Wireless Communication

Introduction

Wireless communication, like their wired counterparts rely on the manipulation of electrical charge to enable communication between devices, however they use a specific type of signal known as radio frequency or RF. Following the demonstration by Marconi, led to the widespread use of radio waves for communication. Radio communication is hence the process in which radio waves are used as a carrier for transmitting and receiving intelligent information through atmosphere or deep space and sky (Poole, 2006, p. 8). This article explains the fundamentals of radio communication starting from the basics of radio signals, then going on to explain how radio waves can be used for communication. In the later part of the article, the popular cellular radio communication schemes are discussed.

The nature of radio signals

1. What radio signals are? Radio Signals are electromagnetic waves, almost exactly similar to visible and infrared light except for their frequency and wavelength. The frequency of radio waves is much lower than the visible and infrared light. And in consequence there wavelength is much longer (Poole, 2006, p. 19). Here,  represents the wavelength of electromagnetic radiation,  represents the frequency of electromagnetic radiation, and  is the constant speed at which any electromagnetic wave travels equal to 3×108 m/s.
2. How radio signals propagate over a wireless medium? Radio waves travel outwards much like waves in a water pond and become weaker as they travel longer distances. However, the distances covered by the radio waves are very large and are in fact the signals that scientist look for from the farthest galaxies to find the outer extremities of the universe. Since they are electromagnetic waves, radio signals do not need any medium in order to propagate. Light waves, like radio waves travel, in straight lines and are subject to reflection, refraction, diffraction, absorption and scattering. The entire radio spectrum is divided into very low, low, medium, high, very high, ultra high, super high and extremely high frequencies, and a group frequencies is called a band (Haslett, 2008, p. 87).
3. Factors that adversely affect radio signal propagation? There are several factors that affect the radio transmission. At different frequencies some of these factors affect radio waves more than others. Many of the factors lead to attenuation, which means the weakening of a radio signal as it passes through the atmosphere. All the radio signals are attenuated as they pass through rain or any type of water in the air, such as cloud, snow sleet etc, but radio signals at higher frequencies are attenuated more than the radio signals at lower frequencies (Xiao, 2007, p. 352).

In addition to this radio communications are also affected by the ionosphere layer present in the earth’s atmosphere. This layer affects the radio waves due to the presence of a large number of electrons and other ions. This layer causes two major disturbances in the transmission of radio waves:

• Faraday Rotation – This phenomena is whereby the polarization plane of radio waves rotates due to the interaction between radio waves and earth, especially magnetic flux lines and electrons in the ionosphere. This interference causes a lot of problems chiefly in the satellite communication, especially when plane-polarized waves are used in the 850 MHz band (Haslett, 2008, p. 141)
• Ionosphere Scintillation – This phenomenon arises from spatial and temporal fluctuations in the ionosphere electrical characteristics, and is observed as irregular transient fluctuations in the received signal strength. This phenomenon occurs more often in summer months during the periods of intense solar activity and in equatorial regions. The level of ionosphere scintillation is inversely proportional to frequency of radio waves (Haslett, 2008, p. 142).

Using radio signals to carry information

1. How information can be added to a radio signal? A radio wave carries information bearing signals through space. Each carrier may have information encoded directly on it by periodically interrupting its transmission as in Morse code telegraphy, or encoded on it by what is known as a modulation technique. There are many modulation techniques used to encode the messages the most common ones being amplitude modulation, frequency modulation and phase modulation (Haslett, 2008, p. 145).
2. How a number of different radio signals can be sent from a transmitter to a receiver simultaneously by employing modulation and multiplexing? Modulation and multiplexing are principles of moving information in progressively more efficient methods. Modulation schemes are used to maximize the limited resources of the spectrum. Multiplexing is a technique whereby several message signals are combined into a composite signal for transmission over a common channel. To transmit a number of these signals over the same channel, the signals must be kept apart so that they do not interfere with each other and thus they can be separated at the receiver’s end. The two basic techniques of multiplexing are frequency division multiplexing FDM and time division multiplexing TDM. As the name suggests, in the former case the signals are separated in frequency, while in latter the signals are separated in time (Haslett, 2008, p. 148).

Conclusion

The article presented a discussion of the use of radio signals of communication along with giving a description of the various commercial protocols used presently in the cellular radio communication. As can be seen, radio communication finds many applications not only for home entertainment and military applications but also for commercial communications.

In fact wireless communication applications have exploded in popularity over the last decade, with the onslaught of products such as pagers, cellular phones, radio navigation and wireless data networks. The radio based communication system is expected to have a  strong hold in future too with many advances on various fronts such as global coverage, improved interoperability, wireless-wireline integration for broadband services, and the support of high bit rate data, the internet and increased multimedia usage (Meites, Zuman and Golio, 2008, p. 4)

Bibliography

1. Bedell, P., 2005. Wireless Crash Course, 2nd Edition, McGraw-Hill Professional,
2. Berndt, H., 2008. Towards 4G Technologies: Services with Initiative, Germany: John Wiley and Sons
3. Buehrer, RM., 2006. Code Division Multiple Access (CDMA). Morgan & Claypool Publishers.
4. Goransson, P.,Greenlaw, R., 2007. Secure Roaming in 802.11 Networks, Massachusetts:  Newnes with IEEE and Elsevier
5. Haslett, C., 2008. Essentials of Radio Wave Propagation. New York: Cambridge University Press
6. IIT Kharagpur. n.d., Broadcast Communication Networks, [Online], Available at http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Computer%20networks/pdf/M5L9.pdf (Accessed on 13th September 2008)
7. Meites L., Zuman P., Golio M., RF and Microwave Passive and Active Technologies, 2nd Edition, Florida: CRC Press with Taylor and Francis Group
8. Mercedes Benz, 2004, Integrated Cell Phones, [Online], (Updated 4th August 2004), Available at http://www.mercedestechstore.com/pdfs/416_Telematics/416%20HO%20Integrated%20Cellphones%20(Cookson,I)%2004-08-04.pdf, Accessed on 13th September 2008)
9. Poole, I., 2006. Cellular Communications Explained: From Basics to 3G, 1st Edition. Massachusetts: Newnes with Elseiver Ltd.
10. Private Line Communications, 2006, Cellular Telephone Basics, [Online], (Updated 1st January 2006), Available at http://www.privateline.com/mt_cellbasics/x_appendix/c_early_bell_system_overview_of_amps/, (Accessed on 13th September 2008)
11. Xiao, Y., 2007. WiMAX/MobileFi: Advanced Research and Technology, Florida: CRC Press with Taylor and Francis Group