FCCH in GSM

FCCH stands for the Frequency correction channel in GSM.
It is a base to mobile channel that provides information for carrier synchronization. It is a special data burst that occupies the TS0 slot for the first GSM frame. It is repeated every ten frames within a control channel multi-frame.


The FCCH allows the mobile subscriber to synchronize its internal frequency standard with the frequency of the base station.


In the first burst of FCCH, all zero bits are sent to indicates the unmodulated carrier.

FCCH burst structure

AGCH in GSM

AGCH stands for Access grant channel in GSM. 

The AACH is used by the base station to provide forward link communication to the mobile. It carries data that instructs the mobile to operate in a specific channel with a particular dedicated control channel.

It is the message sent by the base station before a subscriber is moved off the control channel.

The AGCH is used by the base station to respond to RACH sent by the mobile station in the earlier CCCH frame. 

RACH in GSM

RACH stands for Random access channel in GSM.

It is a reverse link channel. With the help of RACH, the mobile station originates a call, send signaling message when not on call, acknowledges message.

It uses a slotted ALOHA access method. All mobile must access or respond to a PCH alert within TS0 of a GSM frame.

At the BTS each frame will accept the RACH transmissions from the mobiles during TS0. The base station responds to the RACH transmission by allocating a channel and a stand-alone dedicated control channel for signaling in the presence of a call. The connection is confirmed by the BS full form ( base station ) over the access grant channel.

Random access burst

DCCH channel in GSM

DCCHs stands for dedicated control channels in GSM. 

The dedicated control channel comes into the picture after a call is established. The dedicated control channels are bidirectional. They have the same formats and function in the forward and the reverse links.

Refer the following link to know details of the PCH, AGCH, RACH channel, and their processing.
  • GSM Fast associated control channel ( FACCH )
  • GSM Slow associated control channel ( SACCH )
  • GSM Stand dedicated control channel ( SDCCH )

SACCH in GSM

SACCH stands for Slow associated control channel GSM. 

It is related to the traffic channel or SDCCH.

On the forward link, it is used to send regularly changing information like: 
  • Transmit power channel 
  • Broadcast messages
  • Specific timing advance instruction for each user
On the reverse link, it carries information about 
  • Received signal strength 
  • Quality of TCH and BCH
  • Measurement results from neighboring cells
  • It is used to inform the base of power measurements made by the mobile of signal strength in the adjacent cells
  • It is transmitted during the total 13th frame of every dedicated control channel multi-frame
  • SACCH exchanges control information between the base station and mobile station a call or call set up

SDCCH in GSM

The full form of SDCCH is Stand-Alone Dedicated Control Channel GSM. 

The Standalone dedicated control channel is allocated for every mobile station.

It contains the signaling data that follows the connection of the mobile with the base station, prior to the allocation of TCH by the base station ( BS ) to the MS.

It guarantees that the mobile station, as well as the base station, will remain connected. The base station and mobile switching center will verify the subscriber unit and assign the needed resources to the mobile.

This channel that accepts the newly completed call from the BCH. It holds the traffic while waiting for the base station to assign a TCH channel.

The SDCCH is also used to transmit authentication and alert messages as the mobile synchronize itself with the frame structure and wait for TCH.

SDCCH can be assigned its own physical channel. Also, they can occupy the TS0 slot of the BCH if there is a low demand for BCH or CCCH traffic. 

FACCH in GSM

FACCH full form is Fast associated control channel.

 FACCH carries important messages. It is used for the exchange of time-critical information between the mobile and the base station during the process of the cell.

 The FACCH  is assigned whenever SDCCH is not dedicated to a user and there is an urgent message like a handoff request.

 The FACCH was transmitted control information by stealing capacity from the associated traffic channel. It is done by setting two special bits called stealing bits. In the TCH forward channel burst.

 If a stealing bit is set, the time slot contains FACCH data for that frame.

Synchronization channel

This channel acts as a base to the mobile channel. The mobile channel carries the information for identification and frame synchronization of the base station transceiver.

It also comprises the frame number in relation to the hyper frame and the BASIC ( Base station identity code ).

In the frame that after the FCCH, in time slot TS0 BTS transmit with SCH. The SCH has a unique burst structure. It comprises of 64-bit binary sequence that is common throughout the GSM networks.

The BASIC is assigned to each BTS in the GSM system. The SCH is transmitted once every ten frames within the control channel multi-frame.
Synchronization burst structure

Full form of IMEI

What is the full form of IMEI?


 Answer :
  • International Mobile Equipment Identity 

What does IMEI mean?


IMEI number is usually unique to identify GSM, WCDMA mobile phones as well as some satellite phones.

 IMEI is a generally 15 or 17 digit code that uniquely identifies mobile phone sets. The IMEI code can enable a GSM or UMTS network to prevent a misplaced or stolen phone from initiating calls.

IMEI is mostly printed inside the battery compartment of the phone device. It also can be displayed on the screen by entering the following code using the keypad device : *#06# 


Explore more information:

GSM channel types

GSM channels help to maintain the GSM network. It also helps GSM mobile phones connect to the GSM network and maintain the connection. 

This article is very helpful in GSM network and also to learn more details about the different types of channels used in GSM system and how to work. 

The figure below mentions all the channels used in GSM. 

There are two main types of GSM channel : (i) Traffic channel (ii) Control channel


The following logical channels are defined in GSM :

TCH : Traffic channel. 

TCH/F : Full rate traffic channel.

TCH/H : Half rate traffic channel.

BCCH : Broadcast control channel for describing the current control channel structure.
BCCH is a point to multi point channel ( BSS to MS ).

SCH : Synchronization channel for the MS.


FCCH : Frequency correction channel.

CCCH : Common control channel. 

PCH : Paging channel terminating call announcement.

AGCH : Access grant control channel.

RACH : Random access control channel for access requests, response to call announcement, location update etc.

DCCH : Dedicated control channel. 

SACCH : Slow associated control channel for TCH in-band signaling for link monitoring.

SDCCH : Standalone dedicated control channel for signaling exchanges during call setup, registration / location updates.

FACCH : Fast associated control channel for time-critical signaling over the TCH for handover signalling.

Notes : For more detailed information about these channels click on the respective channel name.  

EIR full form

What is the full form of EIR?


 Answer :

  • Equipment Identity Register 


What does EIR mean?


The EIR is the world's most advanced software solution for authentication of mobile devices in the network, including IoT devices.

 EIR is one type of database that contains a record of all the MS full form Mobile Station that are allowed in a network as well as a database of all equipment that is banned.  The main identity of the mobile station is given by the IMEI full form of International Mobile Equipment Identity.

 EIR provides a single, unified access point, fully standards-compliant, 4G/LTE, 5G and IT interfaces, active triggering, reporting, alarming, and many more features.

Power electronic systems

Power electronics is a technology associated with the efficient conversion, control, and conditioning of electric power by static means from its available input form into the desired electrical output form.

 The main component of the power electronic system is shown in the form of a block diagram in a figure. The main power source may be an AC supply system or a DC supply system.
The output from the power electronic circuit, it may be variable DC or AC voltage, or it may be a variable voltage and frequency. In general, the output of a power electronic converter circuit depends upon the requirement of the which type of load.
The feedback component in the figure measures a parameter of the load, says speed in case of a rotating machine and compares it with the command.

The difference between these two, through the digital circuit components and controls the instant of turn-on of semiconductor devices forming the solid-state power converter system.
In this manner, the behavior of the load circuit can be controlled as desired, over a wide range with the adjustment of the command. 
Block diagram of a typical power electronic system
You can check more details about power electronics system: POWER ELECTRONICS 

Difference between thyristor and thyratron

Thyratrons were used for industrial control before the discovery of thyristors device but now they have been replaced by the thyristors in nowadays. They both are three-terminal devices still the construction of gate terminal are different form. Now let check it out the difference between them to know more about that.

Difference between thyristor and thyratron :


  • Thyristor is a current controlled device while thyratron is a voltage-controlled device.
  • Thyristor is light in weight and require less space, thyratron heavy and requires more space.
  • Thyristor is more reliable whereas thyratron is not reliable.
  • Thyristor is higher Turn-ON and Turn-OFF time and smaller Turn-ON and Turn-OFF time in case of thyratron device.
  • A thyristor is more accurate comparison to the thyratron.
  • A thyratron is costlier compared to the thyristor.
  • Thyristor needs only one low power supply and control signal to perform the operation while Thyratron needs too much large power supply between anode and cathode.
  • The life of thyristor is greater than to thyratron.
  • Internal losses are more in the case of thyratron as compare to the thyristor device.
  • The thyristor is a more accurate comparison to the thyratron.
  • Thyratron takes a long time in ionizing and deionizing, therefore, is unsuitable for higher frequency but thyristor can operate a wide range of frequencies.







GSM network block diagram

Before we learn about the GSM block diagram first let us check out what is the full form of GSM. The transceiver antenna transmits or receives the RF signal. The analog to digital and digital to analog conversion are done in the opposite direction depending on transmission or reception.
Functional block diagram of a GSM phone 

 The microphone and loudspeakers are used in opposite directions.

 The channel coding is done in the opposite direction with the help of the interleaving method.

 Modulation is done by using the Gaussian minimum shift keying method.

 The antenna is MIMO. User authentication is also possible with GSM phones.

 Depending on the services provided by the GSM technology standard there are six examples :
  • Transnational service - shopping, booking
  • Traveling related -  roaming, weather
  • Mobile office - modem, fax, email
  • Fun - gambling, online games
  • Personal services - budgeting, health monitoring, paying bills
  • Security services - emergency calls, alarm provision

Full form of NSS

What is the full form of NSS?


Answer :

  • Network and Switching Subsystem


What does NSS mean?


NSS is the component of the GSM system full form that carries out the call out and mobility management function for mobile phones roaming on the network of base stations.

 NSS is responsible for managing and providing external access to various customer databases.

 NSS  has to handle the switching of GSM calls between the BSCs in the radio subsystem and external networks.
The central component of this subsystem is the MSC full form. It controls all the traffic among all the BSCs.

Full form of OSS

What is the full form of OSS?


Answer :

  • Operation Support System

What does OSS mean?


The OSS one or many operation maintenance centers that are used to monitor and maintain the performance of different subsystems within a GSM system.

 The three functions of OSS are :
  • To manage subscription management
  • OSS also have to manage all telecommunication hardware and network operation within a market
  • To manage all mobile equipment in the system

Full form of AUC

What is the full form of AUC?


Answer :

  • Authentication Center 

What does AUC mean?


AUC is a protected database that can store a copy of the secret key stored in each subscriber SIM card that is used for authentication and encryption over the radio channel.

 The authentication center maintains authentication keys and algorithms. It provides security triplets like RAND, SRES, and Kc to the VLR.

The authentication center handles authentication and encryption keys for each subscriber in the HLR full form is Home Location Register and VLR full form is Visitor Location Register.

Full form of VLR

What is the full form of VLR?


Answer :

  • Visitor Location Register

What does VLR mean?


 A VLR is a database that contains information about the subscriber roaming within a mobile switching center (full form of MSC) location area. The primary role of the VLR is to minimize the number of queries that MSCs have to make to the home location register, which holds data regarding the cellular network subscriber.

VLR contains selected administrative information from Home Location register - ( full form of HLR ) essential for call control and provision of subscribed services. The VLR is a temporary database. 

 It stores the IMSI full form number and customer information for each roaming customer visiting the coverage area of a specific MSC.

 Ideally, there should be only one visitor location register per MSC, but it is also possible for single VLR to serve multiple MSCs.

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Full form of MS

What is the full form of MS?


Answer :

  • Mobile Station

What does MS mean?


MS comprises of mobile equipment smart card called SIM.

SIM provides personal mobility to have access to subscribed services irrespective of the mobile equipment. After inserting the SIM card into a GSM handset, the user can receive calls, make calls and enjoy other subscribed services.

The mobile equipment is uniquely identified by the international mobile equipment identity number.

GSM system architecture

A GSM network consists of various functional entities. Those functional entities' functions and interfaces are specified. The figure shows the generic architecture of a GSM network. First of all, you should know the full meaning of GSM.

A  GSM architecture consists of three major subsystems that interact between themselves with the users through some network interfaces. 

The subsystems are :
  • BSS (Base station subsystem)
  • NSS (Network and switching subsystems)
  • OSS (Operation support subsystem)
Notes: You can check more basic information about that then check the link in the end of this post.
GSM architecture
The MS full form is Mobile station is also a subsystem. but it is considered to be part of BSS for architecture purposes.

The mobile station communicates with the base station subsystems over the radio interface

The BSS called as the radio subsystem provides and manages the radio transmission path between the mobile stations and the mobile switching centre. It also manages radio interface between mobile stations and other subsystems of GSM.

Each BSS comprises many base station controllers that connect the mobile station to the network and switching subsystem through the mobile switching center.

The NSS controls the switching function of the GSM system. It allows the mobile switching center to communicate with networks like PSTN full form, ISDN, CSPDN, PSPDN, and other data networks.

The operation support system ( OSS ) allows the operation and maintenance of the GSM system. It allows system engineers to diagnose troubleshoot and observe the parameters of the GSM system. The OSS subsystems interact with the other subsystems and is provides for the GSM operating company staff that service facilities for the network.

You may also know about full form of BSS, BSC, HLR, VLR, MSC, EIR, AUC, OMC
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