Difference between revisions of "Basics of Communication (A1-A3)"

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* Signal strength
 
* Signal strength
  
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=⌘ What will we learn today =
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{{:Building Networks/Electromagnetic signals}}
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[[File:Multipathpropagation.png|450px|right]]
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* basics of radio communication
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* sampling theorem
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* typical radio transmission
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* what effects the signal strengths
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=⌘  Heinrich Hertz - Radiowave propagation =
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[[File:HertzWaves.png|450px|right]]
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Basics of wave propagation:
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* The variation of an electrical field creates a magnetic field
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* The variation of a magnetic field creates an electrical field
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=⌘ Electromagnetic channel =
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[[File:fig1-2architeurewireless.png|450px|right]]
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The radio channel is always affected by noise, which restricts the information flow to the receiver
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[Source:Neelakanta et. al., Fig1.2]
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=⌘ Sources of noise =
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* Electronic parts of transmitter and receiver (components)
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* Spurious electromagnetics (lines radiating on the chip)
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* Fluctuations in power (switching CMOS circuits)
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[[File:two-sources-interference.gif|right]]
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Radio
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* In-band interference
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* out-of band interference, e.g. GSM/NMT interference
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* radio channel, e.g. scattering, multi-path
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[Source:Wikipedia, "interference"]
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[[File:NoiseFloorReceiver.png|450px|right]]
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Figure: Noise floor in a receiver
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* further explanations: Telektronikk 4/95, Rækken and Løvnes, Multipath propagation
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== Comments ==
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* in-band: a source having the same signal
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* out-of-band: modulations/filters which are not perfect
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[[File:Inband-outofband.png|450px|Figure: In-band (top) and out-of-band interference (bottom)]]
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<span style="color:#000B80"> explain Fourier-transform and overlap</span>
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[[File:CapacityCellNetwork.png|450px|Figure: Cell capacity (left) and system capacity (right)]]
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The capacity of a system consists of both the cell capacity (depending mainly on OSI layer 1-3) and on network design, meaning: how much interference do I get from other cells.
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[[File:UMTScells.png|450px|Figure: UMTS macro and microcells in a 6-operator environment]]
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In a network where the available 60 MHz in the UMTS band are distributed to 6 operators, each operator will only have 2x 10 MHz available for operation, which typically means that one frequency block (5MHz) will be used for micro-cells and the other frequency block (5 Unik/MHz) will be used for macro-cells.
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[[File:UMTSneighbour.png|right|Figure: Factors influencing interference (6-operator environment)]]
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The amount of interference will depend on
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# the filter characteristics of the handset (<span style="color:#0B0080"> check separation</span>)
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# the distance from the transmitter
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# the transmit power
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Receiver sensitivity might play a role, but is considered as being constant in the selected frequency band.
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[[File:WLANinterference.png|450px|Interference of WLAN cells in a 3-floor building]]
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802.11b has only three non-overlapping channels, ch 1, 6, and 11. In a normal business building radio waves will propagate not only along one floor, but also through the roof/floor. The visibility of WLAN will make it necessary to plan the frequencies in order to support the person on the ground floor with wireless access.
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[[File:UMTScodeusage.png|450px|UMTS code usage for capacity and coverage]]
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In UMTS coverage and capacity can be adopted not only through the power level of the transmitting unit, but also through the selection of codes. If the same code or code-class is selected in neighbouring cells, a simultaneous connection to the mobile phone can be achieved. This will increase the coverage (<span style="color:#000B80">why?</span>) but decrease the total capacity of the system (<span style="color:#000B80">why?</span>)
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=⌘ Electromagnetic signals =
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* Prerequisite: Ohm's law, current, dielectric constant <math>\epsilon_r</math>, conductivity <math> \sigma</math>
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** <span style="color:#000B80">"Pappa, what is voltage?"
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[[File:EMwave.png|450px|right]]
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* Alternating electric and magnetic field
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* Direction of wave from "right-hand rule"
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[Source: Wikipedia]
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=⌘ Maxwell's Equation in a source free environment =
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Source free environment and free space:
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<math> \nabla \cdot \vec E = 0  \qquad \qquad \qquad \ \ (1) </math>
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<math>\nabla \times \vec E = -\frac{\partial}{\partial t} \vec B \qquad \qquad (2) </math>
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<math>  \nabla \cdot \vec B = 0 \qquad \qquad \qquad \ \ (3) </math>
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<math> \nabla \times \vec B = \mu_0 \epsilon_0 \frac{\partial}{\partial t} \vec E  \qquad \ \ \ (4) </math>
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where div is a scalar function<br />
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<math>\mbox{div}\,\vec v = {\partial v_x \over \partial x} + {\partial v_y \over \partial y} + {\partial v_z \over \partial z} = \nabla \cdot \vec v </math><br />
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and curl is a vector function <br />
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<math>\mbox{curl}\;\vec v = \left( {\partial v_z \over \partial y} - {\partial v_y \over \partial z} \right) \mathbf{i} + \left( {\partial v_x \over \partial z} - {\partial v_z \over \partial x} \right) \mathbf{j} + \left( {\partial v_y \over \partial x} - {\partial v_x \over \partial y} \right) \mathbf{k} = \nabla \times \vec v</math>
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[Source: Wikipedia]
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=⌘ Wave equation =
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Taking the curl of Maxwell's equation
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<math>\nabla \times \nabla \times \vec E = -\frac{\partial } {\partial t} \nabla \times \vec B = -\mu_0 \varepsilon_0 \frac{\partial^2 \vec E }  {\partial t^2} </math>
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<math>\nabla \times \nabla \times \vec B = \mu_0 \varepsilon_0 \frac{\partial } {\partial t} \nabla \times \vec E = -\mu_o \varepsilon_o \frac{\partial^2 \vec B}{\partial t^2} </math>
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yields the wave equation:<br />
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<math>{\partial^2 \vec E \over \partial t^2} \ - \  {c_0}^2 \cdot \nabla^2 \vec E  \ \ = \ \ 0 </math>
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<math>{\partial^2 \vec B \over \partial t^2} \ - \  {c_0}^2 \cdot \nabla^2 \vec B  \ \ = \ \ 0 </math>
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with <math> c_0 = { 1 \over \sqrt{ \mu_0 \varepsilon_0 } } = 2.99792458 \times 10^8 </math> m/s
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[Source: Wikipedia]
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=⌘ Homogeneous electromagnetic wave =
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single frequency
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<math>\vec E(\vec r) = E_0 e^{j(\omega t  - \vec k \cdot \vec r) }  </math>,
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<math>\vec B(\vec r) = B_0 e^{j(\omega t - \vec k \cdot \vec r) }  </math>,
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[Source: Wikipedia]
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where
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* <math>\vec r = (x, y, z) </math> and  <math>\vec k = (k_x, k_y, k_z) </math> <span style="color:#000B80">so?
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* <math>j \, </math> is the imaginary unit
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* <math>\omega = 2 \pi f \,  </math> is the angular frequency, [rad/s]
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* <math> f \,</math> is the frequency [1/s]
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* <math>  e^{j \omega t} = \cos(\omega t) + j \sin(\omega t)  </math> is Euler's formula
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with <math>c = { c_0 \over n } =  { 1 \over \sqrt{ \mu \varepsilon } } </math> and
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<math>n = \sqrt{ \mu \varepsilon \over  \mu_0 \varepsilon_0  </math>
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== room for comments ==
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* What is the difference between a static and a dynamic field
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* Develop the relations for a plain wave
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{{:Building Networks/Radio Communication principles}}
  
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* Assume a plane wave: <math>E_x, H_y</math>. Show that <math>\frac{E_x}{H_y}=Z_0 = \sqrt{\mu_0/\varepsilon_0}</math>
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{{:Building Networks/Digital Communication principles}}
  
  

Revision as of 10:29, 21 September 2014

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Basics of Communication (A1-A3)

Course UNIK4700, UNIK9700
Title Basics of Communication and Assignments
Lecture date 2014/09/05 0900-1200 h
presented by Josef Noll
Objective The objective of this lecture is to explain the principles of radio communication
Learning outcomes What will we learn today
  • Basics of radio communication
  • Typical radio transmission
  • What effects the signal strengths
Pensum (read before) Read before:
References (further info) References:

A Practical Evaluation of Radio Signal Strength:

Propagation characteristics of wireless channels:

Keywords SNR, Transmit Power, Scattering, Reflection, Diffraction

this page was created by Special:FormEdit/Lecture, and can be edited by Special:FormEdit/Lecture/Basics of Communication (A1-A3).


Test yourself, answer these questions

  • What factors affect Wireless signal strength?
  • Explain the meaning of the term diffraction
  • How is diffraction used for radio communications?
  • What is the difference between diffraction and interference?
  • What is the difference between Scattering and Diffraction?
  • What is non line of sight (NLOS)?
  • Does WiMAX possess NLOS capability?
  • How is UMTS different from current second generation networks?

Lecture notes

earlier notes


To Do

Towards next lecture:

  • Select papers related to your topics
  • Come with a suggestion on the direction of your presentation
  • Josef to define a time schedule
  • No assignment, talk to Josef!


Test yourself, answer these questions

  • What factors affect Wireless signal strength?
  • Explain the meaning of the term diffraction
  • How is diffraction used for radio communications?
  • What is the difference between diffraction and interference?
  • What is the difference between Scattering and Diffraction?
  • What is non line of sight (NLOS)?
  • Does WiMAX possess NLOS capability?
  • How is UMTS different from current second generation networks?


S5-unik-preview.png
Slide Show

Title
UNIK4700/UNIK9700 Basics of Propagation
Author
Josef Noll,
Footer
Basics of Communication (A1-A3)
Subfooter
UNIK4700/UNIK9700




⌘ UNIK4700 Radio and Mobility

Lecture 2: Basics of communications

⌘ Principles of radio communication

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

Building Networks/Electromagnetic signals

Building Networks/Radio Communication principles

Building Networks/Digital Communication principles


⌘ Boundary conditions

  • What is happening on electrical walls, magnetic walls?
Figure: Reflection of an electromagnetic wave at the ground plane

Scattering, reflection and diffraction (explain differences) are the three major components in wave propagation. Ideal reflection environments are characterised through

Figure: UMTS macro and microcells in a 6-operator environment


⌘ Nyquist Theorem

BandlimitedSignals.png
  • Shannon: If a function contains no frequencies higher than [cycles/s], it is completely determined by giving its ordinates at series of points spaced seconds apart
InsufficientlySampled.png
  • 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

Shannons theorem will be part of next lexture...


⌘ Summary

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

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