M O M OBILE W IRELESS W SS C OMMUNICATIONS C OMMUNICATIONS Aditya K. Jagannatham Indian Institute of Technology Kanpur Indian Institute of Technology Kanpur Commonwealth of Learning Vancouver MOOC on M4D 2013
Wireless Communications Wireless Communications • Channel is the air medium. • Multiple users can simultaneously transmit y over the air medium • For instance, different cell phone users in a cell are phone users in a cell are trying to transmit to the Base Station. Base Station. MOOC on M4D 2013
Wireless Communications Wireless Communications How to allocate The answer is the medium to a h di M l i l A Multiple Access certain user? (MA) technology! MOOC on M4D 2013
Multiple Access Technologies Multiple Access Technologies • FDMA • FDMA – Frequency Division for Multiple “Frequency Division for Multiple Access” • Each user is allocated a different frequency E h i ll t d diff t f band. – Forms the 1 st Generation or 1G Mobile Technology User 1 User 2 User 3 User 4 User 5 Frequency (Hz) q y ( ) MOOC on M4D 2013
An FDMA Phone An FDMA Phone MOOC on M4D 2013
Multiple Access Technologies Multiple Access Technologies • TDMA – Time Division for Multiple Access. p • Each user is allocated a certain time “slot” for information transmission information transmission. User 1 User 2 User 3 User 4 User 5 Time (seconds) GSM GSM uses TDMA! TDMA! MOOC on M4D 2013
Introduction to GSM Introduction to GSM • GSM ( Global System for Mobile GSM ( Gl b l S t f M bil Communication )is an ETSI (European Telecommunication Standards Institute) standard – For 2G pan ‐ European digital cellular with international roaming international roaming. • Formed in 1982 by allocating the bands 890 ‐ 915 MHz and 935 ‐ 960 MHz for Pan ‐ European PLMN ( Public Land Mobile Network ). MOOC on M4D 2013
Introduction to GSM Introduction to GSM • Main Charter – To develop a unified 2G standard to resolve the p roaming problem in Europe, with six 1G standards. MOOC on M4D 2013
Introduction Introduction • GSM went beyond the air ‐ interface and defined a system that complied with ISDN y p ( Integrated Services Digital Network ) like services services. – ISDN provides data services over traditional telephone network or PSTN ( Public Switched telephone network or PSTN ( Public Switched Telephone Network ) • Hence, GSM is a robust digital cellular standard. MOOC on M4D 2013
Timeline – Brief History of GSM Frequency bands allocated for Pan ‐ European 1982 PLMN ( Public Land Mobile Network ). GSM Task Force formed 1986 Memorandum of understanding signed. 1987 ETSI officially included GSM in its domain. Name of the group was changed to Special Mobile Group (SMG). Hence, the resulting 1989 standard was named GSM ( Groupe Spécial Mobile ) Mobile ). Specification completed. 1991 First deployment 1992 32 Operators in 22 countries. 1993 Deployed in close to 150 countries. 2001 MOOC on M4D 2013
GSM Services GSM Services • Analog cellular systems were designed for the sole purpose of voice traffic similar to PSTN. p p • GSM is an integrated voice ‐ data service that provides a number of services beyond voice provides a number of services beyond voice. MOOC on M4D 2013
GSM Reference Architecture GSM Reference Architecture • Wireless standard description involves i l d d d i i i l – Detailed terminal specs. – Fixed hardware (H/W) backbone. – Software (S/W) databases for operational ( / ) p support. • GSM is organized into three major segments. GSM is organized into three major segments. – Mobile station (MS). – Base station subsystem (BSS). Base station subsystem (BSS) – Network and switching subsystem (NSS). MOOC on M4D 2013
GSM Reference Architecture GSM Reference Architecture Networking and Switching Mobile Station Subsystem (NSS) (MS) VLR HLR Base Station SIM subsystem (BSS) User User PSTN PSTN UE BTS BSC MSC AUC EIR Other MSCs MOOC on M4D 2013
Mobile Station (MS) Mobile Station (MS) Mobile Station (MS) SIM UE • Functionality – Communicates information with user. – Demodulates radio signals, extracts digital voice – Modifies user info for transmission over the air ‐ Modifies user info for transmission over the air interface to communicate with the BS. • MS has two elements – Mobile Equipment (ME) q p ( ) • Purchased from equipment vendor. • Components include speaker/microphone and the p p / p radio modem (modulation ‐ demodulation). MOOC on M4D 2013
Mobile Station (MS) Mobile Station (MS) Mobile Station (MS) SIM UE – Subscriber Identity Module (SIM) • Smart card issued at the subscription time • Smart card issued at the subscription time identifying the user specs such as operator, service type service type. – Identity of user in the mobile network • Calls in GSM are directed to the SIM rather than the terminal • SMS (Short Message Service) messages are also stored in the SIM. MOOC on M4D 2013
Mobile Station (MS) Mobile Station (MS) Mobile Station (MS) SIM UE • SIM has a significant impact on the way that a g p y user transacts with the service provider. – For instance, determines charging, roaming , g g, g etc. • SIM carries the user personal information, p , which enables a number of useful applications. • SIM is identified with an IMSI ( International Mobile Subscriber Identity ) for the internal network. MOOC on M4D 2013
Base Station Subsystem (BSS) Base Station Subsystem (BSS) Base Station subsystem (BSS) y ( ) Wireless Wired BTS BSC Signaling Infrastructure • BSS communicates with the user through the wireless air ‐ interface (through ME). • Communicates with the wired infrastructure through a different set of wired protocols. g p • BSS provides for the translation from air ‐ interface protocols to the wired medium interface protocols to the wired medium protocols. • Separates packet data from PSTN traffic Separates packet data from PSTN traffic. – To implement packet data services such as GPRS. MOOC on M4D 2013
Base Station Subsystem (BSS) Base Station subsystem (BSS) BTS S BSC SC • BSS has two architectural elements • BSS has two architectural elements – Base Transceiver Station (BTS) • Counterpart of MS for physical communication. • Includes Tx, Rx and signaling equipment for Demod • One BSS may have several BTSs in its domain. – Base Station Controller (BSC) • Small switch inside the BSS that is in charge of frequency administration. • Also in charge of handover among the BTSs inside a MOOC on M4D 2013 BSS.
Network and Switching Subsystem • NSS is master system responsible for network operation operation. Networking and Switching • It is responsible for Subsystem (NSS) – Communication with other wired C i ti ith th i d VLR HLR and wireless networks. – Also support for registration and Also support for registration and PSTN PSTN maintenance of the connection MSC with the MSs. • Connects to the PSTN (Public ( AUC EIR Switched Telephone Network) through ISDN protocols through ISDN protocols. Other MSCs • It has one H/W element i.e. MSC and four S/W elements – MSC and four S/W elements – VLR, HLR, EIR and AUC. MOOC on M4D 2013
NSS Architectural Elements • Mobile Station Controller (MSC) – The H/W part of the NSS. – Communicates with other MSCs in Networking and Switching the coverage area of the service Subsystem (NSS) provider provider. VLR HLR – Also communicates with the PSTN switches. PSTN PSTN • This is the Gateway MSC (GMSC) MSC • Home Location Register (HLR) – Database S/W that handles AUC EIR management of the mobile subscriber account subscriber account. Other MSCs – Stores the subscriber’s address, service type, current location, forwarding address etc. MOOC on M4D 2013
NSS Architectural Elements • Visitor Location Register (VLR) Networking and Switching Subsystem (NSS) – Temporary database S/W in Temporary database S/W in VLR HLR Visiting Cell , similar to the HLR. HLR. PSTN PSTN MSC – Identifies the subscribers visiting inside the coverage visiting inside the coverage AUC EIR area of the MSC. – Thus, calls from Home MSC Th ll f H MSC Other MSCs can be forwarded to visiting MSC MSC. MOOC on M4D 2013
NSS Architectural Elements NSS Architectural Elements • Authentication Center (AUC) Networking and Switching Subsystem (NSS) – Holds different algorithms g VLR HLR that are used for authentication and PSTN PSTN encryption of subscribers. MSC – Different SIM cards have Different SIM cards have AUC EIR different algorithms and the AUC collects all of these AUC collects all of these algorithms. Other MSCs MOOC on M4D 2013
NSS Architectural Elements NSS Architectural Elements • Equipment Identification q p Register (EIR) Networking and Switching Subsystem (NSS) • Keeps the IMEI (International • Keeps the IMEI (International VLR HLR Mobile Equipment Identity) PSTN PSTN that reveals the manufacturer, h l h f MSC country of production, terminal type. AUC EIR – Used to report stolen phones Used to report stolen phones and to check if the phone is Other MSCs operating according to the operating according to the service type. MOOC on M4D 2013
GSM B ASIC GSM B ASIC O PERATION MOOC on M4D 2013
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