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Important Short Questions and Answers: Multi-User Radio Communication

Analog and Digital Communication - Important Short Questions and Answers: Multi-User Radio Communication




1. Define GSM.


Global system for mobile communication (GSM) is a globally accepted standard for digital cellular communication. GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz. It is estimated that many countries outside of Europe will join the GSM partnership.



2. Define Subscriber Identity Module (SIM).


It is a memory device that stores information such as the subscribers identification number, the networks and countries where the subscriber is entitled to service, privacy tax and other user specific information A subscriber uses the SIM with a four digit personal ID number to activate service from GSM phone.



3. What is meant by super audio tone (SAT)?


• SAT is superimposed on the voice signal on both the forward and reverse link and is barely audible to the user


• The particular frequency of the SAT denotes the particular base station location for a given channel and is assigned by the MSC for each call.



4. What is meant by signaling tone?


The signaling tone is a 10 kbps data base which signals call termination by the subscriber. It is a special end of call message consisting of alternating 1s and 0s which is sent on the RVC by the subscriber unit for 200ms. The signaling tone alerts the base station that a subscriber has ended the call.



5. What is meant by Telephone services in GSM?


Teleservices provides communication between two end user applications according to a standard protocol. GSM mainly focuses on voice oriented tele services. This service includes emergency calling and facsimile. GSM also supports video text and tele text.


6. Name the different types of GSM services


Telephone services


Data services


Supplementary services



7. Define Advanced Mobile Phone Services (AMPS).


AMPS is a Standard Cellular Telephone Service (CTS). The AMPS system uses a seven cell reuse pattern with provisions for sectoring and cell splitting to increase channel when needed. AMPS uses frequency modulation and frequency division duplex for radio transmission.



8. What are the three orbits of satellite? Low Earth orbit


Medium Earth orbit  &  Geosynchronous Earth orbit



9. Define VLR.


Visitor location register (VLR)—The VLR is a database that contains temporary information about subscribers that is needed bythe MSC in order to service visiting subscribers. The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time.


10. Define MSC.


Mobile services switching center (MSC)—The MSC performs the telephony switching functions of the system. It controls calls to and from other telephone and data systems. It also performs such functions as toll ticketing, network interfacing, common channel signaling, and others.


11. What is Bluetooth?


Bluetooth is a standard developed by a group of electronics manufacturers that allows any sort of electronic equipment from computers and cell phones to keyboards and headphones to make its own connections, without wires, cables or any direct action from a user. Bluetooth is intended to be a standard that works at two levels.



12. Define HLR.


Home location register (HLR)—The HLR is a database used for storage and management of subscriptions. The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. When an individual buys a subscription from one of the PCS operators, he or she is registered in the HLR of that operator.


13. State Kepler’s laws of planetary motion


1. A satellite will orbit a primary body following an elliptical path


2. For equal intervals of time a satellite will sweep out equal areas in orbital plane


3. The square of the periodic time of orbit is proportional to the cube of the mean distance between the primary and the satellite.


14. What are the links in satellite communication?


i) Uplink


ii) Downlink


iii) Crosslink


15. Define apogee

The point in an orbit that is located farthest from earth.

Define perigee

The point in an orbit that is located closest to earth .


16. Define Handoff.


When a user/call moves to a new cell, then a new base station and new channel should be assigned (handoff)


Handoffs should be transparent to users, while their number should be kept to minimum


A threshold in the received power (Pr, handoff) should be determined to trigger the handoff process. This threshold value should be larger than the minimum acceptable received power (Pr, acceptable)


• Define: Δ=Pr,handoff - Pr,acceptable


– If is large then too many handoffs


– If is small then insufficient time to complete a handoff.


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