A Brief History and a Basic Reference Model of Wireless Communication

LECTURE 8 A BRIEF HISTORY AND A BASIC REFERENCE MODEL OF WIRELESS COMMUNICATION

 For a better understanding of today’s wireless systems and developments, a short history of wireless communication will be discussed.  The use of light for wireless communications reaches back to ancient times.  The light was either “modulated” using mirrors to create a certain light on / light off pattern (“amplitude modulation”).  Using light and flags for wireless communication remained important for the navy or fishermen until radio transmission was introduced.  In 1794, Claude Chappe invented the optical telegraph where a long distance wireless communication was made.

1  Wired communication started with the 1st commercial telegraph line between Washington and Baltimore in 1843.  Alexander Graham Bell’s invention and marketing of the telephone in 1876.  The first regular public voice and video service was already available in 1936 between Berlin and Leipzig.  Wireless communication did not really take off until the discovery of electromagnetic waves and the development of equipment to modulate them.  It all started with Michael Faraday and Joseph Henry demonstrating electromagnetic induction in 1831 and James C. Maxwell laying the theoretical foundations for electromagnetic fields with his famous equations (Maxwell’s Equations) in 1864.  Heinrich Hertz was the first to demonstrate through an experiment the wave character of electrical transmission

2 through space in 1886, thus proving Maxwell’s equations.  Nikola Tesla soon increased the electromagnetic transmission distance.  Guglielmo Marconi is the person who was closely connected with the success of wireless communication.  He gave the 1st demonstration of wireless telegraphy in 1895 using long wave (LW) transmission with very high transmission power (> 200 kW).  The 1st transatlantic transmission followed in 1901 and set up commercially in 1907.  Huge base stations using up to thirty 100 m high antennas were needed on both sides of the Atlantic Ocean.  Around that time, the 1st World Administration Radio Conference (WARC) took place, coordinating the worldwide use of radio frequencies.  The 1st commercial radio station took place in 1906 when Reginald A. Fessenden transmitted voice and music for Christmas.

3  The 1st commercial radio station started in 1920 (KDKA from Pittsburgh) where sender and receiver still needed huge antennas and high transmission power.  In 1920, Marconi discovered short waves (SWs).  In connection with wireless communication, SWs have the advantage of being reflected at the ionosphere.  This way it was now possible to send short radio waves around the world bouncing at the ionosphere (still used today).  The invention of the electronic vacuum tube in 1906 by Lee DeForest and Robert von Lieben helped to reduce the sender and receiver size.  Vacuum tubes are still used, e.g. for the amplification of the output signal of a sender in today’s radio stations.  1 of the 1st mobile transmitters was on board a Zeppelin in 1911.  The 1st telephone in a train was available on the Berlin-Hamburg lines where wires

4 parallel to the railroad track worked as antenna.  The 1st radio for cars was commercially available in 1927; indeed in 1922 the 18- year old George Frost from Chicago had integrated a radio into a Ford Model T.  1928 was the year of many TV broadcasting field trials.  John L. Baird transmitted TV across the Atlantic and demonstrated color TV.  Up to then, all wireless communication used amplitude modulation. That offered relatively poor quality due to interference.  Edwin H. Armstrong invented frequency modulation in 1933 resulting in a much better quality.  By the early 1930s, many radio stations were already broadcasting all over the world.  The 1st network in Germany was the analog A-Netz from 1958, using a carrier frequency of 160 MHz.  In 1972, the B-Netz was introduced.

5  In the early 1970s, the northern European countries of Denmark, Finland, Norway and Sweden agreed upon the Nordic Mobile Telephone (NMT) system.  In 1982, the ‘Groupe Spe’ciale Mobile’ (GSM) was founded to develop the new system using a 900 MHZ spectrum allowing roaming throughout Europe.  In 1983 the US analog mobile phone system working at 850 MHz namely Advanced Mobile Phone (AMPS) was started.  The early 1990s marked the beginning of fully digital systems.  In 1991 the standard Digital European Cordless Telephone (DECT) for digital cordless telephony was adopted in Europe.  DECT works at a spectrum of 1880~1900 MHz with a range of 100~500 m and can carry up to 1.2 Mbps for data transmission thru 120 duplex channels.  Then, DECT has been officially renamed to Digital Enhanced Cordless Telecommunications to indicate that it

6 has capabilities to transport multimedia data streams.  In 1991, the GSM was standardized in a document of more than 5 000 pages.  The 1st version of GSM is called Global System for Mobile Communication, works at 900 MHz, and uses 124 full- duplex channels.  GSM services are full international roaming, automatic location services, authentication, encryption on the wireless link, efficient interoperation with ISDN systems, and a relatively high audio quality.  Then there is the GSM-1800 networks (using 1800 MHz spectrum), which also known as Digital Cellular System 1800 (DCS 1800) that can operate with a better voice quality and smaller cells, and thus are better adapted to business use in big cities.  Nowadays, GSM-1900 or PCS 1900 (using spectrum at 1900 MHz) is also available in the US.

7  In 1996, the High Performance Radio Local Area Network (HIPERLAN), was standardized for wireless local area networks.  HIPERLAN type-1 operates at 5.2 GHz and offers data rates up to 23.5 Mbps.  HIPERLAN type-4 going up to 155 Mbps at 17 GHz.  In 1997, the IEEE 802.11 standard was becoming more popular for LANs.  IEE 802.11 works at the license-free Industrial, Science, Medical (ISM) band at 2.4 GHz and infrared offering 2 Mbps up to 10 Mbps.  1998 finally marked the beginning of mobile communication using satellites with the Iridium system.  Iridium consists of 66 satellites in Low Earth Orbit (LEO) and uses 1.6 GHz band for communication with the mobile phone.  In 1998 also, the Europeans agreed on the Universal Mobile Telecommunications

8 System (UMTS) as the European proposal for the International Telecommunication Union (ITU) International Mobile Telecommunications-2000 (IMT-2000).  The IMT-2000 recommendations define a common, worldwide framework for future mobile communication at 2 GHz.  The current trend is a unification of at least some of the technologies toward IMT-2000 for global communication and some kind of a Mobile Broadband System (MBS) for local wireless communication with much higher bandwidth and additional Quality of Service (QoS) features.  Basically there are 5 layers in the basic reference model used in the field of communication.  The 5 layers and its functions, respectively are: 1. Physical layer. . This lowest layer is responsible for the conversion of a stream of bits

9 into signals that can be transmitted on the sender side. . The physical layer of the receiver then transforms the signals back into a bit stream. . For wireless communication, the physical layer is responsible for frequency selection, generation of the carrier frequency, signal detection, modulation of data onto a carrier frequency and encryption. 2. Data Link layer. . The main tasks include accessing the medium, multiplexing of different data streams, correction of transmission errors and synchronization. . Multiplexing describes how several users can share a medium with minimum or no interference. . For wireless communication, multiplexing can be carried out in four dimensions, which are space, time, frequency and code.

10 . In this field, the task of multiplexing is to assign space (Space Division Multiplexing or SDM), time (Time Division Multiplexing or TDM), frequency (Frequency Division Multiplexing or FDM) and code (Code Division Multiplexing or CDM) to each communication channel with a minimum of interference and a maximum of medium utilization. . Altogether, this layer is responsible for a reliable point-to- point connection between 2 devices or a point-to-multipoint connection between one sender and several receivers. 3. Network layer. . This layer is responsible for routing packets through a network or establishing a connection between two entities over many other intermediate systems.

11 . Important topics are addressing, routing, device location and handover between different networks. . Involves the use of the Internet Protocol (IP). 4. Transport layer. . This layer is used to establish an end-to-end connection. . Topics like QoS, flow and congestion control are relevant if the transport protocols, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are to be used over a wireless link. 5. Application layer. . Service location, support for multimedia applications, adaptive applications for large transmissions characteristic variations, and also for wireless access to the World Wide Web (WWW) using a portable device.