with your sfh 1×3, you were using 21 freq. I guess your cells are using 4 TRX ?
1 trx bcch + 3 trx “tch”
that was a little too much, in terms of radio load.
41 to 80 = 40 channels
depending on your urban topology, you could achieve a reuse cluster size of 10 to 13.
RCS 10 = create 10 groups of 4 frequencies
to be used in case of good downtilt planning, little overlap between neighbours and basically a “flat” topology (all cells have same antenna height, about same coverage)
group A = 41, 51, 61, 71
group B = 42, 52, 62, 72
group C = 43, …
group J = 50, 60, 70, 80
RCS 13 = create 13 groups. In that case, you cannot use 4 trx/cell. You are limited to 3 trx/cell.
Use this in case of more difficult areas (hills, lakes, lots of overlap between cells)
group A = 41, 54, 67
group B = 42, 55, 68
group M = 53, 66, 79
(freq 80 is not used)
This is a simple example, but you can decide to create 2 fixed freq plan = 1 for BCCH and 1 for TCH. But that’s difficult to do manually. However, I don’t recommend this : when you will activate BBH, the benefit of having this split is useless.
For automatic freq plan, you can use your vendor’s own planning tool. It probably does automatic frequency planning based on radio counters or drive tests, and consequently it will probably generate valid plans. I know the ALU tool is quite good in this regard.