Introduction
In today’s wireless communications the technology has come a long way since its beginnings back in the early nineteen hundreds and has become so advance that most countries have their own regulator. In the UK the regulator for wireless standards is called Ofcom which has been established since 2003. In the US the regulator is Federal Communications Commission and has been established since 1934. These regulators govern what frequency band companies can purchase to provide a wireless mobile service to customers.
The term spread spectrum is used in data communications and is a technique in which the transmitted signal is distributed over a wide frequency band, much wider than the minimum bandwidth required to transfer the information. The signal distributing is accomplished by deploying a pseudo-noise code which is not directly connected to the data. The pseudo-noise code is used as a modulation waveform to expand the baseband signal over a bandwidth much greater than the signal information bandwidth. At the receiver a reception synchronized to the code is used to demodulate the signal and collect the data.
In the diagram above you can see what the information signal looks like before it’s been modulated and after.
Spread spectrum first became well known way back in 1942 when it received U.S patent which was granted to Hollywood actress Hedy Lamarr and pianist George Antheil. It was described as a safe radio link to control torpedoes but the technology never became commercial available until the 1980s and is now used for applications that involve radio links in hostile environments.
The spread spectrum technology became popular with the military because it provides a low probability of intercept and anti-jam featur...
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...he carrier to hop from frequency to frequency at random but predictable sequence over a wide band according to the pseudo-random noise (PN) code. The higher the data rate of the information the faster the hops occur.
The next modulation technique is Direct-Sequence Spread Spectrum (DSSS) which applies the (PN) code directly to the data entering the carrier modulator. The baseband signal is spread out into a much larger bandwidth greater than the minimum bandwidth required to transmit the information.
Another modulation technique is time-hopping spread spectrum (THSS) which is used to achieve anti-jamming (AJ) or low probability of intercept (LPI).
The final modulation technique is chirp spread spectrum (CSS) that uses wideband linear frequency modulated chirp pulses to encode information. (A chirp is a signal in which a frequency increases or decreases in time).
"Radar during World War II." - GHN: IEEE Global History Network. N.p., n.d. Web. 16 Feb. 2014. .
“G.726: 40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM)”, International Telecommunication Union, 1991.
Fourier transform is applied on digital images to interprets their content in terms frequency information. To illustrate, Flat areas, where the intensity is slowly changing, result in low frequencies. Rough areas, on the other hand, result in high frequencies because of the dramatic change in the intensity value. this paper discusses the impact of manipulating the frequency information of digital images and how the frequency spectrum can be used to address a real world situation.
Morse Code is still used today in the military as a way of communication during harsh conditions due to universal means of communication. Experienced operators can copy text they received without the need to write what they receive, and when transmitting, they can easily converse at 20 to 30 words per minute. Morse Code can be conveyed using sound or light, which sometimes happens between ships at sea using lights. In emergencies, people use Morse Code to transmit distress signals when there is no other option. The standard international distress signal is ...---... (SOS). Since December 2003, Morse Code has even included the “@” symbol and it is a combination of a and c “.--.-.”. This is the first
A normal radio communication system is made of two separate components, a transmitter and a receiver. The transmitter emits an electrical fluctuation at a frequency known as the carrier frequency. Frequency modulation has more than just one pair of sidebands, which produces the variations that translate into the speech or any ot...
Analysis of the Environment of the Mobile Network System Executive Summary 3 Glossary of Abbreviations 4 Introduction 5 Recent History
The information theory is the extentsion of Nyquist's and Hartley's origingal ideas on the subject. However, Claude Shannon includes new factors such as "the effect of noise in the channel, and savings possible due to statistical structure of the original message and due to the nature of the final destination of information." Shannon's ideas were based on the fundamental problem in communication, which he described as the "difficulty of reproducing at one point the message selected at another point." The most significant aspect is that the actual message sent is one "selected from a set" of possible messages. A system had to be formed to work for each possible selection. Shannon also constructed the Linear Model of Communication. It is rare to see a communication text book that doesn't include this model, or a model that is based on this one. However, modifications had to be made because Shannon and Weaver both overlooked the importance of feedback.
The uses of Digital Signal Processing in communications has become so large scale that nearly any form of analog communication is considered obsolete. Today, nearly any form of communication used, aside from verbal communication, relates to Digital Signal Processing. Some of the more prominent uses for DSP in communications are; local area networks, cell pho...
A digital communication system uses discontinuous transmission that may vary in frequency, amplitude and/or phase to represent binary data.
In 1921 the Detroit Michigan Police Department first used mobile radio in a vehicle. Digital wireless and cellular roots started in the 1940s. In the 1940s new frequencies between 30 and 40 MHz were available. There was an increase of availability in channels which police systems were encouraged to use. Mobile units were available within private companies, individuals, and public agencies. In St. Louis, 1945 the first mobile telephone system in the US was introduced. Along the highway between New York and Boston a Public mobile system carried greater frequency distance in 1947. In 1n 1949, the FFC authorized separate radio channels to common carriers. A new system was developed with automatic channel selection in 1964. With this new system each call allowed customers to dial for themselves and it eliminated the need to push-to-talk operation. In 1975, in Chicago, AT&T was authorized to develop a cellular system. After this AT&T and Bell labs work with other cellular vendors to develop their cellular phones. Their phones were made so consumers would have the quality products available to use on cellular networks. There are many reasons why the mobile wireless has not progressed further in the last 60 years, this is because of cautiousness and federal regulation. The Federal Communications Commission controlled frequency availability. Their regulations and unresponsiveness had the most significant factors hindering radiotelephone development. The Federal Communication Commission delayed the technology in America by ten years.
Spectrum Decision Making calls for reconfiguration for the channel and protocol required for constantly adapting to mobile changing environments and adjustment of output power or even alteration of transmission parameters (such as modulation formats (e.g. low to high order QAM), variable symbol rates, different channel coding schemes) and characteristics by the Cognitive radio devices. CR should be able to use multiple antennas for interference knolling, capacity increase or range extension.
...ssesses the communication capabilities using the percent of communications sent and received that are comprehendible without ambiguities or at 90 percent ambiguity by the receiver or the sender. They also check for frequency of communication back-up during emergencies in the case of communications failures or overloads.
Communication begins with transmitting information to another person and the way one format of transmi...
Frequency modulation is, of course, used on the FM band. And it is used for
One of the latest advancements in wireless data. It is used in GSM (Global System for Mobile Communications) for transferring data in packets.