Cellular communications uses radio waves to carry telephone conversations and data between land based transmitters and receivers. The main alternatives are conventional land-based telephone or cable-TV type networks, and satellite telecommunications.

A wireless frequency band, like any other kind of communication channel, can support only a limited number of callers, so this bandwidth must be shared in some way.

In cellular communications, rather than have one powerful transmitter and large receiving antenna, with every wireless phone caller having to transmit to this, the geographical region is split up into smaller areas called cells. Each cell has its own low-power transmitter which in principle will not interfere with its neighbours. Callers in different cells can then use the same frequency band. This is known as frequency reuse, resulting in a great saving of bandwidth, effectively multiplying the number of potential callers by the number of cells. When a caller moves between cells, their call is automatically handed over to the new cell.

Digital signals are used to improve frequency reuse. Digital signals are streams of numbers representing a speech signal, or numerical data, whereas an analogue signal represents the actual waveform of the speech. It may be surprising to note that whilst digital signals actually consume more bandwidth than analogue signals, their resistance to interference means that the effect of signals overlapping into adjacent cells (co-channel interference) is reduced so frequency reuse is improved and overall capacity is increased. Digital electronics are ever cheaper to manufacture compared to analogue.

There are 3 ways the frequency band may be split up amongst multiple callers within a cell:

• Frequency Division Multiple Access (FDMA) - each caller has a non-overlapping portion of the frequency band. This is a simple solution but low on security and has a fixed limit to the number of callers in a cell.
• Time Division Multiple Access (TDMA) - callers can use the same frequencies, but not all the time, and available time slots are continually switched between callers, resulting in signals being communicated in bursts. Handover time delay between callers causes echos which must be suppressed. TDMA is more flexible than FDMA but also has security problems.
• Code Division Multiple Access (CDMA) - also known as spread spectrum, the signals are coded in such a way that all users use the same frequency range all of the time, but the signals can be still be distinguished. CDMA has advantages of security, higher network capacity, and is more immune to multi-path fading (caused by signals bouncing of buildings and other objects).

In practice, combinations of time-division and frequency division are the norm, and code-division may also be restricted to portions of the available frequency range (known as narrow-band CDMA).

The original first generation (1G) mobile phone networks were purely analogue. Most countries of the world which have a mobile network are currently using second generation (2G) networks, some of which are fully digital, and some which are dual-mode digital and analogue. 2G networks are mostly geared towards mobile voice communications, but also support data to a limited extent. Japan is currently the pioneer in 3G systems, which have 3 important improvements over 2G. Firstly, 3G uses packet switching like the Internet, whereas 2G opens a channel for the duration of the call, known as circuit switching. Secondly, 3G is much faster, allowing data rates comparable with the Internet, up to 2Mbps (mega bits per second). Thirdly they can be always-on, meaning the caller is continually connected to the network. CDMA is preferred for access. Future 4G systems are intended to be even faster, around 100Mbps. Jamaica's cellular networks are currently 2G.

The Cable & Wireless 2G network, which migrated from a 1G analogue system, uses a dual- mode system known as TDMA IS-136, popular in the USA. This allows the network to support both analogue and digital phones, although the digital signal may not extend to all areas. Voice mail and text messaging is supported. Digicel's new digital network is also a TDMA based system known as Global System for Mobile communications (GSM) which is widespread in Europe. GSM has a potential route to 3G via General Packet Radio Service (GPRS) and Enhanced Data rates for Global Evolution (EDGE).

These and Centennial's forthcoming third cellular network need to connect to the land-line telephone network controlled by C&WJ in order to reach outside those networks. This is intended to occur though a set of switches in various parts of the island (see Further Reading, C&WJ RIO document).

One promise of cellular communications is having access to the internet anywhere: in your home; in a car; on foot...

The Wireless Application Protocol (WAP) is the means by which today's 2G networks are able to handle data. There are a number of limitations however, not least a maximum 19.2Kbps (kilo bits per second) data rate which is nearly 3 times slower than a standard 56Kbps modem, and much slower than ISDN or ASDL land-line telephone services, so 2G is not really suitable for images or video. Furthermore, the maximum data rate is for stationary callers in the open. The data rate is generally decreased further when the caller is moving, or inside a vehicle.

Since the adoption of 3G increases the data communication rate above ISDN and is comparable to ADSL, it allows richer content and streamed media such as digital video and audio. Software application design for the mobile internet is predicted to be a major industry, one which is within the reach of developing countries, which may not have an electronics industry, but do have a computer literate workforce.

Health and safety is an important issue in cellular and mobile communications, for example:

• Transmission power from mobile phones can interfere detrimentally with other electronic systems, some of which are safety critical. In particular, sensitivity of aeroplane electronic systems (avionics) for navigation, presently requires phones to be turned off at certain times (e.g. at take off), and operation of hospital equipment is also susceptible to lack of electromagnetic compatibility (EMC).
• Frequencies of mobile phones include high-frequency bands in the hundreds of megahertz (MHz) and gigahertz (GHz) range which at sufficient power can cause heating of bodily tissue (like a microwave oven).
• Low-frequency signals under 1kHz are also generated (due to switching), which can affect hearing aids and heart pacemakers.

Research into solving or minimising these problems continues, which may include redesign of affected equipment or other technological solutions, careful implementation strategies, and consumer awareness.

The following articles were found useful in the writing of this information leaflet. Local newspaper articles, especially the business sections, are also sources of information about developments in Jamaica's cellular networks.

1. Cable and Wireless Jamaica, Reference Interconnect Offer (RIO) document, via www.cwjamaica.com
2. The Economist, The Shape of Phones to Come, Technology Quarterly supplement, March 24 - 30, 2001, via www.economist.com
3. IEEE Spectrum magazine, Always on - Living in a networked World, Vol 38, No. 1, January 2001, via www.ieee.org
4. IEEE Transactions on Electromagnetic Compatibility, via www.ieee.org
5. PC Magazine, Wireless Superguide, April 24 2001, Vol. 20, No. 8, via www.pcmag.com
6. Third Generation Partnership Project (3GPP), http://www.3gpp.org
7. Wireless - The Revolution in Personal Telecommunications, by Ira Brodsky, Artech House, Norwood MA, USA, 1995.

This leaflet is for educational purposes. The Institute of Electrical and Electronics Engineers (IEEE) aims to help advance global prosperity by promoting the engineering process of creating, developing, integrating, sharing, and applying knowledge about electrical and information technologies and sciences for the benefit of humanity and the profession. The Jamaica Section does not endorse any specific commercial communications solution.

For more details and information about the IEEE Jamaica Section and its activities, please visit our Home Page: http://www.ewh.ieee.org/r3/jamaica/

© IEEE Jamaica Section, 2001.

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