MOB 2 wireless transmission 2010 lập trình mobi

Wireless Transmissions   frequencies & regulations   signals   Signal   Signal propagation   Antennas,   Link budget   multiplexing, modulation, spread spectrum, cellular systems Internet & Mobile Communications - 2009 2 Analog and Digital Message   Message = data that a user wants to transmit   Analog message –  Set of continuous values and time –  ex : voice, video, sensor collected data   Digital message –  Discrete time, set of discret values –  ex : text, integer x(t) t 0 1 0 0 0 1 1 0 0 … Internet & Mobile Communications - 2009 3 Analog versus Digital Signal   Signals are the physical representations of the message to transmit. –  They usually exist as an electrical value (voltage, intensity) that can then be converted into an electric or electromagnetic form for transmission –  Analog signal: signal that represents a analog message –  Digital signal: signal resulting from a digital message   It is represented as a succession of wave forms that can take one value among a given and finite set of possibilities Internet & Mobile Communications - 2009 4 Signal transmission any signal is composed of several frequential components. For a periodic signal these components are all multiple of the fundamental frequency f –  Example : ( ) ( ) ( ) s t ft f t( ) sin sin= +2 1 3 2 3 π π s2(t) = 1/3 sin(2Π(3f)t) s1(t) = sin(2Πft) s(t) = s1(t) +s2(t) Internet & Mobile Communications - 2009 5 Signal transmission   19th century : Fourier shows that a simple periodic function g(t) can be decomposed into a sum of sine and cosine with q fundamental freauency of f= n/T –  an and bn are the sine and cosine of the nth harmonics (terms). ( ) ( ) ∑∑ ∞ = ∞ = ++= 11 2cos2sin 2 1 )( n n n n tfnbtfnactg ππ ∫ ∫ ∫ = = = T T n T n dttg T c dttfntg T b dttfntg T a 0 0 0 )( 2 )2cos()( 2 )2sin()( 2 π π The amplitudes of an,bn and c for a given function g(t) are : Internet & Mobile Communications - 2009 6 Signal transmission   Example : –  Let’s consider the transmission of “b” coded with the following 8 bits : “01100010” Signal transmission Internet & Mobile Communications - 2009 7 Internet & Mobile Communications - 2009 8 Signal transmission –  b coded with 8 bits : “01100010” the frequency spectrum associated to a given periodic function is the comb spectrum. Each ray of the comb corresponds to the amplitude of each harmonic. a n n n n n b n n n n n c n n =       −       +       −             =       −       +       −             = 1 4 3 4 6 4 7 4 1 3 4 4 7 4 6 4 3 4 π π π π π π π π π π cos cos cos cos sin sin sin sin Internet & Mobile Communications - 2009 9 Signal transmission Internet & Mobile Communications - 2009 10 Data signal characterisation –  Spectral support of the signal is the set of frequencies it uses –  Spectral support at n dB –  Bandwidth is the width of the support f LB à 3 dB Max/2 Max 0 F c x f ^ ( ) 2 [...]... “thin black” 50 “ big black” 50 22 22 14 12 Internet & Mobile Communications - 20 09 Cable loss - connectors & lightning arrestors       Allow at least - 0 .25 dB (loss) for each connector in your cabling Check data sheets for loss at your frequency for your connector type Lightning arrestors: loss 1 dB 31 Internet & Mobile Communications - 20 09 Amplifiers   optionally, 32 amplifiers might be used -... Ghz 1 km 92 100 108 10 km 1 12 120 128 100 km 1 32 Internet & Mobile Communications - 20 09 140 148 Free Space Propagation: Fresnel zones     36 The concept of Fresnel zones may also be used to analyze interference by obstacles near the path of a radio beam The first zone must be kept largely free from obstructions to avoid interfering with the radio reception Internet & Mobile Communications - 20 09 ... budget -what does this mean? Adding up all gains and losses from start to end,much like:   24 –  “I gain 10 here, I lose 5 there, I gain 2 there, …” and so forth And then, to know how to judge the result Internet & Mobile Communications - 20 09 Elements of a radio link 25 Internet & Mobile Communications - 20 09 Elements of a radio link   Effective Isotropic Radiated Power (EIRP): –      Transmit... diversity   –  receiver chooses antenna with largest output diversity combining combine output power to produce gain   cophasing needed to avoid cancellation   λ /2 λ/4 λ /2 + 23 ground plane λ/4 λ /2 λ /2 + Internet & Mobile Communications - 20 09 Radio Links Propagation   Goals –  –  –    To introduce all the elements and tools that are needed to calculate a radio link To discuss some of these elements... Internet & Mobile Communications - 20 09 Signal propagation ranges   Transmission range –  –    Detection range –  –    communication possible low error rate detection of the signal possible no communication possible Interference range –  –  signal may not be detected signal adds to the background noise sender transmission distance detection interference 14 Internet & Mobile Communications - 20 09 Signal... cable loss [dB] - receiver sensitivity [dBm] 26 Internet & Mobile Communications - 20 09 The elements one by one         Complete radio link calculation is simply a sum of all contributions, with all values in dBs All positive values are gain All negative values are losses Realistic knowledge of component is key! 27 Internet & Mobile Communications - 20 09 Terms you will encounter          ... 10(dBm/10) 28 Internet & Mobile Communications - 20 09 Transmit (TX) power             What comes out of the radio unit Depends on regulatory limits and therefore on country/ region and time Check vendor's technical specifications - and verify! may vary with temperature, voltage supplied etc Typical in 8 02. 11b: 15 20 dBm (30 100 mW) Example from a 8 02. 11a/b card datasheet: –  –  –  Output Power: 8 02. 11b:... 8 02. 11b: 18 dBm (65 mW) peak power 8 02. 11a: 20 dBm (100 mW) peak power 29 Internet & Mobile Communications - 20 09 Cable loss           30 Rule: antenna cable should be as short as possible Typical loss values range from 1dB/m down to less then 0.1 dB/m Frequency dependent Check datasheets (and verify) Cable loss: typical values Cable Type RG 58 ca RG213 ca LMR -20 0 LMR-400 Aircom plus LMR-600 Flexline... received (long term fading) short term fading 18 Internet & Mobile Communications - 20 09 t Effects of mobility   Doppler-Fizeau effect -  The Doppler effect, named after Christian Doppler, is the change in frequency and wavelength of a wave that is perceived by an observer moving relative to the source of the waves 19 Internet & Mobile Communications - 20 09 Antennas: isotropic radiator     Radiation and... are better than brute force amplification   consider legal limits Internet & Mobile Communications - 20 09 A bit off-topic: Amplifiers 33 Internet & Mobile Communications - 20 09 Antenna - Transmitter side   Antenna gains range from : –  –  –  –    2 dBi (simple integrated antennas) 5 dBi (standard omnidirectionals) up to 25 -30 dBi (parabolas) Can even be negative for some ceramic miniature antennas . ) ( ) s t ft f t( ) sin sin= +2 1 3 2 3 π π s2(t) = 1/3 sin (2 (3f)t) s1(t) = sin (2 ft) s(t) = s1(t) +s2(t) Internet & Mobile Communications - 20 09 5 Signal transmission   19th century. (terms). ( ) ( ) ∑∑ ∞ = ∞ = ++= 11 2cos2sin 2 1 )( n n n n tfnbtfnactg ππ ∫ ∫ ∫ = = = T T n T n dttg T c dttfntg T b dttfntg T a 0 0 0 )( 2 )2cos()( 2 )2sin()( 2 π π The amplitudes of an,bn and. & Mobile Communications - 20 09 12 Solution: 10 log10(S/N) = 30 dB <=> S/N = 10 3 Capacity = 3000. log 2 (1+S/N) = 30000 bit/s Internet & Mobile Communications - 20 09 13