vers, while the sig- nalling channels will have an increment at every alternate TRX addition (which means that a decrease in SCHs in the TRX increases the TCHs in it). Average Antenna Height The concept of the average antenna height is the basis of the frequency re-use pattern determining capacity calculations in a cellular network. The average antenna height is the basis of the cellular environment (i.e. whether it is macro-cellular or micro-cellular). If the average antenna height is low, then the covered area is small in an urban environment. This will lead to the creation of more cells, and hence increase the number of times the same frequency can be re-allocated. Exactly the opposite is the case in a macro-cellular environment. Here the coverage area would be more, SO the same frequency can be re- allocated fewer times. All these calculations are based on the interference analysis of the system as well as the topography and propagation conditions. Frequency Usage and Re-use Frequency usage is an important concept related to both coverage and capacity usage. Frequency re-use basically means how often a frequency can be re-used in the network. If the average number of the transceivers and the total number of frequencies are known, the frequency re-use factor can be calculated. Example 5: Frequency re-use factor If there are 3 TRX that are used per base station and the total number of frequencies available is 27, then the total number of frequencies available for re-use is 27/3 = 9. 2.4.6 Spectrum Efficiency and Frequency Planning Spectrum efficiency is simply the maximum utilisation of the available frequencies in a network. In the radio planning process, this is known as frequency planning. Capacity and frequency planning do of course go hand-in-hand, but the concepts described SO far in this chapter provide the inputs for frequency planning. A good frequency plan ensures that frequency channels are used in such a way that the capacity and coverage criteria are met without any interference. This is because th