 intersite distances are around 400 m, the call's radius can be estimate a to be X 400 ~ 266 m. The number of model sites is K = 7. Then the Radio Network Optimisation Figure 2.50 (a) SFH BCCH clean; (b) SFH BCCH with interference closest re-use distance for a single channel is D = R X 3K 266 X 21 ~ 1219 m. This distance quite comfortable in a dense network. This applies in both urban and rural areas except that in rural areas the regular design is usually not respected. Site design follows revenue constraints for the operator; sites cover villages and roads regardless of any theoretical grid. Therefore, in rural areas the network planner may need to use joker frequencies. The configuration illustrated in Figure 2.50 (b) shows the example of usage of the 1 to 21 band (19 instead of 20, 20 instead of 21 and 21 instead of 22). Unavoidable adjacent interference can be seen to be present between channels 19 and 18. TCH Strategy In the case of usage of SFH, the TCH layer is allocated sets of frequencies called MALists in a 1/1 (the same MAList for all sectors) or a 1/3 (one different MAList for each of the three sectors) configuration. How is MAList length calculated in each case? The frequency load calculation is the answer. Frequency load = fractional load X hardware load where (2.71) Fractional load = number of hopping TRXs/MAList length Hardware load = traffic (Erl) at busy hour/number of TCH timeslots Generally it is recommended not to exceed a 30 % frequency load for the 1/3 model and 8 % for the 1/1 model. Therefore: MAList Length_1/3 > (Traffic_BH X Nbr hopping TRXs)/(Number of TCH Timeslots X 0.3) MAList Length_1/1 > (Traffic_BH X Nbr hopping TRXs)/(Number of TCH Timeslots X 0.08) An example of an MAList organisation can be through interleaving in order to make the best use of the frequency band and maximise space between frequencies used at the same time (see Figure 2.51). Radio Network Planning and Optimisation MAList 1: MAList 2 MAList 3: Figure 2.51 The 1/3 model MAList attribution example HSN Planning Th