THE EFFECT OF PULSE SHAPING QPSK

ON BANDWIDTH EFFICIENCY

Josua Bisuk Mubyarto Purba, S.T.

Sheila Horan

NMSU-ECE-97-009 June 1997

https://ntrs.nasa.gov/search.jsp?R=19970025033 2018-07-04T07:10:59+00:00Z

THE EFFECT OF PULSE SHAPING QPSK ON BANDWIDTH EFFICIENCY

OVER A NON-LINEAR CHANNEL.

BY

JOSUA BISUK MUBYARTO PURBA, S.T.

A technical report in partial fulfillment

of the requirements for the Degree

Master of Science in Electrical Engineering

New Mexico State University

Las Cruces, New Mexico

June 1997

ABSTRACT

THE EFFECTOFPULSESHAPINGQPSKON BANDWIDTH EFFICIENCY

OVERA NON-LINEAR CHANNEL.

BY

JOSUABISUK MUBYARTO PURBA, S.T.

Masterof Sciencein ElectricalEngineering

NewMexico StateUniversity

LasCruces,NewMexico,1997

Dr. SheilaB. Horan,Chair

This researchinvestigatesthe effect of pulse shapingQPSK on bandwidth

efficiency over a non-linear channel.This investigation will include software

simulationsand the hardwareimplementation.Threekinds of filters: the 5th order

Butterworthfilter, the3rd orderBesselfilter andthe SquareRoot RaisedCosinefilter

with a roll off factor (cz)of 0.25,0.5and 1, havebeeninvestigatedaspulseshaping

filters. Two differenthigh power amplifiers,one a TravelingWave Tube Amplifier

(TWTA) andthe othera SolidStatePowerAmplifier (SSPA)havebeeninvestigated

ii

in the hardware implementation.A significant improvement in the bandwidth

utilization (p) for the filtered datacomparedto unfiltereddatathroughthe non-linear

channelis shownin the results.Thismethodpromisesstrongperformancegains in a

bandlimitedchannelwhencomparedto unfilteredsystems.This work wasconducted

at NMSU in theCenterfor SpaceTelemeteringandTelecommunicationsSystemsin

the Klipsch Schoolof Electrical and ComputerEngineering Departmentand is

supportedby a grant from the National Aeronauticsand Space Administration

(NASA) # NAG 5-1491.

111

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................. vi

LIST OF FIGURES ........................................................................................... vii

LIST OF ABBREVIATIONS ............................................................................ x

Chapter

1. INTRODUCTION AND BACKGROUND .................................................. 1

2. SOFTWARE SIMULATION ......................................................................... 3

2.1 QPSK Source ......................................................................................... 5

2.2 Spectrum Shaping ................................................................................... 7

2.2.1 Butterworth Filter ........................................................................... 7

2.2.2 Bessel Filter .................................................................................... 9

2.2.3 Raised Cosine Filters ...................................................................... 10

2.3 Solid State Power Amplifier (SSPA) ........................................................ 14

2.4 Software Simulation Results .................................................................... 16

2.4.1 The 5th Order Butter-worth Filter .................................................... 17

2.4.2 The 3rd Order Bessel Filter ............................................................. 18

2.4.3 The Square Root Raised Cosine (SRRC) Filter ............................... 19

2.5 Bandwidth Utilization .............................................................................. 20

3. HARDWARE IMPLEMENTATION ............................................................. 24

3.1 The QPSK Modulator ............................................................................ 26

iv

3.2 The Filters ............................................................................................... 30

3.2.1 The 5th Order Butterworth Filter .................................................... 32

3.2.2 The 3rd Order Bessel Filter ............................................................. 36

3.2.3 The Square Root Raise Cosine (SRRC) Filters ................................ 41

3.3 The Power Amplifier ............................................................................... 44

3.4 Bandwidth Utilization ............................................................................. 49

4. CONCLUSION AND RECOMMENDATIONS ............................................ 54

4.1 Conclusion .............................................................................................. 54

4.2 Recommendations ................................................................................... 55

REFERENCES .................................................................................................. 57

APPENDIX A. The Test Procedure For Hardware Implementation .................... 59

A. 1 The Set Up For The Unfiltered Signal ..................................................... 60

A.2. The Set Up For The Filtered Signal ........................................................ 63

A.3. The Set Up For The Measurement Of The Power Amplifier ................... 65

APPENDIX B. SPW Detail Program .................................................................. 66

APPENDIX C. The Listing Program .................................................................. 67

V

LIST OF TABLES

Table 2.1 - Values of Ci for the BPSK, QPSK and 8PSK Simulation Model .... 7

Table 2.2 - Utilization Ratio with various BT by using QPSK ............................... 21

Table 2.3 - Utilization Ratio on QPSK ............................................................. 22

Table 2.4 - Utilization Ratio QPSK Vs. 8PSK ................................................. 23

Table 3.1 - Utilization Ratio with TWTA ......................................................... 50

Table 3.2 - Utilization Ratio with SSPA ........................................................... 51

Table 3.3 - Utilization Ratio on QPSK software and hardware with SSPA ...... 51

Table 3.4 - Utilization Ratio with various BY by using SSPA ........................... 52

vi

LIST OF FIGURES

Figure 2.1 - The Block Diagram of The System .............................................. 3

Figure 2.2 - QPSK Signal Constellation ........................................................... 5

Figure 2.3 - Block Diagram For The BPSK, QPSK and 8PSK Modulator onSPW

............................................................................................

Figure 2.4 - Simulated Amplitude Response of 5th Order Butterworth Filter ... 8

Figure 2.5 - Simulated Phase Response of 5th Order Butterworth Filter .......... 8

Figure 2.6 - Simulated Amplitude Response of 3rd Order Bessel Filter ............ 9

Figure 2.7 - Simulated Phase Response of 3rd Order Bessel Filter ................... 10

Figure 2.8 - Frequency Response: Raised Cosine Filters with c_=0,0.25,0.5

and 1 ............................................................................................ 11

Figure 2.9 - Time Response of Raised Cosine Filters for oc=0,0.25,0.5 and 1 ... 12

Figure 2.10 - The eye diagram if the SRRC with o_= 0.5 is applied .................. 13

Figure 2.11 - SSPA, ESA 10 Watts, Magnitude Characteristic Curve .............. 14

Figure 2.12 - SSPA, ESA 10 watts, Phase (degrees) Characteristics Curve ...... 15

Figure 2.13 - The Spectrum and the phase of Unfiltered Signal at The Outputof SSPA ..................................................................................... 16

Figure 2.14 - The magnitude and the phase of the signals ................................. 17

Figure 2.15 - Magnitude and Phase at the output of SSPA with 5th order

Butterworth ............................................................................... 17

Figure 2.16 - Spectrum and Phase at the output of SSPA with 5th order

Butterworth ............................................................................... 18

Figure 2.17 - Magnitude and Phase at the output of SSPA with 3 rd order

Bessel ........................................................................................ 18

vii

Figure2.18- SpectrumandPhaseattheoutputof SSPAwith 3rdorder 19Bessel .......................................................................................

Figure2.19 - MagnitudeandPhaseatthe outputof SSPAwith SRRCcz=0.5.. 19

Figure2.20- SpectrumandPhaseat theOutputof SSPAwith SRRCor=0.5... 20

Figure2.21- TheUtilizationRatioof QPSKand8PSK................................... 23

Figure3.1- TheBlock Diagramof TheHardware........................................... 24

Figure3.2- TheQPSKSignalthatProducedBy HP 8782B............................ 26

Figure3.3- TheSpectrumof theQPSKSignalat IF 90MHz .......................... 27

Figaare3.4- TheHardwareSetUp of UnfilteredSignal.................................. 28

Figure3.5- The Spectrumof TheUnfilteredSignalat TheOutputof SSPA .... 28

Figure3.6- The SetUp for FilteredSignal...................................................... 31

Figure3.7 - The Signal at The Output of The 5th order Butterworth Filter ...... 32

Figure 3.8 - The Spectrum at The Output of The 5th Order ButterworthFilter ............................................................................................ 33

Figure 3.9 - The Measured Phase Characteristic of the 5th Order Butterworth

filter ............................................................................................. 33

Figure 3.10 - The 5th Order Butterworth Simulated Frequency Response ........ 34

Figure 3.11 - The 5th Order Butterworth Simulated Phase Response ............... 35

Figure 3.12 - The Spectrum at The Output of SSPA of The 5th orderButterworth ............................................................................... 36

Figure 3.13 - The Signal at The Output of The 3rd Order Bessel Filter ............ 37

Figure 3.14 - The Spectrum at The Output of The 3rd Order Bessel Filter ....... 37

Figure 3.15 The Measured Phase of the 3rd order Bessel Filter ........................ 38

Figure 3.16 The 3rd Order Bessel Filter Simulated Frequency Response .......... 39

viii

Figure 3.17 - The 3rd Order Bessel Filter Simulated Phase Response ............... 40

Figure 3.18 - The Spectrum at The Output of SSPA of The 3rd Order Bessel

Filter .......................................................................................... 40

Figure 3.19 - The Signal at The Output of The SRRC Filter with ot = 0.5 ....... 41

Figure 3.20 - The Spectrum at The Output of The SRRC Filter with ot = 0.5 .. 42

Figure 3.21 - The Phase Measured at The Output of The SRRC Filter with

ot = 0.5 ....................................................................................... 42

Figure 3.22 - The SRRC filter (or = 0.5) Simulated Phase Response ................. 43

Figure 3.23 The Spectrum at The Output of SSPA with The SRRC Filter

ot = 0.5 ........................................................................................ 44

Figure 3.24 - The Measurement of The Characteristic of Power Amplifier ....... 45

Figure 3.25 - The Characteristic of Magnitude of TWTA ................................ 46

Figure 3.26 - The Characteristic of Phase of TWTA ........................................ 47

Figure 3.27 - The Characteristic of Magnitude of S SPA .................................. 47

Figure 3.28 - The Characteristic of Phase of SSPA .......................................... 48

Figure 3.29 - The Example of The Output of TWTA With 3rd Order BesselFilter .......................................................................................... 48

Figure 3.30 - The Comparison Between So,ware and Hardware on TheBessel and The Butterworth Filters ............................................. 53

ix

Ot

9

dB

dBm

BPSK

BW

CCSDS

ESA

GMSK

GHz

HP

IF

ISI

JPL

MSK

NASA

NMSU

NRZ-L

OQPSK

PSK

LIST OF ABBREVIATIONS

Rolloff Factor for SRRC filters

Bandwidth Utilization Ratio

Decibels

Decibels (1 milliwatt reference)

Binary Phase Shift Keying

Bandwidth

Consultative Committee for Space Data Systems

European Space Agency

Gaussian Minimum Shift Keying

Giga Hertz

Hewlett Packard

Intermediate Frequency

InterSymbol Interference

Jet Propulsion Laboratory

Minimum Shift Keying

National Aeronautics and Space Administration

New Mexico State University

Non-Return-to-Zero Logic

Offset Quaternary Phase Shift Keying

Phase Shift Keying

QPSK

Rb

Rs

SFCG

SPW

SSPA

SRRC

TWTA

TDRSS

QuartenaryPhaseShiftKeying

Bit Rate

SymbolRate

SpaceFrequencyCoordinationGroup

SignalProcessingWorksystem

SolidStatePowerAmplifier

SquareRootRaisedCosine

TravelingWaveTubeAmplifier

TrackingandDataRelaySatelliteSystem

xi

Chapter 1

INTRODUCTION AND BACKGROUND

In recent years, the demand for communications systems that transmit more data

through a bandwidth limited channel is increasing rapidly. The need for bandwidth

efficient modulation schemes has driven a great deal of research in this area. One such

method for bandwidth efficiency is Pulse Shaping or Spectrum Shaping. Spectrum

shaping is a technique that concentrates the signal energy near the carrier and reduces

the power contained in the side lobes. This pulse shaping can be done at baseband or

at ban@ass. In this research, both of them will be investigated.

At the 12th annual meeting of the Space Frequency Coordination Group (SFCG-

12), held during November 1992 in Australia, the SFCG requested the Consultative

Committee for Space Data Systems (CCSDS) Radio Frequency (RF) and Modulation

Subpanel to study and compare various modulation schemes with respect to the

bandwidth efficiency, power efficiency, spurious emissions and interference

susceptibility. As a result of this meeting, some research regarding spectrum shaping

combined with modulation techniques such as Binary Phase Shift Keying (BPSK),

Offset Quaternary Phase Shift Keying (OQPSK) and Gaussian Minimum Shift Keying

(GMSK) were conducted for the CCSDS-SFCG [1]-[4] by the Jet Propulsion Lab

(IPL) and by European Space Agency (ESA) [14]. The simulations of pulse shaping

on 8-PSK signaling over non linear satellite channels were performed on the Signal

Processing Worksystem (SPW) _ simulation software at New Mexico State University

(NMSU) in the Center for Space Telemetring and Telecommunications Systems where

the power containment, spurious emissions, symbol error rates and non-constant

envelope effect on the bandwidth were measured for different types of spectrum

shaping filters [ 11 ].

The purpose of this research is to investigate the effect of pulse shaped QPSK on

bandwidth efficiency over a non-linear channel with software simulations and hardware

implementation. Two different high power amplifiers, a Traveling Wave Tube

Amplifier (TWTA) and a Solid State Power Amplifier (SSPA), have been utilized and

analyzed in the hardware implementation. This work was conducted at NMSU in the

Center for Space Telemetering and Telecommunications Systems in the Klipsch

School of Electrical and Computer Engineering Department and is supported by a

grant from the National Aeronautics and Space Administration (NASA) # NAG 5-

1491.

The first chapter of this report has given a brief introduction and background of

the work. Chapter 2 will describe the software simulations including the results and

Chapter 3 will explain the hardware implementation with the results. Finally,

conclusions and suggestions for further work are given at the end of this report in

Chapter 4.

SPW is a registered trademark of COMDISCO systems, a Business Unit of Cadence DesignSystems, Inc. 919 East Hillsdale Blvd., Foster City, CA 94404.

Chapter 2

SOFTWARE SIMULATIONS

This section will describe the software simulations on the effect of pulse shaping QPSK

on bandwidth efficiency over a non-linear satellite channel including the results. The

software simulations were conducted on Signal Processing Worksystem (SPW) software

installed on a SUN Sparc Station 10 and a Hewlett Packard (I/P) Model 715/100 Unix

Station. The block diagram of the system is given in the Figure 2.1 below:

QPSK

Modulator

Spectrum

Shaping PowerAmplifier

Figure 2.1 - The Block Diagram of The System

Quaternary Phase Shift Keying (QPSK) modulates the Non-Return to Zero Level

(NILE-L) ideal data formats that have symmetric data and the probabilities of 0 and 1 are

equal to 0.5. The QPSK signal is at baseband. All simulations were produced at baseband

using the complex envelope signal representation. The advantage of using baseband

representation is that the computer takes longer to simulate at bandpass since the sampling

frequency must be at least twice the highest frequency. The pulse shaping filter or in this

case the baseband spectrum shaping filter is used at the output of the modulator. The

filters that areusedfor this researchare the 5th order Butterworth filter, the 3rd order

Besselfilter andthe SquareRootRaisedCosine(SRRC)filter with roll off factor 0.25,0.5

and 1. All of thesefilters arechosento be consistentwith JPL's work and the CCSDS

request.ThesimulationsusetheSolidStatePowerAmplifier (SSPA)at its saturationlevel

to maximize the power. Since the main concern of this research is the bandwidth

utilization of the signal bandwidth over the non-linear channels, the bandwidth of the

signal with and without the pulse shaping filters are measured at the output of the SSPA.

The bandwidth is defined as a point where the power spectra has -50 dB down from the

maximum value on the main lobe. Another parameter that is used to measure the

bandwidth is BT, which is defined as the multiplication of the bandwidth of the filter and

the symbol rate (Rs).

The following specifications were implemented in SPW for the system:

1. The format of the data is NRZ-L.

2. The data is ideal (data is symmetric and the probabilities of 0 and 1 are equal

to 0.5).

3. The symbol rate of the QPSK signal is 1 symbol per second (sps).

4. The sample rate is 256 samples/second

5. The carrier frequency = 0 Hz (baseband simulations).

6. The baseband pulse shaping filters (do not include resistive and reactive losses):

- Butterworth 5th order (BT=l,2,3)

- Bessel 3rd order (BT=l,2,3)

- SRRC with rollofffactor (or) = 0.25, 0.5 and 1

7. The Solid State Power Amplifier (SSPA) model is based on the European Space

Agency (ESA) requirements and is 10 watts.

Note: this SSPA was recommended for deep space missions.

2.1 QPSK Source

QPSK is one type of MPSK signal that has constant envelope and modulates 2 bits of

data within its 4 phases. Figure 2.2 shows the QPSK signal constellation. It can be seen

that each signal point (x) corresponds to one of four phases given by:

01 = 45 ° for symbol 00 (decision region: 0 ° to 90 °)

02 = 135 ° for symbol O1

03 = 225 ° for symbol 11

(decision region: 90 ° to 180 °)

(decision region: 180 ° to 270 °)

04 = 315 ° for symbol 10 (decision region: 270 ° to 360 °)

1.5

1

0.5

0

-0.5

-1

-1.5

QPSK constellation

I

ol *_x II ,/--, oo× [ x

IJI1

x ] ×

11 J ] X_ 10

II I I I I I

-1 .{5 -1 -0.5 0 0.5 1I

1.5

Figure 2.2 QPSK Signal Constellation

One way to describe the QPSK signal is by using two orthogonal carriers modulated by

x and y components of the complex envelope thus

g(t) = Ace i°(tl = xi (t) +j yi (t)

where xi (t) = Ac cos 0i (t) and Yi (t) = Ac sin 0i (t) where i = 1 to 4 for QPSK as shown

in Figure 2.2.[1 l]

For the simulations, a QPSK modulator can be made from the MPSK modulator used

for the 8PSK simulations [11] as shown in Figure 2.3 below where the values of Ci vary

depending on the desired modulator as given in Table 2.1.

DATA _ _1

MAG/PHASE

out_hase to

/ I

?COMPLEX

SPECTRAL

SHIFTER

OUTPUT

Figure 2.3 - Block Diagram For The BPSK, QPSK and 8PSK Modulator on SPW

Table2.1Valuesof Ci for theBPSK,QPSKand8PSKSimulationModel

ModulationType C1 C2 C3 C4 C5 C6 C7BPSK 0.0 0.0 0.0 2rt/2 0.0 0.0 (2)lt2QPSK 2.0 0.0 0.5 2rt/4 0.0 0.0 (2)1/28PSK 2.0 4.0 0.5 27t/8 0.0 0.0 (2)In

For QPSK,C1=2.0,C2=0.0,C3=0.5,C4=27t/4,C5=C6=0.0andC7=(2)1/zarechosen.

2.2 SpectrumShaping

As mentionedbefore, the filters that are usedfor this researchare the 5th order

Butterworth filter, the 3rd orderBesselfilter andthe SquareRoot RaisedCosine(SRRC)

filter with roll offfactor of 0.25,0.5and 1.

2.2.1 Butterworth Filter

The Butterworth family of filters is known to have a "maximally" flat response in the

passband region [9]. This is why Butterworth Filters are commonly used. For an

example, Figure 2.4 and Figure 2.5 (programmed with Matlab) show the amplitude

response and phase response for the 5th order Butterworth filter with cut off frequency 1

Hz. In Figure 2.4 it appears that the amplitude is almost fiat as the frequency approaches

the cutoff frequency. It can be seen from Figure 2.5 that the phase response changes from

a negative number to a positive number when the frequency is close to the cut off

frequency in the passband region.

The Spectrum of The 5th Order Butterworth With fc=l Hz

10°

lO,

104 10° 101

Frequency(Hz)

Figure 2.4 - Simulated Amplitude Response of 5th Order Butterworth Filter

%-.

(13

(D

q)

¢-

13-

200

100

0

-100

-20010"1

5th order Butterworth Filter with fc=l Hz.I I I I I ] I I I I I I I I

i i i i i i i , i i

i i i i i i i i i i

: : : : : ' : : : : : :

i _ I i i i i i _ i i i

i i I 1 i i i i i i i iI

ii _ i i i i i i i i i i

i i i i I i i i i | i

i i I i i i i i i I _ i i i i i i

.............. , :::

! .............

i I I ii

100 101

Frequency (Hz)

Figure 2.5 - Simulated Phase Response of 5th Order Butterworth Filter

2.2.2 Bessel Filter

The main characteristic of the Bessel family of filters is that they have a relative linear

phase in the passband region. This linear phase will have a tendency to prevent dispersion

of the signal and therefore would be good for digital pulses. For an example, Fignare 2.6

and Figure 2.7 (were programmed with Matlab) show the amplitude response and phase

response of the 3rd order Bessel Filter with cut off frequency 1 Hz. The amplitude

response for the Bessel filter is not as fiat in the passband region as for the 5th order

Butterworth filter and the transition from the passband to the stopband region is not as

rapid as for the 5th order Butterworth filter. It can be seen in Figure 2.7 that the phase

changes from a negative value to a positive value at a frequency after the cut off frequency

(1 Hz). This change will have little effect the signal since it is outside of the pass band.

3rd order Bessel Filter with fc=l Hz10o

101

<

1[I.2

10.310"1 10o 101

Frequency (Hz)

Figa_re 2.6 - Simulated Amplitude Response of 3rd Order B essel Filter

%-.6D

(D

O)

O,1

tel

¢.-

13_

200

100

-100

3rd order Bessel Filter with fc=l Hz.

..... ............. "- - .'- -'-" 4---'- ....

-200 .........10 -1 10 o

Frequency (Hz)

Figaare 2.7 - Simulated Phase Response of 3rd Order Bessel Filter

2.2.3 Raised Cosine Filters

The Raised Cosine filters are used to eliminate the ISI in a linear channel. The idea

behind the Raised Cosine Filter is that the time signal goes through zero at adjacent

sampling points therefore eliminating the interference of other symbols.

The transfer function of the Raised Cosine Filter is [5]

(1 -cz)

ITiI I--_ =]) O-<f< 2---____.C.___ (1+o0

Xrc(f)= 1+cos (f_ zi ),1-a (12TOO<f < 2T

(1+o_)Lo, Ifl>

where the zeros will occur at t=nT (T is the sampling interval) and ct is the rolloff factor of

the excess bandwidth which can be varied from 0 to 1. For an example, Figure 2.8 and

10

Figure 2.9 (were programmed with Matlab) show the frequency response and the time

domain response of the Raised Cosine filter with different rolloff factors (or = 0, 0.25,

0.5 and 1) and T = 1 second. The Raised Cosine filters satisfy the Nyquist pulse shaping

criterion or Nyquist condition for zero ISI as mentioned in [8][5].

L..

-r"

Frequency Response of Raised Cosine Filter with alpha=O,O.25,0.5 and

°_=0 ' _N_o_=0.25 ',

(x,=l

0.8 ...............................

0.6 .................. -__/// ,.................

0.4

0.2

0-0.5

I

0

frequency (Hz)

0.5

Figure 2.8 - Frequency Response: Raised Cosine Filters with ot=0,0.25,0.5 and 1

11

Time Response of Raised Cosine Filter with r = O. 0.25, 05 and 1

06Sampling Times:

T and 2T

-0.2 .........................

-3 -2 -1 0Time (t)

1 2

Figure 2.9 - Time Response of Raised Cosine Filters for o_=0,0.25,0.5 and 1.

To produce a zero ISI channel the frequency response shown before has to be created.

If the frequency response of the transmitter filter and receiver filter are XT and XR

respectively and the frequency response of the channel is C, then to get the zero ISI the

total frequency respolise of XT, XR and C must be equal to Xrc as given above or :

x,o(t)= x_(0.c (t).x_(f)

If the channel has a large bandwidth compared to the bandwidth of the transmitter and the

receiver frequency response or C(f) = 1 for Ifl -< W where W is the bandwidth of the X7

and XR then

X_c(f) = X_(0- X_(t)

12

To get the optimum result, the transmitter filter has to be matched to the receiver filter so

we need to make Xx (f) = XR (f). Thus

x,o (0 = IXT(t)l2

and

XT (f) = XR (f) = (Xrc)v2= Square Root Raise Cosine Filter = SRRC

Figure 2.10 shows the eye diagram if the SRRC filter with a=0.5 is applied to both the

transmitter filter and receiver filter. Again, if we sample the signal at the right sampling

frequency, i.e. at a sampling frequency equal 1,or 2, we will get no ISI; otherwise the ISI

will occur.

3

2

m

m

go°m

co

-1

-2

-30

Eye diagram of the signal

I

I

I

I................... 1 .......... ¢" .............................

: Ii o

i i

I I I I s

I i ! I !

¢ i t i I

.......... _ ......... .I .......... 1 .......... t- ......... A ..........I

Ii

lI I i I

0.5 1 1.5 2 2.5

Relativefrequency to samplin9 frequency

Figure 2.10 The eye diagram if the SRRC with o_ = 0.5 is applied

13

2.3 Solid State Power Amplifier (SSPA)

Power amplifiers can be utilized in one of two regions, either in a linear region or in a

non-linear region. High frequency power amplifiers such as Traveling-Wave Tubes

(TWT) and Solid State Power Amplifiers (SSPA) can be linear amplifiers when operated

well below the saturation level. If the amplifiers work in their saturation level, the

efficiency, e.g., RF output/Direct Current (DC) input is improved, but the amplifier then

becomes a non-linear device. Figure 2.11 and Figure 2.12 show the magnitude and phase

characteristics' curve for the European Space Agency (ESA) 10 Watts S SPA.

-5

-10

_L

,3).-J

C5

o -20

-25

SSPA 10 Watts Amplifier

-30-30

iiiiiiiiiii

4 i i-25 -20 -15 -10 -5 0

Input Level Power (dB)

Figure 2.11 - SSPA, ESA 10 Watts, Magnitude Characteristic Curve

14

SSPA, ESA 10 Watts Amplifier: Phase Response C:urve

:t........i i........................i.......i................

-30 -25 -20 -15 -10 -5 0 5

Input Level Power (dB)

Figure 2.12 - SSPA, ESA 10 watts, Phase (degrees) Characteristics Curve

The non-linearities that occur in the nonlinear region of this amplifier will cause non-

linear distortion and Amplitude Modulation-to-Phase Modulation (AM-to-PM) and AM-

to-AM conversion effects (linear channels are channels without AM-AM and AM-PM

conversions). The AM-to-PM conversion is the change in the output RF voltage that is

produced by the variations in input signal level, usually expressed in dB/dB or dBm/dBm.

The AM-to-AM conversion is the change in the phase angle of the output RF voltage

produced by variations in the input signal level, usually expressed in degrees/dB or

degrees/dBm. As mentioned in [8], the analyses of these non-linearities are very

complicated.

15

To reduce the effect of these non-linearities, a signal with constant envelope is needed.

Therefore constant envelope signals such as BPSK, QPSK, etc. are preferred. However,

the pulse shaping used in this work creates a non-constant envelope signal.

2.4 Software Simulation Results

The main focus of this research is the bandwidth efficiency or the bandwidth utilization

of the system. The bandwidth in this paper is defined as a -50 dB down from the maximum

value. For example, Figure 2.13 shows the unfiltered spectrum and phase at the output of

the SSPA. It can be seen that up to _+25 Rs (Rs = symbol rate), the spectrum does not

reach -50 dB point. The spectrum reaches -50 dB at _+45 Rs (this can be seen from Figure

2.13). The magnitude and the phase of the signal are shown in Figure 2.14. It can be seen

that the signals have constant envelopes.

Mag(dB)

Phase

(radiams)

-15--

-30--

-45--

-60---75--

-90--

-SOR Rs 0 2S Rs _'Freq.ORs

Freq.

Figure 2.13 The Spectrum and the phase of Unfiltered Signal at The Output of SSPA

16

[_] data

. _].............".............Tf.........T.............T.............T-_.........................,_.............................,...............,_..(v) _] ' , j

s I u ii m m

m ' e # m

200-7 ............. T ............. T"'r ......... T ..............................: :_d_'_°-t_-_-n-_-__ -___----_--,

-200[-- : : , , ,

Figure 2.14 The magnitude and the phase of the signals

#of points

#of points

2.4.1 The 5th Order Butterworth Filter

Figure 2.15 shows the magnitude and the phase of the QPSK signal at the output of the

SSPA when the 5th order Butterworth filter with BT=I is utilized. Comparing this to the

original signal (Figure 2.14), Figure 2.15 does not have constant envelope. This is the

effect of this spectrum shaping on the signal, it creates a signal with non-constant

envelope. The frequency response and the phase response of the system at this time can be

seen in Figure 2.16. From the frequency response we get that the -50 dB bandwidth is

5.28 Rs. Section 2.5 on bandwidth utilization gives the complete results of this filter.

_i] data

,., ti:: II1 I::! IIII I(v) _ ---7..................:...................

,, ,, :m _,_ m aNN #of points

-200_,, _ m #of points

Figure 2.15 Magnitude and Phase at the output of SSPA with 5th order Butterworth

17

-15

-30

-45

Mag(dB) -6o

-75

-90

|

-20_s -10 p,s 0 10Rs 20_ eq"

Phase 3.142 .Freq.

(radians)

-3.142

Figure 2.16 Spectrum and Phase at the output of SSPA with 5th order Butterworth

2.4.2 The 3rd Order Bessel filter

The 3rd order Bessel filter with BT = 1 is chosen for this example. Figure 2.17 shows

the magnitude and the phase of the QPSK signal at the output of the SSPA. It can be

seen that the envelope of the signal is not constant anymore. The frequency response and

the phase response of the system is given in Figure 2.18. The frequency response gives the

-50 dB bandwidth as 5.65 Rs. This result is larger than the result for the 5th order

Butterworth filter, therefore the utilization ratio for this filter is less than for the 5th order

Butterworth filter. The complete results will be given in the section on bandwidth

utilization, Section 2.5.

i I! ! po nt 2oo]....._i-?i_i_ ....._{:-!............:--__:...._............

•_,o .... i - , ...... _ ......

_a_o , :mm ,,m, Jaw _ #of points

Figure 2.17 Magnitude and Phase at the output of SSPA with 3rd order Bessel

18

Mag(dB)

Phase

(rad/_)

--20Rs --10Rs 0 10RsFreq.

20 Rs

Figure 2.18 Spectrum and Phase at the output of SSPA with 3rd order Bessel

2.4.3 The Square Root Raised Cosine (SRRC) Filter

From the SRRC family, SRRC with oc=0.5 is chosen as an example. Figure 2.19 shows

the magnitude and the phase of the QPSK signal at the output of the SSPA. Again, the

signal envelope is not as constant as the source was. The frequency response and the

phase response of the system can be seen in Figure 2.20. From the frequency response we

get the -50 dB bandwidth is 4.60 Rs. The complete results are given in the following

section.

[%-Z data

(v)

2-1-- .......... T ............. T-'-r ......... T ............. T

-2_1 / i im _ o _ #of points

200-1 ...... i.j--- :i i_T--'" :-222m-i" T U-_1"-",: ..... T, .......... ii'T ............. T--

(degrl,haS_re_O0__] -_f-_ -_-- _i ...............

_. 4, w _ #of points

Figure 2.19 Magnitude and Phase at the output of SSPA with SRRC c_=O. 5

19

Mag(dB)

Phase

(radiams)

Figure 2.20 Spectrum and Phase at The Output of SSPA with SRRC or=0.5

Freq.

2.5 Bandwidth Utilization

To see the overall effect of spectrum shaping on the bandwidth efficiency, a frequency

band Utilization Ratio (p) was defined as [3]:

p = The Bandwidth of the signal without Filterin_o

The bandwidth of the signal with Filtering

This ratio is an estimate of how many more signals with shaped spectra can be included in

the bandwidth of the original signal with no filtering. This ratio was derived by using the

following assumption. The spectra from adjacent channels will be permitted to overlap one

another at the point where the signals are at least 50 dB below the main lobe. For an

example, Table 2.2 shows the utilization ratio of the the 5th order Butterworth filter and

the 3rd order Bessel filter for various BT. The -50 dB bandwidth is defined in terms of

symbol rate (Rs). The -50 dB point for the unfiltered data is at 90 Rs and for the 5th order

20

Butterworth filter is at 5.28 Rs. The utilization ratio is then p = (90/5.28) = 17.05 and

therefore if this pulse shaping filter is used, 17 signals can be sent in the same bandwidth

as one unfiltered signal was.

Table 2.2 - Utilization Ratio with various BT by using QPSK

Filter Type

None,

Unfiltered Data

Butterworth

5th order

Bessel, 3rd

order

BW -50

dB point

(BT=I)

90 Rs

5.28 Rs

5.65 Rs

Util.

Ratio

BW -50

dB point

(BT=2)

I 90 Rs

17.05 8.74 Rs

15.93 10.26Rs

Util.

Ratio

10.29 Rs

8.77 Rs

BW -50

dB point

(BT=3)

90 Rs

11.15 Rs

13.93 Rs

Util.

Ratio

8.07

6.46

Table 2.2 shows the utilization ratio for various BT for the 5th order Butterworth filter

and the 3rd order Bessel filter. The 5th order Butterworth filter gives higher utilization

ratios than the 3rd order Bessel filter.

Table 2.3 shows the results of all three kinds of pulse shaping filters for QPSK, with

BT=I for the 5th order Butterworth and the 3rd order Bessel filters. For the SRRC filter,

it can be seen from Table 2.3 that the smaller _c is the higher the utilization ratio. The

SRRC filter with oc = 0.25 has the largest utilization ratio, then followed by the SRRC

filter with oc = 0.5 and oc = 1. The SRRC with oc = 0.25 and 0.5 have higher utilization

ratios than the 5th order Butterworth filter and the 3rd order Bessel filter. The SRRC with

oc = 1 has similar performance to the 5th order Butterworth filter.

21

Table2.3- UtilizationRatiofor QPSK

Filter Type -50dBBW (Rs) UtilizationRatio

None,UnfilteredData 90 1Butterworth5th order(BT=I) 5.28 17.05Bessel,3rdorder(BT=I) 5.65 15.93

4.28 21.034.60 19.565.30 16.98

SRRC(oc= 0.25)SRRC (_ = 0.5)SRRC (oc = 1)

Table 2.4 shows the utilization ratios for 8PSK and QPSK. In this case, the bandwidth

is defined in terms of bit rate (Rb). It can be seen that the utilization ratio of 8PSK is

higher than QPSK and from these results it would appear that 8PSK should be used rather

than QPSK However,

both before making a

advantages and disadvantages are:

1. QPSK has better signal to noise ratio (Eb/No) than 8PSK [5][8].

2. An 8PSK is a more complex and difficult system to implement than QPSK. Thus,

it is cheaper to implement QPSK in hardware than 8PSK.

3. QPSK has been used more otien than 8PSK so we do not need to change the system

that already exists.

4.8PSK is more bandwidth efficient.

one needs to compare the advantages and the disadvantages of

decision whether 8PSK or QPSK should be used. The other

Figure 2.21 was made from Table 2.4 to visualize the differences between the

utilization ratios of QPSK and 8PSK. It can be seen that the difference is almost 50% or

the utilization ratios for. 8PSK are twice of the utilization ratio of QPSK

22

Table2.4- UtilizationRatioQPSKVs. 8PSK[11]

Filter Type UtilizationRatio UtilizationRatio(QPSK) (8PSK)

1None.UnfilteredDataButterworth5thorder(BT=I)Bessel,3rdorder (BT=I)SRRC (oc = 0.25)SRRC (oc = 0.5)

SRRC (oc = 1)

8.52

7.96 16

117.39

10.51 23.59.78 23.5

8.49 18.18

Utilization Ratio on QPSK vs. 8PSK

25

20.

.£

15.n,

o

lO

5

r r r r r r r rr r r r - r r: r _r r r r:rr r :::r:: r:r:r:r:r:::-::r::::::W:::::: : : : ::; : ::i: :: :_:_::i:!::_:_:!:_:_:!::T:_:!:I::! !: : :: :_:: : : : : : : :_

iiiiiliiiiiiiiiii!iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii!iiii................iiiiiiii.................iiiiiiiiiiiiiiii!iiiiiii!iiii!iiiiiiiiiiiiiiii!iiiiiiii

1 2 3 4 5

Filter Type

i I_18PSK 1

Figure 2.21 The Utilization Ratio of QPSK and 8PSK

Note: 1 is the 5th order Butterworth filter

2 is the 3rd order Bessel filter

3 is the SRRC with oc = 0.25

4 is the SRRC with oc = 0.5

5 is the SRRC with oc = 1

23

Chapter 3

HARDWARE IMPLEMENTATION

This section will describe the hardware implementation of the system including the

results. The block diagram of the system is given in the Figure 3.1 below:

PowerQPSK _ Spectrum _ b_ AmplifierModulator Shaping

Up Converter

Figure 3.1 - The Block Diagram of The Hardware

The Quadrature Phase Shift Keying (QPSK) signal is produced by a QPSK

modulator at an Intermediate Frequency (IF) of 90 MHz. The pulse shaping filters or

spectrum shaping filters are used at the output of the modulator. The filters that are

used for this research are the 5th order Butterworth filter, the 3rd order Bessel filter

and the Square Root Raised Cosine (SRRC) filter with roll off factor of 0.25, 0.5 and

1. The selection of the filters was determined by the previous work done at JPL

[3],[4]. The up converter is needed to shift the signals to 2 GHz which is in the S-band

frequency range (1.55 GHz - 5.20 GHz). These shifted signals will enter the Power

Amplifier that is operated in its non-linear region to get the maximum power. Two

24

types of power amplifier are implemented: the Traveling Wave Tube Amplifier

(TWTA) and Solid State Power Amplifier (SSPA.) All of them work in the S-band

frequency range. The bandwidth utilization will be measured at the output of the

power amplifiers. This configuration follows the recommendation from the CCSDS for

spectrum shaping at the Intermediate Frequency (IF) [ 14],

The specifications that are designed and implemented on the system are:

1. The format of ideal data is NRZ-L.

2. Symbol rate : 5 Mbps (the maximum symbol rate that can be produced by liP

8782B ).

3. The modulation is QPSK with a carrier frequency = 90 MHz (at Intermediate

Frequency - IF).

4. The bandpass pulse shaping filters (do not include resistive and reactive losses)

with center frequency 90 MHz and bandwidth 5 MHz (BT=I), 10 MHz (BT=2)

and 15 MHz (BT=3):

- Butterworth 5th Order

- Bessel 3rd Order

- SRRC (roll of factor a =0.25, 0.5 and 1)

5. Power Amplifier works at S-band (1.55 GHz - 5.20 GHz) frequency range :

- For TWTA, the output power is 10 watts

- For SSPA, the output power is 0.6 watts

Note: 1. These two HPA's were selected because ESA currently uses the SSPA

type amplifier and the Tracking and Data Relay Satellite System (TDRSS)

25

usestheTWTA typeamplifier.Theactualsatellitewouldusemorepower,

but basedon the information from [15] the characteristics of the higher

power amplifiers have the same general shape. This being the case, lower

power was desired for safety purposes.

2. The complete procedure of the experiments are given in the appendix A.

3. All of the measurements of the power spectra are in dBm.

3.1 The QPSK Modulator

The HP 8782B is utilized to produce the 90 MHz QPSK signal as shown in Figure

3.2 below which was captured with the Digital Storage Oscilloscope (DSO) Lecroy

9384L. We can see that the signal has a constant envelope. The symbol rate of this

signal is 5 Mbps, thus the first nulls of its spectrum as shown in Figure 3.3 are 95 MHz

and 85 MHz respectively.

29-May-9718:38:43

.1 ps

8.58 V

682 mV

x axis

(time _s)

.2 ps

il.s v2 .5 v

3 .s

4 .5

i

L--12_J

_anpnmae I................

i 682"mV [ [ _[ [y axas (voltage)

51_22

AC

V f_C

V AC1 DC 8.21 q

MEASURE

Pepameteps

i_mode_

i_---tgpe_I Relative [

[ r=_-_,-,,,-aJ

I cupsop ]Position

1 GS/s

[] STOPPED

Figure 3.2 - The QPSK Signal that Produced By HP 8782B.

26

29-Mag-9718:22:41

:PS(RVGP(R))18 M_ I5.@ al_ I

541 m_]55 swps j

2 2 mV AC3 2 mV AC4 2 mV RC

ZOOM + MATH

.5 II=PS(FFT(1) )

- __ I-- xa_s t - REDEFINE C |

C:I I

REDEFINE0=2 O I, _ ,, ,, .. : ,, ; :, ; ,, ,. ,, i : .. i t

'vtVt90.00 MHz

,A:,!:_q_!,,,A,, &............li,Ar,,,,

AAA , a_z_JVv!,,

Fr'eq

1 DO0.28 v

FoP Math use lmax points /

10888 ]

1 GS/s

[] STOPPED

Figure 3.3 The Spectrum of the QPSK Signal at IF 90 MHz.

To count the bandwidth utilization or the bandwidth efficiency of the system, we

need to compare the bandwidth of the signal without the filters and with the filters at

the output of the high power amplifier. The hardware set up for the unfiltered signal is

shown in Figure 3.4. The QPSK signal is shifted up to S-band by using HP8657 B

Signal Generator. The spectrum analyzer Tektronix 492 is used to measure the

spectrum of the signal at S-band. For an example, Figure 3.5 shows the spectrum of

the unfiltered signal at the output of the SSPA. The figure was taken with the camera

since the spectrum analyzer Tektronix 492 does not have a printer feature.

27

90MHz

odulator8782B)

I

S-band : 2 GHz

Amplifier

Up Converter (HP 8657)2 GHz

DSO_'_ Lecroy

(9384L)

To measure and print the signaland the spectnmt at IF

I SpectrumAnalyzer

'](Tektronix 492)

To measure the

magnitude at S-Band

Figure 3.4 - The Hardware Set Up of Unfiltered Signal.

Figure 3.5 The Spectrum of The Unfiltered Signal at The Output of SSPA.

28

It can be seen in Figure 3.5 that the carrier frequency (2 GHz) is in the middle and

it has two side bands. Each side band represents the modulated signal in the IF. For an

example, the main lobe of the upper side band which is on the right side of the carrier

frequency has a center frequency at 2.091 GHz. The lower side band has a 1.909 GHz

center frequency. For analysis purposes, the upper side band is chosen. To measure the

bandwidth, the point -50 dB down from the peak of main lobe needs to be identified.

The bandwidth of the signal is measured from both sides of the center of the QPSK

spectrum that reach -50 dB from the main lobe. Both side bands are necessary due to

the lack of symmetry in the spectrum of the signal. All the bandwidths are measured

with respect to the symbol rate (Rs). By using the SSPA, the highest magnitude for the

upper side band which is at the right side of the 2GHz carrier is -2dBm. The -50 dB

point down is at 2.262 GHz on the right side of the main lobe and at 1.9195 Gt-Iz on

the left side of the main lobe. The difference between these frequencies is 342.5 MHz.

These results show that the unfiltered bandwidth at the output of the SSPA is 68.5 Rs

(68.5*5 Mbps = 342.5 ). The same procedure is used on the TWTA and the result is

67.9 Rs. All other output spectra of the HPA are performed using the same procedure.

The results are given later in this chapter. Note that the bandwidth that was found in

the software simulation (which has bandwidth 90 Rs), is larger than these results since

in hardware there is power dissipation. On the other hand, there is no power

dissipation in the software simulation and the system is close to the ideal system.

29

3.2 The Filters

A programmable Transversal Filter (PTF) is utilized as a pulse shaping filter by

downloading the coefficients of its 127 taps from a Personal Computer (PC). These

coefficients are created with MATLAB 2. The program listing is given in Appendix B.

The following steps are followed to create the program:

1. Matlab provides the functions to create the Butterworth and the Bessel filters. For

the SRRC, the Matlab function has to be programmed by using the equations that

are given in Chapter 2.

2. 128 coefficients are taken from the frequency response of the filters and they will be

used as the raw data for the 128 points of the taps of the PTF. The first coefficient

has to be deleted since the PTF has only 127 taps.

3. The odd coefficient has to be multiplied by -1.

4. Each coefficient has to be quantized to to have an integer value between -31

(minimum value) and 31 (maximum value). Then, the coefficients are ready to be

loaded to the filter by using the program : "loaddata.exe"

Figaare 3.6 shows the hardware set up for the filtered signal. As mentioned in

Chapter 2, there are three types of filters that are used: the 5th order Butterworth

filter, the 3rd order Bessel filter and the SRRC with ot = 0.25, 0.5 and 1. The symbol

rate for the QPSK signaling is 5 Mbps. The results from each filter will be explained in

the next section.

2 Matlab is a registered trademark of The MatWorks Inc., Cochituate Place, 24 Prime

Park Way, Natick, Mass. 01760.

3o

9O MHz

QPSKModul_or

(I-[P8782B)

I Computer [

90MHz S-band ' 2 GHz!

.._ Pulse ] _/,'_ _ Power

"- Shaping _ Amplifier[Filter (PTF)[ A (SSPA &

[ _ TWTA)

Up Converter 2GHz

DSOLecroy9384L

To measure the

magnitude and

phase at IF

Spectrum Analyzer

(Tektronix 492i

To measure the

magnitude at S-Band

Figure 3.6 - The Set Up for Filtered Signal

As mentioned before that to input the coefficients of the PTF's 127 taps, a

computer (PC) is needed. Two signals enter the Lecroy DSO, one from the QPSK

modulator and one from the PTF. These two signals are used to measure the phase

characteristic of the filter. The characteristic of the magnitude of the filters also will be

given later in the next section. The signals are shifted to the S-band frequency by using

the signal generator liP 865713. Two high power amplifiers have been used, the first is

a Traveling Wave Tube Amplifier (TWTA) that was made by the Hughes Aircraft

Company with serial number 8010H. The second one is the Solid State Power

Amplifier (SSPA) that was made by Mini Circuits with serial number ZHL-42. Both of

them were applied in the S-band frequency range.

31

3.2.1 The 5th Order Butterworth Filter

A 5th order Butterworth filter with BT of 1,2 and 3 (BT = the bandwidth of the

filter times the symbol rate (Rs) of the signal) was implemented. The signal at the

output of the filter for BT =2 is shown in Figure 3.7. It can be seen that it has a non-

constant envelope. The frequency response at the output of the filter is shown in

Figure 3.8 and the measured phase is given in Figure 3.9.

38-Mag-9719: 17:20

.1 ps

58 mV

68. _mV

x axis Itime (p s) [

I

HRROCOPY

-o_ut to--

|GPIB]RS232

Amplitude |Cent ton i CS60.8 mV

/ l

e Feed--On

i_11 protocol--

_ HP7478HP 7558--. TIFF

TIFF compr.

.1 ps

58 mV 50_2 .5 V RC 1GS/s

3 .s v nc _ I DC 27mV4 .5 V RC [] STOPPED

Figure 3.7 The Signal at The Output of The 5th order Butterworth Filter

32

38-May-9719:24:I8

I il_d,6°mlL|_.]t9o_t-.... _

I .... I ........ i

-42.4_m

Ij .... i

28 ns ?

50 mV _ Freq2 .5 V aC3 .5 U AC _ I DC 27mY

4 .5 V aC

MERSURE

B. I I

' ' ''__..... ' .... ''''I III

K 1-42.4dBm

I\t/" I'°_ t

99.88 MHz

[]

[ jOFF"Parametens

r--_--q[ nmp | irude Ii_t y p e-i----]

cursor ]Position

1 GS/s

STOPPEO

Figure 3.8 The Spectrum at The Output of The 5th Order Butterworth Filter

123

O)

aJ

t_

t--¢-j

The Measured Phase Response of The 5th Butterworth With BT=2200 , ,

, i

: i

-oo.i::!::::i::!i;iiiiiiiiiiiiiiii:ii-50

......... , .... i

a m

i I ! i I I

75 80 95 1O0 05

-100

-1507O 85 9O

#equency (MHz.)

Figure 3.9 The Measured Phase Characteristic of the 5th Order Butterworth filter

33

As a comparison,Figures3.10and 3.11showthe frequencyresponseand phase

responsethat werecreatedin Matlabwith BT=2 (thesameBT usedfor the hardware

implementation).Theoretically,with BT=2, thebandwidthis 10MHz andthe cut off

frequency(-3dB down)areat 85MHz and95MHz. However,we arenot concerned

with the -3dB bandwidth, we are concerned with the -50 dB andwidth. From the

hardware implementation results, we get that the -50dB point are at 60 MHz and 101

MHz, thus, the bandwidth is 41 MHz. It can be seen that they have similar forms. For

an example, the phase response on the simulation has a similar pattern with the

measured one. The phase has transitions on the cut off frequency that will affect the

signal in the passband region.

Figure 3. l 0 The 5th Order Butterworth Simulated Frequency Response

34

Q9

(1)

if)

t'-

£L

150

100

50

0

-5O

-10010_

The Phase of The 5rd Order Butte_orth with BT=2

I I I I I I I I I I , ! I I I I Ii t I i _ i i i u i i I | i

, i i | _ _ I i I | i i i ! i

i : .............i M i 1 i U I J i J I i m

I S i N 1 i i m i , i

I i Z i _ i i J I J | iS I , I I i i I J I I

i I I | i i I i I 1 I...... "-,---_ ......., "i- ''ii ............. _--_'-t-T_-,

i i i i i

, ' i : : i'i , , i I s

l l i , i i I

..... it i !

i i I

i g I i ,

, i i l , ,

I I i i I i

i I i J i i

i | i i i i

i | i i i i

, i i , i ,

, l i , i i ,

| i i , i _ ,

! i I i

i i i |

i i I Ii i i i

i i iJ i i i

i i i i

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108

Frequency (Hz)

, , , | | i

, _ i i , !............ ¢- - i- -i- T..I =._

, i , i ! ,

i i , i i i

, i ! _ , | s

10 g

Figure 3.11 The 5th Order Butterworth Simulated Phase Response

The frequency response of the signal at the output of the high power amplifier, for

the SSPA, is given in Figure 3.12. The maximum point of the upper side band

spectrum is -26 dBm By using the same procedure as was given previously, the -50

dB points for the SSPA (operated at its saturation region) are at 2.128 GHz and

2.0535 GHz. Thus the bandwidth is equal to 14.9 Rs or 74.5 MHz. The difference

between this bandwidth and the bandwidth at IF is 74.5 MHz - 41 MHz = 33.5 MHz.

This is due to the fact that the SSPA is in its saturated region. The complete results

are given in section 3.4 (section on bandwidth utilization).

35

Figure3.12 TheSpectrumat TheOutputof SSPAof The5thorderButterworth

3.2.2The 3rd Order Bessel filter

The second filter that has been used is the 3rd order Bessel filter with BT 1,2 and

3. The filter output for BT=2 is shown in Figure 3.13. It can be seen that it also has a

non-constant envelope. Comparing this to the signal at the output of the 5th order

Butterworth filter shows that this signal has a larger deviation in its amplitude. The

frequency response at the output of the filter which was taken with the Lecroy DSO

93 84L is shown in Figure 3.14 and the measured phase is given in Figure 3.15.

36

38-Mag-9719:33:88

2 Us

8 mV

95.2 mV

x axis Itime (_LS) I

I

MEASURE

/-, 95.2 mV__Jy axis

I__ _-_ "aVe" - a'--mplitude/

lllpr,,I,"

Parameters

(mV) r-----mode--_

I Relative I

.2 ps

58 mv _2 .5 v AC

3 .5 V nC4 .s v AC

Amplitude100mV :/ ..... :f_:_;e4,L ....

- 0.2_s_ _90MHz.

1 DC 27 mV

cursorPosition

I GS/s

[] STOPPED

Figure 3.13 The Signal at The Output of The 3rd Order Bessel Filter

30-May-9719:35:51

r_:PS(aVGp(R)) _' _ _ + " XisPOwer(dBm)lie MH_ t/ 7.6 _" I1-iZ.526 d8, /

15 4 SUps ) ...................

...................LI :,_651Vfl-I_ [ [\ /_./ t _ffl ll°MH_

100MHz

MEASURE

Parameters

p i itude J

cursor ]Position

28 ns

58 RV 51_ Freq 98.88 M

2 .5 V AC 1 GS/s

3 .5 v AC __F I DO 27mY4 .5 V AC [] STOPPED

Figure 3.14 The Spectrum at The Output of The 3rd Order Bessel Filter

37

150The Measured Phase Response of The 3rd Order Bessel with BT=2

100

50

0

El_

-50

-I00

-150

i i i, , o

1

70 75 80 85 90 95 100 105Frequency (MHz.)

Figure 3.15 The Measured Phase of the 3rd Order Bessel Filter.

Again, as a comparison, Figure 3.16 and 3.17 show the frequency response and

phase response that were created with Matlab with BT=2 (the same BT used for the

hardware implementation). It can be seen that the frequency response for the hardware

implementation has a wider bandwidth than the software simulation. The software

simulation has cutoff frequencies at 85 MHz and 95 MHz. The -50 dB points are at

65 MHz and 110 MHz. Thus the bandwidth is 45 MHz.

The frequency response of the signal at the output of the high power amplifier, in

this particular case the SSPA is chosen again, is given in Figure 3.18. The maximum

value of the upper side band spectrum is -20 dBm. By using the same procedure as

that mentioned previously, the -50 dB points for the SSPA are at 2.1335 GHz and

38

2.049 GHz. Thus the bandwidth is equal to 16.9 Rs or 84.5 MHz. The difference

between the bandwidth at IF and the bandwidth at S-band is 84.5 MHz - 45 MHz =

39.5 MHz. The phase response on the simulation also has a pattern similar to the

measured one. The complete results are given in the section on bandwidth utilization,

Section 3.4.

.i0°

._. -101m

t--

05

.10

.103107

The Spectrum of The3rd OrderBessel With BT=2I I I I I I I I ! I I I I I I I

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........ 4, .... .J... J- * J. -I. -I,..I _ I ......... I- .... J- -. &__&.,.I. J_ J_L........ s .... J___J..J._L_L ............ L.... ,___ ,_.__J. J_J_-

I I I I I I I I I I I I I I I

I I I I I I I I I I I I I I

I I I I I I I I I I I I I I

I I I I I I I I I I I I I I

........ T .... "_" - "_" - "l- -r -i- "T ........ i" .... 1--- T-'T''_- _-]-r

i i l i i i i i i i i i i i i i

i i i i i i i i i i i i i i i I i

........ T ..... ,-- "',- "-,--,--_ ,-T', ........ ,..... _ - -- T -" T "-,--,-_ "FI I I I I I I I I I I I I I I I

:::::::::::::::::::::::::::::........T ..... ,'''_--_- mI---- --I" 7"1 ....... I ..... "1-- m-- _ "-- T --ml-- --I" ]'_"

........ .@ .... ,=4. -- .-4 = ==,@= . . I,..I. 4,. I........ 1,. .... =0 = .. ,_ = = 4, = _..,if..4. k

l I I I I I I I I I I I I I I I

........ T ..... ,--'', .... _'_'," T', ....... F .... _-'" T'" T-',* 3" 3"P

....... .jjJ>___=_J_ _ .J.._l_ -L _L_l. L.' ......... L -.. _ ...L .J- J. J .L......... •-I- - -.-4- -.4- -I,- - I- -I- e-I ......... I- .... ,4 .... -I- ,4 -p-,=-=-'--"-_ ," -- "F-- _- -", "F-F': ,-_---------F .... _---_

| I I | I I I | I I I | I I I I I

| I I I I | I | I I I | I I I I I

I I I I I I I I I I I I I I I I I

I I I I I I I I I I I I I I I I I

I I I I I I I I I | I I I I I I I

| I I I I I I I I I I I I I I I I

........ T .... "1- " "'1 = "'1" "1" "r'l" f'I ......... /" .... 1 - "" T -" T ''_- "_" 1 -r

........ ¢ .... j_..j..j_ _1. _L i 11 ......... L .... j. _. i _. I _J. J_ J _L

i i i i i i i i i | i i i i I i I

........ T .... "1" " "'l- "'1" "r" " I"'1" T-I ......... r .... '1 - "" T "" '1' "-i" "l" 1 "r........ , .... ,._.,_ _.,__,..,._,_,.,......... ,..... .,._.,_.,..,..,.,_,

........ T .... -I" - - "l- "'1 - "1- -i'-I" T "1 ......... I" ......... 1T T "'1" "1" "1 -r

........ T ..... ,----,---,""£ -F',"T"i......... ,".... _" "" T-'T --_"-,"3-r

10 109

Frequency(Hz)

Figure 3.16 The 3rd Order Bessel Filter Simulated Frequency Response.

39

The Phase of The 3rd Order Bessel with BT=2200 .............

, i i , i , i i , i i , i

i i i i i i I i i _ ii , i i i i , i I i i i

i i , i , , i i, I I i _ i , i , i i i I I

i i i i I i t i i i i i i ii i i i i i i i t i m ; i i i

100 .........•....---'--"--"_-'-T-I

I I I , I , I q

I I I I | I I I ; I I I I I I

I I o | I I 1 1

, D I , I I I I , i I I I i | ,

I I I I I I I , , I i I , I I

I t I l I I I I I I

I I I I I I , I I I I , , I I

l I I I I j , I , i , I I

| J I I I I I | II i , * I I I , , , I , i i I

0 .......................................................... ;'"i i I i m i t i i i i i i I

i i i i i i , i , i i i |

i i i i t i ; i J i i i i

i I i i i I _ i i I i i i i

-100 ............................................................. ,, ,, ,, ,, ,,..... , : :':', : ', ', , ',, ', .....

-200 .....10_ 10_ 10_

Frequency (Hz)

Figure 3.17 The 3rd Order Bessel Filter Simulated Phase Response.

Figure 3.18 The Spectrum at The Output of SSPA of The 3rd Order Bessel Filter

40

3.2.3 The Square Root Raised Cosine (SRRC) Filter

The last filter that has been used is the SRRC with the roll offfactor ot=0.25, 0.5

and 1. For an example, the SRRC with (z=0.5 is chosen. The signal at the filter output

is shown in Figure 3.19 below. It can be seen that it also has a non-constant envelope.

It's envelope is close to a constant envelope for a particular time range and then has a

zero crossing. The frequency response at the output of the filter which was taken with

Lecroy DSO 9384L is shown in Figure 3.20 and the measured phase is given in Figure

3.21. The -50 dB points at IF are 88 MHz and 102 MHz, the bandwidth is 34 MHz or

6.8 Rs.

.1 IJS

58 mV

64.2mV

X axis ÷

time (g s)

.1 ps

58 mV _2 .5 v nc3 .s v Ac4 .s v Ac

MEASURE

amplitude 1 I I [ off•I t lya-_samp"tude(m'_LI [Po_a_ete_s]

[ m_nnm 1NINIIWHIIIUli ,JNWliIUfl$ ,.,J IlU,"llllt $N WlllrrlMmm oF om

r..... ],'"ll_nlp \ ",pllltltll[' 'tl'tll,,' I""m}'"'rqll' 'FIrlqlll|

............ 50 mV .......... cupsoe

[ Position 1

I GS/s

__I-- I De 3mvi-I STOPPED

Figure 3.19 The Signal at The Output of The SRRC Filter with ot = 0.5

41

39-May-97 MEASURE

Fie M_ I I I I/_m I J $ lYaX'sp°wertaum) l I I [ Parameter's J

17.3 aB, 1 _N_---I90MHz _----_/-16.232 dB, t t 1 t I1 /I\1 t I 't .... I t_---- 8_O_p_ __

I_ I/ $ \1 I I I I I_--type-------Q

Lpos,t,ooj28 ns

D 58 mV 51:_ FPeq 98.88 M Hz2 - 5 b' AC l GS/s

3 .5 v ac _ l OC tmv4 .5 v AC [] STOPPED

Figure 3.20 The Spectrum at The Output of The SRRC Filter with o_ = 0.5

A

..¢::Q_

IO0

60

0

-50

The 3hase measured of SI_IRC with alpha=O 5

,, ,

i

-10070 75 80 85 90 95 1O0 105

frequency (MHz)

Figaare 3.21 The Phase Measured at The Output of The SRRC Filter with o_ = 0.5

42

For the SRRC filters, the measured phase response cannot be compared with the

software because the phase with the software was made with respect to the number of

Fast Fourier Transform Coefficients (FFT) not with respect to the frequency (see

Figure 3.22 Below). It can be seen that Figure 3.21 and Figure 3.22 are totally

different.

200

160

100CD

O_

c-"

c_

5O

The Phase Response of SRRC with alpha=0.5

- -] ..... t" "

/

- - _ ..... r .... I

!

|

2O

I

i

-'i -°'

00 40

I

Im

.... I--"

i

i

i

ir

b

t

t

t--'

t

i

i

i

i

i

i

i

i

i

:i°-

60 80# of FFT point

I I

, t

i

..... 1 ........ L_

;I

!l,

100 120 140

Figure 3.22 The SRRC filter (et = 0.5) Simulated Phase Response

The frequency response of the signal at the output of the high power amplifier, in

this particular case the SSPA is chosen again, is given in Figure 3.23. The -50 dB

points for this SRRC filter are at 2.109 GHz and 2.073 GHz. Thus the bandwidth is

equal to 36 MHz or 7.2 Rs. The complete results are given in Section 4.3.

43

Figure3.23 TheSpectrumatTheOutputof SSPAwith TheSRRCFilter c_= 0.5

3.3 The Power Amplifier

As mentionedin Chapter2, the power amplifierscanbe utilized in one of two

regions,eitherin a linear regionor in a non-linearregion. High frequency power

amplifiers such as Traveling-Wave Tubes (TWT) and Solid State Power Amplifier

(SSPA) can be linear amplifiers when operated well below the saturation level. In this

work, both of" them have been utilized in their non-linear (saturation) region to

maximize the signal power

Figure 3.24 shows the set up configuration to measure the characteristics of the

TWTA and the SSPA In this case, we define the characteristic of the high power

44

amplifierasa magnitudecharacteristic(the output power as a function of the input

power) and as a phase characteristic (the output phase as a function of the power

input). To measure the output magnitude of the power amplifier, a 2 GHz sinusoid

signal generated by the HP 8657B was used. Tektronix 492 spectrum analyzer was

used to measure the magnitude of the signal spectrum. To measure the phase

shift, the down converter is needed to shift the frequency of the signal down from S-

band to the IF. The DSO Lecroy 9384L was used to see and measure the phase

difference between the signal before and after the power amplifiers.

SignalGenerator

HP 8657B

S-band " 2 GHz

Down Converter

2GHz

--rAmplifier

Spectrum

Analyzer

(Tektronix 492)

To measure the

magnitude at S-band

DSO Lecroy9384L

To measure the

phase shift

Figure 3.24 - The Measurement of The Characteristic of Power Amplifier

45

The plot of the characteristics of the TWTA are given in Figure 3.25 for the

magnitude and Figure 3.26 for the phase. The SSPA characteristics are given in

Figure 3.27 and in Figure 3.28. As mentioned in Chapter 2, the SSPA has less power

and a lower dynamic range, which is verified from these results. For the magnitude, the

characteristic of the TWTA has a wider non linear region than the S SPA. The TWTA

has a larger phase shift than the SSPA. Comparing these results to the SSPA European

Space Agency (ESA) 10 Watts Magnitude and Phase characteristics' (Figure 2.11 and

Figure 2.12), we can see that both of the magnitude characteristics are similar,

however the phase characteristics are different.

The Magnitude Characteristic of TWTA6 I I I

32

I I I I

-10 -5 0 5 10Power in (dbm)

15

Figure 3.25 - The Characteristic of Magnitude of TWTA

46

-5O

%--100

O")

-15013_

The Phase Characteristic of TWTA

-200

-250-10

j i, ,, ,

-5 0 5 10 15

Power in (dbm)

Figure 3.26 - The Characteristic of Phase of TWTA

22

21

20

E

"_19

o

$18O

[3-

17

16

15-8

The Magnitude Characteristic of SSPA, , )K )K )K _i i ,/ i i

......... i... ....... J ........ /. .......... .L ........ '- ........

, i , I , I

, , , , ,, ,,........ i. ....... j ...... .i......... i. ........ .L ........ _ ........

| t , z i i

:_ .................... ,......... ,......... ,- .......

: , i i , ,

i... d ___.1 ....... i.. ........ ,- ....... -' ........

; , , , , ,,

z ', "

Ji i izrx

-6 -4 -2 0 2 4 6

Power in (dbm)

Figure 3.27 - The Characteristic of Magnitude of S SPA

47

-10

-15

o.)

-20

13._

-25

-30-8

The Phase Characteristic of SSPA

,,

,,

.....iiiiiiiiiiiiiiiiiIIIIILiii i i i i n

-6 -4 -2 0 2 4 6Power in (dbm)

Figure 3.28 - The Characteristic of Phase of SSPA

3.29 The example of the output of TWTA with 3rd order Bessel filter

48

Figure 3.29 and Figure 3.18 (shown in page 40) show the effects on the spectrum

of the signal with the same filter (3rd order Bessel filter) but with different high power

amplifiers. It can be seen that with the TWTA (Figure 3.29), there is a spurious

emission in the spectrum between the carrier frequency (2 GHz) and the filtered

spectrum. Figure 3.29 shows that the upper side band has the maximum magnitude -19

dBm and the spurious emission has the maximum magnitude -38 dBm. It means that

the spurious emission is still within the -50 dB range of the filtered spectrum. On the

other hand, with the SSPA (Figure 3.18) there is no spurious emission. This spurious

emission will reduce the utilization ratio of the TWTA as shown in the next section.

3.4 Bandwidth Utilization

The purpose of this section is to investigate the bandwidth efficiency or the

bandwidth utilization by using pulse shaping on QPSK over a non-linear channel As

mentioned in Chapter 2 that to see the overall effect of spectrum shaping, a frequency

band Utilization Ratio (p) was defined as [3]:

O = The Bandwidth of the signal without Filtering

The bandwidth of the signal with Filtering

Table 3.1 shows the utilization ratio for filters used with the TWTA. Without

spurious emissions, the pulse shaping gives significant improvement on bandwidth

efficiency. It can be seen that if the spurious emissions from the TWTA are counted,

49

the utilization ratio becomes smaller. The SSPA utilization ratios are shown in Table

3.2. The SSPA has no spurious emissions and the pulse shaping here also gives

significant improvement on the bandwidth efficiency compared to the unfiltered signal.

If the SSPA and the TWTA without spurious emissions are being compared, the

results are about the same. The only disadvantage for the TWTA is that the spurious

emission exists and it takes up more of the bandwidth. This will reduce the utilization

ratio.

For the SRRC filter, it can be seen from Table 3.1 and Table 3.2 that the smaller oc

is the higher the utilization ratio becomes. This pattern follows the pattern from

software simulation results. The SRRC with oc = 0.25 has similar performance to the

5th order the Butterworth filter and the SRRC with oc = 0.5 has similar performance

to the 3rd order Bessel filter and the SRRC with oc = 1 has the worst utilization ratio.

Table 3.1 - Utilization Ratio with TWTA

Filter Type

None, Unfiltered Data (reference

Butterworth 5th order

Bessel, 3rd order

SRRC (oc = 0.25)

SRRC = 0.5)SRRC (oc = 1)

only filter-50 dB

point w/o

spu.emis67.9 Rs

Utilization

Ratio of

TWTA

with

spu. emis.

spec -50

dB point67.9 Rs

Utilization

Ratio of

TWTA

1 1

7.4 Rs 9.17 26.8 Rs 2.53

8.5 Rs 7.98 27.2 Rs 2.49

6.6 Rs 10.28 24.9 Rs 2.73

7.3 Rs 9.30 26.1 Rs 2.60

9.0 Rs 7.54 28.1 Rs 2.41

50

Table3.2 - UtilizationRatiowith SSPA

FilterType

None,UnfilteredData (reference)Butterworth5th order(BT=I)Bessel,3rdorder(BT=I)SRRC(oc= 0.25)

se,Rc = 0.5)SRRC (oc = 1)

SSPA

-5O dB

point68.5 Rs

Utilization

Ratio of

hardware

1

7.5 Rs 9.13

8.3 Rs 8.25

6.1 Rs 11.23

7.2 Rs 9.51

9.1 Rs 7.53

Table 3.3 shows the comparison between the software simulations and the

hardware implementations. The utilization ratios from the hardware implementations

are smaller than the results for the software simulation. Even with the differences, the

hardware implementation still gives a significant improvement over the non-filtered

system. The pulse shaping technique does give significant improvement in bandwidth

efficiency for QPSK signaling over a non-linear channel.

Table 3.3 - Utilization Ratio on QPSK software and hardware with SSPA

Filter Type -50 dB Util. Ratio -50 dB Util. Ratio

BW (SW) (SW) BW (HW) (HW)

None, Unfiltered Data 90 Rs 1 68.5 Rs 1

Butterworth 5th order (BT=I) 5.28 Rs 17.05 7.5 Rs 9.13

Bessel, 3rd order (BT=I) 5.65 Rs 15.93 8.3 Rs 8.25

SRRC (oc = 0.25) 4.28 Rs 21.03 6.1 Rs 11.23

!SRRC (oc = 0.5) 4.60 Rs 19.56 7.2Rs 9.51

SRRC (oc = 1) 5.30 Rs 16.98 9.1 Rs 7.53

* Note : SW = software simulation and HW= hardware implementation

51

Table 3.4 and Figure 3.30 show the comparisonof utilization ratios for the

software and the hardwareresults for the 3rd order Bessel and the 5th order

Butterworth filters with BT=I,2 and 3 using the SSPA.As the BT increases,the

utilization ratio decreasesrapidly from BT=I to BT=2, and decreasesslowly from

BT=2 to BT=3. The utilization ratios for the hardwareimplementationfor the 5th

orderButterworth aresmallerthanthe softwareimplementation.The utilization ratio

of the hardwareimplementationfor the 3rd order Besselare also less than the

softwareimplementation.It canbeseenfrom Table3.4that the 5thorderButterworth

is recommendedover the 3rd order Besselfilter. Theseresultsalso show that the

hardware implementationis not perfect but does follow the software simulation

results.

Table3.4- Utilization Ratiowith variousBT byusingSSPA

FilterType

None,(sw)Unfiltered

Butterworth5th (sw)

Bessel,3rdorder(sw)

None,(hw) Unfiltered

Butterworth5th(hw)

Bessel,3rdorder (hw)

BW -50dB point(BT=I)90 Rs

Util.Ratio

BW -50dB point(BT=2)90 Rs

Util.Ratio

BW -50dB point(BT=3)90 Rs

5.28Rs 17.05 8.74Rs 10.29 11.15Rs

5.65Rs 15.93 10.26Rs 8.77 13.93Rs

68.5 Rs 1 68.5Rs 1 68.5Rs

4.59

4.05

7.5 Rs

8.3Rs

9.13

8.25

14.9Rs

16.9Rs

22.16Rs

25.47Rs

* Note : sw= softwaresimulationhw= hardwareimplementation

Util.ratio

1

8.07

6.46

1

3.09

2.69

52

18___ :: :: j16 .... _.lB_ [ .... i ..........

14 ........ 4............... :...... '-............

_......._.-4_o_o_-_ ............/hardware| [ ',

i i

2 ' 'I I

1.5 2 2.5 3

Figure 3.30 The Comparison between software and hardware on the Bessel and

the Butterworth filters

53

Chapter 4

CONCLUSION AND RECOMMENDATIONS

This section will explain the conclusions and suggestions for further study from the

research of the effect of pulse shaping QPSK on bandwidth efficiency over non-linear

channels that consists of the software simulations and the hardware implementations.

4.1 Conclusion

For the simple but practical systems studied, pulse shaping on QPSK signaling does

provide the bandwidth efficiency that was indicated through software simulations.

Regarding QPSK and 8PSK schemes, with the same filters and with respect to bit

rate (Rb), the results show that 8PSK has higher utilization ratios than QPSK. In

general, 8PSK contains more information than QPSK, however QPSK has better

performance against noise (Eb/No)[5][8]. From the hardware point of view, QPSK is

used more often than 8PSK and QPSK has a simpler and less expensive hardware

implementation than 8PSK So, there are trade offs that should be considered in

making decisions whether QPSK or 8PSK is utilized.

Regarding the software simulations, the SRRC filters with (z=0.25,0.5 have the

highest utilization ratio. Then, they are followed by the 5th order Butterworth filter,

SRRC ot=l and the 3rd order Bessel. For the SRRC family, we can see that the higher

the roll off factor the lower the utilization ratio.

54

Concerning the hardware implementations, the SRRC filter with ot=0.25 has the

highest utilization ratio. Then, followed by the 5th order Butterworth filter, the SRRC

filters with c_=0.5 and the 3rd order Bessel filter. The SRRC filter with o_=1 has the

lowest utilization ratio. The 5th order Butterworth filter is recommended over the 3rd

order Bessel filter. For the SRRC, it can be seen that the smaller the roll offfactor the

narrower the bandwidth and the higher utilization ratio. This result follows the

software simulation results. It is shown that the hardware implementation results are

not as good as the software simulation results. This follows from the fact that the

hardware implementations include non ideal components while the software

simulations reflect ideal conditions.

The SSPA provides a more linear magnitude characteristic and less phase shift

compared to the TWTA. Eventhough the TWTA has higher power and a wider

dynamic range, the SSPA still gives better frequency response since it has no spurious

emissions in its spectrum when it is utilized in its non-linear region (saturation region).

These spurious emissions reduce the utilization ratio of the bandwidth.

4.2 Recommendations

For future investigation, there are some suggestions for further study:

1. Build a receiver and perform the Bit Error Rate (BER) data runs.

2. Implement 8PSK signaling scheme in hardware.

3. To place the pulse shaping filter before the modulator and hold everything else

55

fixed.This would need three PTF filters.Thiswill also givea constantenvelope

signal.

4. To use the 3rdorderButterworthfilter andthe5thorderBesselfilter on thepulse

shapingfiltersandcomparetheresults.

56

REFERENCES

[1] Warren L. Martin and Tien M. Nguyen, "CCSDC - SFCG Efficient Modulation

Methods Study, A Comparison of Modulation Schemes, Phase 1: Bandwidth

Utilization (Response to SFCG Action Item 12/32)," SFCG-13, Ottawa Canada,

13-21 October 1993, report dated 24 September 1993.

[2] Dr. Manfred Otter, "CCSDC - SFCG Efficient Modulation Methods Study, A

Comparison of Modulation schemes, Phase lb: A Comparison of QPSK,

OQPSK, BPSK, and GMSK Modulation Systems (Response to SFCG Action

Item 12/32)," European Space Agency/ESOC, Member CCSDS Subpanel 1E,

(RF and Modulation), June 1994.

[3] Warren L. Martin and Tien M. Nguyen, "CCSDC - SFCG Efficient Modulation

Methods Study, A Comparison of Modulation Schemes, Phase 2: Spectrum

Shaping (Response to SFCG Action Item 12/32)," SFCG Meeting, Rothenberg,

Germany 14-23 September 1994, report dated August 1994.

[4] Warren L. Martin, Tien M Nguyen, Aseel Anabtawi, Sami M. Hinedi, Loc V.

Lain and Mazen M. Shihabi, "CCSDC - SFCG Efficient Modulation Methods

Study Phase 3: End-to-End System Performance," Jet Propulsion Laboratory,

April 1997.

[5] John G. Proakis, "Digital Communications," McGraw-Hill, 1995, Third Edition.

[6] "Acoustic Charge transport Technology: Principles and Applications," Comlinear

Corporation, 1992.

57

[7] AndreasAntoniou,"Digital Filters:AnalysisandDesign,"McGraw-Hill,1979.

[8] Leon W. Couch II, "Digital and Analog CommunicationSystems,"Macmillan

PublishingCompany,1993, FourthEdition.

[9] StephenHoran, "Introduction to PCM TelemeteringSystems,"CRC PressInc.

1993.

[ 10]LonnieC. Ludeman,"Fundamentalsof Digital Signal Processing," John Wiley &

Sons, 1986.

[ 11] Ruben Caballero, B.Eng, "8-PSK Signaling Over Non-Linear Satellite Channels,"

Master Thesis, New Mexico State University, May 1996.

[12]"Noise Generator NC 6108 Operating Manual," Noise Com. Inc, 1990.

[ 13] "RF/IF Designer's Handbook," Mini Circuits, 1993.

[14] G. Block, "Efficient Modulation Study," Consultative Committee For Space Data

System, Interim Report, April 1997.

[15]"TWT/TWTA Handbook", Hughes Aircraft Company, Electron Dynamics

Division, 1992.

58

Appendix A

THE TEST PROCEDURE FOR

HARDWARE IMPLEMENTATION

This section will explain the test procedure for the hardware implementation. The

block diagram of the system is given in Figure A. 1.

QPSK

Modulator

Spectrum

Shaping

Up Converter

Figure A. 1 - The Block Diagram of The System

Power

Amplifier

The liP 8782B Vector Signal Analyzer is utilized to produce the 90 MHz QPSK

signal. The QPSK signal goes to the spectrum shaping filter. The filters that are used

for this research are the 5th order Butterworth filter, the 3rd order Bessel filter and the

Square Root Raised Cosine (SRRC) filter with roll of factor 0.25, 0.5 and 1. The up

converter is needed to shift the signals to S-band frequency (1.55 GHz - 5.20 GHz).

These shifted signals will enter the Power Amplifier that is operated in its non-linear

region to get the maximum power. There are two kinds of power amplifier that have

59

been used: the Traveling Wave Tube Amplifier (TWTA) and Solid

Amplifier (SSPA.) All of them work in the S-band frequency range.

There are three different hardware configurations that have been used:

1. To measure the unfiltered signal.

2. To measure the filtered signal.

3. To measure the characteristic of the high power amplifier.

State Power

A.1. The Set Up For The Unfiltered Signal

The hardware set up for the unfiltered signal is given in Fig_are A. 1 below.

S-band " 2 GHz90MHz

.I owerodulator Amplifier

[(HP 8782B)

Up Converter (HP 8657)2 GHz

SP ectrumAnalyzer

(Tektronix 492)

To measure the

magnitude at S-Band

DSO [Lecroy

(9384L)

To measure and print the signal

and the spectrum at IF

Figure 3.4 - The Hardware Set Up of Unfilter Signal

The following steps are utilized:

1. The QPSK modulator (HP 8782B) should have the following condition:

1.1 The modulation on.

6O

1.2 The Rf output on.

1.3 Prbs on.

1.4 Set frequency to 90 MHz.

1.5 Set the modulation to QPSK

1.6 Set level as desired, usually from the lower value, for example -10 dBm to the

higher value.

1.7 Connect the Rf output to channel 1 ofDSO Lecroy 9384L by using the RG

58A/u coaxial cable. Use the same cable to the mixer.

2. The signal generator for up converter (HP 8657) should have the following set up:

2.1 Set the Rf output on.

2.2 Set the frequency 2000 MHz.

2.3 Set the amplitude as desired.

2.4 The RG 8A/u 50 ohms cable (the thick one) is used to connect the output to the

mixer.

3. The mixer is ZFM 4212 of Mini Circuits.

4. There are two high power amplifiers that have been used. The first one is a

Traveling Wave Tube Amplifier (TWTA) that was made by the Hughes Aircraft

Company with a serial number 8010H. The second one is the Solid State Power

Amplifier (SSPA) that was made by Mini Circuits with a serial number ZHL-42

Both of them were implemented in the S-band frequency range.

4.1 For the 8010 H TWTA, the following steps should be followed:

61

4.1.1 Before operating the TWTA, be sure that the

coaxial directional

directional coupler

output is connected to a

coupler and the load. In this case, the coaxial

of Narda Corp., model: 3003- 10 with a serial

number21540 has been used. The directional coupler has two outputs,

one goes to the load and the other one which has-10 dB attenuation

is connected to the spectrum analyzer the Tektronix 492 with The

RG 8A/u50 ohms cable (the thick one). The load is the N 9525

ARRA load with serial number 858.

DO NOT OPERATE THE TWT WITHOUT THE COAXIAL

DIRECTIONAL COUPLER AND THE LOAD. YOU WILL

DESTROY THE TWTA.

4.1.2 Turn on the power, but don't turn on the operate switch. It is

necessary to wait for 15 minutes to let the tube warm up.

4.1.3 Turn on the operate switch. During the operation, pay attention to

the helix current light, faults light and operate light. If the faults light

comes on and gives an error message, turn off the operating switch

immediately. If it is necessary, turn off the power switch also.

4.1.4 For safety reasons, turn offthe operating switch after it has been used for

more than 15 minutes. The power does not need to be turned off. Wait

for about l0 minutes then turn on and start operating again.

5. The following steps are used to measure the spectrum of the signal by using DSO

62

Lecroy9384L:

5.1Usechannel1asaterminalto theDSO.

5.2Pressautosetup.

5.3Pressmathsetup,followedbyredefinedA andansweryesto confirm.

5.4SelectFFT andpowerspectrafrom themenu.

5.5Don't forget to selectof channel1, sincethe signal canusechannelI asa

terminalinput.

5.6AverageFFT is desired.In orderto do that,pressmath setup againand

redefinedB.

5.7SelectFFTAVG andpowerspectrafrom themenu.

5.8 Selectof A, to get FFT average of the FFT of the signal.

6. The following steps are used to save the signal to the floppy disk and insert it into

the word processor i.e. Microsoft word:

6.1 Press utilities.

6.2 Select hardcopy setup.

6.3 Select flpy for floppy disk and insert the floppy disk into the drive.

6.4 Select protocol : BMP, the format of the file that will be saved.

6.5 Press screen dump and the file will be saved.

63

A.2. The Set Up For The Filtered Signal

The hardware set up for the filtered signal is given in Figure A.2

9o MHz

QPSKModulator

(HP8782B)

..._ Pulse

"- ShapingFilter (PTF)

DSOW-- Lecroy

9384L

To measure the

magnitude andphase at IF

Computer I

I 90MHz S-band " 2 GHz

Power

Amplifier(SSPA &

TWTA)

Up Converter 2GHz

_T Spectrum Analyzer

(Tektronix 492) I

magnitude at S-Band

Figaare A.2 - The Hardware Set Up of Filter Signal

Most of the system and the set up steps are same as before, but add the following

steps:

1. A programmable Transversal Filter (PTF) of Comlinear Corp is utilized as a

pulse shaping filter by downloading the coefficients of its 127 taps through the

Personal Computer (PC). These coefficients are created with MATLAB. The

program listing is given in appendix B.

2. Connect the parallel port of the computer to the parallel port of the PTF.

3. Don't forget to connect the PTF to the power supply with polarity +12 and -5.

4. REMEMBER THAT THE MAXIMUM POWER INPUT IS 10 dBm. IF WE

64

EXCEED THIS VALUE, WE MAY DESTROY THE PTF.

5. Everytime we want use the PTF, we need to load the coefficients that have been

made with MATLAB to the PTF by using the file "Loaddataexe".

A.3. The Set Up For The Measurement Of The Power Amplifier

The hardware set up for the filtered signal is given in Figure A.3.

SignalGenerator

HP 8657B

S-band • 2 GHz

] PowerA m plifier

Down Converter

2GHz

Spectrum

Analyzer

(Tektronix 492)

To measure the

magnitude at S-band

DSO Lector

9384L

To measure the

phase shift

Figure A.3 - The Measurement of The Characteristic of Power Amplifier

Follow the same steps as before, but add:

1. The signal generator 8657B is used as a source to the power amplifier and as a

signal multiplier to the output of the signal output of power amplifier.

2. All of the connections on the S-band frequency range have to use the RG 8a/u 50

ohm (the thick one).

65

Appendix B

THE SPW DETAIL PROGRAM

W

g

Z

O_

I

U)

66

Appendix C

THE LISTING PROGRAM

%%%%%%%%%%%%%%%%%%%%

% For Butterworth and Bessel filter

% filename: filterph.m%%%%%%%%%%%%%%%%%%%%

clear all;

% for butterworth filter;

w1=[85000000 95000000]; % the cutoff freq in this case for BT=2.[b,a]=butter(5,wl,'s'); % 5th order Bessel filter% for bessel 3rd order

% [b,a]=besself(3,wl);

h=freqs(b,a, 128); % take 128 point of freq response and

%quantize the coefficients to become from -31 to 31hq=h* (31/max(abs(h)));

hq=round(hq)

for k=1:127 % odd coeffmultiply with -1•hql(k)=hq(k)*(-1)^k;end;

fid----fopen('butter5.dat','wt'); % save to the text file. for bessel filter give namefprinff(fid,'%o6i_n',hql); % with bessel3.dat

fclose(fid)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%0/0%%%% %

% for different BT, need to change the cut off frequency of the flter

% then the coefficients will be put into the PTF by using computer and file "loaddata.exe"%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%0/0%%%%%o/0%%

%%%%%%%%%%%%%%%%%%%%%%%%% for SRRC

%%%%%%%%%%%%%%%%0/0%%%%%%%clear all;

nff-t=128;

beta=.5; (will change for different beta, 0.25 and 1)

step=l;

67

t=((-nfft/2+1):nfftJ2)/step+1e-9;

rcos=(sin(pi*t)./(pi*t)).* (cos(beta*pi*t)./(l -(4*beta^2*t.^2)));RCOS---fft(rcos,nfft);

SRRC=sqrt(abs(RCOS));

srrc=real(ifft(SRRC,nfft));

h=[srrc(nffl/2+ 1 :nfft) srrc(1 :nfft/2) srrc(nfft/2+l)];

%quantize the coefficients to become from -31 to 31

hq=h*(3 I/max(abs(h)));

hq=round(hq);

for k= 1:127 % odd coeff multiply with - 1

hql(k)=hq(k)*(-1)^k;end;

fid---fopen('SRRC5.dat','wt'); % save to the text file.

fprintf(fid,'%6i\n',hq 1);

fclose(fid)

%%%%%%%%%%%%%%%%%%%%%%%%%0/o%%%0/0%%%0/o%%%%%%%%%

% for different alpha, need to change the alpha frequency of the filter

% then the coefficients will be put into the PTF by using computer and file "loaddata.exe"%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

68