigates the effects of fading and interference and provides a finer granularity of modulation order for link adaptation. Besides, the repetition coding scheme is also applied to a hybrid automatic repeat request (HARQ) protocol to recover error packets because of poor channel conditions. The proposed method incorporates the ICI cancellation into the conventional incremental redundancy HARQ and automatically activates the cancellation of ICI without Doppler shift/mobility estimation. Simulations show that the proposed algorithms outperform the conventional schemes in time-varying Rayleigh fading channels, especially in high-mobility environments.

Link Adaptation of MIMO-OFDM Transmission Exploiting the Rician Channel K-factor

This paper presents a link adaptation scheme for the MIMO-OFDM system to achieve high spectral efficiency in a required BER performance. The modulation order and MIMO transmission mode are selected via a look-up table according to the SNR and Rician channel K-factor instead of the channel relative condition number. The BER and spectral efficiency performance of the MIMO-OFDM system is evaluated by simulation. Result shows that the spectral efficiency can be achieved up to 9bps/Hz under Rician channel K-factor of 3.3dB when SNR is 30dB. The spectral efficiency is higher under low K-factor Rician channel than in high K-factor one. The throughput of the proposed adaptive MIMO-OFDM system considers both K-factor of the Rician channel and SNR can be achieved up to 80Mbps higher than the method without considering the Rician channel K-factor.