Base Band Hopping (BBH)
Radio Frequency Hopping (RFH)Using hopping channels, we can obtain sixty three pseudo random sequences. Those sequences are numbered and they are called as Hopping Sequence Number (HSN). Now these Sequences are used instead of direct single frequencies. RFH causes quality degrades of voice calls. More hopping channels used, higher will be the quality. Hopping channels used in RFH are given a number called Mobile Allocation Index (MAI). Following Table shows an example of allocating MAI. Hopping sequences are formed using MAIs. Consider a situation where there are four sectors in sector and we need to allocate frequencies for that. First we may assign BCCH frequency for TRE1. Other TREs are assigned the chosen HSN with an offset in MAI. This offset is called as Mobile Allocation Index Offset (MAIO). Two TREs at same site should have at least offset difference of two. See Figure: RFH Example for more details.
Further explanation into MAIOConsider there are four frequencies F1, F2, F3 and F4. See table 2.3.
Now let’s see how MAIO sequences are defined.
MAIO = 0 >> F1 F2 F3 F4
MAIO = 1 >> F2 F3 F4 F1
MAIO = 2 >> F3 F4 F1 F2
MAIO = 3 >> F4 F1 F2 F3
Also it is evident that why I say that two TREs of the same site should have at least an offset of two. That means we can use MAIO 0 and 4 in the same site. Because they don’t interfere each other. When MAIO 0 transmits F1 MAIO 2 transmits F3. They apart by one channel. If we uses MAIO 0 and 1, during the first time interval F1 and F2 will interfere.
HSN and MAIO allocation of three nearby site
Site1 – 2, 3, 3
Site2 – 4, 4, 4
Site3 – 4, 4, 4
|Sites with number of TREs included in them|
HSN and MAIO allocation is given in the following table.