Physical, logical and control channels each have different functions as described below. While handover instruction is transmitted using a fast associated control. Gsm global system for mobile communications is an open, digital cellular technology used for transmitting mobile voice and data services. Logical channels further can be divided into two categories as control channels and traffic channels. 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.
Logical channels tells what kind of information is transferred. This chapter first covers how to introduce a cdma carrier in an existing amps or tdma system, establishing the number of amps or tdma channels that should be removed in order to introduce the first and second cdma carrier of 1. Mario jorge leitao gsm 3 performance characteristics of gsm communication mobile, wireless communication. Download it once and read it on your kindle device, pc, phones or tablets. From the physical layer, the mac layer uses services in the form of transport channels.
Different bursts are mapped to these channels uniquely as per gsm technical specification 05. In gsm as well, we have many different types of physical and logical channels and each of these channel types are using its own physical structure at the level of a slot burst. The physical channels are determined by the timeslot, whereas the logical channels are determined by the information carried within the physical channel. Viewing 11 posts 1 through 11 of 11 total author posts 17th august 2008 at 14. Different logical channels are used for different tasks. The following picture depicts the logical channel hierarchy. For example bcch is broadcast control channel which broadcasts the information about the system. Gprs uses the same modulation and frame structure that is employed by gsm, and in this way it is an evolution of the gsm standard. In 3gpp specifications, several types of data transfer services are offered by mac. Study and learn these interview mcq questions and answers on 2g gsm logical channels and types. Theses are actual physical rf channels 79 frequenc. In gsm, these channels are separated into physical channels and logical channels.
Physical channels, logical channels, network, and operation. Physical downlink control channel pdcch informs the ue about the resource allocation of pch and dlsch, and harq information related to dlsch. Halfrate tchs double the capacity of a system effectively by making it possible to transmit two calls in a single channel. Gsm physical layer, 2g gsm global system for mobile communications, 1991 frequency bands. All these kinds of messages are classified in logical channels. Logical channel type in gsm as we know, every cell has several trx and every trx includes 8 timeslots i. Gsm is a circuitswitched system that divides each 200 khz channel into eight 25 khz timeslots. Channels and arfcn slightly different in other frequency bands a tdma frame is defined on the radio carrier 8 users per carrier channel rate is 270. It also covers gsm noncombined channel configuration51 frame multiframe and gsm combined channel configuration51 frame multiframe. This page on gsm tutorial covers channel types logical gsm channels,physical gsm channels and mapping between them. 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.
Gsm uses number of channels to carry data over air interface, these channels are broadly divided in to following two categories. Every gsmgprs physical channels are mapped to one of these burst types and the mapping is described below. Wireless systems with updated information 2004 by the althos publishing inc. Each logical channel type is defined by the type of information that it transfers. A physical channel may carry different messages, depending on the information that is to be sent. These channels are defined by gsm architecture or structure. Chapter 7 physical and logical channels of is95 cdma 7. Umts logical channels and transport channels 3glteinfo. What is difference between the physical and logical.
Logical channels can be broadly divided into two types. Introduction to physical and logical channels tel3pedia. Arfcn x, timeslot y, frame number n logical channels control channels traffic channels logical channel. Gsm uses a variety of channels in which the data is carried. Gsm channels part 3 call flow in gsm using logical channels. Physical channels a physical channel is determined by the carrier frequency or a number of carrier frequencies with defined hopping sequence and the time slot number.
Physical and logical channels gsm uses a mix of frequency division multiple access fdma and time division multiple access tdma. Each timeslot on a tdma frame is called a physical channel. The physical channel is the medium over which the information is carried, in the case of a terrestrial interface this would be a cable 2. For example, on one of the physical channels used for traffic, the traffic itself is transmitted using a traffic channel tch message. The defintion of logical channels and details of traffic channels has been discussed in the previous. It is used by many logical channels like ccch, dcch dtch. Gsm global system for mobile communications is an open. Nu tek india limited traffic channels tch one physical channel 1 timeslot can support. Aug 03, 2017 it is used by many logical channels like ccch, dcch dtch. These channels are used to convey information from the network to mss and provide access to the network.
Structure introduction we discuss the logical channels that are used in gsm system. A physical channel may carry different messages, depending on information that is to be sent. 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. However, lte provides additional logical channels for features not yet supported by nr but likely to be introduced in upcoming releases. What are the different types of channels in gsm and their function answer m. Gsm is the name of a standardization group established in 1982 to create a common european mobile telephone standard.
These channels are also in both direction downlink and uplink directions. These gsm logical channels are responsible for effectively using the radio interface between a mobile and base transceiver station bts. Nu tek india limited channels in gsm air interface logical channels. Logical channels are transmitted on physical 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. Gsm logical channels free download as powerpoint presentation. Logical channels the data, whether user traffic or signaling information, are mapped onto the physical channels by defining a number of logical channels. Therefore, there are 8 physical channels per carrier frequency in gsm. I understand the different types of channels common continue reading gsm logical vs physical channels.
Followings are the types of burst being used in gsmgprs. Logical channel physical channel similar to computers, we need a set of the physical layer specifies how the information instructions and ports to instruct different from different voice and data. There is a variety of channels used within gprs, and they can be set into groups dependent upon whether they are for common or dedicated use. May 20, 2015 all these kinds of messages are classified in logical channels. Carries user data speech and data halfrate channel tchh. In p25 phase 2, a physical channel is divided into two time slots or logical channels. Every gsm gprs physical channels are mapped to one of these burst types and the mapping is described below.
In p25 phase 1, a physical channel and logical channel are the same thing. A variety of information is transmitted between the bts and the ms. Naturally the system does use the gsm control and broadcast channels for initial set up, but all the gprs actions are carried out within the gprs logical channels carried within the pdch. Study and learn these interview mcq questions and answers on 2g gsm channels, types and functionalities. Based on, as mentioned earlier, whether they carry gsm traffic ie, speech or data or gsm. The video explains the orderly use of pch, rach, sdcch, sacch and tch. Gsm channels in order to transmit information, we required the channels. In summary, a physical radio channel is the frequency or frequency pair allocated by the regulatory body. As shown in the figure there are two main types of channels in the gsm. Based on, as mentioned earlier, whether they carry gsm traffic ie, speech or data or. Gsm owns a market share of more than 70 percent of the worlds digital cellular subscribers.
There are two types of gsm logical channels, called traffic channels tch and control channels cch. One ts on a tdma frame is called a physical channel, i. Gsm differs from first generation wireless systems in that it uses digital technology and time division multiple access tdma transmission methods. Introduction to physical and logical channels home unlabelled introduction to physical and logical channels. What is the difference between physical and logical channel. The broadcast channels bch carry only downlink information. Jan 14, 2011 logical channels in gsm are defined by the type of information that is carried over them. Each logical channel is used for a specific purpose such as paging, call setup and speech. This topic has 10 replies, 1 voice, and was last updated 9 years, 3 months ago by deepak.
May 26, 2016 this video explains the logical channels in the gsm global system for mobile and their usage. Common control channels ccch a group of uplink and downlink channels between the ms and the bts. Radio channels, physical channels and logical channels. Introduction to wcdma physical channels, logical channels. Traffic channels are used to send speech or data services. They are used to transport speech, user data, high layer signally, cell specific information to name a few. These channels assist in call terminations and sms delivery. While most logical channels take only one time slot to transmit, some take more. Gsm architecture or structure defined various channels in the air interface or radio interface.
So we can divide these into downlink physical channels and uplink physical channels. Gsm operates on the mobile communication bands 900 mhz and 1800 mhz in most parts of the world. In the radio subsystem, the physical channel supports the logical channel based on the type of message transmitted. Physical channels, logical channels, network, and operation you will then discover the different types of available services such as voice services, data services, group call, and messaging services. Nu tek india limited logical channel one or more logical channel can be transmitted on a physical channel. Sice gsm is a tdm system these logical channels are multiplexed onto physical channels and then transmitted over the air interface. Physical downlink shared channel pdsch carries the dlsch and pch. Use features like bookmarks, note taking and highlighting while reading introduction to gsm. In the us, gsm operates in the bands 850 mhz and 1900 mhz. The information transmitted on a logical channel depends on a particular task. Since channels and links are not similar things to differentiate or compare, im just going to define and elaborate bit on each of them. Jan 11, 20 logical channels reside between rlc sublayer and mac sublayer which are layer 2 protocols in lte protocol stack. Aug 25, 2009 logical channels define what type of information is being transferred and transport channel defines how the information is being transferred.
The method of placing logical channels on physical channels is called mapping. Physical channels, logical channels, network, and operation at. Physical channels, logical channels, network, and operation kindle edition by harte, lawrence. Physical channels can be used to transmit speech, data or signaling information.
Global system for mobile communication gsm definition global system for mobile communication gsm is a globally accepted standard for digital cellular communication. In this tutorial different types of logical channels and transport channels and their mappings are described. Learn more about introduction to wcdma physical channels, logical channels, network, and operation on globalspec. Easily attend job interviews and college exams with these multiple choice questions. Logical channels in gsm are defined by the type of information that is carried over them. Followings are the types of burst being used in gsm gprs. Channel types decide whether to carry traffic or signalling information. Described are the fundamental capabilities and operation of the gsm radio channel including channel coding, modulation types, speech coding, rf power control, and mobile assisted handover. Traffic channels carry digitally encoded user speech or user data and have identical functions and formats on both the forward and reverse link. Introduction to global system for mobile communication gsm. Logical channels can be classified into two general groups.
The above logical channels are in general present also in an lte system and used for similar functionality. Logical channels are sch, fch,bcch, sacch, facch, rach, agch, etc. Number of logical channels per physical channel number of time slots in tdma frame. What are the allowed logical channel combinations in gsm. May 27, 2016 this lecture is about how the logical channels are used in global system for mobiles gsm for the mobile terminating call. Professionals quickly discover that, although the technical specifications for gprs cover all parts of the engineering functions in detail and depth, they are lacking in one important feature. The information is grouped into different logical channels. Physical channels, logical channels, network, and operation through a thorough description of key functional sections of a gsm network and how they communicate with each other, you will learn how and why gsm is evolving into 3rd generation broadband systems including gprs, edge, and. Gsm logical channels telecommunications engineering.
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