Engineering wide area radio systems

Since its general introduction, more than forty years ago, radio communications has had a profound impact on the way that police forces, across the world, have carried out their operations. This experience has been mirrored in many business sectors. For example the advantage that radio initially gave to some taxi operators quickly meant that it was impossible to operate a taxi service competitively without radio communications. The author has chosen to concentrate on the police since their systems are in many cases the most demanding and since they illustrate many of the problems associated with the introduction of speech protection onto current radio schemes. To understand the problems, that are faced when implementing speech security, it is necessary to review the sort of systems that police forces have, why the systems themselves are used the way they are, and why protection is needed in any case