annel being termed the Forward Control Channel (FOCC) A regular polygon shape for a given cell coverage is convenient for and the corresponding mobile transmit channel being termed the use when planning u.h.f. trunked systems, with clusters of adjacent Reverse Control Channel (RECC). cells thus easily modelled for frequency re-use strategies. It must be borne in mind that local geography may radically alter this coverage 46.3.7 Control channel recognition shape in practical cases, however the commonly used hexagon will be used for the purposes of demonstration. Once a signalling channel has been identified, the signalling infor- This hexagon will allow a wide degree of cluster sizes which fit mation is examined by the mobile and a check performed to ensure together in a repeating pattern. The integer number of cells in each the correct system, control category, and area or zone information cluster may be given by Equation 46.2, where a and b are any is present, dependent upon the mobile unit's individual network positive integers and a N b (Parsons, 1989). personalisation. If the received data is valid, the mobile locks on to this channel (46.2) and, dependent upon the system being used, sends a registration identification to the relevant base station. This updates the system This yields typically used cell clusters of 3, 7, and 12 cells as records on the presence and area of operation of the mobile unit. If shown. Where a given number of channels are available for use in the unit is not registered onto the system being received, the mobile a dedicated trunked system, these may be divided for use in repeat- relinquishes that channel and commences a further control signall- ing numbers of cell clusters, the number of cells within each cluster ing channel search. depending upon the number of channels available together with acceptable degradation requirements between each cluster. This 46.3.8 Handoff usage strategy is also dependent upon signal propagation, communication bandwidth, and signalling methods used. Diff