Gprs slot or gprs burst
Some upgrades to the GPRS radio interface to GPRS radio interface are carried in order to increase the data rates. GPRS slot or GPRS burst have been upgraded to provide new scheme.
Modulation scheme for GPRS:
- GPRS uses the same signal format of 200 kHz channel bandwidths as in GSM.
- It uses GMSK modulation as it offers advantages good spectral efficiency, resilience to interference, low levels of interference outside the wanted bandwidth, and the ability to use a non-linear RF power amplifier.
- GPRS slot structure:
- The figure8.15 shows the GPRS slot structure.
- The overall slot structure for GPRS is the same as that used within GSM .
- It has the same power profile, and timing advance attributes to overcome the different signal travel times to the base station dependent upon the distance the mobile is from the base station.
- Thus GPRS burst easily fit into GSM structure.
- GPRS burst structure
Figure 8.15 GPRS slot Structure
As shown in figure 8.15 Each GPRS burst of information is 0.577 mS in length.
- GPRS burst carries two blocks of 57 bits of information in line with a GSM burst, giving a total of 114 bits per burst.
- Four GPRS burst are required to carry each 20 mS block of data i.e. 456 bits of encoded data.
- Assigning the slots
- Slots can be assigned dynamically by the BSC to GPRS dependent upon the demand, the remaining ones being used for GSM traffic.
- The BSC assigns PDCHs to particular time slots.
Figure 8.16 GPRS frame structure
The GPRS slot may also be used by the base station to judge the time delay using a logical channel known as the Packet Timing Advance Control Channel (PTCCT).