Introduction

Wireless communication has been around for a century; radio, television and mobile phones being successive prominent examples. However, wireless data communications for commercial use is a relatively new phenomenon. It started only twenty years ago and is evolving rapidly.

The early adopters were warehouses and distribution centres where real time data combined with bar code scanning to drive inaccuracy and time out of the business. They used proprietary narrow band communication systems that were expensive, inflexible and incapable of handling large amounts of data. But they brought such massive savings to their organisations that the investment was justified.

Within a few years of the introduction of the mobile phone, digital data communication has become a practical reality. The Universal Mobile Telecommunications System (UTMS) is now being introduced. In techno-speak it's a third generation, broadband, packet based telecommunication system often referred to as 3G. In practice it will deliver permanent internet connection at a data rate of up to 2 Mbps and secures the future of mobile wide area communications.

In the last few years wireless communication has linked up with TCP/IP, the protocol at the heart of modern networking and the internet. Local and wide area networks (LANs and WANs) can now be extended wirelessly. Wireless communication has been pushed to the forefront of mainstream computing. Economies of scale have brought the costs down and the technology is being adopted at an exponential rate. For many businesses, ignoring it could be commercial suicide.

Basic Principles

In all commercial wireless systems for mobile devices there access points and client devices. Access points are also called base stations or transmitters, and connect to the host computer system or network This connection is usually wired, but can be wireless. They contain a radio transceiver. Client devices also contain a radio transceiver. They may be an integral part of a mobile device (a phone for example) or they might plug into a mobile device (a PCMCIA card for example).

Each radio transceiver will operate at over a certain frequency range and below a certain power level, as defined by national or international standards. The power limits the range over which other devices are able to communicate with it. This could be 30km for a telecommunications mast, down to a few metres for a Bluetooth client. When two radios are within range of each other they can communicate data.

In most wireless systems a number of access points can be linked together to form a greater area of coverage. The telecommunications networks effectively cover the whole country. A Bluetooth network will cover about a hundred square metres. Each wireless system has a limit on the number of access points that can be used in the same area. Providing they are within range, a number of client radios will be able to communicate simultaneously with each access point. The number varies with each wireless system. As they move around, the client radios usually have the ability to roam form one access point to another (from one 'cell' to another) to obtain the best signal quality and therefore the best connection to the network. This is the key feature of wireless communications for mobile devices, and usually occurs without the user even knowing about it. Data can thus be exchanged between the host computer system and the wireless device anywhere within the total area of coverage. The technology that does this is highly complex, but at a sufficiently low level that is of little concern to the user.

Most wireless systems allow a special configuration mode called point-to point or ad hoc. That allows two client radios to talk to each other, or limits one access point to talk to one specific client radio. Several paired devices can thus operate independently in the same area. Each wireless system has a practical limit on the number of paired devices that can operate in close proximity.

A license is required to operate powerful wireless systems. These are indirectly controlled by the government. The output power of most client radios is set below a certain level such that they may be operated license free. The same applies to access points being used for local area networks.

Other key factors are noise immunity, data rates and usage.

Noise immunity is the ability of the wireless system to keep open communication when there is a high level of background radio noise. Even if the wireless system is inherently very tolerant of noise, communication can be disrupted by local sources such as air conditioning motors, refrigerators and alarm systems. A site survey is used prior to installation to determine the background noise levels and identify specific sources of noise that might need some attention. The site survey is a very effective way of determining where access points should be positioned in order achieve good coverage and good noise immunity.

The data rate is a simplistic indication of how much data can be sent across a wireless network and is usually expressed in bits per second. The real data rate that will be achieved is affected by a number of other factors - whether the system uses full or half duplex communication (see glossary for explanation), the operating distance from the access point, the amount of interference, the amount of traffic on the host network, the density of access points, the number of client radios operating in the same area, and the communication overheads (additional information for protocol formatting, error checking and encryption).

Usage is related to density of radio equipment operating on the same wireless system in the same area. If the usage is high, it will take longer for each radio client to communicate data to the host. If the usage is very high communication could clog up completely. Each wireless system will give some kind of indication of usage, but in practice it is prudent to stay well away from the maximum.

Different Types

Three main categories of - wireless wide area networks (WWAN), wireless local area networks (WLAN) and wireless personal area networks (WPAN). Synergix works in each of these categories where they relate to mobile computing:

GSM originally stood for Group Special Mobile, later commonly changed to Global System for Mobile Communication, and sometimes also referred to as 2G (second generation). It is part of the nationwide cellular radio network run by the major telecoms companies and is essentially a wide area network infrastructure for providing voice quality digital wireless communication. The data rates is (from a practical point of view) 9,600 bits per sec. Use of the network is generally charged by the minute, so it is not financially viable to stay 'on line'. There is a significant amount of time required (10 to 40 seconds) to establish a connection, so it can be inconvenient to send small amounts of data if the connection / disconnection time is taken into account.

GPRS and EDGE: GPRS stands for General Pack Radio Service, and is sometimes referred to as 2.5G. It is a technology for providing reasonably high bandwidth wireless networking and uses the same cellular network as GSM. Its theoretical data rate is a maximum of 115K bits per sec, but in practice it is well below - typically 21.4K bps. Use of the network is generally charged by the 'packet' (ie by the amount of data, not the transmission time). That means the communicating device can be permanently 'on line'; if it is not sending or receiving data it is not incurring any cost. It is ideal for small amounts of infrequent data, and avoids the connection delays associated with GSM. However for large amounts of data transfer (eg tens of megabytes) it can work out ten times more expensive than GSM. The data rate of GPRS is being improved using EGPRS (Enhanced GPRS). It is currently being standardised within the European Telecommunications Standards Institute and uses EDGE technology (EDGE stands for Enhanced Data for GSM Evolution), the final evolution of data communications within the GSM standard. EDGE uses a different modulation scheme to enable threefold increase in data throughput speed, still using the existing GSM infrastructure.

UMTS stands for Universal Mobile Telecommunications System, sometimes referred to as 3G (third generation). It is broadband, packet based telecommunication supporting data rates up to 2 Mbps. It is the future of mobile communications, the replacement for GSM. As with GPRS, use of the network will be charged by the 'packet', and like GPRS it will be expensive to transmit large amounts of data.

Narrow Band uses the frequency range 418 to 470 MHz. It is relatively simple, has good noise immunity and an access point can cover a relatively large area (typically 300m radius in free air). It is used for local area wireless communication at a typical maximum data rate of 19,200 bits per second. The wireless systems are generally proprietary to each manufacturer.

IEEE802.11b is a worldwide standard for wireless local area networking that is particularly suited to mobile computing. With an estimated 30 million users it is the most widely adopted standard and as such is the most cost effective to implement. It operates in the 2.4GHz radio band. The success of 802.11b is down to the fact that equipment from different manufacturers can be used on the same network. Any equipment carrying the 'WiFi' logo has been specifically tested for interoperability.

802.11b supports a maximum data rate of 11Mbits/sec, although this falls off quickly to 2Mbits as the range from access point to client increases to the practical indoor maximum of about 100m. The access points interconnect using Ethernet, making it easy to add them on to an existing wired network. Any number of access points can be wired together to create the area of coverage required for the wireless network. The radio clients use relatively little power making them suitable for use in battery operated mobile computers and the data rate is acceptable for most applications.

The greater the number of devices operating off one access point, the slower the data rate becomes. By increasing the number of access points the data rate can be improved. The 802.11b specification allows for three 'non-overlapping' radio channels. This determines how many access points can be crammed into the same area. Any more than three overlapping in the same area will cause interference and slow down the data rate.

Other IEEE802.11 standards exist, most notably 802.11a and 802.11g. 802.11a is designed for applications where a higher data rate is desirable, for example intensive use of laptops handling large amounts of graphical data in an office environment. It operates in the 5GHz radio band and supports a maximum data rate of 54 Mbits/sec, although in practice 6, 12 or 24 Mbps is more realistic. 802.11a access points cost more than their 802.11b equivalents and have a shorter range, so it is more expensive to implement. The radio signal doesn't travel as well as 802.11b through obstructions such as walls, adding to the number of access points required. The radio clients use more power than those of 802.11b power making them less suitable for use in battery operated mobile computers. The 802.11a specification allows for 8 'non-overlapping' radio channels, and so will operate well with a much higher density of radio clients. 802.11a and 802.11b products are not interchangeable, although they can be operated in the same area. Dual Band products are being introduced, offering 802.11b and 802.11a wireless in the same unit. Whilst expensive, this offers the best of both worlds, especially where the user density is high (as it provides 11 non overlapping channels). 802.11g operates on the same frequency as 802.11b, but supports a data rate of 54Mbps. It is 'backwards compatible' with 802.11b, offering a good future upgrade path for existing 802.11b users. However it will take time to establish and for most non-data intensive applications 802.11b offers a more proven, cost effective solution. Dual band products will soon become available, supporting 802.11a and 802.11g.

Bluetooth operates in the same general frequency band as 802.11b, however it is fundamentally different. Bluetooth is a wireless personal area network (WPAN). It supports ad hoc (point to point) networking, so there are no access points. Bluetooth uses very low power communication and is designed to operate with a 10m range, the 'personal operating space'. It is designed to eliminate interconnecting cables. Up to 8 Bluetooth devices can operate together on the same WPAN. The data rate is approximately 800Kbps.

Despite the fact they operate in the same frequency band and therefore raise interference issues, Bluetooth and 802.11b are complimentary and some mobile devices will support both - the 802.11b providing the local area network connection, and Bluetooth supporting a mobile printer connection for example.

Integration

Wireless networks have to be integrated with existing business systems. With narrowband systems this is usually a proprietary RS232 or USB connection that is only effective with low data rates. 802.11 systems have the major benefit of supporting TCP/IP protocols and physically linking onto a standard Ethernet network. That makes the integration process very easy. GSM, GPRS and UMTS similarly support TCP/IP and are therefore also relatively easy to integrate and share with the internet.