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Radio propagation equation (A4,B1)
Course | UNIK4700, UNIK9700 |
---|---|
Title | Radio propagation for mobile and wireless communications |
Lecture date | 2014/09/12 0915-1200 |
presented | by Josef Noll |
Objective | The objective of this lecture is to explain the principles of radio propagation. |
Learning outcomes | What will we learn today
|
Pensum (read before) | |
References (further info) | References: |
Keywords | Propagation, Free space attenuation, propagation equation, transmit power, Attenuation, Permittivity, Permeability, EIRP, Reflection, Diffraction, Scattering |
this page was created by Special:FormEdit/Lecture, and can be edited by Special:FormEdit/Lecture/Radio propagation equation (A4,B1).
Test yourself, answer these questions
- Convert to dB, dBm: Pr = Pt . Gt . Gr . L(free)
- What is the exact difference between permeability and permittivity?
- What is Relative permittivity? and Relative Permeability?
- Define Propagation constant
Lecture notes
- Media:UNIK4700h14-RadioPropagation.pdf
- Video: mms://lux.unik.no/UNIK4700-JN/UNIK-20140912.wmv
- Streaming
- Media:UNIK4700-L3H13.pdf
- Media:UNIK4700-L4H12.pdf
Discussions from earlier years
How much is 0 dB_m and 10 dB_m?
- Convert dBm to mW is: mW = 10^(x/10), x = number of dBm
- Convert mW to dBm is: dBm = 10*log10(y), y = number of mW
So you get:
- 0 dBm = 10^(0/10) = 1 mW
- 10 dBm = 10^(10/10) = 10 mW
Power received in an area in a distance R from transmitter:
- area of a sphere is
- power transmitted from isotropic antenna is
- antenna area of receiver is
- power received in A_r = P_r
Free space propagation Calculation: http://spreadsheets.google.com/pub?key=p0EyjWrbirGKJXK43uluJfg Josef, check numbers in spreadsheet
- Title
- UNIK4700/UNIK9700 Signal and Capacity
- Author
- Josef Noll,
- Footer
- Radio propagation equation (A4,B1)
- Subfooter
- UNIK4700/UNIK9700
⌘ UNIK 4700: Radio & Mobility
3rd lecture block
Radiowave propagation
⌘ Propagation
Main focus in this lecture is on propagation effect. We will first repeat the main conclusions from last lecture on electromagnetic signals, and then introduce the capacity of a system based on Shannon's theorem.
New literature:
- J. Noll, K. Baltzersen, A. Meiling, F. Paint , K. Passoja, B. H. Pedersen, M. Pettersen, S. Svaet, F. Aanvik, G. O. Lauritzen. '3rd generation access network considerations'. selected pages from Unik/FoU R 3/99, Jan 1999 (.pdf]])
- H. Holma, A. Toskala (eds.), "WCDMA for UMTS", John Wiley & sons, Oct 2000, selected pages
⌘ Left over discussions
- Bandwidth separation between signals and adjacent channel separation (ACS) [Holma2000, p183]. ACS requirements 33 dB. Measurements performed by [Potman et.al. ]
- E versus B: later today
Comments
Figure: Illustrating reduction of capacity in network A (top) and blinding of phones in cell (B)
More detailed discussions on these effects can be found in the literature indicated above.
⌘ Summary
- radio wave propagation
- Electromagnetic signals
- Nyquist Theorem
- Signal/noise ratio
- Shannon Theorem
- Signal strength
⌘ Nyquist Theorem
- 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]
⌘ Signal/noise ratio
,
where P is average power
- why talking about noise?
- dB,
- near-far problem
[source: Wikipedia]
⌘ Shannon Theorem
- The fundamental theorem of information theory, or just Shannon's theorem, was first presented by Claude Shannon in 1948.
- Given a noisy channel with channel capacity C and information transmitted at a rate R, then if R < C there exist codes that allow the probability of error at the receiver to be made arbitrarily small. This means that theoretically, it is possible to transmit information nearly without error at any rate below a limiting rate, C.
- See File:LarsLundheim-Telektronikk2002.pdf: The channel capacity of a band-limited information transmission channel with additive white, Gaussian noise. This capacity is given by an expression often known as “Shannon’s formula”:
[bits/s]
with W as system bandwidth, and in case of interference free environment, otherwise
, where
with
as Boltzmann constant and
as temperature in Kelvin.
Exercises:
- If the SNR is 20 dB, and the bandwidth available is 4 kHz, what is the capacity of the channel?
- If it is required to transmit at 50 kbit/s, and a bandwidth of 1 MHz is used, what is the minimum S/N required for the transmission?
[source: Wikipedia, Telektronikk 2002]
Comments
⌘ Hartley's law
- 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]
⌘ Shannon - examples
[bits/s]
Examples
- calculate capacity for W= 200 kHz, 3.8 Unik/MHz, 26 Unik/MHz, (all cases P/N = 0 dB, 10 dB, 20 dB)
Comments
Figure: Calculation of Shannon capacity for GSM (GPRS, EDGE), UMTS (packet data, HSDPA) and 802.11b
Figure: Log_10 funtion and related power. The power expressed in dB is 10 times the log_10 of the normalised power.
There are also the abbreviations
-
stands for power with respect to 1 mW. How much is 0 dB_m and 10 dB_m?
-
Power of a sound (or music).
⌘ Cell capacity in UMTS
UMTS has good efficiency with respect to Shannon
⌘ Range versus SNR
[Source:Valenzuela, BLAST project]
Comments
[Source Valenzuela, BLAST project]
why is there no relation to frequency?
⌘ Coding and Modulation
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]
Comments
Figure: A frequency band consists of n channels.
Example GSM: the upload band is from 880-915 Unik/MHz, which is 35 Unik/MHz. With a carrier of 200 kHz we have 175 channels, which have to be divided between the various operators.
⌘ Modulation types
- Amplitude shift keying (ASK)
- Frequency shift keying (FSK)
- Phase shift keying (PSK)
[Source:K.E. Walter, Basics of Mobile Communications]
⌘ Frequency and time division multiplexing
- 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]
⌘ Code division multiple access
UMTS as an example (in one of the future lectures)
room for Comments
⌘ Propagation and absorption
- Free space loss
- Antenna types
- Radiation patterns
- Antenna gain
- basic propagation models (ground wave, sky wave and line of sight (Unik/LoS) propagation)
- optical vs radio Unik/LoS
- attenuation (free space)
- Noise (thermal, intermodulation, crosstaal, impulse noise)
- Atmospheric absorption
- Multipath propagation
- refraction, reflection, diffraktion and scattering
- fading (fast, slow, flat, selective, rayleigh, rician,..)
⌘ Recall: Plane wave propagation
Assume a plane wave: . Show that
What is the relation between a plane wave and an omnidirectional wave?
Comments
⌘ Free space propagation
develop propagation equation, see (http://www.antenna-theory.com/basics/friis.php)
- convert into dB
- provide examples for f = 10 MHz, 1 GHz, 100 GHz
- discuss influences on radiation pattern
Free space attenuation
Comments
Figure: Free space propagation from a transmit (t) to a receive (R) station.
= Next lecture: Antennas =