Wideband Code Division Multiple Access Cellular Systems Research Articles

Optimisation of soft handoff margin in WCDMA cellular system

The focus of the paper is to analyse the downlink performance of a wideband code division multiple access (WCDMA) system with site selection diversity transmission (SSDT) power control during soft handoff (SHO) mode and to find the optimum SHO margin (MSH) in terms of maximum system capacity under energy-per-bit to noise spectral density ratio (Eb/N0) quality requirements. Analysing the dependency of the connection probabilities, percentage of users connected to one, two, or three base stations (BSs) simultaneously as a function of the MSH. We analysed the system capacity and required resources dependency on MSH for voice service and combined multimedia mobile services. System capacity dependency on MSH is analysed, by considering two types of user distributions, namely: 1) uniform user distribution; 2) a concentration of all the users in the location that requires maximum transmitted power (the worst case). The result of this analysis shows an increase in user capacity of about 16%-20% for the optimum MSH of 5-5.5 dB. Nevertheless, the resources required (number of scrambling codes) by the base station increases faster than the number of active users in terms of MSH.

Call admission control in multiservice high altitude platform (HAP) W-CDMA cellular systems

Of the various radio resource management functions, in this paper we focus on call admission control (CAC). We propose a CAC scheme for multiservice High Altitude Platform (HAP) wideband code division multiple access (W-CDMA) cellular systems that caters for multimedia services . HAPs have known increasing popularity during the past few years and are expected to play a pivotal role in the telecommunications arena by virtue of their appealing features. We first study the uplink capacity of a multiservice HAP W-CDMA cellular system taking into consideration power control imperfections and evaluate the degradation that a new call induces in the quality of service of ongoing calls. Based on the obtained statistics, we then develop a CAC scheme that takes account of power control imperfections and user mobility and compare it to a CAC scheme that is based on instantaneous energy per bit to noise power spectral density ratio ( E b / N 0 ) measurements. Additionally, we examine these algorithms for two different criteria that apply to both new and handoff call requests. The first criterion is based on the minimum E b / N 0 of the first tier cells, while the second bases its decision upon the mean E b / N 0 of the cells of the first tier. Simulation studies further document and confirm the positive characteristics of the proposed CAC scheme.

Reduction of cochannel interference in WCDMA cellular systems

In this paper, a novel cochannel interference reduction technique is proposed for wideband code division multiple access (WCDMA) cellular systems. Cochannel interference for the proposed cellular architecture is considered and analyzed. An analytic expression for the proposed method is derived. Simulation results demonstrate that the proposed method provides better signal-to-noise (S/N) ratio than the existing cochannel interference reduction methods. A significant reduction of cochannel interference is achieved compared to sectoring and omnidirectional architectures in the proposed microzoning architecture. In particular, it is shown here that the proposed architecture exhibits a larger number of users per cell while maintaining an adequate S/N ratio in comparison with other architectures.

Effects of Discontinuous Transmission on the Performance of a WCDMA Cellular System

In this paper, we investigate some side effects of discontinuous transmission (DTX) on the performance of a wide-band code-division multiple-access (WCDMA) radio interface with signal-to-interference-ratio-based closed-loop power control. More precisely, we study how the DTX mechanism affects the transmission of some user signals. It is shown that the mobile terminals, when they turn on their data channels after some frames without any data to transmit, can cause a sudden increase of the interference level, leading, for some neighboring users, to a temporary performance degradation that lasts until the power control has completely reacted to this event. The main parameters that characterize the dynamics of the DTX mechanism are described and the tradeoffs in the choice of their values are evaluated; we also propose a suitable variation to the DTX mechanism that reduces the unwanted effects. For our investigation, a suitable simulation tool, which integrates the system-level and link-level analysis, has been developed, including most of the actual details and features of the WCDMA physical layer.

Analysis and results for the orthogonality factor in wcdma downlinks

The presence of multipaths leads to a loss of orthogonality between signals transmitted simultaneously on a wideband code-division multiple access (WCDMA) downlink. We derive general analytical expressions for the orthogonality factor (OF), which quantifies this loss of orthogonality, as a function of the instantaneous multipath fade realization of the channel. We show that the OF exhibits a significant temporal variation for the three channel profiles suggested in the WCDMA standard, namely, typical urban and rural areas and hilly terrain, which span a wide range of realistic cases. Moreover, its temporal variations and statistics vary significantly from one channel profile to another. Also, while the pulse shape and the number of RAKE fingers has only a marginal impact on the OF's statistics, the granularity in setting the finger positions has a considerable impact. The results of the work can be directly used for evaluation of the system performance of WCDMA cellular systems.

Delay profile measurement system using common pilot channel for W‐CDMA cellular system

AbstractThe communication quality in Wideband Code Division Multiple Access (W‐CDMA) is improved by temporally separating the arriving multipaths and combining them by RAKE combining. Thus, the delay profile measurement is essential in understanding the number of arriving paths and the received power in each path in the actual propagation paths. In this paper, we propose a system using the Common Pilot Channel (CPICH) to measure the delay profile from the base station that has already started a service. This system's features are (1) synchronous detection using only CPICH and (2) power delay profile and SIR delay profile measurements and their properties are clearly illustrated. We also present the experimental results of a prototype developed based on the proposed method. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(6): 33–45, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10030

Hybrid TDOA/AOA mobile user location for wideband CDMA cellular systems

This paper proposes a mobile user location scheme for wideband code-division multiple-access (CDMA) wireless communication systems. To achieve high location accuracy and low cost of the mobile receiver, the location scheme combines the time difference of arrival (TDOA) measurements from the forward link pilot signals with the angle of arrival (AOA) measurement from the reverse link pilot signal. High chip rates in wideband CDMA systems facilitate accurate TDOA measurements, and a smart antenna used at the home base station (BS) can provide accurate AOA measurement in a macrocell environment. A two-step least square location estimator is developed based on a linear form of the AOA equation in the small error region. Numerical results demonstrate that the proposed hybrid TDOA/AOA location scheme gives a much higher location accuracy than TDOA only location, when the number of base stations is small and/or when the TDOA measurements have a relatively poor accuracy.

42% high-efficiency two-stage HBT power-amplifier MMIC for W-CDMA cellular phone systems

This is the first paper to report on a high-efficiency two-stage heterojunction-bipolar-transistor power-amplifier monolithic microwave integrated circuit (MMIC) for 1.95-GHz wide-band code-division multiple-access (W-CDMA) cellular phone systems. Power amplifiers for W-CDMA systems are required to operate at high efficiency and high linearity over a wide range of output power levels. To obtain high efficiency at low output power (P/sub out/) as well as at the required maximum P/sub out/ and obtain a high linearity at the maximum P/sub out/, we chose near-class-B operation. To improve linearity at a medium P/sub out/ range, we suppressed the gain distortion resulting from near-class-B operation by using an adaptive biasing technique. The MMIC exhibited a power-added efficiency of 42%, the highest ever reported, a gain of 30.5 dB, and an adjacent channel leakage power ratio at a 5-MHz offset frequency of -38 dBc at a P/sub out/ of 27 dBm under a supply voltage of 3.5 V with 3.84-Mcps hybrid phase-shift keying modulation.