Mobile Phones: Introducton
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Mobile Phones: Introducton
A Mobile Telephone (also known as a Cellular Telephone) is defined as a 'portable electronic device for the purpose of telecommunications over long distances'. Which boils down to 'a telephone you can roam freely with'. Most current mobile phones actaully connect to a cellular networi of base stations (the cell sites themselves) which overlap to yield coverage and which also link to the standard landline public switched telephone network. It should be noted that mobile phones are distinct from household cordless telephones which generally operate only within range of a dedicated base station (though the distinction is blurring with mobile phones that can link via bluetooth to a home internet base station).
It should be noted, however, that the term mobile phone can refer to any type of mobile telephony device and also includes satellite phones and radio phones. In contrast cell(ular) phones refers only to those mobile phones that function via cellular base stations. Despite these distinctions, in common parlance the terms are used almost interchangeably.
History of the Mobile Phone
The history of the mobile phone actually goes back quite a long way. Indeed, the immediate precursor of the modern mobile phone could be considered to be the radio telephone developed for battlefield communications during the Second World War. Indeed what's now considered as the 0G (zeroth generation) of mobile telephones were introduced. Systems such as the Mobile Telephone Service used a VHF radio system to link the telephone directly to the PSTN landline system. The problems with these systems were a combination of network congestion and interference and it was the problem of network congestion that ultimately led to the search for a replacement system. In 1947 the modern concept of using hexagonal 'cells' as mobile phone base stations was invented by Bell Labs engineers at AT&T though the concept had to wait until the 1960s before serious development began.
A major breakthrough cam in 1970 when Amos Joel of Bell Laboratories solved the problem of how a call could be maintained as an user moved from the range of one cell (technically the base station coverage area) to the next and the next. This problem is one that's termed the 'handover' and what Amos Bell invented was the 'call handoff' feature. This allowed users to roam freely between any number of cells, allowing mobile telephony to be used in long-distance journeys and the first mobile phones were fitted in vehicles as car phones.
It is generally accepted that the first truly portable 'modern' mobile phone was invented by Martin Cooper of Motorola Corp in 1973 and he made the first call on this handheld device on April 3rd and thus changed our world forever. However, it wasn't for a further eight years that NMT (Nordisk MobilTelefoni or Nordiska MobilTelefoni-gruppen, Nordic Mobile Telephone in English) introduced the first fully-automatic cellular telephone system. The father of this system (and of the modern mobile telephone symstem is considered to be Östen Mäkitalo). This system led directly to the 1G (first generation) of mobile phones introduced from the middle to the late 1980s. Because of power requirements and poor battery performance these cellular telephones were still to large and bulky to be properly hand-held devices and most were still fitted as permanent in-car devices. 1G mobile telephones use analogue signals to connect the telephone to a base station though the base station network itself communicates digitally from one base station to the next.
1G Systems
The image above shows the evolution of the mobile phone from the early so-called 'bricks' to the latest hand-held devices of 2007. The technologies that led to this revolution in telephone design and performance include increased miniturization, improvements in signal strength and, above all, huge advances in battery technology.
2G Systems
Following the 1G standard, above, came the 2G specification. Most of the world has standardized on TDMA (Time Division Multiple Access) with the most well-known version being GSM (Global System for Mobile Communications) whereas the Americas have both TDMA-based and CDMA-based (Code division multiple access) systems. 2G ststems use digital communications between the handset and the base station which increases the overall system capacity as data can be compressed and multiplexed. Also, digital systems emit less radio power from the handsets, meaning that cells can be smaller so more cells can be positioned in the same overall space. And the more cells you have, the more capacity you have.
Of course, use of lower power by the phones mean that phone batteries last much longer. Also, digital encoding signal allowed error checking to be built into the handset so that noise levels could be reduced. Digital handsets could also be employed to transmit and receive digital data, allowing internet access from handsets and the transmission of SMS (Short Message Service) text messages and emails. More importantly, perhaps, is the fact that 2G phones are far more secure than their 1G predecessors. Indeed, the 1G phone had no protection whatsoever against eavesdropping and it was possible to 'clone' (clectronically duplicate) a phone's settings so that more than one telephone could bear the same number. Despite this, 2G telephones are not as secure as they could be and it is still possible to hack into these telephones.
As always, where there are advantages to digital-based 2G systems there are also disadvantages. These are most apparent in rural errors where the weeker digital signal may not be sufficient to reach a more distant cell tower. Analogue signals have a smooth decay curve, so even though the quality of a transmission decreases with decreased signal strength and the call becomes noisier and more garbled it is still possible to have an intelligible conversation at very low signal strengths. Digital's strenght, that of clear calls, is also it's weakness in that when the signal strength decreases somewhat (and an analogue user might experience static) the digital user may notice occasional dropouts. If the signal strength falls further the digital signal may fail totally as dropouts become dropped or unintelligible calls. This is because the signal curve for a digital phone is stepped rather than being a smooth curve so you only have to decrease slightly in signal strength to have a very dramatic drop in quality.
It should also be noted that digital telephones utilize compression to maximize both data througput and data densities at and with base stations. But compression always degrades the original data, inducing losses and it signal strength is low then this can significantly impair call quality.
The vast majority of today's mobile telephones adhere to the 2G standard, or it's immediate successor, the 2.5G system.
2.5G Systems
In effect the 2.5G system (second and a half system) is a direct extension of 2G where features such as packet-switched connection and enhanced data rates and these networks support WAP, MMS (Multimedia Messaging Service), SMS mobile games, and search and directory but they exclude EDGE (Enhanced Data GSM Environment) and GPRS (General Packet Radio Service) technologies. The reality is that most non-3G telephones sold today adhere to 2.5G standards and technologies rather than 2G and texting services such as SMS, MMS and picture messaging have become standard features of mobile telephones. In most cases 2.5G is seen as a stepping stone to 3G networks.
3G Systems
3G is the third generation of mobile telephony technology. Like broadband for landlines, 3G technology the simultaneous of both voice date (the call itself) and non-voice data (text, video, email, web browsing and instant messaging). In this context it has long been thought that video telephony would be the killer aplication that would drive the sales of 3G systems. For most of the world (apart from the USA) 3G services are delivered on separate parts of the radiofrequency spectrum to 2G. This meant that 3G operators had to license new regions of the spectrum and had to build new cellular networks to work separately on these frequences. This has significantly driven-up the price of 3G licenses and has delayed the worldwide rollout of the technology. A notable exception being Japan where by 2005 almost 40% of subscribers were already on 3G only networks and in 2006 upgrade from 2G to 3G was complete. Japan also shows that the true killer app for 3G wasn't video calls, as the pundits expected; rather, it was the downloading of music.
In Europe, 3G operators were given a boos when the EU council suggested that 3G operations should cover 80% of the European population by the end of 2005. 3G is slowly entering other markets with the greatest growth, as of 2007 being in the emerging African markets.
Features of 3G
As compared with 2G systems, 3G systems have the capacity to support larger numbers of voice and data centres (most especially in crowded urban centres where base stations are at a premium) as well as supporting higher data-transfer rates. And all this is supported at a lower per-unit cost that 2G.
Again, as compared with 2G the 3G systems utilize a 5 MHz channel carrier that allows costs to be optimized whilst giving a very high speed of data transfer. This also allows the transfer of 385 kbi/s for mobile systems and up to 2Mbi/s for stationary systems. Because 3G handsets have improved spectrum efficiency and the system has greater capacity. This should allow 3G users to access global roaming between different 3G networks.
As of 2007 a new standard, High-Speed Downlink Packet Access (HSDPA) (Sometimes known as High-Speed Downlink Protocol Access) (often called 3.5G) is being implemented which allows for data transfer at 3.6 Mbi/s with an allowance of 30 Gb of data per month per user.