RF Circuits and Systems, EEE 6374, Spring2015, Project Report 1

AbstractCommunication satellites plays a vital role not only in the global telecommunications system but also in communication between earth and objects in space. We propose a radio based communication system design to exchange data between earth and moon antennas, using an intermediate geostationary satellite. Data rate achievable is 1 Gbps and BER requirement is 1 . Two set of transceivers with QPSK modulation are employed to operate in the Ka band wherein 28 GHz and 18 GHz are the uplink and downlink frequencies respectively at the Earth/Moon station. In this report, the transceiver design is elaborated and component details are included along with SysCalc6 budget link analysis and ADS simulation.

Index Terms Satellite Communication, QPSK, Transceiver design, Antennae, Radio frequency, K bands, sensitivity, SNR, ADS, and SysCalc6.

I. INTRODUCTION or earth to moon communication, laser has been proposed as a high speed solution. But Laser is prone to refraction

or absorption in the channel owing to obstructions like rain, smoke, fog, glass etc. This leads to reduction of signal intensity. As an alternative to laser, an artificial satellite is a self-contained communications system which receives and retransmits signals from Earth with the use of a transponder (an integrated transmitter and receiver of radio signals) [2].

II. SYSTEM DESIGN In order to design our system, we first analyzed Satellite

communication for earths base stations using homodyne architecture for satellite communication. [6] Since, the transceiver antenna installed on earth and moon would be identical, we carried out calculations for Power output and Sensitivity. Free space path loss between earth and satellite, satellite and moon, transmitter/receiver antenna gain, transmitter/receiver antenna temperature and uplink/downlink frequency range are accounted for. (The calculations are detailed in later sections). Now, the frequency band range and type of modulation must be decided such that BER is below 1x10 -5 and sensitivity is well below the received power. The second phase consists of finding the right components in the market (BPF, LNA, PA, mixer etc.) which conform to the above operation parameters.

A. FREQUENCY PLANNING Satellite communications use high-frequency range of 150

GHz for transmitting and receiving signals. The frequency bands are identified by: (in order from low to high frequency) L-, S-, C-, X-, Ku-, Ka-, and V-bands. Signals in the lower range of the satellite frequency spectrum are transmitted with low power and received by large antennas. Signals in the higher end bands like X-, Ku-, Ka-and V-bands are more in power and require smaller size antenna for signal reception. Because of this reason, Ku-band and Ka-band spectrum is ideal for DTH broadcasting, broadband data communications, and mobile data applications. [2] Moreover, the Ka band (28-31 GHz for the ground-to-satellite link and 18-31GHz for satellite-to-earth offers sufficient capacity (1Gbps) [8].

B. MODULATION Communication channels in satellite-communications have power and bandwidth constraints. For power-limited channels, coding schemes save power at the expense of bandwidth. In bandwidth-limited channels, spectrally efficient modulation schemes are used to conserve bandwidth. A modulation scheme is chosen such that it maximizes bandwidth efficiency with minimum signal power. The reason why we have chosen QPSK modulation is because it is simple and it fulfils both these constraints when the data rates for the (I) and (Q) signal components are the same [1]. For the same transmitted power as BPSK, QPSK can be used to achieve a longer transmission range. It processes 2 bits per symbol has four possible states. For a data rate R=1Gbps, the basebands first null occurs at 0.5R i.e. at 500 MHz and null to null bandwidth occurs at R i.e. 1 GHz.

III. SYSTEM ARCHITECTURE Since we are implementing a homodyne architecture,

theres no intermediate frequency (IF) involved. Also, all the conversions are direct and theres no image frequency. The received signal is amplified and filtered at baseband rather than at some high intermediate frequency. Our design consists of a transceiver block wherein the antenna used for RX/TX on earth and moon is identical. This antenna is designed to receive signals from the Satellite at 18 GHz and transmit at 28 GHz. Satellite uses two antennas operating at different frequencies. The satellites receiver antenna operates at 28 GHz and transmitter antenna at 18Ghz. Illustration is provided

Earth-Moon Wireless Data Link at 1Gbps speed via Geostationary Satellite

Manmeet Singh Khurana, Rishu Sharma, Department of Electrical and Computer Engineering, University of Florida, Gainesville Florida, 32608

F

RF Circuits and Systems, EEE 6374, Spring2015, Project Report 2

in Fig.1. All the Antenna parameters are tabulated in Table1. The earth/moon transceiver antenna uses FDD and Satellites uses TDD while establishing the link.

Fig.1. Earth-Satellite-Moon communication system

Earth/Moon Rx/Tx Antenna

Satellite RX Antenna

Satellite Tx Antenna

Frequency (GHZ) 28/18 28 18 Modulation QPSK QPSK QPSK Data Rate (Gb/s) 1 1 1 Symbol Rate (Mb/s) 500 500 500 Null to Null Bandwidth (GHz)

1 1 1

BER

RF Circuits and Systems, EEE 6374, Spring2015, Project Report 3

RF signal after LNA is down-converted to baseband signal through a tunable VCO and a wideband 90o continuous phase shifter. Fig.4 shows the schematic of the receiver in ADS environment

C. PA considerations: We are using PA in linear region and so we need to make sure that it doesnt move into saturation as the output may deform. For that we did saturation test and it passed. The results are shown in Fig.5 and Fig.6.

Fig.5. Pout vs Pin of Fundamental and third harmonic of PA

From Fig.6, P1dB, out is 52.4dBm so it means below this range PA works linearly. Also Table 2 shows the output signal power from PA for all the four links and they all are less than 52.4dBm. From the first and third harmonics in Fig.5 we can make sure that the PA saturates near 52dBm.

Fig.6. Saturation test of PA

Fig.7 shows the input and output spectrum of the PA having gain 70dB with input being -18.69dBm and output being 49.97 for link 1.

Fig.7. Input and Output power spectrum of PA

D. Antenna Considerations: Due to high FSPL in the order of 200dBm which are a result of large distances, high gain antennas are required. We are utilizing parabolic antennas which have gains around 60-70dBi apart from receiver antenna of satellite, which has minimum gain of 39.5dBi. A single antenna is used at the earth as well as moon stations having transmitting gain of 70.2dBi at 28GHz and receiving gain of 67.2dBi at 18GHz. So we can see that they work well in Ka Band. All the components used for transmitter and receiver simulations are available in the market. The parameters of the components are extracted from the datasheets and listed in Table.3. The criteria for selection of components was based on loss, bandwidth, and noise figure considerations, since device operation at high frequencies is generally problematic.

V. ASSUMPTIONS

1. The distance between earth and Geostationary satellite is rounded to 36,000 Km and that between moon and satellite is rounded to 350,000 Km (384400Km - 36000Km = 348,400Km) for ease of calculation [4, 5].

2. All calculations have been done for the worst case. Maximum orbital distances between earth and moon is considered. The maximum temperature at the surface of Moon is 390K, which is used for sensitivity calculations.

3. The attenuation factor alpha = 2 for free space. All the FSPL calculations are carried out with alpha = 2. From Fig.8, the losses due to oxygen and water vapor add to atmospheric attenuation. Since the atmosphere covers the earth around 100 Km above the surface, atmospheric losses at 100 Km for 18 GHz is 0.05dBm/Km which accounts to 5dB. Similarly, at 28 GHz 0.1dBm/Km accounts to 10dB attenuation [3, 17].

RF Circuits and Systems, EEE 6374, Spring2015, Project Report 4

4. In order to model the losses in the attenuator while simulating in ADS, the total losses (Pout Pin) for a link is calculated as follows: FSPL [Antenna Gain (receiver) + Antenna Gain (transmitter)] + Atmospheric losses (if Earth is Rx/Tx). So the affective losses for all the four links are shown below.

Link 1 Link 2 Link 3 Link 4 Losses 113.5 100.1 122.5 86.1

5. The system is designed on the assumption that there are no cost constraints. Homodyne architecture requires high level of integration and the RF chip cost would be considerably high. Also, many components selected are available at expensive prices in the market. So, the overall cost will be high.

Fig.8. Attenuation due to atmospheric losses [17]

VI. SYSTEM PERFORMANCE AND CALCULATIONS

Parameters Link1 (Earth to Sat)

Link2 (Sat to Moon)

Link3 (Moon to Sat)

Link4 (Sat to Earth)

Distance (Km) 36000 350000 350000 36000 Frequency of operation (GHz)

28 18 28 18

Transmitted signal strength(Ptx) (dBm)

49.97 49.96 49.97 49.96

Gain (TX) (dBi) 70.2 60.7 70.2 60.7 Gain (RX) (dBi) 39.5 67.2 39.5 67.2 Free Space Path Loss(FSPL) (dB)

213 228 232 209

Losses Due to Atmosphere (dB)

10 N/A N/A 5

Sensitivity (dBm) -69.02 -86.67 -86.67 -67.77 Received Signal Strength(Prx) (dBm)

-63.53 -50.14 -72.53 -36.14

RSS(SysCalc6) (dBm)

-52.9 -50.8 -72.6 -31.0

Pfinal (dBm) -41.43 -31.61 -50.42 -19.69 Table.2. Link Performance

The BER requirement is 1 x 10-5. From SysCalc66, Eb/No is calculated as 9.588dB.

A. Formulae: During signal propagation, a part of signal strength is lost due to the distance between the transmitter and receiver. This is modeled as FSPL.

1. Free Space Path losses = 20 log (4d/) (dB)

The resulting power at receiver is transmitted power added with the antennae gain and subtracted by losses occurred in the channel.

2. Pout (dBm) = Pin (dBm)+ Gt (dBi) + Gr (dBi) FSPL(dB) Atm Atten (dB)

The Signal to noise ratio of the signal at the receiver must be sufficient despite the losses introduced during channel propagation.

3. SNR (req.) = Eb/No (dB) + 10log (R) -10 log (B)

Sensitivity of the receiver is calculated based on its noise figure, ambient temperature and SNR required calculated in equation 3. The sensitivity of a receiver antenna must be much below the output power for successful reception of the transmitted signal.

4. Sensitivity (dBm) = kT (dBm/Hz) + F (dB) + 10logR + Eb/No (dB)

We are detailing the above mentioned equations for calculations of link1:

FSPL = 20 log (4*36000*10^3/0.0103) = 213 dB

SNR (req.) (dBm) = 9.588 + 90 90 = 9.588

Sensitivity = kT (dBm/Hz) + F (dB) + 10logR + Eb/No (dBm)

= -174 + 5.32 + 90 + 9.588 = -69.02 dBm

Similarly, for Links 2, 3 and 4, these calculations have been carried out and the resulting values are updated in Table.2.

VII. SIMULATION RESULT

Fig.9. I/P and O/P power spectrum of Link1 simulation

RF Circuits and Systems, EEE 6374, Spring2015, Project Report 5

The three power spectrum shown in Fig.9 corresponds to Transmitted signal after PA (PTX), Received signal (PRX) and Final Signal (Pfinal) after LNA of receiver but before de-modulation into IQ signal for link 1. The corresponding values of these power signals for other three links (2, 3 & 4) are mentioned in Table 2). The constellation diagram of the Input and Output signals for link1 i.e. Earth to Satellite is shown below in Fig. 10 & 11. It can be seen that the 4 symbols are easily identifiable for both input and output. So, it wont be incorrect to assume that EVM is less than 3%.

Fig.10. Constellation diagram of input signal

Fig.11. Constellation diagram of output signal

VIII. COMPONENT LISTING Component Mixer BPF PA LNA

Frequency (GHz) 18 Reference No. [10] [16] [12] [14] Gain/Loss (dB) -15 -3.2 70 18.5

Bandwidth (GHz) 5 1 17.3-18.4 6-20 F(dB) N/A N/A N/A 2.5

P1dB_out (dBm) -5 N/A 55.8 11 OIP3(dBm) 5.6 N/A 66.4 20

Frequency (GHz) 28 Reference No. [10] [11] [15] [13] Gain/Loss (dB) -15 -3.2 70 22

Bandwidth (GHz) 5 1 27.5-30 28-36 F(dB) N/A N/A N/A 2.3

P1dB_out (dBm) -5 N/A 52.4 12

OIP3(dBm) 5.6 N/A 63 22 Table.3. Component parameters from Datasheets

Fig.12. Link budget analysis for link1

Fig.13. Link budget analysis for link2 The link budget of SysCalc6 doesnt include the

atmospheric losses between earth and satellite. This is the reason that Ant. Pout for link 1 in SysCalc6 fig. 12 is -52.9dBm and not around -63dBm as in fig. 9 whereas it should have included a loss of 10dB due to atmospheric losses as explained in our assumptions. Same goes for the link between satellite and earth. There difference between SysCalc6 Ant. Pout and received signal strength at receiver on earth is 5(-31dBm vs -36.14dBm).

RF Circuits and Systems, EEE 6374, Spring2015, Project Report 6

IX. CONCLUSIONS The calculations in SysCalc6 and ADS simulation confirm that it is feasible to establish an earth to moon communication system design proposed by us which will successfully establish wireless links 1, 2, 3 and 4 with the data rate of 1Gbps. The sensitivity and SNR requirements are fulfilled maintaining BER as 1x10-5 before error correction. However, we have taken a few assumptions for convenience (section V) and the cost of building such a system would be very high since a lot of components utilized by us are pricey. The scope of further improving this project would be cost optimization.

X. ACKNOWLEDGMENT We would like to extend our gratitude to Dr. Jenshan Lin

for providing us with the opportunity to work on this project and also for his continuous support and guidance.

XI. REFERENCES [1] http://mwrf.com/systems/qpsk-modulator-transmits-satcom-data [2]http://www.britannica.com/EBchecked/topic/524891/satellite communication/288217/How-satellites-work [3] http://en.wikipedia.org/wiki/Earth [4] http://en.wikipedia.org/wiki/Moon [5] http://en.wikipedia.org/wiki/Geostationary_orbit [6]https://www.ri.cmu.edu/pub_files/pub1/bapnadeepak19961/bapnadeepak19961.pdf [7]https://www.viasat.com/files/assets/13.5mka-bandearthstation017web.pdf [8]Grard Caille, Yann Cailloce, "High-gain multibeam antenna demonstrator for Ka-band multimedia via satellite mission," Alcatel Telecommunication Review. 4th 2001 [9] www.vincor.com/pdf/asc/asc76mkspecs.pdf [10]http://ieeexplore.ieee.org/xpls/absall.jsp?arnumber=5517957&tag=1 [11]http://www.diplexers.com/products/bandpass/center-frequency-24000mhz-or-greater/b0428g02.html [12]http://www.xicomtech.com/products/documents/XTD-500DBS%20Rev%205.pdf [13] http://www.triquint.com/products/p/TGA4507 [14]http://www.rflambda.com/pdf/lownoiseamplifier/R06G20GSB.pdf [15]http://www.xicomtech.com/products/documents/XTD-150-175Ka%20Rev%209.pdf [16] http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5704718&tag=1 [17] Jenshan Lin, EEL 6374 Lecture Notes