Performance of optimum and suboptimum combining at the antennaarray of a W-CDMA system

The performance of an array of antennas combined with a RAKE receiver at the base station of a wideband code division multiple access system with quaternary phase shift keying modulation is investigated for single-user reception. This receiver structure is also known as a multidimensional RAKE receiver. Expressions for the interference correlation matrix are derived, and subsequently, an analysis of the error probability is provided. With regard to antenna weights, the optimum combining linear receiver, which takes into account the spatial distribution of all the users in the system, is compared with the suboptimum combining receiver (SOC), which exploits knowledge of the desired user array vector only. It is shown how the two receivers, ideal in the sense that perfect channel estimation is assumed, achieve very similar performances under realistic conditions. Consequently, the investigated pilot assisted combining receiver, which estimates the channel based on limited overhead, calculates weights according to the SOC strategy by a very simple algorithm     

Retracted and replaced: Enabling technologies for the ‘always best connected’ concept

This article has been retracted and replaced. Retraction notice DOI: 10.1002/wcm.426 ‘Always Best Connected’ (ABC) is considered one of the main requirements for next generation networks. The ABC concept allows a person to have access to applications using the devices and network technologies that best suits his or her needs or profile at any time. Clearly, this requires the combination of a set of existing and new technologies, at all levels of the protocol stack, into one integrated system. In this paper, a considerable set of the technologies, that are expected to play a key role towards the ABC vision, are presented. Starting from a reference architecture, the paper describes the required enhancements at certain levels of a traditional protocol stack, as well as technologies for mobility and end‐to‐end Quality of Service (QoS) support. The paper concludes with a case study that reveals the advantages of the ABC concept. Copyright © 2004 John Wiley & Sons, Ltd.     

Resource information acquisition for QoS provision in mobile ad hoc networks

Quantifying available resources is the main concern for the design of an efficient admission control protocol in mobile ad hoc networks. Proposed is a novel signalling strategy for efficient acquisition of bandwidth information and this is evaluated through accuracy and overhead analysis.     

Cross-layer cooperation for accurate admission control decisions in mobile ad hoc networks

Mobile ad hoc networks (MANETs) are unpredictable by nature. Providing any kind of reliability for quality of service (QoS) in such networks is challenging. Quantifying available resources accurately, avoiding interference with ongoing QoS traffic and adapting to QoS violations caused by nodes' mobility are the main concerns for the design of an efficient admission control protocol in MANETs. Adaptive admission control (AAC), a novel admission control protocol which uses robust and accurate resource estimation and prediction techniques for relevant admission decisions has been proposed. Furthermore, AAC uses statistical QoS provision to counteract the QoS threatening mobility. Through simulations, we show that our proposed scheme outperforms existing approaches in terms of correctness and overall performance.     

A distributed dynamic resource allocation for a hybrid TDMA/CDMAsystem

A distributed dynamic resource allocation (DDRA) strategy for a hierarchical cellular structure (HCS) is proposed. In the DDRA, resources are shared not only between cells of the same hierarchy, but between layers. The proposed DDRA strategy is evaluated using the hybrid time-division multiple-access/code-division multiple-access (TDMA/CDMA) proposal made in the future radio wide-band multiple-access system (FRAMES) Project Mode I (FMI) as a case study. A mixed environment is suggested for the evaluation of the DDRA, which consists of Manhattan-like microcells covered by hexagonal-shaped umbrella cells (macrocells). Users are classified according to their speed as slow- and fast-moving users and are attended to by the most suitable layer of the hierarchy according to their speeds. Two types of real-time circuit-switched services are considered in the evaluation: speech and data at different rates. The DDRA is compared with the fixed resource allocation (FRA) strategy with overflow and with FRA with overflow, handdown, and channel reallocations (FRANR)     

Fully digital M-ary PSK and M-ary QAMdemodulators for land mobile satellite communications

A fully digital implementation of digital modems is the preferred option of system designers because high performance can be achieved at reasonable cost. The author explains the beneficial features inherent in fully digital demodulator implementations. Other features which are required for land mobile satellite communication systems are also discussed. Recently reported techniques for the synchronisation and detection of M-ary PSK and M-ary QAM modulation schemes are reviewed with emphasis placed on those which are well suited to digital implementation     

High level trellis-coded modulation with slow frequency hopping forland mobile communications

The use of high level modulation systems such as trellis-coded 8-PSK and trellis-coded 16-QAM, with slow frequency hopping, pilot symbol aided and small-sized interleaving techniques is proposed for land mobile communications. The bit error rate (BER) performance of those systems in the presence of additive white Gaussian noise (AWGN), cochannel interference (CCI), and slow Rayleigh fading are evaluated by computer simulation. Space diversity is applied to enhance the system performance. The authors show that by choosing optimum interleaving size and number of frequency hopped (FH) channels, the proposed systems give considerable performance improvement and much less delay, especially in a slow fading environment