Mobile Communication

Frequency alloted by WPC to Indian Railway is 146.2 - 167.95 Mhz

VHF -

Line of sight,Reflection, Scattering.

Type of operation : Half Duplex ( for present Railway operations)

Equipment- Walkie-talkie set,Base radio

Antenna- Whip, Ground Plane 

Feeder cable- 50 Ohms Unbalanced Coaxial cable 

Mobile Station 

The Mobile station represents the terminal equipment used by cellular subscriber by GSM system.

Mobile system has two entities.

Mobile Equipment (ME)

Subscriber Identify Module ( SIM)

Functions of SIM card-

User authentication 

Storage of subscriber related information. 

Base Station Subsystem ( BSS)

BSS has two entities.

1. Base Transceiver Station( BTS)

2. Base Station Controller ( BSC)

BTS- It facilitates wireless communication between User equipment( mobile)  and network.

Antenna is also part of BTS.

It serves as Accesss point for Mobile devices to connect to network.

Transmit and receive radio signals to and from mobile devices.

Each BTS has a defined coverage area called Cell.

Size of cell depends upon various factors.

BTS generates carrier frequency for voice and data transmission.It modulates these carriers with the information from mobile devices,creating radio signals that can be received by mobile stations. These signals are then transmitted over air to mobile devices.

At reception end BTS demodulates these signals to extract transmitted voice/ data content.

Signal will reach from mobile to BTS , then BTS to BSC.

BSC-

Controls Call hand over between BTS stations under its jurdiction.

Manages multiple BTSs within a given area.

Monitors and controls BTS Hardware.

It ensures efficient use of radio frequency spectrum by allocating and releasing radio channels to mobile devices.

Connection to MSC for calls.

BSC provides authentication and encryption services to ensure security of communication between Mobile and network.

BSC records call details such as call duration,called number and other information for billing and accounting purposes.

MSC-

Gateway for all mobile communications 

Overseeing both inter BSC and Inter MSC handovers.

Network and Switching Subsystem ( NSS)

Manage communication between Mobile station and other users of the cellular network.

Home Location Register ( HLR)-

Subscriber relevant data are kept in database called Home Location Register ( HLR)

GSM radio spectrum-

Three main frequency bands 

GSM -900,GSM-1800,GSM -1900

IMEI ( International Mobile subscriber equipment identity)

Each mobile Equipment has IMEI number for its authentication and identification.

IMEI is 15 digit number.

EIREN - European Integrated Railway Enhanced Network 

GSM (R) is communication standard choosen by EIREN to meet the Railway requirements.

Enhanced Multilevel Precedence and Preemption ( eMLPP)

1. A telecom feature that provides prioritized Call handling in mobile and fixed network.

2. Often used in emergency Communication system to ensure high priority calls are connected even during network congestion.

3. Assigns priority level to each call based on its importance.

4. High priority calls are given preference.

5. Allows high priority calls to interrupt lower priority calls if network resources are scare.( Preemption)

6. Used in emergency services ( police,fire,medical).

PCM TDM -

PCM is a technique used to represent analog  signal into digital.

In practice many PCM signals representing different messages and transmitting them over same channel using TDM ( Time division multiplexing).

With PCM TDM system,two or more voice channels sampled,converted to PCM codes and then time division multiplied into onto a single metallic or optical fibre cable.


HDB3 Line Encoding used in PCM TDM-

It does not have any DC components in encoded signal.

It doesn't increase or decrease data rate.

Suitable for high data rate transmission over long distances 

It has the built in error detection facility.

LTE standard-

Developed by 3GPP ( 3rd Generation Partnership Project)

MAC address-6 bytes( 48 bits)

Spectrum alloted to IR for LTE - 5MHz of Spectrum in 700 MHz band.

Evolved packet core ( EPC) is core network of LTE.

Root Bridge-

Switch which has lowest bridge ID in Spanning tree process is Root Bridge.It is first Bridge elected in spanning tree process.

LTE downlink multiplexing - OFDM (Orthogonal Frequency Division Multiplexing).

2 G Technology 

Data speed - 64 kbps

Uses digital signal in place of Analog 

Bandwidth 30-200 khz

Enables services such as SMS and MMS.

Provides better voice calls

Technology- GSM

Internet - Narrow band

3 G Technology 

Data speed- 2 Mbps

Bandwidth 15-20  Mhz

Used for GPS and video calls 

Technology- WCDMA

Internet - Broad band

Comments

Post a Comment

Popular posts from this blog

Telecom

                                                    Basics of Telecom Mobile Communication   Emergency Communication  Emergency Communication is provided by following means a) Emergency Socket b) 5/25 Watt VHF sets c) GSM - R ( very less percentile) d) Mobile phones available with driver, guard and staff. Disadvantage of above mode of Emergency Communication - Section controller is not able to contact train crew in moving train It can be initiated only in static condition SOS facility is not available Weight of emergency control phone is fairly heavy. GSM - R is used at very less percentile. To avoid these Shortcoming MTRC ( Mobile train radio communication) is implemented. Accidents, unusual situation, robbery in train, Locomotive failure and chain pulling etc. Features of MTRC  - Driver to Control Guard to Control Driver to station maste...
Read more

Data Communication & Networking

  Data Components - A data communication system has five components. 1.  Receiver  2. Sender 3. Message  4. Transmission media- Path by which message travels. Ex Twisted pair wires, Coaxial cable,fibre optic cable and radio waves 5. Protocol  Protocol is set of rules used by computers to communicate with each other across network.  Protocols can be classified as Proprietary Protocol ( specific make) Open source Protocol ( Any make). Bandwidth -  It is defined as amount of data that can be transmitted into a fixed amount of time. Usually expressed in bps ( bits per   second) Fundamental Characteristics of Data Communication   1. Delivery- System must deliver data to correct destination  2. Accuracy- System must deliver data accurately  3. Timeliness- System must deliver data in a timely manner  4. Jitter- Jitter refers to variation in packet arrival time. It is uneven delay in the delivery of audio and video packets,which r...
Read more

Railway Establishment and Stores

  Max LAP approved one time - 180 days .( if available in his account). Max LHAP approved one time - 24 months ( if available in his account). Leave not due - Max 360 days in service. Can be sanctioned on medical grounds  Compensatory casual leave granted to Group C &D employees other than supervisory staff for attending on Sundays and holidays. Special casual leave    It is sanctioned for participation in sporting events/events of national importance,for scouting duties and family welfare. Special casual leave can be granted in following cases. Administration of operative society members. Participation in scouts . Participation in sports activities  Participation in railway union activities etc In bandh,curfew and national calamity. A railway Servant,who has taken CL for half a day on the afternoon of a working day due to unexpected sickness or compelling grounds and he has no CL at his credit, may as an exception to general rule,be permitted to combine h...
Read more