CDMA TECHNOLOGY

TABLE OF CONTENTS
PAGE
Dedication i
Table of Contents ii
Acknowledgement iv
Introduction v

1. BRIEF HISTORY OF STARCOMMS PLC 1
2. INTRODUCTION TO TELECOMMUNICATIONS
2.1 What is telecommunication? 5
2.2 How telecommunication works 5
2.3 Wireless communication 6
2.3.1 Cellular telephony 7
3. CDMA NETWORK TOPOLOGY
3.1 Difference between GSM and CDMA 11
3.2 CDMA Architecture 14
3.2.1 CDMA Network Structure 14
3.2.2 CDMA Network Areas 18
3.2.3 Signalling in CDMA 20
3.3 Transmission of digital signal in CDMA 22
3.3.1 Modes of transmitting digital signals 22
3.3.2 Cell Site 24
3.3.3 How the Mobile Station (cell phone) works 27
3.4 CDMA Subscriber Services 31


4. BASE STATION SUBSYSTEM
4.1 Introduction 32
4.2 Base Station Controller (BSC) 33
4.3 Base Transceiver Station (BTS) 34
4.3.1 System Overview 34
4.3.2 System Structure 36
5. RADIO UNIT AND ALARM MANAGEMENT
5.1 Introduction 40
5.2 Features 40
5.3 System Description 40
5.4 Alarm Management 43
5.5 Transmission Problem and Solutions 44
Conclusion 47




























INTRODUCTION
Engineering is a practical course. It requires a good knowledge of, not just the theoretical, but the practical aspect of the course. Most Nigerian Universities unfortunately are under-equipped and therefore cannot provide adequate practical knowledge needed in Engineering.
The Students Industrial Work Experience Scheme(SIWES) was set up to enhance the knowledge of Engineering in the sense that while the Universities(lectures) cater for the theoretical aspect of the course, SIWES provides students with the opportunity to work in industries and firms and acquire skills & knowledge in Engineering.
Telecommunications is a very vital tool in our world today. It is practically inevitable in every aspect of life including: businesses, companies, schools, religious gatherings, e.t.c.
In the age of information technology in which EEE is a major stakeholder, telecommunications is a major area of interest which is hardly addressed by the course curriculum. It was in order to redress this imbalance that I decided to use this IT opportunity to acquaint myself of the knowledge of telecommunications with Starcomms Plc.





CHAPTER ONE
BRIEF HISTORY OF STARCOMMS PLC
Starcomms, Nigeria’s leading telecommunications operator and leading "triple-play" (mobile, fixed wireless voice, wireless broadband) provider, is quoted on the Nigerian Stock Exchange having being listed on July 14, 2008. It is the first telecommunications operator in Nigeria to be listed on the domestic Exchange. Starcomms commenced operations in 1989 with a customer base of less than 2,000, at the end of June 2008, the network had crossed over 2.9 million subscribers; making it the 4th largest telecommunications operator and largest CDMA 3G Mobile network in the country. It is also the first CDMA 3G network to cross the one million subscriber base in Nigeria.
Between 2002 and 2005, Starcomms focused on providing fixed wireless services (due to PTO license restrictions), becoming the leading fixed line provider in the country. Starcomms is the leading provider of 3G services in Nigeria using CDMA 2000 EV-DO and was the first company in Africa to launch EV-DO high-speed broadband services in June 2006. In February last year, the network launched its nationwide mobile services after being awarded a 10-year (renewable) technology-neutral national unified license in May 2006, which allows it to offer the full range of telecommunication services on a national basis, as well as international gateway services.
Starcomms is currently present in 28 major cities covering over 100 towns while work is in progress to provide coverage in 31 major cities, 140 towns and 20 States. Major cities such as Lagos, Abuja, Port Harcourt, Kaduna, Kano, Zaria, Ibadan, Benin, Ijebu Ode, Shagamu, Calabar, Warri, Owerri, Oyo, Uyo, Ogbomosho, Abeokuta, Aba, Onitsha, Asaba, Maiduguri, Sapele, Umuahia, Nnewi, Awka, Ilorin and Katsina are on the network. In 2007 Starcomms was named both Nigerian Telecoms Company of the Year (Nigeria Telecoms Awards) and Nigerian Wireless Telecoms Company of the Year (Nigeria Information Technology and Telecoms Awards)
Commercially launched in 1999, Starcomms is today the largest Fixed Wireless Telecommunications provider in West Africa. With our deployment of the world class CDMA technology in 2002, they have exponentially broadened their subscriber base to over 2,900,000 customers all over Lagos, Ibadan, Port-Harcourt, Maiduguri, Kano, Aba, Onitsha, Abuja, Asaba, Zaria, Benin, Kaduna, Abeokuta, Calabar, Warri, Owerri, Uyo, Ilorin, Shagamu, Ijebu Ode, Calabar, Sapele, Umuahia, Awka, Nnewi, Kano, Ogbomosho and Katsina - a subscriber base that continues to grow in leaps.
In 2006, Starcomms launched 3G EVDO mobile broadband Data service that gives customers a smart, fast, convenient and mobile access to the internet (a first in Nigeria, and in West Africa). This followed the launch of the Value added services Fun Box; offering a variety of services that enhance the lifestyle of our users. These services include: 'Dash me credit' (airtime transfer), 'Talk Your Text' (Voice SMS), Voice conferencing involving up to 30 users at a time. Starcomms were the first operator to launch 'Instant messenger' on mobiles in Nigeria.

Still in 2006, Starcomms took yet another giant leap when the Nigerian Communications Commission (NCC) granted it a Unified License. This enabled them to operate as a mobile CDMA network nationwide. Early in 2007, they redefined voice services, in 2 distinct categories; Mobiles and Fixed. Their 0702-8 mobile number series, introduced Freedom Roaming Tariffs for mobiles and the use of RUIM cards - offering subscribers full mobility – subscribers can now roam from one Starcomms coverage city to another on the same number and charging plan.
As the African leader in the commercialization of CDMA, Starcomms continues to demonstrate its expertise in maximizing the performance of new technologies across its infrastructure equipment and subscriber products in order to meet customer expectations.
Today with their 0702-8, 0702-9, 08190, 08191 series, they remain the most poised in providing customers’ great experience of mobile and fixed/wireless with a wide range of flexible and innovative services some; the first of their kind in Nigeria. They have continuously partnered with major telecommunication and service providers around the world. At Starcomms, they believe in deploying the latest telecommunication equipments for future communication needs. With investments in innovative technologies running into billions of Naira, they consistently seek to provide better voice and data services for their consumers.
Also, they seek to encourage local businesses (for instance, all their CDMA base stations were built by local contractors and are maintained by them).
With investments in innovative technologies running into billions of Naira, we consistently seek to provide better voice and data services for our consumers. They are in strategic alliance with other world class telecommunication providers. These include: Qualcomm, CDG, Huawei, Hisense, Harris, Haier, LG, Neratel, CoolPad, Nokia, Motorola, and ZTE.
The world is demanding more from wireless communication technologies than ever before, and CDMA is positioned to respond to those demands. Add in exciting data services and applications such as wireless email, web, digital picture taking/sending and assisted-GPS position location applications, yet tomorrow they will be asked to do even more.
CDMA, incorporating spread-spectrum technology, works by digitizing multiple conversations, attaching a code known only to the sender and receiver, and then dicing the signals into bits and reassembling them. CDMA enables many more people to share the airwaves at the same time than do alternative technologies.
Starcomms has a long standing history with CDMA. They were the first in Africa to implement CDMA ONE using the IS-95A in 1998, and in 2002 Starcomms expanded its platform and network to provide fully functional fax & data at 14.4 kb/s - a first for Nigeria. In line with their pioneering heritage, and to match global standards, Starcomms implemented Africa's premier CDMA 2000 1X system, and was the first West Africa’s Mobile Operator to offer 3G Services based in EVDO Rev. 0, services upgraded in 2007 by introducing super-fast 3G EVDO Rev.A services.
Starcomms became a public limited company in 2008. It has over 2000 staff nationwide. Its national headquarters is located in Victoria Island, Lagos. It has so many departments including: Human Resources, Finance, Customer Care, Engineering/Technology, and Administration. There are eight other sub-departments under Engineering/Technology which include: Field Operations, Information Technology, Power, Transmission, Switch, Radio Frequency, Project, Planning and Implementation. Each of the departments has their own specific functions of which all of them work towards achieving a clear signal in the network. The heart of the Engineering/Technology is Field Operations because they actually do the bulk of the work.
There are about 170 cell sites in Lagos State with four backbones (BSCs) in Victoria Island, Ketu, Apapa, and Mouka (Ikeja). The cell sites are divided into six zones: A-F with two to three field engineers assigned to each zone. I worked with the engineers in zone E. There were 39 sites in zone E in addition to a customer care centre in Ikotun. The location of the cell sites include: Agbara, Alaba, Alaba Market, Aspanda, Okota, Festac town, Ejigbo, Ojo, Satellite town, Badagry, Kweme, e.t.c.





CHAPTER TWO
INTRODUCTION TO TELECOMUNICATIONS
2.1 WHAT IS TELECOMMUNICATION?
As we all know, communication is the process of sharing ideas, information, and messages with others in a particular time and place. Communication includes writing and talking, as well as nonverbal communication (such as facial expressions, body language, or gestures), visual communication (the use of images or pictures, such as painting, photography, video, or film), and electronic communication (telephone calls, electronic mail, cable television, or satellite broadcasts). Communication is a vital part of personal life and is also important in business, education, and any other situation where people encounter each other.
Telecommunications uses devices and systems that transmit electronic or optical signals across long distances. The IEEE Standard Dictionary (Ref. 2) defines telecommunications as the transmission of signals over long distance, such as by telegraph, radio, or television. Telecommunications usually involves a sender of information and one or more recipients linked by a technology, such as a telephone system, that transmits information from one place to another.
2.2 HOW TELECOMMUNICATION WORKS
Telecommunications begin with messages that are converted into electronic or optical signals. Some signals, such as those that carry voice or music, are created in an analogue or wave format, but may be converted into a digital or mathematical format for faster and more efficient transmission. The signals are then sent over a medium to a receiver, where they are decoded back into a form that the person receiving the message can understand. There are a variety of ways to create and decode signals, and many different ways to transmit signals. They include: Wires and cables, Fibre cables, Radio Waves and Communication Satellites. This report which will be dealing on wireless communication will be focused on Radio Waves of which the former is transmitted through. The different telecommunication systems include:
- Telegraph.
- Telephone.
- Teletype, Telex and Facsimile transmission
- Television.
- Radio.
- Global Positioning and navigation systems.
- Personal Computers.
-Voice over Internet Protocol (VOIP).
2.3 Wireless Communication
Wireless telecommunications use radio waves, sent through space from one antenna to another, as the medium for communication. Radio waves are used for receiving AM and FM radio and for receiving television. Cordless telephones and wireless radio telephone services, such as cellular radio telephones and pagers, also use radio waves. Telephone companies use microwaves to send signals over long distances. Microwaves use higher frequencies than the radio waves used for AM, FM, or cellular telephone transmissions and they can transmit larger amounts of data more efficiently. Microwaves have characteristics similar to those of visible light waves and transmit pencil-thin beams that can be received using dish-shaped antennas.
Wireless communications systems include cellular telephones, pagers, radio telegraphs, satellite telephones, laptop computers, personal digital assistants (PDAs), shortwave radios, and two-way radios.
Currently, telecommunications companies throughout the world are activating more wireless service subscriptions than they are conventional wire-based service subscriptions.
Wireless communications systems involve either one-way transmissions, in which a person merely receives notice of a message, or two-way transmissions, such as a telephone conversation between two people. An example of a device that only receives one-way transmission is a pager, which is a high-frequency radio receiver. Two-way transmissions require both a transmitter and a receiver for sending and receiving signals. A device that functions as both a transmitter and a receiver is called a transceiver. Cellular radio telephones and two-way radios use transceivers, so that back-and-forth communication between two people can be maintained.

Fig1. How wireless telecommunication works

2.3.1 Cellular Telephony
This involves the use of cell phones which combine their portable radio capability with the wired, or wire-based, telephone network to provide mobile users with access to the rest of the public telephone system used by non-mobile callers. Modern cellular telephones use a network of several short-range antennas known as towers that connect to the telephone system. Because the towers have a shorter range and cover a smaller area, often as short as 1.5 to 2.4 km (1.0 to 1.5 mi), frequencies can be reused a short distance away without overlapping and causing interference.
Cell phone towers pick up requests from cell phones for a dial tone and also deliver inbound calls to the appropriate cell phone or deliver calls to people using regular telephones on the wire-based system. To do any of these things, the cell phone must have a singular identity that can be recognized by computers housed in a central mobile service switching centre (MSC). When a cell phone is turned on, it connects by radio waves to the nearest cell tower (tower receiving the strongest signal). The cell towers are spaced so their receiving ranges slightly overlap. This continuous contact makes it possible for the MSC to transfer a call from tower to tower as a mobile cell phone user (in a moving vehicle, for instance) moves from one cell area to another.







Fig2. A Cell Phone and its parts


Cellular telephony is of two categories: mobile and fixed of which the rest of this report is going to be based on the later.
-Cellular Access Technologies
There are three common technologies used by cell-phone networks for transmitting information:
• Frequency division multiple access (FDMA)
• Time division multiple access (TDMA)
• Code division multiple access (CDMA)
FDMA puts each call on a separate frequency. TDMA assigns each call a certain portion of time on a designated frequency. CDMA gives a unique code to each call and spreads it over the available frequencies. The last part of each name is multiple access. This simply means that more than one user can utilize each cell. FDMA is not considered to be an efficient method for digital transmission.
Time Division Multiple Access (TDMA)
TDMA is the access method used by the Electronics Industry Alliance and the Telecommunications Industry Association for Interim Standard 54 (IS-54) and Interim Standard 136 (IS-136). Using TDMA, a narrow band that is 30 kHz wide and 6.7 milliseconds long is split time-wise into three time slots. Narrow band means "channels" in the traditional sense. Each conversation gets the radio for one-third of the time. This is possible because voice data that has been converted to digital information is compressed so that it takes up significantly less transmission space. Therefore, TDMA has three times the capacity of an analogue system using the same number of channels. TDMA systems operate in either the 800-MHz (IS-54) or 1900-MHz (IS-136) frequency bands. TDMA is also used as the access technology for Global System for Mobile communications (GSM). However, GSM implements TDMA in a somewhat different and incompatible way from IS-136. Think of GSM and IS-136 as two different operating systems that work on the same processor, like Windows and Linux both working on an Intel Pentium III

Fig3. TDMA splits a frequency into time slots
Code Division Multiple Access
CDMA takes an entirely different approach from TDMA. CDMA, after digitizing data, spreads it out over the entire available bandwidth. Multiple calls are overlaid on each other on the channel, with each assigned a unique sequence code. CDMA is a form of spread spectrum, which simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range.

Fig4. In CDMA, each phone’s data has a unique code
CHAPTER THREE
CDMA NETWORK TOPOLOGY
As have already explained, CDMA (Code division Multiple Access) which is one of the technologies for transmission of cellular phone networks. In CDMA, each phone’s data has a unique code. All of the users transmit in the same wide-band chunk of spectrum. Each user's signal is spread over the entire bandwidth by a unique spreading code. At the receiver, that same unique code is used to recover the signal. Because CDMA systems need to put an accurate time-stamp on each piece of a signal, it references the GPS system for this information. Between eight and 10 separate calls can be carried in the same channel space as one analogue AMPS call. CDMA technology is the basis for Interim Standard 95 (IS-95) and operates in both the 800-MHz and 1900-MHz frequency bands.
CDMA technology has evolved from the IS95A→IS95B→CDMA2000 1X→CDMA 1X EV→CDMA 1X EV-DO→CDMA 1X EV-DV→CDMA MC 3X→WCDMA→TD-SCDMA. Starcomms highest technology is the CDMA 1X EV-DO where EV-DO stands for Evolution Data Optimised.
In cellular service there are two main competing network technologies: Global System for Mobile Communications (GSM) and Code Division Multiple Access (CDMA). Understanding the difference between GSM and CDMA will allow one to choose a carrier that uses the preferable network technology for his needs.
3.1 DIFFERENCE BETWEEN GSM AND CDMA
-Coverage: The most important factor is getting service in the areas you will be using your phone. Upon viewing competitors' coverage maps you may discover that only GSM or CDMA carriers offer cellular service in your area. If so, there is no decision to be made, but most people will find that they do have a choice.
-Data Transfer Speed: With the advent of cellular phones doing double and triple duty as streaming video devices, podcast receivers and email devices, speed is important to those who use the phone for more than making calls. CDMA has been traditionally faster than GSM, though both technologies continue to rapidly leapfrog along this path. Both boast "3G" standards, or 3rd generation technologies.
EVDO, also known as CDMA2000, is CDMA's answer to the need for speed with a downstream rate of about 2 megabits per second, though some reports suggest real world speeds are closer to 300-700 kilobits per second (kbps). This is comparable to basic DSL. As of fall 2005, EVDO is in the process of being deployed. It is not available everywhere and requires a phone that is CDMA2000 ready.
GSM's answer is EDGE (Enhanced Data Rates for GSM Evolution), which boasts data rates of up to 384 kbps with real world speeds reported closer to 70-140 kbps. With added technologies still in the works that include UMTS (Universal Mobile Telephone Standard) and HSDPA (High Speed Downlink Packet Access), speeds reportedly increase to about 275-380 kbps. This technology is also known as W-CDMA, but is incompatible with CDMA networks. An EDGE-ready phone is required.
In the case of EVDO, theoretical high traffic can degrade speed and performance, while the EDGE network is more susceptible to interference. Both require being within close range of a cell to get the best speeds, while performance decreases with distance.
-Subscriber Identity Module (SIM) cards: In the United States only GSM phones use SIM cards. The removable SIM card allows phones to be instantly activated, interchanged, swapped out and upgraded, all without carrier intervention. The SIM itself is tied to the network, rather than the actual phone. Phones that are card-enabled can be used with any GSM carrier. The CDMA equivalent, a R-UIM card, is only available in parts of Asia but remains on the horizon for the U.S. market. CDMA carriers in the U.S. require proprietary handsets that are linked to one carrier only and are not card-enabled. To upgrade a CDMA phone, the carrier must deactivate the old phone then activate the new one. The old phone becomes useless.
-Roaming: For the most part, both networks have fairly concentrated coverage in major cities and along major highways. GSM carriers, however, have roaming contracts with other GSM carriers, allowing wider coverage of more rural areas, generally speaking, often without roaming charges to the customer. CDMA networks may not cover rural areas as well as GSM carriers, and though they may contract with GSM cells for roaming in more rural areas, the charge to the customer will generally be significantly higher.
-International Roaming: If you need to make calls to other countries, a GSM carrier can offer international roaming, as GSM networks dominate the world market. If you travel to other countries you can even use your GSM cell phone abroad, providing it is a quad-band phone (850/900/1800/1900 MHz). By purchasing a SIM card with minutes and a local number in the country you are visiting, you can make calls against the card to save yourself international roaming charges from your carrier back home. CDMA phones that are not card-enabled do not have this capability, however there are several countries that use CDMA networks. Check with your CDMA provider for your specific requirements.
According to CDG.org, CDMA networks support over 270 million subscribers worldwide, while GSM.org tallies up their score at over 1 billion. As CDMA phones become R-UIM enabled and roaming contracts between networks improve, integration of the standards might eventually make differences all but transparent to the consumer.
The chief GSM carriers in the United States are Cingular Wireless, recently merged with AT&T Wireless, and T-Mobile USA. Major CDMA carriers are Sprint PCS, Verizon and Virgin Mobile. There are also several smaller cellular companies on both networks.
3.2 CDMA ARCHITECTURE
A CDMA network is composed of several functional entities, whose functions and interfaces are specified. The figure shows the layout of a generic CDMA network. The CDMA network can be divided into three broad parts.
3.2.1 CDMA Network Structure
-The Mobile Station is carried by the subscriber.
-The Base Station Subsystem controls the radio link with the Mobile Station.
-The Network Subsystem or Switching system, the main part of which is the Mobile services Switching Centre (MSC), performs the switching of calls between the mobile users, and between mobile and fixed network users.

Fig5. CDMA Network Structure

Mobile Station (MS)
The MS, i.e. the GSM handset, is logically built up from the following components:
• Mobile equipment (ME) – this is the CDMA terminal, excluding the SIM card;
• Subscriber identification module (SIM) – this is the chip embedded in the SIM card that identifies a subscriber of a CDMA network; the SIM is embedded in the SIM card. When the SIM card is inserted in the ME, the subscriber may register with a CDMA network. The ME is now effectively personalized for this CDMA subscriber. The SIM card contains information such as IMSI, advice of charge parameters, operator-specific emergency number, etc.

The Base Station System (BSS)
All radio-related functions are performed in the BSS, which consists of base station controllers (BSCs) and the base transceiver stations (BTSs).
• BSC—The BSC provides all the control functions and physical links between the MSC and BTS. It is a high-capacity switch that provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in base transceiver stations. A number of BSCs are served by an MSC.
• BTS—The BTS handles the radio interface to the mobile station. The BTS is the radio equipment (transceivers and antennae) needed to service each cell in the network. A group of BTSs are controlled by a BSC.
The Switching System
The switching system (SS) is responsible for performing call processing and subscriber-related functions. The switching system includes the following functional units:
- Home location register (HLR)—The HLR is a database used for storage and management of subscriptions. The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. When an individual buys a subscription from one of the PCS operators, he or she is registered in the HLR of that operator.
• Mobile services switching centre (MSC)—The MSC performs the telephony switching functions of the system. It controls calls to and from other telephone and data systems. It also performs such functions as toll ticketing, network interfacing, common channel signalling, and others.
• Visitor location register (VLR)—The VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time.
• Authentication centre (AUC)—A unit called the AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network operators from different types of fraud found in today's cellular world.
• Equipment identity register (EIR)—The EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR node.
The Operation and Support System
The operations and maintenance centre (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional and local operational and maintenance activities that are required for a GSM network. An important function of OSS is to provide a network overview and support the maintenance activities of different operation and maintenance organizations.
-Note that the MSC contains no information about particular mobile stations --- this information is stored in the location registers.

Fig6. CDMA Network Elements
Additional Functional Elements
Other functional elements are as follows:
• Message centre (MXE)—The MXE is a node that provides integrated voice, fax, and data messaging. Specifically, the MXE handles short message service, cell broadcast, voice mail, fax mail, e-mail, and notification.
• Mobile service node (MSN)—The MSN is the node that handles the mobile intelligent network (IN) services.
• Gateway mobile services switching centre (GMSC)—A gateway is a node used to interconnect two networks. The gateway is often implemented in an MSC. The MSC is then referred to as the GMSC.
• CDMA interworking unit (CIWU)—The CIWU consists of both hardware and software that provides an interface to various networks for data communications. Through the CIWU, users can alternate between speech and data during the same call. The CIWU hardware equipment is physically located at the MSC/VLR.
3.2.2 CDMA Network Areas
The GSM network is made up of geographic areas. As shown in Figure 3, these areas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN) areas.









Fig7. Network Areas
The cell is the area given radio coverage by one base transceiver station. The GSM network identifies each cell via the cell global identity (CGI) number assigned to each cell. The location area is a group of cells. It is the area in which the subscriber is paged. Each LA is served by one or more base station controllers, yet only by a single MSC (see Fig8). Each LA is assigned a location area identity (LAI) number.

Fig8. Location Areas

An MSC/VLR service area represents the part of the GSM network that is covered by one MSC and which is reachable, as it is registered in the VLR of the MSC (see Fig9).
Fig9. MSC/VLR Service Areas
The PLMN service is the area serviced by one network operator. PLMN comes in three categories:
• Home PLMN (HPLMN) – the HPLMN is the CDMA network that a CDMA user is a subscriber of.
That implies that CDMA user’s subscription data resides in the HLR in that PLMN.
• Visited PLMN (VPLMN) – the VPLMN is the CDMA network where a subscriber is currently registered. The subscriber may be registered in her HPLMN or in another PLMN.
• Interrogating PLMN (IPLMN) – the IPLMN is the PLMN containing the GMSC that handles mobile terminating (MT) calls. MT calls are always handled by a GMSC in the PLMN, regardless of the origin of the call.

3.2.3 Signalling in CDMA
The various entities in the GSM network are connected to one another through signalling networks. Signalling is used for example, for subscriber mobility, subscriber registration, call establishment, etc. The connections to the various entities are known as ‘reference points’. Examples include:
• A interface – the connection between MSC and BSC.
• Abis interface – the connection between BSC and BTS.
• D interface – the connection between MSC and HLR.
• Um interface – the radio connection between MS and BTS.
When it comes to call establishment, CDMA makes a distinction between signalling and payload. Signalling refers to the exchange of information for call set up while payload refers to the data that is transferred within a call, i.e. voice, video, fax etc.
In PSTN, signalling is a means for transferring network-related information between switching nodes, and also between the end office switches and their subscribers. Signalling is used to do the following:
• Request service from the central office switch (via going off-hook).
• Provide central office switch with the information necessary to route a telephone call (via DTMF addressing digits in a specific format).
• Alert destination address of incoming call (ringing).
• Provide status information and call supervision for billing.
• Manage network lines/trunks (set up and teardown calls).
The two forms of signalling used by the network are:
• Channel Associated Signalling (CAS)
• Common Channel Signalling (CCS)
The principal advantage of CAS is that it is inexpensive to implement and can be used on any transmission medium.
However, CAS has the following disadvantages:
• Fraud— “phone freaks” can build boxes to play call setup and teardown tones.
• Interference is possible between signalling tones used by the network and frequencies of human speech patterns.
• Speed—call setup and teardown is slower, less efficient use of resources.
CCS employs a separate, dedicated path for signalling. Voice trunks are used only when a connection is established, not before. Call setup time is quicker because resources are more efficiently used. CCS is the technology that makes ISDN and SS7 possible.
ISDN and SS7 are similar in the sense that they make use of the Primary Rate Interface (PRI) which is divided into E1-PRI and T1-PRI. E1 is two (2) way transmission of digital signal operating at 2.048Mbps and has 32 timeslot/channels (30B+2D at 64 Kbps per PCM channel). T1 is two (2) way transmission of digital signal operating at 1.54Mbps and has 24timeslots/channels (23B+1D at 64 Kbps per PCM channel).
However the standard signalling system for transmitting digital data approved by ITU-T is SS7 because it uses different messaging for call setup and teardown. SS7 lets any SS7-enabled node to talk to any other, regardless of whether they have direct trunk connections between them.
Signalling is of three modes namely:
• Associated Signalling—uses one dedicated path between switches as the signalling link. Examples: ISDN-PRI and E1-CAS.
• Non-Associated Signalling—uses separate logical paths and multiple nodes.
• Quasi-Associated Signalling—uses a minimal number of nodes (preferred for SS7, causes less delay).


3.3 TRANSMISSION OF DIGITAL SIGNALS IN CDMA
3.3.1 Modes of transmitting digital signals
They include:
-By Coaxial cables (E1 cables).
-By Optic Fibre.
-By Microwave (Radio).
-By Satellite (VOIP).
Before transmission can go on, the network specifications/characteristics as well as the availability of the cell-sites should be considered.
3.3.2 Network Specifications/Characteristics:
• Frequency band—Frequency is the number of complete oscillations in a second. The frequency range specified for CDMA is 800 and 1,900 MHz (mobile station to base station).
• Wavelength—This is the length of one complete oscillation and is measured in metres. Frequency and wavelength are related via the speed of propagation. Lower frequencies with longer wavelengths are better suited to transmission over large distances, because they bounce on the surface of the earth and in the atmosphere e.g. television and FM radio transmission. Higher frequencies with shorter wavelengths are better suited to transmission over large distances, because they are sensitive to such problems as obstacles in the line of the transmission path. The frequencies used by mobile systems comprise between the large coverage advantages offered by lower frequencies and the closeness to the receiver advantages offered by use of higher frequencies.
• Bandwidth—This is the amount of frequency range allocation to one application. The bandwidth given to an application depends on the amount of available frequency spectrum. The amount of bandwidth is an important factor in determining the capacity of the mobile system i.e. the number of calls, which can be handled. The bandwidth size for all CDMA modes is 1.25MHz.

• Channels—This is a frequency which can be allocated for the transmission and possibly the receipt of information. Communication channels can be of three forms: simplex, half duplex and full duplex. A simplex channel such as FM radio station uses a single frequency in a single direction only. A duplex channel, such as used during a mobile call, uses two frequencies: one to the MS and one from the MS. The direction from the MS to the network is called uplink. The direction from the network to the MS is called downlink. In CDMA the number of channels is 20 (798 users per channel).
• Duplex distance—The duplex distance is 80 MHz. Duplex distance is the distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart.
• Channel separation—This is the separation between adjacent carrier frequencies. It is required in order to avoid the overlapping of information in one channel into and adjacent channel. The length of separation between the channels is dependent on the amount of information which is to be transmitted within the channel. In CDMA, this is 1,250 kHz.
• Modulation—Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in CDMA via QPSK.
• Transmission rate—This is the amount of information transmitted over a channel over a period of time. CDMA is a digital system with an over-the-air bit rate of about144kbps for 1x, 384-2.4Mbps for 1x EV-DO and 4.8Mbps for 1x EV-DV.
• Capacity and Frequency Re-use —Capacity is the number of frequencies that determines the cell’s capacity. Each company with a license to operate a mobile network is allocated a limited number of frequencies. These are distributed throughout the cells in their network.
Groups of frequencies can be placed together into patterns of cells called clusters. A cluster is a group of cells in which all available frequencies have been used once and only once. Since the same frequencies can be used in neighbouring clusters, interference may become a problem. Therefore, frequency re-use pattern is employed. The frequency re-use patterns ensure that any frequencies being re-used are located at a sufficient distance apart to ensure that there is little interference between them. However, to maximize capacity the frequency re-use distance should be kept as low as possible.


Fig10. A Frequency Re-use Pattern
• Access method—CDMA utilizes the code division multiple access concept. It is a technique which gives a unique code to each call and spreads it over the available frequencies.
3.3.2 Cell Site
This contains equipment which communicate directly with the mobile station. There are three distinct contents in a cell-site. They include: the shelter, the tower (mast), the diesel generator.
-The Shelter: This is a small enclosed compartment which houses the indoor equipment including: the Base Transceiver Station(BTS), Indoor Unit of the Radios, the chrome block, the power rectifiers, air conditioners, environmental alarm chest and fire extinguisher.

Fig11a. A closed shelter








Fig11b. A telecommunication tower

The indoor unit (IDU) are connected to the outdoor unit (ODU) and the BTS. They are used for point to point direction. The power rectifier powers the equipment in the site even during power failure. It has backup batteries that can last for hours in case of power failure. The rectifier is equipped with modules that charge the batteries when on alternating current.

Fig11c. An Emerson Power Rectifier

Fig11d. A Radio Indoor Unit
The air conditioners help to cool the shelter and the equipment. The environmental alarm chest helps in detecting any unusual change in environmental conditions. It serves as a multi detector.

Fig11e. Environmental Alarm Chest
-The Tower (mast): A cell-phone tower is typically a steel pole or lattice structure that rises hundreds of feet into the air. It is always projected very tall above buildings and takes a three or four corner shape. It has an average height of 120-140m. It also has a ladder which is used by the riggers for climbing to install and replace faulty equipment. The equipment that are found on the tower include: the Outdoor Unit (ODU) of the radio, the antennae, the Global Positioning system (GPS) and the aviation light. They are connected to the shelter with their cables.
The ODU is an extension of the IDU. It comprises of the transceiver and the diplexer. It is mainly used for point to point direction with other ODUs in nearby cell sites during handover. The antennae help in boosting the RF frequency. The GPS is used in radio coverage measurement with the help of a tool called Test Mobile Systems (TEMS). The aviation light is connected at the top of the tower and is used for identification.
3.3.3 How the Mobile Station (cell phone) works during transmission
A single cell in an analogue system uses one-seventh of the available duplex voice channels. A cell-phone carrier typically gets 832 radio frequencies to use in a city. Each cell phone uses two frequencies per call -- a duplex channel -- so there are typically 395 voice channels per carrier. (The other 42 frequencies are used for control channels). Therefore, each cell has about 56 voice channels available.
In other words, in any cell, 56 people can be talking on their cell phone at one time. With digital transmission methods, the number of available channels increases. For example, a TDMA-based digital system can carry three times as many calls as an analogue system, so each cell has about 168 channels available. Cell phones have low-power transmitters in them. Many cell phones have two signal strengths: 0.6 watts and 3 watts (for comparison, most CB radios transmit at 4 watts). The base station is also transmitting at low power.
The cellular approach requires a large number of base stations in a city of any size. A typical large city can have hundreds of towers. But because so many people are using cell phones, costs remain low per user. Each carrier in each city also runs one central office called the Mobile Service Switching Centre (MSC). This office handles all of the phone connections to the normal land-based phone system, and controls all of the base stations in the region.
All cell phones have special codes associated with them. These codes are used to identify the phone, the phone's owner and the service provider. These codes include:
- Electronic Serial Number (ESN) - a unique 32-bit number programmed into the phone when it is manufactured.
- Mobile Identification Number (MIN) - a 10-digit number derived from your phone's number.
- System Identification Code (SID) - a unique 5-digit number that is assigned to each carrier by the FCC.
Let's say you have a cell phone, you turn it on and someone tries to call you. Here is what happens to the call:
• When you first power up the phone, it listens for an SID (see sidebar) on the control channel. The control channel is a special frequency that the phone and base station use to talk to one another about things like call set-up and channel changing. If the phone cannot find any control channels to listen to, it knows it is out of range and displays a "no service" message.
• When it receives the SID, the phone compares it to the SID programmed into the phone. If the SIDs match, the phone knows that the cell it is communicating with is part of its home system.
• Along with the SID, the phone also transmits a registration request, and the MSC keeps track of your phone's location in a database -- this way, the MSC knows which cell you are in when it wants to ring your phone.
• The MSC gets the call, and it tries to find you. It looks in its database to see which cell you are in.
• The MSC picks a frequency pair that your phone will use in that cell to take the call.
• The MSC communicates with your phone over the control channel to tell it which frequencies to use, and once your phone and the tower switch on those frequencies, the call is connected. You are talking by two-way radio to a friend!
• As you move toward the edge of your cell, your cell's base station notes that your signal strength is diminishing. Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) sees your phone's signal strength increasing. The two base stations coordinate with each other through the MSC, and at some point, your phone gets a signal on a control channel telling it to change frequencies. This hand off switches your phone to the new cell. As you travel, the signal is passed from cell to cell which results in roaming.
Roaming: If the SID on the control channel does not match the SID programmed into your phone, then the phone knows it is roaming. The MSC of the cell that you are roaming in contacts the MSC of your home system, which then checks its database to confirm that the SID of the phone you are using is valid. Your home system verifies your phone to the local MSC, which then tracks your phone as you move through its cells. And the amazing thing is that all of this happens within seconds. Here is a summary of what happens in an outgoing and incoming call and handovers.

Fig12a. Outgoing Call




Fig12b. Incoming Call

3.4 CDMA Subscriber Services
There are two basic types of services offered through CDMA: telephony (also referred to as teleservices) and data (also referred to as bearer services). Telephony services are mainly voice services that provide subscribers with the complete capability (including necessary terminal equipment) to communicate with other subscribers. Data services provide the capacity necessary to transmit appropriate data signals between two access points creating an interface to the network. In addition to normal telephony and emergency calling, the following subscriber services are supported by GSM: facsimile group III, short message services, cell broadcast, voicemail, fax mail, e.t.c.
Other supplementary services include: call forwarding, barring of outgoing and incoming calls, advice of charge (AOC), call hold, call waiting, multiparty service and call line identification presentation/restriction, e.t.c.

CHAPTER FOUR
BASE STATION SUBSYSTEM (BSS)
4.1 INTRODUCTION
The mobile communication system has experienced the first generation (analogue system) and the second generation (digital system). As one of the main development trends of the second generation, the Code Division Multiple Access 1X (CDMA 1X) technology, advocated by the 3rd Generation Partnership Project 2 (3GPP2), has been widely used for commercial purpose.
The Huawei CDMA 1X mobile communication system comprises the Base Station Subsystem (BSS) and the Core Network (CN). Users can operate and maintain the system through an integrated mobile network management system.










Fig13. Network structure of Huawei CDMA 1X system

The BSS consists of the BTS, Base Station Controller (BSC), and Packet Control Function (PCF). The PCF is usually integrated with the BSC. The ODU3601C, a soft site, is also a part of the Huawei BSS.
4.2 BASE STATION CONTROLLER (BSC)
The BSC performs the following functions: BTS control and management, call connection and disconnection, mobility management, power control, radio resource management, provision of stable and reliable radio connections for the upper-level services through soft/hard handoff.
The PCF manages the Radio-Packet (R-P) connection. As radio resources are limited, they should be released when subscribers are not sending or receiving information. But the Peer-Peer Protocol (PPP) connection must be maintained.
Rack Distribution
Large capacity BSC is divided into following functional blocks. In general each block corresponds to single subrack. These are:
 CDMA Switch Subrack (CSWS)
 CDMA Integrated Processing Subrack (CIPS)
 CDMA Resource and Packet Subrack (CRPS)
 CDMA Packet Module Subrack (CPMS)
 Clock processing Module (CLKM)
 CDMA Integrated Management System (CIMS)


Fig14. Rack Distribution
Configuration for 200,000 Voice Subscribers and 400 M Data Throughput
 Busy hour call attempts (BHCA): 600,000
 Voice traffic volume: 6,000 Erl
 Number of voice subscribers (0.03Erl/sub): 200,000
 Number of channels at Um interface: 13,500TCE
 Number of E1/T1 ports at A-interface: 320
 Number of E1/T1 ports at Abis interface: 576
 Number of 1X carriers: 960
 Number of 1xEV-DO carriers: 768
 Number of packet data service PPP connections: 240,000
 Number of packet data service active PPP connections: 10,000
 Total flow of packet data: 400 Mbps
 Traffic of circuit data services: 237Erl
 Number of circuit data service subscribers (0.03Erl/sub): 7,900

4.3 BASE TRANSCEIVER STATION (BTS)
The BTS transmits and receives radio signals to enable the communication between the radio network system and the Mobile Station (MS). Huawei provides a series of BTS products, including: cBTS3612, BTS3606, BTS3612A, BTS3612A and ODU3601C. The most conversant one BTS3606 though the BTS3606E is now in use. The BTS3606 is located between the BSC and the MS in the CDMA 1X system. Under the control of the BSC, the BTS3606 is the radio transceiver equipment serving one cell or multiple logical sectors.
4.3.1 System Overview
-Technical Features: Supports both the CDMA2000 1X and 1xEV-DO standards. Supports CDMA2000 1X / 1xEV-DO hybrid networking. The ratio of CDMA2000 1X and CDMA2000 1xEV-DO carriers is flexible. Support high-power coverage and large-capacity coverage using carriers of different frequencies for a single sector. Support the mixed insertion of different-band carriers in the same cabinet. The BTS3606 can be cascaded with the ODU3601C to expand the coverage area of radio network flexibly. It can support bands of 450 MHz, 800 MHz, and 1900 MHz. The maximum average transmit power is 25 W. After the high-power combiner is configured, the maximum average transmit power can reach 50 W. The main/diversity receiving technology is employed to optimize the receiving performance.
The BTS3606 supports the networking by using E1 and T1 links, and the interfaces of
Inverse Multiplexing for ATM (IMA) and User Network Interface (UNI), The BTS3606 supports networking modes in chain, star, and tree topologies. The BTS3606 supports the following clock sources: Global Position System (GPS) clock, Global Navigation Satellite System (GLONASS) clock and other external clock sources.
-Convenient Operation and Maintenance:
Users can operate and maintain the BTS3606 through the Local Maintenance Terminal (LMT) and the M2000 integrated maintenance console. The following lists the maintenance functions:
a) System status monitoring: This function provides the indication for the system running status and resource status, the configuration of local cell and logical cell, and their status indication. It can also be used to check for the MPP link and the E1 availability using the RJ45 cable.
b) Data configuration: The BTS3606 adopts dynamic data configuration mode. The configured data takes effect without resetting BTS. It also supports the batch processing of data configuration, which allows the configuration of multiple network elements sharing the same attributes at a time.
c) Alarm Processing: This function covers: alarm collection, alarm clearing, alarm querying, alarm shielding, and alarm filtering.
d) Security Management: The security management functions include: User login authentication, Command authority restriction, Confirmation of crucial operation, User group management, Timeout locking.
e) Site monitoring: Data transmission channels are available for the monitoring equipment in the equipment room to facilitate attendance-free and centralized monitoring of the BTS3606.
f) Upgrade: Users can upgrade the system through remote loading. The upgrade process is retrievable, that is, the system can fall back to the original one when the upgrade fails.
g) Equipment operation and auto re-start.


4.3.2 System Structure:
-BTS3606 Specifications

-Cabinet Configuration:
The BTS3606 cabinet is configured with CDDU, combined subrack, power supply subrack, switch box, fan box, cable trough, and tool kit. The combined subrack is designed for installing CTRM/CHPA and baseband boards. The maximum capacity of a single BTS3606 cabinet is two carriers and three sectors, as shown in Fig15

Fig15. BTS3606 Cabinet


Fig15b. BTS3606 Cabinet (Symmetric View)

-Structure:
The BTS3606 system consists of baseband subsystem, Radio Frequency (RF) subsystem, power supply subsystem, and antenna and feeder subsystem, as shown in Fig. 16 below.







Fig16. BTS3606 System Structure


a) Baseband Subsystem: The baseband subsystem comprises the BCKM, the BCIM, and the CCPM.



Fig17. BTS3606 Baseband Subsystem
BCKM: BTS Control and Clock Module, BCIM：BTS Control Interface Module, CCPM：Compact-BTS Channel Process Module.
BCKM’s functions include: Call procedure control, Signalling processing, Resource management, Channel management, Cell configuration.
BCIM’s functions include: Providing multiple E1/T1 links, realizing the IMA/UNI protocol, Support ATM over Fractional E1/T1, Support 8E1.
CCPM’s functions include: In the forward direction, the CCPM completes the following functions: Encoding (including convolution code and turbo code) Interleaving, Spreading, Modulating, and Data multiplexing. In the reverse direction, the CCPM completes the following functions: Decoding, De-interleaving, De-spreading, Demodulating, Data demultiplexing. The CCPM also Connect to ODU3601C by optical port.
b) Radio Frequency Subsystem: The RF subsystem consists of the CTRM, the CHPA, the CDDU, and the CPCM.
CPCM’s functions include: Combine two high-power RF signals and performing backplane transfer of the CHPA alarm signals.
CDDU’s functions include: Provide duplex isolator and low band filter for two receiving and transmitting signals and Testing the coupling of transmitting and receiving signals.
CHPA’s functions include: RF power amplification, Over-temperature alarm, Over-excited alarm and Gain decrease alarm.

Fig18. BTS3606 RF Subsystem
CTRM’s functions include: In the reverse link, the CTRM receives the main and diversity RF signals from the antenna and feeder subsystem, and then changes them into baseband signals through down conversion, wave filtering and multiplexing. Finally the CTRM sends the baseband signals to the baseband subsystem. In the forward link, the CTRM receives the baseband signals from the baseband subsystem, and then changes them into RF signals through de-multiplexing, wave filtering and up conversion. Finally the CTRM sends the RF signals to the RF subsystem through the CDDU.
c) Antenna and Feeder Subsystem: The antenna and feeder subsystem of the BTS3606 includes two parts: the RF part and the satellite synchronization part.
- RF antenna and feeder: This part covers the transmitting and receiving antennas, and feeders. It transmits and receives signals on the air interface.
- Satellite synchronization antenna and feeder: This part includes the satellite signal receiving antenna, feeder, and lightning arrester. It receives synchronization signals from the satellites (GPS or GLONASS) to provide precise clock source for the BTS.
d) Power Supply Subsystem: Subsystem uses three PSUs in full configuration. The PSUs work in the 2+1 redundancy mode. Can use -48V dc input or +24 v DC input. Input voltage: -40VDC～-60VDC（only-48V input OUT voltage: +27V).
CHAPTER FIVE
RADIO UNIT AND ALARM MANAGEMENT
5.1 INTRODUCTION
The radio unit is found inside the shelter with the BTS. The radio model mostly used in Starcomm’s site is NERA Evolution Radio. The Evolution Series microwave radio is designed to transmit data rates from about 6 Mb/s to 600Mb/s, in the frequency bands 5 GHz to 38 GHz. The configuration of capacity and modulation is software configurable, giving an optimal balance between system gain and spectral efficiency. Available interfaces are: E1, T1, E3, DS3, STM-1/OC-3, STM-4/OC12, 100BASE-TX, Gigabit Ethernet. The Evolution Series products can be configured in two different modes, selected by the SW license namely: the METRO mode and the XPAND mode (ETSI).
5.2 FEATURES
The Evolution Series products can be configured in two different modes, selected by the SW license. The Universal IFU can easily be expanded from a single channel system up to a traffic node handling up to 8 ODUs. The Universal IFU contains the line interface, baseband processing and multiplexing, management and radio interfaces. The Universal IFU can easily be expanded from a single channel system up to a traffic node handling up to 8 ODUs. The Universal IFU contains the line interface, baseband processing and multiplexing, management and radio interfaces. The equipment configuration licences and the operating software version can be stored on the memory key available for plug-in, at the front of the equipment or downloaded to a computer. When a new Supervisory Unit is inserted, the equipment configuration can then easily be restored to the radio equipment.
5.3 SYSTEM DESCRIPTION
The Evolution Series microwave radio system comprises an indoor part (Universal IFU), and an outdoor unit (ODU) and an antenna. The
Universal IFU and ODU are interconnected using a coaxial cable which carries the transmit and receive user traffic, management communication between the Universal IFU and ODU, and the power supply to the ODU. In protected configurations, two cables are used; one for each ODU.
a) Interface Unit Description: The Evolution Series Universal IFU is a 1RU high modular unit, containing 9 plug-in slots for various modules. The modular architecture with plug-in slots enables a high degree of flexibility, easy upgrading/changing configurations and maintenance.



Fig19. Interface Unit
The Universal IFU Basic Frame is common in all configurations and up to four IFU frames can be stacked together by an IFU connection panel.
-When an SU is part of the IFU frame, it will always occupy slot 1. The Supervisory Unit is handling the configuration of all the system units as well as reporting system status to the NMS system.
-Slot 9 houses the FAN unit, handling the ventilation and temperature management of the IFU frame.
-Slot 2and 3 house the various user traffic interfaces and optional DXC unit. The PDH and Ethernet traffic interfaces are full height and cover the upper Aux/Serv. position as well.
-Slot 4 and 5 house the RIU unit(s). The RIU unit provides connection to the ODU and supplies power to the IFU Basic Frame with plug-in units and the ODU. If the DXC unit is used, slot 4 and 5 can be used for traffic interfaces as well.
-Slot 7-9 house any Auxiliary or Service Channel units, such as Alarm Unit, Wayside Traffic Unit, 64 kb/s Data Channels unit and EOW unit.
b) Outdoor Unit Description: The ODU hardware is capacity and modulation independent. It consists of a transceiver and a diplexer. The transceiver is tuneable over the whole frequency band, both high and low part. The diplexer determines the sub-band coverage. The ODU may be mounted directly to the
antenna. In HSB and 1+1/2+0 configurations an RF-coupler is used when connecting the ODUs to a single antenna interface. A pole mount interface is also available.
The ODU is made up of the diplexer and the transceiver joined together.



Transceiver Diplexer





ODU ODU identification label placed opposite side of Diplexer identification label
Fig20. ODU and its component parts

Configuration Examples: The Evolution Series equipment can be arranged in various system configurations by means of plug-in units and software licensing. The examples below show systems without the optional AUX plug-in units.
The different examples include:
METRO
1+0 (Unprotected)
1+0 Add-Drop Repeater w/Cross Connect
1+1 (Hot Standby)
1+1 (Hot Standby) - Dual Baseband
1+1 (Hot Standby) - Dual Antenna/Space Diversity
1+1 Frequency Diversity
1+1 Frequency Diversity - Dual Polarization
2+0 Dual Frequency - Single Polarization (DF-SP)
2+0 Single Frequency - Dual Polarization (SF-DP/CCDP)

XPAND
1+0 (Unprotected)
1+1 (Hot Standby)
1+1 (Hot Standby) - Dual Antenna/Space Diversity
1+1 Frequency Diversity
1+1 Frequency Diversity - Dual Polarization














Fig21. Different configuration of the ODU with the antenna



5.4 ALARM MANAGEMENT
It is important to find the defective unit in order to minimize time consumption for fault finding and traffic downtime. This is normally done based on alarms, meter readings and looping from Evolution Manager. The fault-
finding needs to be performed by skilled engineers. Positional problems are also related to installation of IFU-ODU cables and connectors. Alarms can be noticed at the front panel of the IFU. A red LED indicates alarm status on the unit. A blinking red LED indicates that the specific unit is placed in wrong slot according to "Unit Housekeeping". The alarm status can also be monitored from the Evolution Manager, Fault page. It is done by logging in to the radio through the computer with an RJ 45 cable and putting in the correct i.p address.
The most conversant alarms usually encountered in the IFU include: Alarm Indicator Signal (AIS), Loss Factor Signal (LSF), Remote End Fault (REF), Loss Of Contact (LOC), Link Failure, Tx low and high, Rx low and high, Configuration failure, High Bit Error Ratio (HBER), Low Bit Error ratio (LBER), ODU power failure, DEMOD Sync Loss, RF Input Loss, e.t.c.
Each is solved with strict observation and troubleshooting. At times it might lead to changing one or more of the IFU components or even the ODU. The ODU can also be aligned if need be to solve a problem. All replacements should be done with care.
5.5 TRANSMISSION PROBLEMS AND SOLUTIONS
Even as transmission goes on in mobile telecommunication, transmission problems are also encountered which lead to interference and call drops. Some of the problems encountered include:
Path Loss:
Path loss occurs when the received signal becomes weaker and weaker due to increasing distance between MS and BTS, even if there are no obstacles between the transmitting (Tx) and receiving (Rx) antenna. The path loss problem seldom leads to a dropped call because before the problem becomes extreme, a new transmission path is established via another BTS.
Shadowing:
Shadowing occurs when there are physical obstacles including hills and buildings between the BTS and the MS. The obstacles create a shadowing effect which can decrease the received signal strength.
When the MS moves, the signal strength fluctuates depending on the obstacles between the MS and BTS. A signal influenced by fading varies in signal strength. Drops in strength are called fading dips.
Rayleigh Fading:
This occurs when a signal takes more than one path between the MS and BTS antennas. In this case, the signal is not received on a line of sight path directly from the Tx antenna. Rather, it is reflected off buildings, for example, and is received from several different indirect paths. Rayleigh fading occurs when the obstacles are close to the receiving antenna. The received signal is the sum of many identical signals that differ only in phase (and to some extent amplitude). A fading dip and the time that elapses between two fading dips depend on both the speed of the MS and the transmitting frequency.
Time Dispersion:
Time dispersion is another problem relating to multiple paths to the antenna of either an MS or BTS. However, in contrast to Rayleigh fading, the reflected signal comes from an object far away from the Rx antenna. Time dispersion causes Inter-Symbol Interference (ISI) where consecutive symbols (bits) interfere with each other making it difficult for the receiver to determine which symbol is the correct one. An example of this is shown in the figure below where the sequence 1, 0 is sent from the BTS. If the reflected signal arrives one bit time after the direct signal, then the receiver detects a 1 from the reflected wave at the same time it detects a 0 from the direct wave. The symbol 1 interferes with the symbol 0 and the MS does not know which one is correct.
Time Alignment:
Each MS on a call is allocated a time slot on a TDMA frame. This is an amount of time during which the MS transmits information to the BTS. The information must also arrive at the BTS within that time slot. The time alignment problem occurs when part of the information transmitted by an MS does not arrive within the allocated time slot. Instead, that part may arrive during the next time slot, and may interfere with information from another MS using that other time slot. A large distance between the MS and the BTS causes time alignment. Effectively, the signal cannot travel over the large distance within the given time.
Solutions





CONCLUSION
During the course of the Industrial Training Program, I was able to achieve some of the objectives of the Students Industrial Work Experience Scheme (SIWES) programme. During the two months Industrial Training Programme, I was able to put into practice and observe some of the theoretical knowledge provided by the academic studies in the University.
I got to know the inevitability of mobile telecommunications and its numerous services in our daily activities. I got acquainted with network structure of Starcomms CDMA network. I was involved in alarm and traffic management. I learnt a great deal on the installation, maintenance, upgrade and repair of some of the equipment used in transmission.
The SIWES programme should be continued since through it, the students gain a lot of experience in terms of industrial activities and are better equipped to grapple with the challenges of the outside world. The knowledge so acquired from the SIWES programme will be of immense benefit to students in their various fields and career aspiration.