Frame structure of GSM

Each GSM user transmits data burst during a time slot that is assigned to it. The transmission of bursts occurs in a particular format called the GSM frame.

There are five types of data bursts for controlling the traffic bursts.

Normal burst :

The normal burst is used for TCH and the DCCH transmissions on the forward and reverses link. It consists of 148 bits that are transmitted at a rate of 270.83 Kbps. Only 114 bits are information bits that are transmitted as two sequences of 57 bits.

FCCH burst :

It consists of 3 start bits 3 stop bits with 142 bits between the start bits and stops bits. The stop bits are followed by a guard period of 8.25 bits.
RACH burst : 

 It consists of 8 start bits and 3 stop bits. It 41 bits for synchronization of transmitter and receiver, 36 bits of encrypted data an extended guard period of 68.25 bits.

SCH burst : 

It consists of 3 start bits, 39 bits of encrypted data, 64 training bits, 3 stop bits and a guard period of 8.25 bits.
                 
Dummy burst : 

 It consists of 3 starts and 3 stop bits. It contains two parts of 58 mixed bits that are separated by 26 training bits and a guard period of 8.25 bits.

The frame structure of GSM :



GSM frame structure 

TCH in GSM

TCH stands for a traffic channel in GSM.
This article describes the GSM traffic channel. Traffic channel carries digitally encoded user data or user speech on the forward and reverse link.
TCH support two types of information rates, they are
  • Full rate ( TCH/F )
  • Half rate ( TCH/H )
TCH is a group of 26 consecutive TDMA frame, called multi-frame of the 26 TDMA frames, 24 are used as TCH frames, one frame (thirteen ) is for SACCH and 26th is the unused or idle frame.
TCH data transmitted in 26 consecutive frames

1. Full rate TCH  (TCH/F)

Full rate speech channel  (TCH/FS) - At 13 Kbps the full rate speech channel is digitized. After channel coding, full rate speech channel carries 22.8 Kbps.

Full rate data channel (TCH/F9.6), Full rate data channel (TCH/F4.8), Full rate data channel (TCH/F2.4) channel carries the data at the speed of 9.6 Kbps, 4.8Kbps, 2.4Kbps respectively.

After channel coding is applied is converted to data transferred rate at up to 22.8 Kbps.

2. Half rate TCH (TCH/H)


Half rate speech channel (TCH/HS) - At 6.5 Kbps the half rate speech channel is digitized. After channel coding, half rate speech channel carries up to 11.4 Kbps.

Hull rate data channel ( TCH/H4.8), Full rate data channel (TCH/H2.4) channels carry the data at the speed of 4.8 Kbps, 2.4 Kbps respectively.

After channel coding is applied is converted to data transferred rate at up to 11.4 Kbps.
Explore more information:

  1. CCCH in GSM
  2. BCCH in GSM
  3. AGCH in GSM
  4. FCCH in GSM
  5. RACH in GSM
  6. DCCH in GSM
  7. SACCH in GSM
  8. SDCCH in GSM
  9. FACCH in GSM

CCCH in GSM

CCCH stands for the common control channel in GSM.

GSM  common control channel ( CCCH ) is used for conveying from network to the mobile subscriber and provide access to the mobile subscriber,

There are three types of different channels  : (I) PCH, (II) AGCH, (III) RACH

Refer the following link to know details of the PCH, AGCH, RACH channel, and their processing.
  • GSM Paging channel ( PCH )
  • GSM Access grant channel ( AGCH )
  • GSM Random access channel ( RACH )

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BCCH in GSM

BCCH stands for the broadcast control channel. This article learns to GSM broadcast control channel.

The BCCH  is a forward channel and also is a unidirectional base to mobile channel that provides information about the network, the cell in which the mobile is currently located and adjacent cells. BCCH is transmitted in 51 frames multi frame structure in a frame next to SCH on TS0. It broadcast a list of the channel that is currently in use within the cell.

The BCCH includes two channels, they are : (I) FCCH  (II) SCH

Refer the following link to know details of the PCH, AGCH, RACH channel, and their processing. 
  • Frequency correction channel ( FCCH )
  • Synchronization Channel ( SCH )

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# 


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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
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