At present, two networking strategies are available:
l Strategy 1 (f1: R99; f2: R99+HSPA) l Strategy 2 (f1: R99+HSPA; f2: R99+HSPA)
The access in the case of dualband networking involves direct retry and re-direction in the RRC connection stage and RAB direct retry. RAB direct retry includes service-based direct retry and that after admission failure. The direct retry and re-direction algorithms are used to increase first put-through ratio of the UE.
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3.10.1 RRC direct retry and re-direction during setup of the RRC
Functions and process of RRC direct retry and re-direction during setup of the RRC connection
Figure 3-8 RRC direct retry and re-direction during setup of the RRC connection
If the RNC receives a RRC connection request, the admission algorithm decides whether a RRC connection is allowed between the UE and the current cell based on the load over the current cell.
l If the RRC connection is allowed, the RNC sends a RRC CONNECTION SETUP message to the UE, and then the UE sets up a RRC connection.
l If the RRC connection is not allowed, the RNC direct retry algorithm module searches for a cell that complies with the direct retry algorithm in the UE candidate list.
− If a suitable target cell exists, the RNC sends the target cell data to the UE through a RRC CONNECTION SETUP message.
− If no suitable cell exists, the RNC re-direction algorithm selects another suitable frequency or radio access system (such as GSM), and then notifies the UE of the REDIRECTION cell through a RRC CONNECTION REJECT message. The UE originates an access request in the specified frequency or system.
3.10.2 The RAB Direct Retry
l If the RRC connection is allowed, the RNC sends a RRC CONNECTION SETUP message to the UE, and then the UE sets up a RRC connection.
l If the RRC connection is not allowed, the RNC direct retry algorithm module searches for a cell that complies with the direct retry algorithm in the UE candidate list.
− If a suitable target cell exists, the RNC sends the target cell data to the UE through a RRC CONNECTION SETUP message.
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− If no suitable cell exists, the RNC re-direction algorithm selects another suitable frequency or radio access system (such as GSM), and then notifies the UE of the REDIRECTION cell through a RRC CONNECTION REJECT message. The UE originates an access request in the specified frequency or system.
The RAB direct retry includes service-based direct retry and RAB direct retry after admission failure.
l Service-based direct retry
If a R99 cell and a HSPA cell are at different frequencies but with the same coverage, subscribers who are requesting for the R99 service are assigned to the R99 cell and those who are requesting for the HSPA service are assigned to the HSPA cell if possible. Thus, the R99 service is separated from the HSPA service.
l Direct retry after admission failure
After admission failure, the subscriber can be connected to a cell at another frequency with the same coverage, a HCS cell at another frequency, or a cell in another system (for the AMR service only).
If admission of the HSPA service fails and the direct retry fails in all cells, the service returns to the DCH of the local cell and a RAB connection is set up on the DCH again.
3.10.3 Analyzing Access Problems in the Case of Dualband Networking
In dualband scenario 1, the services are carried in R99 cells as the strategy. In this case, the real-time services do not need inter-frequency direct retry during call setup. Thus, the impact on real-time services decreases and the HSPA subscribers can access the cells that support HSPA through service-based direct retry. To make the UE reside in F1, modify the cell selection and reselection parameter Qoffset2,n of F1 to 50 dB and that of F2 to -50 dB, or bar F2.
In dualband scenario 2, the strategy of random cell residence is used. The UE originates service access in the serving cell. All cells that use two carriers adopt the default value of the Qoffset2, n parameter.
In both scenarios, RRC or RAB direct retry is available for the R99 service and RAB direct retry after admission rejection is available for the HSPA service. If the direct retry of the HSDPA service fails, the service returns to the DCH of the local cell and an RAB connection is set up on the DCH again.
Example 1: In scenario 1, the HSDPA data card resides in the R99 cell. If the PDP is activated, the subscriber accesses the HSDPA cell through direct retry. Figure 3-9 shows the signaling for a service-based direct retry.
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Figure 3-9 Signaling for service-based direct retry of a HSDPA subscriber
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Example 2: In scenario 1, the admission threshold of the R99 service is exceeded if several R99 subscribers access the cell. If one more R99 subscriber tries to access the cell, the admission is rejected in the R99 cells at F1. In this case, the subscriber accesses a R99+HSDPA cell through direct retry. Figure 3-10 shows the signaling for direct retry after admission rejection.
Figure 3-10 Signaling for direct retry of a R99 subscriber after admission rejection