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Lecture 03
Wireless Applications, TF Transmission, Data and Signals,…
Lecture 03
Wireless Applications, TF Transmission, Data and Signals, Period, Amplitude, Frequency, Phase, Wavelength
Wireless Applications
- Education
- Home Entertainment
- Medical and Health Care
- Government and Military
- Office Environments
- Event Management
- Travel
- Environment Research
- Construction and Warehouse and Logistics Management
- Industrial Control
- Slide 5-9, Lecture 03
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WDT - Data and Signals
To transmit data, data must first be converted (encoded) into the appropriate carrier signals Hence data is transmitted using carrier signals
Modulation
The carrying of information data on a carrier signal is called Modulation - the amplitude, frequency or phase of a carrier is changed proportional to information data
- Data and signals can be analogue or digital:
- Analogue signals are used to carry both analogue or digital data
Data
- Analogue: Continuous value (sound, image, light)
- Digital: Discrete (text, integers, symbols, MP3 audio, JPEG images, AVI video)
Signal
- Analogue: Continuous varying EM wave
- Digital: Series of voltage pulses (square wave)
The data you want to transmit can be analogue or digital, but you use analogue signals to carry either, as this is wireless
Analogue Signal
- Signal intensity (voltage or amplitude) varies in a smooth fashion over time
- No discontinuities in the signal
- Broadcast continuously
- Eg: Audio, Video, Voice, Light
Digital Signal
- Consists of discrete or separate pulses
- Has numerous breaks throughout the signal stream
- Signal intensity maintains a constant level for some period of time and then changes to another constant level
- Digital audio, digital video, digital voice
Computers operate using digital data, hence analogue data has to be converted into digital format for processing and storage
Picture - slide 15, lecture 03
The green plot shows a typical analog signal, the variations in amplitude and frequency convey the degree of loudness and pitch in speech or music.
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How do we convert to digital data?
We take samples. So for example every one second we take samples. You lose the accuracy – the data – the digital becomes a approximation
Amplitude – the higher voice Frequency – like men has deeper voices – lower frequency. Girls higher pitch
WDT - Carrier Signal Components
Slide 16, lecture 03
Digital signals are used to communicate and relay information within computer networks but are not used as carriers of information in wireless networks
Wireless communications commonly use periodic analogue signals, in particular, sine wave, as data carriers, to carry analogue or digital data
Periodic Signal
- Simplest type of signal
- Repeats over time
- T is the period where T = 1 / f
- f is the repeating frequency where f = 1 / T
Period (T)
the time for one complete cycle of a soundwave. You must know the relationship between the period and the frequency.
Amplitude (A)
- Height of the wave above or below a given reference point, typically measured in volts
- In sound, it relates to loudness
- In radio wave, it relates to signal strength
- What is the unit of measure for amplitude?
Frequency (f)
- The rate at which a radio circuit creates the waves
- Number of times a signal makes a complete cycle within a second, usually measured in Hertz (Hz)
Rate of change with respect to time
- Change in a short span of time => High frequency
- Change over a long duration => Low frequency
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Picture slide 18, lecture 03
- Note a change in voltage does not create a change in frequency
- Period (T) is the amount of time it takes a wave to complete a cycle
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Phase (ø)
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Eg on right shows a 90‐degree phase lag (Picture slide 19, lecture 03)
The second radio wave has a 90 degree phase lag with reference to reference signal/wave
360 degree is the same – no lag.
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Wavelength (λ)
- Is the distance between successive waves
- Higher frequency waves have shorter wavelength
- Lower frequency waves have longer wavelength
- Notice here the x axis is distance and not time – hence period in slide 52, and here is wavelength
- Always look at the x axis to know
- Why are we concerned about wavelength? It affects the size of the antenna
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- Speed of light wave in air, c ≈ 3 x 10^8 m/s
- Speed of sound wave in air, c ≈ 344 m/s
- EM waves travel at the speed of light (c) in a vacuum
- Atmospheric conditions and the frequency of a wave affect its speed but only by a small amount
- For radio and light waves travelling in air, speed of the wave is essentially the speed of light
- When EM waves enter a medium from the air, their propagation speed is reduced by a factor but the frequency of the wave is unchanged
- As speed of light is constant, that means that if the wavelength increases, it means the frequency has to decrease.
- Waves in the air are almost speed of light. Going through water, walls and so on decreases it.
- In course take it as C is a constant.