Black Crawling Systems Archive Release 1.0/Black Crawling Systems Archive Release 1.0 (L0pht Heavy Industries, Inc.)(1997).ISO/blackcrwl/commcom/datacom/spreadsp.txt

Text File | 1996-09-23 | 32KB | 673 lines

Spread Spectrum Article in QEX

(Reprinted from Digital Communications, column by Harold E. Price,
NK6K, from QEX, 1995)

---------------------------------------------------------------------------
Harold E. Price, NK6K

Don't blame me, the title is the work of this month's guest columnist,
STEVE BIBLE, N7HPR ([e-mail]).  While cruising the net recently,
I noticed a sudden bump in the number of times Spread Spectrum (SS)
techniques were mentioned in the amateur digital areas.  While QEX
has discussed SS in the past, we haven't touched on it in this forum.
Steve was a frequent cogent contributor, so I asked him to give us
some background. Steve enlisted in the Navy in 1977 and became a
Data Systems Technician, a repairman of shipboard computer systems.
In 1985 he was accepted into the Navy's Enlisted Commissioning Program
and attended the University of Utah where he studied computer
science.  Upon graduation in 1988 he was commissioned an Ensign and
entered Nuclear Power School.  His subsequent assignment was onboard
the USS Georgia, a trident submarine stationed in Bangor, Washington.
Today Steve is a Lieutenant and he is completing a master's degree
in computer science at the Naval Postgraduate School in Monterey,
California.  His areas of interest are digital communications, amateur
satellites, VHF/UHF contesting, and QRP.  His research area closely
follows his interest in amateur radio.  His thesis topic is Multihop
Packet Radio Routing Protocol Using Dynamic Power Control.   Steve
is also the AMSAT Area Coordinator for the Monterey Bay area.


---------------------------------------------------------------------------
CONTENTS


   Introduction

   Historical Background

   What is Spread Spectrum?

Direct Sequence Systems  Frequency Hopping Systems
Time Hopping Systems  Pulsed FM (Chirp) Systems
Hybrid Systems


   Why Spread Spectrum?

   Other Properties

   Building Blocks

   Where does Part 15 fit into all this?

   Further Part 97 Rules and Regulations


Sec. 97.119 Station identification | Sec. 97.305 Authorized
emission types | Sec. 97.311 SS emission types


   Rules Reform

   Getting Around the Rules -  Legally

   Areas to expand and research

   This isn't new

   PANSAT - A Spread Spectrum Satellite

   Future and Summary



   WEB Crawling

   Selected Bibliography


---------------------------------------------------------------------------


Spread Spectrum - It's not just for breakfast anymore!

Steve Bible,N7HPR
(Reprinted from Digital Communications, column by Harold E. Price,
NK6K, from QEX, 1995)


The column title says it all. What was once a communications mode
shrouded in secrecy has entered the consumer market in the form of
wireless ethernet links, cordless telephones, global position
service (GPS), Personal Communications System (PCS), and digital
cellular telephony (CDMA).  And what are radio amateurs doing with
spread spectrum today?  Perhaps very little since AMRAD performed
early experiments in amateur spread spectrum in the 1980's and formed
the early regulatory rules that govern amateur radio today.  In this
column I would like to reintroduce the topic of amateur spread spectrum
communications, discuss what it is and how we can experiment with
spread spectrum today.  Hopefully this column will prod you into
thinking again about spread spectrum communications and see that
there are several low cost building blocks available on the market
today.  Interspersed throughout the column I'll throw in the Part
97 rules and regulations that deal directly with amateur spread spectrum.


Historical Background

In 1980, the FCC expressed a desire to extend spread spectrum
communications outside of the military-only realm and allow radio
amateurs to experiment with spread spectrum communications.  The
FCC in following Title 47, Section 303 of the Code of Federal
Regulations (CFR) shall ...

   (g) Study new rules for radio, provide for experimental uses of
   frequencies, and generally encourage the larger and more effective
   use of radio in the public interest...


What this meant was that a new mode of communications was opening
up for experimentation and exploration by radio amateurs.

In 1980 AMRAD took the lead and forged the beginnings of amateur
spread spectrum experimentation.  The results of their experimentation
were documented in the AMRAD Newsletter, QEX, QST, and compiled into
a single book entitled "The ARRL Spread Spectrum Sourcebook."
This is a good book and recommended for anyone learning about spread
spectrum communications.  Though it is becoming a bit dated by today's
standards and advances in technology since the late 1980's, it is
nonetheless a good guide and provides a historical perspective into
the merging of SS into amateur radio.  At the end of the column I
will include a selected bibliography so that you can find other sources
of information ranging from the practical to theoretical.


What is Spread Spectrum?

A spread spectrum system is one in which the transmitted signal is
spread over a wide frequency band, much wider, in fact, than the
minimum bandwidth required to transmit the information being sent
(ref. 1).  Spread spectrum communications cannot be said to be an
efficient means of utilizing bandwidth.  However, it does come into
its own when combined with existing systems occupying the frequency.
The spread spectrum signal being "spread" over a large bandwidth
can coexist with narrowband signals only adding a slight increase
in the noise floor that the narrowband receivers see.  As for the
spread spectrum receiver, it does not see the narrowband signals
since it is listening to a much wider bandwidth at a prescribed code
sequence which I'll explain later.

First, let's introduce five types of spread spectrum techniques:


   DIRECT SEQUENCE SYSTEMS - Direct sequence is perhaps one of the
   most widely known and utilized spread spectrum systems and it
   is relatively simple to implement.  A narrow band carrier is modulated
   by a code sequence.  The carrier phase of the transmitted signal
   is abruptly changed in accordance with this code sequence.  The
   code sequence is generated by a pseudorandom generator that has
   a fixed length.  After a given number of bits the code repeats
   itself exactly.  The speed of the code sequence is called the
   chipping rate, measured in chips per second (cps).  For direct
   sequence, the amount of spreading is dependent upon the ratio
   of chips per bit of information.  At the receiver, the information
   is recovered by multiplying the signal with a locally generated
   replica of the code sequence.  See figure 1.

Figure 1.  Comparison of a narrowband signal with a Direct Sequence
Spread Spectrum signal.  The narrowband signal is suppressed when
transmitting spread spectrum.

FREQUENCY HOPPING SYSTEMS - In frequency hopping systems, the carrier
frequency of the transmitter abruptly changes (or hops) in accordance
with a pseudo random code sequence.  The order of frequencies selected
by the transmitter is dictated by the code sequence.  The receiver
tracks these changes and produces a constant IF signal.  See figure
2.


Figure 2.  An example of Frequency Hopping Spread Spectrum signal.


TIME HOPPING SYSTEMS - A time hopping system is a spread spectrum
system in which the period and duty cycle of a pulsed RF carrier
are varied in a pseudorandom manner under the control of a coded
sequence. See figure 3. Time hopping is often used effectively with
frequency hopping to form a hybrid time-division, multiple-access
(TDMA) spread spectrum system.

Figure 3.  Time Hopping Spread Spectrum.  Each burst consists of
k bits of data and the exact time each burst is transmitted is determined
by a PN sequence.

PULSED FM (CHIRP) SYSTEMS - A pulsed FM system is a spread spectrum
system in which a RF carrier is modulated with a fixed period and
fixed duty cycle sequence.  At the beginning of each transmitted
pulse, the carrier frequency is frequency modulated causing an additional
spreading of the carrier.  The pattern of the frequency modulation
will depend upon the spreading function which is chosen.  In some
systems the spreading function is a linear FM chirp sweep, sweeping
either up or down in frequency.

HYBRID SYSTEMS - Hybrid systems use a combination of spread spectrum
methods in order to use the beneficial properties of the systems
utilized.  Two common combinations are direct sequence and frequency
hopping.  The advantage of combining the two methods is to capitalize
on characteristics that are not available from a single method.


Why Spread Spectrum?

To answer the question "why should I use spread spectrum" could easily
degenerate into a simple listing of advantages and disadvantages.
However, spread spectrum has many different unique properties that
cannot be found in any other modulation technique.  As radio amateurs,
we should exploit these properties and search for useful applications.
Think of spread spectrum as another useful tool in our repertoire
of modulation methods toolbox.  For completeness, I will list some
advantages and disadvantages that you will see for typical spread
spectrum systems.  Bare in mind that these come about because of
the nature of spread spectrum, not because they are direct attributes.


   Advantages:
-Resists intentional and non-intentional interference
-Has the ability to eliminate or alleviate the effect of multipath
interference
-Can share the same frequency band (overlay) with other users
-Privacy due to the pseudo random code sequence (code division multiplexing)


Disadvantages:
-Bandwidth inefficient
-Implementation is somewhat more complex.


Other Properties

There are several unique properties that arise as a result of the
pseudo random code sequence and the wide signal bandwidth that results
from spreading.  Two of these are selective addressing and code division
multiplexing.  By assigning a given code to a single receiver or
a group of receivers, they may be addressed individually or by group
away from other receivers assigned a different code.  Codes can also
be chosen to minimize interference between groups of receivers by
choosing ones that have low cross correlation properties.  In this
manner more than one signal can be transmitted at the same time on
the same frequency.  Selective addressing and Code Division Multiple
Access (CDMA) are implemented via these codings. A second set of
properties is low probability of intercept (LPI) and anti-jamming.
When the intelligence of the signal is spread out over several megahertz
of spectrum, the resulting power spectrum is also spread out.  This
results in the transmitted power spread out over a wide frequency
bandwidth and makes detection in the normal sense (without the code),
very difficult.  Though LPI is not a typical application for radio
amateurs, it would best to rename this property as "reduction of
interference." Thus spread spectrum can survive in an adverse environment
and coexists with other services in the band.  The anti-jamming property
results from the wide bandwidth used to transmit the signal.  Recall
Shannon's Information-rate theorem


   C = W log (1 + S/N)

   C = capacity in bits per second

W = bandwidth
S=signal power
N=noise power


where the capacity of a channel is proportional to its bandwidth
and the signal-to-noise ratio on the channel.  By expanding the bandwidth
to several megahertz and even several hundred megahertz, there is
more than enough bandwidth to carry the required data rate and have
even more to spare to counter the effects of noise.  This anti jamming
quality is usually expressed as "processing gain."

So for the radio amateur, the properties of code division multiplexing,
coexistence in an adverse environment, and processing gain, are all
excellent reasons to experiment with and find useful applications
for spread spectrum in the amateur radio service.  Coupled with these
reasons, amateurs can also enjoy increased data rates in digital
data (packet radio) that cannot be done with conventional amateur
or commercial radios due to physical (i.e. bandpass filters) and
rules restrictions.  For example, narrowband systems in the 70 cm
band are limited to a maximum data rate of 56 kbps and a bandwidth
of 100 kHz, there are no such restrictions in the 33 cm band and
up.

Perhaps one of the most important reasons to use spread spectrum
is its ability discriminate against multipath interference.  A RAKE
receiver implementation for direct sequence allows individual signal
paths to be separately detected and the coherently combined with
other paths.  This not only tends to prevent fading but also provides
a path diversity effect resulting in very rugged links in terrestrial
mobile communications (ref. 2).


Building Blocks

Spread spectrum signals are demodulated in two steps:  1) the spectrum
spreading (direct sequence, frequency hopping) modulation is removed,
and 2) the signal is demodulated.  The process of despreading a signal
is called correlation.  The spread spectrum signal is despread when
the proper synchronization of the spreading code between the transmitter
and receiver is achieved.  Synchronization is the most difficult
aspect of the receiver.  More time, research, effort, and money has
gone into the development and improving of synchronization techniques
than in any other area of spread spectrum.  The problem of synchronization
is further broken down into two parts: initial acquisition and tracking.


There are several methods to solve the synchronization problem.
Many of these methods require a great deal of discrete components
to implement.  But perhaps the biggest break-through has been from
Digital Signal Processing (DSP) and Application Specific Integrated
Circuits (ASIC).  DSP has provided high speed mathematical functions
that can slice up in many small parts and analyze the spread spectrum
signal to synchronize and decorrelate it.  ASIC chips drive down
the cost by using VLSI technology and creating generic building blocks
that can be used in any type of application the designer wishes.
With the fast growing Part 15 and Personal Communications System
(PCS) spread spectrum market, many ASIC manufactures have been designing
and selling ASIC chips that take care of the most difficult problem
in spread spectrum--despreading and synchronization.  With a few
extra components, the amateur can have a fully functioning spread
spectrum receiver.

One manufacture of a spread spectrum demodulator ASIC is Loral Communications
Systems (recently Unisys Communications Systems Division) DSP Components,
Dept. 9065, M/S F1F12, 640 North 2200 West, Salt Lake City, Utah
84116-2988; Phone: [phone].  Their PA-100 performs the functions
of despreading and demodulation, carrier recovery loop (frequency
or phase), Pseudo Noise (PN) code detection, PN code tracking loop,
data synchronization, and automatic gain control.  It is programmable
and offers a wide range of choices in data rates, modulation types,
processing gains, PN codes, loop bandwidths, and tracking and acquisition
procedures.  It is capable of chipping rates up to 32 Mcps and data
rates up to 64 Mbps.  The PA-100 is controlled via a simple 8-bit
interface.  The chip is a 208-pin plastic Metrix Quad Flat Package
(MQFP).  The cost of the chip is $167.00 in single qty and $67.00
in lots of 1000.


Where does Part 15 fit into all this?

Many of the spread spectrum devices on the market today are listed
as Part 15 devices.  This refers to the device operating under the
provisions of Title 47 Section 15.247 of the Code of Federal Regulations
(CFR).  There are three frequency bands allocated to this service:


      902 - 928 MHz (26 MHz bandwidth)
2400 - 2483.5 MHz (83.5 MHz bandwidth)
5725 - 5850 MHz (125 MHz bandwidth)


Operation under this provision of this section is limited to frequency
hopping and direct sequence spread spectrum.  No other spreading
techniques are permitted.  Section 15.247 defines the technical standards
that these systems must operate under. For example, the maximum peak
output power of the transmitter shall not exceed 1 watt.  If transmitting
antennas of directional gain greater than 6 dBi are used, the power
shall be reduced by the amount in dB that the directional gain of
the antenna exceeds 6 dBi.  This equates to a maximum transmitter
EIRP of +6dBW (1 watt into a 6 dBi gain antenna) Part 15 equipment
operates on a secondary basis.  Users must accept interference from
other transmitters operating in the same band and may not cause interference
to the primary users in the band.  Primary users are government systems
such as airborne radiolocation systems that emit a high EIRP; and
Industrial, Scientific, and Medical (ISM) users.  Thus the Part 15
device manufacturer must design a system that will not cause interference
with and be able to tolerate the noisy primary users of the band.
And this is where spread spectrum systems excel because of their
low noise transmissions and ability to operate in an adverse environment.


Amateurs should realize that under the present Part 97 rules and
regulations governing amateur spread spectrum today, taking a Part
15 spread spectrum device and adding an amplifier to it would break
the rules.  Even though it would be transmitting within the amateur
spectrum, it more than likely would not be using one of the specified
spreading codes assigned to amateur operation (refer to Sec. 97.311
Section (d) - SS emission types).  However, this should not deter
the radio amateur from using Part 15 devices in their experimentation
or use in the amateur service.  The device should be monitored to
ensure that it remains under the Part 15 regulations and as such,
no Part 97 regulations apply.  Amateur traffic can flow though Part
15 devices, and they do not require a callsign since they do not
require a license.  However, the radio amateur should realize that
when the traffic enters the amateur bands, for example, through a
gateway, then Part 97 rules begin to apply.


Further Part 97 Rules and Regulations

Any radio amateur contemplating experimentation of spread spectrum
in the amateur bands (excluding Part 15 devices) should become familiar
with the present Part 97 rules and regulations governing it.  Here
are some excerpts that bare emphasizing:

SEC. 97.119 STATION IDENTIFICATION

   (a)(5) By a CW or phone emission during SS emission transmission
   on a narrow bandwidth frequency segment.  Alternatively, by the
   changing of one or more parameters of the emission so that a conventional
   CW or phone emission receiver can be used to determine the station
   call sign.
SEC. 97.305 AUTHORIZED EMISSION TYPES.

Spread Spectrum is permitted on the following bands (over the entire
band unless otherwise indicated):
   UHF: 70 cm (420-450 MHz), 33 cm (902-928 MHz), 23 cm (1240-1300
   MHz), 13 cm (2300-2310 and 2390-2450 MHz*)
SHF: 9 cm (3.3-3.5 GHz), 5 cm (5.650-5.925 GHz), 3 cm (10.00-10.50
GHz), 1.2 cm (24.00-24.25 GHz)
EHF: 6 mm (47.0-47.2 GHz), 4 mm (75.5-81.0 GHz), 2.5 mm (119.98-120.02
GHz), 2 mm (142-149 GHz), 1mm (241-250 GHz), Above 300 GHz


Operation on all of the above bands are on a secondary basis.  No
amateur station transmitting in these bands shall cause harmful interference
to, nor is protected from interference due to the operation of the
primary service. (*Note:  Recent rule making has allocated 2390-2400
MHz and 2402-2400 MHz to the Amateur community on a primary basis.)


SEC. 97.311 SS EMISSION TYPES
[Note: Sections (a) through (d) set the technical standards for spread
spectrum emissions.]
   (e) The station records must document all SS emission transmissions
   and must be retained for a period of 1 year following the last
   entry.  The station records must include sufficient information
   to enable the FCC, using the information contained therein, to
   demodulate all transmissions.  The station records must contain
   at least the following:

   (1) A technical description of the transmitted signal;
(2) Pertinent parameters describing the transmitted signal including
the frequency or frequencies of operation and, where applicable,
the chip rate, the code rate, the spreading function, the transmission
protocol(s) including the method of achieving synchronization, and
the modulation type;
(3) A general description of the type of information being conveyed,
(voice, text, memory dump, facsimile, television, etc.);
(4) The method and, if applicable, the frequency or frequencies used
for station identification; and
(5) The date of beginning and the date of ending use of each type
of transmitted signal.

(f) When deemed necessary by an EIC to assure compliance with this
part, a station licensee must:

   (1) Cease SS emission transmissions;
(2) Restrict SS emission transmissions to the extent instructed;
and
(3) Maintain a record, convertible to the original information (voice,
text, image, etc.) of all spread spectrum communications transmitted.

(g) The transmitter power must not exceed 100 W.


Rules Reform

Needless to say, by today's standards, practices, and improvements
in technology, the above Part 97 rules and regulations on amateur
spread spectrum are extremely restrictive  especially in the case
of the few fixed spreading codes dictated by section 97.311 (d)(1).
The ARRL is reviewing the suggestions from the ARRL Futures Committee
for changes to these rules and regulations to allow less restriction
and freer experimentation.


Getting Around the Rules -  Legally

In the mean time there is a Special Temporary Authority (STA)
to allow amateur spread spectrum experimentation.  Under this STA
Section 97.305(c) is waived to the extent that particular amateur
stations are authorized to transmit spread spectrum emissions on
frequencies in the 6 meter (50 - 54 MHz), 2 meter (144 - 148 MHz),
and 1.25 meter (222 - 225 MHz) bands.  Section 97.311(c) is waived
for these stations to the extent that the prohibition against hybrid
spread spectrum emissions is lifted; and Section 97.311(d) is waived
for these stations to use other spreading codes.

To participate in this STA it is requested that you have a bonafide
purpose of experimenting and advancing the art of amateur spread
spectrum.  Contact Robert Buaas, K6KGS, 20271 Bancroft Circle,
Huntington Beach, California 92646.  Please include your name, address,
callsign, expiration date of your license, and the details of your
experiment.  Do include an abstract of the project and a proposed
set of goals you are trying to obtain.  The information that you
collect through your experimentation will be helpful in the advancement
of Amateur spread spectrum but will also be useful for justification
for rules changes before the FCC.


Areas to expand and research

Typical SS applications such as wireless ethernet use point-to-point
communications.  They link two subnets over distances of several
miles with external Yagi antennas and less than one watt of power.
Amateurs would rather use the traditional CSMA/CA technique they
are familiar with in today's packet radio.  However, with the requirement
of correlating the spreading code it would require a network node
to have multiple receivers to listen in on the channel and detect
when an outlying node is trying to communicate with it.  Here's where
amateur radio experimentation can advance the art of spread spectrum,
by creating a CDMA spread spectrum packet radio network.  By using
the techniques employed by GPS, relatively short codes can be use
to minimize receiver acquisition time.  These codes would also need
to have good cross-correlation properties to minimize multiple access
interference between nodes.

Power control is required to control the reuse of the frequency beyond
code division multiplexing.  It also behooves us to explore good
power control to limit interference and to reduce the power consumption
and drain on batteries. Routing of packets through a network is typically
a software issue, but with the ability to do code division multiplexing,
how do we route packets from one subnet to another when they do not
use the same code sequence?

Driving cost down has always been a top goal of any designer, and
even more so since the Amateur is experimenting with their own money.
Amateurs tend to be a frugal lot and will find any means available
to build a system that costs as little as possible.  This spawns
innovative and creative methods to achieve this means.  Then these
means tend to be passed back to the commercial sector and benefit
everybody.

CDMA is not the exclusive province of direct sequence systems; CDMA
can also be used with frequency hopping.  TDMA is not the exclusive
province of narrowband systems; TDMA can also be used with direct
sequence or frequency hopping.


This isn't new

In the 1982 AMRAD letter (reprinted on page 4-11 of the ARRL SS Handbook),
Hal Feinstein, WB3KDU, wrote,
     Spread spectrum has found its way into packet radio.  Spread
   spectrum allows each node to have a unique code which acts as
   a hard address. Another node in the system can send data to that
   node by encoding that data with the spread spectrum address for
   the receiving node.  Traffic for other nodes does not interfere
   because it would have a different code.  Among the reasons cited
   for employing spread spectrum for packet switching are privacy,
   selected addressing, multipath protection and band sharing.
   But it is interesting to note that a load is taken off the contention
   collision approach because now a single frequency is not in contention
   among the nodes wishing to transmit.  The load is divided among
   the nodes addresses, and each that is interested in sending data
   to a target node competes for that node only.
This is the CDMA part of SS.  This is one of those areas the FCC
really wants hams to experiment with.  I think the paper has a lot
of insight and it was even written over 13 years ago.


PANSAT - A Spread Spectrum Satellite

The Space Systems Academic Group (SSAG) at the Naval Postgraduate
School (NPS) in Monterey, California is actively designing and building
an amateur satellite named PANSAT (see figure 4).  PANSAT is the
acronym for Petite Amateur Navy Satellite.  PANSAT is to become a
packet digital store-and-forward satellite vary similar in capabilities
as the existing PACSATs in orbit today. The tentative launch date
of PANSAT is late 1996, early 1997 as a Get Away Special (GAS)
payload from the Space Shuttle.

One big difference between today's PACSATs and PANSAT is that
PANSAT will use direct sequence spread spectrum as the communications
up and downlink.

PANSAT is being designed from the ground up as an amateur satellite.
The only military mission of PANSAT is as a training vehicle for
the education of military officers in the Space Systems Curricula
by the design, fabrication, testing and operation of a low-cost,
low earth orbit (LEO), digital communications satellite.  One of
the engineering objectives of PANSAT includes the evaluation and
performance of spread spectrum packet radio communications using
the Amateur community as the user base.

In order to facilitate the evaluation of spread spectrum performance
the SSAG is designing a low cost spread spectrum modem and RF package
to be presented to the amateur community in a kit form.  The goal
is to have the design of the spread spectrum radio/modem available
before the launch of PANSAT to allow Amateurs to build and become
operational via terrestrial means.  This presents an exciting exchange
of technology and the ability for the Amateur to build a low cost
unit to experiment with.  As the design and development progresses
they will be presented in the Amateur press.


Future and Summary

Now is the time to begin experimenting with spread spectrum communications
on a wider scale.  Technology has advanced to the point where Amateurs
can afford to build systems.  The building blocks are available now
in the form of Application Specific Integrated Circuits.  The recent
flood of consumer devices that employ spread spectrum has also driven
the price down.  In many cases the Amateur can either use these devices
under their present type acceptance or modify them for Amateur operations.
However, the Amateur should remain aware of the rules and regulations
governing the particular device whether it falls under Part 15 or
Part 97 of the FCC Rules and Regulations and remain within their
guidelines.  If the Amateur wishes to expand beyond the present Part
97 rules in bonafide experimentation, they are encouraged to join
in the Special Temporary Authority.

Spread spectrum systems exhibit unique qualities that cannot be obtained
from conventional narrowband systems.  There are many research avenues
exploring these unique qualities.  Amateurs in their inherent pioneering
nature can and will find new and novel applications for spread spectrum
communications that the commercial sector may not even think of.
And due to the frugal propensity of the Radio Amateur, they will
certainly find the least expensive way to implement it, thus driving
down the cost.

Amateurs should realize that there is plenty of room to explore spread
spectrum techniques.  All that remains now is to pick up a few good
books on the subject and warm up the soldering iron.  And as you
progress upon this road less traveled, make sure you take notes along
the way.  Then share your discoveries with your fellow Amateur to
help all of us expand the horizon with this exciting mode of communications
call spread spectrum.  It is no longer shrouded in secrecy and it's
not just for breakfast anymore!


---------------------------------------------------------------------------


WEB Crawling

Here are two WEB pages of interest.
I've started a general amateur radio SS page, http://www.tapr.org/
ss.
See also the PANSAT page at http://www.sp.nps.navy.mil/pansat/
pansat.html.


Selected Bibliography

BOOKS - Extensive research oriented analysis -
   M.K. Simon, J. Omura, R. Scholtz, and K. Levitt, Spread Spectrum
   Communications Vol. I, II, III.  Rockville, MD. Computer Science
   Press, 1985.
Intermediate level -
   J.K. Holmes, Coherent Spread Spectrum Systems, New York, NY. Wiley
   Interscience, 1982.
D.J. Torrieri, Principles of Secure Communication Systems.  Boston.
Artech house, 1982.
Introductory to intermediate levels -
   G.R. Cooper and C.D. McGillem, Modern Communications and Spread
   Spectrum, New York, McGraw-Hill, 1986.
R.E. Ziemer and R.L. Peterson, Digital Communications and Spread
Spectrum Systems, New York, Macmillan, 1985.
R.E. Ziemer and R.L. Peterson, Introduction to Digital Communications,
New York, Macmillan, 1985.
Practical -
   R.C. Dixon, Spread Spectrum Systems, John-Wiley & Sons, 1984.
JOURNALS - There have been several special issues of IEEE publications
that are devoted to spread spectrum systems.  IEEE Transactions on
Communications: August 1977 and May 1982.  IEEE Journal of Selected
Areas in Communications: May 1990, June 1990, and May 1992.

REFERENCES
   (1) R.C. Dixon, Spread Spectrum Systems, John-Wiley & Sons, 1984,
   page 7.
   (2) K. Gilhousen, Qualcomm Inc., USENET newsgroup discussion.