Final Project Report EEL 6374 2012

7/25/2019 Final Project Report EEL 6374 2012

1/5


2/5

As the Moon revolves around the earth, a direct link

between a ground station on earth and moon is not

practically implementable. The solution is to design the

link in two parts, the first link connects a geo-stationary

satellite to earth and the second part of it connects the

satellite to the moon. The equatorial plane makes an angle

of which has amean radius of .The orbit of the geostationarysatellite lies in the Equatorial plane of earth and it has an

average radius of. From Figure.1, we can seethat there can be a situation where the earth comes inbetween the moon and the satellite, which might hinder

the existing Line of Sight (LOS) between the moon and

the satellite. But in this case, the LOS between the moon

and the satellite is still maintained by a path, which is

away from the center of the Earth and has aradius of .

Now, the orbit of the moon around the earth is elliptical

in nature, which causes the moon to be at varying

distances from the centre of the earth, at different times.

When moon is at the shortest (368000 km) and longest

(432000 km) distance from earth, moons positions are

known as Perigee and Apogee respectively. Therefore

in order to account for the weakest received signal at

Apogee, we will consider the maximum distance to be the

distance between the stations. Our link budget will have 2

sets of forward and reverse links, as follows:

1) Earth ----> Satellite (36000 km - Downlink)

2) Satellite ----> Earth (36000 km - Uplink)

3) Satellite---->Moon(432000-36000=39600km,

Downlink)

4) Moon---->Satellite (39600 km, Downlink)

III. ASSUMPTIONS FOR MATHEMATICAL

MODELWe need to make certain assumptions for our design to

hold:

1) As derived in the above section, the distance

between moon and satellite is taken to be constant

at 396000 km, although in reality it varies over

time.

2) Also as discussed, in the last section there always

exists an LOS over the link.

3) There exists no certain constraint on transmitted

power in order to make the received signal

detectable at the receiver for effective

communication to take place.

4) There is no constraint on availability of practicalcomponents as well.

IV. FREQUENCIES,MODULATION TECHNIQUES,

DUPLEXING TECHNIQUE,BANDWIDTH REQUIREMENT.

BER, energy efficiency, and bandwidth efficiency are

the metrics that are usually considered while making a

choice of modulation technique. In our case the

communication takes place over a huge distance, which

makes the transmitted symbols more vulnerable to noise,

fading and other channel impairments, and thus a

modulation technique with a lower BER is required.

Along with a low BER, we also aim to achieve higher

energy efficiency, so as to transmit as less power as

possible to reduce the cost to its optimum. Although these

set of requirements can be fulfilled by various modulation

techniques as BPSK, QPSK, M-are QAM and so on, our

situation has added requirement of high data-rate, and

hence QPSK, QAM and other higher order PSK

modulations are preferred to BPSK although BPSK has

same BER as QPSK. Although in terms of achieving highdata rate, QAM is more effective than QPSK, we do need

to take care of the spectral congestion and be able to

design our system for available limited bandwidth. Since

QPSK as higher bandwidth efficiency as compared to

QAMs, we narrow down our choice of modulation to

QPSK. QPSK also has better energy efficiency as

compared to FSK.

In order to be able to transmit and receive at the same

time, we need to incorporate channel duplexing methods

in our system. In order to lower the complexity of the

communication system we choose Frequency Division

Duplexing, and it also provides nominal interference

between the forward and reverse traffic.

Our aim is to choose an operating frequency that will

lead to lower pathloss, lower atmospheric attenuation, be

compatible with high data-rate and have sufficient suitable

components available for practical components. After

computing losses with various frequencies and performing

an extensive component search, we found that the

frequencies that offer optimal solution are as follows:

1) Earth-->Satellite(22.5-27.5GHz,fcenter=25 GHz)

2) Satellite-->Earth (17-22 GHz, fcenter=19.5 GHz)

3) Satellite-->Moon(11.5-16.5GHz,fcenter=14GHz)

4) Moon-->Satellite (6 - 11 GHz, fcenter =8.5 GHz)

We know that if data rate increases, which mean

faster variation of signal amplitude in time domain,

more number of harmonics is required for

representation of the same signal in frequency

domain, leading to larger bandwidth. Our data rate

is R=10 Gbps, for QPSK, Bandwidth efficiency,

=2 bps/Hz = R/B. therefore we would be requiring

5 GHz channel bandwidth to accommodate

transmitted data at 10Gbps using QPSK. (As

channel narrower than transmission bandwidth

leads to severe symbol distortion)

V.COMPUTING SYSTEM PARAMETERS

As we already know, and as it is evident from [2], [3]

there has been intensive research on building and

improving earth to satellite links in past. Therefore we

decide to lay more emphasis on building the satellite to

Moon link. So we will be discussing the parameters for

satellite to Moon to link elaborately.

1. Antenna Temperature

The Antenna temperature depends only on the object on

which the antenna beam impinges. As the Earth to


3/5

Satellite link points towards to satellite, which lies in the

horizon of the sky, and the typical antenna temperature for

sky horizon, is 5K, the antenna temperature for the earth

station would be 5K. Similarly for the Moon to satellite

link, the temperature will be 50K. Typical antenna

temperature for earth is 300K, so antenna temperature for

satellite to Earth is 300K. The Antenna temperature of

satellite pointing to Moon is assumed to be 2900K, t the

Ku band.

2. Receiver Sensitivity

For QPSK BER is given by:

(1)

Required BER ==> .Data rate, R = 1 Gbps , SNRreq=10dB, Noise Figure,

(typical of receivers), T=5K, =>10log(KT)=-191.63 dBm/Hz

Now, we know that sensitivity of a receiver is given by:

(2)

Hence -71.dBm.

3. Path Loss

As discussed earlier, distance between Earth and the

satellite is . The total pathloss in given asfollows:

Pathloss = 20 log (/4*pi*d) + loss due to O2, H2O, rain

But in case of moon-satellite link, the atmospheric

attenuation is not included, pathloss in this case is only

due to free space pathloss.

= Wavelength = C/f

For satellite to Moon link, f = 14 GHz. From the above

equation, pathloss = 227.3 dB. Similarly the pathloss for

Earth to satellite link is 211.1 dB

4. Transmitter Power Requirement

The transmitted power should be sufficient to overcome

the pathloss and additional attenuation and still produce

power atleast equal or greater than the receiver sensitivity,

in order to make the received signal detectable. If Pt is the

transmitted power, Gt and Gr are the transmitting and

receiving antenna gains, then received power,

(3)

While carrying out the link-budget analysis, we use

various values of Gtand Gr, in order to find out the

optimal transmitted power and gain margin.

VI.TRANSMITTER AND RECEIVER DESIGN USING ADS

Here we are using direct-conversion architecture for our

transceiver design. Some of the several advantages that

this architecture has to offer are:Very high level

integration and elimination of image frequency (single

carrier). The transmitter and receiver are is designed and

simulated using ADS to obtain the optimal power

requirement. Figure.(3) displays the schematic developed

in ADS. The transmitter does not a local oscillator, as in

our transmitter, digital modulation is perfromed on digital

signal from LFSR sources. have a Following available

components can be used for the practical implementation

of the design:

1) The Transmitter input IQ modulator is IQ-0917by

Marki microwave.2) Model GT-1000A Microwave Power Amplifier 2

GHz to 20 GHz by Giga-tronix.

3) Customized bandpass filters are obtained by quoting

appropriate specifications to manufacturers.

4) Raised Cosine filters are used for pulse shaping of

modulated signal in order to produce a clearer

spectrum and a faster roll off.

One of the main objectives of receiver design is to meet

the low noise figure requirement, where LNA plays a key

role. In the receiver we amplify and filter the signal in two

stages in order to get clearer spectrum and keep Q-factor

of the bandpass filters relaxed. the The schematic is shown

in Figure.(4). Following componets are suggested for

implemenattion:

1) The LNA is 2-18 GHz Low Noise Amplifier with

AGC TGA2525 by Triquint

2) Customized bandpass filters are obtained by quoting

appropriate specifications to manufacturers.

3) AD8333 DC to 50 MHZ, Dual I/Q Demodulator by

Analog devices

VII.TRANSMITTER AND RECEIVER PERFORMANCE

ANALYSIS

From the figure we can see, that there is not much

distortion, as the amplifiers are operated in the linear

region. However it is observed that the gain in the side

lobe is little more. The RF null to null bandwidth is easily

observed to be same as the data rate, thus giving high

bandwidth efficiency. Fig.(2) shows the input and

output spectrum.

Fig. 2. Power spectrum at the input and out of the HPA


4/5

Figure.3 Transmitter Schematic

The Constellation received at the output of the IQ

demodulator at the receiver is shown in Fig. 4. Since we

have not introduced noise and fading in our simulation we

do not see any symbol going in error. However on a

practical channel there will be some errors. Hence we

have to stick to the required receiver sensitivity as well as

provide some margin if possible.

Fig.5 Link Budget Analysis using SysCalc

VIII.LINK BUDGET CALCULATION USING SYSCALC

The link budget analysis is carried out using SysCalc tool.

First we build a block diagram of the intended

receiver/transmitter in SysCac, enter the parameters

related to them, input the antenna gain, temperature, total

pathloss as calculated in section and run the simulation.

In output we get the power required to be transmitted,

Noise Figure, gain margin and so on. The standard

analysis performed along with link budget analysis yields

parameters like: MDS, Sensitivity, Eb/No, IIP3, OIP3,

Figure.4 Receiver Schematic

SFDR3 and so on. The Gain Margin obtained from the

simulation turned out to be positive, which implies that the

system can deliver the required power to the receiver,

which is truly essential for an effective communication to

take place. Suitable values of antenna gains are fed and

system is calibrated. The optimum values of the satellite

antenna and the moon ground station are found to be 50dB

and 70dB respectively. Snapshots of the simulation areshown in figure.5 and figure.6

Fig.6 Satellite to MoonLink Budget Analysis using SysCalc.

IX.CONCLUSION

After carrying out the design, simulation and

component-search suitable for practical implementation,

we hereby conclude that it is possible to create a 10 Gbps

link that achieves an error rate of 10 -5, without error

control coding. As seen from our simulation, lower

bandwidth leads to lower receiver sensitivity and hence

lesser transmitted power. Therefore to design the

optimally economic link, one should strive to achieve

lower bandwidth requirement, which is possible by 1)

using a bandwidth efficient modulation technique, 2)

using an efficient pulse-shaping method, 3) dividing up

channels into a number of narrower subcarriers by method

of OFDM and so on. These all techniques can be


5/5

incorporated in the future design of such links, in order to

attain lower power and hence gain requirements.

ACKNOWLEDGEMENT

We would like to thank Dr. Jenshan Lin for giving us

this fine opportunity work on such projects and thus gain

the much needed hands-on experience. We are also highly

indebted to Ms. Yan Yan for her kind help and valuable

suggestions during the course of the project.

REFERENCES

[1] [1] FUTURE VISION OF SATELLITE COMMUNICATIONSFOR EXPANDING HUMAN ACTIVITIES Yoshiaki Suzuki,Hiromitsu Wakana and Takashi Iida

[2] Gigabit Satellite Network Using NASA's AdvancedCommunications Technology Satellite (ACTS):Features,Capabilities, and Operations by Marcos A. Bergamo, Ph.D.,Principal Investigator and Doug Hoder, M.S.E.E., ACTSHigh Data Rate Project Engineer

[3] System Study on Advanced Gigabit SatelliteCommunications Rhai, A.Saifudin, H.Okazawa, NhdowakiandM.Yamamoto Communications Research Laboratoty,Ministry of Posts and Telecommunications

[4] Wikipedia Earth at http://en.wikipedia.org/wiki/Earth asof April 21, 2011

[5] http://www.odyseus.nildram.co.uk/Systems_And_Devices_Files/Sat_Comms.pdf

[6] Wikipedia Moon at http://en.wikipedia.org/wiki/Moon asof April 21, 2011

[7] WikipediaGeostationary orbithttp://en.wikipedia.org/wiki/Geostationary_orbit as of April21, 2011

Final Project Report EEL 6374 2012

Documents

Transcript of Final Project Report EEL 6374 2012