Wireless Access Technologies

During the past few years there has been a ‘boom’ in the area of wireless access technologies in telecommunications. Many new technologies emerged on the market and some, like Bluetooth or Wireless LAN, are widely discussed in public. This tutorial wants to give a short overview of major wireless access technologies, including their main features and application fields, as well as a short comparison.
In the past, access systems in telecommunications or computer networks were mainly based on fixed wired access, making the device quite immobile. The introduction of wireless access technologies allowed a certain degree of mobility. This enabled users to communicate or to transfer data independent of their current location or their movement. A second important aspect was that users got rid of cumbersome cables. Wireless access as described here will focus on bi-directional connections between the user’s device and a counterpart on the network side using radio waves. Other technologies, for instance infrared access or unidirectional ones like Digital Audio/Video Broadcasting, are not considered here.
Mobile or only wireless
The aspect of ‘wireless vs. mobile’ might need some clarification before the article as it seems that there has been some confusion around these terms recently: A wireless access itself can allow only a very limited mobility within the range of this access point. True mobility can however only be achieved by an underlying mobile network, which implements the mobility across the whole covered area. This may be important to keep in mind when comparing access technologies. The below tutorial focuses on the wireless access part mainly and does not discuss a possible mobile network behind.
Cordless phones
Cordless phones became very popular in the early 1990s. The first terminals were using some analogue transmission technologies. Very soon another standard called DECT (Digital Enhanced Cordless Telecommunications) was introduced and is now the dominant standard in cordless phones. DECT was developed by the European Telecommunication Standard Institute ETSI from 1988 on. DECT can be applied to implement wireless to Private Branch Exchanges (PBX), residential cordless phones, wireless access to the public switched telephone network, Closed User Groups (CUGs), Local Area Networks, and more. In spite of all these capabilities DECT is today mainly used in residential cordless phones. Today there are about 60 million DECT phones on the market. DECT transmits radio signals at around 1900 MHz in a reserved band, which minimises interference problems. Good voice quality is achieved by digitally coding voice into a 32 kbit/s signal. The range can be up to 300 m if there is a clear line of sight.
A mobile phone, in contrast to cordless phones, is based on an underlying mobile network, which increases the range of operation to the area covered by the mobile network. There have been several regional variants of mobile networks in operation in the 1970s and 1980s until the Global System for Mobile Communications – GSM – was introduced in the early nineties. There are currently about 500 million mobile users world-wide using a GSM terminal. The GSM standard uses the radio spectrum around 900, 1800 or 1900 MHz in a licensed band. Due to the scarcity of bandwidth, the designers of the GSM standard allowed only 13 kbit/s for speech transmission, which leads to a noticeable reduction of the voice quality in GSM phone calls compared to fixed line telephones. Data transmission in GSM is limited to 9.6 kbit/s only.
As a bit rate of 9.6 kbit/s is far to slow for most of the current data services, an extension to the GSM standard was defined, the General Packet Radio Service - GPRS. Existing GSM networks can be upgraded to GPRS, which reduces the costs for its introduction, but it also requires a new GPRS-capable terminal. The GPRS standard in theory allows a transmission of up to 171 kbit/s, but current networks and terminals in practice allow not more than 50 kbit/s for receiving and 13,4 kbit/s for sending data. A more essential new aspect of GPRS is probably the fact that data is sent in packets, and the pricing can be based on the number of transmitted data. Thus a GPRS telephone can always be ‘online’ without causing any costs as long as no data service is used. Most of all WAP users are likely to profit from this effect. Faster download and lower costs may allow a breakthrough for WAP services. Most of the European GSM networks have already been upgraded to GPRS, but availability of only very few models of GPRS telephones and missing roaming agreements between GPRS operators have impeded broad use of this technology by now. What many don’t know: GPRS has laid the basis for UMTS, as the UMTS core network is based on GPRS.
Yet before the deployment of GPRS networks had started, another extension to GSM networks had been standardised to further increase the transmission speed: EDGE – Enhanced Data for GSM Evolution. By an enhancement of the radio interface, speeds of up to 384 kbit/s allow data services and applications to exchange data at 6 times the speed of an ISDN channel. The efforts for the introduction of EDGE are like with GPRS still relatively low, as existing GSM networks can be upgraded and new terminals will be needed, but e.g. no new license like with UMTS is required. As the transmission rate compares with the full-coverage bandwidth of UMTS, EDGE might be the technology of choice for all network operators that were not successful in achieving a licence for UMTS. The reason that EDGE hasn’t taken off by now can be seen in the still ongoing introduction of GPRS and probably has a political reason as well, as operators are focussing on the introduction of UMTS. In spite of UMTS, many users could benefit from an introduction of EDGE: As UMTS in the beginning will be available only in larger urban areas, users in rural areas would benefit from the immediate full availability of EDGE, allowing the use of high-speed UMTS like services.
With UMTS two new access technologies will be used in Europe: The Wideband Code Division Multiple Access (W-CDMA) and Time Division CDMA (TD-CDMA). UMTS uses radio bands at around 1900 – 2000 MHz and 2100 – 2200 MHz. It allows a maximum data rate of 2 Mbit/s in hot spots and 384 kbit/s for full coverage. This will allow a whole set of new services and, although manufacturers and operators are still struggling with developing handsets and setting up networks, the key for the success of UMTS will lie in the provision of a great variety of customer driven, easy-to-use and affordable services.
Wireless access for data terminals
Where the technologies described above mainly focus on voice terminals, there have also several standards been defined to enable wireless access for data terminals like PCs or notebooks. In 1997 IEEE finished the definition of the Wireless Local Area Network – WLAN - standard 802.11, and in 1999 standards 802.11a and 802.11b have been approved. 802.11b has spread quickly and has already been widely deployed in company networks, but became, due to the decreasing prices, also an option for home users. 802.11b, also referred to as ‘WiFi’, operates in the license free 2.4 GHz band, allows 11 Mbit/s data speed and a range of up to 300 m. There are various application fields, like the easy and comfortable setup of an Adhoc network, or simply the individual mobility of employees in their company or home users in their home. The use of 802.11b for offering Internet access to guests and customers in hot spots like hotels, coffee shops or airport lounges has triggered a discussion about its capabilities to offer UMTS type of services, taking away part of the UMTS business or even making UMTS obsolete. In this respect it has to be kept in mind that 802.11b is rather a wireless access standard than a full mobile network specification with e.g. Quality of Service, charging mechanisms and sufficient security, although WLAN might be an option to complement UMTS at so called hot spots.
Further standards like IEEE 802.11a or the ETSI standard Hiperlan/2, enabling data rates of up to 54 Mbit/s, are waiting for their take-off. Both operate at around 5 GHz and can in fact be seen as competing technologies. Hiperlan/2 technology seems to be more advanced than 802.11a, as it e.g. allows for power management and dynamic frequency change in case of interference, features, which are currently not defined in 802.11a. The outcome is however not clear yet, but first products for the European market are still expected for 2002.
Although all the above technologies of course go along with a cableless connection of terminals and devices, there has one more standard been defined with the primary goal of replacing cables between any device: the Bluetooth standard. With a range of 0.1 - 10 m Bluetooth is intended to replace cables e.g. for all connections of PCs or notebooks and periphery like printers, mobile phones or a digital camera, but also between a mobile phone and a headset, just to name a few examples. The standardisation of Bluetooth was finished in 2001, finally solving e.g. the interference problems with 802.11b devices. First Bluetooth devices are now emerging on the market. Bluetooth allows up to 721 kbit/s in asynchronous mode (57.6 kbit/s in the other direction) or 432.6 kbit/s in synchronous mode. In power class 1 range can be even up to 100 m, which can put Bluetooth into some competition with 802.11 devices, for which the lower data rates and range is uncritical. This is e.g. the case for a ISDN connection for Internet access of home user PCs, but also the provision of Internet access in hot spots like described with 802.11b is possible.
Long distance wireless access
Finally another type of wireless access technology shall be briefly mentioned: Hiperaccess – the high performance radio access. Hiperaccess is a immobile, wireless access network and can be seen as a wireless alternative to fixed line high-bandwidth access networks implemented with fibre cables. It achieves 25 Mbit/s and can be used to connect e.g. to company building or residential areas. Hiperaccess operates at 40 / 43 GHz, and the range is up to 5 km. As such it allows the creation of an access network without the need of digging cables.
Technology Standardisation Frequency Data rate Range Typical usage Links
DECT ETSI EP DECT 1,9 GHz 552 kbit/s, up to 2 Mbit/s 300 m cordless phones, local loopwww.etsi.org/dect
GSM ETSI SMG 0.9 / 1.8 / 1.9 GHz 13 kbit/s for voice, 9.6 kbit/s for data max 30..50 km to next base station voice and data, WAPwww.gsmworld.com
GPRS ETSI SMG see GSM 171 kbit/s see GSM, less for max. data rates data services, WAPwww.gsmworld.com
EDGE 3GPP GERAN see GSM 384 kbit/s see GSM, less for max. data rates data services, 3G systems in the U.S.www.gsmworld.com
UMTS (WCDMA, TD-CDMA) 3GPP 1.90..1.98,
2.01..2.025
2.11..2.17 GHz
144, 384 kbit/s,
2 Mbit/s
depending on number of users in cell voice, data, multimedia serviceswww.3gpp.org
802.11b IEEE 2.4 GHz 11 Mbit/s 150 m WLANwww.standards.ieee.org
802.11a IEEE 5.15 GHz 54 Mbit/s 150 m WLANwww.standards.ieee.org
Hiperlan/2 ETSI BRAN 5,2 GHz (in 4 and 5 GHz band licensed) 54 Mbit/s 30..200 m WLAN, local access to ATMwww.etsi.org/branwww.hiperlan2.com
Bluetooth Bluetooth SIG 2.4 GHz 721 kbit/s 0.1 .. 10 .. 100 m periphery deviceswww.bluetooth.com
Hiperaccess ETSI BRAN 40.5 / 43.5 GHz 25 Mbit/s 5 km remote access to IP / ATMwww.etsi.org/bran
Conclusion
There are much more wireless technologies, which, however, couldn’t be covered in this small tutorial. For more information on the described technologies the reader is referred to the links given in the table above.