Structure introduction we discuss the logical channels that are used in gsm system. The forward channel is the direction of the communication or mobiletocell downlink path. The traffic channels are the resources available to the user for either speech or data. This page on gsm tutorial covers gsm logical channels and their functions. A tutorial, description, overview of gsm channels including transport and logical channels, sacch, sdcch, facch, etc. Global system for mobile communications gsm january 31, 2006. In gsm, these channels are separated into physical channels and logical channels. Mapping in frequency of logical channels onto physical channels. The major advantage of p25 is the ability to reduce the amount of noise heard in a transmission, and also to encrypt a call without any loss of audio quality. In radio communication, a control channel is a central channel that controls other constituent radios by handling data streams. The defintion of logical channels and details of traffic channels has been discussed in the previous. Channel types decide whether to carry traffic or signalling information.
Lcid logical channel id lcid is one of the most important component of a mac header. It uses the same carrier frequency of the logical channel with. The gprs slot may also be used by the base station to judge the time delay using a logical channel known as the packet timing advance control channel ptcct. Types of channels used in gsm and there discription. These gsm logical channels are responsible for effectively using the radio interface between a mobile and base transceiver station bts. In gprs each vendor is making his own version of the a bis protocol not speci. Firstly, logical traffic channels carry data in the user plane, while logical control channels carry signalling messages in the control plane. Gsm architecture or structure defined various channels in the air interface or radio interface. Gprs channel allocation although gprs uses only one physical channel pdch for the sending of data, it employs several logical channels that are mapped into this to enable the gprs data. May 26, 2016 this video explains the logical channels in the gsm global system for mobile and their usage. The set of logical channel types specified for nr includes.
Gsm logical channels telecommunications engineering. The channel used in the air interface is divided into two types. Broadcast control channel bcch it used for broadcasting mibssibs. Global system for mobile gsm david tipper associate professor graduate program of telecommunications and networking university of pittsburgh telcom 2720 slides 8 based largely on material from jochen schiller, mobile communications 2nd edition telcom 2720 2 second generation cellular systems motivation for 2g digital cellular. For example, on one of the physical channels used for traffic, the traffic itself is transmitted using a traffic channel tch message, while a handover instruction is transmitted using a fast associated control channel facch message. Sometimes, it can also be classified as the traffic channel and control channel. Different logical channels are used for different tasks. This lecture is about how the logical channels are used in global system for mobiles gsm for.
May 21, 2015 in the radio subsystem, the physical channel supports the logical channel based on the type of message transmitted. Rlc block 20 to 50 octets of data into normal radio bursts 58bit8 456bit. Study and learn these interview mcq questions and answers on 2g gsm channels, types and functionalities. Gprs general packet radio service a packet oriented data service for ip and x. Physical channels, logical channels, network, and operation kindle edition by harte, lawrence. This paper proposes the utilization of gsm logical channels rach, agch and tch and umts signaling mib and sibs of the broadcast channel to transmit a cognitive beacon channel cbc.
Different bursts are mapped to these channels uniquely as per gsm technical specification 05. This video explains the logical channels in the gsm global system for mobile and their usage. Download it once and read it on your kindle device, pc, phones or tablets. Fdma parts involves the division by frequency of the 25 mhz bandwidth in to 124 carrier frequencies also called arfcn spaced 200 khz for gsm900. Cdma channels can be broadly categorized as forward channel and reverse channel. Gsm logical channels free download as powerpoint presentation.
In downlink there are 4 control channel which carried common channel information as well as dedicated channel information. Umts channels logical,transport,physical umts channels. These channels are defined by gsm architecture or structure. The signalling channels are used for maintenance of the call and for enabling call set up, providing facilities such as handover when the call is in progress, and finally terminating the call. A logical channel is defined by the type of information it carries and is generally classified as a control channel, used for transmission of control and configuration information necessary for operating an nr system, or as a traffic channel, used for the user data. Traffic channel traffic channels carries speech and data.
In the gsm system, the logical channel is classified as the dedicated channel dch and the common channel cch. Jan 11, 20 lte logical channels structure and mapping between logical channels and transport channels. Aug 25, 2009 logical channels define what type of information is being transferred and transport channel defines how the information is being transferred. As shown in the figure there are two main types of channels in the gsm. Catching and understanding gsmsignals institute for computing. The physical channels are determined by the timeslot, whereas the logical channels are determined by the information carried within the physical channel. It consist of information carried over a physical channel. Both of the examples above looked at how the transmission that begins when the user presses the push to talk, or ptt, and ends when he or she releases the ptt, occurs on a conventional channel.
In this way, the physical channels are mapped as different logical channels. Gsm uses a variety of channels in which the data is carried. A logical channel is defined by the type of information it carries and is generally classified as a control channel, used for transmission of control and configuration information necessary for operating an lte system, or as a traffic channel, used for the user data. In this tutorial different types of logical channels and transport channels and their mappings are described. Therefore, there are 8 physical channels per carrier frequency in gsm. This tutorial on umts covers umts logical channels, transport channels and physical channels. This topic has 10 replies, 1 voice, and was last updated 9 years, 3 months ago by deepak.
As shown in the figure, there are three types of umts channels viz. Gsm technology global system for mobile communication or groupe special mobile to standardize cellular communication thoughout europe. The information transmitted on a logical channel depends on a particular task. Aug 03, 2017 in lte we have 7 logical channel in downlink and 3 logical channels in uplink. Study and learn these interview mcq questions and answers on 2g gsm logical channels and types. In p25 phase 2, a physical channel is divided into two time slots or logical channels. Depending on the quantity of information to transmit and on their consistency, several logical channels may be mapped onto one physical channel, in order to use its successive time slots as much as possible optimization of the resources number by maximizing the occupancy duration of each. The logical channels carry user information and control signalling data. Carries user data speech and data halfrate channel tchh. Gsm channels part 3 call flow in gsm using logical channels. Physical and logical channels gsm uses a mix of frequency division multiple access fdma and time division multiple access tdma. In p25 phase 1, a physical channel and logical channel are the same thing.
Physical channels, logical channels, network, and operation harte, mr. For gsm1800 frequency spectrum of 75 mhz bandwidth is. A logical channel will carry information of a specific type and a number of these channels may be combined before being mapped onto the same physical channel. Traffic channels tchs are intended to carry either encoded speech or user data. Nu tek india limited traffic channel carries the voice data two blocks of 57 bits contain voice data one tch is. It covers fcch, sch, bcch, ccch, rach, agch, pch, cbch, sacch, sdcch and facch. Halfrate tchs double the capacity of a system effectively by making it possible to transmit two calls in a single channel. Logical channels reside between rlc sublayer and mac sublayer which are layer 2 protocols in lte protocol stack. A logical traffic channel in gsm is abbreviated by tch. Logical channels are distinguished by the information they carry and can be classified in two ways. May 20, 2015 all these kinds of messages are classified in logical channels.
This lecture is about how the logical channels are used in global system for mobiles gsm for the mobile terminating call. Following table lists the logical channels that are used by lte. Two types of logical channels map onto physical channels control channels call setup, power adjustment, etc traffic channels voice or data 22. Introduction in telecommunications a channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel. For example speech is sent on the logical channel traffic channel which during the transmission is allocated a certain physical channel, say ts 6 on carrier 0. Nov 12, 2011 a physical channel may carry different messages, depending on the information that is to be sent. To understand the mapping of the logical channels onto physical channels, it is good to understand the two dimensions in time used by the gsm frame structure for more details on the frame structure, see section 3. Jan 14, 2011 this should serve as a basic explanation towards the gsm logical channels. This chapter explains the functionalities of these channels. Basically it tells the characteristics or the destination of the mac data.
Gsm, gprs, edge, channel allocation, tdma, time slot. The cross reference between gsm, umts, 3gpp and etsi identities can be found under. Cellular telephone system, gsm channels, gsm identities. In the western world most gsm traffic is encrypted using an algorithm. In summary, a physical radio channel is the frequency or frequency pair allocated by the regulatory body. The traffic channel tch carries voice or data, which are the fullrate traffic channel tchf and halfrate traffic channel tchh. Logical channels the data, whether user traffic or signaling information, are mapped onto the physical channels by defining a number of logical channels. Introduction to physical and logical channels tel3pedia. As mentioned at the beginning of the post, a more detailed treatment of the channel content will be done as part of another post where it is more appropriate. It is most often used in the context of a trunked radio system, where the control channel sends various data which coordinates users in talkgroups.
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