Mobile devices: a buyer's guide

Charles McLellan & CNET staff ZDNet.co.uk

Published: 26 Sep 2007

Mobile connectivity
A key consideration with any mobile device is how it connects to the internet, as this largely detemines what useful work you'll be able to do with it. Notebooks routinely have wired Ethernet connections with data transfer rates up to 1000Mbps (Gigabit Ethernet), but handhelds and smartphones don't, and it's wireless connectivity that's the key to truly mobile productivity. Here's a tour of the available options.

Personal-area wireless networks
Infrared Increasingly rare on mobile devices, infrared — standards for which are handled by the Infrared Data Association, or IrDA — requires line-of-sight access, which somwhat limits its utility. Most of the functions for which infrared was used on mobile devices — such as connecting peripherals and beaming small files — have been, or are being, taken over by Bluetooth.
Bluetooth This low-power, short-range technology operates in the same 2.4GHz frequency band as 802.11b/g Wi-Fi, but supports lower data transfer rates (721Kbps for Bluetooth 1.2 and 2.1Mbps for Bluetooth 2.0+EDR) over shorter distances. Like infrared, Bluetooth is commonly used as a cable-replacement technology, for connecting peripherals such as printers and audio headsets, and for device-to-device file transfer.

Local-area wireless networks
Wi-Fi The IEEE 802.11 family of standards form the basis of most wireless LANs worldwide. 'Wi-Fi' is the term coined by the Wi-Fi Alliance, which exists to promote and certify the interoperability of different vendors' 802.11-based products. Wi-Fi networks provide connectivity and internet access to homes, offices and public hotspots; Wi-Fi can also be used for ad hoc peer-to-peer connections between devices — in a meeting room, for example.
802.11a A 54Mbps WLAN standard using the 5GHz frequency band, which cuts out interference from equipment that uses the crowded 2.4GHz band (microwave ovens, Bluetooth devices and cordless phones, for example); 802.11a is used for wireless networking within enterprises, but is rare elsewhere.
802.11b An 11Mbps WLAN standard using the 2.4GHz frequency band, 802.11b has largely been superseded by the faster 802.11g but is present in a large number of mobile devices (which can connect to 802.11g access points).
802.11g Like 802.11a, 802.11g has a maximum data rate of 54Mbps, but it operates in the same 2.4GHz band as the popular 802.11b, making it backwards-compatible. However, a mixed 802.11b/g network will experience slower throughput than a pure 802.11g LAN. Newer mobile devices commonly come with 802.11g Wi-Fi.
802.11n A 100Mbps+ standard supporting both 2.4GHz and 5GHz frequency bands, 802.11n supports legacy a, b and g traffic in a mixed mode or n-only for maximum performance. The key advance in 802.11n is the use of multiple antennas: Multiple Input/Multiple Output (MIMO) allows multiple data streams to be sent simultaneously over longer distances. Although the 802.11n standard has yet to be finalised, vendors are already selling 'Pre-N' and 'Draft-N' products. The Wi-Fi Alliance has endorsed this practice by certifying Draft 2.0-compliant kit. Intel's latest Santa Rosa notebook platform uses Draft-N Wi-Fi modules.

Wide-area wireless networks
GSM (2G) The Global System for Mobile communications (GSM) was the first digital mobile phone network in Europe, replacing first-generation analogue networks. The 900MHz and 1800MHz fequency bands are used by dual-band phones; tri-band and quad-band 'world' phones also support the 1900MHz and/or 850MHz bands, which are used in the USA and Canada. Data transmission rates for GSM are a paltry 9.6Kbps — enough to support text messaging (SMS) but little more.
GPRS (2.5G) The General Packet Radio Service (GPRS) adds a packet-switched channel to GSM, boosting the data transmission rate to 80Kbps (download) and 20Kbps (upload) or 60Kbps/40Kbps depending on the configuration employed. This is enough to support services such as MMS (Multimedia Messaging Service), push-to-talk, instant messaging (IM), push email, web browsing and Voice over IP (VoIP).
EDGE (2.75G) Enhanced Data rates for GSM Evolution (EDGE) boost the data speed for GSM/GPRS networks to around 200Kbps. In the UK, Orange and T-Mobile offer EDGE connectivity, while O2 is in the process of upgrading its network.
UMTS (3G) The Universal Mobile Telecommunications System (UMTS) is the technology behind Europe's third-generation (3G) mobile networks, which are operated by O2, Orange, T-Mobile, Vodafone and 3. Data rates are typically 384Kbps, which allows services such as video calling and TV to be added to those available on GPRS/EDGE networks. A wide range of handhelds, smartphones and notebooks have integrated 3G connectivity; external 3G modems are also available in several formats including USB, PC Card and ExpressCard.
HSDPA/HSUPA (3.5G) High-Speed Downlink Packet Access (HSDPA) allows 3G networks based on UMTS to have higher data transfer speeds: HSDPA technology supports download speeds of 1.8, 3.6, 7.2 and 14.4Mbps, although the maximum currently available on UK networks is 3.6Mbps. HSUPA is the uplink counterpart of HSDPA, providing upload speeds up to 5.76Mbps; all of the UK's 3G networks except O2 are now rolling out HSUPA connectivity.
Mobile WiMAX (4G?) Worldwide Interoperability for Microwave Access (WiMAX) is a term coined by the WiMAX Forum, which promotes the interoperability of IEEE 802.16-based products in a similar way to the Wi-Fi Alliance/802.11 combination. WiMAX is a long-range system that delivers a point-to-point connection to the internet from an ISP to an end user; the 802.16e-2005 version of the standard is often called 'Mobile WiMAX' and is seen by some as a contender for '4G' mobile networks. Although there's a lot of noise about WiMAX elsewhere, it has had little impact on Europe up to now thanks to the presence of well-established 3G UMTS networks.

Satellite communications
GPS The Global Positioning System (GPS) was originally conceived as a US military project, but is now also available for civilian use worldwide. It allows mobile devices equipped with a GPS receiver to get accurate location and time data, and when coupled with suitable software and maps can provide a navigation service. A European equivalent to GPS, Galileo, is currently under development.

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