SATELLITE AND SPACE COMMUNICATIONS

SSC

http://www.comsoc.org/socstr/org/operation/techcom/ssc/index.html

IEEE
COMMUNICATIONSSOCIETY
SSC Newsletter
CONTENTSSSC Committee Meetings........................... 1
ICC 2009 SSC Activities ............................ 1
How to join SSC Committee and mailing
list………………………………………….2
Officers ....................................................... 2
Message from the Chair .............................. 2
Scanning the World..................................... 3
Forthcoming ICC and GLOBECOM
Cosponsoring/Related Conferences
and Workshops............................................ 4
Conference Calendar................................... 5
Perspective Articles .................................... 6

Vol. 19, No. 1, June 2009The Satellite and Space Communications (SSC)
Committee is a volunteer group actively involved inadvancing satellite and space communication
technologies within the IEEE. This committee isapproved by the IEEE Communications Society andis governed by the constitution and bylaws of theIEEE as well as the other twenty-three TechnicalCommittees in the Society. The committee belongs
to the Technical Committee Clusters ofCommunication/Signal Processing (C/SP).

SATELLITE & SPACE- JOIN US -ICC2009 SSC Committee Activities

All conference attendees arewelcome to join us in the SSC
Committee meeting.

Wireless Communication Symposium
WCS-P1: Topics in Transmission Technologies
Room: Poster Area 1
Time: Mon, 15 Jun, 10:50 am - 12:20 pm

Location: Konferenz 7&8
Convention Center
Date: Monday, June 15, 2009
Time: 7:30 – 9:30

Future SSC Meetings
Nov.-Dec. 2009, Honolulu, U.S.A
May 2010, Capetown, South Africa
Dec. 2010, Miami, FL, U.S.A.

Wireless Networking Symposium
WN-P1: Relays, Gateways, and Satellite Systems
Room: Poster Area 2
Time: Wed, 17 Jun, 9:00 am - 10:30 am

SSC Newsletter

HOW TO JOIN SSC COMMITTEE AND MAILING LIST
If you like to join SSC Technical Committee: Please send your name and e-mail address to the SSC Secretary,
optionally include your mail address, telephone and fax numbers.
If you like to join SSC Mailing List: Instructions on how to subscribe/unsubscribe are available at
http://lists.scnl.dist.unige.it/listinfo/ssc.

SSC COMMITTEE OFFICERS
CHAIR
Prof. Takaya Yamazato
Department of ElectricalEngineering and Computer Science
Nagoya University
Nagoya, 464-8603, Japan
Tel: +81-52-789-2743
Fax: +81-52-789-3173
e-mail: yamazato@ieee.org

VICE CHAIR / EDITOR
Dr. Tarik Taleb
NEC Europe Ltd.
Heidelberg, Germany 69115
Tel: +49-6221-4342-179
Fax: +49-6221-4342-155
e-mail: talebtarik@ieee.org

PAST CHAIR
Prof. Mario Marchese
Department of Communications,
Computer and System Science
University of Genoa
Via Opera Pia 13,
16145, Genoa (Italy)
Tel. +39-010-3536571 (Office)Tel: +39-010-3532806 (Lab)Fax: +39-010-3532154
e-mail: mario.marchese@unige.it

COMMITTEE HISTORIAN
Mr. Louis Pollack
c/o Pollack Associates
15321 Delphinium Lane
Rockville, MD, USA 20853
Tel: +1 301 929 1295

COMMITTEE ADVISOR
Dr. Desmond P. Taylor
Dept. of Electrical & Electronic
Engineering
University of Canterbury
Private Bag 4800
Christchurch, New ZealandTel: +64 3 364 2213
Fax: +64 3 364 2761
e-mail: taylor@elec.canterbury.ac.nz

MESSAGE FROM THE CHAIR

Prof. Takaya Yamazato
I would like to thank our vice chair, Dr. Tarik Taleb,for editing the SSC newsletter and our secretary, Dr.
Igor Bisio, for SSC web page and membership
information updates.
Concerning the technicalactivities, we have endorsed ICC2009 Wireless
Networking Symposia (co-chair, Dr. Mario
Marchese) and Wireless Communication Symposia(co-chair, Dr. Takaya Yamazato). Dr. Claudio
Sacchi takes a lead as a co-chair of Selected Areas inCommunications, and Dr. Sastri Kota and Dr. Tarik
Taleb are co-chairs of Wireless Networking
Symposium, IEEE Globecom 2009 (30 Nov. - 4 Dec.
2009, Honolulu, Hawaii, USA). For ICC2010 (23-27
May 2010, Cape town, South Africa), the SSC isendorsing the SAC Symposium and Dr. Tarik Taleb
is a co-chair and for Globecom2010 (5-10 Dec. 2010,
Miami, Florida, USA), Dr. Takaya Yamazato is a cochair of Other Selected Areas in Communications
Symposia. TC representatives for ICC2011 (5 - 9June 2011, Kyoto, Japan) and Globecom2011 will bedecided at the next SSC meeting. At the moment, my

Welcome to the nineteenth issue of the Satellite andSpace Communications newsletter. The goal of theSatellite and Space Communication (SSC) TechnicalCommittee (TC) is to develop, organize anddistribute technical information in the area of thesatellite and space communications. The engineersand professionals from universities, government andresearch originations throughout the Globe
participate as members and officers of thiscommittee. At the moment, we have 158 members
and 58 associate members. All conference attendees
are welcome to attend and those who are attending
the SSC TC meeting for the first time willautomatically become a member of the TC. Pleasejoin us to discuss mutual topics of interest in thisimportant field in communications technology. The
meeting agenda and other information about SSC TC
activities and operation can be found at the TC web
page:
http://www.comsoc.org/socstr/org/operation/techcom/ssc/index.html

http://www.comsoc.org/~ssc/

SECRETARY
Dr. Igor Bisio
Department of Communications,
Computer and System Science
University of Genoa
Via Opera Pia 13,
16145, Genoa (Italy)
Tel: +39-010-3532806
Fax: +39-010-3532154
e-mail: igor@dist.unige.it-2-Vol. 19, No. 1, June 2009

SSC Newsletter
http://ww2.comsoc.org/drupal/conferences/EventSponsorship.
In addition, I ask to add a link from the conference
web page to SSC web page to the endorsed
conference TPC. I hope this will help our
membership development.

name is on the list for ICC2011. We have also
endorsed SPECTS 2009, IWSSC 2009, TELSIKS
2009, WCNC 2010, WCSP 2010, Array 2010, ICT2010, ICSOS 2011. For details, please check thefollowing pages or SSC web site.
By the way, the endorsement approval process of aconference sponsorship application has beenchanged. It is now decided by the TC chairs, not by
the cluster chairs. TAC Vice President, Dr. Andrzej
Jajszczyk, wrote the email dated on April 25, 2009that “it was decided to suppress the positions ofCluster Chairs, as their role in the conference
approval process has been diminished by distributing
this responsibility among Technical Committee
Chairs. The Cluster Chair positions are suppressed
immediately.” For ComSoc sponsorship approval, theevent must have the endorsement of a ComSoc TC.
This means that the scope of the technical program
falls within the TC's scope, that there is a quality,
independent peer review process for paper selection,and that three members of the ComSoc TC will be
active members of the event's TPC. For more detail,please visit:

The nomination for our next award for DistinguishedContribution to Satellite Communications is due
shortly (15th August, 2009). All members areencouraged to consider this important event tonominate anyone who they know with a good
contribution to the satellite research. Finally, I would
like to thank all members for their support. Without
your help, we could not organize any conference orreview any paper. I look forward to work with you inother occasions toward enhancing the knowledge inthe field of mobile communications in general and ofsatellite communications in particular.
Prof. Takaya Yamazato, Chair
Satellite and Space Communications
Technical Committee

SCANNING THE WORLD

Prof. Fotini-Niovi Pavlidou
The attendance reached the number of 14 people andthe discussion was quite interesting for the whole dayof the workshop. Some interesting issues which havebeen intensively discussed are the joint investigationof aerial and space platforms and the importance ofthe regulatory activities.

The IEEE Globecom08 Workshop on Aerial andSpace Platforms was organized for the first time inthe context of this conference. Since the scientificcommunity dealing with this topic is small and wellconnected internationally the workshop has been
publicized mainly through mailing lists createdthrough local relevant events. The presentations
selected, around 12, have been solicited by invitation
but they were gone through a review process. Thus agood range of topics were covered and theparticipation was quite international.

http://www.comsoc.org/~ssc/

The presentations can be found on the workshop
page: http://newton.ee.auth.gr/aerial_space/Prof. Fotini-Niovi Pavlidou
Dept. of Electrical & Computer Engineering
Aristotle University of Thessaloniki, Greece-3-Vol. 19, No. 1, June 2009

SSC Newsletter

FORTHCOMINGGLOBECOM AND
ICC CONFERENCESCOSPONSORING / RELATEDCONFERENCES AND WORKSHOPS
information on the latest developments in voice, data,
image, and multimedia.

MILCOM 2009
October 16- 21, 2009, Boston, MA, USA
http://www.milcom.org/
MILCOM 2009 is soliciting both unclassified andclassified papers (up to DoD Secret) relevant tocommunications and information processing systemtechnologies and capabilities that address the 21st
century challenges of National Defense, Homeland
Security, Disaster Response and Interoperability assummarized above. Industry, academic andgovernment organizations from both the US andcountries around the globe are invited andencouraged to participate.

ICC 2010
May 23-27, 2010, Capetown, South Africa.
http://www.comsoc.org/confs/icc/2010/index.html
The IEEE Communications Society will, in 2010
being
holdingits
flagshipInternational
Communications Conference (ICC) in Cape Town,
South Africa. This will be the first time that ICC has
been held in Africa and with Cape Town being voted
one of the most beautiful cities in the World, thispromises to be an exceptional conference.
Conference participants will have a wide range of
exciting options to add to their conference tour: hikes
up the famous Table Mountain; whale watching;tours of the Cape Winelands, Robben Island and even
CapePoint where two oceans meet. The FIFA World
Cup Soccer tournament, held all around South Africa
starts just after the conference ends.

GLOBECOM 2009
November 30-December 4, 2009, Honolulu, Hawaii,USAhttp://www.ieee-globecom.org/2009
The theme of the IEEE GLOBECOM 2009conference is “Riding the Wave to Global
Connectivity,” the conference covers the entire rangeof communications technologies, offering in-depth

http://www.comsoc.org/~ssc/-4-Vol. 19, No. 1, June 2009

SSC Newsletter

CONFERENCES CALENDARCONFERENCEDATE ＆ LOCATION

July 13-16, 2009,
SPECTS 2009
International Symposium on
Istanbul, Turkey
Performance Evaluation ofComputer andTelecommunication Systems
July 20-25, 2009,
SPACOMM 2009
The First International
Colmar, France
Conference on Advances inSatellite and Space
Communications
10-11 September 2009,
IWSSC 20092009 International Workshop on Siena, Italy
Satellite and Space
Communications
23-25 September 2009, Sardinia,
Ka and Broadband
Communications Conference Italy
October 7-9, 2009TELSIKS 2009
International Conference on
Niš, Serbia
Telecommunications in Modern
Satellite, Cable and Broadcasting
Services
April 18-21, 2010
WCNC 2010
IEEE Wireless Communications Sydney, Australia& Networking Conference
Feb 4-6, 2010
PSATS 2010
2nd International Conference on Rome, Italy
Personal Satellite Services
November 13-15, 2009
WCSP 2010
International Conference on
Nanjing, China
Wireless Communications andSignal Processing
October 12-15, 2010
Array 2010
IEEE International Symposium Boston, MA, USA
on Phased Array Systems &Technology
April 4-7, 2010
ICT 2010
17th International Conference on Doha, Qatar
Telecommunications
May 2011
ICSOS 2011
International Conference on
Los Angeles, CA, USASpace Optical Systems andApplications

INFORMATION
http://atc.udg.edu/SPECTS2009/http://www.iaria.org/conferences2009/SPACO
MM09.html

http://iwssc09.dii.unisi.it/

http://www.kaconf.org/
http://www.telsiks.org.yu/

http://www.ieee-wcnc.org/

http://www.psats.eu/

www.ic-wcsp.org

www.array2010.org

www.qu.edu.qa/ict2010

Web Site not yet available

To all SSC members: If your postal address, telephone or fax numbers have changed, please
update them with the committee secretary. You can review our current records on our web
page at http://www.comsoc.org/~ssc/.

http://www.comsoc.org/~ssc/-5-Vol. 19, No. 1, June 2009

SSC Newsletter

PERSPECTIVE ARTICLE

June 2009

Applicability of Wireless Terrestrial Technologies to Satellite
Communications
Mauro De Sanctis, Ernestina Cianca, Tommaso Rossi
University of Rome “Tor Vergata”
Dept. of Electronics Engineering
via del politecnico 1, 00133 Roma (Italy)
Correspondence to: mauro.de.sanctis@uniroma2.it
the minimization of risks. Moreover, the strict spacequalification process contributes to limit useable technologies.
Furthermore, the resources of a satellite payload such as
memory, complexity and energy consumption are limited.
However, it should be considered that complexity, memory
size and energy consumption of a set-top box can be muchhigher than that of a mobile wireless device such as a mobile
phone or a wireless card for a notebook. This higher resource
availability allows to implement a broader set of technologies.

Abstract — Fixed broadband satellite communications involve
challenges at every layer of the protocol stack. However, physicallayer technologies for satellite communications are notdeveloping as fast as for wireless terrestrial communications. In
this perspective article, transmission technologies borrowed fromthe wireless terrestrial field (i.e. UWB and OFDM) are proposed
as possible solutions for increasing channel data rate, system
capacity and spectrum utilization. Challenges related to theirapplications and open research areas are identified.
Index Terms — UWB, OFDM, satellite communications,
unlicensed spectrum, spectral efficiency, RF impairments, circuit
complexity.

The objective of the research on new technologies analyzed inthis paper is to increase channel data rate, system capacity andspectrum utilization.

I. INTRODUCTION
While terrestrial wireless networks often witness abreakthrough in the development of communications
technologies, satellite communications technologies are quite
stationary in their progress. Consider the new standard for
Digital Video Broadcasting via Satellite, i.e. DVB-S2 [1]. This
new standard has small incremental innovations with respect
to the older DVB-S. The main innovations are: introduction of
Low Density Parity Check (LDPC) codes and the possibilityof using Adaptive Modulation and Coding (AMC). On theother hand, wireless terrestrial technologies experienced
several radical changes. Some of the most important
technology trends in wireless terrestrial communications are
represented by Ultra Wideband (UWB) and Orthogonal
Frequency Division Multiplexing (OFDM). Some attempts toapply those techniques to satellite communications have been
made, but they are far from becoming consolidated
technologies in the satellite world. Obviously satellite andterrestrial
communications
systemshavedifferent
requirements and constraints and not all the techniques that are
attractive in terrestrial systems are attractive in satellite
systems. However, more often their application to satellite
systems would require just some modifications andenhancements and even if they have interesting advantages,
they need much more time to become a consolidated
technology in the satellite scenario.

In this perspective article, we propose the use of terrestrial
communications technologies such as UWB and OFDM for
fixed communications between ground terminals andGeostationary Earth Orbit (GEO) satellites, considering thedifferent characteristics of satellite fixed channels with respect
to terrestrial mobile channels: more severe Radio Frequency(RF) circuit impairments and negligible multipath.
The objective of this article is to draw the perspective use ofsome of the key technologies of current wireless systems insatellite communications, outlining advantages, needed
modifications and thus identifying new research areas.
The paper is organized as follows. Section II proposes the useof UWB technologies in satellite communications anddiscusses possible advantages. In Section III OFDM is
proposed as a possible solution to improve the spectral
efficiency. Finally conclusions are drawn in Section IV.
II. UWB FOR SATELLITE COMMUNICATIONS
A. UWB FOR WIRELESS TERRESTRIAL
COMMUNICATIONSUWB is a terrestrial communication technology fortransmitting information free of license over a very large
bandwidth without interfering with narrowband licensed
systems and is typically concerned with short range terrestrial
communications. The reason for applying UWB only to shortrange wireless applications is a consequence of the limitations
to the radiated power. Essentially, UWB devices are allowed
to interfere with existing systems, ideally at a low enoughpower level that existing services would not experience
performance degradation. The operation of UWB devices intandem with existing users is a significantly different approach

It is not easy to justify the different development speed
between satellite and wireless terrestrial communications
technologies. From the Authors point of view, the main cause
is the different level of system reliability required by satellite
and wireless terrestrial systems. The high cost of a satellite
system and the impossibility to upgrade or repair a satellite
lead to the exploitation of only well tested technologies with
http://www.comsoc.org/~ssc/-6-Vol. 19, No. 1, June 2009

SSC Newsletter
satellites where the position with respect to any terrestrial
system is fixed and known. This characteristic allows tocompute the minimum distance between a satellite and aterrestrial communications system so that the maximum powerreceived by a terrestrial system is known. Therefore, it ispossible to apply different power emission constraints tosatellite UWB systems with respect to terrestrial UWB
systems.

to spectral efficiency than achieving the highest possible data
rates in a channel with precisely defined bandwidths.
On September 1, 1998, the FCC issued a Notice of Inquiry
pertaining to the revision of Part 15 rules to allow theunlicensed use of UWB devices. The FCC defines UWB as asignal with either a fractional bandwidth of 20% of the center
frequency or 500 MHz (when the center frequency is above 6
GHz). The formula proposed by the FCC commission for
calculating the fractional bandwidth is 2(fH - fL)/(fH + fL) wherefH represents the upper frequency of the -10 dB emission pointand fL represents the lower frequency limit of the -10 dB
emission point. Therefore, the definition of UWB is only
concerned with bandwidth, but not with emission power, andhence, UWB communications technologies can also be used inlicensed systems if a large bandwidth would be available.

In imaginary satellite systems employing UWB
communication technologies, if the power transmitted fromthe satellite to the Earth is at the same level as terrestrial UWB
devices, the received signal on the Earth is very low, andreliable communication is impossible. However, if the power
spectral density of signals transmitted by UWB satellites on
the Earth’s surface is assumed to be greater than that ofterrestrial UWB transmitters, then transmission at high data
rate is possible.

The key benefits of UWB can be summarized as follows:
1. unlicensed use;

Furthermore, for fixed satellite services, the level ofinterference between different satellite systems depends on therelative spacing between satellites, the directivity of theantennas and eventually the processing gain of thetransmission technique. Highly directional aperture antennas
allow several broadcasting satellites to share the same
spectrum in a given coverage area. In this case, newcommunication channels can be added without an assignmentof new frequencies to the existing satellite communications
services and without license.

2. low equipment complexity and cost;
3. multipath immunity;
4. ranging and communication at the same time;
5. low probability of intercept;
6. low power consumption.
A primary driving application of UWB communications is ahigh rate Wireless Personal Area Network (WPAN) confined
to a small coverage area (less than 10 m of radius). Anotherimportant application is in distributed sensor communications
or low rate WPANs. However, some of the key benefits of
UWB can also be exploited for satellite communications.

Few studies of using UWB signals on satellite communication
links are available [2-3] and a very rich area of research is
opened.
In [2] a satellite modem supporting 800-Mbps QuadraturePhase Shift Keying (QPSK) in a single 650-MHz Ka-bandchannel was demonstrated. This experiment remains therecord of demonstrated UWB systems as defined by the FCC.

We propose two solutions to allow the use of UWBtechnologies in satellite communications: to reshape theemission limits to allow license-free satellite UWB
communication or to move to frequency bands higher than the
Ka band, i.e. Q/V and W bands, where ultra-wide portions ofband are available to be allocated for licensed use.

The first and unique attempt to study the performance of
UWB signals over satellite links with the limitations imposedon terrestrial UWB systems is reported in [3]. Authors showthat it is possible to achieve a data rate of 236 Mbps bylimiting the power spectral density of the signal received on
Earth to a signal level lower than the level imposed for aterrestrial UWB device, and by using a multi-band UWBtransmission scheme.

B. ADVANTAGES IN TERMS OF CAPABILITY
TO SHARE THE FREQUENCY SPECTRUM
Unlicensed or license-free spectrum simply means a spectrum
band that has rules pre-defined for both the hardware anddeployment methods of the radio in such a manner thatinterference is mitigated by the technical rules defined for thebands rather than it being restricted for use by only one entity
through a spectrum licensing approach.

To this respect, the study of the interference with terrestrial
systems is a key point. Many other points should be analyzed
in this area: which band is more suitable for allocating thelicense-exempt spectrum for satellite UWB communications
services? How much interference is generated to other satellite
systems at orbits near or below the considered one?

The limit imposed by the FCC to the radiated power of UWB
systems does not depend on the system characteristics, but are
applied to any kind of mobile or fixed UWB communications
system. This is in general a conservative method since it is notpossible to control the location of a terrestrial system(especially mobile systems) and, hence, it is not possible tocontrol the distance of a UWB terrestrial license free systemfrom a terrestrial licensed communications system. However,this is not true for satellite systems and in particular for GEO
http://www.comsoc.org/~ssc/

It should be demonstrated whether sufficient transmission
speed (>1 Gbps) is obtained or not by satellite UWB
communications with a transmission power compliant with
future satellite UWB power limitations. In fact, regulations instep with modern developments, have to adapt to permit futuresatellite UWB systems. The arrival of the technology should-7-Vol. 19, No. 1, June 2009

SSC Newsletterfor the digital processing of the signals. In impulse-based
UWB multiple access can be provided by means of Time
Hopping (TH) or Direct Sequence (DS) Code Division
Multiple Access (CDMA) techniques. Pulsed amplifiers withhigh output power are typically designed for pulse radar andare effectively applicable to low duty cycle signals such as
impulse-based UWB signals. However, for very short pulses,
it is needed to consider the bandwidth of the amplifier, so thatit maintains the pulse shape.

reshape the concepts of spectrum management to allow
modern satellite UWB technology. Finally, it is needed tostandardize license-free UWB on satellite links so that thesatellite maximum Effective Isotropic Radiated Power (EIRP)
is increased with respect to the maximum EIRP for terrestrial
links.
In the case we do not aim to deploy unlicensed satellite
systems and, hence, there is no need to meet the power
constraints of UWB systems, the exploitation of UWB signals
is still interesting from the system performance point of view.
In fact, novel UWB signals can be effectively exploited onsaturated power amplifiers typical of satellite systems and canincrease the performance of classical modulation methods.

Carrier-based UWB communications use traditional
heterodyning architectures and can be realized as either single
band or multi-band. Carrier-based UWB has better spectral
control properties with respect to impulse-based UWB. An
example of carrier-based UWB is the Multi-Band (MB)OFDM scheme which is based on frequency-hopped
PSK/QAM OFDM modulation. Basically, MB-OFDM is a
low-complexity radio technology implemented by means ofFast Fourier Transforms (FFT). By using the QPSK
constellation the resolution of A/D and D/A can be reduced.
Furthermore, increasing the spacing between sub-carriers
relaxes the phase noise requirement of OFDM technology andimproves the synchronization errors.

For licensed UWB satellite systems, advantages in terms oflower circuit complexity and lower sensitivity to RF
impairments are discussed below. To this respect, the ultimate
goal of using UWB transmissions is to increase the channel
data rate and the system capacity with respect to standardtransmission techniques which are more sensitive to RF
impairments and require more complex circuitry.
C. ADVANTAGES IN TERMS OF LOWERCIRCUIT COMPLEXITY
While communications technologies used by current satellite
systems are quite standard and simple, the circuit required forthe implementation of these transmission techniques are quite
complex.

As previously mentioned, UWB satellite communications
could be a very interesting field of research at “beyond Kaband” frequencies (i.e.: Q/V and W bands). In this frequency
range, UWB satellite transmission power will not be
constrained by previously described emission limits, being theRF “beyond Ka-band” spectrum almost free. The very narrow
EHF (Extremely High Frequency) beams could also decreaseinterference problems.

One of the main characteristics of satellite communications is
the need to transmit signals at high power so that the signal
received on the ground has enough power for a correct
reception. Therefore one of the most important element of the
RF transmission chain is the power amplifier.

As a matter of fact, “beyond Ka-band” satellite
communication is limited by present technology (in particular
Tx front-end power generation); in case of the use of UWB
pulsed signals, these problems can be faced considering theconsolidated state of the art space technology related to Wband satellite radar for cloud profiling (see CloudSat Mission[4]). In particular wideband space qualified EIK (Extended
Interaction Klystron) radar pulsed amplifiers could be
modified (decreasing pulse width and increasing pulse
repetition frequency) to be used for UWB EHF broadband
communications [5].

Despite recent advances in microwave solid state power
amplifiers, tube amplifiers such as Traveling-Wave Tubes(TWTs) and klystrons still provide the best combination of
power output, power efficiency and bandwidth.
Power amplifiers can be categorized into Continuous Wave
(CW) amplifiers or pulsed amplifiers. CW amplifiers areamplifiers designed to handle continuous waveforms, whilepulsed amplifiers are designed to handle pulse signals. A
pulsed amplifier produces high RF power for short durations
for a duty cycle of less than 10%. Because pulsed amplifiers
run cooler, they often can provide higher power and efficiency
compared to similar CW amplifiers.

D. ADVANTAGES IN TERMS OF LOWERSENSITIVITY TO RF IMPAIRMENTSUWB transmission technologies can demonstrate a lower
sensitivity to RF impairments such as: High Power Amplifier(HPA) non-linearity, phase noise, I/Q imbalance.

CW and pulsed amplifiers can be used in carrier-based UWB
and impulse-based UWB respectively.

Some innovative UWB pulse shaping, as Prolate Spheroidal
Wave Functions (PSWF) waveforms, can provide RF
modulated signals characterized by a near-optimalcompromise between spectral compactness and envelope
compactness. Therefore, the effect of nonlinear distortions canbe drastically reduced, while maintaining a spectral efficiency
rather similar to bandwidth-limited raised cosine waveforms.
In [6] authors simulated a W-band satellite communication
PHY-layer based on PSWF waveforms, evaluating effects of

In impulse-based UWB communications, pulses of very shortduration (typically in the order of sub-nanosecond) aretransmitted. Because of very narrow pulses the spectrum of
the signal reaches several GHz of bandwidth. Impulse-based
UWB is a carrier-less transmission and, hence, theimplementation of this technique is very simple and costeffective since no mixers and local oscillators are required. On
the other hand, high speed D/A and A/D converters are needed
http://www.comsoc.org/~ssc/-8-Vol. 19, No. 1, June 2009

SSC Newsletterbased on the OFDM principle could be a very interesting
research field;

linear, nonlinear distortions and phase noise on link
performances. PSWF demonstrated their favorable
characteristics in the presence of nonlinear distortion with anevident performance gain improvement with respect to theraised cosine, providing an improved service availability with
better net payload rates.

d) in some hybrid terrestrial-satellite communications
scenario where the terrestrial part uses an OFDM-based
air interface, the use of the same technique for thesatellite component would reduce the complexity of theterminal.

A further example of UWB technology that can be effectively
exploited in satellite communications is the Frequency
Modulation Ultra WideBand (FM-UWB) scheme [7]. FMUWB is a constant-envelope UWB communication scheme
which uses low modulation index Frequency Shift Keying(FSK) followed by high-modulation index analog FM toachieve the wide bandwidth. This approach has two attractive
properties for satellite communications: very low complexityof implementation and low sensitivity to HPA nonlinearities.

The latter reason has motivated the adoption of OFDM for thenovel standard DVB-SH, with proper modifications andenhancement with respect to the DVB-H OFDM air interface.
DVB-SH is a broadcast standard for delivering multimedia
services over hybrid satellite/terrestrial networks to a varietyof small mobile and fixed terminals with compact antennas
and very limited directivity such as handheld devices. OFDM
has been also recently applied to military communications. In
particular, it has been chosen as physical layer in the Joint
Tactical Radio System (JTRS) Wide-Band Networking
Waveform (WNW) to support network centric operations [12].
OFDM modulation has recently been explored in JTEO’s
research efforts for identifying the optimal air-interface for
MILSATCOM networks through Wideband Global SATCOM(WGS) systems. In all these applications, one critical issue
that remains is the high PAPR and hence, low power
efficiency. PAPR reductions techniques have been extensively
studied and can be applied to satellite communications.
However, one breakthrough in the utilization of OFDM insatellite communications is represented by the novel conceptof Constant Envelope OFDM (CE-OFDM) [13]. CE-OFDM
transforms the OFDM signal, by way of phase modulation, toa signal designed for efficient power amplification. At thereceiver, the inverse transformation—phase demodulation—isapplied prior to the conventional OFDM demodulator. The
phase modulation transform results in 0 dB PAPR constantenvelope signals. It is demonstrated that uncoded CE-OFDM
exploits multipath diversity. CE-OFDM is shown to compare
favorably to conventional OFDM in multipath fading channels
when the impact of nonlinear power amplification is taken into
account. On the other hand, it is now well known that thesame advantages of multicarrier communications, can beachieved by cyclic-prefixed single carrier systems with
Frequency Domain Equalization (FDE). It is also worth notingthat the Long Term Evolution (LTE) standard, which
represents the evolution of wireless communications towards
4G, foresees an OFDM-based multiple access scheme, such as
OFDMA, for the downlink and the Interleaved FDMA(IFDMA), which is a Single Carrier scheme with FDE (SCFDE), for the uplink. SC-FDE systems have performanceclose to the ones of a multicarrier system but much lower
PAPR, which makes the user terminal more power efficient.
Therefore, for the same reasoning, this transmission scheme
could be a better candidate for satellite communications withrespect to OFDM itself, having also the advantage of being
compatible with OFDM based transmitter/receiver as it
foresees the introduction of the cyclic prefix and theequalization is performed in the frequency domain. In [14] afirst attempt to evaluate the performance of an air interface
similar to the uplink of the LTE-standard has been performed

Finally, low sensitivity to RF impairments can be achieved byusing impulse-based UWB, where phase noise and I/Q
imbalance are not an issue.
III. OFDM
Orthogonal frequency Domain Multiplexing (OFDM) has
become a very popular transmission technique for wirelesscommunications for two main reasons: a) it offers a lower
complexity solution (in terms of receiver computational loadand hence on the hardware receiver architecture) than current
single carrier systems to the problem of performancedegradation over severely frequency selective channels, suchas wireless channels for very high speed communications(several tens of Mbps); b) it potentially offers good spectral
efficiency. OFDM has been adopted as physical layer scheme
for important broadband wireless interface standards, such as
IEEE 802.11/WiFi, IEEE 802.16/WiMAX, as well as DigitalVideo Broadcasting-Terrestrial (DVB-T) [8], [9]. On the other
hand, the application of this transmission technique has been
considered unfit for satellite communications. An OFDM
signal is characterized by high amplitude fluctuations that
produce large Peak-to-Average-Power-Ratio (PAPRs). This
makes OFDM sensitive to non-linear distortion caused bytransmitter’s power amplifiers, which is one of the criticalfactor to be considered when dealing with satellite systems.
However, recently it has been proved that the adoption ofstrong channel coding techniques in conjunction with the useof non linear distortion compensation techniques can lead tosatisfactory performance even when operating close toamplifier saturation [10], [11]. The use of OFDM for satellite
communication is attracting interest mainly for the following
reasons:a) in fixed broadband communications, even if there is
negligible multipath, its high spectral efficiency is
attractive;b) OFDM could be efficiently used in order to reduceoverall satellite payload receiver complexity (consideringa regenerative architecture);c) in case of a strong channelized payload architecture,
the analysis of an innovative channelization architecture,
http://www.comsoc.org/~ssc/-9-Vol. 19, No. 1, June 2009

SSC Newsletterwith the objective to identify proper modifications andparameters optimization for the satellite scenario.
Finally, we should consider that future broadband satellite
systems are going to work at frequency bands above 40 GHz(Q/V bands but eventually W-bands). This communication
scenario is also in favor of SC-FDE transmissions rather than
OFDM. Some works have already outlined how SC-FDE areless sensitive to RF impairment than OFDM and they can beapplied to high frequency bands communications in a more
efficient way [15].
IV. CONCLUSION
The final aim of this article is to identify new research areas in
fixed satellite communications adopting technologies welldeveloped for wireless terrestrial communications.
In this article the use of UWB and OFDM technologies areproposed for fixed satellite communications with the aim to
improve channel data rate, system capacity and spectrum
utilization.
In fact, UWB could allow unlicensed satellite systems bymeans of permissive un-assigned airwave use within emission
limits implicitly defined by the future regulations. However, it
must be verified that interference and power limitations do notlimit the success of license free UWB satellite
communications.
On the other hand, UWB can be also used in licensed satellite
EHF communications without any power constraint. This will
not increase spectrum utilization but could be an advantage interms of lower circuit complexity and lower sensitivity to RF
impairments, and, hence improving the channel data rate.
OFDM satellite communications could be an attractive
solution for three reasons: increasing the spectral efficiency of
fixed satellite communications, reducing overall satellite
receiver complexity, decreasing the complexity of integration
between satellite and terrestrial mobile communications
systems. However, SC-FDE systems can offer the sameadvantages of multicarrier systems while noticeably reducing
their drawbacks over satellite. Therefore, Authors believe thatthe use of SC-FDE transmissions in satellite systems
represents an interesting research area.
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