A presentation of Pirmin Vogel, Benjamin Weber and Marco Karch 2008 by P.V.B.M.M.K. Ltd. & Co KG (release date , ver. 1.

Transcription

1 A presentation of Pirmin Vogel, Benjamin Weber and Marco Karch 2008 by P.V.B.M.M.K. Ltd. & Co KG (release date , ver. 1.02)

2 introduction Cablecom canceled many TV channels out of the program to get the needed bandwidth for digital TV now a new technology is needed to provide higher bandwidth ti l fib! optical fibers! but what the hell is that?!?

3 basic principle total reflectance which means look at the eqations for Gamma: parallel polarization vertical polarization

4 Snellius s refraction law with refraction indexes:

5 structure of a single fiber core glass, n=1.48 cladding glass, n=1.46 buffer some kind of resin jacket plastic

6 dispersion if the entering angle is near the ray gets reflected more often than a ray with a higher entering angle propagation delay

7 dispersion If an impulse consisting of several rays with different angles enters the fiber some rays are reflected more often than others an therefore need more time to pass the fiber. the impulse gets streched dispersion limits the transfer rate!

8 different modes light of highmode: small angle, often reflected light of low mode: high angle, less often reflected, travels almost parallel to the axis of the fiber

9 multimode step index fiber constant refractive indexes of core and cladding a lot of different modes high dispersion only for short distances used

10 multimode graded index fiber refractive index of core gets smaller as radius increases, therefore the light rays bend smoothly as they approach the cladding the resulting paths reduce the dispersion because light with a high g p p g g mode (high angle) passes more through regions of small index than those of small mode

11 monomode / singlemode fiber very small core diameter rays pass the fiber almost parallel to the axis of the fiber only light of one wavelength is transmitted onlyweak dispersion very long ranges and transfer rates possible

12 comparison

13 bandwidth length product characterstical quantity typical values: multimode step index: 100 MHz * km mulitmode graded index: 1 GHz * km Monomode/singlemode: 10 GHz * km Gigabit ethernet (1000Base T): maximum length = 100m, bandwidth = 62.5 MHz

14 comparison to copper cables + very high transfer bandwidth + small damping even at long ranges + external electromagnetic fields do not affect the transmission + high termic and chemical stability + almostunlimited resources (glass sand) + less material for shielding, optic fiber cables are much lighter than copper cables expensive installation and equipment low cost effectiveness at close range

15 additions light source: LED oder laser) damping due to splices: multimode step index: 5 6dB/km at 850nm mulitmode graded index: db/km at 850nm Monomode/singlemode: 0.36 db/km at 1310nm different wavelenghts: 850nm, 1310nm or 1550nm

16 different DVB s DVB S (satellite) DVB T (terrestrial television) DVB C (cable) DVB H (handhelds)

17 about DVB s same frequencies as analogue TV bandwidth: 7 MHz VHF (47 68 and MHz) 8 Mhz UHF ( MHz) bandwidth is used more efficiently through COFDM (Coded Orthogonal Frequency Division Multiplex) each subcarrier is modulated with QAM

18 about DVB s data rate Mbits/s 4 programs per channel Mbits/s per program PAL (3 5 Mbits/s) DVD 9.8 Mbits/s encoded in DVB MPEG contains MPEG 2 streams redundant information

19 FEC (Forward Error Correction)

20 FEC (Forward Error Correction)

21 QAM (Quadrature Amplitude Modulation) sender receiver low pass filter multiplication

22 QAM (Quadrature Amplitude Modulation) sender

23 QAM (Quadrature Amplitude Modulation) receiver

24 QAM (Quadrature Amplitude Modulation)

25 Uetliberg Specifications 16 QAM 1/16 guard 8 MHz channel splits into 6817 subcarriers distance between subcarriers: khz Mbits/s 5/6 code rate sampling rate MHz

26 Advatages multitude of programs low transmitting power diversity reception (synchronisation, guard) coverage recording low costs

27 Disadvatages interference prone video quality fast moving receivers (subcarriers overlap) transmission delay

28

29 dipole antennas first developed 1886 by H. Herz for transmitting or receiving radio frequency energy those antennas are theoretically the most simplest ones

30 technical specification (half wave antenna) folded dipole λ/2 typical LC oscillator elongated dipole λ/2 only difference is only difference is the impedance (300 Ohm 75 Ohm)

31 technical specification (half wave antenna) λ/2 dipole (75 Ohm) λ/4 λ/4 feed line formed dby two quarter wavelength conductors or elements transforms high frequency AC into electromagnetic waves

32 technical specification (half wave antenna) AC voltage anti nodes nodes at the ends λ/2 dipole (75 Ohm) energized with UHF AC (several GHz) U I phase shift AC current nodes at the ends at the ends

33 emission diagrams electricand magnetic UHF field the resulting emission i diagram of a of a λ/2 dipole λ/2 dipole is a slightly flattened torus

34 general emission diagram the length of a dipole can be varied in its resonant load most common is the λ/2 dipole other wave length antenna designs exist (L= λ, 2 λ, ) due to the used length the radiation emission varies in different directional radio patterns

35 antenna gain G (antenna gain) is the ratio of surface power radiated by the antenna to the surface power radiated by a hypothetical isotropic antenna isotropic radiator: theoretical point source of waves which exhibits the same magnitude (measuring in all directions) (reference radiator with which other sources are compared G = 0 dbi )

36 antenna gain calculation of the gain of a λ/2 dipole Gain of dipole antennas length L in λ Gain Gain(dB) << dB dB dB dB dB dB dB dB

37 antenna gain gain of a half wave dipole (same as left), the scale is in dbi (decibels over isotropic) the maximum theoretical gain of a λ/2 dipole is [10*log (1.64)] or 2.15 dbi.) maximum radiation gain follows this direction