3G intra-frequency: 1. Intra-frequency neighbors are used for cell reselection, soft handover, softer handover and intrafrequency hard handover 2. Missing neighbors result in unnecessarily poor signal to noise ratios Disadvantage of Excessive number of neighbors: 1. 2.
increase the UE measurement time may lead to important neighbors being deleted during soft handover
Intra-frequency neighbor lists are combined for both intra-RNC and inter-RNC soft handover (assuming inter-RNC soft handover is supported). Intra-frequency neighbor lists are transmitted in SIB11 and dedicated measurement control messages.
3G inter-frequency: Inter-frequency neighbors are used for inter-frequency cell re-selection and interfrequency handover. RNC allows a maximum of 48 inter-frequency neighbors to be defined with a maximum of 32 on any one RF carrier. 3GPP specifies that a max. of 32 inter-frequency neighbors can be broadcast in SIB11. inter-frequency handover from CELL_FACH does not supported. inter-frequency handover while anchoring an RNC does not supported. Inter-frequency neighbors are usually introduced after the network has been launched and so refining them is usually a post launch optimization task.
3G inter-system: GSM neighbors are used for inter-system cell re-selection and inter-system handover. 3GPP specifications allow a maximum of 32 inter-system neighbors to be defined. Inter-system neighbours are broadcast in SIB11 for cell re-selection and are transmitted in dedicated measurement control messages for inter-system handover. The RNC instructs the UE to measure all GSM neighbors for RSSI measurements but one specific neighbor for BSIC verification. GSM neighbor lists can be based upon existing BSC 2G neighbor lists when sites are cosited. If an operator has both GSM900 and DCS1800 networks then it is possible to define inter-system neighbors only for the GSM900 layer or only for the DCS1800 layer.
2G inter-system: BSC inter-system neighbors are used for inter-system cell re-selection and inter-system handover. Implementation of the BSS allows the definition of 32 UMTS FDD neighbors. The definition of 3G neighbors has an impact upon the maximum number of GSM neighbors which can be defined within the BSC. When a UE is in GSM idle mode, GPRS packet idle mode or GPRS packet transfer mode then it reads the 3G neighbor list from SI2quater and PSI3quater system information messages. When a UE is in GSM connected mode then it reads the 3G neighbor list from measurement information messages which are sent on the SACCH. The length of a single SI2quater message is not sufficient to accommodate 32 intersystem neighbors.
A single SI2quater message is able to accommodate 10 3G neighbors. This means that it is beneficial if 3G neighbor lists can be limited to a length of 10. If multiple SI2quater messages are required then the UE must wait until it has received the complete set before it is able to make a cell re-selection decision. If neighbors are missing then UE may fail inter-system handovers and may remain on the GSM system longer than necessary. If 3G sites are co-sited with 2G sites then 3G neighbor lists configured within the BSC can be based upon the existing 2G neighbor lists.
