GSM architecture Complete

Gsm archt.

1. The Mobile Station (MS)
2. The Base Station Subsystem (BSS )
3. The Network Switching Subsystem (NSS)
4. The Operation Support Subsystem (OSS)

MS

consists of the physical

equipment, such as the radio

transceiver, display and digital signal

processors, and the SIM card.

MS also provides access to the

various data services available in a

GSM network.dg Gprs and high speed data.

BSS

The BSS is composed of two parts:

• The Base Transceiver Station (BTS)
• The Base Station Controller (BSC)

BTS and the BSC communicate

across the interface,

enable operations between

components that are made by

different suppliers.

The radio components of a BSS may consist of

four to seven or nine cells. A BSS

may have one or more base stations.

The Base Transceiver Station (BTS ) :

The BTS hold the radio

transceivers that define a cell and

handles the radio link protocols with

the MS.

In a large urban area, a large

number of BTSs may be deployed.

A BTS is usually placed in the center of a cell.

Its transmitting power defines the size of a cell.

Each BTS has between 1 and 16 transceivers, depending on

the density of users in the cell 

Function

Encoding, encrypting,

multiplexing, modulating,

Uplink channel measurements

The Base Station Controller (BSC)

The BSC manages the radio resources

for one or more BTSs.

It handles radio channel setup, frequency hopping, and handovers.

The BSC is the connection between the mobile and the MSC.

 Also linked to the Public

Switched Telephone Network (PSDN) or ISDN.

It assigns and releases frequencies

and time slots for the MS.

The

function of the BSC is to allocate the

necessary time slots between the BTS

and the MSC.

Control of frequency hopping

Performing traffic concentration

to reduce the number of lines

from the MSC

Providing an interface to the

Operations and Maintenance

Center for the BSS

Reallocation of frequencies

among BTSs

Time and frequency

synchronization

Power management

Time-delay measurements of

received signals from the MS

NSS

The Network switching system (NSS),

the main part of which is the Mobile

Switching Center (MSC), performs the

switching of calls between the mobile

and other fixed or mobile network

users, as well as the management of

mobile services such as

authentication.

The switching system includes the

following functional elements:

The HLR is a database used for

storage and management of

subscriptions. The HLR is considered

the most important database, as it

stores permanent data about

subscribers, including a subscriber's

service profile, location information,

and activity status.

Mobile Services Switching Center

(MSC )

The central component of the

Network Subsystem is the MSC. The

MSC performs the switching of calls

between the mobile and other fixed

or mobile network users,

Visitor Location Register ( VLR)

The VLR is a database that contains

temporary information about

subscribers that is needed by the

MSC in order to service visiting

subscriber or raoming.

Authentication Center ( AUC )

The Authentication Center is a

protected database that stores a copy

of the secret key stored in each

subscriber's SIM card, which is used

for authentication and ciphering of

the radio channel.

Equipment Identity Register (EIR )

The Equipment Identity Register (EIR)

is a database that contains a list of

all valid mobile equipment on the

network, where its International

Mobile Equipment Identity (IMEI)

identifies each MS.

Read More

OFDMA, SDMA, PDMA, CSMA-DA, CSMA-CA Difference between GSM CDMA

Orthogonal frequencyvdivision multiplexing (OFDM)

• Access technique used in Long-Term Evolution (LTE) to accommodate multiple users in a given bandwidth

• Modulation method that divides a channel into multiple narrow orthogonal bands that are spaced so they don’t interfere with one another.
• DATA divided into many lower bit streams.
• Time slot bw each subchannel are used to package the data.
• This technique is very spectrally efficient, so it provides very high data rates. It also is less
• affected by multipath propagation effects.
• To implement OFDMA, each user is assigned a group of subchannels and related time slots.

Space division multiple access SDMA

• SDMA uses physical separation methods that permit the sharing of wireless channels.
• single channel may be used simultaneously if the users are spaced far enough from one another to avoid interference. Known as frequency reuse.
• Useful in gsm

Pdma polarization division multiple access (PDMA)

• One unique variation of SDMA, polarization division multiple access (PDMA), separates signals by using different polarizations of the antennas. 
• Two different signals then can use the same frequency, one transmitting a vertically polarized signal and the other transmitting a horizontally polarized signal.

CSMA-CD

• A unique and widely used method of multiple access is carrier sense multiple access with collision detection (CSMA-CD).
• used in Ethernet local-area networks (LANs). 
• It allows multiple users of the network to access the single cable for transmission. 
• All network nodes listen continuously. When they want to send data, they listen first and then transmit if no other signals are on the line. 
• If two or more transmissions occur simultaneously, a collision occurs.
• The network interface circuitry can detect a collision, and then the nodes will wait a random time before retransmitting.

Csma ca

variation of this method is called carrier sense multiple access with collision avoidance (CSMA-CA).

This method is similar to CSMA-CD. However, a special scheduling algorithm is used to determine the appropriate time to transmit over the shared channel.

 While the CSMA-CD technique is most used in

wired networks, CSMA-CA is the preferred method in wireless networks.

Differentiate between GSM and CDMA

GSM

- GSM uses multiple frequencies.

- Uses TDMA and FDMA for accessing

signals.

- The voice rate is 9.6 KBPS.

- Uses less bandwidth.

CDMA

- CDMA uses single frequency as

carrier.

- The voice rate is 14.4 KBPS.

- CDMA power control to access

method is better as Phased Locked

Loops are used.

- Follows soft handoff, hence call

handling is more efficient.

Read More

CDMA - Basic points

Cdma

• Use spread spectrum techniques.
• Every  channel uses full frequency channel.
• Conversation are encoded with pseudo random digital signal.
• Better capacity for data and vioce.
• Common tech in 3g umts and wcdma.
• Also in gps.
•  A spread spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power.
• Code run at much higher speed than data.
• Data is bitwise xor with code.
• The separation of the signals is made by correlating the received signal with the locally generated code.  If the signal matches User code then the correlation function will be high and the system can extract that signal. If the user's code has nothing in common with the signalthe correlation then zero (thus eliminating the signal); this is referred to as cross-correlation .

Read More

FDMA - Basics

Fdma

• Divide channel into multiple bands.
• Users share the same frequency channel But use a single frequency.
• Between these feq glad band is used.
• Used in analog radio and analog cellular system. Can be used in digital too.
• Req high fiters
• Crosstalk may occur.
• No time problem and near far problem as in tdma and cdma.
• Also support demand assigned, freq assigned on temp basis.
• Tv sysyem.

Read More

TDMA-Main Points

Tdma

1. N users share same radio channel
2. But uses only particular slot
3. Only gsm technology
4. Data streams divided in frames which contains N slots.
5. Duplex mode
6. Bw is N times the Bw required to transmit for single user.
7. Less expansive and smaller
8. N down link it is simple - just multiplexing.
9. In unlink - hard as user has to be aligned in time.

Read More

Networking Basics and Types of Computer Networks

Computer networking is basically the way to connect different computer devices by using the different components mainly hardware and software across the large distances. Thus networking makes us to easily access the information, sends the information from one device to other devices and makes our life easier.

Basic benefits of Networking

There could be many benefits and advantages of connecting through networking but if we talk in basics there are some main basic benefits of computer networking which are as follows

Information or file sharing: It is the need of the modern technology that information should be easily accessible and easily transferable. It could be in any type, a signal, a file or a file or folder. If you want to send information from one computer to other then networking is the essential part.

Resource Sharing : In case you want to share your computer resources using computer networking such as printers, fax machines, Storage Devices, Webcam, Scanners, Modem and many more devices can be shared using computer networking.

Program sharing and remote services:
You can easily share and send any program from one computer to the other computer by using different techniques of networking and by using remote services you can access the resources far away from the actual computer

Different types of computer networks:

LAN (Local area network):

LAN is called as Local area network and as name suggests it is used to connect networking devices which are geographically close to each other. This type of networking include the examples such as a floor of a building, a building itself, or a campus environment.

WAN (Wide area networks)

Wide area network is used when the geographical locations are not that much close so that we can bind them together with the help of LAN, so we make use of wide area network in that case.

MAN (metropolitan area network)

A metropolitan area network (MAN) is considered the mixture of LAN and WAN to connect the devices in a particular geographical area.

Intranet:

Intranet is a network which is local to an organization. All the information that will be available is from that network only and to access that information; they would not need to rely on the other network. This network comprises the LAN, MAN and WAN too.

Extranet:

Extranet is bit wider that of intranet where some of the information or services can be accessible by the thirds party, so the data can be share to outside an oragnisation up to some extent.

Internet:

Internet is used when the information and resources are too made available to all the external and outside users.

VPN: Virtual private network

VPN is a kind of secured network that is used to provide a secure connection over internet or any other public network. VPN use the three way secure connection which include authentication, confidentiality and integrity to ensure that data is sent between two devices is not been tempered by others.

Read More