The objective of wireless location is to determine the mobile station (MS) location in a wireless cellular communications system. Due to the measurement with large errors, location schemes give poorer performance in non-line-of-sight (NLOS) environments. To determine MS location, Taylor-series algorithm (TSA) is commonly used scheme. TSA can give a least-square (LS) solution to a set of simultaneous linearized equations. The disadvantage of TSA is the need for an initial position guess to start the solution process. The iteration process may not converge due to a poor initial estimate of the MS location. To improve the location accuracy with less complexity, the initial MS location selection criterion is proposed. Numerical results demonstrate that the proposed criterion always provides more accurate positioning.
Orthogonal frequency division multiplexing (OFDM) system which provides high spectral efficiency has obvious advantages in robustness against the multipath delay spread and the fading channel. One of the major disadvantages of such a multi-carrier modulated system is the sensitivity of its performance to synchronization error, such as phase noise and frequency offset. Phase noise is caused by the mismatch between the transmitter and the receiver oscillators. Phase noise in an OFDM system can destroy the orthogonality of the subcarriers and cause inter-carrier interference (ICI). Phase noise resulting in common phase error (CPE) and Inter-Carrier Interference is a critical challenge to the implementation of OFDM systems. In this paper, the phase noise effects of the IEEE 802.16e OFDMA systems are compensated. The practical cluster-based method which is used to estimate either the CPE or the ICI coefficients in the fading channel and compensate the effects of phase error is also proposed. Numerical results demonstrate that the proposed algorithm can effectively improve the performance caused by phase noise.
Geometric dilution of precision (GDOP) represents the geometric effect on the relationship between measurement error and positioning determination error. In the calculation of GDOP value, the maximum volume method does not guarantee the optimal selection of the four measurement units. The conventional method for calculating GDOP is to use matrix inversion to all subsets. In this paper, we employ GDOP using the matrix inversion method to select appropriate base stations (BSs) in cellular communication systems. The proposed BS selection criterion performs better than the random subsets of four or five BSs chosen from all seven BSs. The performances of MS location strongly depend on the relative position of the MS and BSs. Therefore, it is very important to select a subset with the most appropriate BSs rapidly and reasonably before positioning.
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