Sunday, 19 August 2012

Mobile technology

The Basics of Mobile Technology

                       Mobile operators use radio spectrum to provide their services.  Spectrum is generally considered a scarce resource, and has been allocated as such.  It has traditionally been shared by a number of industries, including broadcasting, mobile communications and the military. At the World Radio Conference (WRC) in 1993, spectrum allocations for 2G mobile were agreed based on expected demand growth at the time.  At WRC 2000, the resolutions of the WRC expanded significantly the spectrum capacity to be used for 3G, by allowing the use of current 2G spectrum blocks for 3G technology and allocating 3G spectrum to an upper limit of 3GHz.   

                      Before the advent of cellular technology, capacity was enhanced through a division of frequencies, and the resulting addition of available channels.  However, this reduced the total bandwidth available to each user, affecting the quality of service.  Cellular technology allowed for the division of geographical areas, rather than frequencies, leading to a more efficient use of the radio spectrum.   This geographical re-use of radio channels is knows as “frequency reuse”.  

                      In a cellular network, cells are generally organized in groups of seven to form a cluster.  There is a  “cell site” or “ base station” at the centre of each cell, which houses the transmitter/receiver antennae and switching equipment.  The size of a cell depends on the density of subscribers in an area: for instance, in a densely populated area, the capacity of the network can be improved by reducing the size of a cell or by adding more overlapping cells. This increases the number of channels available without increasing the actual number of frequencies being used.    All base stations of each cell are connected to a central point, called the Mobile Switching Office (MSO), either by fixed lines or microwave. The MSO is generally connected to the PSTN (Public Switched Telephone Network):  

Mobile Computing Networks

Temporary or Switched Connection via Wire-line WAN

                          Permanent connection between a mobile user and information source is not only expensive but is not always practical because mobile users are constantly on the move. Therefore, the most popular (though not most ubiquitous or pervasive or persistent - using the new lingo) method of providing connectivity to mobile workers continues to be one of a temporary wireline connection for a specific use and a required period of time. This can be achieved by using a dial-up connection on a traditional public telephone or cellular network. You call it switched because you switch a circuit from one user to another user for the duration of the call. You may have a switched wireline connection directly between a remote location where the user is at a given moment and the information server or indirectly through the Internet. In either case, you still need to locate a telephone jack of one kind or another. Go to PSTN, ISDN, ADSL, or VPNs (Internet based Virtual Private Networks) for further information on these temporary connections for mobile workers.

Wireless PANs (Personal Area Networks)

 These are wireless networks that can be installed in a small office or home within 5-15 metre distances. Two technologies being used for this purpose are IrDA which is based on line of sight requirement within two devices, usually a few feet apart. For more details on IrDA, please go to IrDA site. The second technology is Blue Tooth. Blue tooth technology supports multipoint connection without line of sight requirement. Go to Blue Tooth topic under "Hot Topic" menu item on our site's home page.

Wireless LAN

Where the movement is within a contained geographical area, you can provide mobility by implementing a wireless LAN and equipping your mobile device with a corresponding wireless adapter - a PC card variety that goes into a notebook, hand-held PDA, a Windows CE-compatible device or Palm Pilot organizer. Go to Wireless LANs page for more info.

Wireless MAN (Metropolitan Area Network)

etric-om's Ricochet, a specialized wireless network is available at 128 kbps, 24 hours 7 days always on, in the following major metropolitan areas: Atlanta, Baltimore, Dallas, Denver, Detroit, Houston, Los Angeles, Minneapolis St. Paul, New York City, Philadelphia, Phoenix, San Francisco Bay Area and San Diego and 15 airports nationwide. These areas join the Washington DC and Seattle 28.8 kbps service areas. The service is offered through WWC, Worldcom, Earthlink, GoAmerica and Juno for $79.95/month and under. " (circa Spring 2001). Go to Metricom network description on this site for more.

Wireless WAN - Private or Public

                  Once we move out of the limited geography of a wireless LAN in a campus or factory setting, we have to utilize wide area wireless network. These networks may be private or public. Large organizations, such as Fedex or public safety agencies, have implemented private CDPD or SMR networks to give wireless connectivity to courier drivers and police officers. However, the current trend is to move towards shared public networks, such as Motient or BellSouth (ex RAM Mobile Data - called Mobitex in Europe and Canada). Go to wireless WANs for more info.

Satellite Networks

Even wireless wide area networks may not provide coverage in extremely remote areas, because networks can not justify the economics of installing a base station everywhere. True universal coverage for these types of mobile users is possible only through wireless networks based on satellites. There are several GEOS, LEOS, and MEOS satellite-based networks that transmit from different heights from the surface of the earth. Refer to these terms in the glossary.

The Last Mile Problem for Wireless Networks

One thing worth noting is that it is only the last mile (or so!) where we need wireless or radio-frequency-based connection. Once we reach a terrestrial network, we can utilize the bandwidth of traditional wireline permanent connections. By the same token, once we reach the Internet Service Provider through a wireless hub or concentrator, we can be home free for riding high-speed connection to the universal information highway.


This module provides a brief introduction to the basic concepts and technologies associated with mobile communication

Wireless vs. Mobile Communications

Wireless telecommunications can be divided into two broad categories: mobile communications and fixed wireless communications. Each category has its own unique market in terms of customer needs and technology requirements. The mobile communications market requires mobility or non-tethered communications.The goal of mobility is anytime, anywhere communications. Mobile communications technology must be able to allow roaming - the ability to provide service to a mobile phone users while outside their home system. On the other hand, fixed wireless is simply an alternative to wired communications. The fixed wireless user does not need mobility. Instead, the fixed wireless user needs cost effective telecommunications from fixed locations. Wireless is an alternative means of providing service. It is sometimes the only means. When the customer is in a remote location, satellite is the only alternative.

Cellular and PCS

llular networks were deployed. Personal Communications Service (PCS) technologies were designed to meet the needs of anytime, anywhere personalized communications. PCS networks were deployed utilizing cellular RF designs similar to cellular. However, many PCS carriers initially deployed larger groupings of smaller cell sites to cover densely populated urban areas. PCS also uses a higher portion of the RF spectrum (1900 MHz in the US versus 800 MHz for cellular). Being deployed after the initial cellular networks, PCS networks also initially had more advanced technologies than PCS, including SS7 network infrastructure for services such as calling number identification. However, cellular would soon catch up due to competitive pressures. In aggregate, there are now no substantive differences between the initial "cellular" networks and "PCS". In fact, they both utilize the same underlying technologies. 
Mobile Communications Protocols
Radio Frequency Protocols

Interim Standard 136 (IS-136) is a specific Time Division Multiple Access (TDMA) based radio frequency (RF) standard.
IS-95 is a specific Code Division Multiple Access (CDMA) based radio frequency (RF) standard. With TDMA, multiplexing occurs within time slots within dedicated frequency band for each call or data session. On the other hand, CDMA is a "spread spectrum technology", utilizing all available frequency and time slots within an allocated service band.
It is important to be aware that TDMA and CDMA are digital RF protocols. There are various analog RF protocols that are still in commercial service, but they are being replaced with TDMA and CDMA as mobile operators upgrade their networks.
Mobile Networking Protocols

IS-136 and IS-95 based networks both utilize ANSI-41 as a protocol for mobile networking. ANSI-41 based networks are deployed primarily in the Americas and parts of Asia.
Global System for Mobility (GSM) is a global standard based on TDMA. GSM utilizes the GSM Mobile Application Part (MAP) as a mobile networking protocol.
Mobile Networking

Cellular/PCS networks can use different type of mobile networking protocols that allow for roaming – the use of a mobile phone while away from the home area – and advanced services.
Global System for Mobility (GSM) networks deployed in Europe and throughout the world utilizes a protocol called the GSM Mobile Application Part (MAP), standardized by the European Telecommunications Standards Institute (ETSI). Other TDMA based networks and CDMA networks utilize a protocol called ANSI-41, a protocol standardized by the Telecommunications Industry Association (TIA) and the American Standards Institute (ANSI).
Mobile networking entails communication between Home Location Registers (HLR) and Visiting Location Registers (VLR) - databases used to store information about subscribers. Communication between these databases allows roaming.

GSM MAP and ANSI-41 are key protocols that utilize SS7 to allow roaming and advanced as well as more advanced capabilities. Communication between the VLR in the serving system and the HLR of the home area is facilitated by these mobile networking protocols and signaling based on a signaling protocol called Signaling System number Seven (SS7).
In GSM networks, the MAP rides on top of SS7, allowing VLR to HLR (and HLR to VLR) communications.
In non-GSM networks (such as many of those found in the United States), ANSI-41 is deployed (which also uses SS7) for HLR/VLR communications.

Mobile IN for GSM & ANSI-41

While there are various proprietary-based mobile intelligent network (IN) technologies, the standards based technologies are often of most value to the mobile network operator and their customers. These standards based technologies are referred to as Customized Applications for Mobile Enhanced Logic (CAMEL) and Wireless Intelligent Network (WIN) and are used in GSM and ANSI-41 based networks respectively. 

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