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Bandwidth optimization

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Bandwidth optimization

  1. 1. INTRODUCTION  Satellite communications systems exist because earth is a sphere.  Radio waves travel in straight lines at the microwave frequencies used for wideband communications.  Satellites are important in: voice communications, video & radio transmission, navigation (GPS),remote sensing (maps, weather satellites) etc.  They cover large areas.  Inherent broadcast.  Inherent capability of by-passing the whole terrestrial system.
  2. 2. HOW DO SATELLITES WORK? Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means. The two stations can use a satellite as a relay station for their communication. One Earth Station transmits the signals to the satellite. Up link frequency is the frequency at which Ground Station is communicating with Satellite. The satellite Transponder converts the signal and sends it down to the second earth station. This frequency is called a Downlink.
  5. 5. Ku Band The Ku band is a portion of the electromagnetic spectrum that ranges from 10.95- 14.5 GHz More flexibility For the End users Ku band is generally cheaper and enables smaller antennas The satellite operator's Earth Station antenna do require more accurate position control when operating at Ku band than compared to C band.
  6. 6. C Band Range : 4 – 8 GHz At frequencies higher than 10 GHz in heavy rain fall areas, a noticeable degradation occurs The C-band perform better in comparison with Ku band under adverse weather conditions The Ku band satellites typically require considerably more power to transmit than the C-band satellites.
  7. 7. •Available bandwidth is limited and insufficient to meet demand • Existing capacity is usually running at maximum capacity – As a result it is often unusable – Universal flat lining during working hours •The cost of bandwidth is extremely high •Expanding bandwidth capacity is limited due to finances, supply, technology THE BANDWIDTH CHALLENGE
  8. 8. optimizing the traffic advanced modulation techniques to reduce the bandwidth allocated to a given service HOW TO REDUCE BANDWIDTH
  11. 11. MODULATION TECHNIQUES  Modulation is the process by which information is conveyed by means of an electromagnetic wave.  The power and bandwidth necessary for the transmission of a signal with a given level of quality depends on the method of modulation. 1. QPSK 2. 8-PSK
  12. 12. QPSK v/s 8PSK QPSK occupies 1/2 of the bandwidth of BPSK whereas 8PSK uses 1/3rd of the bandwidth that BPSK for a given bit rate With a 8PSK capable satellite receiver you can demodulate QPSK as well as 8PSK 8PSK makes better use of bandwidth than QPSK 8PSK is not as phase-tolerant as QPSK and has a slightly longer acquisition time
  13. 13. UP/DOWN CONVERTER Up converter accepts IF signal in the 70±18 MHz band Convert to an RF signal in 5.925-6.425 GHz band Down converter accepts RF signal in 3.7-4.2 GHz band convert to an IF signal in 70±18 MHz band Same transponder is used for transmitter and receiver channels
  14. 14. HIGH POWER AMPLIFIER Obtain Necessary EIRP (Equivalent Isotropic Radiated Power) from an earth station Three types: - klystron power amplifier(KPA) - traveling wave tube amplifier(TWTA) - solid state power amplifier(SSPA) For large power of the order of few kilowatts, traveling wave tube amplifiers (TWTAs) or Klystron are used Klystrons amplifiers are used in ONGC Klystrons have narrow instantaneous bandwidth around 40MHz tunable over 500MHz range TWTAs have wide bandwidth typically around 500MHz
  15. 15. LOW NOISE AMPLIFIER Amplify very weak signals Located very close to the detection device Placed at the front-end of a radio receiver circuit The effect of noise from subsequent stages of the receive chain is reduced Low NF (like 1db) Large enough gain (like 20db) Large enough intermodulation and compression point (IP3 and P1dB) The gain of the LNA That is used in satellite earth station, ONGC is 60db
  16. 16. Modems Modems currently in use at ONGC : - DMD15 Universal Satellite Modem - DMD20 Universal Satellite Modem
  17. 17. DMD15 Universal Satellite Modem Main Features: •BPSK and QPSK modulation. •9.6 Kbps to 8.448 Mbps in 1 bps steps. •Configuration, monitor and control features are fully user-programmable. •Excellent spurious performance. •Fully-compliant with IESS 308/309. •Industry standard I/O interfaces. •Customize for closed network applications. •50-90,100-180 MHz IF in 1 Hz steps.
  18. 18. DMD20 Universal Satellite Modem Highlights: •BPSK/QPSK/OQPSK/8-PSK/8-QAM/16-QAM Operation • 2.4 Kbps to 20 Mbps in 1 bps Steps • FEC - Viterbi, Reed-Solomon, Sequential, Trellis, Turbo Product Code, Low Density Parity Check Code • Configuration, Monitor and Control Features Fully User-Programmable • Excellent Spurious Performance • Fully Compliant with IESS 308/309/310/314/315 •Industry-standard Universal Interface Module •50 to 90 MHz and 100 to 180 MHz IF, and 950 to 2050 MHz L-Band in 1 Hz Steps • Standard Features Include: Reed-Solomon,Asynchronous Overhead, Satellite Control Channel and Automatic Uplink Power Control
  19. 19. The required occupied bandwidth is B = k ( Rb / m )(1/ r ) Where, Rb = information bit rate m = number of bits per symbol r = code rate K = bandwidth expansion factor used to minimize intersymbol interference
  20. 20. Link Design, Link Budget and Power
  21. 21. Link Power Budget 25 Transmission: HPA Power Transmission Losses (cables & connectors) Antenna Gain EIRP Tx Antenna Pointing Loss Free Space Loss Atmospheric Loss (gaseous, clouds, rain) Rx Antenna Pointing Loss Rx Reception: Antenna gain Reception Losses (cables & connectors) Noise Temperature Contribution Pr
  22. 22. Link Budgets  The transmission formula can be written in dB as:  The calculation of received signal based on transmitted power and all losses and gains involved until the receiver is called “Link Power Budget”, or “Link Budget”.  The received power Pr is commonly referred to as “Carrier Power”, C. 26 rrotherrapolaptar LGLLLLLLEIRPP
  23. 23. Why calculate Link Budgets?  System performance tied to operation thresholds.  Operation thresholds Cmin tell the minimum power that should be received at the demodulator in order for communications to work properly.  Operation thresholds depend on:  Modulation scheme being used.  Desired communication quality.  Coding gain.  Additional overheads.  Channel Bandwidth.  Thermal Noise power. 27
  24. 24. Simple Link Power Budget 28 Parameter Value Totals Units Parameter Value Totals Units Frequency 11.75 GHz Transmitter Receive Antenna Transmitter Power 40.00 dBm Radome Loss 0.50 dB Modulation Loss 3.00 dB Diameter 1.5 m Transmission Line Loss 0.75 dB Aperture Efficiency 0.6 none Transmitted Power 36.25 dBm Gain 43.10 dBi Polarization Loss 0.20 dB Transmit Antenna Effective RX Ant. Gain 42.40 dB Diameter 0.5 m Aperture Efficiency 0.55 none Received Power -98.54 dBm Transmit Antenna Gain 33.18 dBi Slant Path Summary Satellite Altitude 35,786 km Transmitted Power 36.25 dBm Elevation Angle 14.5 degrees Transmit Anntenna Gain 33.18 dBi Slant Range 41,602 km EIRP 69.43 dBmi Free-space Path Loss 206.22 dB Path Loss 210.37 dB Gaseous Loss 0.65 dB Effective RX Antenna Gain 42.4 dBi Rain Loss (allocated) 3.50 dB Received Power -98.54 dBm Path Loss 210.37 dB
  25. 25. BANDWIDTH OPTIMIZATION Transponder bandwidth is usually the most expensive resource in a satellite communication link. For maximum efficiency, a satellite link should be engineered to balance bandwidth and power. Available bandwidth can be optimized by using one of the following techniques: •Using higher modulation •lower order FEC technique •Increased Antenna size Our project is based on using higher order modulation techniques for efficient utilization of available bandwidth.
  26. 26. FORWARD ERROR CORRECTION  In communication forward error correction(FEC) a system of error control for data transmission, whereby the sender adds systematically generated redundant data to its messages, also known as an error-correcting code (ECC).  The carefully designed redundancy allows the receiver to detect and correct a limited number of errors occurring anywhere in the message without the need to ask the sender for additional data. FEC gives the receiver an ability to correct errors without needing a reverse channel to request retransmission of data.
  27. 27. Benefits of Forward Error Correction (FEC) Reduce bandwidth by 50%. Increase data throughput by a factor of 2. Reduce antenna size by 30%. Reduce transmitter power by a factor of 2. Provide 3dB more link margin.
  28. 28. if we have bandwidth to spare, then use a lower order modulation or a higher rate FEC (like 1/2 or 2/3) to spread the signal out.  If we have power to spare then use a higher order modulation and/or lower rate FEC (like 3/4 or 7/8). Ideally use all of both the available bandwidth and power simultaneously to obtain the highest user information rate. Bandwidth-Power Trade-Off
  29. 29. RESULTS The following results were derived from these calculations: Bandwidth requirement has been reduced by a considerable amount when 8PSK is used as compared to QPSK. Different FEC rates used also has an effect on the bandwidth requirement of the transmission and receiving link. By using a proper combination of modulation technique and FEC rate we can achieve efficient utilization of bandwidth.
  30. 30. Allocated Bandwidth Bandwidth, Allocated Bandwidth or Occupied Bandwidth is the frequency space required by a carrier on a transponder. E.g. : a duplex E1 (2.048 Mbps) circuit with 8-PSK modulation, FEC rate 3/4 and 1.4 spacing requires: Bandwidth = data rate/(no. of bits per symbol * FEC)* frequency spacing * 2 [for duplex circuit] B = 2.048 / (3 * 0.75) * 1.4 * 2 = 2.548 MHz  For a 36 MHz transponder, 2.548 MHz corresponds to 7.078% bandwidth utilization.
  31. 31. Power Equivalent Bandwidth Power Equivalent Bandwidth (PEB) is the transponder power used by a carrier, represented as bandwidth equivalent. PEB calculation example: • Transponder EIRP = 37 dBW • Output Backoff (OBO) = 4 dB • Available EIRP = 37 – 4 = 33 dBW = 10^3.3= 1995.26 Watts • Transponder Bandwidth = 36 MHz • Power Available / MHz = 1955.26 / 36 = 55.424 W • If a carrier uses 24 dBW, then PEB = Power used by your carrier/transponder saturated power PEB = 10^2.4/ 55.424 = 4.532 MHz This corresponds to 12.59% of available transponder power.
  32. 32. CONCLUSION In the design of a communication system, the choice of modulation is of fundamental importance and always involves tradeoffs between power and bandwidth. In the past, frequency spectrum was relatively plentiful but the power available on a satellite was limited. Today, the equation has been reversed. Spectrum is now scarce. More spectrum efficient forms of digital modulation such as 8PSK and 16QAM are becoming more attractive, even though the power requirements are higher. Coupled with powerful coding methods such as concatenated Reed Solomon/Viterbi coding, these methods offer the prospect of enhanced spectral efficiency with virtually error-free digital signal transmission.
  33. 33. Thank You