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NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite ASSIGNMENT # 1 Cellular TechnologyValladolid, Charles Edison October 03, 2011Communications 1/ BSECE 41A1 Score: Eng’r. Grace Ramones Instructor 1|Page
Cellular Networks and Access to Public NetworksA cellular network is a radio network distributed over land areas called cells, each served by atleast one fixed-location transceiver known as a cell site or base station. When joined togetherthese cells provide radio coverage over a wide geographic area. This enables a large number ofportable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and withfixed transceivers and telephones anywhere in the network, via base stations, even if some of thetransceivers are moving through more than one cell during transmission.Cellular networks offer a number of advantages over alternative solutions: increased capacity reduced power use larger coverage area reduced interference from other signalsAn example of a simple non-telephone cellular system is an old taxi drivers radio system wherethe taxi company has several transmitters based around a city that can communicate directly witheach taxi.Cellular networks consist of cellular base stations, mobile telephone switching offices (MTSO),and mobile communication devices. Each base station contains a radio transceiver and controllerand provides radio communication to the mobile units located in its cell. The cells are arrangedin a honeycomb pattern in order to provide local, regional, or national cellular coverage. TheMTSO links calls together using traditional copper, fiber optic, or microwave technology andacts as a central office exchange allowing users to place a call on the local and long distance 2|Page
public telephone systems. It also allows mobile communication devices in the cell to dial out andalerts devices in the cell of incoming calls. The MTSO continuously monitors the quality of thecommunications signal and transfers the call to another base station which is better suited toprovide communication to the mobile device.The mobile communication devices consist of hand held phones, car phones, notebookcomputers, personal digital assistants, pen-based computers, palm-top computers, and portabledata collection devices. Since only two percent of the cellular traffic is d ata, the most popularmobile units are cellular telephones (Gareiss, 1995). When these mobile units communicate tothe network, they must register with the system by subscribing to a carrier service. Most carrierservices have arrangements with other pr oviders allowing users to roam. Roaming occurs whenthe mobile unit is outside the coverage of their cellular service provider and an alternativecellular provider places the call.Cellular technology extends the bounds of a corporations existing telecommunicationsinfrastructure by connecting mobile units to the public network operated by the local exchange orlong distance carriers. The cellular users have special features an d functions specific to cellularcustomers but they can also use the features and functions of the public phone systems. Thisallows cellular technology to be flexible enough to take advantage of features and functions ofalmost any public or private net work. 3|Page
Fundamental Concepts in Cellular TechnologyThe radio spectrum contains many bands that are allocated and used for commercial, personal,and military applications. Fifty (50) MHz of spectrum allocated to cellular networks exists in the824-849 MHz and the 869-894 MHz bands (Pagett, 1995). These bands are then furthersubdivided into 832 channels allowing many users in the same area to simultaneously access thenetwork (DeBelina, 1995).Types of Cellular Network AccessThe types of network access in the United States are advanced mobile phone systems (AMPS),time division multiple access (TDMA), and code division multiple access (CDMA). AMPS is thecellular standard that has been extensively deployed in North America and has beencommercially available since 1983 (Khan & Kilpatrick, 1995). The current cellular standarddescribing access methods to the network is IS-553 and divides 50 MHz of spectrum into 832frequency channels, each 30 KHz wide (Amin, 1995; Pagett, 1 995; Pagett, Gunther, & Hattori,1995). Organizations such as the Portable Computer and Communications Association (PCCA)consist of modem manufacturers, computer manufactures, and service providers work together indefining the IS-553 interoperability s tandard (Khan & Kilpatrick, 1995).Time Division Multiple Access (TDMA) is a digital access method that allocates time slots todifferent users allowing them to share similar radio frequency channels. TDMA divides eachfrequency channel into six time slots and allocates two slots to each user increasing the networkcapacity by 300% (Pagett et al., 1995). Standard IS-54 describes a dual mode network accessmethod allowing mobile units the choice of using TDMA or AMPS operation (Amin, 1995;Honig & Madhow, 1990; Khan & Kilpatrick, 1995; Tawfik, 1993; Sasaoka, 1993; Williams &Ong, 1995).Code Division Multiple Access (CDMA) sends multiple messages over a wide frequencychannel that is decoded at the receiving end. Each mobile unit in a cell is assigned a differentspreading sequence and allows multiple users to share the same frequency spectrum improvingnetwork capacity over the AMPS systems by a factor of ten (DeBelina, 1995; Pagett et al., 1995;Pagett, 1995). The details for CDMA network access are referenced in standard IS-95 whichdescribes the mobile units access to the cellula r network (Honig & Madhow, 1990; Khan &Kilpatrick, 1995; Sasaoka, 1993; Williams & Ong, 1995).Although TDMA and CDMA digital access methods are just starting to be deployed in theUnited States (Tawfik, 1993), this author believes these access methods will become widelydeployed because of their superior performance characteristics. These networ ks have a highercapacity, improved voice quality, encryption for communication privacy, and integration withdigital terrestrial networks (Padgett, Gunther, & Hattori, 1995). Digital access has its advantages,but it does not have the ubiquitous access that AMPS systems have (Amin, 1995). Therefore, totake advantage of the widely available coverage of todays cellular services, portable units needto be compatible with the analog AMPS systems. 4|Page
Cell signal encodingTo distinguish signals from several different transmitters, frequency division multiple access(FDMA) and code division multiple access (CDMA) were developed.With FDMA, the transmitting and receiving frequencies used in each cell are different from thefrequencies used in each neighbouring cell. In a simple taxi system, the taxi driver manuallytuned to a frequency of a chosen cell to obtain a strong signal and to avoid interference fromsignals from other cells.The principle of CDMA is more complex, but achieves the same result; the distributedtransceivers can select one cell and listen to it.Other available methods of multiplexing such as polarization division multiple access (PDMA)and time division multiple access (TDMA) cannot be used to separate signals from one cell tothe next since the effects of both vary with position and this would make signal separationpractically impossible. Time division multiple access, however, is used in combination witheither FDMA or CDMA in a number of systems to give multiple channels within the coveragearea of a single cell.Cellular Digital Packet Data (CDPD)Cellular Digital Packet Data (CDPD) is a technology standard sponsored by the regional belloperating companies and McCaw Cellular. CDPD was introduced by IBM, overlays packetswitching onto the existing cellular voice network, and transmits data packet s over the idlecapacity. This packet overlay is based on transmission control protocol/internet protocol(TCP/IP) and does not need the call setup procedures required for switched voice calls. Thismakes CDPD ideal for short bursty message applications such as point-of-sale (POS) credit cardverification, vehicle dispatch, package tracking and e-mail (Gareiss, 1995). Although thiscomplex overlay generally increases the network utilization, excessive data traffic may causeinterference with existing cellular calls (Lee, 1993). Therefore, managers should examine thetraffic of voice and data users in a particular service area before designing applications that put alarge load on the network.Competing Wireless Communications TechnologiesThe advancement of radio technology has resulted in the development and deployment of manyforms of wireless communication systems. The most formidable competitors of cellularcommunications are personal communications systems (PCS), cordless telephones , paging,specialized mobile radio (SMR) and satellite communication (Perry, 1993).PCS is a wireless communications network which operates at a radio frequency of 1850-1990MHz and has a greater capacity for carrying voice and data traffic. Currently, a cellular mobileunits throughput peaks at 14.4 K bps (Gareiss, 1995) where curren t PCS systems using thepersonal access communications services (PACS) standard have channel throughput of 384 Kbps with an upside potential of 25 M bps (Raychaudguri, 1995). PCS allows greater data 5|Page
throughput over the air links whereas the existing cel lular infrastructure is insufficient to carrythe growth of bandwidth intensive applications (Colmenares, 1994; Tang & Sobol, 1995; Kobb,1993). Therefore, PCS is well positioned to handle the bandwidth intensive applications of thefuture.PCS will be less expensive than cellular communication because of government regulationpromoting and increasing competition (Bernier, 1995). Government regulators will effectcompetition by assigning each major trading area (MTA) with five PCS provider s compared tothe traditional two cellular providers in each MTA. Additionally, cellular providers will not bepermitted to provide PCS service in areas where they provide cellular service (Novak, 1995).Some members of congress are trying to remove the restrictions that prevent cellular carriersfrom owning and operating PCS networks in areas they provide cellular service because theybelieve these restrictions "will impede the development of PCS." (Congressional Record, 1993).This author believes PC S will capture the growth of new subscribers and cut into the imbeddedbase of cellular subscribers because of the PCS networks (PCN) cost and performanceadvantages over cellular networks.Another competing wireless technology is cordless telephony which provides wirelesscommunications between a handset and a base station connected to the public phone system. Themain differences between cellular and cordless technologies are the single cell architecture ofcordless and the fact that the two systems operate at different frequencies. Although cordlesstelephones are inexpensive, they are not as suited to business applications as cellular telephonesbecause of the cordless telephones lim ited range and their lack of privacy. There are however,handsets on the market that have dual mode (cordless and cellular) operation that may be used inbusiness situations to take advantage of both technologies. (Pagett, 1995; Pagett et al., 1995).Paging is a wireless communication technology that provides an inexpensive one waytransmission of alpha numeric and full text data. It is a viable alternative to cellular specificallywhen data needs to be transmitted in one direction, to the mobile us ers. [Since this paper waswritten, companies, such as SkyPage and MCI, have introduced two-way paging services.] Fortwo-way real time, communication, users need to have access to some form of service such ascommon business phone lines or cellular phones. There are many mobile users who use bothpaging and cellular with cellular allowing the mobile user to c all back and respond to the page.When used properly, paging may provide similar results as cellular when users are in pagingrange and have access to communications resources. The major difference between paging andcellular is that cellular provides tw o way direct communication while paging provides one waydirect communication.Specialized Mobile Radio (SMR) is a wireless communication technology that operates in the800 Mhz range and was designed for integrating voice and data over the same wireless network.SMR supports voice dispatch, wireless phone, voice mail, and data tr ansmission applications. Itis capable of transmitting data at 4.8 K bps with the ability of going up to 64 K bps in certainmetropolitan areas. SMR does have some limitations for business applications because it doesnot have wide coverage, deep in-bui lding penetration coverage, is available in only a fewmetropolitan areas, and is limited in its ability to interoperate with other networks. 6|Page
Satellite communication provides wireless communication with base stations in orbit around theearth. This technology is very expensive and has high network and handset costs. There aremany vendors such as GTE Airfone, TRW, Motorola, and GlobalStar, w ho are developingsatellite communication systems that can be accessed from almost anywhere in the world. Oneexample is Globalstar which will have a global, wireless, low-earth-orbit, satellite-basedtelephone system operational by 1998 (Loral Annual Re port, 1995).A new technology called software defined radio allows users to redefine the operation of amobile unit to allow interoperability with any of the aforementioned communicationstechnologies (Mitola, 1995). It is this authors belief that once software def ined radios arecommercially available and cost competitive, portable units will be able to seamlesslyinteroperate with many other networks. If there are different network technologies in a specificgeographical area, the handsets will be programmed to s elect the least expensive, most private,or highest bandwidth service. For example, a users handset will operate in cordless mode whenat home or in the office, in PCS mode when in PCS capable cells, in cellular mode when drivingregionally, and in sate llite mode when traveling internationally or in remote areas. 7|Page
Example of a cellular network: the mobile phone network The most common example of a cellular network is a mobile phone (cell phone) network. Amobile phone is a portable telephone which receives or makes calls through a cell site (basestation), or transmitting tower. Radio waves are used to transfer signals to and from the cellphone.Modern mobile phone networks use cells because radio frequencies are a limited, sharedresource. Cell-sites and handsets change frequency under computer control and use low powertransmitters so that a limited number of radio frequencies can be simultaneously used by manycallers with less interference.A cellular network is used by the mobile phone operator to achieve both coverage and capacityfor their subscribers. Large geographic areas are split into smaller cells to avoid line-of-sightsignal loss and to support a large number of active phones in that area. All of the cell sites areconnected to telephone exchanges (or switches) , which in turn connect to the public telephonenetwork.In cities, each cell site may have a range of up to approximately ½ mile, while in rural areas, therange could be as much as 5 miles. It is possible that in clear open areas, a user may receivesignals from a cell site 25 miles away.Since almost all mobile phones use cellular technology, including GSM, CDMA, and AMPS(analog), the term "cell phone" is in some regions, notably the US, used interchangeably with"mobile phone". However, satellite phones are mobile phones that do not communicate directlywith a ground-based cellular tower, but may do so indirectly by way of a satellite.There are a number of different digital cellular technologies, including: Global System forMobile Communications (GSM), General Packet Radio Service (GPRS), Code Division MultipleAccess (CDMA), Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution(EDGE), 3GSM, Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), and Integrated Digital Enhanced Network (iDEN). 8|Page
Structure of the mobile phone cellular networkA simple view of the cellular mobile-radio network consists of the following: A network of Radio base stations forming the Base station subsystem. The core circuit switched network for handling voice calls and text A packet switched network for handling mobile data The Public switched telephone network to connect subscribers to the wider telephony networkThis network is the foundation of the GSM system network. There are many functions that areperformed by this network in order to make sure customers get the desired service includingmobility management, registration, call set up, and handover.Any phone connects to the network via an RBS (Radio Base Station) at a corner of thecorresponding cell which in turn connects to the Mobile switching center (MSC). The MSCprovides a connection to the public switched telephone network (PSTN). The link from a phoneto the RBS is called an uplink while the other way is termed downlink.Radio channels effectively use the transmission medium through the use of the followingmultiplexing schemes: frequency division multiplex (FDM), time division multiplex (TDM),code division multiplex (CDM), and space division multiplex (SDM). Corresponding to thesemultiplexing schemes are the following access techniques: frequency division multiple access(FDMA), time division multiple access (TDMA), code division multiple access (CDMA), andspace division multiple access (SDMA) 9|Page