Intelligent networks

Intelligent Network techniques (IN), are not, of course unique to cellular systems and have already become well established in fixed networks for the provision of 'free fone' or 'toll-free' type services, for example. However, the ability of an IN architecture to provide customised services is particularly valuable to a mobile user, who can have improved control over the handling of incoming calls. IN techniques also provide the ability to create a wide variety of advanced services.

Second generation cellular systems such as GSM are already designed around an architecture which can support IN type applica­tions. In particular, the HLR function is closely related to the IN service control point. We can expect further developments in the near future which will bring a range of IN features to both the mobile user and the service provider.

Personal communications

The term PCN, Personal Communications Network, is used widely in the UK, whilst PCS, Personal Communications Services is used in the USA. Both aim at the same objective of serving the mass consumer market with mobile communications. The key challenge is to provide a very high capacity network to support a large number of users at low cost. Microcellular techniques will certainly be needed, and in order to keep costs down, the concept of regional service, and local access to the PSTN is being considered. IN techniques may offer personal numbering across a variety of net­works.

PCN is dealt with in detail in Chapter 48. The standard in Europe, known as DCS1800 is based on the GSM standard but operating at 1800MHz. There is therefore unlikely to be a significant technical difference between Cellular GSM and PCN, with microcellular techniques being equally applicable to either system.

In the USA, the use of CDMA, code division multiple access, is being trialled for PCS. CDMA works on the principle of transmit­ting unique (orthogonal) codes to identify different users. Detection of signals is achieved by using correlating receivers such that other users appear as pseudonoise. CDMA thus allows a large number of users to share the same (wideband) radio channel.

There is considerable debate about the advantages and disadvant­ages of CDMA, in particular how to control near/far user inter­ference; the extent to which this can be achieved is crucial to the ultimate capacity of CDMA. One of the key benefits of CDMA is the potential to share spectrum with other users, forexample fixed links, and for this reason it is particularly attractive where additional spectrum for mobile systems cannot be made available.

Conclusion

Cellular radio is a comparatively young technology. Networks em­ploying analogue systems have developed rapidly and now provide high quality service and excellent coverage in many of the de­veloped countries. Technology developments are now increasing the potential network capacity, reducing the size of mobiles, and bringing advanced features and services to the mobile user. The decade ahead with the opportunity to introduce new digital systems and create a world-wide land mobile standard looks particularly exciting.

Date: 2015-12-11; view: 702