Gsm logical vs physical channels this topic has 10 replies, 1 voice, and was last updated 9 years, 3 months ago by deepak. This page on gsm tutorial covers gsm logical channels and their functions. Physical channels where to send this information these all three types of channel are present in downlink as well as uplink direction. Every gsm gprs physical channels are mapped to one of these burst types and the mapping is described below. 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. A traffic channel tch is used to carry speech and data traffic. The gsm radio spectrum 9001800 mhz the network layer 3 cc, mm, rr propagation cellular principles ci ratio traffic and grade of service path loss and cell planning tools section 2 the physical channels and logical channels terminating a datalink time division multiple access physical channel structure of air bursts. Logical channels reside between radio link control rlc and medium access control mac layer. These logical channels are mapped onto the physical channels. Dedicated control channel an overview sciencedirect topics.
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. 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. Radio channels, physical channels and logical channels the. Gsm network architecture, channelisation, signalling and. Gsm architecture or structure defined various channels in the air interface or radio interface. Feb 01, 2018 lte physical logical transport channel and mapping fundamentals of 4g lte by pankaj kumar telecom world. Mapping of these channels is shown in below pictures. Logical channel type in gsm as we know, every cell has several trx and every trx includes 8 timeslots i. Explained are the physical and logical radio channel structures of the gsm system along with the basic frame and slot structures.
The above logical channels are in general present also in an lte system and used for similar functionality. Gsm logical channels traffic channels tch a traffic channel tch is used to carry speech and data traffic. Gsm logical channels a large amount of information is transmitted between the ms and the bs, particularly, user information and control signalling data. Gsm logical channels telecommunications engineering. They are used to transport speech, user data, high layer signally, cell specific information to name a few. Fdma parts involves the division by frequency of the 25 mhz bandwidth in to 124 carrier frequencies also called arfcn spaced 200 khz for gsm 900. 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. The physical channels are determined by the timeslot, whereas the logical channels are determined by the information carried within the physical channel. Physical and logical channels gsm uses a mix of frequency division multiple access fdma and time division multiple access tdma. Logical channels reside between rlc sublayer and mac sublayer which are layer 2 protocols in lte protocol stack. The channel used in the air interface is divided into two types.
Lte physical logical transport channel and mapping. This combination of time slot and carrier frequency forms what is termed a physical channel. Cellular telephone system, gsm channels, gsm identities. It covers fcch, sch, bcch, ccch, rach, agch, pch, cbch, sacch, sdcch and facch. While most logical channels take only one time slot to transmit, some take more. In gsm, these channels are separated into physical channels and logical channels.
It is the medium over which the information is carried. Umts channels logical,transport,physical umts channels. Different bursts are mapped to these channels uniquely as per gsm technical specification 05. In summary, a physical radio channel is the frequency or frequency pair allocated by the regulatory body.
This tutorial on umts covers umts logical channels, transport channels and physical channels. Gsm uses a variety of channels in which the data is carried. Easily attend job interviews and college exams with these multiple choice questions. After adding gsm channel coding to the digitized speech, the half rate speech channel will carry 11.
In gsm, the core network consists of two service domains cs circuit switched and ps packet switched, in the cs domain there is. May 20, 2015 all these kinds of messages are classified in logical channels. 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. Like any form of wireless data link, the data needs to be managed to enable the system to handle it efficiently and effectively. There are broadly two categories of logical channels available. Types of channels used in gsm and there discription. Wireless course physical vs logical channels on air interface physical channels. It can be further summarised by saying that several recurring timeslots on a carrier constitute a physical channel. 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. Logical channels at the service access point sap of layer 1 physical layer. The figures clearly indicate how dlsch and ulsch are the main downlink and uplink transport channels, respectively. 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 channels in order to transmit information, we required the channels. The half tate speech channel can carry digitized speech that is sampled at a rate half that of full rate channel.
However, lte provides additional logical channels for features not yet supported by nr but likely to be introduced in upcoming releases. 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. The method of placing logical channels on physical channels is called mapping. A physical channel is specified by a specific time slot in a specific channel carrier frequency logical channels.
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. Slow associated control channel sacch, uses the same physical channels as the traffic channel tch or sdcch for sending measurement. Control channels for the transfer of control plane information traffic channels for the transfer of user plane. There are several forms of control channels in gsm, and they can generally be divided into three categories according to the manner in which they are supported on the radio interface and the type of signalling information they carry.
In the gsm system, the logical channel is classified as the dedicated channel dch and the common channel cch. Traffic channels are defined using a 26frame multi frame, or group of 26 tdma frames. As shown in the figure there are two main types of channels in the gsm. Global system for mobile gsm university of pittsburgh.
Download it once and read it on your kindle device, pc, phones or tablets. For gsm 1800 frequency spectrum of 75 mhz bandwidth is divided in to 374 carrier frequencies spaced. Logical channels many types of logical channels exists, each designed to carry a different message to or from an ms. 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. Logical channels can be broadly divided into two types. Gsm logical channels free download as powerpoint presentation. These channels are also in both direction downlink and uplink directions. Chapter 7 physical and logical channels of is95 cdma 7. All these kinds of messages are classified in logical channels. Broadcast control channel, carry cgi,mnc,mcc which is received by ms.
These channels define the datatransfer services offered by the mac layer. When an ms and a bts communicate, they do so on a specific pair of radio frequency rf carriers, one for the uplink and the other for the downlink transmissions, and within a given time slot. A physical channel may carry different messages, depending on the information that is to be sent. As they tranverse between layers they map to other layer frames. Reference model fro the gsm usernetwork interface uni um. Cdma channels can be broadly categorized as forward channel and reverse channel. Use features like bookmarks, note taking and highlighting while reading introduction to gsm. Logical channels are transmitted on physical channels. The following picture depicts the logical channel hierarchy. Mapping in frequency of logical channels onto physical channels.
Jan 11, 20 logical channels reside between rlc sublayer and mac sublayer which are layer 2 protocols in lte protocol stack. Radio channels, physical channels and logical channels. It consist of information carried over a physical channel. In this tutorial different types of logical channels and transport channels and their mappings are described. In the figures, the corresponding physical channels, described later, are also included. This topic has 10 replies, 1 voice, and was last updated 9 years, 3 months ago by deepak.
The defintion of logical channels and details of traffic channels has been discussed in the previous. Firstly, logical traffic channels carry data in the user plane, while logical control channels carry signalling messages in the control plane. Physical channels can be used to transmit speech, data or. So we can divide these into downlink physical channels and uplink physical channels. Catching and understanding gsmsignals institute for computing.
Logical channels the physical channels one timeslot per radio channel shown in the previous slides represent the entity transmitted through the air interface each physical channel is used totrasmit a logical channel with different functions logical channels can be divided in 2 main groups traffic channel. From the physical layer, the mac layer uses services in the form of transport channels. Jan 14, 2011 logical channels in gsm are defined by the type of information that is carried over them. Gsm channels gsm telecommunications free 30day trial. Two types of logical channels have been introduced, namely traffic channels and control channels. For gsm 1800 frequency spectrum of 75 mhz bandwidth is divided in to 374 carrier frequencies spaced 200 khz. Logical channels are mapped into physical channel burst structure. Physical is logical channel which consists of the information. The mapping between logical channel types and transport channel types is given in figure 4. Logical channels the data, whether user traffic or signaling information, are mapped onto the physical channels by defining a number of logical channels. Following table lists the logical channels that are used by lte. Gsm channels free download as powerpoint presentation. Aug 03, 2017 it is used by many logical channels like ccch, dcch dtch.
Logical channels the physical channels one timeslot per radio channel shown in the previous slides represent the entity transmitted through the air interface each physical channel is used totrasmit a logical channel with different functions logical channels can be divided in 2 main groups traffic channel tch. For example bcch is broadcast control channel which broadcasts the information about the system. Physical channels, logical channels, network, and operation kindle edition by harte, lawrence. Three subtypes of control channels have been defined for gprs. 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. Physical, logical and control channels each have different functions as described below. I understand the different types of channels common continue reading gsm logical vs physical channels. The forward channel is the direction of the communication or mobiletocell downlink path. These channels assist in call terminations and sms delivery. Gsm uses number of channels to carry data over air interface, these channels are broadly divided in to following two categories. 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. User data across air interface using traffic channels, tch. Aug 25, 2009 logical channels define what type of information is being transferred and transport channel defines how the information is being transferred. 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.
Gprs, like gsm, uses the concept of logical channels mapped on top of the physical channels. Gsm physical layer, 2g gsm global system for mobile communications, 1991. In p25 phase 1, a physical channel and logical channel are the same thing. Umts logical channels and transport channels 3glteinfo. In the radio subsystem, the physical channel supports the logical channel based on the type of message transmitted. Followings are the types of burst being used in gsm gprs. If so, the logical channel information is carried in the same physical channel. Logical channels define what type of information is transferred. Introduction to physical and logical channels tel3pedia. Viewing 11 posts 1 through 11 of 11 total author posts 17th august 2008 at 14.
Sice gsm is a tdm system these logical channels are multiplexed onto physical channels and then transmitted over the air interface. In this way, the physical channels are mapped as different logical channels. In p25 phase 2, a physical channel is divided into two time slots or logical channels. Section 3 and 4 treats the channel types in gsm as well as the mapping from the logical channels on to the physical channels. Logical channels are sch, fch,bcch, sacch, facch, rach, agch, etc. Two types of logical channels map onto physical channels control channels call setup, power adjustment, etc traffic channels voice or data 22. Physical channels, logical channels, network, and operation. Lte physical logical transport channel and mapping fundamentals of 4g lte by pankaj kumar telecom world. Study and learn these interview mcq questions and answers on 2g gsm logical channels and types. This chapter explains the functionalities of these channels. 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. 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.
As shown in the figure, there are three types of umts channels viz. Gprs physical and logical channels the gprs physical layer, e. Other channel next to physical is logical channel which consists of the information carried over the physical channel. Physical channel when an ms and a bts communicate, they do so on a specific pair of radio frequency rf carriers, one for the uplink. Logical channels are distinguished by the information they carry and can be classified in two ways. Logical channels define what type of information is being transferred and transport channel defines how the information is being transferred logical channels. Based on, as mentioned earlier, whether they carry gsm traffic ie, speech or data or. May 26, 2016 this video explains the logical channels in the gsm global system for mobile and their usage.