Packet Data System Design Issues
- System synchronization is achieved by closed loop operation between SAS and UT.
- Unlike circuit switched voice system, uplink is dynamically allocated by SAS (using USF in the downlink burst). Hence there may be long time period between the two consecutive transmissions from a UT. In such a case, uplink may get out of sync.
- Solution: PTCCH (packet timing control channel). When in packet transfer mode, a UT has to transit a burst on PTCCH periodically. Feedback signal is transmitted to the UTs through downlink PTCCH.
Random access channel capacity
- Packet switch system generates more random accesses for resource requests
- Solution: PRACH (works with proper synchronization mentioned above). PRACH is dynamically allocated as needed.