Note: Descriptions are shown in the official language in which they were submitted.
~ 2158269
L'` 1
ND APP~TUS FO~ T~E LJ~V~l~N
MULIInEaNG T~ USE OF SPRE~DING CODES
IN.~ r~1Ur'UNr~'~nONSYS~
Field of the Llvé~lliOn
The illvt~ ion relates generally to c~ .-ication ~ys~--s,
and more particularly to time division multiplexing the use of
1 0 spre~i~ codes in such Cc~ ;r~*rln ayah.~ 5.
Back~lou.~d of the L.v~.lion
C~o---~ ication ~ySlell1S take many forms. In general, the
~u~ose of a communication :~y:.L~I is to ~ ;t il~...ation-
I,ea.il~ 5ign~1c from a source, lor~t~l at one point, to a user
dea~ ;orl, located at another point some ~icPrlc~ away. A
communication system generally consists of three basic
20 CQ.~ ls; transmitter, channel, and r~eeiv~n The h.l..~...;ll~.
has the function of processing the mf~cç~ge signal into a form
suitable for transmission over the channel. This ~rocêssil~ of the
m~cs~ge signal is .cfe..ed to as modulation. The function of the
channel is to provide a physical connection between the
25 tral~,~ l output and the receivel input. The function of the
~eceiv~. is to process the received signal so as to produce an
estimate of the original message signal. This ~ cec~ g of the
rèceiv~:d signal is referred to as demodulation.
Analog and digital trar~cmicsion methods are used to
3 0 transmit a message signal over a communication channel. The
use of digital methods offers several c,yc~ Lonal advantages over
analog methods, including but not l;~ e~ to~ eased il~ Ul ily
to chalu~el noise and inlL.r~ ce, flexible o~_.ali;)n of the ~ysle..-,
L ~ ~ ~ 1 5 8 2 ~ ~
commorl fonn~t for the ~ C~ c~;on of dir~.e~ll kinds of mPcc~e
sigls, i,l~.o-ved sec~ily of ccs~ u~ication through the use of
el,~ly~tion~ and il~s~d r~r~rity.
To l-~-L~---;l a m~cs~p signal (either analog or digital) over a
5 co~ rA*on ~ nnPl ~-vi,.~, an ~c~ci~pd cl a,u,el bandwidth,
the mess~ge signal must be ~u~llated into a form suitable for
PffiriPnt trarlcmission over the c~nnP1 Mo~lific~tion of the
meSS~e signal is achieved by means of a process termed
modulation. This process involves Vd~yil~ some par~metp~ of a
10 carrier wave in accordance with the mesS?~e signal in such a way
that the s~e.hu"l of the morlnl~tefl wave matches the ~ssig~prl
.1.~.1..~1 bandwidth. P~.-...et~-s of a carrier wave that can be
varied include amplitude, frequency, and or phase.
Co~cs~u~lLllgly, the receiv~ is l~Uil.,d to recreate the original
15 mpscs~ge signal from a degraded version of the trarlcmitte~l signal
after propagation through the c~nnPl. The re-creation is
accc,ll,ylished by using a process known as rl~moc~ Qn, which is
the inverse of the modulation ~rDcess used in the tral~
A spread s~e-Llulll ~y~Lèlll provides, among other things,
2 0 robllc~nPcs to jamming, good il.Lelrerel,ce and mlll*p~th rejec*Qn,
and inhLlelllly secure communications from eavesdf~ . In a
spread spectrum ~y~Lélll, a modulation têchnique is utilized in
which a Ll.~ itted signal is spread over a wide frequency band
within the communication channel. The frêquency band is much
25 wider than the minimum bandwidth required tû transmit the
il~lll,ation being sent. A voice sign~l, for example, can be sent
with ~mE~ e modulation (AM) in a bandwidth only twice that
of the ~Ifol...~tion itself. Other forms of modulation, such as low
deviation frequency modulation (FM) or single si~ nd AM, also
3 0 ~l.llit il,fol~l,ation to be trancmitte~l in a bandwidth comparable
to the bandwidth of the information itself. However, in a spread
s~e.hulll ayaLelll, the modulation of a signal to be trarlcmitterl
often includes taking a b~ceb~n~ signal (e.g., a voice channel) with
2158269
a bandwidth of only a few l~iloh~rtz, and dish;L uh~l~ the signal to
be t~ e~ over a frequency band that may be many megahertz
wide. This is accomplished by modulating the signal to be
h~ æll with the ;~.~o~ *on to be sent and with a wideband
S ~nror~ signal (c~mmorlly hlo~ l as a spr~ i~ code).
Thus, a spread s~e~l.u l. sr~le..l must have two ~,o~ ies:
(1) the hd~ æ~ balldwidth sh~ be much g~æal., than the
bandwidth or rate of the ;~ro~ tion being sent and (2) some
function other than the i.~,l,lation being sent is employed to
10 let~- -.i-P the resulting modulated cl,a~ulel bandwidth.
The essence of the spread s~ec~, um communication
involves ~cp~i~ the l~".lwitth of a sign~ .a~.~...ill;.lg the
e~ signal and l~CCsv~ the desired signal by remapping
the received spread specl, u,,. into the ori~in~l i,lfo."lation
15 bandwidth. Furthermore, in the ~,ocess of c~..y,.~ out this series
of bandwidth trades, the purpose of spread s~.hulll techni~ues is
to allow the sy~lel" to deliver error-free il~o,ll.ation in a noisy
signal e,l~i,wullent.
With digital communication, user i,lfcsl"lation such as
20 speech is encoded into sequences of binary il~ lation. This
encoding is convenient for modulation and is easily error-
co.,ecLon coded for tr~ncmicsion over a ~o~ lly degrading
co...~ ..;c~tion channel. Such binary il~o....~*s~n is part~ rly
amenable to transmission using "direct sequence" spread ~ecL,
2 5 modulation. With direct sequence, digital illfG"llation is spread
with a spreading code whose bit rate is much higher than the
il,forlllation signal itself. Although the spreading can be
~rCQmpliched by several methods, the most co~nmon is to add
each bit of inform~tion (generally after a~ .iale error colle-lion
3 0 ~ ,) to a sequence of bits of the spr~ i~ code. Thus as desired
for the sprP~Ai~ process, many bits are grnPr~ted for each coded
information bit that is desired to be ~ e~
.~ 2IS8269
Advantages from direct sequence spread spech ul~l
communication sysleùls are obtained since the receiver is
knowlerlgPA~le of the sprPA~ code used to spread the user
signal. As is well known in the art the ~c~;v._., after a~,u~,;ate
5 synchrorli7~*on to the ~eceive signal, is able to decode the wide
~all.lwidth spread signal using a replica of the spreA~li~ sequence.
A~lotl.~ adv~ ge of spread s~chu~l cC~ Ation sy~ s is
the ability to provide multiple access capability. Specif
C~PlllllAr telephone ~ommlmirAtion :iyal~u~s have been designed to
10 incûr~orate the characteristic of communicating with many
remote units on the same cQm~ nir~tion channel.
One type of multiple access spreat spectrum
communication ~ysLelll utilized with direct sequence spread
spectrum is a code division multiple access (CDMA)
commnni~A*on sy:,L~ . In a CDMA co.. ~.. ;rAtion sy:~le
communication between two communication units is
cQmplished by spre~ing each tral~c~ e~ signal over the
frequency band of the co~ t~l;rAtion rh~nnPl with a unique user
spreading code. As a result, trallc....lle~ signals are in the same
2 0 frequency band of the communication charmel and are separated
only by unique user spreading codes. Particular tran~ lle(l
signals are retrieved from the communication channel by
desprPA~ing a signal representative of the sum of sign~lc in the
ro....u...ucation charmel with a user spreading code related to the
25 particular transmitted signal which is to be retrieved from the
- commurucation channel. Specially suited spreading codes may be
employed to reduce the il~Le~fe,.:llce created by the sum of all the
other 5ign~1c present on the same channel. OrthogonaI codes are
typically used for this purpose, and of these, the Walsh codes are
3 0 most roTnmon.
Many digital cellular pleco~ irAtion ~y~le~l~s have the
ability to provide reduced data rate traffic rhAnnPlc. These ~ysle~ls
have traffic channels designed to o~elale at a particular data rate
2158269
and also have rer~ e~l data rate kaffic rh~nrlPlc which provide
more kafflc data r~rarity than that at the designed data rate. ~is
il,.lcased kafflc data r~ rity in a~l~e~ed at the cost of reduced
quality and/or ~l~leased co~ yity a~l~ coders and ~lero~
Thus, a need exists for a ro.. ~.. ;c~tion :,y~Le~l~ which
provides increased or high data rate trafflc channels which allow
for tral.c...icsion of data at a rate higher than ~e designed data rate
traffic c~ lc without ~lt~ri~ .;u~.~,L l~a~lw."~ ~esi~r~c and air-
; "1~ . ~a~æ spnr~rds.
1 0
Brief Des..;~tion of the D.a-vu~s
FIG. 1 generally depicts, in block ~ F~m form, a prior art
15 spread s~e.~ " transmitter.
FIG. 2 generally depicts, in bloclc di~F~m form, a prior art
spread s~ecl~ l transmitter for l~ ittirlg il~fG~ tion for two
users.
FIG. 3 generally depicts, in block rli~ m form, a ylëLe~ed
20 emboflirn~rlt spread spectrum traI~cmitte- which ye~LGlllls timê
division multiplexing of spreading codes for two users in
accordance with the invention.
FIG. 4 is a chart showing how a spreading (Walsh) code is
shared ~mongct two users to provide a rate 1/2 capability for each
2 5 user in accordance with the invention.
Detailed Description of a r~eLe.,ed Embo~lim~rlt
A communication sy:,Lelll time division multiplexes the
use of spreading codes. The coll,l~,u~ucation ~y~lelll accepts
in~rmAtion (301, 302) from at least h~ro users and codes each users
il~ro~ on utilizing error co.-~.lion coders (303, 306). The coded
2158269
6
info.l..a*on is then time mlll*plP~e~l by a mlll*rlexer (312) into
*nnPslots. The ol,lyul of the mnl*plexer t312) is spread by a
common sprr~ ~ (Walsh) code, srr~mhl~ with a pseudo-noise
sequence, and ccl~ ed to a mo~ tor for ~ ...;qciott. In this
5 manner, i.~o,...~*on for two users may be transmitted utilizing
only a single spr~iin~ (Walsh) code.
Many embo~imenb exist. In the ~refe..ed embodiment,
first (USER 1) and second (USER 2) user i..ro~ tion 301, 302 is
mall*~ prl in at least partially non-ove.l~y~ time pPno~s by a
10 multiplexer 312 to produce m~ll*rlexed first and second user
il~o...-~*o-l The mlll*rleYerl first and sec~ user ;~.f.~ *Qn
is then spread with a coInmon spr~ ~ code. In an ~lter~te
emboAim~rlt, the first and seco~ user ;.. fc.. ~*~n 301, 302 may
first be spread by a common spre~ling code, then mtll*pl~Ye~ into
at least partially non-overlapping time periods. In either
embodiment, the common spreading code is a common
orthogonal spreading, and typically a Walsh code. As one of
ordinary skill in the art will appreciate, the first and seco~l user
ation may be coded or llnro~P-I, Any Pmhorlim~nt chosen
2 0 may be implemented in either a base-station or a mobile unit
which is compatible with the spread specl~ulll corn~ lnication
~y~l~.l
Referring now to FIG. 1, a prior art spread spectrum
trar~cmitter is shown. In the prior art spread spe~u.l~ trar~cm~ r
2 5 of PIG. 1, USEl~ 1 data bits 100 are input to an encoder 102 at a
partirlllPr bit rate ~e.g., 9.6 kbps). USER 1 data bits 100 can include
either voice converted to data by a vocoder, pure data, or a
rc-mh;rlation of the two types of data. F.nrnrl~r 102 convolutionally
encodes the USER 1 data bits 100 into data symbols at a fixed
3 o ~ncorling rate. For example, encoder 102 ptlrorlpc ~ecei.~ed data bits
100 at a fixed ~nro~-rlg rate of one data bit to two data symbols such
that the encoder 1~2 o.lL~ul~ data symbols 104 at a 19.2 ksym/s rate.
2I58~69
-~ 7
l~e encoder 102 may ~c~ orl~te the input of USER 1
data bit_ 100 at variable lower rates by e~ ~rn~ on. That L,
when the data bit rate is slower than the particular bit rate at which
the ~ncorler 102 is .l~ci~ to o~e,al~, Pnc~r 102 repeats USER 1
- S data bits 100 such that the USER 1 dah Wts 100 are provided the
f~n~o~ g Phmentc within the ~ncorl~r 102 at the desired full rate.
For eY~mple, if the input rate were 1/2 rate, the inforrnation
would be repeated twice (i.e., to 5im~ te a full rate). If the input
rate were 1/4 rate, the il~ro~ nrl would be ~ four times,
and so on. Thus, the encoder 102 ou~ ls data symbols 104 at a the
same fixed rate regardless of the rate at which data bits 100 are
input to the encoder 102.
The data symbols 104 are then input into an interleaver 106.
Tnt~rle~ver 106 interleaves the input data symbols 104. The
l 5 interleaved data syrnbols 108 are uul~-li by the interleaver 106 at
the same data symbol rate that they were input (e.g., 19.2 ksyrn/s)
to one input of an exclusive-OR combiner 112.
A long pseudo-noise (PN) generator 110 is operatively
coupled to the other input of exclusive-OR combiner 112 to
2 0 enhance the security of the cc~ ?tion .l~a~u~cl by 5~r~mhli~
data symbols 108. The long PN generator 110 uses a long PN
sequence to generate a user specific sequence of symbols or unique
user code at a fixed rate equal to the data symbol rate of the data
symbols 108 input to exclusiv~OR gate 112 (e.g., 19.Z ksym/s). The
2 5 scrambled data symbols 114 are output from exclusive-OR
combiner 112 at a fixed rate equal to the rate that data symbols 108
are input to the exclusive-OR combiner 112 (e.g., 19.2 ksym/s).
Scrambled data symbols 114 are then input into exclusiYe-OR
combiner 118.
3 0 A code division channel s~lec*~n generator 116 provides a
particular predetermined length spreading (Walsh) code to
another input of exclusive-OR combiner 118. The code division
d~lulel s~lection generator 116 can provide one of 64 orthogonal
~=
.` 2158269
_ 8
codes c~ O~G~ to 64 Walsh codes from a 64 by 64 ~Ad~mArd
matrix, wherein a Walsh code is a single row or column of the
m~triy ~ . l,.e;v~OR comhin~r 118 uses the particular Walsh code
input by the code division .l~alulel gel~ 116 to spread the
input scrambled data symbols 114 into Walsh code spread data
symbols 120. The Walsh code spread data symboLc 120 are oul~
from ~y~ c;v~oR combiner 118 at a fixed chip rate (e.g., 1.2288
Mchips/s).
The Walsh code spread data symbols 120 are provided to an
1 0 input of two eYcll~cive-OR comhirlers 122 and 128. A pair of short
PN sequences (i.e. short when ro ~ ed to the long PN sequence
used by the long PN g-..e.dlor 110) are ~ .e" l~l by I-charmel PN
generator 124 and Q-channel PN generator 130. These PN
ge~ Q~ 124 and 130 may ~,~ ...o., te the same or diLL.e.ll short
1 5 PN seq~ r~e F~ cive~oR combiners 122 and 128 further spread
the input Walsh code spread data 120 with the short PN sequences
generated by the PN I-channel generator 124 and PN Q-channel
generator 130, respectively. The resulting I-channel code spread
sequence 126 and Q-channel code spread sequence 132 are used to
2 0 bi-phase modulate a quadrature pair of sin~lcoi~ls by driving the
power level controls of a the- pair of si~?lcoi~C. The sinusoid's
ouL~ ci~Alc are summed, bandpass filtered, trAnclAted to an RF
~requency, amplified, filtered and radiated by an anlel.lla to
complete transmission of USER 1 data bits 100 via a
2 5 communication channel.
FIG 2 shows the typical confi~uration used to Accc,~ orlAte
two users. In essence, the apparatus of FIG 1 is replicated for the
- second user. Each apparatus' q~lA~rAtllre oul~ut signals are
combined together by combiner 134 prior to modulation and radio
3 o tr~nen~ieeion. Each user always uses a rlictinct Walsh code to
spread its i~.fo~.l.ation 114. This is true even when the input data
100 rate is reduced, for example, to 4.8 kbps max. As previously
mentioned, .~eLLon coding expands this data rate to an eL~e.Lve
,`~ 21S826g
9.6 kbps rate so that the Walsh code spr~i~ always results in the
desired 1.2288 Mchips/s desired oult,u~. Thus, to trancmit the
il.fc,.l..ation of any two users, for cx~u,~le USER 1 and USER 2,
re~lUil~S the use of two (of the m~ ---. 64) Walsh codes.
S ~IG. 3 ~PnPrAlly r~epictS, in block ~ m form, a ~lere~èd
embodiment spread s~ecll ù~l transmitter apparatus which
~.lru~ll s time division mlll*pl~Yirl~ of spreading codes for two
users in accordance with the u,~ n The l ~a..~ . a~a~alus
of PIG. 3 ill~iC~v~ s upon the prior art s~ e~hull~ tral~
10 shown in PIG. 2 when used for ~ , the i.~folll,ation of
two users. As can be seen, FIG. 3 does not .~quir~ the dup~ AtiQn
of trAncmitter hardware to transmit ;..fol...A*on for two users
while only requiring a single spreA~lin~ (Walsh) code for
.icsion of the il,[c~ Atior~
I2Ff~-,;-,~, to FIG. 3, USER 1 data bits 301 and USER 2 dah
bits 302 enter respective error cûll~cLion coders 303, 306. Time
division multiplexing of spreading codes is acco~,~lished by
cor~ first user data 301 to prûduce coded first user data 304 and
codil.g second user data 302 to produce coded secul,.i user data 307.
2 0 Coded first user data 304 and coded second user data 307 are then
m~ plexed in at least partially non-overlapping time periods by
multiplexer 312. The partially non-overla~il,g time periods are
given by l/fc~ where fc is the frequency of a clock signal 309 input
into mlll*plexer 312. The multiplexed coded first user data and
2 5 the coded second user data is then spread, by spreader 315, with a
common spreading code (Wj) to create modulator data 316.
Important to note is that only a single, common orthogonal
spreading (or Walsh) code is required in this implem~rltAt;Qn.
Modulator data 316 is then srrAmhled by s~r~mhler 318. In
3 0 the ~le~cl~ed embodiment, scrambler 318 scrambles modulator
data 316 with a psel~o-noise s~r~mhli~ se~uence. The s~ramhl~
modulator data 319 is then collveyed to a mo~ tor where it is
transmitted via a wireless il.lel~ace to a destination. In the
~ ` 2158269
~el~e;l embo~lim~nt, the c,l~ui~ of FIG. 3 and the method
f may be imrl~m~nte~l in either a ~a~e st~ion or a mobile
unit ~o~ ;hle with the spread s~ o~ ication Syale--
~
It is well known in the art to ay~..lu~.~e the mlll*plexingof mlll*ple data streams on an ~lt~ ting basis to the Walsh
spreader. Of course, this method and synchronization
illfo~ll.ation must also be known at the feceivel (i.e., the
deslil~lion) to allow sllcc~csr~ ieco~ of the ;--rol---~*Qn D~
CDMA sy~l~ms have very well ~Ct~ clock signals, through
10 use of synchronization sequence and PN tracking, thus no
~itior~ 3, il,fo.~ tion is l~r~c5~ . Again, through this
method, it is seen that only a single Walsh code is l~t~ er1 for the
tr~ncmicsiQn of two user's i~ l.ation.
FIG. 4 shows a timing chart of how a single Walsh code, Wl,
1~ is shared for transmitting the i~ ation of two users. In
alternate trarlcmicsion blocks, the il~~ tion for USER 1 and
then USER 2 is repetitively transmitted in partially non-
overla~ æ time periorlc given by fc-
While the invention has been particularly shown and
20 described with ,ere~ .ce to a particular embori~ t~ it will be1ln~rctoo-l by those skilled in the art that various changes in form
and details may be made therein without d~a~ , from the spirit
and scope of the invention.
What I claim is:
