8/6/2019 DB4----FINAL

1/49

Introduction to CDMA

What is CDMA? Code Division Multiple Access (CDMA) is a digital technology pioneered byQUALCOMM that provides crystal clear voice quality in a new generation of wireless

communications products and services. Bandwidth of CDMA is 824MHz to 849MHz for

uplink and 869MHz to 894MHz for downlink. Using digital encoding and "spreadspectrum" Radio Frequency (RF) techniques, CDMA provides better and more cost

effective:

Voice quality

Privacy

System capacity

Flexibility

than other wireless technologies. CDMA also provides enhanced services such as:

Short messaging

E-mail

Internet access

CDMA and other wireless communication have become very popular in the last few

years, but people have been trying to accomplish the goals of wireless telecomm. Sinceshortly after the invention of the telephone.

While designing communication system, the main points to be considered are:

Capacity Delay

Error detection/correction.

Capacity concerns how much information you can deliver from the source to the

destination. Delay issues are those involving delivery of information in the shortest time.Error detection/correction is a method to reduce errors in the delivery of information.

Think about problems you may have experienced due to these issues. For example, there

may be a capacity problem in your carrier's system if you experience trouble placing acall.

Multiple Access Systems: -

Wireless telecommunications has dramatically increased in popularity, resulting in the

need for technologies that allow multiple users to share the same frequency. These arecalled "multiple access systems." The three types of multiple access system are:

1) Frequency Division Multiple Access (FDMA)

2) Time Division Multiple Access (TDMA)

3) Code Division Multiple Access (CDMA)

1

8/6/2019 DB4----FINAL

2/49

Frequency Division Multiple Access (FDMA)Each FDMA subscriber is assigned a specific frequency channel. No one else in the same

cell or a neighboring cell can use the frequency channel while it is assigned to a user.

This reduces interference, but severely limits the number of users.

Time

Division Multiple

Access (TDMA)TDMA users share a

common frequencychannel, but use the

channel for only a very

short time. They are each given a time slot and only allowed to transmit during that timeslot. When all available time slots in a given frequency are used, the next user must be

assigned a time slot on another frequency. These time slices are so small that the human

ear does not perceive the time slicing.

Code Division Multiple Access (CDMA)CDMA users share a common frequency channel. All users are on the same freq.

at the same time. However, each pair of users is assigned a special code thatreduces interference while increasing privacy.

2

8/6/2019 DB4----FINAL

3/49

Features of CDMA: -

The following features are unique to CDMA technology:

Universal frequency reuse

Fast and accurate power control

Rake receiver

Different types of handoff

Frequency reuseThe frequency spectrum is a limited resource. Therefore, wireless telephony,

like radio, must reuse frequency assignments. For example, two radio stations might

transmit at 91.3 FM. There is no interference as long as the radio stations are far enough

apart.

Cell interference: -

Cell A and B of a conventional, analog system are using the same frequency.The area of overlap, area C, has a frequency conflict and interference. This is similar to

what you experience when you are driving between the broadcast zones of two radio

stations transmitting at the same frequency.

FDMA and TDMA frequency reuse planning

3

8/6/2019 DB4----FINAL

4/49

A frequency (channel) can be used again within an FDMA or TDMA

network, but an appropriate distance must separate cells using the same frequency.

Adjacent cells must be assigned a different set of frequencies. For example, a cell usingfrequency A must not be adjacent to another cell using frequency A. As a result, each cell

site in the site is able to use only 1/7 of the possible frequencies.

CDMA frequency reuse planning

Each BTS in a CDMA network can use all available frequencies. Adjacent

cells can transmit at the same frequency because code channels, not frequency channels,separate users. This feature of CDMA, called "frequency reuse of one, eliminates the

need for frequency planning.

Power control

4

8/6/2019 DB4----FINAL

5/49

Power control is a CDMA feature that enables mobiles to adjust the power

at which they transmit. This ensures that the base station receives all signals at the

appropriate power. The CDMA network independently controls the power at which eachmobile transmits. Both forward and reverse links use power control techniques.

Why power control is neededIf all mobiles transmitted at the same power level, the base station would

receive unnecessarily strong signals from mobiles nearby and extremely weak signals

from mobiles that are far away. This would reduce the capacity of the system. Thisproblem is called the near-far problem.

Reverse link power control

Reverse link power control consists of two processes: Open loop

Closed loop

Open loop is an initial estimate of the power the mobile needs to transmit to the BTS.

Closed loop is a refinement of the open loop estimate.

Open loop power control

5

8/6/2019 DB4----FINAL

6/49

Open loop is the mobile's estimate of the power at which it should transmit.

The open loop estimate is based on the strength of the pilot signal the mobile receives. As

the pilot signal gets weaker or stronger, the mobile adjusts its transmission strengthupwards or downwards. Open loop is used any time the mobile transmits

Closed loop power control

In closed loop, the BTS sends a command to the mobile to increase or

decrease the strength at which it is transmitting. The BTS determines this commandbased on the quality of the signal it receives from the mobile. Closed loop is only used

during a call. Closed loop commands are sent on the forward traffic channel.

Forward link power controlThe BTS independently adjusts the power for each forward traffic channel

based on the information it receives from the mobile.

Rake ReceiverThe rake receiver is a CDMA feature that turns what is a problem in other

technologies into an advantage for CDMA. Signals sent over the air can take a direct path

to the receiver, or they can bounce off objects and then travel to the receiver. Thesedifferent paths, called multi-paths, can result in the receiver getting several versions of

the same signal but at slightly different times. Multi-paths can cause a loss of signal

through cancellation in other technologies.

6

8/6/2019 DB4----FINAL

7/49

CDMA's rake receiver is a multiple receiver in one. The rake receiver identifies the three

strongest multi-path signals and combines them to produce one very strong signal. The

rake receiver therefore uses multipath to reduce the power the transmitter must send.Both the mobile and the BTS use rake receivers.

Handoff in CDMAHandoff is the process of transferring a call from one cell to another. This is

necessary to continue the call as the phone travels. CDMA is unique in how it handles

handoff. CDMA has three primary types of handoff: 1)Hard,(2) Soft (3) IdleThe type of handoff depends on the handoff situation.

Soft handoffA soft handoff establishes a connection with the new BTS prior to breaking

the connection with the old one. This is possible because CDMA cells use the same

frequency and because the mobile uses a rake receiver. The CDMA mobile assists thenetwork in the handoff. The mobile detects a new pilot as it travels to the next coverage

area. The new base station then establishes a connection with the mobile. This newcommunication link is established while the mobile maintains the link with the old BTS.

Soft handoffs are also called "make-before-break."

Variations of the soft handoff: -

There are two variations of soft handoffs involving handoffs betweensectors within a BTS:

Softer

Soft-softer

7

8/6/2019 DB4----FINAL

8/49

The softer handoff occurs between two sectors of the same BTS. The BTS

decodes and combines the voice signal from each sector and forwards the combined

voice frame to the BSC. The soft-softer handoff is combination handoff involvingmultiple cells and multiple sectors within one of the cells.

CDMA hard handoff

A hard handoff requires the mobile to break the connection with the old BTS

prior to making the connection with the new one. CDMA phones use a hard handoffwhen moving from a CDMA system to an analog system because soft handoffs are not

possible in analog systems. A Pilot Beacon Unit (PBU) at the analog cell site alerts the

phone that it is reaching the edge of CDMA coverage. The phone switches from digital to

analog mode as during the hard handoff. Hard handoffs are also called "break-before-make."

The CDMA hard handoff may be used when moving from a CDMA network

to an analog one. It may also be used when moving to a different:

RF channel

MTSO (Mobile Telephone Switching Office)

Carrier

Market

Analog to CDMA handoff is not available due to the limitations of analog technology.

CDMA idle handoff

An idle handoff occurs when the phone is in idle mode. The mobile will

detect a pilot signal that is stronger than the current pilot. The mobile is always searching

for the pilots from any neighboring BTS. When it finds a stronger signal, the mobilesimply begins attending to the new pilot. An idle handoff occurs without any assistance

from the BTS.

8

8/6/2019 DB4----FINAL

9/49

TDMA and FDMA handoffTDMA and FDMA systems use a hard handoff when the mobile is moving

from one cell site to another. These technologies do not allow for any type of make-

before-break handoff. A hard handoff can increase the likelihood of a dropped call.

Advantages of CDMA

CDMA technology has numerous advantages including:

Coverage

Capacity

Clarity Cost

Customer satisfaction

Coverage CDMA's features result in coverage that is between 1.7 and 3 times that of TDMA:

Power control helps the network dynamically expand the coverage area. Coding andinterleaving provide the ability to cover a larger area for the same amount of available

power used in other systems.

Capacity: -CDMA capacity is ten to twenty times that of analog systems, andit is up to four times that of TDMA. Reasons for this include:

9

8/6/2019 DB4----FINAL

10/49

CDMA's universal frequency reuse

CDMA users are separated by codes, not frequencies

Power control minimizes interference, resulting in maximized capacity. CDMA's soft handoff also helps increase capacity. This is because a soft handoff

requires less power.

Clarity: -Often CDMA systems can achieve "Wire line" clarity because ofCDMAs strong digital processing. Specifically:

The rake receiver reduces errors

The variable rate vocoder reduces the amount of data transmitted per person,reducing interference.

The soft handoff also reduces power requirements and interference.

Power control reduces errors by keeping power at an optimal level.

CDMA's wide band signal reduces fading.

Encoding and interleaving reduce errors that result from fading.

Cost: - CDMAs better coverage and capacity result in cost benefits: Increased coverage per BTS means fewer are needed to cover a given area. This

reduces infrastructure costs for the providers.Increased capacity increases the service provider's revenue potential.

CDMA costs per subscriber has steadily declined since 1995 for both cellular and

PCS applications.

Customer satisfaction: -CDMA results in greater customer satisfaction because CDMA provides better:

Voice quality

Longer battery life due to reduced power requirements

No cross-talk because of CDMA's unique coding

Privacy--again, because of coding.

Security because of coding.

10

8/6/2019 DB4----FINAL

11/49

Difference between CDMA and GSM: -

Topic CDMA GSM

CapacityHigher spectral efficiency than

GSM/TDMA/analog

Higher spectral efficiency than

analog

CoverageInherently sensitive receiver implies

excellent cell range

Limited by lesser receiver

sensitivity

Fraud Very secure network Secure network

Frequency

Planning

N=1 frequency reuse pattern nearly

eliminates frequency planning

N=7 frequency reuse patternrequires standard frequency

planning

Spectral

EfficiencyVery High Low

PrivacyAir interface security prevents

eavesdropping

Air interface security prevents

eavesdropping

Frequency

Diversity

Spread spectrum provides frequency

diversity

Possible through slow frequency

hopping

PathDiversity

Favorably utilizes multi-path to enhanceoverall signal quality (via rake receivers)

Susceptible to signal degradationdue to multi path interference

Call Stability-

Handovers

Hard, Soft and Softer Handovers Hard handovers

Make before break for soft/softer

handoversBreak before make

Power

Control

Key to achieving multi-fold capacity

gains over other tech.

Key to extending life of mobiles

battery

Technique of Spreading: -

11

8/6/2019 DB4----FINAL

12/49

CDMA is a digital wireless air interface and networking standard based on the

principle of spread-spectrum techniques, which allow multiple users to access thesystem simultaneously on the same carrier frequency.

CDMA is a method in which users occupy the same time and frequency

allocations, and are channelized by unique assigned codes. The signals are separated

at the receiver by using a correlator that accepts only signal energy from the desired

channel. Undesired signals contribute only to noise. The technique of spreading theuser waveform with code is called Spread spectrum.

Why Spreading? Spread spectrum multiple access transmits the entire signal over a bandwidth that

is much greater than that required for standard narrow band transmissions in order to

gain signal-to-noise (S/N) performance.

In channels with narrowband noise, increasing the transmitted signal bandwidth

results in an increased probability that the received information will be correct.Because each signal is a compilation of many smaller signals at the fundamentalfrequency and its harmonics, increasing the frequency results in a more accurate

reconstruction of the original signal.

The effective drawback of narrowband data communications is the limitation of

bandwidth; thus signals must be transmitted with enough power so the corruption bygaussian noise isn't as effective and the probability that the data received is correct

will remain low. This means that the effective SNR must be high enough so that the

receiver can recover the transmitted code without error.

From a system viewpoint, the performance increase for very wideband systems is

referred to as "process gain". This term is used to describe the received signal fidelity

gained at the cost of bandwidth. The signal may be spread over a large bandwidthwith smaller spectral power levels and still achieve the required data rate.

Two Types of spread spectrum technique:

Frequency Hopping (FH)

Direct Sequence (DS)

In frequency hopping, the carrier frequency in frequency hopping is changed very

rapidly. The frequency is changed rapidly, in a pseudorandom sequence.

In Direct Sequence the narrowband signal is spread and we're going to spread that signal

using a wide bandwidth pseudonoise sequence, or a code sequence. Also known as PNcodes, pseudonoise codes.

Tata Tele Services uses Direct Sequence Spread Spectrum technique for spreading the

signal.

DS-SS: -

12

8/6/2019 DB4----FINAL

13/49

CDMA technology focuses primarily on the "direct sequence" method of spread

spectrum. Direct sequence is spread spectrum technique in which the bandwidth of asignal is increased by artificially increasing the bit data rate. This is done by breaking

each bit into a number of sub-bits called "chips".

Assuming this number is 10, each bit of the original signal would be divided up

into 10 separate bits, or "chips." This results in an increase in the data rate by 10. Byincreasing the data rate by 10, we also increase the bandwidth by 10.

The signal is divided up into smaller bits by multiplying it by a Pseudo-Noise

code, PN-code. A PN-code is a sequence of high data rate bits ("chips").

Spread the narrowband signal with a code; (that code must be known by the

receiver). And with the receiver knowing that code, the original information cane be

extracted.

Methods for spreading the bandwidth of the transmitted signal over a spectrum, or

band of frequencies, much wider than the minimum bandwidth required to transmitthe signal.

Spreading is often used to:-Reduce the effect of jamming (intentional interference)

-Reduce effect from other interference.e.g narrow band transmitter, other spreadspectrum transmitters.

Traditional technologies try to squeeze signal into minimum required bandwidth.

Direct Sequence Spread Spectrum: -

CDMA is a multiple access scheme where users are identified by codes. Commercial

CDMA systems use Direct Sequence Spread Spectrum (DS-SS)

13

8/6/2019 DB4----FINAL

14/49

In DS-SS, the transmitter spreads the signal power over a wide bandwidth using a

unique code. The receiver de-spreads the signal using a synchronized version of thespreading code

During the spreading of a signal, it is multiplied by a random Pseudorandom Noise

signal (sequence) at a rate higher than the source data rate. As it is well known that

when the transmission data rate is increased in time domain that means the bitduration is decreased, which is equivalent to an increase of bandwidth in the

frequency domain.

The main parameter in spread spectrum systems is the processing gain: the ratioof transmission and information bandwidth. The processing gain defines how much

spreading is applied to the signal.

Spreading: Source signal is multiplied by a PN signalProcessing Gain: Chip Rate / Data Rate.

Despreading: Spread signal is multiplied by the spreading code

In digital systems the energy per bit needs to be a certain level above the totalinterference density in order to detect the transmitted bit. This is referred to as Eb/Io.

The receiver performance depends on Eb/No. The effective noise, No, is theresidual interference caused by other users at the de-spreader output. No fluctuates

with time depending on who is transmitting during the frame. Different users canoperate at different data rates with different frame activities.

Major factors that impact Eb/No values are as follows:

Desired FER performance, Subscriber Speed, Delay spread, TX and Rx DiversityMethods.

Introduction to CDMA signal

The words Code and Division are important parts of how CDMA works.CDMA uses codes to convert between analog voice signals and digital signals. CDMA

also uses codes to separate (or divide) voice and control data into data streams called

Channels. These digital data streams channels should not be confused with frequency

channels.

Generating a CDMA signal Analog to Digital conversion.

Vocoding

Encoding and interleaving.

Channelizing the signal.

Conversion of the digital signal to RF signal.

The use of codes is the key part of this process. The block diagram and the required

components for generating the CDMA signal are as shown in figure 1.

14

8/6/2019 DB4----FINAL

15/49

1. Analog to Digital Conversion: -The first step of CDMA signalgeneration is analog to digital conversion. CDMA uses a technique called pulse code

modulation (PCM) to accomplish A/D conversion.

2. Vocoder: -The second step of CDMA signal generation is voice compression.CDMA uses a device called a vocoder to accomplish voice compression. The term

Vocoder is a contraction of the words voice and code.

Vocoder is located at the BSC and in the phone. People pause between syllables and

words when they talk. Thus CDMA takes advantage of these pauses in speech activity byusing a variable rate vocoder.

Variable Rate Vocoder:A CDMA vocoder varies compression of the voice signal into one of four data

rates based on the rate of the users speech activity. The four rates are:

Full 9.6Kbps

4.8Kbps

2.4Kbps1/8 1.2Kbps

The vocoder uses its full rate when a person is talking very fast. It uses the 1/8 rate whenthe person is silent.

3. Encoding and Interleaving: -Encoders and interleavers are built into theBTS and the phones. The purpose of the encoding and interleaving is to build a

redundancy into the signal so that information lost in transmission can be recovered.The type of encoding done at this stage is called Convolutional Encoding. A

simplified encoding scheme is shown below:

15

8/6/2019 DB4----FINAL

16/49

Bit A B C D

Encoded Symbol A A A B B B C C C D D D

Error A A A B B ? ? ? C D D D

Decoded Bits A B ? D

A digital message consists of four bits (A, B, C, D) of vocoded data. Each bit is repeated

three times. These encoded bits are called symbol.. The decoder at the receiver uses amajority logic rules.

4. Interleaving: Interleaving is a simple but powerful method of reducing theeffect of burst errors and recovering lost bits. In this example shown here the symbolsfrom each group are interleaved in a pattern that the receivers know.

Bit A B C D

Symbol AAA BBB CCC DDD

Interleaved ABC DAB CDA BCD

Symbol

Errors ABC D?? ??A BCD

Deinterleaved A?A B?B C?C D?D

Decoded bits A B C D

5. Channelizing: - The encoded voice data is further encoded to separate it fromother encoded voice data. The encoded symbols are then spread over the entire

bandwidth of the CDMA channel. This process is called Channelization.

CDMA Channels: -

16

8/6/2019 DB4----FINAL

17/49

CDMA Physical Channel: -

CDMA physical channel is 1.25MHz wide. All users in a cell share same physical

channel. All cells in a CDMA system may use the same frequency. Forward and reversechannels are separated by 45MHz.

CDMA Logical Channels: -CDMA logical channels are uniquely identified by digital codes. All logical channelsshare same physical channel

Different Channels: -

Forward Link

Channels:

The forward link usesfour types of channels

to transmit voice and

control data to themobile. The types of

forward link channels

are:

1) Pilot Channel:

The BTS

constantly transmitsthe pilot channel. The mobile uses the pilot signal to acquire the system. It then uses the

pilot signal to monitor and adjust the power needed in order to transmit back to the BTS.Provide a reference signal for all MSs that provides the phase reference for COHERENT

demodulation 4-6 dB stronger than all other channels. Walsh code 0 is used for pilotchannel. It provides unique reference clock, which is attained by GPS from satellite.

2) Sync Channel:

The BTS constantly transmits over the sync channel so the mobile cansynchronize with the BTS. It provides the mobile with the system time and the

identification number of the cell site. The mobile ignores the sync channel after it is

synchronized. Synchronization is provided by phase locked loop.Used to acquire initialtime synchronization Synch message includes system ID (SID), network ID (NID), the

offset of the PN short code, the state of the PN-long code, and the paging channel datarate (4.8/9.6 Kbps). W32 is used for Sync channel.

3) Paging Channel:

CDMA uses up to seven paging channels. The paging channel transmits overheadinformation such as commands and pages to the mobile. The paging channel also sends

commands and traffic channel assignment during call setup. The mobile ignores the

paging channel after a traffic channel is established. Used to page the MS in case of an

17

8/6/2019 DB4----FINAL

18/49

incoming call, or to carry the control messages for set up Uses W1-W7 There is no power

control Additionally scrambled by PN long code, which is generated by LFSR of length

42 The rate 4.8 Kbps or 9.6Kbps. One paging channel can give signaling to 32 users.

4) Forward Link Traffic Channels:

CDMA uses between 55 and 61 forward traffic channels to send both voice andoverhead control data during a call. Once the call is completed, the mobile tunes back in

to the paging channel for commands and pages. Also carry power control bits for the

reverse channel.

Reverse Link Channels:The reverse link uses two types of channels to transmit voice and control data to

the BTS. The types of reverse link channels are:1) Access Channel:

The mobile uses the access channel when not assigned to a traffic channel. The

mobile uses the access channel to:

Originate the calls Respond to pages and commands from the base station

Transmit overhead messages to the base station.

2) Reverse Link Traffic Channel:

The reverse traffic channel is only used when there is a call. The reverse traffic

channel transmits voice data to the BTS. It also transmits the overhead controlinformation during the call.

Call Processing Stages: -

There are four stages or modes in CDMA call processing:

1) Initialization Mode: During initialization, the mobile:- Acquires the system via the Pilot Code Channel

- Synchronizes with the system via the Sync Code Channel.

2) Idle Mode: The mobile is not involved in a call during idle mode, but it must stayin communication with the base station:

- The mobile and the base station communicate over the access and pagingcode channels.

The mobile obtains overhead information via the paging code channel.

3) Access Mode: The mobile accesses the network via the Access code channelduring call origination. The Access channel and Paging channel carry the required

call setup

communication between the mobile phone and the BTS until a traffic channel isestablished.

4) Traffic Mode: During a Land To Mobile (LTM) call:

The mobile receives a page on the paging channel

18

8/6/2019 DB4----FINAL

19/49

The mobile responds on the access channel.

The traffic channel is established and maintained throughout the call.

During a Mobile To Land (MTL) call:

The call is placed using the Access channel.

The base station responds on the paging channel.

The traffic channel is established.

Codes Used in CDMA system: -

CDMA uses three different Codes:(i) Walsh Codes

(ii) PN Short Codes and

(iii) PN Long Codes

1.Walsh Codes: -This type of coding is used in forward link. Walsh codes provide a means touniquely identify each user on the forward link. Walsh codes have a unique mathematicalproperty they are orthogonal. In other words, Walsh codes are unique enough that the

voice data can only be recovered by a receiver applying the same Walsh code. All other

signals are discarded as background noise. The Walsh code is 64 chips long; it's asequence of 64 chips, 1s and 0s, that repeats after every 64 chips.

Generation of Walsh codes: - Starting with a seed of 0 and same bit in horizontally and same bit vertically

while complements in diagonally generates orthogonal codes. This process is to be

continued with newly generated block until the desired codes with proper length aregenerated. So in this way we will get total 64-walsh codes each have 64 bit long. Walsh

codes are used in the forward CDMA link to separate users. In any given sector, each

forward code channel is assigned a distinct Walsh code. The process is shown on next

page.

0 0 0 00 00

01 010 1 00 11

01 10

0000 0000

0101 01010011 0011

0110 0110

19

8/6/2019 DB4----FINAL

20/49

0000 1111

0101 10100011 1100

0110 1001

00000000 00000000

01010101 01010101

00110011 00110011

01100110 0110011000001111 00001111

01011010 01011010

00111100 00111100

01101001 01101001

00000000 11111111

01010101 10101010

00110011 11001100

01100110 1001100100001111 11110000

01011010 10100101

00111100 1100001101101001 10010110

And so on up to 64 bits horizontally and vertically as shown in the Figure

64 bit Walsh codes (providing 64 bit orthogonal codes) are used to provide 64 channels

within each frequency band. They are used for spreading in the forward link. In thereverse link it is used to provide orthogonal modulation but not spreading to the full

1.2288 Mcps rate. The specific Walsh function on to which the data is modulated defines

the forward link channelization.1. Pilot Channel (always used Walsh code W0)

Mobile acquires phase, timing and signal strength via the pilot channel.

2. Paging Channel (use Walsh codes W1-W7)

Mobile gets system parameters via the paging channel.

3. Sync Channel (always uses Walsh code W32)Mobile synchronizes via the sync channel.

4. Traffic Channel (use Walsh codes W8-W31 and W33- W63)

Mobile and BTS communicate over the traffic channels during a connection.

20

8/6/2019 DB4----FINAL

21/49

Walsh sequences are also referred to as Wash Functions. These codes are

generated at 1.2288 Mbps (Mcps) with a period of approximately 52 s as illustrates

below. These are used to identify users on the forward link. For this reason they are alsoreferred to as either Walsh Channels or TCH. All base stations and mobile users have

knowledge of all Walsh codes.

Walsh Code generator Rate = 1.2288 Mcps

Time duration for the one Chip = 1/1.2288 Mcps= 0.813 micro second

Total 64 chips are in one Walsh code so time between two Walsh code generations

= 0.813* 10-6 * 64

= 52.08 * 10-6 Second

What is Correlation

Correlation is a Measure of how well a given signal matches a desired code.The desired code is compared to the given signal at various test times.

Orthogonal Spreading and De-Spreading: -

The principle behind spreading and de-spreading is that when a symbol is

XORed with a known pattern and the result is again XORed with the same pattern, theoriginal symbol is recovered. Hence, the effect of XOR operation if performed twice

using the same code is null. In orthogonal spreading, each encoded symbol is XORed

with 64 chips of the Walsh code.

Recovery of Spread Symbol

At the receiver side the signal is de-spreads using the same Walsh code used atthe transmitter side. Under no Noise conditions, the symbols or digits are completelyrecovered without any error. But, the channel is not noise free. So, cdmaOne systems

employ FEC (Forward Error Control) techniques to combat effects of noise and enhance

the performance of the systems. When the wrong Walsh sequence is used for dispreading,the resulting correlation yields an average of zero. This is a clear demonstration of the

advantage of the orthogonality property of the Walsh codes. Whether the wrong code is

by receiver or other users attempting to decode the received signal, the resultingcorrelation is always zero.

21

8/6/2019 DB4----FINAL

22/49

Figure 5

Recovering data using correct function

Rx Data 1001 0110 0110 1001 1001 XORFunction 0110 0110 0110 0110 0110

1111 0000 0000 1111 1111Recovered Data 1 0 0 1 1

Recovering data using incorrect function

Rx Data 1001 0110 0110 1001 1001 XOR

Function 0101 0101 0101 0101 0101

1100 0011 0011 1100 1100

Recovered Data ? ? ? ? ?

Pseudo random Noise (PN) code: - PN code has randomness properties. If the current state and the generating

function of the PN code are known, the Future state of the code can be predicted. InCDMAOne system each base stations and all mobile in that base station use same set of

three PN sequence (two short codes and one long code).

2. Short code: -Two short code I and Q are used in CDMAOne. We have total

215 = 32,768 codes.

22

Received

Tim

Correlation =

Correlation =

Correlation =

Correlation =

8/6/2019 DB4----FINAL

23/49

They are generated at the rate of 1.2288Mcps. So after

32768/1.2288* 106 =26.67ms

The code will repeat itself. Unique PN offset serve as identifiers for a cell or a sector. InCDMAOne there are 32768/64 = 512

Total offset each have 64 bits long. So total effective offset in one cell would be 512/3 =

170.

3. Long Code: -One long code of length 242 = 4400 billion are used in CDMAOne system. It is used forspreading and scrambling. They are generated at the rate of 1.2288Mcps. So after

4398046511104/1.2288*106 = 3579139.4133 second

or 42 days (35791.4133/24*60*60) the code will repeat itself.

Generation of PN codes: -

The most important element in the transmitter and receiver in a CDMA

system is the PN sequence generator, which is used for spreading and de-spreadingsignals.

The PN sequence has a random set of words, which repeat after a specificsequence length. Pure sequence is highly predictable and a pure random signal makes

it difficult even for the desired receiver to recover the signal. Hence, the PN sequenceis the best choice.

Masking is used to produce offsets in both the short codes and long code. Theoffsets of the short PN codes are used to uniquely identify the forward channels of the

individual sectors or cells. The offsets of the Long code are used to separate code

channels in the reverse direction.

PN Offset Masking: Masking provides the shift in time for

PN codes. Different masks correspond to different time shifts. In cdmaOne systems,ESN are used as masks for used on the Traffic code channel.

If the current state and the generating function of the PN code are known,

the Future state of the code PN codes mimic randomness properties can be

predicted. In cdmaOne system each base stations and all mobile in that base stationuse same set of three PN sequences (two short codes and one long code).

23

8/6/2019 DB4----FINAL

24/49

Forward Channel

Generation: -

The forward link uses the frequency spectrum 824-849 MHz. Each carrier in

forward link channel is of 1.25MHz wide. Each channel is separated using different

spreading codes. QPSK is the modulation scheme used in forward channel.

After orthogonal codes, they are further spread by short PN spreading codes.

Short PN spreading codes are of length 15 with a period of 32768 chips.

Why we have two spreading codes?

The orthogonal codes are used to differentiate between the transmissions within a

cell. The PN spreading codes are used to isolate different cells (BSs) that are

24

8/6/2019 DB4----FINAL

25/49

using the same frequencies. The same PN sequence is used in all BSs.The offset

for each BS is different. Of course, this requires synchronization Synchronizationis achieved by GPS.

Reverse Channel Generation: -

BASIC STRUCTURE OF CDMA NETWORK: -

25

8/6/2019 DB4----FINAL

26/49

The basic structure of the network is shown in the figure. The components are described

below:1) Microwave Antenna

2) ODU (Out Door Unit)

3) IDU (In Door Unit)4) MUX

5) DDF (Digital Distribution Frame)

6) BTS (Base station Transceiver Subsystem)

7) Sector antenna8) GPS antenna

1) Microwave antenna MW antenna is used to transmit MW signal in air. This antenna is a

directional antenna (DA). It means it will transmit in one direction only. This is used to

connect E1 link between two sites. Two MW antennas are there in each site to establish aring network. It sends traffic to BSC (Base Station Controller). The transmitting

frequency is in terms of GH. Parabolic types of antenna are used in TTL.

2) ODU (Out Door Unit)

26

8/6/2019 DB4----FINAL

27/49

ODU is attached to the MW antenna. Its function is to modulate the incoming

signal from IDU with higher carrier frequency signal. Means frequency up conversion is

performed here.

3) IDU (In Door Unit)IDU converts between RF (Radio Frequency) signal and optical signal. To

establish ring network more then one IDU can be required.MUX

Here MUX are used to carry E1 from one site to the other site. BTS is connectedto the MUX via DDF. Here MUX can carry both data and voice traffic. MUX uses SDH

(Synchronous Digital Hierarchy) technology. Different types are:

Type Capacity

STM 0 21E1

STM-1 63E1STM-4 4x63 E1

STM-16 16x63 E1STM-64 64x63 E1STM-256 256x63 E1

Single E1 has a capacity of 2.048 Mbps. MSH11c (STM-1) and MSH41c (STM-4) areused in TTL.

4) DDF DDF stands for Digital Distribution Frame. DDF is a point where E1 isterminated. It provides only connectivity between two points.

5) BTSBTS stands for Base Station Transceiver Subsystem. BTS is connected with

GPS antenna via RF cable. The CDMA signal is processed by BTS. BTS include filters,

amplifier and other control module. BTS receive and transmit signal via sector antenna.

6) Sector antenna Sector antenna communicates with mobile. 360 Degree Is divided in to threeparts Alpha, Beta and Gamma. Also known as intra, metro and ultra. All three parts are

separated by maximum up to 120 degree. Here because of sector the coverage is increase.Sector antenna is a directional antenna.

7) GPS system A GPS stands for Global Positioning System. A GPS receiver is located in theBTS and is connected to antenna via RF cable. This provides synchronization signal and

timing signal to CDMA network for channel coding. This antenna communicates withsatellite continuously.

27

8/6/2019 DB4----FINAL

28/49

Introduction to E1 Link

What is E1?

E1 is a digital communication link that enables the transmission of voice,data, and video signals at the rate of 2.048 Mbps. It was introduced in the 1960s.

E1: -

Speech signal Fm=4 kHz. So from sampling theorem the freq = 2 * Fm= 8 kHzNow 1 byte is = 8 bit

Each channel have a rate of 8 kHz * 8 bit = 64 kbps

There are 32 channels - channel no 0 to 31. Channel no. 0 is used for synchronizationand channel 15 is used for signaling. Other 30 channels are used for communication.

So the total data rate is 32 * 64kbps = 2.048 Mbps

Communication Standard-Data Rates: -

Mainly there are two types of data rates:1.PDH: Plesiochronous data hierocracy (PDH) consists of E1, E2, E3, and E4communication standard. Mainly E1 is used.

2.SDH: Synchronous data hierocracy (SDH) consists of STM1, STM4, STM16,

and STM64. Mainly STM1 is used.

Why is E1 in demand?The current demand for E1 services can be linked to a number of tangible benefits.

1) Simplification

E1 simplifies the task of networking different types of communication equipment. To

illustrate, figure 1 shows what your companys communication network might be look

like without E1 and figure 2 shows companys communication network with E1 link.Figure shows that telephone, fax, and computer applications would all require separates

lines. Typically, voice and low speed data serviced by analogue line, while high-speed

data application like computer are serviced by digital line. In figure 2 same things isshown with E1 link installed.

E1 link carry both data and voice on a single digital communication link. In this way we

can reduce the task of managing many different network.

2) Quality of services

E1 also provides a signal, which is superior in quality, then the analogue signal

provides. In analogue signal, noise and distortion is also amplified so it degrades the

quality of signal. While, in E1 system because of signal regeneration we got exact signalat the receiver side.

28

8/6/2019 DB4----FINAL

29/49

8/6/2019 DB4----FINAL

30/49

How E1 works Making voice and data compatible: -Many benefits of E1 are attributable to the fact that voice and data

transmitted over a single digital communication link. Since computer data consists of

ones and zeros (the symbol of the binary system), it is already compatible with E1s

digital format. However, because voice signals are actually complex analogue waveform,they must be digitized to achieve compatibility with E1.

SDH-PDH: -

Introduction: - Traditionally, transmission systems have been asynchronous, with each terminal

in the network running on its own recovered clock timing. In digital transmission,timing is one of the most fundamental operations. Since these clocks are not

synchronized, large variations can occur in the clock rate and thus the signal bit rate.

So, synchronism is important in communication between two links.

To correctly understand the concepts and details of SDH, its important to be clearabout the meaning of Synchronous, Plesiochronous, and Asynchronous. In a set of

Synchronous signals, the digital transitions in the signals occur at exactly the same

rate. If two digital signals are Plesiochronous, their transitions occur at almost thesame rate, with any variation being constrained within tight limits. In the case of

Asynchronous signals, the transitions of the signals dont necessarily occur at the

same nominal rate. Asynchronous, in this case, means that the difference between twoclocks is much greater than a plesiochronous difference.

PDH (Plesiochronous Digital Hierarchy): - Traditionally, digital transmission systems and hierarchies have been

based on multiplexing signals, which are plesiochronous (running at almost the samespeed). Also, various parts of the world use different hierarchies which lead toproblems of international interworking; for example, between those countries using

1.544 Mbit/s systems (U.S.A. and Japan) and those using the 2.048 Mbit/s system.

To recover a 64 kbit/s channel from a 140 Mbit/s PDH signal, itsnecessary to demultiplex the signal all the way down to the 2 Mbit/s level before the

location of the 64 kbit/s channel can be identified. PDH requires steps (140-34, 34-

8, 8-2 demultiplex; 2-8, 8-34, 34-140 multiplex) to drop out or add an individual

speech or data channel (see Figure 1). This is due to the bit stuffing used at eachlevel.

PDH contains 16E1s and to drop any E1 at any site it was necessary todrop all the 16 E1s at the site and then required E1 is to be fetched from the mux

manually, and others are to be forwarded to further sites.

30

8/6/2019 DB4----FINAL

31/49

SDH (Synchronous Digital Hierarchy): - It is a standard for telecommunications transport formulated by the

International Telecommunication Union (ITU). Before SDH, the first generations of

fiber-optic systems in the public telephone network used proprietary architectures,

equipment line codes, multiplexing formats, and maintenance procedures. The usersof this equipment wanted standards so they could mix and match equipment from

different suppliers. The resulting international standard is known as (SDH).

Synchronizing SDH: The internal clock of an SDH terminal may derive itstiming signal from a Synchronization Supply Unit (SSU) used by switching systems

and other equipment. Thus, this terminal can serve as a master for other SDH nodes,

providing timing on its outgoing STM-N signal. Other SDH nodes will operate in a

slave mode with their internal clocks timed by the incoming STM -N signal.

To solve the problem, SDH is replacing PDH. SDH can contain up to 63

E1s for microwave and for fiber, it can be up to STM 256. In SDH, 63 lines fromODU comes to the add drop mux which drops required E1s to that exchange and

bypass other lines using software. It doesnt require dropping all lines, instead onlyrequired lines are taken.

SDH defines synchronous transport modules (STMs) for the fiber-opticbased transmission hierarchy.

31

8/6/2019 DB4----FINAL

32/49

CCS#7: -

Classification of Signalilng Systems: -1. Topological Classification: -In telecommunication network, two core functions can be found:

The information has to be transported in a cost efficient way from a source to

destination over a physical line = Transmission

In a telephone exchange, an inlet has to be through connected to the correctoutlet = Switching

This is shown in figure 1:

In order to be able to perform switching function, a communication will be

required between the calling subscriber and his own switching unit. This is the user

to network interface (UNI). A communication will also be required between each

switching unit and the next one in the call sequence. This is the network to network interface(NNI).

Thus, topologically, too large families of signaling systems can immediately beintroduced:

UNI Signaling System: - Analogue Subscriber Signaling System (ASSS)

Digital Subscriber Signaling System# 1 (DSS1)

Commonly Called ISDN Signaling or D- Channel protocol.

Digital Subscriber Signaling System # 2(DSS2)

The adoption of DSS1 for Broad band Purpose( ATM-Switching)

32

8/6/2019 DB4----FINAL

33/49

NNI Signaling system: - Channel Associated Signaling System (CAS)

Common Channel Signaling System # 7 (CCS#7)

2. Functional Classification: -At least two types of information will always have to be signaled between adjacent

points:

The intention to seize or to release a local line (for UNI) or a trunk circuit (for

NNI) = Line Signaling

The call destination will have to be passed from the register of previous step to

register of the next exchange = Register Signaling The line signals carry very simple information. Most of the signals used in CASare line signals, apart from the register signal, which carries the number information.

Line signals can be sent at any time during a call. By comparison, a register signal is

sent only once. Also, a register signal carries more complex information than a linesignal. Because of their differences, line and register signals are often handled by

different equipment. Line signalling equipment must be available for the entire

duration of a call. However, as a register signal is sent only once, register equipmentcan be freed quickly to deal with other calls.

33

8/6/2019 DB4----FINAL

34/49

Definition:

Signaling System 7 (SS7) is an architecture for performing out-of-band signaling

in support of the call-establishment, billing, routing, and information-exchange functions

of the public switched telephone network (PSTN). It identifies functions to be performedby a signaling-system network and a protocol to enable their performance.

What is Signaling?

Signaling refers to the exchange of information between call components required

to provide and maintain service.

As users of the PSTN, we exchange signaling with network elements all the time.

Examples of signaling between a telephone user and the telephone network include:

dialing digits, providing dial tone, accessing a voice mailbox, sending a call-waiting

tone, dialing *66 (to retry a busy number), etc.

SS7 is a means by which elements of the telephone network exchangeinformation. Information is conveyed in the form of messages. SS7 messages canconvey information. SS7 is characterized by high-speed packet data and out-of-band

signaling.

Signaling Network Architecture:

If signaling is to be carried on a different path from the voice and data traffic it

supports, then what should that path look like? The simplest design would be to allocate

one of the paths between each interconnected pair of switches as the signaling link.Subject to capacity constraints, all signaling traffic between the two switches could

traverse this link. This type of signaling is known as associated signaling, and is shown

below in Figure 1.

Figure 1. Associated Signaling

Associated signaling works well as long as a switchs only signalingrequirements are between itself and other switches to which it has trunks. If call setup and

management were the only application of SS7, associated signaling would meet that need

34

8/6/2019 DB4----FINAL

35/49

simply and efficiently. In fact, much of the out-of-band signaling deployed in Europe

today uses associated mode.

The North American implementers of SS7, however, wanted to design asignaling network that would enable any node to exchange signaling with any other SS7

capable node. Clearly, associated signaling becomes much more complicated when it is

used to exchange signaling between nodes which do not have a direct connection. Fromthis need, the North American SS7 architecture was born.

The North American Signaling Architecture:

The North American signaling architecture defines a completely new and

separate signaling network. The network is built out of the following three essentialcomponents, interconnected by signaling links:

Signal switching points (SSPs)SSPs are telephone switches (end officesor tandems) equipped with SS7-capable software and terminating signaling links.They generally originate, terminate, or switch calls.

Signal transfer points (STPs)STPs are the packet switches of the SS7network. They receive and route incoming signaling messages towards the properdestination. They also perform specialized routing functions.

Signal control points (SCPs)SCPs are databases that provide informationnecessary for advanced call-processing capabilities.

Once deployed, the availability of SS7 network is critical to call processing.

Unless SSPs can exchange signaling, they cannot complete any interswitch calls. For this

reason, the SS7 network is built using a highly redundant architecture. Each individualelement also must meet exacting requirements for availability. Finally, protocol has been

defined between interconnected elements to facilitate the routing of signaling traffic

around any difficulties that may arise in the signaling network.To enable signaling network architectures to be easily communicated and

understood, a standard set of symbols was adopted for depicting SS7 networks. Figure 2

shows the symbols that are used to depict these three key elements of any SS7 network.

Figure 2. Signaling Network Elements

STPs and SCPs are customarily deployed in pairs. While elements of a pair are not

generally co-located, they work redundantly to perform the same logical function. When

35

8/6/2019 DB4----FINAL

36/49

drawing complex network diagrams, these pairs may be depicted as a single element for

simplicity, as shown in Figure 3.

Figure 3. STP and SCP Pairs

Basic Signaling Architecture:

Figure 4 shows a small example of how the basic elements of an SS7 network are

deployed to form two interconnected networks.

Figure 4. Sample Network

The following points should be noted:

1. STPs W and X perform identical functions. They are redundant. Together, they are

referred to as a mated pair of STPs. Similarly, STPs Y and Z form a mated pair.

36

8/6/2019 DB4----FINAL

37/49

2. Each SSP has two links (or sets of links), one to each STP of a mated pair. All SS7

signaling to the rest of the world is sent out over these links. Because the STPs of a

mated pair are redundant, messages sent over either link (to either STP) will betreated equivalently.

3. The STPs of a mated pair are joined by a link (or set of links).

4. Two mated pairs of STPs are interconnected by four links (or sets of links). Theselinks are referred to as a quad.

5. SCPs are usually (though not always) deployed in pairs. As with STPs, the SCPs of a

pair are intended to function identically. Pairs of SCPs are also referred to as matedpairs of SCPs. Note that they are not directly joined by a pair of links.

6. Signaling architectures such as this, which provide indirect signaling paths between

network elements, are referred to as providing quasi-associated signaling.

SS7 Link Types:

SS7 signaling links are characterized according to their use in the signaling network.Virtually all links are identical in that they are 56kbps or 64kbps bi-directional datalinks that support the same lower layers of the protocol; what is different is their use

within a signaling network. The defined link types are shown in Figure 5 and defined asfollows:

Figure 5. Link Types

A Links:

A links interconnect an STP and either an SSP or an SCP, which are

collectively referred to as signaling end points ("A" stands for access). A links are usedfor the sole purpose of delivering signaling to or from the signaling end points (they

could just as well be referred to as signaling beginning points).Signaling that an SSP or SCP wishes to send to any other node is sent on

either of its A links to its home STP, which, in turn, processes or routes the messages.

Similarly, messages intended for an SSP or SCP will be routed to one of its home STPs,

which will forward them to the addressed node over its A links.B-Links:

37

8/6/2019 DB4----FINAL

38/49

The links between local STP pairs form a bridge over which messages can be

transferred from one local network to another. This links are called Bridge links or

simply B-links.

C Links:

C links are links that interconnect mated STPs. As will be seen later, they areused to enhance the reliability of the signaling network in instances where one or severallinks are unavailable. C stands for cross-links. Regardless of their name, their function

is to carry signaling messages beyond their initial point of entry to the signaling networktowards their intended destination.

D Links:The D denotes diagonal and describes the quad of links interconnecting

mated pairs of STPs at different hierarchical levels. Because there is no clear hierarchy

associated with a connection between networks, interconnecting links are referred to as

either B, D, or B/D links

E Links:

While an SSP is connected to its home STP pair by a set of A links, enhanced

reliability can be provided by deploying an additional set of links to a second STP pair.These links, called E (extended) links provide backup connectivity to the SS7 network in

the event that the home STPs cannot be reached via the A links. While all SS7 networks

include A, B/D, and C links, E links may or may not be deployed at the discretion of thenetwork provider. The decision of whether or not to deploy E links can be made by

comparing the cost of deployment with the improvement in reliability.

F Links:

F (fully associated) links are links which directly connect two signaling end

points. F links allow associated signaling only. Because they bypass the security featuresprovided by an STP, F links are not generally deployed between networks. Their use

within an individual network is at the discretion of the network provider.

Basic Call Setup Example:

Before going into much more detail, it might be helpful to look at several basiccalls and the way in which they use SS7 signaling (see Figure 6).

Figure 6. Call Setup Example

38

8/6/2019 DB4----FINAL

39/49

In this example, a subscriber on switch A places a call to a subscriber on switch B.

1. Switch A analyzes the dialed digits and determines that it needs to send the

call to switch B.2. Switch A selects an idle trunk between itself and switch B and formulates an

initial address message (IAM), the basic message necessary to initiate a call. TheIAM is addressed to switch B. It identifies the initiating switch (switch A), thedestination switch (switch B), the trunk selected, the calling and called numbers, as

well as other information beyond the scope of this example.

3. Switch A picks one of its A links (e.g., AW) and transmits the message overthe link for routing to switch B.

4. STP W receives a message, inspects its routing label, and determines that it is

to be routed to switch B. It transmits the message on link BW.

5. Switch B receives the message. On analyzing the message, it determines thatit serves the called number and that the called number is idle.

6. Switch B formulates an address complete message (ACM), which indicates

that the IAM has reached its proper destination. The message identifies the recipientswitch (A), the sending switch (B), and the selected trunk.

7. Switch B picks one of its A links (e.g., BX) and transmits the ACM over the

link for routing to switch A. At the same time, it completes the call path in thebackwards direction (towards switch A), sends a ringing tone over that trunk towards

switch A, and rings the line of the called subscriber.

8. STP X receives the message, inspects its routing label, and determines that it

is to be routed to switch A. It transmits the message on link AX.9. On receiving the ACM, switch A connects the calling subscriber line to the

selected trunk in the backwards direction (so that the caller can hear the ringing sent

by switch B).10. When the called subscriber picks up the phone, switch B formulates an answer

message (ANM), identifying the intended recipient switch (A), the sending switch

(B), and the selected trunk.

11. Switch B selects the same A link it used to transmit the ACM (link BX) and

sends the ANM. By this time, the trunk also must be connected to the called line inboth directions (to allow conversation).

39

8/6/2019 DB4----FINAL

40/49

12. STP X recognizes that the ANM is addressed to switch A and forwards it over

link AX.

13. Switch A ensures that the calling subscriber is connected to the outgoing trunk(in both directions) and that conversation can take place.

14. If the calling subscriber hangs up first (following the conversation), switch A

will generate a release message (REL) addressed to switch B, identifying the trunkassociated with the call. It sends the message on link AW.

15. STP W receives the REL, determines that it is addressed to switch B, and

forwards it using link WB.16. Switch B receives the REL, disconnects the trunk from the subscriber line,

returns the trunk to idle status, generates a release complete message (RLC)

addressed back to switch A, and transmits it on link BX. The RLC identifies the trunk

used to carry the call.17. STP X receives the RLC, determines that it is addressed to switch A, and

forwards it over link AX.

18. On receiving the RLC, switch A idles the identified trunk.

Database Query Example:

People generally are familiar with the toll-free aspect of 800 (or 888) numbers,

but these numbers have significant additional capabilities made possible by the SS7

network. 800 numbers are virtual telephone numbers. Although they are used to point to

real telephone numbers, they are not assigned to the subscriber line itself.When a subscriber dials an 800 number, it is a signal to the switch to suspend

the call and seek further instructions from a database. The database will provide either a

real phone number to which the call should be directed, or it will identify anothernetwork (e.g., a long-distance carrier) to which the call should be routed for further

processing. While the response from the database could be the same for every call (as, forexample, if you have a personal 800 number), it can be made to vary based on the callingnumber, the time of day, the day of the week, or a number of other factors.

The following example shows how an 800 call is routed (see Figure 7).

40

8/6/2019 DB4----FINAL

41/49

Figure 7. Database Query Example

1. A subscriber served by switch A wants to reserve a rental car at a company's

nearest location. She dials the company's advertised 800 number.2. When the subscriber has finished dialing, switch A recognizes that this is an800 call and that it requires assistance to handle it properly.

3. Switch A formulates an 800 query message including the calling and called

number and forwards it to either of its STPs (e.g., X) over its A link to that STP (AX).4. STP X determines that the received query is an 800 query and selects a

database suitable to respond to the query (e.g., M).

5. STP X forwards the query to SCP M over the appropriate A link (MX). SCP

M receives the query, extracts the passed information, and (based on its storedrecords) selects either a real telephone number or a network (or both) to which the

call should be routed.

6. SCP M formulates a response message with the information necessary toproperly process the call, addresses it to switch A, picks an STP and an A link to use

(e.g., MW), and routes the response.

7. STP W receives the response message, recognizes that it is addressed toswitch A, and routes it to A over AW.

8. Switch A receives the response and uses the information to determine where

the call should be routed. It then picks a trunk to that destination, generates an IAM,and proceeds (as it did in the previous example) to set up the call.

Layers of the SS7 Protocol:

As the call-flow examples show, the SS7 network is an interconnected set of

network elements that is used to exchange messages in support of telecommunicationsfunctions. The SS7 protocol is designed to both facilitate these functions and to maintain

the network over which they are provided. Like most modern protocols, the SS7 protocolis layered.

41

8/6/2019 DB4----FINAL

42/49

1. Physical Layer:

2. Message Transfer PartLevel 2

3. Message Transfer PartLevel 3

4. Signaling Connection Control Part:

5. ISDN User Part (ISUP):

6. Transaction Capabilities Application Part (TCAP):

7. Operations, Maintenance, and Administration Part (OMAP):

What Goes Over the Signaling Link:

Signaling information is passed over the signaling link in messages, which arecalled signal units (SUs).

Three types of SUs are defined in the SS7 protocol.

message signal units (MSUs) link status signal units (LSSUs)

fill-in signal units (FISUs)

SUs are transmitted continuously in both directions on any link that is in

service. A signaling point that does not have MSUs or LSSUs to send will send FISUsover the link. The FISUs perform the function suggested by their name; they fill up the

signaling link until there is a need to send purposeful signaling. They also facilitate link

transmission monitoring and the acknowledgment of other SUs.

All transmission on the signaling link is broken up into 8-bit bytes, referred toas octets. SUs on a link are delimited by a unique 8-bit pattern known as a flag. The flag

is defined as the 8-bit pattern "01111110". Because of the possibility that data within an

SU would contain this pattern, bit manipulation techniques are used to ensure that thepattern does not occur within the message as it is transmitted over the link. (The SU is

reconstructed once it has been taken off the link, and any bit manipulation is reversed.)

Thus, any occurrence of the flag on the link indicates the end of one SU and thebeginning of another. While in theory two flags could be placed between SUs (one to

mark the end of the current message and one to mark the start of the next message), in

practice a single flag is used for both purposes.

SWITCH: -

Network department is basically divided into two sections:(1) Transmission

(2) Switch.

Transmission section deals with transmission media, RF planning, BTSinstallation, NMS, etc.

42

8/6/2019 DB4----FINAL

43/49

Switch section deals with switching of call in MSC, daily health check of

switch, customer complain, etc.

Basically, all the switches are stored program control (SPC) based. In switch to

see the backend activities (ROP Read Only Printer) occurring in switch. We take it

through RJ-45 connector or Ethernet LAN to the terminal. In the terminal mainly twowindow are there:

(1) Command window

(2) Output window

Command window: command window is used to give a command for the

particular activity. For example to see the any alarm occur in switch room, we

directly give the command.

Output window: output window is used to see to output of particular activity

for the given command on command window. Using particular command, we checkthe status of any mobile subscriber using VLR.

In TTSL, basically two type of switch are used: Wireline and wireless. The vendors are

Lucent, Ericsson, Alcatel and Siemens.

Wireline switch:-For wire line, we use Lucent switch, which is totally hardware based. Because ofmore hardware part, it is bulky.

Lucent is user-friendly switch, because it is easily operatable.

Wireline switchs computer has connection with switch by serial port.It contains status of signaling links, faults and alarms related to that switch on the

screen. By giving appropriate command, status of signaling link is known.

(2) Wireless Switch: - Wireless switch is software based and it is compact switch compared

to Lucent switch.

For wireless, we use Ericsson switch.

Digital Path Quality Supervision: In this, 3 types of soft errors

occur:

1. Quality Service (QSV): If one of the 32 frames is lost, than voice is broken and thisalarm is indicated.

2. SESL2 (severely errored seconds): When synchronism in 1 second out of 1000 seconds

is dropped, this error occurs.3. UNACC (Unacceptable Performance): This error occur due to incorrect parity bits.

There are 4 types of alarms in ERICSSON:1. APZ: Software error alarm

2. APT: Hardware fault alarm

3. POW: Power failure alarm4. EXT: Fire alarms and temperature control, etc.

43

8/6/2019 DB4----FINAL

44/49

All the activities done during the week is stored in hard DAT tape. It will containall call details record (CDR) occurring during the week. Capacity to store the data vary

from different types of switch. Lucent contain 4GB of memory to store the data while inEricsson it will contain 24GB of data.

In tata indicom, from the level-5 to level-6 migration is going on. In this we have

to give and take the test call from all the short distance coverage area (SDCA), long

distance coverage area (LDCA) No., for particular given region, to check the connectivity

between any two SDCA or LDCA.

FIG. Differentiate between LDCA & SDCA.

In above fig., we differentiate between LDCA & SDCA. If call is going in same SDCA

then it is not forwarded to LDCA but if call is for other SDCA then it is forwarded to

LDCA and again call is forwarded to particular SDCA. In India any state or district is

work as a LDCA or SDCA.

Daily activities at OMC: -1. Health Check: - It includes hardware failure check, software errors,

interconnectivity with different operators, trunk group status check, etc. REX(Regular Exercise) is also a part of health check, which includes hardware diagnosis.

44

GUJRAT

GUJRAT

8/6/2019 DB4----FINAL

45/49

2. Customer Complaints: - There is ORACLE software for complaints. These

complaints are analysed and checked that is it related to routing, level opening, etc.

and necessary steps are taken to solve these problems.

3.Augmentation: - It includes increasing no. of trunk groups as per therequirements and hence ASR is increased.

CDR (Call Detail Report): - CDR is for billing purpose. It contains call relatedinformation like start time, end time, duration, A number, B number.

Infrastructure equipment: -A CDMA system requires three pieces of infrastructure equipment. They are

Main Switching Centre (MSC)

Base Station Controller (BSC)

Base Station Transceiver Subsystem (BTS).

Description of Individual Components: - Mobile Switching Center (MSC)

The MSC coordinates traffic and signaling within the CCLN. It is responsible

for setup, routing and supervision of calls to and from mobile subscribers. Many other

functions are implemented in the MSC.

Gateway MSC (GMSC): - The GMSC is an MSC which contains the gatewayfunctionality, i.e. interrogating the HLR at the set-up of a mobile-terminating call. The

GMSC has two distinct functions:

Roaming Interrogation (requesting the HLR to send routing

information)

Roaming Rerouting or Call forwarding.

MSC IN THE NETWORK: -Mobile Switching Center (MSC) is the central unit of the network. Each and

every call must terminate at the MSC. It is an intelligent unit. It is used to route the calls.

MSC connects with the other network units as shown in the diagram.

45

8/6/2019 DB4----FINAL

46/49

BTS: Base Transreceiver Station

BSC: Base Station ControllerMSC: Mobile Switching Center

HLR: Home Location RegisterRLU: Remote Location Unit

WIRE LINE SW: Wire line SwitchThe signal from subscriber comes through BTS and BSC to MSC.MSC is connected to

the HLR, which contains the database of each and every subscriber. Every time HLR is

referred, whenever a mobile call is made, for authentication of the subscriber. At MSCthe routing is takes place. The incoming call is routed to desired BSC and BTS in case of

called party is another mobile. In case of called party is wire line phone, and then the

46

B

S

C

MSC

WIRE

LINE SW

HLR

MSC OF

OTHER

OPERATOR

MSC AND

WIRE LINE

SW OF

OTHER

OPERATOR

B

T

S

8/6/2019 DB4----FINAL

47/49

connection is transferred from MSC to the wire line switch. If the called party is near at

the switch, then the calledis transferred directly to the party over copper cable. In casecalled party is at far from switch then the call is transferred to RLU.RLU serve to thatparty. In case the called party belongs to the other service provider, then there isPOI,where different service providers interconnect through each other. The call is transferred

from one service provider to the other one

BSC: -The Base Station Controller (BSC) is part of the link between the BTS and the

MTSO. It

Performs vocoding of the voice signal

Routes calls to the MTSO

Handles call control processes

Maintains a database of subscribers

Maintains records of calls for billing

BTS: -Functions of BTS:

The BTS includes an antenna for transmitting and receiving

Radio frequency signals i.e. it caters to the traffic.

It also performs the CDMA processing of all signals.

The BTS attaches to an antenna. The antenna's three-sided design includesthree sectors called alpha, beta, and gamma, each of which can be further

subdivided.

Adding sectors to a BTS increases its capacity. Each sector operates like anindependent BTS.

BTS sectorization requires additional hardware within the BTS unit.

Home Location Register (HLR): -Each operator has a database with information about all subscribers

belonging to that specific service provider. It is used for the following purposes:

Registering subscribers MDN and IMSI numbers.

Storing subscribers categories and services.Keeping track of which MSC/VLR is serving the subscriber.

Ordering a serving MSC/VLR to delete its record about a subscriber.

Visitor Location Register (VLR): -The VLR is implemented in the same switch as the MSC, which is then

referred to as an MSC/VLR.

47

8/6/2019 DB4----FINAL

48/49

It contains temporary information about the mobile subscriber visiting this

specific MSC/VLR Service Area.

It also performs location updating of the HLR.

The VLR contains a copy of the subscriber information in the HLR, but also

more detailed information about the subscribers location (which Location Area

they are registered in). Since VLR has a set of information about the mobile subscriber in its Service

Area, the HLR does not need to be consulted about subscriber data very often.

This considerably reduces the signaling to HLR.

Switch Identification in CCS#7 network: - To identify particular switch, each switch has its own signaling point codewhich differentiates the specific switch.

When call is routing from one switch to other, the destination switch is identifiedby its signaling point code.

Switch to switch connection is identified with reference of number of E1s

between these two switches.

Each E1 has 32 time slots or trunk circuits. These trunk circuits are divided ingroups. There are two types of trunk groups: FWT and C-MO i.e. as per ex., 16 trunk

circuits are used for FWT and others for C-MO.

CIC (Circuit Identification Code): It is code used in software to check the 1-to-1

connection between two E1 circuits. Whenever new E1 between two points is added

1-to-1 connection must be there i.e. trunk circuit number 1 of one switch must beconnected to the trunk circuit number 1 of remote location of switch.

Point of Interconnection (POI): - It is connection unit between E1s of two switches at MSC.

Performance of POI: -

ASR (Answer to Seizure Ratio): - This ratio defines how many channels out of

occupied channels are actually used. Others, which are wasted, includes no. ofreasons like call failure because of no reply, wrong dialed no., busy no., destination

out of order, internetworking unspecified (CAS-CCS 7 conversion), etc.

Because of above reasons, the ASR is decreased. Through bifurcation, ASR ratio

can be increased. By analyzing the numbers through levels, like analysis on level 2,level 28, level 281, etc., minimizes the wastage occupation of lines and hence no. of

lines seized in actual communication are increased, and hence ASR is increased.

Forward Backward Hunting: - Whenever new E1s between any two service

providers are established, forward and backward hunting is provided. Suppose,

between TATA and AIRTEL, there are 60 trunk lines are provided, then it is decided

that when subscriber of TATA will initiate a call, he will be given a channel from no.60,59,etc. in descending order which is called backward hunting, and for AIRTEL

48

8/6/2019 DB4----FINAL

49/49

subscriber, channel no.s will be 1, 2, 3, etc. which is called forward hunting. So that

there is no clash in channel occupation and channels are easily assigned. TATA

prefers backward hunting.

Current activity at TTSL: - Recently main activity done at TTSL is level 5 to 6 migration for FWT. At

present, TATA is running on level 5, and because of no. of subscribers increasing,

they are changing their numbers for FWT to level 6 as per the information from TRAI(Telecom Regulatory Authority of India).

The subscribers numbers detail is stored in HLR based on the ESN number. In

migration, numbers are changed in HLR and routing is provided for calls.

At a time 10 no.s for particular subscriber in HLR can be created and only one

can be activated.

Test calls are done for checking that call is through between two lines of different

operators and TTSL. It is the process of routing. If the line is not through, we willhave to check the routing path for this line.