1

1Gb/s Earth-Moon Wireless Link Using QPSK Modulation

Xinfei Guo

Department of Electrical and Computer Engineering, University of Florida, Gainesville,

Florida, 32608, USA

Abstract — The design of 1Gb/s Ka Band wireless link

between moon and earth is presented. Two set of transceivers

adopt Quadrature Phase Shift Keying Modulation (QPSK) and direct-conversion to accommodate the data rate and BER requirement of 1 . One is between earth and

satellite and another between satellite and moon. Two antennas operating in 30GHz and 18GHz are used on satellite. The different components used in this structure are

described. Then the systems performance are shown.

Index Terms — 1Gb/s, QPSK, 30GHz, 18GHz

I. INTRODUCTION

With the highly development of human beings’ space

exploring activities, the high speed link between earth and

moon need to be considered. Recently, laser has been

demonstrated as a solution[1], but there still exits many

problems with optical communications like cloud penetra-

tion, visibility and locations[2]. So this paper explores

radio wave communication between earth and moon to

achieve a high speed of 1Gb/s and demonstrate it is

possible to achieve using highly complex architecture.

II. FREQUENCY PLANNING

Ka band (from 26.5 to 40 GHz) is becoming more and

more interesting for the satellite service providers.

Recently, a new Ka band constellation of broadband

commercial satellites is on track to provide remote users

with faster communication speeds [3].

The Earth atmosphere behaves differently for various

frequencies. Figure 1 indicates the average atmospheric

absorption as a function of frequency. At 30G Hz, the

attenuation is the most lowest within Ka band.

Additionallty, the only band which can offer

sufficient-capacity (1Gbit/second) is the Ka-band (28-31

GHz for the ground-to-satellite link and 18-31GHz for the

opposite sense)[4].

But from the demonstrated paper and products[5], the

earth station antenna has different operating frequencies

which is so-called 30/20 GHz band. This means the

antenna can only receive frequency of around 20GHz

and transmit frequency of around 30GHz. So in my design,

I use satellite as a repeater and two antenna operating at

different frequencies at 18GHz and 30GHz on satellite

using as transmitting antenna and receiving antenna,

separately.

Fig. 1. Electromagnetic absorption of the earth’s atmosphere

III. SYSTEM PLANNING

The Modulation scheme used here is Quadrature Phase

Shift Keying (QPSK). It is simple and has the lowest SNR

compared to other modulation. Additionally, With the

same transmitted power, QPSK can be used to achieve a

longer transmission range. It is capable of processing two

bits for each symbol. This is due to the fact that QPSK has

four possible states. So, for R=1Gb/s, the baseband first

null bandwidth and RF first null to null band width can be

derived from (1) and (2),

0.5 0.5 1 / 500basebandBW R Gb s MHz

(1)

1 1 1 / 1RFBW R Gb s GHz (2)

Direct-conversions are used in this project, as direct

architecture has high level integration and no image

frequency(single carrier)[6]. Its fundamental advantage is

that the received signal is amplified and filtered at

baseband rather than at some high intermediate frequency.

Fig.2 shows the overall structure of my design.

Assuming that two same earth station antennas of

30/18GHz with a high gain of 70.7dBi[5] are used on both

earth and moon. A 30GHz antenna is used as the receiving

antenna and 18GHz antenna the transmitting antenna on

satellite. The earth station transmits the 30GHz RF signal

and satellite receiving antenna receives the signal and

demodulated to baseband frequency 500MHz, then

modulated to 18GHz. The transmitting antenna then

transmits the modulated 18GHz signal to the moon

antenna station, which can only receives 18GHz signal.

The data transmission from moon to earth is just the same.

During this process, the earth station adapts FDD in which

one frequency band is used to transmit and another used to

2

receive. The satellite antennas adapt TDD in case the data

being distinguished.

Fig.2. Overall system structure

Table 1 gives the specifications of the proposed wireless

system.

TABLE 1

SPECIFICATIONS OF THE PROPOSED WIRELESS SYSTEM

Earth

Antenna

Receiving

Antenna

Transmitting

Antenna

Frequency 30GHz 30GHz 18GHz

Modulation QPSK QPSK QPSK

Data Rate 1 Gb/s 1Gb/s 1Gb/s

Symbol Rate 500 Mb/s 500 Mb/s 500 Mb/s

Null to Null

Bandwidth

1 GHz 1GHz 1GHz

BER <1 10-5 <1 10-5 <1 10-5

Antenna Gain 70.7dBi[5] >39.5dBi[7] 60.7dBi[8]

Duplex FDD TDD TDD

IV. TRANSMITTER ARCHITECTURE

Fig.3. Transmission Schematic in ADS environment

The two transmitters both use Direct-conversion to

reach a high level integration. They have the same

schematic but the different LO frequency and antenna

temperature.

Fig. 2 shows the schematic of the transmitter part in

ADS environment. Two input signals are given as I and Q

baseband signal. Typically, the input digital data should be

converted to analog signal using high speed DAC. But in

this case, the input signals are both analog signals, so

DACs are not required. The baseband signal is shaped by

using a root raised-cosine filter (RCF) to avoid an

undesirable inter-symbol-interference (ISI). The baseband

I and Q signals are up-converted to an RF frequency of 30

GHz through a tunable VCO and a wideband 90 continuous phase shifter. To realize sufficient maximum

output power and reduce spurious emission two-stage BPF

and PA combination is implemented. Considering

attenuation and path loss, an attenuator is added. Overall

output power will be fed to the receiver node, which will

be discussed later.

The components used in this structure have been

demonstrated feasible. They are tabulated in Table2.

V. RECEIVER ARCHITECTURE

The same homodyne structure of direct-conversion is

used for all the receivers. After the output of the

transmitter following a Band Pass Filter (BPF) to avoid

unwanted interference outside of the BPF which may

saturate the LNA. BPF should have the low noise figure to

determine the noise figure of the whole system. The

transmitter output RF signal is down-converted to

baseband signal through a tunable VCO and a wideband

90 continuous phase shifter. Fig. 4 shows the schematic

of the receiver part in ADS environment.

The components used for this part are also tabulated in

Table2.

As worth to mention, the power amplifier we used is

called 500 W Ka-band Antenna Mount High Power

Amplifiers. The saturated output power is

415W(56.2dBm)[9], and the 1-dB compressed power is

around this value. This is fairly high among high

frequency PAs. So the output power of our transmitter can

reach a maximum 56.2dB and the amplifier still works in

linear region within this value.

Another important component is antenna, because the

gain of antenna is a great contributor in LOS equation. We

chose a demonstrated Model VA-135-KA 13.5 meter

Ka-Band Broadband Gateway Earth Station Antenna with

high gain of 70.7dBi at 30GHz, which is ideally suited to

high-performance Ka-band geostationary application[5].

The shape Cassegrain reflector provides superior gain and

sidelobe performance at Ka-band frequencies.

For other kind of components, we also need to consider

the loss, bandwidth, noise figure and so on. Especially at

high frequency, devices do not easy to operate normally.

so choosing a proper component for our system is

important and not easy. Table 2 shows all the component

parameter I can find .

3

Fig.4. Receiver Schematic in ADS environment

V. SIMULATION RESULT

Fig.5. shows the input and output of PA based on ADS

simulation tools,

Fig. 5. Input and Output of Power Amplifier

Fig.6. Saturation Case

From the spectrum, we can see the null to null band width

is around 1GHz, the output power is amplified by 70 dB,

properly. Fig.6. shows the saturation case of the amplifier,

Fig. 7. Transmitting output spectrum from earth to satellite

If the output power is larger than P1dB output power, the

amplifier will be in saturation region. Fig.7 shows the

output spectrum of the transmitter. The peak value is

about -56.176dBm. This will be compared with the result

calculated using syscalc.

VI. SYSTEM PERFORMANCE

Due to BER requirement, which is 1 10-5

.We can

determine the Eb/N0 is about 9.588dB using SysCalc6.

Based on (3) and (4), sensitivity can be calculated,

0/ ( / ) ( / )bS N E N R B (3)

,

/ 0 ,

( )

( ) ( / ) 10log( )

dbm dbm dB dB reqd

dbm Hz dB b dB reqd

Sensitivity kTB F SNR

kT F E N R

(4)

For the propagation channel is LOS combined with

the additional atmospheric absorption, we use free

space path loss equation(5) to calculate Pr:

2

( ) ( ) ( ) ( )

10log( / 4 )

r dBm r dBm t dB r dBP P G G

R Attenuation

(5)

Pr should be larger than Sensitivity and then

demonstrated the feasibility of the system. The

attenuation can be read through fig.1, which is around

0.05dB/km at 18GHz and 0.1dB/km at 30GHz. A

100 km is often regarded as the boundary between

atmosphere and outer space. So the attenuation is

about 5dB and 10dB, separately.

Table 3 shows the parameter we needed to calculate

Pr and Sensitivity. By using syscalc we get the

accurate results, which is fairly close to what we get

from ADS. Fig.8 shows the syscalc result of

transmission process from earth to satellite, the output

power is about -46.7dBm-10dB=-56.7dBm, which is

close to the output power shown in fig.7.

4

TABLE Ⅲ

ENVIRONMENTAL PARAMETER

D(earth-satellite) 35,786 km

D(satellite-moon) 370,000km

T(moon) 390 K

T(satellite) 5K

T(earth) 290K

Fig.8. Syscalc Simulation Result

Table IV shows system performance after sycalc6

simulation.

TABLE IV

SYSCLC SIMULATION RESULT Earth-Sat

ellite

Satellite-

Moon

Moon-Sat

ellite

Satellite-

Earth

f/Hz 30G 18G 30G 18G

Pout/dBm -56.7 -41.8 -61.5 -26.6

Sensitivity/

dBm

-64.3 -65.2 -64 -65.2

VII. CONCLUSION

A 1Gb/s ka band wireless link between earth and moon

has been investigated. QPSK modulation is used to

achieve BER requirement of 1 . A set of

direct-conversion architectures are used. Based on the

published paper, ADS and Syscalc simulation, it has been

demonstrated feasible to build this high speed wireless

link. But the cost for building the antenna on the moon

may be fairly large.

ACKNOWLEDGEMENT

The author wish to acknowledge the assistance and

support of Prof. Jenshan Lin and TA Jaime.

REFERENCES

[1] Gregory Konesky, " Application of Adaptive Optics to a Moon-to-Earth Optical Data Link, " Report. [2] www.lunarpedia.org/index.php?title=Communication [3] http://www.defensesystems.com/Articles/2011/04/15/In

marsat-satellite-system-on-track.aspx [4] J.P. Silver, "Satellite Communications Tutorial," RF, RFIC

& Micrwave Theory, Design.

[5] VIASAT, http://www.viasat.com/files/assets/8013_13_

meter_earth_station_010_web.pdf

[6] EEL6374 Lecture Notes.

[7] Gérard Caille, Yann Cailloce, "High-gain multibeam

antenna demonstrator for Ka-band multimedia via satellite

mission," Alcatel Telecommunication Review. 4th 2001

[8] ASC SIGNAL, "7.6 Meter Ku-band, K-band Earth Station

Antenna, " www.ascsignal.com

[9] COMTECH, "500 W Watt DBS-Band Antenna Mount

High Power Amplifier," http://www.comtechtel.com/

[10] J Chen,C Kuo,Y Hsin,H Wang, "A 15-50 GHz Broadband

Resistive FET RingMixer Using 0.18-um CMOS Technology",

MicrowaveSymposium Digest (MTT), 2010 IEEE MTT-S

International , May 2010.

[11] Shaolun, Jiang, Qike Chen, "A Compact Ku-Band filter

based on Substrate Integrated Circular Cavity, " ISPAC.

[12] D.SYu, C.Cheng ,"Narrow-Band Band-pass Filters on

siliconsubstrates at 30GHz", Microwave Symposium Digest,

2004 IEEE MTT-S International , June 2004.

[13] E.Adabi, B. Heydari, M. Bohsali,"30GHzCMOS Low

Noise Amplifier", RadioFrequency Integrated Circuits (RFIC)

Symposium, June 2007 IEEE.

[14] Agilent, Agilent AMMP-6220 6-20GHz LNA DataSheet.

TABLEⅡ

SUMMARY OF COMPONENTS PARAMETER Frequency Component Reference

No.

Frequency

(GHz)

Gain/Loss

(dB)

Bandwidth

(GHz)

F(dB) P1dB_out

(dBm)

OIP3(dBm)

18GHz Mixer [10] 20 -15 5 N/A -5 5.6

BPF [11] 20 -3.2 1 N/A N/A N/A

PA [9] 20 70 17.3-18.4 N/A 55.8 66.4

LNA [14] 20 22 N/A 2.5 10 20.6

LO N/A 20 N/A

Phase Shift N/A 20 90 LPF Square Root Raised cosine filter Alpha=0.35

30GHz Mixer [10] 30 -15 5 N/A -5 5.6

BPF [12] 30 -3.2 1 N/A N/A N/A

PA [9] 30 70 27.5-30 N/A 56.2 66.8

LNA [13] 30 20 27.6-30.2 2.9 1 11.6

LO N/A 30 N/A

Phase Shift N/A 30 90°

LPF Square Root Raised cosine filter Alpha=0.35

Table IV indicates all the output power are above the sensitivity

level, which demonstrate the feasibility of high speed wireless

data link between earth and moon.