Rajib Dewan of the Department of Electronics and Telecommunications Engineering, Daffodil International University, has been accepted as satisfactory in partial fulfillment of the requirements for the degree of Bachelor of Science in Electronics and Telecommunications Engineering and approved in terms of style and content. I hereby declare that the work presented in this project report entitled “Regional Management and Maintenance in Today's GSM Network” has been carried out by us under the supervision of Mohashin Uddin Pathan, Lecturer, Department of Electronics and Telecommunications Engineering Daffodil International University, in partial fulfillment of the requirements for the degree of Bachelor of Science in Electronics and Telecommunications Engineering.
Internship Objectives
Report Objective
Internship Profile
The discussion on the basic concepts of the GSM network contributes to a better understanding of the following parts of the report. This chapter on the fundamental aspects of the GSM network mainly focuses on the background, core technology, architecture, call origination, signaling process and performance concepts related to GSM.
Background Study of the GSM Network
On the other hand, the first generation of mobile communications was actually the beginning of mobile communications. The most successful standard of the first generation was NMT (Nordic Mobile Telephone), which used the 900 MHz and 450 MHz bands.
Core Technologies in GSM Network
Spectrum Regulation
Modulation Scheme
Multiple Access Method
Hand off is the process that connects the mobile station to the cell when it switches to a new one. There are basically two types of hand removal: soft hand removal and hard hand removal.
Architecture of GSM Network
The Switching System (SS)
MSC/VLR: MSC (Mobile Services Switching Center) is a very central part of the GSM network. HLR: The HLR (Home Location Register) is a network database that contains all administrative information of every subscriber registered in the GSM network.
The Base Station System (BSS)
BTS: Base Transceiver Station houses the radio transceivers that define a cell and handle the radio link protocols with the Mobile Station. Performance-related concepts for these connections between the mobile station (MS) and the BTS will be discussed later in the chapter.
The Operation and Support System (OSS)
In the setup shown above, the BZs would divide the air interface of its coverage into several cells.
Call Set Up Process in GSM
The call setup process illustrates the involvement of the overall GSM architecture as each component plays its role. To do that, A's MSC needs information from B's VLR via B's HLR and B's HLR responds to the interrogation of A's MSC.
Signaling Process in GSM
Basic Signals Used in GSM
¾ A's MSC recognizes B's HLR and establishes a voice connection with the MCS/VLR where user B resides. If it identifies its own mobile subscriber identity number on the PCH, it will respond.
SS7 Architecture
They convert other types of messages into SS7 format. SSP can also send database queries through SS7 network.
Performance Related Concepts in GSM
Cellular Concepts
¾ For a cellular system with the number of available channels S and the number of channels k allocated to each cell, the total number of cells N would use the entire range of channels if and only if each of the number of cells N is disjoint and unique [1 ]. Here i = number of cells taken along any line of the hexagon and j = number of cells taken at 60 degrees counterclockwise after crossing i. In the image above, cells with the same letters use the same frequency range or co-channel cells.
¾ The co-channel noise ratio Q is the ratio between the distance between co-channel cells (D) and the cell radius (R). Therefore, Q=D/R, which means that if Q has a small value, the cluster size is small and the capacity is increased, but the transmission quality is compromised. If Q has a large value, then the cluster is large, which means that the capacity decreases with the improvement of transmission.
Wireless Concepts
Path loss: Path loss occurs when the received signal becomes weaker due to increasing distance between MS and BTS [8]. Multipath Fading: Very simply, multipath fading occurs as the signal reflects, bends and scatters along the path. Details about their application are subject to the discussion in the subsection 'Network coverage' in chapter 3.
The operation and maintenance of contemporary GSM network evolves around two major issues: the overall management of the network and the infrastructure of the network itself. They provide the principles of operation and maintenance and the network elements to be looked after. This chapter therefore discusses the operation and maintenance of GSM network from these two main perspectives.
GSM Network Management
- GSM Network Planning
- GSM Network Implementation (Roll Out)
- GSM Network Operation and Maintenance
- Network Management Domains
Interestingly, this flow completely represents the standard representation of the functional groups mentioned in network management theories. It is the RP's sole responsibility to ensure correct reuse of the frequency and reduce co-channel interference. As an activity is planned and cleared financially, Implementation division, which is more popularly termed as 'Roll Out' division in mobile companies, takes responsibility to meet any problem related to the implementation of the task.
As mentioned, the internship was on this transmission and access network under ROM. In addition, customer complaints regarding poor network performance are also physically monitored and resolved. ¾ Dealing with BTS outages: One of the most important tasks is to respond to BTS outages, in which case the site may be down or cause the entire area to be out of coverage.
Finally, in this section, network domains will be discussed for a broad understanding of the entire management.
Contemporary GSM Network Infrastructure
- Contemporary Services in GSM network
- Network Coverage
- Cellular Coverage
- Premises Coverage
- High Demand Area Coverage
- Road Intersections and Rural Coverage
- Network Nodes and Components
- GSM-900/1800 (BTS)
- The IDU/ODU Units
- MSC-BSC Components
- Network Links
- PCM Links
- E1 Digital Carrier System
- PDH Links
- SDH Links
The IBS is placed at the top of the building which acts as a signal source for the premises. The main reason is that the GSM-1800 operates in the higher range of the GSM spectrum. At the operational level, however, the modern GSM network introduces several intermediate nodes for hierarchical traffic distribution.
The cable entry for the antenna feeders, transmission cables and power is concentrated in the upper part of the cabinet as shown in figure 3.12. DTRU (Double Transceiver Unit): DTRU performs all kinds of tasks related to signal transmission and reception. The outputs are taken from the MUX ports which are connected to optical to electrical converters.
The minimum industry level optical carriers, STM -1, can accommodate 63 E1 channels giving a data rate of 129.024 Mbps. The 7 core switches of Teletalk in regional Dhaka are connected by STM-64 level.
Fault Categories in GSM
- BTS Fault Management
- IDU-ODU Faults
- IBS Faults
- Fiber Optic Faults
- Power Related Faults
It is the ratio of reflected to incident signal on a given TX/RX link. If the reflected signal is greater than the incident signal, fewer signals pass through, resulting in call drop and TRU blocking. At this point, power can be drawn from the emergency backup battery and shut down the generator.
For example, failure of RF diversity or exceeding VSWR can be caused by faults at any point in the circuit. To locate a VSWR alarm, the entire path from the antenna to the BTS connector must be checked. ¾ Poor reception level: Poor reception levels are often reported at the receiving ends of fiber optic connections.
On the other hand, microbending is very rarely with a greater attenuation factor than macrobending.
Complete Overview of GSM Fault Management
¾ Once the failure is assessed, it is determined whether its management can be carried out remotely or requires the presence of a work team on site. ¾ If physical presence is required, appropriate team assigned for that area is sent to rectify the fault. If any ports or interfaces are changed, the physical configuration is done by the on-site team.
Therefore, the overall process requires close coordination between the on-site personnel, NM and NIC. Finally, it should be noted that NM and NIC would exchange information with the planning department at times when necessary. The operation and maintenance aspects in the GSM network, especially the fault management process, directly correspond to the performance issues in the GSM network.
Before concluding the report, this chapter therefore specifically analyzes its effects on the various services offered by today's GSM network.
Voice Call Drops
Cellular Issues
Practical field studies have shown that most customer complaints about dropped calls revealed that the neighboring cell was too strong and dominant.
Hardware Inefficiency
Bit Error Rate (BER)
Poor IBS Coverage
However, on the upper floors of a high-rise building, one specific type of difficulty arises with regard to this coverage.
Fiber Optic Issues
Performance Monitoring Flow Chart
The flow chart above briefly suggests that in case of error occurrence, it should be noted whether the error can be managed with the resources in hand or not. If no fault exists, preventive maintenance should be continued to secure the network against faults. Commissioning was actually a new concept to me, so I tried to understand as much as I could.
I took as many pictures of the sites and tried to note down as much as possible.
The BTS Room
Due to the connection with Teletalk Bangladesh Limited, I visited at least four different BTS as an intern during the period I was interning. Sometimes the country's power grid fluctuates, in this case this AVR (Automatic Voltage Regulator) maintains a constant voltage for the air conditioner operation. Now usually the daytime optical fiber connection is used instead of the microwave, especially in urban areas, because there are problems with path fading and weakening of the signal often occurs in urban areas due to tall buildings. a) (b) Figure 6.2: (a) Shows AVR (b) Shows fiber optic connection instrument.
BTS Commissioning
The data is then placed in the software called LTM Evolution for the commissioning of the BTS.
ALARMS
Major alarms
LP-RDI
The operation and maintenance related aspects of the GSM network were intensively learned and observed during the work experience with a contemporary GSM operator such as Teletalk Bangladesh Ltd. The outcome of this internship ranges from learning the basic concepts of the GSM network to analyzing the very practical and operational state of affairs such as; had the opportunity to observe BTS's fault and management procedures and gain knowledge about the base station system. This program also gives me the opportunity to come into close contact with a company's environment and management system before entering the field.
I have also benefited from the experience of how to work as a team member in a team environment to perform the given responsibility in a limited time in a business organization like Teletalk Bangladesh Ltd.
![Figure 3.2: Roles of the functional group in network management theory [9]](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10827906.0/33.918.142.757.509.873/figure-3-roles-functional-group-network-management-theory.webp)
