Mobile communication system optimization category and content
Keywords: mobile communications, GSM, CDMA, switching subsystem, base station subsystem, CQT / DT
Summary
The development process of a mobile communication network is generally divided into three stages:
1. Initial demonstration and initial engineering construction: At this stage, the operator shall design the switching and wireless capacity of the network construction based on the population, geographical environment, future mobile user development penetration rate and possible traffic model of the region, with emphasis It is network coverage, and the capacity and quality of the network is not the point. The GSM network from 1996 to 1998 was at this stage;
2. Medium-term high-speed network development period: After a period of operator market promotion and promotion, the network will experience a high-speed development period. At this stage, the biggest problem facing the network is the capacity problem, and the network coverage problem at this time It is also important, but the network quality at this stage is already prominent. At this stage, due to the good numbers of the operators and the development of users, the competition is not fierce, so the quality of network operations is not very prominent. The GSM network from 1999 to 2001 was at this stage;
3. The stable period of network development in the later period: The most important issue in network development to this stage is the quality of network operation. After the network has undergone multiple expansions and new base stations are added, the overall network switching and wireless capacity are relatively advanced, and the number of new users per day is stable, and many of the new users at this time are network transfer or more critical users. Therefore, the main task of operators at this stage is to retain old users and develop new users. This is the most competitive stage. From 2002 to the present GSM network is at this stage.
China's second-generation digital mobile mobile communication network GSM system has experienced an initial construction, high-speed development, and mature and stable process from the beginning of 1996 and 1997 to the promotion of operators such as China Mobile and China Unicom this year; The CDMA system, the new generation mobile communication system, has also matured with the vigorous development of China Unicom. Whether it is GSM or CDMA, the current basic wireless coverage of the network, the development of switching and wireless capacity have developed to a relatively perfect stage, and the main work of operators has been transformed into how to achieve the best state of network operation: how to improve the depth of the network In terms of coverage and breadth, improve clear and reliable call quality to improve end user satisfaction; and how to tap the potential of existing networks and improve equipment utilization; and develop additional services and data services.
If major operators in China want to meet the above-mentioned requirements at the current stage and are in an advantageous position in the increasingly fierce competition, they must increase investment in network optimization projects.
Mobile communication network optimization category and content:
A mobile communication network is mainly composed of the following four parts:
* Exchange subsystem (NSS)
* Base Station Subsystem (BSS)
* Network management subsystem (NMS)
* Mobile terminal (MS)
The switching subsystem is in the core network position in traditional circuit services, and mainly completes the mobility management of land mobile network (PLMN), call-related functions, and other network interfaces, billing and other functions. The switching system has many related operational indicators to monitor the operation of the network, among which several indicators such as the switching rate of the switching system, the voice system connecting rate, and the paging success rate are the most critical. The connection rate of the switching system is the core of the above indicators, which reflects the rationality of the setting of additional functions such as voice connection of the entire system, exchange recording notification, call forwarding, exchange routing, inter-office trunk line selection method and Reasonableness, network coverage on the wireless subsystem side, wireless connection rate, user behavior and a series of network operations. Through the optimization of this indicator, you can achieve the following multiple effects:
1. High voice system connection rate, correspondingly directly increase the operator's call revenue and at the same time increase end user satisfaction;
2. Improve the recording notification settings, increase and strengthen the promotion of additional services such as call forwarding and secretarial desk, and accordingly increase user satisfaction;
3. Reasonably select the exchange route and set office parameters, standardize the trunk line selection method between offices, improve the access speed and the utilization rate of trunk and transmission, reduce the call loss on the wired side of the system, and improve the business income and customer satisfaction .
The impact of other items on the wireless side on the switching rate of the switching system will be mentioned later. The influencing factors of the connection rate of the voice system are mainly divided into: system, wireless and user behavior. The system also includes influencing factors such as relay, line selection method, signaling load, and office parameter settings; the influence of the wireless side will be described in detail later; user behaviors include: should not be called (no ANC), and the caller intentionally hangs after ringing After the functions such as disconnection and super call forwarding are enabled, the user terminal will also hang up. The impact of paging success rate includes wireless mainly signaling load and wireless side coverage problems, overflow problems and so on.
The base station subsystem is in the part of the access network in the entire mobile communication. According to the system protocol and application specifications of the GSM / CDMA second generation technology, it mainly completes the first and second layers of the three-layer protocol, and mainly completes the third layer. Management and allocation of wireless resources. However, due to the wide variety of wireless environments, the complexity of the geographical environment and the lack of openness between the base station controller (BSC) and the base station (BTS). Therefore, the design, planning, and optimization of base station subsystems are more complex than switching subsystems. In addition to directly affecting the wireless operation index of the network, the operation status of the base station subsystem also indirectly affects the key operating indicators of the switching system. For example, if the wireless connection rate is too low, it will directly affect the switching system and the voice connection rate. Brings down the paging success rate of the switching side, which also affects the switching rate of the switching system and voice.
The operation indicators of the base station subsystem are mainly divided into the following major aspects:
1. The cell planning, capacity design, antenna selection and design, and BSS wireless parameter settings are related to the network traffic, access failure rate, wireless connection rate, dropped call rate, and handover success rate (CDMA system also includes Several key indicators, such as the soft handover ratio, the occupancy ratio of each user ’s CE and Sector), have a significant impact;
2. It is related to the operation status of the wireless subsystem equipment, including TRX of the base station (CEM, XCEM in CDMA system), Combiner, diversity receiving board, power amplifier, main clock board (CDMATM board of CDMA), antenna feeder hardware, transmission, BSC The signal processing board, TCU's DSP (SBS vocoder in CDMA) and other hardware equipment failures mainly affect the system's key wireless operation indicators such as allocation failure rate, channel availability rate, dropped call rate, and switching failure rate;
3. The impact of the combination of the above two on the worst cell, super busy cell, and super idle cell ratio of the system;
4. The impact of extra-network interference on the network operation quality and indicators, including the non-decoding level of the uplink RACH (Base Station Noise Figure in CDMA), the abnormally high uplink handover ratio that is not unbalanced in the uplink and downlink Problems such as the self-protection of the base station caused by interference outside the network, the GPS receiver's inability to lock the reference clock of the even-second pulse output by the satellite, the sleep of the base station, etc.);
5. Network operation quality problems related to the interference caused by the network design between microcells, indoor distribution, repeaters and macrocells, dropped calls, handover failures, and poor wireless connection rate caused by improper traffic balance (in CDMA systems) There are also problems such as pilot search window setting problems, intelligent soft handoff boundary offset and other access failures, handover failures, etc.);
6. The rationality of dual-band and double-layer traffic sharing caused by the parameter planning and design between the dual-band network and the double-layer network (the double-layer network here mainly refers to the two-layer network built on the same GSM900 frequency band It is used by many operators in Hong Kong, and it is two wireless solutions with GSM900 / 1800 dual-band network, but it can be mixed in design and use. I have experimented with a double-layer network solution in Beijing Mobile in 1999. Frequency, double-layer network switching success rate, dual-band, double-layer network hanging problem, etc. (in CDMA system, there are traffic balance and switching problems between double carriers). The network management subsystem mainly completes the network hardware and parameters Tasks such as management, software download, engineering cutover, and system operation alarm monitoring and network traffic statistics collection are the eyes of operators.
Since GSM / CDMA cell planning, parameter adjustment, and traffic statistics cannot achieve coverage and interference analysis of specific points in the wireless environment (because the wireless propagation model of cell planning is generally inaccurate), drive testing is important for network optimization and detection Means, can simulate and verify the actual end user call situation, reflecting the coverage, call and interference problems of the actual point, so China Mobile and China Unicom China Mobile and China Unicom have increased the DT (Drive Test) assessment of the branch evaluation.
In addition, DT test cannot be conducted in indoor and some residential areas. China Mobile and China Unicom headquarters have added CQT (Call Quality Test) test.
So the main directions of mobile communication system network optimization are:
* Switch subsystem optimization (NSS)
* Base Station Subsystem Optimization (BSS)
* CQT / DT test and third-party evaluation
to sum up
The complexity of the mobile communication network mainly lies in its aerial part, so the wireless network optimization in the traditional sense generally refers to the optimization of the base station subsystem part and DT work, and the CQT test generally belongs to the category of wireless system optimization (if the wireline or system side is optimized If the response time is too long, such problems generally belong to the optimization category of the switching subsystem). However, the optimization of the switching subsystem should not be neglected. On the one hand, China Mobile and China Unicom headquarters have strict assessments in this regard. In addition, other countries are also directly related to local business revenue, so optimization in this area should also be strengthened. A complete network optimization should first conduct CQT / DT testing, objective and comprehensive third-party evaluation, and then formulate the optimization objectives and implementation plans of the base station subsystem, and at the same time combine the optimization of the switching subsystem to comprehensively improve the local network Operation quality to achieve comprehensive network optimization effect.
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