Physical & Logical Channels. Frame Structure. GSM Channels. Engr. Mian Shahzad Iqbal. Lecturer. Department of Telecommunication. Types of channels used in GSM and there discription. Two groups of logical channels: • Traffic Channels, for call data • Control channels. GSM Logical bestthing.info - Download as PDF File .pdf), Text File .txt) or read online. basics.
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Cellular Telephone System, GSM Channels, GSM Identities. GSM Logical Channels consists of two types: Control Channels . deepesh/hie bestthing.info billion people around the world depend on GSM for at least a part of their day to It defines logical channels and bursts; the basic units used to send information. bestthing.info, December A tutorial, description, overview of GSM channels including transport and logical channels, SACCH, SDCCH, FACCH, etc.
RACH is transmitted on the uplink, pointto-point. It is termed random because there is no mechanism to ensure that no more than one MS transmits in each RACH time slot and there is a finite probability that two mobiles could attempt to access the same RACH at the same time. Use Access Burst.
The AGCH is used by the network to grant, or deny, an MS access to the network by supplying it with details of a dedicated channel, i. The AGCH is a down-link only channel. On the uplink MS sends averaged measurements on own base station signal strength and quality and neighboring base stations signal strength. On the downlink the MS receives system information, which transmitting power and what timing advance to use.
It is transmitted at 13 th Frame of TCH. This channel is always present when a dedicated link is active between the MS and BTS, and it occupies one timeslot in every SACCH messages may be sent once every ms, i.
FACCH works in stealing mode, meaning that one 20 ms segment of speech is exchanged for signalling information necessary for the handover.
The subscriber will not recognize this interruption in speech since the speech coder will repeat the previous speech block. This would, however, be a waste of the limited radio resources. Also used in call setup process.
Cyclic Hopping - The transceiver hops through a predefined list of frequencies in sequential order. Random Hopping - The transceiver hops through the list of frequencies in a random manner.
The sequence appears random but it is actually a set order. There are a total of 63 different hopping algorithms available in GSM.
When the MS is told to switch to frequency hopping mode, the BTS will assign it a list of channels and the Hopping Sequence Number HSN , which corresponds to the particular hopping algorithm that will be used.
The base channel on the BTS does not frequency hop. This channel, located in time slot 0, holds the Broadcast Control Channels which the MS needs to monitor to determine strength measurements, determine access parameters, and synchronize with the system.
All of the other TRXs may use time slot 0 for traffic or signaling and may take part in the frequency hopping.
There are two types of frequency hopping method available for the BTS: synthesizer hopping and baseband hopping. Synthesizer Hopping - This requires the TRX itself to change frequencies according to the hopping sequence. Baseband Hopping - In this method there are several TRX and each one stays on a fixed frequency within the hopping frequency plan.
GSM Logical & Physical Channels
So, the data on each time slot would be sent on a different frequency each frame, but the TRXs on the BTS do not need to change frequency.
We also know that the duration of a TCH multiframe is ms.
Convert milliseconds ms to seconds: Now we need to put the value into terms of seconds. There are milliseconds in a second, so we simply multiply the value by Convert bits to kilobits: Finally, we want to put it into terms of kilobits per second, wich is the most common term for referring to data throughput. We know a kilobit is bits, so we simply divide the term by What affects channel 23 may not affect channel 78 at all. Within a given cell, some frequencies will have good propagation in a certain area and some will have poor propagation in that area.
In order to take advantage of the good propagation and to defeat the poor propagation, GSM utilizes frequency hopping. Frequency hopping means that a transceiver hops from one frequency to another in a predetermined sequence. If a transceiver hops through all of the avilable frequencies in a cell then it will average out the propagation.
It is considered slow becuase the system hops relatively slow, compared with other frequency hopping systems.
The main reason for using slow frequency hopping is because the MS must also change its frequency often in order to monitor adjacent cells.No notes for slide. Embeds 0 No embeds. The broadcast channels are used to broadcast synchronization and general network information to all the MSs within a cell.
You can also read about the numbering schemes used in GSM. Different time slots will carry different logical channels, depending on the structure the BSS uses.
The uplink is exactly 3 time slots behind the downlink. Cellular Network Organization.