Pakistan Telecommunication

Company Limited

Internship Completion Report

Department

Of

Wireless Karachi

Submitted by: Muhammad Khalid Ansari

Student of

Sir Syed University of Engineering &

Technology, Karachi.

Internship letter no. TRG.15-66-2011

Submitted to: Mr. Israfeel

ES Operation, Wireless-I, Karachi

2

Executive Summary

This report presents the construction and working of PTCL wireless net-work. There are

a number of techniques to manage a wireless network and the one is adopted according to the

requirement. The technique being used by PTCL is CDMA which is an efficient technique to

handle a wireless network. The network can be widened using latest equipments since the need

of cellular communication is increasing day by day.

3

Contents

Background 4

Introduction 6

Cellular Fundamentals 7

BTS 7

BSC 8

MSC 8

PSTN 8

Communication Using Base Stations 8

A Call from a Mobile 8

A Call to a Mobile 8

Registration 8

Multiple Access Schemes 9

Code Division Multiple Access Scheme 9

CDMA capacity: single-cell case 13

Soft Handoff 14

Power Control 15

RAKE Receiver 15

Code Division Multiple Access Digital Cellular System (IS -95) 16

PTCL Structure 18

WLL (Wireless Local Loop) 19

D.R.S (Digital Radio System) 19

O.F (Optical Fiber) 19

Huawei BTS 3606e 20

BTS 36XX Brief 20

BTS 3606e Cabinet 21

BTS 3606e Functions 21

Specifications of Transmitters 22

BTS 3606e Structure 22

BTS 3606e Logical Structure 23

4

BTS 3606e Baseband Subsystem 23

BTS 3606e RF Subsystem 24

Connections of RF Subsystem 25

Power Supply Subsystem 25

Huawei BTS 3900 26

Components 26

BTS3900 Cabinet 27

BTS3900 Cabinet Structure 27

BTS 3900 Hardware consists of 27

Important Points 28

Call types 29

Conclusion 32

References 33

5

Background

Wireless communications is, by any measure, the fastest growing segment of the

communications industry. Cellular systems have experienced exponential growth over the last

decade and there are currently around many billion users worldwide. Indeed, cellular phones

have become a critical business tool and part of everyday life in most developed countries, and

are rapidly supplanting antiquated wire line systems in many developing countries. [1]

Wireless communication is one of the most vibrant areas in the communication field

today. While it has been a topic of study since the 1960s, the past decade has seen a surge of

research activities in the area. The research thrust in the past decade has led to a much richer set

of perspectives and tools on how to communicate over wireless channels, and the picture is still

very much evolving. [2]

Guglielmo Marconi invented the wireless telegraph in 1896.1 In 1901, he sent telegraphic

signals across the Atlantic Ocean from Cornwall to St. John's Newfoundland; a distance of about

3200 km. His invention allowed two parties to communicate by sending each other alphanumeric

characters encoded in an analog signal. Over the last century, advances in wireless technologies

have led to the radio, the television, the mobile telephone, and communications satellites. All

types of information can now be sent to almost every corner of the world. Recently, a great deal

of attention has been focused on satellite communications, wireless networking, and cellular

technology.

The cellular or mobile telephone is the modern equivalent of Marconi's wireless

telegraph, offering two-party, two-way communication. The first-generation wireless phones

used analog technology. These devices were heavy and coverage was patchy, but they

successfully demonstrated the inherent convenience of mobile communications. The current

generation of wireless devices is built using digital technology. Digital networks carry much

more traffic and provide better reception and security than analog networks. In addition, digital

technology has made possible value-added services such as caller identification. Newer wireless

devices connect to the Internet using frequency ranges that support higher information rates.

Figure 1 highlights some of the key milestones in the development of wireless

communications. Wireless technologies have gradually migrated to higher frequencies. Higher

frequencies enable the support of greater data rates and throughput. [

6

Figure 1: Some Milestones in Wireless Communications

7

Introduction

The earliest wireless networks used analog communication. The first cellular networks to

be developed were analog. The analog networks are often referred to as “first-generation”

cellular networks; the currently deployed digital networks are referred to as “second-generation”

networks. There are three principal types of second-generation networks in operation throughout

the world: GSM, D-AMPS or IS-136, and IS-95 or CDMA. [4]

PTCL is using Code-division multiple access (CDMA) principle for its V-fone and

eVo wireless broadband services. CDMA is the third type of multiple access technique used in

cellular systems. It is the access technique used in the second-generation system IS-95. [5].

CDMA is one of spread spectrum multiple access techniques.

Spread spectrum multiple access uses signals which have a transmission bandwidth that

is several orders of magnitude greater than the minimum required RF bandwidth. A pseudo-noise

(PN) sequence converts a narrowband signal to a wideband noise-like signal before transmission.

Many users can share the same spread spectrum bandwidth without interfering with one another.

There are two main types of spread spectrum multiple access techniques; frequency hopped

multiple access (FH) and direct sequence multiple access (DS). Direct sequence multiple access

is also called code division multiple access (CDMA).

In code division multiple access (CDMA) systems, the narrowband message signal is

multiplied by a very large bandwidth signal called the spreading signal. The spreading signal is a

pseudo-noise code sequence that has a chip rate which is orders of magnitudes greater than the

data rate of the message. All users in a CDMA system use the same carrier frequency and may

transmit simultaneously. Each user operates independently with no knowledge of the other users.

[6]. Thus, not only all users in the same cell share all the time-frequency degrees of freedom, so

do the users in different cells. Universal frequency reuse is a key property of CDMA systems.

[7]. CDMA with different forms of multiuser detection achieves the Shannon capacity of both

the uplink and the downlink, although the capacity-achieving transmission and reception

strategies for the two channels are very different. Finally, it is simple to allocate multiple

channels to one user with CDMA by assigning that user multiple codes. CDMA is used for

multiple access in the IS-95 digital cellular standards. [8]

8

Cellular Fundamentals

The area served by mobile phone systems is divided into small areas known as cells.

Each cell contains a base station that communicates with mobiles in the cell by transmitting and

receiving signals on radio links. The transmission from the base station to a mobile is typically

referred to as downstream, forward-link, or downlink. The corresponding terms for the

transmission from a mobile to the base are upstream, reverse-link, and uplink. Each base station

is associated with a mobile switching center (MSC) that connects calls to and from the base to

mobiles in other cells and the public switched telephone network.

A typical setup depicting a group of base stations to a switching center is shown in Figure

2. In this section, terminology associated with cellular systems is introduced with a brief

description to understand how these systems work.

Figure 2: A typical cellular system setup.

9

BTS

The Base Transceiver Station houses the radio transceivers that define a cell and handles

the radio-link protocols with the Mobile Station. In a large urban area, there will potentially be a

large number of BTSs deployed, thus the requirements for a BTS are ruggedness, reliability,

portability, and minimum cost.

BSC

The Base Station Controller manages the radio resources for one or more BTS. It handles

radio-channel setup, frequency hopping, and handovers, as described below. The BSC is the

connection between the mobile station and the Mobile service Switching Center (MSC).

MSC

Mobile services Switching Center (MSC). It acts like a normal switching node of the

PSTN or ISDN, and additionally provides all the functionality needed to handle a mobile

subscriber, such as registration, authentication, location updating, handovers, and call routing to

a roaming subscriber.

PSTN

It connects MSC to landline telephones and other mobile networks. Calls for landline and

other mobile networks are routed via PSTN.

Communication Using Base Stations

A base station communicates with mobiles using two types of radio channels, control

channels to carry control information, and traffic channels to carry messages. Each base station

continuously transmits control information on its control channels. When a mobile is switched

on, it scans the control channels and tunes to a channel with the strongest signal. This normally

would come from the base station located in the cell in which the mobile is also located. The

mobile exchanges identification information with the base station and establishes the

authorization to use the network. At this stage, the mobile is ready to initiate and receive a call.

A Call from a Mobile

When a mobile wants to initiate a call, it sends the required number to the base station.

The base station sends this information to the switching center that assigns traffic channel to this

call because the control channels are only used for control information. Once the traffic channel

10

is assigned, this information is relayed to the mobile via the base station. The mobile switches

itself to this channel. The switching center then completes the rest of the call.

A Call to a Mobile

When someone calls a mobile, the call arrives at the mobile switching center. It then

sends a paging message through several base stations. A mobile tuned to a control channel

detects its number in the paging message and responds by sending a response signal to the

nearby base station. The base station informs the switching center about the location of the

desired mobile. The switching center assigns a traffic channel to this call and relays this

information to the mobile via the base. The mobile switches itself to the traffic channel and the

call is complete.

Registration

A mobile is normally located by transmitting a paging message from various base

stations. When a large number of base stations are involved in the paging process, it becomes

impractical and costly. It is avoided by a registration procedure where a roaming phone registers

with an MSC closer to itself. This information may be stored with the switching center of the

area as well as the home switching center of the phone. The home base of the phone is the one

where it is permanently registered. Once a call is received for this phone, its home switching

center contacts the switching center where the phone is currently roaming. Paging in the vicinity

of the previous known location helps to locate the phone. Once it responds, the call may be

connected as discussed previously.

Multiple Access Schemes

The available spectrum bandwidth is shared in a number of ways by various wireless

radio links. The way in which this is done is referred to as a multiple access scheme. There are

basically four principle schemes. These are frequency division multiple access (FDMA), time

division multiple access (TDMA), code division multiple access (CDMA), and space division

multiple access (SDMA). [9]

11

Code Division Multiple Access Scheme

The CDMA scheme is a direct sequence (DS), spread-spectrum method. It uses linear

modulation with wideband pseudo noise (PN) sequences to generate signals. These sequences,

also known as codes, spread the spectrum of the modulating signal over a large bandwidth,

simultaneously reducing the spectral density of the signal. Thus, various CDMA signals occupy

the same bandwidth and appear as noise to each other. [10]

Figure 3: General Model of Spread Spectrum Digital Communication System

All users in a CDMA system, as seen from Figure 4, use the same carrier frequency and

may transmit simultaneously. Each user has its own pseudorandom codeword which is

approximately orthogonal to all other codeword. The receiver performs a time correlation

operation to detect only the specific desired codeword. All other codeword appear as noise due to

decorrelation. For detection of the message signal, the receiver needs to know the codeword used

by the transmitter. [11]

Each user spreads its signal over the entire bandwidth, such that when demodulating any

particular user’s data, other users’ signals appear as pseudo white noise. [12]

12

Downlinks typically use orthogonal spreading codes such as Walsh-Hadamard codes. Uplinks

generally use non-orthogonal. A non-orthogonal CDMA scheme also requires power control in

the uplink. [13]

It uses orthogonal and non-orthogonal codes on the uplink.

Figure 4: Code-Division Multiple Access.

This codeword is used both for spreading the signal at the time of transmission and

dispreading the signal at the time of reception. Cellular systems using CDMA schemes use FDD,

thus employing two frequency channels for forward and reverse links. On forward-link a base

station transmits to all users synchronously and this preserves the orthogonality of various codes

assigned to different users. The orthogonality, however, is not preserved between different

components arriving from different paths in multipath situations. On reverse-link each user

transmits independently from other users because of their individual locations. Thus, the

transmission on reverse link is asynchronous and the various signals are not necessarily

orthogonal. It should be noted that these PN sequences are designed to be orthogonal to each

other. In other words, the cross correlation between different code sequences is zero and thus the

signal modulated with one code appears to be orthogonal to a receiver using a different code if

the orthogonality is preserved during the transmission. This is the case on forward-link and in the

13

absence of multipath the signal received by a mobile is not affected by signals transmitted by the

base station to other mobiles.

On reverse link the situation is different. Signals arriving from different mobiles are not

orthogonalized because of the asynchronous nature of transmission. This may cause a serious

problem when the base station is trying to receive a weak signal from a distant mobile in the

presence of a strong signal from a nearly mobile. This situation where a strong DS signal from a

nearby mobile swamps a weak DS signal from a distant mobile and makes its detection difficult

is known as the “near–far” problem. [14]

The near-far problem occurs when many mobile users share the same channel. In general,

the strongest received mobile signal will capture the demodulator at a base station. In CDMA,

stronger received signal levels raise the noise floor at the base station demodulators for the

weaker signals, thereby decreasing the probability that weaker signals will be received. To

combat the near-far problem, power control is used in most CDMA implementations. Power

control is provided by each base station in a cellular system and assures that each mobile within

the base station coverage area provides the same signal level to the base station receiver. This

solves the problem of a nearby subscriber overpowering the base station receiver and drowning

out the signals of far away subscribers. [15]

Figure 5: CDMA Transmitter

14

Figure 6: CDMA Receiver

Figure 7: CDMA Forward Link

15

Figure 8: CDMA Reverse Link

CDMA capacity: single-cell case

In this section we show how one determines the capacity of a CDMA system, for the

simplest case of interference due to mobile users within a single cell only. Say there are K users

within the cell. Hence each user has K – 1 interfering users. We focus on the uplink, mobile to

BS, direction since this is the one in which communication is most difficult to control. All users

in this cell are assumed to be power controlled to have the same power PR as received at the BS.

If the number of users transmitting is large enough, each using its own pseudo-random code, it

may be assumed that the composite, interfering behavior approaches that of white Gaussian

noise. The basic problem then becomes that of detecting a signal in the presence of noise. It is

well-known from communication theory that the detectability of a (binary) signal in the presence

of white Gaussian noise (noise whose probability density function is Gaussian or Normal, and

whose frequency spectrum is flat) depends on the ratio of received signal bit energy Eb to noise

spectral density N0. In the case of mobile wireless communication, noise is usually small or even

negligible. It is the noise like interference power that dominates. This is the power due to the K −

16

1 interfering users, given by (K – 1)*PR. We thus use the signal bit energy to interference noise

power spectral density as a measure of signal detectability.

Since the bandwidth of the wideband coded CDMA signals is taken to be a value W Hz

>> 1/R, R the information bit rate, the power spectral density I0 of the interference, found by

dividing the interference power by the spectral bandwidth, is given by (K−1)PR/W. The received

signal bit energy is Eb=PR/R. The ratio Eb/I0, comparable with the signal bit energy-to-noise

spectral density Eb/N0 determining the detectability of signals in the usual communication theory

context, is thus given by

(1)

The larger the spreading gain W/R, the more users K can be accommodated. Given the desired

value of Eb/I0, based on an acceptable value of bit error probability, and the value of spreading

gain W/R possible in a specified system, the number of users that may be accommodated in a

cell, neglecting at this point interference from other cells, is, from (1) readily determined to be

K = (W/R)/ (Eb/I0) + 1 (2)

As an example, say Eb/I0 = 5 (or 7 dB), with the information bit rate

R = 10 kbps and the transmission bandwidth W = 1.25 MHz (the values selected for IS-95). Then

K = 26 users/cell may be accommodated within this 1.25 MHz bandwidth. The total number of

system users in the 25 MHz spectrum allocated to cellular systems in North America would then

be 20 × 26 = 520 users. Note that frequency reuse plays no role here in a CDMA system because

users are individually assigned pseudo-random codes and all frequencies are used in all cells;

this is the essence of universal frequency reuse made possible through the use of spread spectrum

CDMA technology. [16]

17

Universal frequency reuse means that users in all cells get the full bandwidth or degrees of

freedom of the system. [17]

Soft Handoff

In CDMA systems, since all the cells share the same spectrum, soft handoffs are possible:

multiple base-stations can simultaneously decode the mobile’s data, with the switching center

choosing the best reception among them (Figure 9). Soft handoffs provide another level of

diversity to the users.

Figure 9: Soft Handoff

In the process of soft handoff, the mobile is able to communicate with more than one

base station. It receives signals from more than one base station and the received signals are

combined after appropriate delay adjustment. Similarly, more than one station receives signals

from mobiles and the network combines different signals. This scheme is also known as

macroscopic diversity and is mostly employed by CDMA systems.

18

The soft handoff process is mobile-initiated and works like this. While a user is tracking

the downlink pilot of the cell it is currently in, it can be searching for pilots of adjacent cells

(these pilots are known pseudo-noise sequences shifted by known offsets). In general, this

involves timing acquisition of the adjacent cell as well. Since, timing acquisition is a

computationally very expensive step. Thus, a practical alternative is for the base-station clocks to

be synchronized so that the mobile only has to acquire timing once. Once a pilot is detected and

found to have sufficient signal strength relative to the first pilot, the mobile will signal the event

to its original base-station. The original base-station will in turn notify the switching center,

which enables the second cell’s base-station to both send and receive the same traffic to and from

the mobile. In the uplink, each base-station demodulates and decodes the frame or packet

independently, and it is up to the switching center to arbitrate. Normally, the better cell’s

decision will be used. [18]

Power Control

It is important that a radio receiver receives a power level that is enough for its proper

function but not high enough for this level to disturb other receivers. This is achieved with

maintaining constant power level at the receiver by transmitter power control. The receiver

controls the power of the transmitter at the other end. For example, a base would control the

power transmitted by mobile phones and vice versa.

It is done by a receiver monitoring its received power and sending a control signal to the

transmitter to control its power transmission as required. Sometimes a separate pilot signal is

used for this purpose. [19]

Power control is implemented at the base station by rapidly sampling the radio signal

strength indicator (RSSI) levels of each mobile and then sending a power change command over

the forward radio link. Despite the use of power control within each cell, out-of-cell mobiles

provide interference which is not under the control of the receiving base station. [20]

Power control reduces the near–far problem in CDMA systems and helps to minimize the

interference near the cell boundaries when used in forward-link. [21]

19

RAKE Receiver

In CDMA spread spectrum systems, the chip rate is typically much greater than the flat

fading bandwidth of the channel. Whereas conventional modulation techniques require an

equalizer to undo the inter symbol interference (ISI) between adjacent symbols, CDMA

spreading codes are designed to provide very low correlation between successive chips. Thus,

propagation delay spread in the radio channel merely provides multiple versions of the

transmitted signal at the receiver. If these multipath components are delayed in time by more

than one chip duration, they appear like uncorrelated noise at a CDMA receiver, and equalization

is not required. However, there is useful information in the multipath components. CDMA

receivers may combine the time delayed versions of the original signal transmission in order to

improve the signal to noise ratio at the receiver. A RAKE receiver does just this. It attempts to

collect the time-shifted versions of the original signal by providing a separate correlation

receiver for each of the multipath signals. The RAKE receiver, shown in Figure 4, is essentially a

diversity receiver designed specifically for CDMA, where the diversity is provided by the fact

that the multipath components are practically uncorrelated from one another when their relative

propagation delays exceed a chip period.

A RAKE receiver utilizes multiple correlators to separately detect the M strongest

multipath components. The outputs of each correlator are weighted to provide a better estimate

of the transmitted signal than is provided by a single component. Demodulation and bit decisions

are then based on the weighted outputs of the M correlators. [22]

20

Figure 10: RAKE Receiver

Code Division Multiple Access Digital Cellular System (Interim

Standard-95)

This system uses CDMA as a multiple access technique and occupies the same frequency

band as that occupied by AMPS; that is, the forward-link frequency band is from 869 to 894

MHz and the reverse-link band is from 824 to 849 MHz. Forward-link and reverse-link carrier

frequencies are separated by 45 MHz. Each channel in IS-95 occupies a 1.25-MHz bandwidth

and this is shared by many users. The users are separated from each other by allocating 1 of 64

orthogonal spreading sequences (Walsh functions). The user data are grouped into 20-ms frames

and are transmitted at a basic user rate of 9600 bps. This is spread to a channel chip rate of

1.2288 Mchip/s giving a spreading factor of 128.

RAKE receivers are used at both base station and mobiles to resolve and combine multipath

components.

21

During handoff the standard allows for base station diversity whereby a mobile keeps

link with both the base stations and combines signals from both the stations to improve signal

quality as it would combine multipath signals.

In forward-link a base station transmits simultaneously to all users using 1 of 64 spreading

sequences for each user once the user data are encoded using a half-rate convolution code and

are interleaved. All signals in a cell are also scrambled using a PN sequence of length 215 to

reduce the co-channel interference. During the scrambling process the orthogonality between

different users is preserved. The forward channel consists of 1 pilot channel, 1 synchronization

channel, up to 7 paging channels, and up to 63 traffic channels. The pilot channel transmits

higher power than other channels and is used by mobiles to acquire timing for forward channel

and to compare signal strength of different base stations. It also provides phase reference for

coherent detection.

The synchronization channel operates at 1200 bps and broadcasts a synchronization

message to mobiles. The paging channels are used to transmit paging messages from the base

station to mobiles and to operate at 9600, 4800, or 2400 bps. The traffic channels support

variable data rate operating at 9600, 4800, 2400, and 1200 bps.

On reverse channels, mobiles transmit asynchronously to the base, and orthogonally

between different users in a cell are not guaranteed. A strict control is applied to the power of

each mobile so that a base station receives constant power from each user, thus eliminating the

near–far problem. Power control command is sent by the base to mobiles at a rate of 800 bps.

The reverse channels are made up of access channels and reverse traffic channels. The reverse

channels contain up to 32 access channels per paging channel, operate at 4800 bps, and are used

by mobiles to initiate communication with base and to respond to paging messages. The reverse

traffic channel is a variable data rate channel and operates similar to the forward channels at

9600, 4800, 2400, and 1200 bps. [23]

Table 1: Comparative capacity, mobiles/cell, 1.25 MHz band

AMPS D-AMPS GSM IS-95

(analog) (TDMA) (TDMA) (CDMA)

6 18 12-13 4-96

22

PTCL Structure

BTS (Base Transceiver Station):

These are the site BTS located in coverage areas. These BTS provide link to users.

Hub BTS:

These are the BTS located at different PTCL exchanges. These BTS provide coverage to users

and also communicate with site BTS. The site BTS and Hub BTS are connected via microwave

link.

BSC (Base Station Controller):

It is the BSC located at Pak Capital exchange. It controls all Hub BTS and site BTS. Hub BTS is

connected to BSC via optical fiber.

MSC (Mobile Switching Centre):

It is the MSC located at Pak Capital exchange.

PSTN:

It is also located at Pak Capital exchange.

BTS

BTS

BTS

Hub BTS BSC MSC PSTN

23

WLL (Wireless Local Loop):

Wireless local loop (WLL), is a term for the use of a wireless communications link as

the "last mile / first mile" connection for delivering plain Old Telephone Service (POTS)

and/or broadband Internet to telecommunications customers. [24]. WLL is a system that connects

subscribers to the local telephone station wirelessly. It is an emerging access network technology

based on CDMA principle. This technology is useful for providing cost effective mobile services

and wireless telephone connection in areas where provision of landline telephone connection is

not feasible or where demand for mobile phones is very high.

There are two media of communication

D.R.S (Digital Radio System):

It is an unguided medium. It is used to communicate between site BTS and Hub BTS.

O.F (Optical Fiber):

It is a guided medium. It is used to transfer data from Hub BTS to BSC. Since Hub BTS

has many BTS data as well as PSTN data, it needs more medium bandwidth to send data which

cannot be achieved by DRS.

D.R.S elements

O.D.U (Outdoor Unit) ---capacity dependent

I.D.U (Indoor Unit) ---frequency dependent

I.F cable (Intermediate Frequency)

ODU is connected to parabolic dish. If you have more than one dish then we will connect ODU

alternatively, one horizontal and one vertical.

ODU consists of power amp, crystal oscillator.

ODU is connected to IDU through I.F cable

Polarization is very important

Vertical polarization is best.

Waves are transmitted by reflection, refraction and diffraction.

IDU does modulation and demodulation.

NEC equipments are best in world.

24

Huawei BTS 3606e:

BTS 36XX Brief

25

BTS 3606e Cabinet

BTS 3606e Functions

26

Specifications of Transmitters

BTS 3606e Structure

IDFU/CDDU

Baseband subrack RF subrack

Power Supply subrack

27

BTS 3606e Logical Structure

BTS 3606e Baseband Subsystem

28

BTS 3606e RF Subsystem

29

Connections of RF Subsystem

Power Supply Subsystem

30

Huawei BTS 3900:

Components

31

BTS3900 Cabinet

Cabinet size: H×W×D=900mm×600mm×450mm

Base size: H×W×D=400mm×600mm×420mm

Weight: 57kg(empty) /142kg(full configuration)

BTS3900 Cabinet Structure

Fully configured cabinet (-48VDC)

BTS 3900 Hardware consists of:

BBU

DRFU

DCDU-01

GATM

PMU

PSU

FAN BOX

32

The BBU3900 boards consist of the BSBC, UEIU, GTMU, and UELP; the BBU3900

modules consist of the UBFU and the UPEU.

The BSBC is the backplane of the BBU. The BSBC provides eight board slots,

two power slots, and one fan slot.

The universal environment interface unit (UEIU) supports multiple environment

monitoring signals. The UEIU supports eight Boolean alarm signals and two

RS485 environment monitoring signals.

The GSM transmission, timing, and management unit for BBU (GTMU) controls

and manages the entire BTS. It provides interfaces related to the reference clock,

power supply, OM, and external alarm collection.

The universal E1/T1 lightning protection unit (UELP) provides lightning

protection for four E1/T1 signals.

The universal BBU fan unit type A (2U) (UBFU) communicates with the GTMU

to regulate the temperature, adjust the fan speed, and report alarms. The UBFA

module is hot swappable.

The universal power and environment interface unit (UPEU) supports the –48V/

+24V DC power input, supplies power to the boards, modules, and fan in the

BBU, and provides access to multiple environment monitoring signals.

The DRFU performs modulation and demodulation between baseband signals and

RF signals, processes data, and combines and divides signals.

The direction current distribution unit (DCDU-01) provides -48V DC power of 10

outputs.

The GSM antenna and TMA control module (GATM) is a module that controls the

antenna and TMA. The GATM is optional.

The direction current distribution unit (DCDU-01) provides -48V DC power of 10

outputs.

The PMU manages the power supply and batteries. The PMU is the core of the

power monitoring system.

The fan box regulates the temperature at the air inlet of the cabinet and in the fan

box. It can adjust the rotation speed of the fans to implement ventilation and

dissipation for the cabinet. [25]

33

Conclusion

The aim of the internship was to gain the knowledge of working of PTCL wireless

services. It is known that PTCL wireless network services, V-fone and eVo wireless broadband

internet, is working on CDMA principle. CDMA has greater capacity than FDMA and TDMA;

in essence it is an efficient technique. PTCL is using equipments of Chinese manufacturers.

Mostly used equipments are manufactured by Huawei. PTCL is replacing old equipments by new

equipments to provide better services to their customers.

34

References

[1], [8], [13], Wireless Communications - Andrea Goldsmith

[2],[7], [12], [17], [18], Fundamentals of Wireless Communication - David Tse and Pramod

Viswanath

[3]Wireless Communications and Networks, Second Edition - William Stallings

[4], [5], [16], Mobile Wireless Communication – Mischa Schwartz

[6], [11], [15], [20], [22] Wireless Communications – Theodore S. Rappaport

[9], [10], [14], [19], [21], [23], Handbook of Antenna and Wireless Communication - Lal Chand

Godara

[24] Wikipedia.org

[25] All information and snapshots are taken from Huawei sources.