Sample Down Link Parameter

-
To receive a FTA (Free to Air) or CAS (Conditional Access) channel, an earth station engineer needs know to some parameters of that specific channel. Those are called down-link parameter of that channel.  First need the satellite orbital position. Down-link wave polarization may be horizontal or vertical. Those who use cross polarization, if their up-link polarization is vertical then down-link polarization will be horizontal and vice versa. For most the C band channel, they use cross polarization. As video compression technique MPEG-2 and MPEG-4 are generally used. As DVB system DVB-S and DVB-S2 are used. For HD channel MPGE-4 as video compression technique and DVB-S2 as DVB system are used. The main parameter to receive a channel is down-link frequency. It is related with up-link frequency. Another parameter is FEC--Forward Error Correction. It is used as error detection and correction scheme. Generally FEC value is used ¾ or 7/8.

Sample:

Satellite Name: Apstar 6
Orbital Position: 134 degree East
Frequency Band: C
Downlink Wave Polarization: Horizontal
Demodulation Technique: QPSK
DVB System Type: DVB-S
Video Decompression Technique: MPEG-2
Downlink Frequency: 4150 MHz
Modulation Rate: 9.62830 Mega Baud
FEC: ¾

Comments

Post a Comment

Popular posts from this blog

Symbol rate, Bandwidth and Bit rate Calculation

-
In satellite communication bandwidth (BW), symbol rate and bit rate are the most vital fact for proper signal transmission. There are many commercial software for BW, Symbol rate and bit rate calculation for TV signal transmission. But the equations of these parameter calculation are as follows. BW= (1+Roll of factor)* Symbol rate In general Roll of factor is 35% Symbol Rate =BW / (1+Roll of factor) and Bit Rate = Symbol rate * Modulation* FEC* (188/204)                                     [when 188 is encoder packet length] or Bit Rate = Symbol rate * Modulation* FEC* (204/188)                                     [when 204 is encoder packet length] Here, FEC = Forward Error Correction. In general FEC is in the range from 1/2 to 7/8. 188/204 = constant Unit ** BW= Hz, KHz, MHz, GHZ ** Symbol Rate= sps or baud, Ksps or Kbaud, Msps or Mbaud, Gsps or Gbaud ** Bit Rate= bps, Kbps, Mbps, Gbps Baud: U nit of signalling speed Baud rate: N umber of symbols transm
Read more

Terminology: EIRP, G/T, Input Back-Off, Output Back-Off

-
  EIRP:   Used to indicate the power transmitted from an antenna. EIRP=Power +Antenna Gain, Both EIRP and Power is expressed in dBW and Gain in dBi. G/T:   It is the figure of merit for an earth station and is expressed as dB/K (dB per K). G/T= Antenna Gain-10*Log (System Noise Temperature) The higher the better-G/T can be raised by using a higher gain antenna or a lower temperature LNA. The earth station G/T determines the received carrier to noise ration. Increasing station G/T will increase the C/N of the received carrier. Input Back-Off (IPBO):   The level of a signal at the input of an amplifier relative to that level at the input that would result in the maximum possible output level. For example, if an input level of -20dBm causes max output and the actual input level is -25dBm, the IPBO is 5dB. Both IPBO and OPBO are commonly used to determine the operating levels in a satellite transponder TWTA. Output Back-Off (OPBO)   The level of a signal at the output
Read more

Bit Error Rate (BER) and Roll Off Factor

-
Image
Roll Off  Factor W hen a digital signal is modulated the output would be a waveform with the shape of sin(x)/x. Now this has an infinite bandwidth. So in order to be able to transmit this signal over satellite we need to filter it to reduce the occupied bandwidth. This is done by applying a "raised cosine roll-off filter". This filter is present both at the modulator output stage and at the input of the demodulator (I believe one says these filters are then matched). The steepness and the resulting occupied bandwidth can be set by the parameter roll-off factor. In DVB-S2 it can be 0.20 (20%); 0.25 (25%) or 0.35 (35%) where the  Occupied bandwidth = symbol rate x (1 + roll-off factor). Figure: Occupied bandwidth, Roll off factor and symbol rate 
Read more

Followers