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- 1. TRANSCEIVER DESIGN BY SATYANARAYANA CHETAN SONI HENDRY NEWMAN 10/3/2015 Transceiver Design 1
- 2. Link Budget Link budget determines the necessary parameters for successful transmission of a signal from a transmitter to a receiver. The term link refers to linking or connecting the transmitter to the receiver. The term budget refers to the allocation of RF power, gains, and losses, and tracks both the signal and the noise levels throughout the entire system. 10/3/2015 Transceiver Design 2 PARAMETERS: Required power output level from transmitting antenna and receiver sensitivity Gains and losses in system and link SNR for reliable detection Bit Error Rate.
- 3. Link Power Budget 10/3/2015 Transceiver Design 3
- 4. Understanding Power in dB The decibel enables us to calculate the resultant power level by simply adding or subtracting gains and losses instead of multiplying and dividing. Commonly used notations, dBm is a common expression of power in communication industry. dBm = 10log (Pi), where Pi Power in mW dB is used to express gain and losses. dB = 10log( Po / Pi), where Pi Input Power in mW Po Output Power in mW 10/3/2015 Transceiver Design 4
- 5. Transmitter Power from the transmitter: Pt The power from the transmitter (Pt) is the amount of power output of the final stage of the power amplifier. Pt(in dBm) = PdBm = 10 log10 PmW 10/3/2015 Transceiver Design 5
- 6. Transmitter Component Losses: Lt_comp Transmitter consist of different components like circulator, switchers etc., the losses connected with these components are Transmitter components losses. Lt_comp = Losses in components like circulator, switchers These losses directly affect the link budget on a one-for-one basis. Each dB of loss in this path will either reduce the minimum detectable signal (MDS) by 1 dB or the transmitter gain will have to transmit 1 dB more power. 10/3/2015 Transceiver Design 6
- 7. Transmitter Line Losses from the Power Amplifier to Antenna: Ltll Most transmitters are located at a distance from the antenna, the cable or waveguide connecting the transmitter to the antenna contains losses. Ltll = Losses in coaxial or waveguide line This loss also directly affect the link budget on a one-for-one basis. How to avoid this loss???? Using larger diameter cables or higher quality cables can reduce the loss, which is a trade-off with cost. Locate the transmitter power amplifier as close to the antenna as possible, so that length of the cable is reduced.10/3/2015 Transceiver Design 7
- 8. Transmitter Antenna Gain : Gt Most antennas experience gain because they tend to focus energy in specified directions as compared to an ideal isotropic antenna which radiates in all directions. Example 1: A typical vertical dipole antenna has 2.1dBi of gain. 10/3/2015 Transceiver Design 8
- 9. Example 2: Parabolic dish antenna is commonly used in higher frequencies Gain of Parabolic antenna: Gt = 10 log[ n( D/)2 ] Note: Antenna gain increases both with increasing diameter and frequency. 10/3/2015 Transceiver Design 9
- 10. Transmitter Antenna Losses : Lta Radome Losses: Ltr The radome is the covering over the antenna that protects the antenna from the outside elements. Polarization Mismatch Loss: Ltpol o A mismatch loss is due to the polarization of the transmitter antenna being spatially off with respect to the receiver antenna. o The amount of loss is equal to the angle difference between them. Example: If the angle difference between the polarization of the transmitter and receiver is 20 degrees. then, Ltpol = 20 log( cos ) = 20 log(cos 20) = .54 dB 10/3/2015 Transceiver Design 10
- 11. Focussing Losses: Ltfoc This is a loss caused by imperfections in the shape of the antenna. Mispointed Loss: Ltpoint This is caused by transmitting and receiving directional antennas that are not exactly lined up. Conscan Crossover Loss: Ltcon Conscan means that the antenna system is either electrically or mechanically scanned in a conical fashion, or in a cone-shaped pattern. This loss is only present if the antenna is scanned in a circular search pattern such as in Radar. The total transmitter antenna loss in the link budget is Lta = Ltr + Ltpol + Ltfoc + Ltpoint + Ltcon 10/3/2015 Transceiver Design 11
- 12. Transmitted EIRP : EIRP is the amount of power from a single point radiator that is required to equal the amount of power that is transmitted by the power amplifier, losses, and directivity of the antenna (antenna gain) in the direction of the receiver. where: Pt = transmitter power, Ltcomp = switchers, circulators, antenna connections, Ltll = coaxial or waveguide line losses (in dB), Gt = transmitter antenna gain, Lta = total transmitter antenna losses. EIRP = Pt + Ltcomp + Ltll + Gt + Lta 10/3/2015 Transceiver Design 12
- 13. 10/3/2015 Transceiver Design 13 Recalling previous class discussion -
- 14. 10/3/2015 Transceiver Design 14 Channel : The channel is the path of the RF signal that is transmitted from the transmitter antenna to the receiver antenna Channel Link Budget :
- 15. 10/3/2015 Transceiver Design 15 Free Space Attenuation: This loss is due to dispersion, the spreading out of the beam of radio energy as it propagates through space. The main contributor to channel loss is free-space attenuation. Figure from http://en.wikipedia.org/wiki/Inverse_square Afs = 20log[4Rf/c] where: Afs = free-space loss R = slant range (same units as ), f = frequency of operation, c = speed of light, 300 106 m/sec, R is in meters.
- 16. 10/3/2015 Transceiver Design 16 Multipath losses Lmulti = losses due to multipath cancellation of the direct path signal (in dB).
- 17. 10/3/2015 Transceiver Design 17 Receiver-
- 18. 10/3/2015 Transceiver Design 18 Radome Losses: Lrr The radome is the covering over the antenna that protects the antenna from the outside elements. Polarization Mismatch Loss: Lrpol o A mismatch loss is due to the polarization of the transmitter antenna being spatially off with respect to the receiver antenna. o In general, for two linearly polarized antennas that are rotated from each other by an angle , the power loss due to this polarization mismatch will be described by the Polarization Loss Factor (PLF) Focusing Losses: Lrfoc This is a loss caused by imperfections in the shape of the antenna. Receiver Antenna Losses : Lra
- 19. Mispointed Loss: Lrpoint This is caused by transmitting and receiving directional antennas that are not exactly lined up. Conscan Crossover Loss: Lrcon Conscan means that the antenna system is either electrically or mechanically scanned in a conical fashion, or in a cone-shaped pattern. This loss is only present if the antenna is scanned in a circular search pattern such as in Radar. The total Receiver antenna loss in the link budget is Lra = Lrr + Lrpol + Lrfoc + Lrpoint + Lrcon 10/3/2015 Transceiver Design 19
- 20. 10/3/2015 Transceiver Design 20 Receiver Antenna Gain The receiver antenna is not required to have the same antenna as the transmitter. The gain of the antenna is a direct gain in the link budget a 1 dB gain equals a 1 dB improvement in the link analysis.
- 21. 10/3/2015 Transceiver Design 21 Receiver Line Losses from the Antenna to the LNA Lrll = coaxial or waveguide line losses (in dB). cable length should be kept as short as possible, with the option of putting the LNA with the antenna assembly. Receiver Component Losses - Any components between the antenna and LNA will reduce the SNR of the system. Lrcomp = switches, circulators, limiters, and filters. These losses directly affect the link budget on a one-for-one basis.
- 22. 10/3/2015 Transceiver Design 22 Received Signal Power at the Output to the LNA The received signal level Ps (in dBm) Ps = EIRP + Afs + Lp + Lmulti + Lra + Gr + Lrll + Lrcomp + GLNA, o This equation makes the assumption that all the losses are negative. o Gr , GLNA, and EIRP are positive. The noise out of the LNA (in dBm)- NLNA = kTB dBm + F dB + GLNA dB.
- 23. 10/3/2015 Transceiver Design 23 SNR after LNA SNR = Ps NLNA Where- SNR = signal-to-noise ratio (in dB), Ps = power out of the LNA (in dBm), NLNA = noise power out of the LNA (in dBm). Receiver Implementation Loss Implementation losses (Li) are included to account for the deviation from the ideal design due to hardware implementation.
- 24. 10/3/2015 Transceiver Design 24 Received Power for Establishing the SNR of System The detected power Pd (in dB) that is used to calculate the final SNR used in the analysis is Pd = Ps + Li + Greceiver where: Ps = power to the LNA (in dBm), Li = implementation losses, Greceiver = receiver gain.
- 25. 10/3/2015 Transceiver Design 25 NUMERICAL QUESTIONS 1. Show that a specification of 0 dBm 2 dBm is an impossible statement and write a correct statement for it. 2.What is the diameter of a parabolic antenna operating at 5 GHz, at an efficiency of 0.5 and a gain of 30 dBi? 3. What is the free-space attenuation for the system in Problem 2 with a range of 10 nautical miles? 4. What is the noise level out of the LNA given that the bandwidth is 10 MHz and the LNA NF is 3 dB with To = Ts at room temperature? 5. What is the NF of the receiver, given that the LNA has an NF of 3 dB, a gain of 10 dB, a second amplifier after the LNA with a gain of 20 dB and an NF of 10 dB, and there is a loss of 5 dB between the amplifiers?
- 26. 10/3/2015 Transceiver Design 26 References: 1. Scott R. Bullock, Transceiver and Systems Design for Digital Communications, 3rd Edition, Scitech Publishing. 2. Tranzeo link budget analysis whitepaper, http://www.tranzeo.com/allowed/Tranzeo_Link_Budget_Whitepaper.pdf
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