Why should we test an item "Tx noise at Rx band" (ORFS in Rx band) ?

In GSM system, Tx time-slot & Rx time-slot has separated by time.
It means Tx turned off while Rx turned on and vice verse.
Why should we test an item "Tx noise at Rx band" (ORFS in Rx band) ?
Thanks.

Because when your mobile is talking to the Base Station, is producing interferers to a near by mobile that is in RX mode.
So, ETSI took the decision to specify the limit for TX noise power in RX band.

Tx noise in RX band can be a hard stuff in circuit view of point.
By different TX loop design, many noise source may some into
spurs. Possible sources are,
1. 13MHz harmonics ride on TX RF carrier
2. TX IF frequency and harmonic ride on TX RF carrier
3. Mixing of LO,IF,and RF frequency in TX loop.

And the cause of those above may be substrate coupling, TX frequency plan
design with unsuitable dividers, and some isolation problem stuff.

With regards,