2.1 introduction to cellular architecture
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Cellular systems allow mobile users to communicate wirelessly using a network of base stations and switches. A mobile station communicates with the nearest base station, which connects to a mobile switching center. The switching center routes calls between mobile stations and the public switched telephone network. Coverage areas are divided into cells served by individual base stations to allow frequency reuse that improves system capacity.
2.1 introduction to cellular architecture
- 2. Lecture Videos are available for this slides at www.youtube.com/gurukula Support by Subscribing to my Channel
- 3. Fundamental architecture of Cellular System MOBILE STATION BASE STATION MOBILE SWITCHING CENTRE (MSC) PUBLIC SWITCHED TELEPHONE NETWORK (PSTN)A station in the cellular radio service intended for use while in motion at unspecified locations. Mobile station may be hand held personal units (Portables) or installed in vehicles (Mobiles) A fixed station in a mobile radio system used for radio communication with mobile stations. Base stations are located at the centre or on the edge of a coverage region and consists of radio channels and transmitter and receiver antennas mounted on a tower. Switching centre which coordinate the routing of calls in a large service area. In cellular radio system the MSC connect the cellular base station and the mobiles to the PSTN. An MSC is also called a Mobile Telephone Switching Office (MTSO). PSTN (public switched telephone network) is the world’s collection of interconnected voice-oriented public telephone networks. PTSN comprises all the switched telephone networks around the world that are operated by local, national or international carriers.
- 4. Cellular System to cover a geographical area BASE STATION MOBILE STATION CELL A cell is the geographic area that is covered by a single base station in a cellular network.
- 5. Detailed View of GSM Architecture A base transceiver station (BTS) is a piece of equipment that facilitates wireless communication between user equipment (UE) and a network. UEs are devices like mobile phones (handsets), WLL phones, computers with wireless Internet connectivity. A base station controller (BSC) is a network element that controls and monitors a number of base stations and provides the interface between the cell sites and the mobile switching center (MSC). The Home Location Register is a database from a mobile network in which information from all mobile subscribers is stored. The HLR contains information about the subscribers identity, his telephone number, the associated services and general information about the location of the subscriber. The Visitor Location Register (VLR) is a database contains the exact location of all mobile subscribers currently present in the service area of the MSC. This information is necessary to route a call to the right base station. The database entry of the subscriber is deleted when the subscriber leaves the service area. The Authentication Centre (AUC) is a function in a GSM network used for the authentication a mobile subscriber that wants to be connected to the network. Authentication is done by identification and verification of the validity of the SIM. Once the subscriber is authenticated, the AUC is responsible for the generation of the parameters used for the privacy and the ciphering of the radio link. Operation Maintenance Center (OMC) is used to monitor and maintain the performance of each Mobile Station (MS), Base Station (BS), Base Station Controller (BSC) and Mobile Switching Center (MSC) within a GSM system. Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network.
- 6. GSM Channels MOBILE STATION BASE STATION MOBILE SWITCHING CENTRE (MSC) PUBLIC SWITCHED TELEPHONE NETWORK (PSTN) Wireless Access through Radio Channels Wired Communication – Back Bone Networks The communication between the MS and BS are defined by CAI (Common Air Interface) Standard. VOICE AND DATA CHANNEL CONTROL CHANNEL FORWARD VOICE CHANNEL REVERSE VOICE CHANNEL FORWARD CONTROL CHANNEL REVERSE CONTROL CHANNEL Used for voice transmission from BS to MS Used for voice transmission from MS to BS Used for setting up the calls and exchanging the control messages
- 7. Channel Access Mechanisms In real time scenario a single Base Station will serve several Mobile Stations simultaneously. This gives raise to 2 important questions 1. How Full duplexing is achieved? 2. How mobile users share the available finite amount of spectrum Full Duplex can be achieved by Frequency Division Duplexing (FDD): Frequency-division duplexing (FDD) is a method for establishing a full-duplex communications link that uses two different radio frequencies for transmitter and receiver operation. FDD operation normally assigns the transmitter and receiver to different communication channels. One frequency is used to communicate in one direction, and the other frequency is required to communicate in the opposite direction. The transmit direction and receive direction frequencies are separated by a defined frequency offset. Time Division Duplexing (TDD): Time division duplex (TDD) refers to duplex communication links where uplink is separated from downlink by the allocation of different time slots in the same frequency band.
- 8. How Mobile Users Share the Available Spectrum: The Basic Resource for Wireless Communication is Radio Spectrum. This is to be shared among multiple users. Multiple Access schemes are used to allow many mobile users to share simultaneously a finite amount of radio spectrum. The sharing of spectrum is required to achieve high capacity by simultaneously allocating the available bandwidth or channel to multiple users Duplexing is needed to allow subscribers send and receive information simultaneously. Ex : Mobile Systems Note: This must be done without severe degradation in the performance of the system
- 9. Summary • Basic Components and definition • Architecture of Cellular Systems • CAI Standards for GSM channels • Concepts of Duplexing • Concepts of Multiple Access Techniques