Search

T11e widespread use of personal communication technologies (PCTs) for commercial message dissemination 1 necessitates understanding that PCTs might lead to better commercial performance in different situations. Building primarily on apparatgeist [...]

A high IIP2 direct-conversion receiver for cellular CDMA/PCS/GPS has been developed in a 0.35 [micro]m SiGe BiCMOS process. This receiver consists of a RF front-end chip and a base-band chip. The RF front-end chip includes three LNAs, three mixer cores with a common output stage, and LO distribution blocks. The base-band chip includes a channel selection filter, an output buffer, and a de calibration block. To achieve high IIP2 performance, an even-harmonic reduction technique is proposed based on a simplified analysis of second-order intermodulation. A 40-dB improvement of the IIP2 performance is accomplished by this technique, which reduces sensitivity to operating conditions and to output load mismatches. This receiver also attains high IIP3 and a low-noise figure. Measurement results show 71 dBm IIP2, -1.3 dBm IIP3, and 2.4 dB NF for Cellular CDMA, 68 dBm IIP2, -3.7 dBm IIP3, and 2.9 dB NF for PCS: and 26 dBm IIP2 -30 dBm IIP3, and 2 dB NF for GPS. Index Terms--BiCMOS analog integrated circuits, filter, harmonic analysis, intermodulation distortion, low-noise amplifier, mixers, receivers.

Third-generation mobile systems provide access to a wide range of services and enable mobile users to communicate, regardless of their geographical location and their roaming characteristics. Due to the growing number of mobile users and global connectivity, one of the most critical issues regarding the design of universal mobile telecommunications service (UMTS) networks pertains to the assignment of Node Bs to radio network controllers (RNCs), which is an NP-hard problem. Hence, for real-sized mobile networks, this problem cannot be practically solved by using exact methods. This paper proposes a hybrid genetic algorithm (HA) with migration to solve the problem of assigning Bs to RNCs as a design step of large-scale UMTS mobile networks. Computational results obtained from extensive tests confirm the effectiveness of the HA to provide superior solutions compared to other heuristic methods that are well documented in the literature. Such an algorithm is particularly suitable to design large-scale cellular mobile networks with Node Bs whose quantity varies between 100 and 500 and whose the number of RNCs ranges between five and ten. Index Terms--Cellular networks, genetic algorithms (GAs), migration, multipopulation algorithm, Node Bs' assignment, tabu search, universal mobile telecommunications service (UMTS).

In this paper, we consider the problem of providing highly accurate time-delay or ranging estimates using multiple receptions of ranging signals in multiband communication systems. Specifically, we propose an algorithm to enhance the resolution of range and time-delay estimation in a multiband orthogonal frequency-division multiplexing system that has been proposed for the IEEE 802.15.3a wireless personal area networks. While this paper does not specifically address the problem of accurate localization in multipath nonline-of-sight environments, the proposed approach enhances the resolution and can be combined with any of the known techniques designed for such environments to provide an enhanced localization performance. Prior research has shown that the variance of the time-delay estimation error in white Gaussian noise is inversely proportional to the energy of probe signal and the square of its mean square bandwidth. In a multiband system with M subbands, traditional ranging techniques reduce the variance of the delay estimation from a single subband signal by a factor of M by properly combining M probing signals from all subbands. In contrast, we describe a new approach that synthesizes the return corresponding to a virtual large-bandwidth signal by appropriately merging the returns of M low-bandwidth ranging signals at the receiver. We show that using this technique, the variance of the delay estimation is reduced by a factor of [M.sup.3]. We also show that the proposed scheme achieves the Cramer-Rao lower bound under the high signal-to-noise ratio condition. Index Terms--Cramer-Rao lower bound (CRLB), multiband systems, ranging, ultrawideband (UWB) communications.