Work of MA, HSN and MAIO in GSM
The MA is a list of hopping frequencies transmitted to a mobile every time it is assigned to a hopping physical channel. The MA-list is a subset of the CA list. The MA-list is automatically generated if the baseband hopping is used. If the network utilizes the RF hopping, the MA-lists have to be generated for each cell by the network planner.
The MA-list is able to point to 64 of the frequencies defined in the CA list. However, the BCCH frequency is also included in the CA list, so the practical maximum number of frequencies in the MA-list is 63. The frequencies in the MA-list are required to be in increasing order because of the type of signaling used to transfer the MA-list.
Hopping Sequence Number
The Hopping Sequence Number (HSN) indicates which hopping sequence of the 64 available is selected. The hopping sequence determines the order in which the frequencies in the MA-list are to be used. The HSNs 1 – 63 are pseudo random sequences used in the random hopping while the HSN 0 is reserved for a sequential sequence used in the cyclic hopping.
The hopping sequence algorithm takes HSN and FN as an input and the output of the hopping sequence generation is a Mobile Allocation Index (MAI) which is a number ranging from 0 to the number of frequencies in the MA-list subtracted by one. The HSN is a cell specific parameter. For the baseband hopping two HSNs exists. The zero time slots in a BB hopping cell use the HSN1 and the rest of the time slots follow the HSN2.
Mobile Allocation Index Offset
When there is more than one TRX in the BTS using the same MA-list the Mobile Allocation Index Offset (MAIO) is used to ensure that each TRX uses always a unique frequency. Each hopping TRX is allocated a different MAIO. MAIO is added to MAI when the frequency to be used is determined from the MA-list. MAIO and HSN are transmitted to a mobile together with the MA-list.
The MAIOoffset is a cell specific parameter defining the MAIOTRX for the first hopping TRX in a cell. The MAIOs for the other hopping TRXs are automatically allocated according to the MAIOstep.