The current limitation on the range of a GSM cell site to 35km is mandated by the duration of the standard timeslots defined in the GSM specification. The maximum distance is given by the maximum time that the signal from the mobile/BTS needs to reach the receiver of the mobile/BTS on time to be successfully heard. At the air INTERFACE the delay between the transmission of the downlink (BTS) and the uplink (mobile) has an offset of 3 timeslots. Until now the mobile station has used timing advance to compensate for the propagation delay as the distance to the BTS changes.

This timing advance is defined in the GSM specification as 64 bits, which gives the theoretical maximum BTS/mobile separation as 35km.

With Extended Range Cell Feature, the BTS is able to receive the uplink signal in two ADJACENT timeslots instead of one. When the mobile station reaches its maximum timing advance, i.e. maximum range, the BTS expands its HEARING window with an internal timing advance that gives the necessary time for the mobile to be heard by the BTS even from the extended distance. This EXTRA advance is the duration of a single timeslot, a 156 bit period.

The current limitation on the range of a GSM cell site to 35km is mandated by the duration of the standard timeslots defined in the GSM specification. The maximum distance is given by the maximum time that the signal from the mobile/BTS needs to reach the receiver of the mobile/BTS on time to be successfully heard. At the air interface the delay between the transmission of the downlink (BTS) and the uplink (mobile) has an offset of 3 timeslots. Until now the mobile station has used timing advance to compensate for the propagation delay as the distance to the BTS changes.

This timing advance is defined in the GSM specification as 64 bits, which gives the theoretical maximum BTS/mobile separation as 35km.

With Extended Range Cell Feature, the BTS is able to receive the uplink signal in two adjacent timeslots instead of one. When the mobile station reaches its maximum timing advance, i.e. maximum range, the BTS expands its hearing window with an internal timing advance that gives the necessary time for the mobile to be heard by the BTS even from the extended distance. This extra advance is the duration of a single timeslot, a 156 bit period.