iple In the following section the parameters controlling frequency hopping in the GSM are introduced. The Hopping Sequence Number (HSN) can be selected from 64 options and defines the sequence showing how the frequencies change. In case the HSN is set to 0 cyclic hopping is selected. The HSN values from to 63 are used to select different random sequences. In RF hopping all the timeslots have the same HSN number. With BB hopping the story is different, as the first timeslot (timeslot 0) uses one HSN and the other timeslots another HSN. To avoid different TRXs using the same HSN to transmit simultaneously at the same frequencies a parameter called the Mobile Allocation Index Offset (MAIO) is developed. Setting the MAIO differently to the TRXs in the same cell ensures that those TRXs start to transmit at different frequencies; i.e. they start the sequence from different locations. The maximum length of the MA list is 64 frequencies, which also includes the BCCH frequency, and therefore the maximum number of hopping frequencies on the list is 63. The key advantages of the frequency hopping feature are that it does not require changes in the network configuration and it is automatically applicable to all MS types. 2.7.4 Interference Analysis The target of frequency planning is to allocate the frequencies SO that the network is operational and the quality of service requirements are fulfilled. Co-channel and adjacent channel interference is analysed at the network level and also on a cell-by-cell basis. Frequency planning is often iterative and some allocated frequencies need to be changed in order to decrease the interference level. Naturally later Radio Network Planning and Optimisation during the network live time the frequency plan is renewed either partly or fully when adding more TRXs or new base stations. The GSM specifications define values for co-channel and adjacent channel interference. In addition, the customer may give extra recommendations for the interference analysis. In the case of an option between th