SEMINAR

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PRESENTATION ON GSM AND CDMA NETWORK Submitted By: Sormistha Ganguly VII-B

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Multiple Access Scheme Why there is requirement of multiple access schemes? The answer is that the international authority for frequency management has allocated 25 MHz band to the cellular telephony. As we know that today there are many cellular users and to provide service to all of them a large frequency band is required. But the band is limited to 25MHz.So different multiple access schemes are used. It means that multiple access scheme allow number of users to use the same band. The different multiple access schemes are mentioned below: FDMA TDMA CDMA

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FDMA is the acronym of Frequency Division Multiple Access. FDMA divides radio channels into a range of radio frequencies and is used in the traditional analog cellular system. With FDMA, only one subscriber is assigned to a channel at a time. Other conversations can access this channel only after the subscriber's call has been terminated or after the original call is handed off to a different channel by the system. FDMA cellular standards include AMPS (Advanced Mobile Phone Service) and TACS (Total Access Communications System). FDMA FDMA FDMA is the acronym of Frequency Division Multiple Access. FDMA divides radio channels into a range of radio frequencies and is used in the traditional analog cellular system. With FDMA, only one subscriber is assigned to a channel at a time. Other conversations can access this channel only after the subscriber's call has been terminated or after the original call is handed off to a different channel by the system. FDMA cellular standards include AMPS (Advanced Mobile Phone Service) and TACS (Total Access Communications System).

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tdma TDMA is a common multiple access technique employed in digital cellular systems. It divides conventional radio channels into time slots to obtain higher capacity. Its standards include North American Digital Cellular, Global System for Mobile Communications, and PDC (Personal Digital Cellular). As with FDMA, no other conversations can access an occupied TDMA channel until the channel is vacated.

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CDMA CDMA uses a radically different approach. It assigns each subscriber a unique "code" to put multiple users on the same wideband channel at the same time.Both the mobile station and the base station to distinguish between conversations use the codes, called “pseudo-random code sequences”. Depending on the level of mobility of the system, it provides 4 to 7 times the capacity of TDMA.

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CDMA uses spread spectrum techniques to allow a large number of users to use the same wide bandwidth channel (1.25 MHz) at the same time. CDMA uses “unique” Walsh codes to distinguish each individual user in the system. CDMA receivers receive only the “addressed” wideband signal. • All other users of the same frequency appear as a noise Universal frequency reuse. Sharing the spectrum is by dividing up power rather than dividing up channels or slots. Seamless soft handoff. Multipath propagation used for diversity. Coded speech for maximum capacity. Variable rate transmission. CDMA TECHNIQUES

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CDMA Wireless Network Architecture

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CCLN Identities Mobile Directory Number (MDN) This is the telephone number of a mobile subscriber. It is composed of Country Code (CC), National Destination Code (NDC) and Subscriber Number (SN). The maximum length of the MDN number can be 15 digits. MDN = CC + NDC + SN International Mobile Subscriber Identity (IMSI) This identity is used for all signaling within the CCLN. This IMSI number will be stored in the MS as well as in HLR and VLR. It is composed of three parameters: Mobile Country Code (MCC) is 3 digits, Mobile Network Code (MNC) is 2 digits and Mobile Subscriber Identification Number (MSIN) is a maximum of 10 digits. IMSI will have a length of a maximum of 15 digits. All network related subscriber information is connected to the IMSI . IMSI = MCC + MNC + MSIN IMSI = MCC + MNC + MSIN MDN = CC + NDC +SN

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Temporary Location Directory Number (TLDN) HLR knows in which MSC/VLR Service Area the subscriber is located. In order to provide temporary numbers to be used for routing, the HLR requests MSC/VLR to allocate an TLDN to the called subscriber. HLR will send this number back to the GMSC, which now can route the call to the serving MSC/VLR. TLDN consists of three parts, Country Code (CC), National Destination Code (NDC) and Subscriber Number (SN). The TLDN and MDN have the same format but there is a difference. In the TLDN, the Subscriber Number (SN) is the address to the serving MSC. TLDN = CC + NDC+SN Location Area Identity (LAI) This is used for location updating of mobile subscriber. It has 3 parameters Mobile Country Code (MCC) which is 3 digits, Mobile Network Code (MNC) which is 2 digits and it identifies the CCLN of that country and Location Area Code (LAC) identifies a Location Area within a CCLN. The maximum length of an LAC is 16 bits. LAI is also used for paging. LAI = MCC + MNC + LAC

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The act of transferring support of a mobile from one base station to another is termed handoff. Handoff occurs when a call has to be handed off from one cell to another as the user moves between cells. HARD HANDOFF:- BREAK-BEFORE MAKE TRADITIONAL PROCESS SOFT HANDOFF :- MAKE-BEFORE-BREAK INCREASES CAPACITY AND REDUCES INTERFERENCE HANDOFF

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DISADVANTAGES OF CDMA Due to its proprietary nature, all of CDMA's flaws are not known to the engineering community. CDMA is relatively new, and the network is not as mature as GSM. CDMA cannot offer international roaming, a large GSM advantage

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Mobile Station (MS) Mobile Equipment (ME) Subscriber Identity Module (SIM) Base Station Subsystem (BSS) Base Transceiver Station (BTS) Base Station Controller (BSC) Network Switching Subsystem(NSS) Mobile Switching Center (MSC) Home Location Register (HLR) Visitor Location Register (VLR) Authentication Center (AUC) Equipment Identity Register (EIR) GSM SYSTEM ARCHITECTURE

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MOBILE STATION(MS) The Mobile Station is made up of two entities: Mobile Equipment (ME) 2. Subscriber Identity Module (SIM)

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Base station subsystem Base Station Subsystem is composed of two parts that communicate across the standardized Abis interface allowing operation between components made by different suppliers Base Transceiver Station (BTS) Base Station Controller (BSC)

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Mobile Switching Center (MSC) Heart of the network Manages communication between GSM and other networks Call setup function and basic switching Call routing Billing information and collection Mobility management - Registration - Location Updating - Inter BSS and inter MSC call handoff MSC does gateway function while its customer roams to other network by using HLR/VLR. Network switching subsystem(nss)

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Home Location Registers (HLR) permanent database about mobile subscribers in a large service area(generally one per GSM network operator) database contains IMSI,MSISDN,prepaid/postpaid,roaming restrictions,supplementary services . Visitor Location Registers (VLR) Temporary database which updates whenever new MS enters its area, by HLR database Controls those mobiles roaming in its area Reduces number of queries to HLR Database contains IMSI,TMSI,MSISDN,MSRN,Location Area,authentication key Network switching subsystem(nss)

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Authentication Center (AUC) Protects against intruders in air interface Maintains authentication keys and algorithms and provides security triplets ( RAND,SRES,Kc) Generally associated with HLR Equipment Identity Register (EIR) Database that is used to track handsets using the IMEI (International Mobile Equipment Identity) Made up of three sub-classes: The White List, The Black List and the Gray List Network switching subsystem

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BSS VLR HLR GMSC CHECK FOR IMSI OF CALLED PARTY MSC BSS BSS MS PUBLIC NTK. 1 3 4 5 11 6 2 2 3 4 8 9 12 8 9 12 8 CALL SETUP (GSM) 10 7 8

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LOCATION UPDATE The Mobile Station monitors the information broadcast by the network. The Mobile Station stores the current location area identity in the SIM card. The Mobile Station continues to monitor the broadcast information. If the location area identity being broadcast by the network is other than the one stored in the SIM, the Mobile Station starts the location update procedure ..

Elements involved in a location update: 

Elements involved in a location update VLR MSC (old) VLR MSC (new) HLR SIM Location Update Mobile moves

Location update procedure - first time: 

Location update procedure - first time BSS MSC VLR HLR REQUEST AUTHENTICATION INFO MS LOCATION UPDATE REQUEST SEND SUBSCRIBER ID REQUEST SUBSCRIBER ID SEND AUTHENTICATION INFO AUTHENTICATION AUTHENTICATION RESPONSE LOCATION UPDATE MESSAGE ACKNOWLEDGEMENT, SUBSCRIBER INFORMATION LOCATION UPDATE OK ACKNOWLEDGEMENT

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IMEI CHECKING The validity of a mobile equipment may be checked to ensure its proper operation and as prevention against stolen phones. The Equipment Identity Register (EIR), which is implemented as part of the HLR, can store “black listed” IMEI numbers. The mobile equipment sends its IMEI before a transaction with the network. The MSC can request the EIR to see if the received IMEI is “black listed”. If it is, the MSC can stop the call set-up. An operator can set the MSC to check the IMEI of a mobile equipment at times other than during call set-up as well .

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The GSM stands for global system for mobile communication and CDMA for code division multiple accesses. 2. GSM is a form of multiplexing, which divides the available bandwidth among the different channels. Most of the times the multiplexing used is either TDM (Time division multiplexing) or FDM (Frquency division multiplexing). On the other hand CDMA is a type of multiple access scheme( which means allotting the given bandwidth to multiple users) and makes use of spread spectrum technique which is essentially increasing the size of spectrum. 3. In CDMA each user is provided a unique code and all the conversation between 2 users are coded. This provides a greater level of security to CDMA users than the GSM ones. Difference b/w gsm & cdma

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Difference b/w gsm & cdma 4. It is harder to implement a CDMA network. The tower placement is more difficult. Dealing with hills is more difficult than with GSM/TDMA. 5. GSM have a wider coverage as it has contracts with other GSM carriers. On the other hand the CDMA user does not enjoy the wider coverage. 6. Generally the mobile phone comes to life when the SIM card is inserted, GSM phone duly support this technology. On the other hand the CDMA phones are not card based phones, therefore the carrier needs to deactivate the old phone and then activate the new phone, and this discards the early sets.

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-:THANKS:-