1 Introduction
The UE keeps in touch with the network by receiving system messages sent by the system in the idle or talking state, and correctly performs network selection and cell access. After the advent of WCDMA, UEs are mostly used between two networks. How to make the dual-mode terminal perfectly cooperate with the two networks, the system issues various instructions and control and neighbor description messages.
2 GSM system news introduction
System messages can be divided into two parts:
(1) The system messages sent on the BCCH channel mainly include system messages 1, 2, 2BIS, 2TER, 2quater, 3, 4, which are used in the idle state of the mobile phone.
(2) The system messages sent on the SACCH channel mainly include system messages 5, 5BIS, 5TER, and 6 for the connection status of the mobile phone.
Among them, the system message 2, 2BIS, 2TER describes the neighboring cell information and reselection parameters for the mobile phone in the idle state, the system message 5, 5BIS, 5TER describes the neighboring cell information and switching parameters in the mobile phone connection state; this article mainly introduces 2G / 3G reselection system message 2, 2quater, 3.
3 GSM system message adjustment
In the early GSM protocol, there was no information about the neighboring area of ​​WCDMA. In order to ensure smooth reselection and handover between GSM and WCDMA, relevant adjustments have been made to system messages in GSMR9904.18.
(1) System informaTIon 3 adjustment
System informaTIon 3 mainly releases system information such as LAI, CI, ACCMIN, CRH, CRO, T3212 and other information. However, in the GSM cell where the FDD cell is defined as a neighbor cell, in order to enable the mobile phone to receive some parameters about reselection or handover to UTRAND, the following information is added in the system information 3 "RestOctet" IE:
â— Classmark sending: terminal class mark sending.
â— SI2 quater IND: whether to send SI 2 quater message in this cell.
â— SI2 quater PosiTIon: SI 2 quater sending location, such as SI 2 quater message is sent on BCCH Ext.
The meaning of these messages is to let the terminal report that the terminal supports WCDMA type standard information; tell the terminal whether the cell will send SI 2 quater message; tell the terminal system to send the system message 2 quarter in the BCCH extended channel, let the phone know to receive Messages. This message contains many parameters for GSM to UTRAN reselection or handover.
(2) System informaTIon 2 adjustment
The definition in SI2ter in the 3GPP 04.18 protocol adds frequency information and cell reselection parameters of neighboring 3G cells compared to the definition in the GSM 04.08 protocol.
(3) Increase System information 2 quarter
The GSM protocol does not define SI 2 quater. The GSMR99 04.18 protocol adds the definition of SI 2 quater. The SI 2 quater contains more information about cell reselection, measurement, and reporting. It mainly includes measurement control parameters, FDD neighbor cell information and description, neighbor cell scrambling code list, etc.
4 Interpretation of system messages involving re-election
During the 2G / 3G reselection process, the system message that the UE always pays attention to is: SI 2quarter (System information 2 quarter). SI 2quarter rest octets describes the parameters of 2, 3G reselection and neighbor information. Based on WCDMA, there are mainly indication messages, measurement control parameters, 3G neighbor cell description and FDD cell description. They are introduced as follows:
(1) Indication message
"3G_BA_IND: bit (1)" Indication of the change of the neighbor table.
"MP_CHANGE_MARK: bit (1)" Change indicator of measurement parameters.
"SI2quater_INDEX: bit (4)" The index number of SI 2 quarter.
"SI2quater_COUNT: bit (4)" The index number of the last System information 2 quarter (SI2quater_INDEX). That means the total number of SI 2quater messages delivered this time.
"Index_Start_3G: bit (7)" The first one included in the current SI 2 quarter.
The 3G neighbor cell index number is used in the 3G neighbor cell description message. If the 3G neighboring cell is not configured, a System information 2 quarter message can pack the measurement parameter information of the neighboring cell. If the current serving cell is configured with 3G neighboring cells and the number of neighboring cells is less than or equal to 10, two System information 2 quarter messages are required, and if there are more than 10 neighboring cells, 3 or more System information 2 quarters are required. SI 2quarter Index is 0, 1, 2, etc.
(2) Measurement control parameter message
When the UE is in the idle state, the threshold for WCDMA cell search is triggered. The threshold is based on the reception level of the 2G serving cell.
In the idle mode of the UE, the offset value added to the reception level of the GSM serving cell and the GSM neighboring cell when reselecting from 2G to 3G. Used to adjust the priority of 2G cell and 3G cell reselection.
When the UE reselects 3G, it requires the candidate cell to reach the minimum Ec / Io threshold.
(3) Cell description message
The following is a description of 3G neighboring cells:
3G frequency point (China Unicom mainly uses 10713, 10688, 10663).
The number of 3G neighboring cells (number of scrambling codes) included in this System information 2 quarter.
List of cell scrambling codes contained in this System information 2 quarter. There are p bits in total, which are compressed according to the frequency list coding and decoding algorithm (see 3GPP 44.018 Annex J (informative): Algorithm to encode frequency list information elements for the detailed algorithm), where the number of scrambling codes is equal to NR_OF_FDD_CELLS. Among them, each cell is composed of 10 bits, the first 9 bits represent scrambling codes, and the 10th bit represents diversity reception.
5 Application of system messages
Normally, all system information is transmitted in eight consecutive 51 multiframes.
Generally, it is sent in the order of 1 (3), 2, 3, 4, 3, 2 (bis, ter, quater).
We know the sending order and content, and know the role of these messages. Then some problems in the network can be found and solved directly through the drive test software. The following are two cases that I dealt with in the process of online optimization:
(1) 3G users will not return to the 3G network after camping on the 2G network
â— Phenomenon: The user's mobile phone network display has been 3G, and the mobile phone displays 2G after arriving at a hotel, and it has been unable to return to 3G during the hotel.
â— Test: The hotel 2G and 3G have indoor distribution system, and the signal is very good. However, 3G has not been reselected.
â— Signaling analysis: The test mobile phone is in idle state, strongly selected to 2G, and the drive system found that the receiving system has not delivered SI 2 quarter. After investigation, the hotel's 2G room subsystem uses Huawei 3001C as the source, and Huawei 3001C does not support the 2G to 3G reselection function, so no SI 2 quarter is issued.
â— Conclusion: The UE cannot receive the SI 2 quarter and will not reselect to 3G.
(2) It is difficult for 3G users to re-elect back to the 3G network after camping on the 2G network
â— Phenomenon: Users report that 2G signals often appear during the use of mobile phones, and they cannot return to 3G networks for a long time.
â— Analysis: The user reports that the phenomenon belongs to the difficulty of reselecting 3G, which may be due to the setting of reselection control parameters.
â— Signaling analysis: Through signaling analysis, it is found that Q_search I = 8 in the SI 2 quarter message indicates that the current 2G service cell level is greater than -78dBm, and the mobile phone searches for the 3G network. Therefore, when the level of the 2G network in the area where the user is located has been lower than -78dBm, the mobile phone has not been reselected. This phenomenon often occurs in dense residential areas, hotels, restaurants, and clubs that do not have an indoor distribution system.
◠Conclusion: The timing and principles of 2G to 3G reselection are determined by the system setting parameters, especially the parameter Q_search I. When Q_search I》 7 indicates that the current 2G service cell level is greater than a certain value, it starts to shrink the 3G network; Q_search I》 7 indicates that the current 2G service cell level is less than a certain value, it begins to shrink the 3G network; Q_search I = 7, The phone will always search for 3G networks. That is, when Q_search I is not equal to 7, the timing of reselection depends on the 2G network level.
6 Conclusion
In a certain period, the GSM network will also complement the WCDMA network. However, in order to ensure that users can maximize the use of 3G networks and enjoy 3G services, the strategy and parameter settings between 2G and 3G are crucial. Operators generally distinguish different scenarios according to different periods and geographical locations, and set network parameters reasonably. Therefore, in the process of maintenance and optimization, we must first understand the strategy and parameter settings and uses in order to effectively solve the problems encountered in the work process.
Stainless Steel Hard Belt,Stainless Steel Strip With Holes,Cold Rolled Stainless Steel Strip,Brushed Stainless Steel Trim Strips
ShenZhen Haofa Metal Precision Parts Technology Co., Ltd. , http://www.haofametals.com