wireless telephony

WIRELESS TELEPHONY : 

WIRELESS TELEPHONY HUMA FIROZ MCA 5TH SEM

Outline: : 

Outline: Overview of wireless telephony cellular concept Frequency reuse Advantages and problems GSM Services Components/subsystems network architecture Advantages and disadvantages Comparison between GSM & CDMA

Overview of wireless telephony (cellular concept). : 

Overview of wireless telephony (cellular concept). CELLS

Cell structure : 

Cell structure Implements space division multiplex: base station covers a certain transmission area (cell) Mobile stations communicate only via the base station

Representation of Cells : 

Representation of Cells Ideal cells Fictitious cells Circular cells

Slide 6: 

Cellular System The geographic area is divided into cells Each cell has a Base Station managing the communications A set of cells managed by a single MSC is called Location Area Base Station VLR MSC VLR MSC HLR MSC Mobile Switching Center VLR Visitor Location Register HLR Home Location Register land link land link Radio link

Frequency reuse concept: : 

Frequency reuse concept: Frequency Re-Use Distance is maintained between two same frequencies of clusters. A cluster may be made up of 3,4,7,9, 12, 13, 16, etc., cells; but out of these, 7-cell and 4-cell clusters are most commonly used to cover an area. To avoid co-channel interference, two frequencies are kept apart at least by 45 Hz, but in the case of higher frequencies the separation may be less.

The Cell Structure for K = 7 : 

The Cell Structure for K = 7 FR-DISTANCE

Cell Structure for K = 4 : 

Cell Structure for K = 4

Advantages of cell structures: : 

Advantages of cell structures: higher capacity, higher number of users less transmission power needed more robust, decentralized base station deals with interference, transmission area etc. locally

Problems: : 

Problems: fixed network needed for the base stations handover (changing from one cell to another) necessary interference with other cells

GSM NETWORK &ARCHITECTURE : 

GSM NETWORK &ARCHITECTURE

Introduction : : 

Introduction : GSM(groupe speciale mobile), found in 1982 Further named as GLOBAL SYSTEM FOR MOBILE COMMUNICATION. Second generation system aimed to: Roam throughtout Provide voice services

Base Station : 

Base Station In radio communications, a base station is a wireless communications station installed at a fixed location and used to communicate as part of either: a push-to-talk two-way radio system, or; a wireless telephone system such as cellular CDMA or GSM.

Slide 15: 

A Typical GSM Base Station (Wikipedia.org,2008)

Services offered by GSM: : 

Services offered by GSM:

GSM’s subsystem: : 

GSM’s subsystem: RSS (radio sub system): It comprises all radio specific entities NSS(network sub system): switching, mobility management, interconnection to other networks, system control OSS (operation sub system): enables centralized operation, management, and maintenance of all GSM subsystems

RSS(Radio sub system): : 

RSS(Radio sub system): BSS(base station sub system) it perform all function necessary to maintain radio connection to a MS,coding/decoding of voice & rate adaptation to/from the wireless network part. BTS(base transceiver station) It comprises all radio equipments like antennas etc & can form radio cells. BSC(base station controller) It manages BTS,reserves radio frequencies,handles handoff between BTS.

Slide 19: 

Antenna

NSS(Network and switching subsystem): : 

NSS(Network and switching subsystem): Mobile Services Switching Center (MSC) controls all connections via a separated network to/from a mobile terminal within the domain of the MSC - several BSC can belong to a MSC Databases (important: scalability, high capacity, low delay) Home Location Register (HLR)central master database containing user data, permanent and semi-permanent data of all subscribers assigned to the HLR (one provider can have several HLRs) Visitor Location Register (VLR)local database for a subset of user data, including data about all user currently in the domain of the VLR

OSS (Operation Subsystem): : 

OSS (Operation Subsystem): Authentication Center (AUC) generates user specific authentication parameters on request of a VLR authentication parameters used for authentication of mobile terminals and encryption of user data on the air interface within the GSM system Equipment Identity Register (EIR) registers GSM mobile stations and user rights stolen or malfunctioning mobile stations can be locked and sometimes even localized Operation and Maintenance Center (OMC) different control capabilities for the radio subsystem and the network subsystem

Slide 22: 

Architecture of a GSM Network

Slide 23: 

f Time and Frequency Multiplex Example: GSM Combination of both methods . A channel gets a certain frequency band for a certain amount of time Advantages: Better protection against tapping Protection against frequency selective interference Higher data rates compared tocode multiplex But: precise coordinationrequired t c k2 k3 k4 k5 k6 k1

Advantages of 2G GSM : 

Advantages of 2G GSM GSM is mature; this maturity means a more stable network with robust features. Less signal deterioration inside buildings. Ability to use repeaters. Talktime is generally higher in GSM phones due to the pulse nature of transmission. The availability of Subscriber Identity Modules allows users to switch networks and handsets at will, aside from a subsidy lock. GSM covers virtually all parts of the world so international roaming is not a problem. The much bigger number of subscribers globally creates a better network effect for GSM handset makers, carriers and end users.

Disadvantages of 2G GSM : 

Disadvantages of 2G GSM Pulse nature of TDMA transmission used in 2G interferes with some electronics, especially certain audio amplifiers. 3G uses W-CDMA now. Intellectual property is concentrated among a few industry participants, creating barriers to entry for new entrants and limiting competition among phone manufacturers. GSM has a fixed maximum cell site range of 35 km, which is imposed by technical limitations.

Comparision between GSM & CDMA: : 

Comparision between GSM & CDMA: