1 final multiplexing

8/3/2019 1 Final Multiplexing

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Multiplexing

The process in which multiple channels are combined for transmission over a common

transmission path.Or

It is aprocess where multiple analog message signals or digital data streams are

combined into one signal over a shared medium. The aim is to share an expensiveresource. Multiplexing also known as muxing

Multiple Access Techniques

The connection of a userto two or more switching centers by separate access lines using

a single messagerouting indicatorortelephone number, or a channel access method or

multiple access method allows several terminals connected to the same multi-pointtransmission medium to transmit over it and to share its capacity. ...

Multiplexing schemes by which multiple users that are geographically dispersed gainaccess to a shared telecommunications facility or channel

The current techniques that can accomplish this include

1) Frequency Division Multiple Access (FDMA)2) Time Division Multiple Access (TDMA)3) Code Division Multiple Access (CDMA)

Frequency Division Multiple Access (FDMA)

FDMA is a channel access method used in multiple-access protocols as a channelizationprotocol. FDMA gives users an individual allocation of one or several frequency bands,

orchannels. Multiple Access systems coordinate access between multiple users.

In FDM, multiple channels are combined onto a single aggregate signal for transmission.The channels are separated in the aggregate by their FREQUENCY.

There are always some unused frequency spaces between channels, known as "guard

bands". These guard bands reduce the effects of "bleed over" between adjacent channels,a condition more commonly referred to as "crosstalk".

Traffic channels:

Different frequency bands are allocated to different users,

for example, AMPS and TACS
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Disadvantage: Crosstalk which causes interference on the other frequency and may

disrupt the transmission

Time Division Multiple Access (TDMA)

TDMA is a channel access method for shared medium networks. It allows several users

to share the same frequency channelby dividing the signal into different time slots. The

users transmit in rapid succession, one after the other, each using own time slot. Thisallows multiple stations to share the same transmission medium (e.g. radio frequency

channel) while using only a part of its channel capacity. TDMA is used in the digital 2G

cellular systems such as Global System for Mobile Communications (GSM)

Traffic channels:

Different time slots are allocated to different users,

for example, DAMPS and GSM

Shares single carrier frequency with multiple users Non-continuous transmission makes handoff simpler

Slots can be assigned on demand in dynamic TDMA

Less stringent power control than CDMA due to reduced intra cell interference

Higher synchronization overhead than CDMA

Advanced equalization may be necessary for high data rates if the channel is

"frequency selective" and creates Intersymbol interference
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Cell breathing (borrowing resources from adjacent cells) is more complicated than

in CDMA

Frequency/slot allocation complexity

Pulsating power envelop: Interference with other devices

Digital signaling is used exclusively.

Code Division Multiple Access (CDMA)

CDMA employs spread-spectrum technology and a special coding scheme (where each

transmitter is assigned a code) to allow multiple users to be multiplexed over the samephysical channel. CDMA is a form ofspread-spectrum signaling, since the modulated

coded signal has a much higherdata bandwidth than the data being communicated.

Traffic channels:Different users are assigned unique code and transmitted over the same frequency

band,

for example, WCDMA and CDMA2000

Advantages of CDMA

Voice quality

Privacy

System capacity

Flexibility

WLL Architecture

WLL is a Wireless Network that connects the Subscriber with PSTN using Radio waves

instead of cable network.WLL using radio frequency signals as a substitute for conventional wires for all or part of

the connection between the subscriber and the telephone exchange.It is useful for those subscribers who are located in pockets where immediate telephoneconnections cannot be provided due to lack of underground cable network but radio

coverage is available.

Advantages of WLL

Investment

Maintenance Expansion

Fault Management

Features available with WLLWLL provides features of a normal telephone like:

1. Dynamic STD/ISD locking.

2. Call waiting / Call transfer3. Calling line identification

4. Call forwarding

5. Data / Fax transmission (upto 14.4.kbps).6. Morning alarm / Hotline
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7. STD/ISD call details along with the bill

Difference of WLL from cellular mobile phones

Cellular mobile phones provide access to the telephone network even when the subscriber

is moving fast vehicle in a vehicle in the entire area of the cellular network. This is done

by dividing the service area into manageable cells so that calls will be transferred fromone cell to the other even when the vehicle is on the move rapidly. However, in WLL,

calls can be made from fixed locations where coverage is available. The fringe areas of

the WLL service may experience a weaker radio signal during the heavy calling periods.An outdoor type aerial will be provided in the premises of such type of subscribers, so

that the equipment fixed in their premises will continue to get strong radio signals for

establishing communication.

There are two types of services that will be provided

(1) Fixed WLL

(2) WLL with portability

Fixed WLL service

It is a service provided using a telephone instrument. The Fixed Wireless Terminal(FWT) will be wall mounted and provided with an indoor type or outdoor type aerial

depending on the strength of the radio signal. A short cable will be connected from the

outdoor aerial to the wall set. The conventional telephone instrument will be connected to

the wall set through a short telephone cable. The wall set will be powered by an a.c.supply available in the subscribers premises, like any other a.c. gadget.

Interfaces

Um interfaceUm interface carries all signaling & services between MS and BTS over radiolinks.

Abis interface

Abis interface carries signaling & services between BTS and BSC.

A1 interface

A1 interface carries call control signaling between MSC and BSC.

A2 interface

A2 interface provides 64kbit/s PCM speech channels between MSC and BSC.

A3 interface

A3 interface has two functions: Signaling and traffic. A3 signaling is used tocontrol and allocate the transmission channels for user traffic.

A7 interfaceA7 interface carries signaling between source BSC and target BSC.


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A8 interface

A8 interface carries user traffic between BSC and PCF.

A9 interface

A9 interface carries signaling between BSC and PCF.

A10 interface

A10 interface carries user traffic between PCF and PDSN.

A11 interface

A11 interface caries signaling between PCF and PDSN.

The Mobile Switching Centre (MSC)

The Mobile Switching Centre (MSC) performs almost identical functions to that of a

normal switching node in a fixed network. In addition, it provides the functionality

needed to handle mobile subscribers including registration, authentication, locationupdating etc.

Mobile Station (MS)

The Mobile Station (MS) consists of the Mobile Equipment (ME) and the Subscriber

Identity Module (SIM).

The Mobile Equipment (ME), commonly referred to as a terminal or handset, comes intwo varieties: fixed and portable. A fixed MS is usually installed in a vehicle while

portable MSs are normally carried by subscribers. Due to size limitations and power

requirements, fixed MSs were originally predominant though this situation has changed

dramatically in recent years as the portable MS is by now almost ubiquitous and evenregarded as a fashion accessory. The ME is uniquely identified by its International


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Mobile Equipment Identity (IMEI) number, which is primarily used for security

purposes.

A Subscriber Identity Module (SIM) is a smart card that is inserted into the ME toprovide personal mobility. Each SIM card contains an International Mobile Subscriber

Identity (IMSI) number that uniquely identifies the subscriber to the network thereby

allowing access to subscribed services. To prevent unauthorised access, the SIM card canbe protected using a Personal Identification Number (PIN). Only emergency calls can be

made from a terminal without a SIM card. While the SIM card currently facilitates a

number of services including the standard Short Message Service (SMS), advances insmart card technologies will ensure that the SIM card becomes a cornerstone for any new

services deployed in the future.

The Base Station (BS)

Base Transceiver Station (BTS)

It is the interface for the MS to the network. It handles all

communications with the MS via the air interface (technically referred to as the Uminterface in the GSM specifications). Essentially, the transmitting power of a BTS

defines the cell size i.e. its coverage area. In large urban areas, the number of BTSsdeployed is large so the corresponding cell size is small. In contrast, there is usually a

far smaller number deployed in rural areas so the cell size can be quite large.

Base Station Controller (BSC).

The Base Station Controller (BSC) manages the radio resources for

multiple BTSs, the number of which varies but could be up to several hundred. Aswell as the allocation and release of radio channels, the BSC is responsible for

handover management when the MS roams into an area covered by another BSC.

Similar to all other interfaces in GSM, the interface between the BSC and a BTS isstandardised and is referred to as the Abis interface.

The Home Location Register (HLR) contains all the administrative

information for each subscriber registered in the correspondingGSM network. This includes both the IMSI number and actual

phone number as well as details of a subscribers permitted

supplementary services e.g. call forwarding. The current locationi.e. which Visitor Location Register (VLR) the subscriber is

currently registered with, is also stored in the HLR as, without this,

the MSC could not route any calls to the subscriber. Logically,

there is one HLR for each GSM network, although it can beimplemented as a distributed database.

BTS: Base Station, which creates a single cell

BSC: Base Station Controller, which controls roaming and channel

allocations amongst various BSTs and is also referred to as a Radio Network

Controller (RNC).


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MSC: Mobile Switching Center, which performs the telephony switchingfunctions and is usually connected to an SS7 network.

PDSN: Packet Data Serving Node, maintains IP communications between all

MNs and the Packet Data Network (PDN), which in this diagram is the

Internet.

1 final multiplexing

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