Spread spectrum radio

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to integrated bar code scanner/
palmtop computer/radio modem de-
vices for warehousing, digital dispatch,
digital cellphone communications, and
‘information society’ city-, area-, state-
or country-wide networks for transmit-
ting facsimile, computer data, e-mail
or multimedia data.
History of spread
spectrum
Early spark-gap wireless transmitters
actually used spread spectrum, since
their RF bandwidths were much wider
than their information bandwidth. The
first intentional use of spread spectrum
was probably by Armstrong in the late
1920s or early 1930s with wide-band
frequency modulation (FM). However,
the real impetus for spread spectrum
came with World War II.
Both the allies and the axis powers
experimented with simple spread-spec-
trum systems. Much of what was done
is still shrouded in secrecy, however.
The first publicly available patent
A
dvances in technology have
brought to us a new form of

digital radio service called
‘spread spectrum.’ First developed by
the military as a deterrent to jamming
and eavesdropping (espionage), the
spread-spectrum technique handles ra-
dio signal differently from other forms
of digital radio.
In spread-spectrum operation, the
radio signal is spread across a great
bandwidth with the use of a spread-
ing algorithm based upon a pseudo-
noise (PN) code, or a number that each
unit of the system is programmed
with. The result is a signal that is es-
sentially ‘buried’ in the noise floor of
the radio band.
The receiver is programmed to ex-
amine the bandwidth of the spread sig-
nal and correlate the data (despread it).
The process of correlation also causes
any other signal received to be spread
as the wanted signal is despread. This
causes unwanted signals which appear
as noise. The result is a signal that is
extremely difficult to detect, does not
interfere with other services and still
passes a great bandwidth of data.
Spread spectrum, the art of secure
digital communications, is now being
exploited for commercial and indus-

trial purposes. In the future, hardly
anyone will escape being involved, in
some or the other way, with spread-
spectrum communications.
Commercial applications for
spread spectrum range from wireless
PC-to-PC local area networks (LANs)
 D. PRABAKARAN
on spread spectrum came from Hedy
Lamarr, the Hollywood movie actress,
and George Antheil, an avant-garde
music composer. This patent was
granted in 1942, but the details were a
military secret for many years. The in-
ventors never realised a dime for their
invention; they simply turned it over
to the US government for use in the
war effort, and commercial use was
delayed until the patent had expired.
Most of the work done in spread
spectrum throughout the 1950s, 1960s
and 1970s was heavily backed by the
military and drowned in secrecy. The
global positioning system (GPS) is now
the world’s single largest spread-
spectrum system. Most of the details
on GPS are now public information.
Spread spectrum was first used for
commercial purposes in the 1980s
when Equatorial Communications of

Mountain View, CA, used direct se-
quence for multiple-access communi-
cations over synchronous satellite tran-
sponders. In the late 1980s, the US Fed-
SPREAD-SPECTRUM
TECHNOLOGY AND ITS
APPLICATIONS
In the future, hardly anyone will escape being involved, in some or the other
way, with spread-spectrum—the art of secure digital communications
Fig. 1: Spread-spectrum signals are hard to detect on narrow-band equipment because the
signal’s energy is spread over a bandwidth of maybe 100 times the information bandwidth
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eral Communications Commission
(FCC) opened up the industrial, scien-
tific and medicine (ISM) frequency
bands for unlicenced spread-spectrum
communications.
Applications
Typical applications for spread-spec-
trum radio are:
1. Cellular/PCS base station inter-
connect
2. Last-mile obstacle avoidance
3. Private networks
4. Railroads and transportation
5. Utilities like electricity, oil, gas
and water
6. Banks, hospitals, universities and

corporations
7. Disaster recovery and special-
event PSTN extensions
8. TELCO bypass
9. Rural telephony
10. Videoconferencing
11. LAN/WAN/Internet connec-
tion
How spread spectrum
works
The term ‘spread spectrum’ describes
a modulation technique that makes the
sacrifice of bandwidth in order to gain
signal-to-noise (S/N) performance. Ba-
sically, in a spread-spectrum system,
the transmitted signal is spread over a
frequency much wider than the mini-
mum bandwidth required to send the
signal.
The fundamental premise is that in
channels with narrow-band noise, in-
creasing the transmitted signal band-
width results in an increased probabil-
ity that the received information will
be correct. If total signal power is in-
terpreted as the area under the spec-
tral density curve, signals with equiva-
lent total power may have either a
large signal power concentrated in a
small bandwidth or a small signal

power spread over a large bandwidth.
Spread signals are intentionally
made to be much wider-band than the
information they are carrying to make
them more noise-like. Because spread-
spectrum signals are noise-like, they
are hard to detect. They are also hard
to intercept or demodulate. Further,
spread-spectrum signals are harder to
jam (interfere with) than narrow-band
signals. The low probability of inter-
cept and anti-jam features are the rea-
sons why the military has used spread
spectrum for so many years.
Spread-spectrum signals use fast
codes that run many times the infor-
mation bandwidth or data rate. These
special ‘spreading’ codes are called
‘pseudo random’ or ‘pseudo noise’
codes. They are called ‘pseudo’ be-
cause they are not real Gaussian noise.
The use of special pseudo-noise
codes in spread-spectrum communica-
tions makes signals appear wide-band
and noise-like. It is this very charac-
teristic that makes spread-spectrum
signals possess the quality of low prob-
ability of intercept.
Spread-spectrum transmitters use
the same transmit power levels as nar-

row-band transmitters. Because
spread-spectrum signals are very wide,
they transmit at a much lower spec-
tral power density, measured in watts
per hertz, than narrow-band transmit-
ters. The lower transmitted power den-
sity characteristic gives spread signals
a big plus. Spread and narrow-band
signals can occupy the same band,
with little or no interference. This ca-
pability is the main reason for all the
interest in spread spectrum today.
Since the total integrated signal
density or signal-to-noise ratio (SNR)
at the correlator’s input determines
whether there will be interference or
not, all spread-spectrum systems have
a threshold or tolerance level of inter-
ference beyond which useful commu-
nication ceases. This tolerance or
threshold is related to the spread-spec-
trum processing gain. Processing gain
is essentially the ratio of the RF band-
width to the information bandwidth.
Direct sequence and frequency
hopping are the most commonly used
methods for the spread-spectrum tech-
nology. Although the basic idea is the
same, these two methods have many
distinctive characteristics that result in

completely different radio perfor-
mances.
The carrier of direct-sequence ra-
dio stays at a fixed frequency. The nar-
row-band information is spread out
into a much larger (at least ten times)
bandwidth by using a pseudo-random
chip sequence.
Generation of the direct-sequence
spread-spectrum signal (spreading) is
shown in Fig. 2. The narrow-band sig-
nal and the spread-spectrum signal
both use the same amount of transmit
power and carry the same information.
However, the power density of the
spread-spectrum signal is much lower
than the narrow-band signal. (The
power density is the amount of power
over a certain frequency.) As a result,
it is more difficult to detect the pres-
ence of the spread-spectrum signal. In
this case, the narrow-band signal’s
power density is ten times higher than
the spread-spectrum signal, assuming
the spread ratio as ‘10.’
At the receiving end, the spread-
spectrum signal is despread to gener-
ate the original narrow-band signal as
shown in Fig. 3.
If there is an interference jammer

in the same band, it will be spread out
during despreading. As a result, its
impact is greatly reduced. This is the
way the direct-sequence, spread-spec-
trum radio fights the interference. It
spreads out the offending jammer by
the spreading factor, which is at least
‘10.’ In other words, the offending
Fig. 2: Generation of the direct-sequence
spread-spectrum signal (spreading)
Fig. 3: At the receiving end, the spread-
spectrum signal is despread to generate the
original narrow-band signal
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jammer’s amplitude is greatly reduced
by at least 90 per cent.
Frequency hopping achieves the
same result by using a different carrier
frequency at a different time. Its carrier
will hop around within the band, so it
will avoid the jammer at some frequen-
cies. The frequency hopper is more
popular and the only way to survive in
the 2.45GHz band because the leak-
ages from the microwave oven (from
2.4 to 2.5 GHz) sometimes exceed 10W.
Frequency hopper is not needed in the
915MHz band because there is no legal

big jammer in this frequency.
The frequency-hopping technique
is shown in Fig. 5. It does not spread
the signal, so there is no processing
gain. The processing gain is the in-
crease in power density when the sig-
nal is despread and it improves the
received signal’s SNR. In other words,
the frequency hopper needs to put out
more power in order to have the same
SNR as a direct-sequence radio.
The frequency hopper is also more
difficult to synchronise the receiver to
the transmitter because both the time
and frequency need to be in tune.
Whereas, in a direct-sequence radio,
only the timing of the chips needs to be
synchronised. The frequency hopper
will need to spend more time to search
the signal and lock to it. As a result, the
latency time is usually longer. Whereas,
a direct-sequence radio can lock in the
chip sequence in just a few bits.
Usually, to make the initial
synchronisation possible, the frequency
hopper will park at a fixed frequency
before hopping or communication be-
gins. If the jammer happens to locate at
the same frequency as the parking fre-
quency, the hopper will not be able to

hop at all. And once it hops, it will be
very difficult to re-synchronise if the
receiver ever lost the sync.
The hopper usually costs more and
is more complicated than direct-se-
quence radio because it needs extra
hopping and synchronising circuits to
implement the synchronisation algo-
rithm.
The frequency hopper, however, is
better than direct-sequence radio when
dealing with multipath. This is because
the hopper does not stay at the same
frequency and a null at one frequency
is usually not a null at another fre-
quency if it is not very close to the
original frequency. So a hopper can
usually survive multipath better than
direct-sequence radio. The frequency
hopper can usually carry more data
than direct-sequence radio because the
signal is narrow-band.
When two signals collide, the
stronger one may survive regardless
of the kind of signal. In this band, all
radio must not exceed the power den-
sity limit set by the FCC. In other
words, all radios are equal when in-
terfering with one another. The best
strategy to prevent interference is to

make the important radios close to
each other (strengthen the link) and
prevent using frequency hopper be-
cause they are guaranteed to interfere
with other radios.
The hopper itself will also suffer
when it interferes with other radio. Any
system that can suffer more data loss
will survive better. In general, a voice
system can survive an error rate as high
as 10
–2
, while a data system must have
an error rate lower than 10
–4
. Voice sys-
tem can tolerate more data loss because
the human brain can ‘guess’ between
the words while a dumb microproces-
sor can’t. As a result, the frequency
hopper is more popular for voice than
data communications.
Advantages of spread-
spectrum wireless systems
Some of the advantages of spread-
spectrum wireless systems over con-
ventional systems are:
1. No crosstalk interference. Con-
ventional cordless phones frequently
suffer from crosstalk interference, es-

pecially when used in densely popu-
lated residential areas (such as apart-
ment complexes). This problem disap-
pears in spread-spectrum cordless
phone systems because:
(i) Crosstalk interference is greatly
attenuated due to the processing gain
of the spread-spectrum system as de-
scribed earlier.
(ii) The effect of the suppressed
crosstalk interference can be essentially
removed with digital processing where
noise below certain threshold results
in negligible bit errors. These negli-
gible bit errors will have little effect
on voice transmissions.
2. Better voice quality/data integ-
rity and less static noise. Due to the
processing gain and digital processing
nature of spread-spectrum technology,
a spread-spectrum based system is
more immune to interference and
noise. This greatly reduces the static
noise induced by consumer electron-
ics devices that is commonly experi-
enced by conventional analogue wire-
less system users.
3. Lowered susceptibility to
multipath fading. Because of its inher-
ent frequency diversity properties

(thanks to wide spectrum spread), a
spread-spectrum system is much less
Fig. 4: Direct-sequence spread-spectrum signal
Fig. 5: Frequency hopping
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susceptible to multipath fading. This
makes reception of a spread-spectrum
based cordless phone much less sensi-
tive to the location and pointing di-
rection of the handset than a conven-
tional analogue wireless system.
4. Inherent security. In a spread-
spectrum system, a PN sequence is
used to either modulate the signal in
the time domain (direct sequencing)
or select the carrier frequency (fre-
quency hopping). Due to the pseudo-
random nature of the PN sequence, the
signal in the air is ‘randomised.’ Only
a receiver that has exactly the same
pseudo-random sequence and syn-
chronous timing can despread and re-
trieve the original signal. Conse-
quently, a spread-spectrum system
provides signal security that is not
available to conventional analogue
wireless systems.
5. Co-existence. A spread-spectrum

system is less susceptible to interfer-
ence than other non-spread-spectrum
systems. In addition, with proper de-
signing of pseudo-random sequences,
multiple spread-spectrum systems can
coexist without causing severe inter-
ference to other systems. This further
increases the system capacity for
spread-spectrum systems or devices.
6. Longer operating distances. A
spread-spectrum device operated in
the ISM band is allowed to have higher
transmit power due to its non-inter-
fering nature. Because of the higher
transmit power, the operating distance
of such a device can be significantly
longer than for a traditional analogue
wireless communication device.
7. Hard to detect. Spread-spectrum
signals are transmitted over a much
wider bandwidth than conventional
narrow-band transmissions—20 to 254
times the bandwidth of narrow-band
transmissions. Since the communica-
tion band is spread, these can be trans-
mitted at a low power without suffer-
ing interference from background
noise. This is because when
despreading takes place, the noise at
one frequency is rejected, leaving the

desired signal.
8. Hard to intercept or demodulate.
The very foundation of the spreading
technique is the code used to spread
the signal. Without knowing the code,
it is impossible to decipher the trans-
mission. Also, because the codes are
so long (and quick), simply viewing
the code would still be next to impos-
sible to solve the code, hence intercep-
tion is very hard.
9. Harder to jam than narrow
bands. The most important feature of
the spread-spectrum technique is its
ability to reject interference. At first
glance, it may be considered that
spread-spectrum transmission would
be most affected by interference. How-
ever, any signal is spread in the band-
width, and after it passes through the
correlator, the bandwidth signal is
equal to its original bandwidth plus
the bandwidth of local interference.
An interference signal with 2MHz
bandwidth being input into a direct-
sequence receiver whose signal is
10MHz wide gives 12MHz output
from the correlator. The wider the in-
terference bandwidth, the wider the
output signal. Thus the wider the in-

put signal, the less the effect on the
system because the power density of
the signal after processing is lower,
and less power falls in the band-pass
filter.
Conversely, it may be
guessed that the most effective
interference to a direct-sequence
receiver is one with the narrow-
est bandwidth (a continuous-
wave carrier). This is the most
effective because power density
in the correlator output due to
narrow-band signals is higher
than due to wide-band signals.
10. Use for ranging and ra-
dar. The spread-spectrum technique
can be used to construct precise rang-
ing and radar systems. The spread car-
rier, modulated with the pseudo noise
sequence, permits the receiver to mea-
sure very precisely the time when the
signal was sent; thus, spread-spectrum
technique can be used to time the dis-
tance to an object, as in the case of
radar reflection. Both applications have
been commonly used in the aerospace
field for many years.
Modulation
For direct-sequence systems, the en-

coding signal is used to modulate a
carrier, usually by phase-shift keying
(e.g., biphase or quadriphase) at the
code rate.
Frequency-hopping systems gener-
ate their wide band by transmitting at
different frequencies, hopping from
one frequency to another according to
the code sequence. Typically, such a
system may have a few thousand fre-
quencies to choose from, and unlike
direct-sequence signal, it has only one
output rather than symmetrically dis-
tributed outputs.
The important thing to note is that
Fig. 6: Frequency hopping
Fig. 7: FHSS spectrum
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both direct sequencing and frequency
hopping generate wide-band signals
controlled by the code-sequence gen-
erator. For direct- sequence systems the
code is direct-carrier modulation,
while frequency hopping commands
the carrier frequency.
Considering direct sequencing, bal-
ance modulation is an important tool
in any suppressed carrier system, used

to generate the transmitted signal. Bal-
anced modulation helps to hide the
signal, and there is no power wasted
in transmitting a carrier that would
contribute to interference rejection or
information transfer. When a signal
has poor balance in either code or
carrier, spikes are seen in its spec-
trum. With these spikes, or spurs, the
signal is easily detectable, since once
these spikes are noticed above the
noise, it is obvious to look for the
hidden signal.
Information modulation in spread-
spectrum systems is possible in most
of the conventional ways; both ampli-
tude modulation (AM) and angle
modulation are satisfactory. Normally,
AM is not used for spread-spectrum
signals because it tends to be detect-
able when examining the spectrum.
Frequency modulation (FM) is more
useful because it is a constant enve-
lope signal, but information is still
readily observed. In both AM and FM,
no knowledge of the code is needed
to receive the transmitted information.
Clock modulation is actually fre-
quency modulation of the code clock.
It is usually avoided (e.g., for fre-

quency hopping) because the loss in
correlation due to phase slippage be-
tween received and local clocks can
degrade the performance. For direct
sequence, an FM demodulator tuned
to radio frequency (RF) carrier plus/
minus the clock could recover the data.
Another technique is code modifi-
cation, where the code is changed such
that the information is embedded in
it, then modulated by phase transitions
on an RF carrier.
Demodulation
Once the signal is coded, modulated
and then sent, the receiver must de-
modulate the signal. This is usually
done in two steps:
1. Spectrum-spreading (e.g., direct-
sequence or frequency-hopping)
modulation is removed.
2. The remaining information-bear-
ing signal is demodulated by multi-
plying with a local reference identical
in structure and synchronised with the
received signal.
Coding technique in
spread spectrum
In order to transmit anything, codes
used for data transmission have to be
considered. However, here we will not

discuss the coding of information (like
error-correction coding) but codes that
act as noise-like carriers for the infor-
mation being transferred. These codes
are much longer than those for the
usual areas of data transfer, as these
are intended for bandwidth spreading.
Coding can be of three types:
1. Maximal sequences
2. Composite code sequences
3. Error detection and correction
codes (EDACs)
The properties of codes used in
spread-spectrum systems are:
1. Protection against interference.
Coding enables a bandwidth trade, for
processing gain against interfering sig-
nals.
2. Provision for privacy. Coding
enables protection of signals from
eavesdropping, so even the code is se-
cure.
3. Noise-effect reduction. Error-de-
tection and correction codes can reduce
the effects of noise and interference.
One such coding method is maxi-
mal sequences. Maximal codes can be
generated by a given shift register or
a delay element of given length. In bi-
nary shift register sequence generators,

the maximum sequence length is 2
n
-1
chips, where ‘n’ is the number of stages
in the shift register.
A shift register generator consists
of a shift register in conjunction with
appropriate logic, which feeds back a
logical combination of the state of two
or more of its stages to its input. The
output, and contents of its ‘n’ stages
at any clock time, is a function of the
outputs of the stages fed back at the
proceeding sample time. Some codes
can be 7 to 2
36
–1 chips long.
Use of EDACs is mandatory for fre-
quency-hopping systems to overcome
the high rates of error induced by par-
tial band jamming. These codes’ use-
fulness has a threshold that must be
exceeded before satisfactory perfor-
mance is achieved.
In direct-sequence systems, EDAC
is not advisable because of the effect it
has on the code, increasing the appar-
ent data transmission rate, and may
increase the jamming threshold. Some
demodulators can operate error detec-

tion with approximately the same ac-
curacy as an EDAC, so it may not be
worthwhile to include a complex cod-
ing/decoding scheme in the system.
Applications of spread
spectrum
Wireless local area network (WLAN).
A WLAN is a flexible data communi-
cation system implemented as an ex-
tension to or an alternative for a wired
local area network. WLANs transmit
and receive data over the air,
minimising the need for wired connec-
tions. Thus, WLANs combine data con-
nectivity with user mobility and en-
able movable LANs.
Most WLAN systems use spread-
spectrum technique (both frequency
hopping and direct sequence). WLANs
are being used in health care, retail,
manufacturing, warehousing, aca-
demic and other arenas. These indus-
tries have profited from the produc-
tivity gains of using handheld termi-
In CDMA spread-spectrum transmission, user
channels are created by assigning different codes to
different users. This type of system provides privacy
by controlling distribution of user-unique code
sequences.
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COMMUNICATIONS
nals and notebook computers to trans-
mit real-time information to
centralised hosts for processing.
WLANs offer productivity, conve-
nience and cost advantages over wired
networks.
Space systems. In space stations,
which are continuously accessible to
interference, spread-spectrum methods
have proved effective. This is espe-
cially true for communication satellites.
In general, satellites do not employ
processing on-board as it adds to the
complexity and would limit the num-
ber of satellite users. A simple repeat-
ing satellite is used, so all the spread-
spectrum modulation and demodula-
tion must be done on the ground. With
no on-board processing, the satellite is
forced to transmit an uplink interfer-
ence signal, which reduces the space-
craft transmitter power to send the de-
sired signal. Another disadvantage of
no on-board processing is that every
receiver would have to acquire a
spread-spectrum demodulator.
Global positioning system (GPS).
GPS is a satellite-based navigation sys-

tem developed and operated by the US
Department of Defense. The idea be-
hind GPS is to transmit spread-spec-
trum signals that allow range measure-
ment from an unknown satellite loca-
tion. With knowledge of the transmit-
ter location and the distance to the sat-
ellite, the receiver can locate itself on a
sphere whose radius is the distance
measured. After receiving signals and
making range measurement on other
satellites, the receiver can calculate its
position based on the intersection of
several spheres.
GPS permits users to determine
their 3-D position, velocity and time.
This service is available for military
and commercial users round the clock,
in all weather, anywhere in the world.
GPS uses NAVSTAR (NAVigation
Satellite Timing And Ranging) satel-
lites. The constellation consists of 21
operational satellites and three active
spares. This provides a GPS receiver
with four to twelve usable satellites ‘in
view’ at any time. A minimum of four
satellites allow the GPS card to com-
pute latitude, longitude, altitude and
GPS system time. The NAVSTAR sat-
ellites orbit the earth at an altitude of

10,898 Nautical miles in six 55-degree
orbital planes, with four satellites in
each plane. The orbital period of each
satellite is approximately 12 hours.
The GPS satellite signal contains
information to identify the satellite, as
also positioning, timing, ranging data
and satellite status. The satellites are
identified by the space vehicle num-
ber or the pseudo-random code num-
ber. They transmit on two L-band fre-
quencies: 1.57542 GHz (L1) and 1.22760
GHz (L2). The L1 signal has a sequence
encoded on the carrier frequency by a
modulation technique that contains
two codes, a precision (P) code and a
course/acquisition (C/A) code. The L2
code contains only P code, which is
encrypted for military and authorised
commercial users.
Personal communications
The advantages of using spread spec-
trum in data and voice communica-
tions are:
1. Spread-spectrum signals can be
overlaid onto bands where other sys-
tems are already operating, with mini-
mal performance impact to or from the
other systems.
2. The anti-interference character-

istics of spread-spectrum signals are
important in environments where sig-
nal interference can be harsh, such as
networks operating on manufacturing
floors.
3. Cellular systems designed with
code-division multiple-access (CDMA)
spread-spectrum technology offer
greater operational flexibility and pos-
sibly a greater overall system capacity
than systems built on frequency-divi-
sion multiple-access (FDMA) or time-
division multiple-access (TDMA)
methods.
4. The anti-mutipath characteristics
of spread-spectrum signaling and re-
ception techniques are desirable in ap-
plications where multipath is likely to
be prevalent.
For these reasons, many companies
have begun developing spread-spec-
trum systems. Voice-orientated digital
cellular and personal communication
service providers are using CDMA.
CDMA implemented with direct-
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sequence spread-spectrum signaling is
among the most promising multiplex-

ing technologies for cellular telephony
services.
The advantages of direct-sequence
spread-spectrum signaling for these
services include superior operation in
multipath environments, flexibility in
allocation of channels, privacy and the
ability to operate asynchronously. Also
among the attractive features of
CDMA spread-spectrum is the ability
to share bandwidth with narrow-band
communication without undue degra-
dation of either system’s performance.
In CDMA spread-spectrum trans-
mission, user channels are created by
assigning different codes to different
users. This type of system provides pri-
vacy by controlling distribution of
user-unique code sequences.
Spread-spectrum systems exhibit
unique qualities that cannot be ob-
tained from conventional narrow-band
systems. There are many research av-
enues exploring these unique qualities.
Spread-spectrum technology can
alleviate the problems of conventional
cordless telephones. However, because
the technology was initially developed
for military applications, it could not
be readily applied for commercial use

due to its high cost and large size.
As this technology and the com-
ponents continue to develop, inte-
grated circuit (IC) technology has un-
dergone drastic advancement. This has
made commercial use of spread-spec-
trum technology a realistic proposi-
tion.
In conjunction with increased
cordless phone usage, data applica-
tions are also increasingly finding their
way into homes and small offices. This
is due in part to the maturity of multi-
media technologies and applications
and arrival of the information era
where global information through
powerful networking vehicles (such as
the Internet) is penetrating many
homes and offices.
These developments have created
demands for wireless data for homes
and small offices where wiring can of-
ten be either very costly or very in-
convenient. ISM-band spread-spec-
trum devices can be designed to ad-
dress the wireless data needs of home
and small-office users.
The road ahead
The factors that will determine the com-
mercial success of spread-spectrum

technology are its maturity, advance-
ment of baseband as well as RF IC tech-
nologies, and system integration to of-
fer the best value to end users.
As these elements continue to ad-
vance, spread-spectrum technology
will find more and more commercial
applications ranging from cordless te-
lephony to wireless LAN and wireless
data, digital cellular telephony and
even personal communication services.
The end users will be the ultimate ben-
eficiaries as the quality of these prod-
ucts improves while the cost contin-
ues to decline. z
The author is a lecturer in mechanical engineer-
ing at N.L. Polytechnic College, Mettupalayam,
Tamil Nadu