Problem in the Existing QFR Technique
In today’s world, users and industries require:
- High speed data service (data streaming, video call, video on demand, multimedia services, webcast, real time video, web browsing, database retrieval, etc.)
- Always connected (ON) mode for data service
- Best quality voice service
- No paging miss (if there are networking paging misses, User Equipment will not able to answer to incoming calls)
3G standard (TD-SCDMA or WCDMA) mainly address the first two goals and GSM can provide the best quality voice service. So, fast switching between TD-SCDMA and GSM is the key to fulfill user requirement seamlessly. QFR technique provides a way for quick movement from GSM to TD-SCDMA networks. But everything depends on the QFR success rate. If QFR technique fails, User Equipment needs to select TD-SCDMA using traditional technique. Traditional way of selection is a slow process which can cause user equipment to miss network paging. This results in users being unable to receive incoming calls or even access 3G services for a considerable period of time. Hence, the QFR success rate is critical in meeting user expectations.
QFR technique often fails in the below conditions:
- In field, high mobility of UE is expected. User Equipment can start a voice call while traveling in high speed bullet train. It is observed that QFR method has high failure rate in reselecting TD-SCDMA if the UE is moving at a high speed during long duration CS call. In such cases UE need to perform traditional reselection to TDSCDMA cell which is much more time consuming and leads to network paging misses.
- TD-SCDMA network can use different frequencies in different geographical location. User Equipment receives TD-SCDMA frequency lists in IDLE mode. During voice call UE handovers to the GSM network and can move to different geographical location, where different sets of TD-SCDMA frequency may exist. TD-SCDMA frequency list received in SIB3 may not be suitable or would be very weak in the new location. Due to weak signal or unavailability of those TD-SCDMA frequencies, QFR measurement result will not be able to satisfy the cell reselection criterion. So UE goes for the traditional cell search procedure to camp on TD-SCDMA network
To provide customers and businesses with a seamless user experience, operators need to roll-out high quality data and voice services consistently. To achieve that, User Equipment needs to switch between GSM and TD-SCDMA network very quickly depending upon the user requirement. QFR success rate is a key factor to achieve GSM to TD-SCDMA switching rapidly.
A minor modification in Radio Resource Control layer can solve problems with the existing QFR technique. UE would be able to select proper TD-SCDMA cell using QFR method if it is able to include more TD-SCDMA cells/frequencies (in its search list) which are having good signal strength in the new region. It can be achieved through the below solution.
- Radio Resource Control layer (RRC) needs to store below frequency information from following sources in local data base associated with aging timer
1. Frequencies present in SIB3 (QFR frequencies)
2. Frequencies present in Measurement Control messages (interfrequency measurement)
3. Hand Over frequencies (during TD-SCDMA connected mode) » Serving cell frequency
4. RRC will have a limit on maximum number of stored frequencies depending on its capability of scheduling those frequencies for measurement during CS call in GSM. During CS call in GSM, UE performs measurement on frequencies received during TD-SCDMA to GSM Handover
5. Now GRR can cover most of the available TD-SCDMA frequencies in that region. After CS call ends UE can select the best TD-SCDMA cell to reselect and start its PS data services.
Instead of providing frequencies which are received only in SIB3 if RRC includes above all frequencies during TD-SCDMA to GSM handover from its database, QFR success rate can increase drastically.
QFR method makes very fast reselection to TD-SCDMA network. So, the probability of missing the network paging reduces drastically and high speed business user can get back their 3G services quickly. This enables a continuous delivery of high speed data services to users. Field research has indicated that this new proposed technique can boost the QFR success rate (which is currently estimated to be around 55-60%) by about 25-30%. This will help operators considerably improve their live KPIs and take customer satisfaction to new levels
 Method and system for rapidly switching to TD-SCDMA (Time Division-Synchronous Code Division Multiple Access) network - Patent Application Number CN 201010508878