Lecture 2: Basics of communications

• radio wave propagation
• Electromagnetic signals
• Nyquist Theorem
• Signal/noise ratio
• Shannon Theorem
• Signal strength

Can also be called "Propagation constant". Somewhat misleading, as the propagation usually varies strongly.

Alternative names:

• Transmission parameters
• Propagation parameters
• Propagation coefficients
• Transmission constants
• Secondary coefficients

Propagation constant, symbol γ, is defined by the ratio between the amplitude at the source, and the amplitude at some distance x. Is a complex quantity, so we use α (attenuation constant) and β (phase constant) to define it. Attenuation constant, is the loss of signal, or attenuation of an electromagnetic wave travelling through a medium. Phase constant is the change in phase per meter, along the path travelled.

The frequencies which we use for mobile communications are ranging from 450 MHz (ICE), the old TV bands, 800-900 MHz (GSM), 1800 (GSM), 1900, 2100 MHz (UMTS), 2400 MHz (Wifi), 2650 MHz (LTE), and 5100 MHz (IEEE802.11a..). While previously frequency band were used for a specific technology, refarming started in 2012 to open for communication technologies in other bands. Examples of such refarming are LTE₁₈₀₀ indicating an operation of LTE in the 1800 band. Back in 2013 Apple surprised the European operators, as the iPhone came with LTE only in the 1800 band, and not, as usual in Europe, in the 2600 band.

(Source:http://en.wikipedia.org/wiki/Radio_propagation)

• see Wave Propagation Parameters (by Joachim Tingvold)

• basics of radio communication
• sampling theorem
• typical radio transmission
• what effects the signal strengths

A modulated radio signal can be written in a general form: Any of these three parameters can be varied: amplitude-, frequency- or phase-modulation.

• Channel-coding is used to reduce bit-error-rate, e.g. through forward error correction.
• Multiplexing is used to split the total amount of radio into smaller pieces. Typical: time, frequency or code multiplex. examples

[Source:K.E. Walter, Basics of Mobile Communications]

• Amplitude shift keying (ASK)
• Frequency shift keying (FSK)
• Phase shift keying (PSK)

[Source:K.E. Walter, Basics of Mobile Communications]

• Time domain, e.g. 8 slots in GSM
• Frequency domain, e.g. up- and downlink in specific bands
• Code division (CDM), specific codes

[Source:K.E. Walter, Basics of Mobile Communications]

UMTS as an example (in one of the future lectures)

• radio wave propagation
• Electromagnetic signals
• Nyquist Theorem
• Signal/noise ratio

A4-Signal Strength and Capacity

• Shannon Theorem
• Signal strength

• Shannon: If a function contains no frequencies higher than [cycles/s], it is completely determinded by giving its ordinates at serires of points spaced seconds apart

• band-limitation versus time-limitation
• Fourier transform

[source: Shannon, 1948]

• The amount of information that may be transmitted over a system is proportional to the bandwidth of that system.

• where m is the “number of current values”, which in modern terms would be called “the size of the signalling alphabet”

Why did it take twenty years to fill the gap between Hartley’s law and Shannon’s formula? The only necessary step was to substitute 1+C/N for m in Hartley's law. Why, all of a sudden, did three or more people independently “see the light” almost at the same time? Why did neither Nyquist, nor Hartley or Küpfmüller realize that noise, or more precisely the signal-to-noise ratio play as significant a role for the information transfer capacity of a system as does the bandwidth?

[source: L. Lundheim, Telektronikk 2002]

* Electronic parts of transmitter and receiver (components) Spurious electromagnetics (lines radiating on the chip) Fluctuations in power (switching CMOS circuits)

Radio

• In-band interference
• out-of band interference, e.g. GSM/NMT interference
• radio channel, e.g. scattering, multi-path

[Source:Wikipedia, "interference"]

• further explanations: Telektronikk 4/95, Rækken and Løvnes, Multipath propagation

,

where P is average power

• why talking about noise?
• dB,
• near-far problem

[source: Wikipedia]

Shannon's theorem will be part of next lecture...

• radio wave propagation explain
• Electromagnetic signals
• Nyquist Theorem
• Signal/noise ratio