In such case Trafic is more as compare normal the operator can use Dualband BTS in one cell having both frequency bands 900&1800 Mhz . The 1800 mhz band
Lobe small as compare 900 Mhz band
the 1800 coverd near by the cell and 900 coverd such distance more than 1800 the both bands are having same BCCH . The BCCH in 900 Band only . yout Block the all trx(900) in one cell you con’t able to make a call in 1800 Band . This methode are adopted in highly populated areas.