Multiservice/multirate pure CDMA for mobile communications

Future mobile communication systems should be able to support a wide range of services with different bit rates. Spread-spectrum code-division multiple-access (CDMA) techniques have attracted much attention to be employed in such a system. Different techniques of CDMA could be used to map low-, medium-, and high-bit rates data into the same allocated bandwidth, including pure or wide-band CDMA, FDM/FH/CDMA, TDM/TH/CDMA, or a hybrid of these techniques. This paper investigates multirate pure CDMA using multiuser interference statistics derived for both Gaussian and Rayleigh fading channels. Approximation of multiuser/multipath interference, in general, helps in the theoretical approach to error performance evaluation and, in particular, is quite useful for simulation approach in a fading channel. Some results of a multirate pure CDMA system with two services (low- and high-bit rates), for both BPSK and DPSK modulation schemes, are presented and compared     

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     

Dynamic green self-configuration of 3G base stations using fuzzy cognitive maps

Cellular networks are rapidly evolving towards the fourth generation, thus providing a global infrastructure for wideband mobile network access. Currently, most of the energy consumption of such technology is by cellular base stations, which are not energy efficient—at least in terms of the transmission energy to “from-the-socket” energy consumption ratio. This paper addresses the problem of energy efficiency in cellular networks by taking advantage of the principles of cognitive networking, which promotes the creation of intelligent networks capable of self-configuration with minimal human intervention. In particular, this paper uses the concept of fuzzy cognitive maps to decide upon opportunistic traffic and user reallocations between radio network equipment operating in different spectrum bands to enable power saving modes by some subsets of the radio network equipment, and to utilize spectrum of more appropriate propagation characteristics to save transmission energy. The feasibility and performance of the proposed approach is investigated through simulations. Significant energy savings of some 25–30% are shown over a 72-h period, and blocking rate under the concept is shown to remain reasonable albeit exhibiting a high variance.     

A vision of UMTS/IMT-2000 evolution

A vision is presented for a fully IP-based mobile network which goes beyond UMTS/IMT-2000. A top-to-bottom design approach is introduced that is capable of offering new and innovative services and applications to both fixed and mobile users efficiently, cost effectively and in a user-friendly manner. Some issues and examples in the design steps following this new approach are discussed. It is clearly shown that the convergence of mobile and fixed networks will be achieved naturally through the use of an `all IP' based solution for both access and core networks     

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)     

Miniaturised L-band MIC LNA design

A design technique for LNA size miniaturisation is described which does not compromise electrical performance. The method has been applied to the design of a L-band LNA and results in a measured noise figure of 0.25 dB and 15 dB associated gain. The circuit is realised in MIC technology with a total surface area of less than 4.8*8.8 mm/sup 2/. The reduced size allows the LNA to be cascaded with MMIC gain blocks with little or no volume impact and considerably improved electrical performance compared with a complex MMIC solution.<>     

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     

Location Management Strategies for Cellular Overlay Networks—A Signaling Cost Analysis

In a world driven by the accessibility of data for business, for communication and entertainment, but one populated by an increasingly nomadic society, it is no surprise that the appetite for wireless services continues to grow. The limitations of existing technologies however, particularly for wireless multi-casting and broadcasting, suggest that new approaches are needed to allow users to access services in the all wireless world. A popular approach for improving wireless services proposes to equip mobile terminals (MTs) with more than one radio interface to enable access to services in an always best connected paradigm. One such architecture envisages a co-operating overlay network, or inter-network, that comprises of a cellular telephony network and a digital broadcasting network. MTs in the inter-network have two corresponding radio interfaces and co-operation between the networks provide the user with seamless access to diverse services across the inter-worked platform. In this paper, we introduce novel location management proposals for co-operating overlay networks that incorporate a uni-directional broadcast overlay and provide a cost and latency analysis of the schemes. Our cost analysis demonstrates the soundness of the techniques and the value of the analyses as comparative evaluation tools. In particular, it is shown that there are a wide range of realistic operating conditions where the novel proposals presented here provide an optimum performance in cost terms.     

Enabling technologies for the ‘always best connected’ concept

‘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. This article replaces a previously published version (Wireless Communications and Mobile Computing; 5 (2): 175‐191. [DOI: 10.1002/wcm.207]). Retraction notice DOI: 10.1002/wcm.426 . Copyright © 2006 John Wiley & Sons, Ltd.