Telecommunications Design Project: From 1G to 3G Report

Introduction

Aims of the Project

This is a Report for a Telecommunications Design project. The primary aim is for the students to be familiarized with the design of a cellular mobile telecommunications network. The objective involves the design and simulation of a cellular mobile telecommunications network and the corresponding operational requirements.

One of the main aims of the project is to supply a specific geographical area with mobile telephony, or mobile communications systems. The initial activity for this communication system is the installation of a suitable number of base stations to be put up into operation to form a network

Scope of the Project

The report covers the different aspects in location and configuration of the base stations, the entire network configuration, antenna configuration and other specifications, frequency planning, teletraffic design, and other important aspects of the network design.

The software CelPlanner^TM from CelPlan Wireless Global Technologies played a great role in the formulation of this project. The software is a systems tool that can serve GSM and Wimax Planning. It aids the different aspects of planning and design of a communications network.

Overview of the Project

This project was aimed to provide us with a bird’s eye view of what a mobile network is all about, and how to plan and design a mobile network with the use of the software CelPlanner. This software has various tools that support planning and design capabilities for GSM and Wimax. CelPlan people can assist with planning and design, and assemble a team to conduct site surveys and important network installation. (CelPlan, 2009)

Background of the Project

We formed teams and each team was assigned to each division of 24 local service areas. Each of these service areas was to be designed as a part of the network with a team to work on. Each team was responsible for the quality of service and other aspects of the network, such as the economic aspect, that would be afforded from the service areas. The areas were comprised of different geographic characteristics and dimensions, such as flatlands, wet and rocky lands, and hills and mountains.

To simplify a bit the operations, Base Stations (BS) were established; nine of them were constructed equipped with antennas of different patterns, along with transmitting power and other necessary equipment for a base station. Base stations always require antennas of different patterns to satisfy the required frequencies. Resources were provided, so the problem was settled right away. Moreover, the design has to be economical and the quality of service satisfactory to meet the needs of the supposed users. Each station must have close coordination with the others.

Hilly portions and mountainous areas require high and complicated structures for antennas which also have to be in such a pattern as to acquire and deliver the necessary frequencies. The problem for this was only temporary as the construction allowed the teams to be flexible and attain the requirements for such antennas.

We used omnidirectional antennas which were provided to at least three directions or sectors of all the base stations. They were constructed with a measurement of 40 to 45 meters in height. These could at least cover wet and woody areas, and overpower forested areas of the base stations.

The three directions of the antennas covered a 360-degree area, with 120 degrees each, so that all the areas were covered, and all the necessary frequencies were attained. They were utilized and designed with utmost economical designs but with more room for expansion. Antenna specifications also covered residential and commercial sectors of the networked areas.

Channeling of the desired frequencies was done to acquire the needed results. Positioning of antennas, to include adjusting for heights, acquiring the desired power, and with minimum acceptable co-channel interference, was worked out by the teams. A minimum of three channels was decided, which means N=3.

We could have used four channels to minimize interference, but this was not allowed. We used the minimum number of frequencies for the given Grade of Service or GOS. C/I or carrier-to-interference ratio was 12 dB over 99% of the service area, the acceptable frequency.

We also used a microwave link antenna in connecting sites and the Mobile Switching Centre (MSC), using the logical star topology, whilst traffic load remained at 227.99 erlangs, to lag behind a 2.01 erlangs traffic deficit due to lack of coverage. The blocking probability was 1.6%.

Geographical Data

Service Areas

In the installation of the 24 service areas, we used topographical and morphological mapping. In other words, the map contains the topographical and morphological information of the service areas. The data refer to the terrain and the type of vegetation as presented in a map. From the map that we are presenting, we can see the entire area characteristics that include obstacles that can affect our coverage, such as water, mountains, railways, and so forth.

The figure indicates the direction of morphologies that characterize the landscape, environmental elements, both natural and artificial, and other forms of territorial organizations that can be recognized.

The topographical data reveals the location in a Resolution of 1 second: to the North, we have 33o 45’ 00.0” N; to the South, we 32o 15’ 00.0” N; to the East, we have 093o 30’ 00.0” W, and to the West, there is 094o 00’ 00.0” W. In a Resolution of 3 seconds, we have to the North, 33o 00’ 00.0” N; to the South, we have 32o 00’ 00.0” N; to the East: 093o 00’ 00.0”; and to the West, 095o 00’ 00.0” W.

Wireless Local Loop

Design and installation of a wireless local loop (WLL) network with GSM technology is conceived with the minimum number of base stations to cover the entire area with minimum channel interference.

The map presenting the geographical data is an important aspect in the design, installation, and simulation of the mobile cellular network because this provides information on the service areas.

The CelPlanner^TM bears a database of the different network configurations and information that can aid the different teams in the design and planning of the cellular radio base station network. The information includes the location and configuration of the base stations, the frequency plan, RF coverage, teletraffic design, and other important information.

The Geographical Data of the coverage provides information regarding the terrain, including the type of vegetation and the formation of the land whether it is hilly or mountainous, or covered with water, or with some installed infrastructure such as railway lines, power lines, etc.

The figure below is a snapshot of the topography of the given service areas.

The next figure provides the morphological data of the service area.

Numerical representations for morphologies are the following:

1. Open Water
2. Woody Wetlands, Emergent Herbaceous Wetlands
3. Perennial Ice/Snow, Bare Rock/Sand/Clay, Quarries/Strip Mines/Gravel Pit, Transitional
4. Grasslands/Herbaceous, Pasture/Hay, Row Crops, Small Grains, Fallow
5. Shrubland, Orchards/Vineyards/Other
6. Deciduous Forest
7. Evergreen Forest
8. Mixed Forest
9. Urban/Recreational Grasses
10. Roads
11. Low-Intensity Residential
12. High-Intensity Residential
13. Commercial/Industrial/Transport

The team’s Service Area

The service area for our team was a combination of different types of land including flat land, hilly areas, rocky terrain, wet land and rivers, ice, and commercial region. Moreover, we utilized different antenna patterns for the decided nine bases stations. The types of the antenna were constructed on different heights and transmitting power to gain maximum area coverage with optimum frequency gain and less interference.

The given service area that we covered was about 294.50 square kilometers of land which has a rectangular shape. For purposes of this Report, this area is referred to as Sub-Service Area or SSA.

This was a combination of different types of land and terrain, like rocky, wet, forest, plane, river, hilly, mountainous, and commercial land. We saw to it that we could deliver the desired area and service.

About the antenna, our focus was to design a system of transmitting data with the least antenna structures that we could install, considering the high cost of installation, but not to the point of sacrificing the quality of the service and performance. In other words, we had to install the minimum number of base stations but the system should be able to deliver quality performance.

We selected an antenna type that was suitable to a mixture of different types of terrain; these were the Omni-directional antennas, constructed at 50 to 60m in height of the economical type but suitable for quality but low traffic load. The service areas also were comprised of residential and commercial environments which needed directional antennas to deliver the kind of frequencies required.

The minimum signal level was at -95dBm thereby forcing the teams to increase the power and height of transmitters. The minimum value of the carrier frequency to interference was at 12dB.

Teletraffic handling requirement

Erlang is used as a unit of load intensity. Erlang B traffic is usually used by telephone system designers to estimate the number of channels or private connections.

Vakili and Aziminejad (2003) proposed a resource allocation scheme specifically developed for cellular environments with heterogeneous offered traffic. In a cellular network with heterogeneous offered traffic consisting of audio and video calls, HCBA-UCB uses intra-cell borrowing and inter-cell unilateral cross-borrowing to enhance the teletraffic performance of the system (p. 219).

The authors said that cross-borrowing of a video resource by one or multiple audio calls is allowed only if the QoS requirement for video calls is not violated. Performance evaluation of HCBA-UCB indicates that this allocation scheme is capable of improving audio teletraffic performance of the cellular network while insignificantly affecting video QoS performance.

Vakili and Aziminejad (2003) explained the technical terms traffic engineering. Traffic engineering is one of the main reasons for implementing multiprotocol label switching (MPLS) in IP backbone networks. This capability of MPLS is based on the fact that it efficiently enables explicitly routed paths, called label switched paths (LSPs), to be created between ingress and egress nodes. As a result, traffic flows can be controlled and engineered through the network. For an explicit LSP, the route is determined at the ingress node. (p. 220)

In our given service area, the traffic load was approximately 230 erlangs, as shown here below. We had to identify first the number of traffic channels and transceivers to be able to determine the traffic load. After this activity, frequencies were provided or assigned to the antennas. Erlang B then was used to determine the traffic channels and the number of transceivers.

Literature Review

Growth of wireless communications

This section is for consolidating the various literature relative to the design of a cellular mobile telecommunications network.

There has been tremendous change in mobile communication systems these past few decades. Along with the advancement in the systems is the emergence of the internet and Information Technology; in other words, there is a vast improvement in communications in general.

Communication has been revolutionized. Wireless has become a need in the operations of businesses and organizations. It is so popular with more innovations almost every time we take a breather to see what’s going on in the world of wireless communication. The worldwide web, or what is popularly known as the Net, has become a daily feature in businesses and organizations.

Fiber optical systems technology changed the way we view traditional telephone systems using a cable. The older telephone systems used wired logic. But with the emergence and easy access to Information Technology, we now have software for more flexible and adaptive strategies.

Wireless technology has been improved much and led the way to cell phones and other mobile communications using antennas of various types and forms, and with the use of satellite.

Cellular telephony systems are radio systems that involve distributed transmission. Instead of having a single transmitter service many different users over a wide area of coverage, the coverage area is divided into smaller areas known as cells. Each cell has one stationary transceiver known as a base station. For example, a user (or subscriber) of a cellular system communicates with the base station to place a call. The call can be data or voice, and the base station routes the call to either a terrestrial network to the termination point or another user of the same cellular network. (Mandyam and Lai, 2002, p. 1)

As students of Telecommunications Engineering, we can see that the magnetic frequency spectrum is now divided into different bands, each for specific purposes. In mobile communications, each band is assigned a limited number of radiotelephone channels and is equipped for optimum utilization.

There is a finite amount of radio spectrum allocated for wireless communication systems; hence the telecommunications industry developed multiple access techniques to allow multiple users to share the available communication channels efficiently (De Souza, 2004, p. 1).

The most common multiple access techniques are:

• Frequency Division Multiple Access (FDMA) – this allocates a discrete amount of bandwidth to each user. In this technique, the total system bandwidth is divided into frequency channels that are allocated to the users (Ojanperä and Prasad, 2001, p.1).
• Time Division Multiple Access (TDMA) – this allocates unique time slots to each user; that is, each user has a specific set of time intervals to transmit information (data/voice) (De Souza, 2004, p. 1).
• Code Division Multiple Access (CDMA) – all users share the same frequency all the time, but this uses a unique code to each user that allows it to be distinguished from other users. This system was specifically designed for the military in their communications and navigation systems. It further promoted the development of Spread Spectrum technology. (De Souza, 2004, p. 1).

CDMA has been quite successful as a second-generation cellular system, having achieved widespread use in particular in North America and Korea by the turn of the twenty-first century. But CDMA will once again find widespread use in the form of third-generation cellular systems in the twenty-first century. (Mandyam and Lai, p. vii)

Comparison of cellular systems

The term used for the group of stations that function together as a network on a single wireless channel is a basic service set (BSS). A BSS may or may not be part of a larger network. If it is self-contained it is referred to as an independent BSS (IBSS). If it is part of a larger network it is referred to as an infrastructure BSS. (Okamoto, 1999, p. 31)

Spread Spectrum Concept

The technology of CDMA spread spectrum communications is a fascinating topic. It is composed of so many different facets derived from decades of communications research (military, academic and commercial) as well as the best that mathematics and science have cultivated over the past 150 to 200 years. (Lee, 2002, p. ix)

Transmission systems have two basic characteristics related to frequency spectrum: center frequency (or transmitted carrier signal) and bandwidth.

Ojanperä and Prasad (2001) explain that ‘In CDMA, multiple access is achieved by assigning each user a pseudo-random code (also called pseudo-noise codes due to noise-like autocorrelation properties) with good auto- and crosscorrelation properties’ (p.1).

The code is used to transform a user’s signal into a wideband spread spectrum signal, whilst a receiver transforms the wideband signal into the original signal bandwidth using the same pseudo-random code. The wideband signals of other users remain wideband signals.

The development of Spread Spectrum technology has the following objectives:

• Multiple access over a single carrier frequency
• Interference reduction
• Privacy. This is between users. Information transmitted in the network can only be understood by the intended recipient. Also, unauthorized receivers cannot intercept waveforms and information transmitted/received in the network. (De Souza, 2004, p 2)
• Multipath: reduction of the undesired effects of delayed versions of the same signal arriving at the receiver through different paths, thus causing self-interference and mutual interference.
• Intra system: minimization of interference caused by a different base station or mobile terminal belonging to the same system.
• External: reduction of network operation disturbances caused by external agents.

Transmission systems have two basic characteristics related to frequency spectrum: center frequency (or transmitter carrier signal) and bandwidth. There are mathematical tools that allow the conversion of time to frequency domain functions and vice versa, such as Fourier and Laplace transforms.

CDMA2000

The concept of cdma2000systems following 3GPP2 standards have three traffic channel types:

1. the same used in IS-95A and IS-95B systems, to maintain compatibility among them;
2. Multi-Carriers (MC), that is, three 1.25 MHz carriers in the forward link and one 3.75 MHz carrier in the reverse link; and
3. one 3.75 MHz carrier in both links, almost the same bandwidth used in the multi-carrier case. (De Souza, 2004, p. 4)

CDMA standards

First-generation cellular systems are those that use analog technology, examples are the Advanced Mobile Phone System and Personal Digital Communications. The Second Generation came into existence because of the need for higher capacity. Included in these systems are the CDMA and TDMA in North America and GSM in Europe.

The cellular operational requirements for a 2G using digital technology, as listed by the Cellular Telecommunications and Internet Association were:

• Ten-fold increase in the existing analog system (AMPS).
• Privacy for voice and data users.
• Ability to introduce new services.
• Ease of transition from legacy to new systems.
• Use of dual-mode terminals; that is, mobiles capable of simultaneously operating in analog and digital systems.
• Compatibility with the frequency spectrum of the existing analog system.
• Reasonable infrastructure and mobile terminal costs.

More Research and Development on cellular phones led to the creation of new communication systems now known as the Third Generation (3G), which is characterized by increased data transmission and improved user connectivity.

The industry requirements for the 3G are:

• High traffic capacity – this was to meet the system capacity up to ten times compared to the analog systems.
• High Quality of Service standards (QoS)
• More services such as paging services, data, and fax traffic achieving data rates. (De Souza et al, 2004, p. 18)

CDMA IS-95 System Structure

One full-duplex access method employed by CDMA is the Frequency Division Duplex (FDD) in which one carrier transmits forward link channels from Base Transceiver Stations (BTSs) to Mobile Stations (MSs), whereas another frequency is allocated for the reverse link (or uplink), transmitting from MSs to their server BTSs (De Souza et al, 2004, p. 30).

Protocol Architecture

IS-2000 is a system that has gained popularity in the initial deployment of 3G. IS-2000 calls out explicitly the functions of four different protocol layers, as compared to IS-95. These layers are the physical layer, medium access control, signaling link access control, and upper layer.

• Physical Layer (layer 1) [4] – this is responsible for transmitting and receiving bits over the physical medium; the layer converts the bits into waveforms, as the physical medium is over the air. The physical layer also carries out coding functions to perform error control functions. (Yang, 2004, p. 2)
• Medium access control (MAC sublayer (layer 2) [5] – this controls the higher layer’s access to the physical medium that is shared among different users.
• Signaling link access control (LAC) sublayer (Layer 2) [6] – this is responsible for the reliability of signaling messages that are exchanged. The LAC sublayer performs a set of functions that ensure the reliable delivery of signaling messages.
• Upper layer (Layer 3 [7] – this carries out the overall control of the IS-2000 system by serving as the point that processes all and originates new signaling messages (Yang, 2004, p. 2)

Global System for Mobile Communications

GSM is the most widespread mobile system in the world today. Its development and architecture are the subjects of interest among developers of global communications. Along with this subject is the topic of Universal Mobile Telecommunication Services (UMTS) about its Core Network (CN) and other radio architectures. Wireless voice service is one of the features GSM technology can offer, and the technology of choice in over 120 countries and for more than 200 operators worldwide (Castro, 2004, p. 1).

To state a brief history of wireless standards and systems, it was in the mid-1990s when the International Telecommunication Union (ITU) initiated an effort to develop a framework of standards and systems that would provide wireless and ubiquitous telecommunications services to users anywhere at any time. Here are the performance requirements of a 3G wireless system, as published by the International Mobile Telecommunications-2000 (IMT-2000), a subgroup of ITU:

• A minimum data rate of 144 Kbps in the vehicular environment;
• A minimum data rate of 384 Kbps in the pedestrian environment;
• A minimum data rate of 2 Mbps in the fixed indoor and picocell environment. (Yang, 2004, p. 1)

Third Generation Partnership Project 2 (3GPP2) reference model for 3G cellular system architecture [3].

Each of the squares, triangles, and rectangles in the figure above represents a Network Entity (NE) while circles represent reference points. NEs can be a complete physical device, a part of it, or even distributed over several physical devices.

The NEs represent the following:

• AAA – Authentication, Authorization, and Accounting: Provides Internet Protocol functionality to support authentication, authorization, and accounting functions.
• AC – Authentication Center
• BS – Base Station; consists of a BSC and a BTS and provides the means for MSs to access network services via radio.
• BSC – Base Station Controller. Provides control and management for one or more BTSs, exchanging messages with both the BTS and the MSC. Traffic and signaling related to call control, mobility and MS management pass transparently through the BSC.
• BTS – Base Transceiver Station; consists of radio devices, antenna, and equipment; this also provides transmission capabilities on the air interface between the BS and MS.
• CDCP – Call Data Collection Point: Collects call details in ANSI-124 format.
• CDGP – Call Data Generation Point; provides call details in ANSI-124 format to the CDCP.
• CDIS – Call Data Information Source: Source of call details, may use a proprietary format.
• CDRP – Call Data Rating Point; charges and taxes un-rated call details. (De Souza, B. et al, 2004, pp. 21-22)

Discussion

The Base Stations

The teams decided to utilize at least nine Base Stations to provide the necessary quality performance for our project. The Base Stations (BS) would provide the required traffic handling capacity with minimum interference.

The Base Station is the base for two-way communication. This is situated in a fixed location while acting as receiver/transmitter in signal communication. BSs use low-power two-way radios including mobile phones.

The radio or wireless path in wireless systems corresponds to the radio link between a mobile user station and the base station with which it communicates. The base station in turn connects to the wired network over which communication signals will travel. Modern wireless systems are usually divided into geographically distinct areas called cells, each controlled by a base station. (Schwartz, 2005, p. 16)

Each Base Station was designed to provide minimum interference and optimum handling capacity. The antenna height was at a proper position with specific latitude and longitude.

Below is a snapshot is taken from the CelPlan software indicating the different antenna types and their configuration. The antennas were so designed to provide high directivity and handle good traffic. The operational frequencies for the BSs were in the range of 890 to 960MHz.

The Erlang formula used was the Erlang B. Erlang is the unit for traffic intensity, per ITU recommendation.

Antenna Coordination

An important design aspect in multi-cellular networks is the type of antennas used at the BSs and RSs. Using omnidirectional antennas would be suitable for highly mobile scenarios due to difficulties in tracking MSs. Omnidirectional antennas require relatively low complexity at the MSs. But there is a drawback in omnidirectional antennas, and this is the high interference which is due to the power signal that is uniformly spread and not beamed toward specific directions. (Dawy, 2009, p. 322)

One way to mitigate the effects of interference is by free space loss between offending and offending facilities. Free-space loss (FSL) is a function of distance. Inside this distance, unacceptable interference occurs; outside the distance, interference is negligible. (Freeman, 2007, p. 702)

The omnidirectional antenna used in this network design had three cells using reflectors, each covering an area of 120°, to complete a 360° direction for the entire coverage or requirement. The antenna was positioned at a high altitude to get the required frequency with less interference and also to obtain the maximum coverage and better C/I ratio.

A 3D demonstration of an antenna specification from CelPlan.

Signaling

To implement high-rate packet-switched data, IS-2000 needs to dynamically acquire and release air link resources, and efficient signaling is required to perform quick acquisitions and releases of these resources. There are these new signaling mechanisms:

• On the forward link, there are overhead/signaling physical channels.
• For the reverse link, there are shorter signaling messages. IS-2000 can transmit shorter 5-ms frames on the enhanced access channel (Yang, 2004, p. 8).
• Also on the reverse link, there are shorter signaling messages.
• On the forward link, IS-2000 can also transmit shorter signaling messages.

IS-2000 represents a natural technical extension from its IS-95 predecessor, and this extension can be seen in the fact that IS-2000 users and IS-95 users can coexist in the same carrier (Yang, 2004, p. 7).

Objectives of the network configuration

The team was able to utilize the necessary antenna patterns, concerning form and height. But our main objectives were to meet some specifications:

• A minimum of co-channel interference but an optimum of coverage.
• To obtain no adjacent channel interference.
• To obtain the required C/I ratio of 12 dB.
• To construct towers and antennas to cover up the required cells and by the terrain and type of land in the service area.
• To assign the required frequencies to all base stations, while maintaining a minimum of interference from co-channel, adjacent channels, and composite interference.
• To assign transceivers by the required load and the GoS.
• To connect in an excellent way the base stations to the MSC to provide circuit-switched calling, mobility management, and GSM services to the users’ cellular phones.

Traffic-handling capacity

The intensity of the load, or the traffic load, was maintained at 230 erlangs. This was distributed on the service areas, for the required number of channels. The Grade of Service was approximately 2%. Erlang B formula, which is for Blocked Calls Cleared, has been applied from the start of the design project.

The figure shows traffic load distribution.

Backhaul Network

This involves the transfer of the different data, including voice and other properties to the base station or the controller, and then from the base stations down to the Mobile Switching Centre or MSC.

The MSC is a telephone exchange that provides switching from the Base Station to the roaming mobile phones. It is an automatic switching device run by a particular integrated circuit. It sends and receives back voice, data and fax, and other services, including SMS.

MSC is placed at a suitable position to send back messages to the base station through a star topology. The construction of the MSC was done in such a way that a suitable position could be attained in the microwave radio antenna, and located at the highest position of the service area. This way the Base Station had a clear line of sight.

Moreover, the MSC is responsible for connecting wireless calls by switching digital voice data packets from one network path to another – a process known as call routing. MSCs also provide additional information to support mobile service subscribers, including user registration, authentication, and location updating. The MSC is the location of the switch and peripheral equipment that serves a wireless system. The switch itself is similar in function to a class 5 end-office switch in the PSTN. (Bedell, 2005, p. 236)

All base stations in a wireless system must be electronically connected to the MSC. This is why a backhaul network is required in all wireless systems. All cells must also be able to communicate with all other cells, electronically through the MSC. The MSC coordinates signal strength measurements that are used in the call-handoff process to determine when handoffs are required. All cells must always maintain contact with all other cells.

The hexagon design accounts for conceptual and physical overlapping between all cells because wireless coverage is depicted by circles from an engineering standpoint. The fixed network has to satisfy capacity demands and provide reliable service.

This can be achieved if the following criteria are incorporated in the network’s design (Bedell, 2005, p. 245):

• All routes and links between base stations and the BSC/MSC must be properly sized to meet demands.
• Mobile-originated traffic must be routed most economically through the network, and to the PSTN (if applicable).
• Survivability must be built into the network wherever possible.

Base Station Controller

The Base Station Controller is an integral element of all MSCs. The BSC is a network element used in most wireless network implementations that are used to interconnect cell base stations to the MSC. The BSC facilitates call handoffs from one base station to another. This is common to radio stations who do not have much built-in intelligence to manage and control the network, so they are connected to these controllers. In GSM systems these controllers are called BSCs, and in 3G/UMS systems they are called radio network controllers (RNCs). The controllers manage the radio network and are responsible for call setup and call-handoffs. (Bedell, 2005, p. 237)

In GSM standards, BSCs are a required network element. In those cases where the mobile switch itself is manufactured by one company and the base station equipment is manufactured by a different company, a BSC is a necessity to bridge the different models of equipment together. The current demands of mobile networks dictate that BSCs should be used to offload the management of base station activity from the MSC. In other words, they help in giving out the overload in the network. The MSC can attend to other critical tasks such as the actual switching of calls, managing interactions with the HLR/VLR, seizing PSTN trunks, and managing Internet access transport and related traffic.

BSCs can be located at the MSC site itself, or can also be geographically distributed throughout a wireless system, or both. It all depends on the actual number of base stations existing in the network, real estate owned by the carrier, and so forth. The purpose of the BSC is to offload some of the base station and call-management functions from the switch, so the switch can perform more switching-related and database-related functions (Bedell, 2005, p. 237).

More important functions of MSC and BSC (Bedell, 2005, p. 237-238) are:

• Switching of Mobile Calls and Least-Cost Routing. The switch located at the MSC site switches all wireless system calls. The BSC does call setup and teardown, although the switch manages channel-frequency assignment and call path assignment up to and including interconnection to the PSTN if the destination of the call is a landline telephone.
• Call-handoff. Call-handoff is the process where the BSC coordinates the transfer of a call in progress from one cell to another. MSC is still involved, but the present trend is that BSC manages the handoff process.
• PSTN Interconnection. In this situation, the MSC manages the control of traffic between the wireless network and the PSTN, including the seizure of PSTN trunks and trunk group selection.
• Internet Connectivity. This is managed by the MSC and involves connections between the MSC and dedicated web servers based at the MSC location and the pass-through processing of Internet sessions between mobile subscribers and the Internet.
• Billing. Customer billing is controlled by the MSC. This is done when upon completion of every wireless call, the MSC generates an automatic message accounting (AMA) record, which contains the details of the call. Examples of the details include the customer’s mobile number or account number, the number of minutes the call lasted, and whether it was local, roaming, or long distance.
• Validation of Subscribers. Through MSC databases known as the home location register (HLR) and visitor location register (VLR), the switch tracks which mobiles registering on the system are home subscribers and which subscribers are visiting, or roaming, subscribers. Home subscribers can be identified as wireless customers who obtained service in a particular market and are making a call in that same market.
• Authentication of Subscribers. This is for security purposes; a challenge-response, antifraud process where the mobile issues a secret code when attempting to place calls, and the MSC holds the key to this code. If the calculation that is inherent in the authentication process is validated by the MSC, the mobile is allowed to make calls.
• Network Operations Statistics. The MSC collects data on all system and call-processing functions, including the following:
  • Traffic statistics on base station trunk groups
  • Trunk groups that connect the wireless system to the PSTN
  • Call-handoff statistics
  • Amount of dropped calls

Moreover, maintenance statistics such as the amount and type of alarms are generated at all base stations and the MSC itself.

Network Operations Center (NOC)

This is not to be forgotten because all telecommunication companies and network providers of all types maintain a Network Operations Center. They may include local exchange carriers (LECs), competitive LECs (CLECs), Internet service providers (ISPs), interexchange carriers (IXCs), voice over IP (VoIP) carriers, and so forth.

The operation of a NOC is done this way.

The data that is routed to a NOC by all MSCs is managed by a network management system such as HP Openview or a similar system that may even be proprietary to a wireless carrier based on the maker of its network infrastructure. The data used to provide network status at a NOC will be housed on an independent, fault-tolerant computer system that would operate on its own virtual local area network (VLAN).

The NOC performs all of the core network-management functions of any standard network: fault management (system alarms), configuration management, security management, accounting management (traffic data), and performance management.

A wireless carrier, like other telephone companies, can have one or more NOCs, depending on its size. If more than one NOC exists, they will be regionalized. They will be geographically distant but deployed symmetrically so they can support big regions.

Frequency Management

We have to reduce the interference level as much as possible. An allocation of 200 kHz for each channel and separation of 30 kHz was applied to adjacent channels.

The GSM frequency plan is a combination of FDMA and TDMA access techniques. It consists of a total of 124 FDMA channels of 200 kHz bandwidth of them.

Frequency in conventional terms is not possible, due to the unavailability of well-shielded sites and/or to the necessity of using crowded frequency ranges close to terrestrial radio link repeaters and terminals. The use of spread-spectrum, as discussed in the Literature Review, may help to withstand severe interference environments. If the number of interfering carriers is small and their power levels are not too large, it may be convenient to use interference-canceling devices. This required individual acquisition of each interfering carrier using an RX terminal pointed toward the interfering transmitter, to get a replica which can then be subtracted, with the appropriate power level. (Tirro, 1993, p. 189)

Conclusions

Wireless mobile communication is now the trend in global business and association, and mostly in all human interaction. As has been often said, this is a revolution in communications. As man continues to conduct business, innovations are a part of his business. Still, change and ambiguity continue to abound.

Wireless communication has long been man’s dream. It has been a part of continuous research and development. Now, this is a part of his daily activities. The internet is a daily feature in day-to-day activities. Recently, fiber optic was the latest innovation in cable telephony, but now it’s wireless. Our telephone systems then used wired logic, but with the internet and Information Technology, we use software, for more flexible and adaptive strategies.

The technology that is very much in vogue is cellular telephony, which involves distributed transmission. This uses different cells with a stationary transceiver known as a Base Station.

On the other hand, the magnetic spectrum has been divided into bands with specific purposes. Each band is assigned a limited number of telephone channels. There is a limited amount of radio spectrum allocated for wireless communication.

Meeting Current and Future Requirements

This is one of the major concerns of the Telecommunication Engineering student and future engineer to handle management and infrastructure that will help in the progress of organizations and nations. Maintaining a good QoS is one of the primary concerns because this is what networks, organizations, and users would always like to be maintained in the course of doing business or partnership with them.

Some other factors that need to be addressed are:

1. Frequency – Maintaining frequencies and without interference is a primary concern because this may break or lose confidence on the part of the users. A change in frequency is just like a back job or a backlog that has to be addressed immediately. Any interference can lose the users’ trust, and he/they might just go to other vendors or competitors. This would also mean a lack of expertise on our part. The lower the frequency, the less attenuation, and therefore fewer losses. And the signal can be transmitted farther away.
2. There would be more losses in frequency if a higher frequency would be allocated. Nevertheless, cell splitting can also be implemented and we could accommodate a smaller area.
3. Different antenna types could be used and at suitable height concerning the service area. Directional areas have more capacity than Omni-directional antennas.
4. The availability of equipment is also very important. Microwave links played an important role as these were very reliable but easy to maintenance.
5. The system is designed to handle more load and this could be done by adding more transceivers, or an upgrade in the future will be possible.

Difficulties Encountered

Difficulties in the planning and implementation of the project started to emerge right at the start. Economic considerations had to be addressed, and this was followed by technical difficulties. First of all, this was the work of a team, and so we had to work as a team. Second, it involves a lot of expertise on every member of the team, although we were still starting as real professionals, or should we say amateurs. There were a lot of loopholes from the start and this was because we had to dig it up to arrive at the proper and excellent project.

The selection of the appropriate service areas was difficult but we had to give some cooperation. But it was settled out. Then, the technical side of channeling and interference created a lot of confusion. We had to consult with each other and do a lot of brainstorming and discussion.

There were many confusions and difficulties in the design, formulation, and actual implementation. The construction was such a laborious process that involved a lot of resources and talent on our part to arrive at a completed project worthy of praise and boast to our instructor.

We had to reduce the transmitter power at the base stations to the minimum to reduce co-channel interference. It proved effective. We did a lot of experimentation in the antennas, like tilting or putting it a bit high. It also worked but the extent of the interference level could not be reduced below a certain limit.

The clustering of the channels was a bit problematic. We were not allowed to use N=4, so we had to be content with N=3. This was one of the most difficult parts because in getting rid of the co-channel interference, it was difficult to do it in an N=3 clustering.

We also encountered connecting the BS sites with microwave links. The terrain of the service areas was irregular. It was a mix of rocky and wetland, hilly and mountainous portions, plus some commercial and residential areas. We couldn’t get the line of sight between sites most of the time. We did some calculations and experimentations, and those sites were moved to some alternative locations and at a higher elevation. We implemented a backhaul network and got a clear line of sight between BS sites and MSC.

Lessons from the Exercise

There are a lot of lessons that we have learned from this exercise. First of all, we learned academic lessons, and these engineering lessons were implemented with some simulation and with the help of software that had been very helpful in the planning and implementation of the engineering design.

We learned how to design a cellular mobile network, including defining the boundary of the service area, the perspective of the terrain, understanding the topography and morphology, and analyzing the map, etc.

Understanding the importance and need for appropriate antennas for the Base Stations is one of the important subjects we learned. By knowing the antenna applications, we can have a grasp of the different frequencies in the project implementation. Moreover, this kind of knowledge is a lasting one. In our future endeavors, as we pursue our respective careers, we will be able to implement this knowledge.

Other lessons and knowledge we learned and earned are effective co-channeling, composite channel interference, and how to avoid channel interference. Again this is an important subject that will help us in our future careers.

We also learned how to manage traffic for a given grade of service with a minimum number of frequencies. Other concepts we focused on were transceivers and the number of traffic channels for communication, the concept of frequency reuse for the GSM, the importance of economical aspects during the project, and lastly, the importance of teamwork.

We learned that teamwork becomes a trait when all of the members are focused on attaining a certain goal without selfish interests. During the project implementation, the members created a certain kind of bonding, a sort of brotherhood bond between us. When we started to feel that every knowledge or talent was needed for the success of the project, that was the time when the project started to make fruit. We knew then that we were going to be successful, or that our efforts were having some clear focus ahead.

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