Overview of Radiolocation in CDMA Cellular Systems

Applications for the location of subscribers of wireless services continue to expand. Consequently, location techniques for wireless technologies are being investigated. With code-division multiple access (CDMA) being deployed by a variety of cellular and PCS providers, developing an approach for location in CDMA networks is imperative. This article discusses the applications of location technology, the methods available for its implementation in CDMA networks, and the problems that are encountered when using CDMA networks for positioning. ireless location has received considerable attention over the past few years. A recent Report and Order issued by the U.S. Federal Communications Commission (FCC) in July 1996 requires that all wireless service providers, including cellular, broadband PCS, and wide-area SMR licensees, provide location information to Emergency 911 (E-911) public safety services [1]. Thes

Radio Location in Urban CDMA Microcells

: A radio location method for code-division multiple-access (CDMA) microcellular networks is investigated. The method discussed focuses on the use of time difference of arrival (TDOA) estimates for deriving the position of a mobile unit in a CDMA system, where the transmitted signal is received by several base stations (BSs). The TDOA estimates are obtained by using a delay-lock loop. A similar method is used in the global position system (GPS), but its performance in an urban microcellular propagation environment has not been previously studied. Simulation results are given for different radio propagation environments. I. INTRODUCTION Vehicle location systems have become the focus of intense research over the past few years and there seems to be no shortage of applications for automatic vehicle location technology. In Japan, taxi and delivery drivers use vehicle location technology to navigate through the streets of Tokyo. In the United States, fleet truck operators are using locatio..

Vehicle Location and Tracking for IVHS in CDMA Microcells

: This paper discusses the use of mobile cellular radio networks for providing vehicle location information to intelligent vehicle/highway system (IVHS) services. We review various automatic vehicle location (AVL) techniques in context to their application in a direct-sequence code-division multiple-access (DS/CDMA) system, in particular, the EIA/TIA/IS-95 standard proposed by Qualcomm, Inc. A new matched filter location technique which is suited to the CDMA environment is discussed along with simulated error statistics and recommendations for improvement. We also consider network loading effects in terms of Signaling System 7 (SS7). I. INTRODUCTION IVHS is the application of an electronically controlled system designed to facilitate the flow and enhance interactions between roads, vehicles, and their drivers so as to improve either highway safety, system operating efficiency, environmental quality, or energy utilization in transportation. In IVHS, traffic surveillance and control sys..

Parameter Estimation in DS-CDMA Systems

this report, however, we will only consider those estimators which include time delay. Iltis, et. al. have developed joint estimators for channel coefficients, delays, and Doppler for frequency-selective multipath fading channels based on Kalman filtering [18, 19, 20]. These methods, however, are only applicable to single-user systems. In the area of multiuser detectors, Radovic and Aazhang [21] have extended the original work of Verd'u [22] to maximum likelihood joint estimation of delays and amplitudes using the Expectation-Maximization (EM) algorithm. These methods are developed for non-fading channels only. Since there are several methods for suboptimally estimating other parameters given a reliable estimate of the time delay [17, 23], Strom, et. al. have developed estimators for multiuser environments using an approximate maximum likelihood method and a signal subspace approach [24, 25]. They later extended their work to time delay estimation in a combined multipath fading, multiuser environment in [26]. In this report, we will study the problem of estimating parameters such as channel coefficients (amplitudes), Doppler, phase, and delay in DS-CDMA communication systems, with the primary focus on time delay estimation. In Section 2, a general channel model for a multipath fading, multiuser communication system is presented. Parameter estimation methods for single users only is developed in Section 3, while Section 4 investigates estimation techniques for multiuser environments. The performance and usefulness of these methods is briefly discussed in Section 5. Conclusions are drawn in Section 6, followed by plans for future work in Section 7. 2 Channel Mode

Cytosolic Multiple Inositol Polyphosphate Phosphatase in the Regulation of Cytoplasmic Free Ca2+ Concentration

Multiple inositol polyphosphate phosphatase (MIPP) is an enzyme that, in vitro, has the interesting property of degrading higher inositol polyphosphates to the Ca2+ second messenger, inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), independently of inositol lipid breakdown. We hypothesized that a truncated cytosolic form of the largely endoplasmic reticulum-confined MIPP (cyt-MIPP) could representanimportantnewtoolintheinvestigationofIns(1,4,5)P3-dependent intracellular Ca2+ homeostasis. To optimize our ability to judge the impact of cyt-MIPP on intracellular Ca2+ concentration ([Ca2+]i) we chose a poorly responsive β-cell line (HIT M2.2.2) with an abnormally low [Ca2+]i. Our results show for the first time in an intact mammalian cell that cyt-MIPP expression leads to a significant enhancement of Ins(1,4,5)P3 concentration. This is achieved without a significant interference from other cyt-MIPP-derived inositol phosphates. Furthermore, the low basal [Ca2+]i of these cells was raised to normal levels (35 to 115 nm) when they expressed cyt-MIPP. Noteworthy is that the normal feeble glucose-induced Ca2+ response of HIT M2.2.2 cells was enhanced dramatically by mechanisms related to this increase in basal [Ca2+]i. These data support the use of cyt-MIPP as an important tool in investigating Ins(1,4,5)P3-dependent Ca2+ homeostasis and suggest a close link between Ins(1,4,5)P3 concentration and basal [Ca2+]i, the latter being an important modulator of Ca2+ signaling in the pancreatic β-cell