Wireless Access

History

Marconi

Ever since Marconi discovered radio in 1895, man has been using wireless technology to reduce the cost of infrastructure and improve the flexibility of information exchange. In 1899 he established communication across the English Channel and in 1901 he communicated signals across the Atlantic Ocean between Cornwall, England and Newfoundland, Canada. He took out a number of patents with English patent No. 7777 for tuned communications being awarded in 1898. These major achievements were, in 1909, honored by a Nobel Prize in Physics.

Wireless Communications was championed by the military who used it to strategic advantage in both the first and second world wars. As early as the 1920s mobile receivers were being deployed in police cars in Detroit, USA and by the 1940s the majority of these systems were converted to the improved Frequency modulation (FM) systems. These FM systems are based on the same techniques as used today for radio broadcast.

Detroit Police Radio Dispatch 1925

From as early as 1946 mobile telephony was possible but technical problems hindered full deployment. Europe saw cellular service introduced in 1981, when the Nordic Mobile Telephone System or NMT450 began operating in Denmark, Sweden, Finland, and Norway in the 450 MHz range. It was the first multinational cellular system. In 1983 the Advanced Mobile Phone System (AMPS) was deployed in the US and in 1989 the Groupe Special Mobile (GSM) defined the European digital cellular standard. 1993 saw the IS-95 Code Division Multiple-Access (CDMA) spread-spectrum digital cellular system deployed in the US.

Wireless Access Today:

Auctions of spectrum for Third generation (3G) cellular system standards occurred throughout the world in the late 1990s and due to the success of GSM systems, multi-billion dollar contracts resulted making this one of the most sought after resources owned by wireless service providers. The 3G systems aim is to offer mobile, wireless, high data rate performance system with global roaming capabilities.

Wireless Access, although largely to do with the application of cellular telephony is not entirely focussed on this technology. Other techniques exist which offer complementary, and perhaps, competing services. Bluetooth is an open specification for radio-based voice and data communications, over small distances, and across multiple devices. With such massive and rapidly growing industry support, a billion or more mobile electronic devices could support Bluetooth wireless technology within just a few years, according to market watchers.

Fixed Wireless Access (FWA) System is a wireless system in which office or home users directly connect to the telephone network and internet to use the system. FWA is expected to meet the needs for the promotion of competition in the regional communications market and the needs for the high capacity communication capability brought about by the increase in Internet users. The FWA is standardized under the recently completed IEEE 802.16 standard in which the base station is connected, via wireless communications, with the multiple users.

LAN (Local Area Network) connects computers in offices, factories, etc. Up to now, such networks have mainly been set up using fixed lines. Wireless LAN is a network which utilizes radio waves instead of fixed lines in the construction of a network. This system is more flexible and more functional than LAN built in the conventional way. It can provide internet access to users in airport lounges and city block areas. As the mobility speed of Wireless LAN users is expected to be low, high data rate throughput is possible, providing transmission of megabytes of data per second. This equates to being able to watch live television broadcasts by a user.

The ability to locate a persons exact position also utilizes wireless access. Inexpensive, portable, and wireless devices can now link into the international satellite-based Global Positioning System (GPS), or the Galileo system under development in Europe, to obtain location coordinates to assist in navigation and emergency tracking. Other location finding technologies are emerging that are based upon utilizing mobile phone technologies.

Wireless access is also utilized in communication satellites, where either low earth orbit (LEO) systems allow users to utilize small handsets with low delay, while requiring numerous satellites to cover the world. On the other hand three Geostationary earth orbit (GEO) satellite systems can provide world wide coverage of large spot beams, however a noticeable delay of a fraction of a second occurs. These satellites are used for television broadcast to users as well as television relay between television broadcast companies. Other systems are utilized for mobile voice/data communications.

Problems and Technology unique to Wireless Access:

Wireless access requires specific techniques and methods to cope with the unique problems that wireless channels create. Reflections from objects such as buildings and cars cause the phenomenon of signal fading which severely degrades signal quality. It also generates multiple signal reflections (multipath) which can be used to improve signal quality, but can also degrade signal quality.

For a number of decades wireless communication was only offered between two radio transmission centres, ie. between two large cities, thereby, directly replacing the wire that was previously used. Wireless Access communications is concerned not just with point-to-point systems, but more with systems where multiple users can be connected simultaneously (multiple access systems). Simultaneous multiple access schemes are possible by allocating separate segments to different users. These segments can be split in time or frequency to allow the multiple user access. A recent method which is still undergoing intensive research is the use of direction of arrival of signals as a segmentation method. This is also called smart antennas where a base station uses multiple antennas to differentiate between users that are at different angles to it, much like a radar system can identify different aeroplanes over an airport at different angles to the radar tower.

In the mid 1940s, Bell Labs created the cellular concept and developed the first commercial mobile telephone service. The cellular concept allows users to be mobile and move through a city or region while still maintaining a connection to the telephone network. Here each cell has an associated basestation. As they reach the range of one basestation (the edge of the cell) they perform a handover, or exchange, into the next cell. The handover is a non-trivial process and requires good knowledge of communication systems and channel conditions to prevent the user from being dropped by the system. Multiple access systems also require power control techniques, these algorithms minimize the transmit power and therefore minimize interference and maximize system capacity.

Key Research Challenges:

A key challenge for wireless access systems is to produce transparency to users across systems, standards, countries and terminals. This minimizes the confusion a user faces and enhances the value of the terminal immensely. Just as people configure their computer environment for their needs so should they be able to configure their wireless device for their needs. Specific projects may include:-

Transparent communication across standards and countries (pervasive communications)
Flexibility of terminals to include 3rd party applications
Building services around wireless devices
Convergence of wireless technology and the internet
System designs to overcome the limited spectrum
Cell Size Trade-off: maximize data rates while minimizing infrastructure cost