Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 96/42174 21~ 6 6 81 PCT/US96/0~998
CHANGING A SERVICE OPTION IN A CDMA COMMUNICATION SYSTEM
Field of the Invention
The invention is generally related to code division multiple
access c nmm1mir~tion systems, and more particularly to changing
service option ~ccignm~ntc in a code division multiple access
10 rnmmllnir~tir,n system.
Background of the Invention
Code Division Multiple Access (CDMA) rommllnir~ n systems
are well known. In a CDMA romm11nir~tir,n system, communication
between two rr~mm~mir~tion units (e.g., a central communication site
and a mobile c~mmnnir~ti~m unit) is accomplished by spreading each
tr~ncmittr-d signal over the frequency band of the rr~mmnn;r~tion
channel with a unique user spreading code. Due to the spreading,
L-dn~,..iLLed signals are in the same frequency band of the
commllnir~tion channel and are separated only by unique user
spreading codes. These unique user spreading codes preferably are
orthogonal to one another such that the cross-correlation between the
2 5 spreading codes is a~l,.oxiJIlaL~ly zero. Consequently, when the user
spreading codes are orthogonal to one another, the received signal can
be correlated with a particular user spreading code such that only the
desired user signal (related to the particular spreading code) is despread.
It will be appreciated by those skilled in the art that several
3 0 different spreading codes exist which can be used to separate data
signals from one another in a CDMA ~ u-u dLion system. These
spreading codes include, but are not limited to, pseudo noise (PN) codes
WO 96142174 PCI'/US96/~5998
21~681
and Walsh codes A Walsh code ~ ""~'~1" .. ,.1~, to a single row or column
of the Hadamard matrix. Eor example, in a 64 channel CDMA spread
spectrum system, particular mutually olLl.o~ ldl Walsh codes can be
selected from the set of 64 Walsh codes within a 64 by 64 Hadamard
S matrix. Also, a particular data signal can be separated from fhe other
data signals by using a particular Walsh code to spread the particular
data signal.
It will be further d~ecidLed by those skilled in the art that
spreading codes can be used to channel code data signals. The data
10 signals are channel coded to improve performance of the
communication system, and particularly radiotelephone
communication systems, by enabling Lld~ uLLed signals to better
withstand the effects of various radiotelephone channel ;~
such as noise, fading, and jamming. Typically, channel coding reduces
15 the probability of bit error, and/or reduces the required signal to noise
ratio usually exp}essed as bit energy per noise density (Eb/No). to
recover the signal at the cost of expending more bandwidth than would
otherwise be necessary to transmit the data signal. For example, Walsh
codes can be used to channel code a data signal prior to modulation of
20 the data signal for subsequent frAncmicci~-n. Similarly psuedo-noise
(PN) spreading codes can be used to channel code a data signal.
A typical CDMA transmission involves expanding the
bandwidth of an information signal, L~dl~uLilLillg the expanded signal
and recovering the desired information signal by remapping the
2 5 received spread spectrum into the original information signals
bandwidth. This series of bandwidth trades used in CDMA
trAncm;Ccinn allows the CDMA cl~mm-lni~ ~finn system to deliver a
relatively error-free ;nformation signal in a noisy signal environment
or rnmmnni~Afinn channel. The ~uality of recovery of the tr~nsmiff,~l
30 infnrm~fnnn signal from the comml~ni~fi~n channel is measured by
the error rate (i.e., the number of errors in the recovery of the
1,,."~ .1 signal over a particular time span or received bit span) for
WO 96/42174 ~ PCT/US96/05998
some Eb/No. As the error rate increases the quality of the signal
received by the receiving party decreases. As a result, ~ommllninAiion
systems typically are designed to limit the error rate to an upper bound
or mA~iml-m so that the d~grA~1Ahnn in the quality of the received
5 signal is limited.
In current CDMA rnmmnni~Ahnn systems, such as those defined
by IS-95A ("Mobile Station-Base Station Compatibility Standard for
Dual-Mode Wideband Spread Spechum Cellular System and published
by the Electronic Tnllnctri~c Association (EIA), 2001 Eye Shreet, N.W.,
l 0 Washington, D.C 20006) for Digital Cellula} Systems (DCS) and ANSI-J-
STD-8 for Personal l~nmml~nirAh~n Systems (PCS), the capabilities of a
base station and a mobile station can differ based upon their software
and hardware configurAhnrls. One such example is in the area of
available service options, which for IS-95A, are defined by TSB58. Each
15 service option is defined by data lL~ sL-IILil-g the service option, and as
defined in TSB58 for IS-95A, the data is a 16 bit field l~lJlL'~lLLillg the
service options.
There is no requirement that every service option be supported
by every operator of a DCS/PCS. As such, when a mobile station
2 0 ~ Li-lg to a home base station enters a DCS/PCS which does
not support a service option supported by the home DCS/PCS, the
home base station is required to transmit messages to the mobile
station to change to a service option supported by the target DCS/PCS.
The current process of changing the service option is a cumbersome,
2 5 time consuming negotiation technique, a technique which is
incompatible with the goal of transparent mobile station handoffs
when implemented in DCS/PCSs. Important to note is that the
technique itself is cumbersome; when handoff is included, the overall
ser~ice option change/handoff task is completely ;n~nmpahhle for a
3 0 DCS/PCS.
For example, the current technique required to change a service
option begins when the base station sends a Servtce Req~est Message to
WO 96142174 ~1 g ~ 6 81 PCTIUS96105998
l s ~
the mobi'se station which proposes a change in service option. IS-95A
allows a m~ximnm time period of 5 seconds for the mobile station to
respond to this message. The mobile station then responds with a
Service ~esponse Message which accepts the proposed change in
5 service option. The base station may wait a mAY~mnm of .2 seconds for
t,sis message. The base station then sends a Service Connect Message
which includes the data ,~les~ Lion of the service option to be
employed. The mobile station may wait a m~Yimnm of .4 seconds for
this message. ~inally, the mobile station responds with a Service
0 Connect Completion Message which notifies the base station that the
change in service option has been completed. At tl'sis point, the base
station sends an Extended Handoff Direction Message to the mobile
station. Since a handoff may take up to .4 seconds, the entire
negotiation fr-rl~nirlslr-, from service option change to handoff, may
15 result in up to 6 seconds of "dead time" over the air. This amount of
"dead time" over the air will cause mobile stations to delay entering
into soft handoff, which has the effect of increasing system il~L~lftlc~
and ~uLlt:~uulLdiLI~,ly decreasing system capacity.
Thus a need existing for a method and apparatus to efficiently
20 change a service option in a CDMA communication system without
effecting system capacity.
Brief Description of the Drawings
FIG. 1 generally depicts a CDMA rommlln;r~hnn system which
may beneficially employ service option change in s~rrnrrl~nrr with the
invention.
FIG. 2 generally depicts a Llcsns~lilL~l of a mobile station in
3 0 CDMA rnmmnn;r~*nn with a receiver of a base station in a manner
wl~sich may beneficially implement the present invention.
WO 96/42174 21 9 6 6 ~1 PCT/lJS96/05998
.
FIG. 3 generally depicts a L~ La"liLL~l of a base station in CDMA
r~mmnnir~tion with a receiver of a mobile station in a manner which
may beneficially impl~mPnt the present invention.
FIG. 4 generally depicts the protocol layering structure for a
5 CDMA communicafion system.
FIG. 5 depicts an Extended Handoff Direction Message having the
service option data l~ s~ Lion therein in accordance with the
invention.
1 0
Detailed Description of a Preferred l~ bl)di~ L
A code division multiple access (CDMA) rnmmllni~tinn system
implements a service option change in a mobile station by including
1 5 data l ~ at ~ .g the service option to be employed in a handoff
message ~ cl from a base station to the mobile station. Use of
the handoff message as a medium to change a service option ~ c
the cumbersome negotiation technique currently required to perform a
service option change prior to handoff of the mobile station from a first
2 0 coverage area to a second coverage area or from a first channel to a
second channel within a given coverage area.
Stated generally, a service option in a code division multiple
access (CDMA) ~lmmnni~til~n system is changed in a mobile station
by first ~1Pt~rmining the service option to be employed by a mobile
25 station and ~ " to the mobile station, data ~ a~lliillg the
service option in a ~le~xiaLi~lg message. In the preferred embodiment,
the data l~lea~llLillg the service option is a 16 bit field ~ les~l~LiLLg one
of a plurality of service options, and the preexisting message is a
handoff message, specifically an Ex~ended Handoff Direc~ion Messa~e.
3 0 Also in the preferred embodiment, the tr~ncmitting of the data
representation of the service option in a preexisting message is
L~ a~a~ L to a phvsical layer on which the tr~ncmisci~n occurs.
WO 96142174 PCT/US96/05998
.
8 1
Referring now to FIG. 1, a CDMA rnmmllnirAtir1n system 100
which may bPnPfiriAlly employ service option change in accordance
with the invention is depicted A first base station 102 is located in a
first coverage area 104 and rnmmlln;rAtP4 with a mobile station 106.
5 f~.""""";,,.l;nn is via a digital radio channel 108 which contains data
information compatible with a CDMA cnmmlln;cAtion system as
defined by IS-95A. The mobile station 106 will maintain
rnmmlln;rAtinn with the first base station 102 until the mobile station
106 nears the second coverage area 110.
As the mobile station 106 nears the second coverage area 110, a
cellular handoff from the first base station 102 to the second base station
112 becomes necessary. In CDMA, a feature called "soft handoff" is
supported. Durmg soft handoff, the second base station 110 is notified
in advance that it is the target of a cellular handoff, and as such is told
15 the transmission pattern that the mobile station 106 utilizes to
communicate with the first base station 102 The second base station
112 will begin ll.,ll~,.ll;ll;llg to the mobile station 106 with the same
tr~nsmiC4inn pattern, and the mobile station 106 will
detect/demodulate the l",,~ ,..;nn from both base stations 102, lIZ
2 0 When the mobile determines that the second base station 112 provides
better qualit~ (based on thresholds), the base stations 102,112 are so
notified via the CDMA Base Site Controller (CBSC) 114
Communication from the first base station 102 to the mobile station 106
is terminated, and the second base station 112 assumes the
25 communication LeD~ulLDibilities. The handoff is termed "soft handoff"
because, from the P~:~D~ tiVe of the mobile station 106, no break in
communication has occurred.
When entrance of soft handoff is delayed (by having a lengthy
combination of service option change/handoff procedure), the
3 0 threshold at which the mobile station 106 ~ill initiate soft handoff is
increased. This increase in threshold results in a correspondingly
higher amount of power required to be l,~ d by the mobile
W O 9~42174 PCT~US96/05998
21 g~681
station 106. As in any commllnir~ti~n system, the higher the amount
of power tr~ncm;tt~fl, the mo}e hllelLelellee the commllnir~tion
system will experience. In CDMA I ~ " " " " " ~ irln systems, an increase
in system il~LelLe~ell~e results in a decrease in system capacity, or the
number of mobile stations 106 that may be served by any one base
station 102, 11~
FIG. 2 generally depicts a Ll.lllb~liLLel 200 of the mobile station 106
in CDMA rrmm1mir~tirn with a receiver 203 of the base station 102 in
a manner which may bPnrfiri~lly implement the present invention. In
1 0 the encoding portion 201 of the rrlmmnnir~tion system, traffic channel
data bits 202 originate from a mie~ lo~c~bbl~ LP) 205, and are input to
an encoder 204 at a particular bit rate ~e.g., 9.6 kilobit/second). The IlP
205 is coupled to a block designated related functions 207, where
functions including call processing, link establishment, and other
1 5 general functions related to establishing and m ~ ;llg cellular
communication are performed. The traffic channel data bits 202 can
include either voice converted to data by a vocoder, pure data, or a
combination of the two types of data. Encoder 204 encodes the traffic
channel data bits 202 into data symbols 206 at a fixed encoding rate (1/r)
2 0 with an encoding algorithm which facilitates subsequent maximum
likelihood decoding of the data symbols into data bits (e.g.,
convolutional or block coding ~lgorithmc). For example, encoder 204
encodes traffic channel data bits 202 (e.g., 192 input data bits that were
received at a rate of 9.6 kilobits/second) at a fixed encoding rate of one
data bit to three data symbols (i.e., 1/3) such that the encoder 204
outputs data symbols 206 (e.g., 576 data symbols output at a 28.8 kilo
symbols/second rate).
The data symbols 206 are then input into an interleaver 208.
lnterleaver 208 organizes the data symbols 206 into blocks (i.e., frames)
3 0 and block interleaves the input data symbols 206 at the symbol level. In
the interleaver 208, the data symbols are individually input into a
matrix which defines a predetermined size block of data symbols. The
WO 96142174 F~
2~96681
i,
data symbols are input into locations within the matrix so that the
matrix is filled in a column by column manner. The data symbols are
individually output from locations within the matrix so that the matrix
is emptied in a row by row manner. Typically, the matrix is a square
5 matrix having a number of rows equal to the number of columns;
however, other matrix forms can be chosen to increase the output
iutL~Lledvillg distance between the ~u~ uliv~-ly input non-interleaved
data symbols. The interleaved dah symbols 110 are output by the
interleaver 208 at the same data symbol rate that they were input (e.g.,
I 0 28.8 kilo symbols/second). The ~ P~ size of the block of dah
symbols defined by the matrix is derived from the L.,axiuluu, number
of data symbols which can be 1,", ~ d at a coded bit rate within a
prP~lPtPrminPcl length ~ ll.;~ .u block. For example, if data symbols
206 are output from the encoder 204 at a 28.8 kilo symbols/second rate,
1 5 and if the prPd~ptprminpcl length of the Llanbulission block is 20
millic~cnnris, then the prp~ptprminp~l size of the block of data symbols
is 28 8 kilo symbols~second times 20 milliseconds (ms) which equals
576 data symbols which defines a 18 by 32 matrix
The encoded, interleaved data symbols 210 is output from
2 û encoding portion 201 of t~e cnmmllni~tlL n system and input to a
transmitting portion 216 of the communication system. The data
symbols 210 are prepared for trancmicc;on over a communication
channel by a modulator 217. Subsequently, the modulâted signal is
pro~ided to an antenna 218 for transmission over the digital radio
25 channel 108
The modulator 217 prepares the data symbols 210 for direct
sequence code divided spread-spectrum Llal-LaulibbiulL by deriving a
sequence of fi~ed length codes from the encoded, interleaved data
symbols 210 în a spreading process For example, the data symbols
3 0 within the stream of reference-coded dah symbols 210 may be spread to
a unique fixed length code such that a group of six data symbols is
-~lebL-uLlL d by a single 64 bit length code. The codes LL~~ aL-lLlLLLg the
wo 96/42174 219 6 ~8 ~ r~
group of six data symbols yl~lably are combined to form a single 64 bit
length code. As a result of this spreading process, the modulator 217
which received the encoded, interleaved data symbols 210 at a fixed
rate (e.g., 28.8 kilo symbols/second) now has a spread sequence of 64 bit
length codes having a higher fixed symbol rate (e.g., 307.2 kilo
symbols/second). It will be ~ L~d by those skilled in the a}t that
the data symbols within the stream of encoded, interleaved data bits
210 may be spread according to numerous other ~lgf~rithmc into a
sequence of larger length codes without departing from the scope and
I 0 spirit of the present invention.
The spread sequence is further prepared for direct sequence code
divided spread-spectrum trAncmiCc;~,n by further spreading the spread
sequence with a long spreading code (e.g., PN code). The spreading code
is a user specific sequence of symbols or unique user code which is
1 5 output at a fixed chip rate (e.g., 1.~78 Megachips/second). In addition toproviding an i~ ntifi~Ation as to which user sent the encoded traffic
channel data bits 202 over the digital radio channel 108, the unique user
code enhances the security of the communication in the
communication channel by scrambling the encoded traffic channel dat_
2 0 bits 20~ In addition, the user code spread encoded data bits (i.e., data
symbols) are used to bi-phase modulate a sinusoid by driving the phase
controls of the sinusoid. The sinusoid output signal is bandpass
filtered, translated to an RF frequency, amplified, filtered and radiated
by an antenna 218 to complete ~Ancmissi~n of the traffic channel data
bits 202 in a digit_l radio channel 108 with Binary Phase Shift Keyed
(BPSK) modulation.
A receiving portion 222 of the base station receiver 203 receives
the transmitted spread-spectrum signal from over the digital radio
channel 108 through antenna ~24. The received signal is sampled into
3 0 data samples by despreader and sampler 226. ~1lhSf~qu~ntly~ the data
samples 242 are output to the decoding portion 254 of the
communication system.
WO 96/42174 PCTIU!~96/05998
21~6~1
The despreader and sampler 226 preferably BPSK samples the
received spread-spectrum signal by filtering, tiPmt~ ting, translating
from the RF frequencies, and sampling at a predPtPrminP~I rate (e.g.,
1.2288 MPg~c~mrlPc/second). Subsequently, the BPSK sampled signal is
despread by correlating the received sampled signals with the long
spreading code. The resulting despread sampled signal 228 is sampled
at a prP-lPtPrminP~l rate and output to a non-coherent detector 240 (e.g.,
307.2 lcilo samples/second so that a sequence of four samples of the
received spread-spectrum signal is despread and/or leylesellled by a
1 0 single data sample) for later non-coherent detection of data samples 24~
As will be dt7~7leei~Led by those skilled in the art, multiple
receiving portions 222 through 223 and antennae 224 through 225,
Les~7e.Lively, can be used to achieve space diversity. The Nth receiver
portion would operate in sllhshnti7~lly the same manner to retrieve
l 5 data samples from the received spread-spectrum signal in digital radiochannel 108 as the above described receiving portion 22~ The outputs
242 through 252 of the N receiving portions preferably are input to a
summer 250 which diversity combines the input data samples into a
composite stream of ~uhelellLly detected data samples 260.
2 0 The individual data samples 260 which form soft decision data
are then input into a decoding portion 254 including a deinterleaver
262 which deinterleaves the input soft decision data 260 at the
individual data level. In the deinterleaver 262, the soft decision data
260 are individually input into a matrix which defines a prP~iPt.ormin~-l
2 5 size block of soft decision data. The soft decision data are input into
locations within the matrix so that the matrix is filled in a row by row
manner. The deinterleaved soft decision data 264 are individually
output from locations within the matrix so that the matrix is emptied
in a column by column manner. The deinterleaved soft decision data
3 0 264 are output by the deinterleaver 262 at the same rate that they were
input (e.g., 28.8 kilr~mPtri~ c/second)
~ ~6~81
WO 96/42174 PCT/US96/05998
The predetermined size of the block of soft decision data defined
by the matrix is derived from the maximum rate of sampling data
samples from the spread-spectrum signal received within the
pre~letPrminPd length ~ m block.
The d~ L~lle~lv~d soft decision data 264, are input to a decoder
266 which uses mAYimllm likelihood decoding techniques to generate
estimated traffic channel data bits 268. The ",~1...."" iikpl;h~od
decoding It~ h~ e~. may be angmPntP~1 by using an algorithm which is
substantially similar to a Viterbi decoding Algl7rithm The decoder 266
1 0 uses a group of the individual soft decision dab 264 to form a set of softdecision transition metrics for use at each particular time state of the
maximum likelihood sequence estimation decoder 266. The number of
soft decision data 264 in the group used to form each set of soft decision
transition metrics ~JL~ ds to the number of data symbols 206 at the
I S output of the convolutional encoder 204 generated from each input
data bit 202. The number of soft decision transition metrics in each set
is equal to two raised to the power of the number of soft decision data
264 in each group. For example, when a 1/3 convolutional encoder is
used in the Lla~ iLL~l, three data symbols 106 are generated from each
2 0 input data bit 202. Thus, decoder 266 uses groups of three individual
soft decision data 264 to form eight soft decision transition metrics for
use at each time state in the maximum likelihood sequence estimation
decoder 266. The estimated traffic channel data bits 268 are generated at
a rate related to the rate that the soft decision data 264 are input to the
2 5 decoder 266 and the fixed rate used to originally encode the input data
bits 202 ~e.g., if the soft decision data are input at 28.8
kilometrics/second and the original encoding rate was 1/3 then
estimated traffic channel data bits 268 are output at a rate of 9600
bits/second).
3 0 The estimated traffic channel data bits 268 are input into a IlP 270,which is similar to ~P 207. As in the case of IlP 207, the IlP 270 is
coupled to a block designated related functions 272, this block also
2l~668~
WO 96142174 PCTIUS96/05998
..fu~ i..g functions including call ,ulu~a~lllg, link establishment, and
other general functions related to establishing and ~ , cellular
~:I.~.. ,I.,.. I;nn The ~P 270 is also coupled to an interface 274, which
allows the receiver 203 of the base station 102 to communicate with the
CBSC 114.
FIG. 3 generally depicts a lldl~ ulL~L 300 of the base station 102 in
CDMA rrmmnn;rA~ir.n with a reCeiVOE 303 of the mobile station 106 in
a manner which may br-nPfiriAlly implement the present invention. In
the encoding portion 301 of the rommnnirAh~n system, braffic channel
1 0 data bits 302 are ouhput from a llP 305, and are input to an encoder 304
at a particular bit rate (e.g., 9.6 kilobit/second). The ~P 305 is coupled to
a block designated related functions 307, which performs similar
cellular-related ~ e blocks 207 and 272 of FIG. ~ The IIP 305 is
also c: ~ - . '.09 which allows the iLdlLa~ I uLk l 300 of base
1 5 station . '_ ~ ~mmnnirAt~ with the CbSC 114
The traffic channel data bits 302 can include either voice
converted to data by a vocoder, pure data, or a rr~mhinAti~n of the two
types of data. l~ncoder 304 encodes the traffic channel data bits 302 into
data symbols 306 at a fixed encoding rate (1/r) with an encoding
2 0 algorithm which facilitates subsequent mA~imnm likelihood decoding
of the data symbols intû data bits (e.g., convolutional or block coding
Algnri~hm~). For example, encoder 304 encodes traffic channel data bits
302 (e.g., 192 input data bits that were received at a rate of 9.6
kilobits/second) at a fixed encoding rate of one data bit to two data
symbols (i.e., 1/2) such that the encoder 304 outputs data symbols 306
(e.g., 384 ~ a ~ - output at a 19.2 kilo symbols/second rate).
The c.-n_ ~ymbols 306 are then input into an interleaver 308.
Interleaver 308 organizes the data symbols 306 into blocks (i e., frames)
and block ulLelledv~a the input data symbols 306 at the symbol level. ln
the interleavOE 308, the data symbols are individually input into a
mahix which defines a prr-1etrrmine~1 size block of data symbols. The
data symbols are input into locations within the matrix so that the
WO 96/42174 2 ~ ~ 6 6 ~ ~ PCT/US96/05998
~1
matrix is filled in a column by column manner. The data symbols are
individually output from locations within the matrix so that the matrix
is emptied in a row by row manner. Typically, the matrix is a square
matrix having a number of rows equal to the number of columns;
however, other matrix forms can be chosen to increase the output
interleaving distance between the ~unsL~uli~TL~ly input non-interleaved
data symbols. The interleaved dah symbols 310 are output by the
interleaver 308 at the same data symbol rate that they were input (e.g.,
19.2 kilo symbols/second). The predetermined size of the block of data
1 0 symbols defined by the matrix is derived from the maximum number
of data symbols which can be ~ '",i~ d at a coded bit rate within a
predetermined length ~ l L block. For example, if data symbols
306 are output from the encoder 304 at a 19.2 kilo symbols/second rate,
and if the predetermined length of the LlcLnblLIiL~ion block is 20
1 5 millicernnflc, then the predetermined size of the block of data symbols
is 19.2 kilo symbols/second times 20 milliseconds (ms) which equals
384 data symbols which defines a 18 by 32 matrix.
The encoded, interleaved data symbols 310 are output from
encoding porhc-- '0~ ~- .he communication system and input to a
2 0 tr~ncnnitting portion 316 of the communication system. The data
symbols 310 are prepared for transmission over a communication
channel by a modulator 317. Subsequently, the modulated signal is
provided to an antenna 318 for tr~ncmiccion over the digital radio
channel 108.
The modulator 317 prepares the data symbols 310 for direct
sequence code divided spread-spectrum transmission by pL-lfOlLLLil~g
data scrambling on the encoded, interleaved data symbols 310. Data
scrambling is accomplished by performing the modulo-2 addition of the
interleaver output symbols 310 with the binary value of a long code
pseudo-noise PN chip that is valid at the start of the tr~ncmiccir~n
period for that symbol. This pseudo-noise Pl~ sequence is the
equivalent of the long code operating at 1.2238 MHz clock rate, where
WO 96/42174 i~ PCT/US96/05998
~196~8~
only the first output of every 64 is used for the data scrambling (i.e., at a
19200 sample per second rate).
After scrambling, a sequence of fixed length codes from the
scrambled data symbols are derived in a spreading process. For
S example, each data syrnbol within the stream of scrambled data symbols
may preferably be spread to a unique fixed length code such that each
data symbol is ~ es~-L~d by a single 64 bit length code. The code
es~llLh-g the data symbol preferably is modulo-2 added to the
leb~e-Li~ data symbol. As a result of this spreading process, the
I 0 modulator 31~ which received the encoded, interleaved data symbols
310 at a fixed rate (e.g., 19.2 lsilo symbols/second) now has a spread
sequence of 64 bit length codes having a higher fixed symbol rate (e.g.,
1228.8 kilo symbols/second). It will be appreciated by those skilled in
the art that the data symbols within the stream of encoded, interleaved
1 5 data bits 310 may be spread according to numerous other Algorithmc
into a sequence of larger length codes without departing frorn the scope
and spirit of the present invention.
The spread sequence is further prepared for direct sequence code
divided spread-spectrum llClllb"libbiUII by further spreading the spread
2 0 sequence ~~ ith a long spreading code (e g., Pl~ code). The spreading code
is a user specific sequence of symbols or unique user code which is
output at a fixed chip rate (e.g., 1.2288 Megachips/second). In addition
to providing an ir~Pntifir~tir5l as to which user sent the encoded traffic
channel data bits 302 over the digital radio channel 308, the unique user
2 5 code enhances the security of the communication in the
commllnir~tlrm ch_nnel by scrambling the encoded traffic channel data
bits 302. In addition, the user code spread encoded data bits (i.e., data
symbols) are used to bi-phase modulate a sinusoid by driving the phase
controls of thP c;nllcoid. The sinusoid output signal is bandpass
3 0 filtered, translated to an RF frequency, amplified, filtered and radiated
by an antenna 318 to complete L~dllb~ ibbion of the traffic channel data
bits 302 in a digital radio channel 108 with BPSK mr~ Atirln.
14
WO 96/42174 21 9 ~ 6 8 ~ PCT/US96105998
A receiving portion 322 of the mobile station receiver 303
receives the ~ "";llP~1 spread-spectrum signal from over the digital
radio channel 108 through antenna 324. The received signal is sampled
into data samples by despreader and sampler 326. Subsequently, the
5data samples 342 are output to the decoding portion 354 of the
communication system.
The despreader and sampler 326 preferably BPSK samples the
received spread-spectrum signal by filtering, dPmL dnl~ting, translating
from the RF frequencies, and sampling at a predetermined rate (e.g.,
1 01.2288 M~gac~mrlPc/second). Sl1hcPfll.Pntly~ the BPSK sampled signal is
despread by correlating the received sampled signals with the long
spreading code. The resulting despread sampled signal 328 is sampled
at a prPdPtPrminPrl rate and output to a non-coherent detector 340 (e.g.,
19.2 kilo samples/second so that a sequence of 64 samples of the
1 5received spread-spectrum signal is despread and/or ~ L-lLtL-d by a
single data sample) for non-coherent detection of data samples 342.
As will be d~ .iCLI~d by those skilled in the art, multiple
receiving portions 322 through 323 and antennae 324 through 325,
respectively, can be used to achieve space diversity. The Nth receiver
20portion would operate in sllhst~nti~lly the same manner to retrieve
data samples from the received spread-spectrum signal in digital radio
channel 320 as the above described receiving portion 3~ The outputs
317 through 352 of the N receiving portions preferably are input to a
summer 350 which diversity combines the input data samples into a
2 5composite stream of coherently detected data samples 360.
The individual data samples 360 which form soft decision data
are then input into a decoding portion 354 including a deinterleaver
362 which deinterleaves the input soft decision data 360 at the
individual data level. In the deinterleaver 362, the soft decision data
3 0360 are individually input into a matrix which defines a predetermined
size block of soft decision data. The soft decision data are input into
locations within the matrix so that the matrix is filled in a row by row
WO96/42174 r.~ .'C~
/
8 1
manner. The deinterleaved soft decision data 364 are individually
output from locations within the matrix so that the matrix is emptied
in a column by column manner. The deinterleaved soft decision data
364 are output by the deinterleaver 362 at the same rate that they were
5 input (e.g., 19 2 kilflm~tri~s/second).
The prPd~t~rmin~l size of the block of soft decision data defined
by the matrix is derived from the m~Y;mnm rate of sampling data
samples from the spread-spectrum signal received within the
pr~ t~orm;nf~1 length ~ block.
1 0 The d~ ~ll~ledv~:d soft deci~sion data 364, are input to a decoder
366 which uses m~Y;mllm likelihood decoding te~hni~ s to generate
estimated traffic channel data bits 368. The m~Yimllm lik~l;h~lod
decoding techniques may be :lngm~nt~cl by using an algorithm which is
5llhst~nti~11y similar to a Viterbi decoding algorithm. The decoder 366
1 ~ uses a group of the individual soft decision data 364 to form a set of soft
decision transition metrics for use at each particular time state of the
m~Yimnm likelihood sequence estimation decoder 366. The number of
soft decision data 364 in the group used to form each set of soft decision
transition metrics corresponds to the number of data symbols 306 at the
20 output of the convolutional encoder 304 generated from each input
data bit 302. The number of soft decision transition metrics in each set
is equal to two raised to the power of the number of soft decision data
364 in each group. For example, when a 1/2 convolutional encoder is
used in the 1 l .~ , two data symbols 306 are generated from each
2 S input data bit 30~ Thus, decoder 366 uses groups of two individual soft
decision data 364 to form four soft decision transition metrics for use at
each time state in the maximum likelihood sequence estimation
decoder 366. The estimated traffic channel data bits 368 are generated at
a rate related to the rate that the soft decision data 364 are input to the
3 0 decoder 366 and the fixed rate used to originally encode the input data
bits 302 (e.g., if the soft decision data are input at 19.2
kilometrics/second and the original encoding rate was 1 /2 then
16
WO 96/42174 PCT/US96/0~998
2~9~81
estimated traffic channel data bits 368 are output at a rate of 9600
bits/second). The estimated traffic channel data bits 368 are input into
a ~lP 370 which interprets the estimated traffic channel data bits 368 and
other fields, including the fields of an Exiended Handoff Direcfion
Message, Ll~Lns~LliLLL-d in the digital radio channel 108. The ,uP 370 is
coupled to related functions 372 which performs cellular-related
functions similar to those p~lL,.lLI~:d by blocks 207, 272 and 307.
FIG. 4 generally depicts the protocol layering structure for a
CDMA communication system. As shown in FIG. 4, the protocol is
l 0 logically divided into conceptual layers. Layer 1 400, or the physical
layer of the digital radio channel 108, includes those functions
associated with the trancmiCci-7n of bits. These functions include
m~ 7l~tifm, coding, framing, and .l.alLILeli~cLLion via radio waves. A
multiplex sublayer 402 provides the multiplexing functions which
1 5 allow sharing of the digital radio channel 108 for user data and
signaling processes. Signaling protocol layer 2 is subdivided into a
primary traffic layer 2 404 and a secondary traffic layer 2 406, and is the
protocol ~ccorif7tr-L7 with the reliable delivery of signaling higher layer
messages (for example, from upper layers 408, 410) between the base
station 102 and the mobile station 106. Such upper layer signaling
messages include message I~ hion and duplicate detection.
As previously mr-nti~nr-~7, service options for IS-95A are defined
by TSB58, and currently include basic variable rate voice service (8
kbps), mobile station loopback, enhanced variable rate voice service (8
kbps), asynchronous data service, group 3 facsimile, short message
services, transrnission control protocol/internet protocol packet data
service, and Cellular Digital Packet Data (CDPD) over point-to-point
(PPP) packet data service. All protocol layering above multiplex
sublayer 402 is service option dependent. . ,In other words, signaling
3 0 from the base station 102 to the mobile station 106 to change a service
option is performed at layer 2 404, 406 or above.
WO 96/4Z174 F~
. . ~
2196~81
Another pdr~LIleL~l which is tr~ncmift~l1 to the mobile station
106 by the base station 102 is a parameter called the rate set, which is
used to define the data rate used over the digital radio channel 108. IS
95A currently defines two rate set Fl~r~m.ot~rc, rate set 1 and rate set 2,
5 and each rate set has its own set of service options. Since a rate set
change would alter the digital radio channel 108 (by changing the
vocoding rate over the channel, and hence the bandwidth of the
channel), a rate set change is not LLdllS~JdleLlL to layer 1400, the physical
layer which supports the digital radio channel 108. However, once the
10 rate set parameter is set, a service option can be changed without
altering the physical layer. In other words, any service option change
for a given rate set is LLdiLsl./dl~llL to layer 1400, the physical layer which
supports the digital radio channel 108.
As previously stated, a service option in a code division multiple
l 5 access (CDMA) r~lmmlln;~ 7n system 100 is changed in a mobile
station 106 in ~r~or~n~o with the invention by first determining the
service option to be employed by the mobile station 106 and
l,,.l.~",;ll;,lg, to the mobile station 106, data ~ s~llLill~ the service
option in a pr~sting message. In the preferred embodiment, the data
20 ~ lLLl.g the service option is a 16 bit field l~L~s~ lg one of a
plurality of service options, and the ~le~ LLLIg message is an Extended
Handoff Directlon Message. FIG. 5 depicts a handoff message, and
specifically an Exiended Handoff Dzrection Message 500 having both
data related to handoff and the service option data Le~l~enLaLion
25 therein in ~ccf~r(l~n~-e with the invention. As shown in FIG. 5, the
message 500 has an Additional Fields field 502 which is reserved for use
by a base/mobile station manufacturer to use as required, and is 16 bits
in length. In the preferred embodiment of the present invention, field
502 in the message 500 contains the 16 bit service option data
3 0 representation utilized io change the service option in the mobile
station. Since a change in service option occurs at layer 2 and above tas
best seen in FIG. 4), the Addifional Fields field 502 may contain a
18
W O 96/42174 PCTAJS96/0~998
~ 68~
service option for eithe} primary traffic layer 2 404 (as ~ L~d by
the data field 504) o} secondary traffic layer 2 406 (as lc~ l.Led by the
data field 506)
Certain time division multiple access (TDMA) romml~n;r~tinn
5 systems, such as the ~uropean Digital Cellular System (Global System
for Mobile Communication, or GSM) and the Japanese Digital Cellular
System (Personal Digital Cellular, or PDC) use a handoff message to
change certain layer 1 ~ l".,,.. ~r~ .r~; i.e., the I ~ Ir- ;~Lics related to
the digital radio channel 108. However, as discussed above, a service
1 0 option change in a CDMA rr~mm7lnir~tir1n system, for a given rate set,
is completely LLdn~JalrllL to the digital radio channel 108 since all
signalling related to the service option change is performed at layer 2
404, 406 or above.
A typical example of how a service option might be changed in a
l 5 mobile station is provided as follows, with reference to FIG. 1.
Assurning mobile station 106 was located within a first coverage area
104 and was rr~mmnnir~ting to a first base station 102 which supports a
first set of service options, and was entering a second coverage area 110
serviced by a second base station 112 which supports a second set of
2 0 service options, then the first base station 102 would first identify that a
cellular handoff is necessary. Notwithstanding the service option
requirement, the cellular handoff is necessary to allow the mobile
station 106 to maintain ~ ul~u~ dLion from the first coverage area 104
to the second coverage area 110.
At this point, since the first base station 102 is aware that a
cellular handoff is necessary, the first base station 102 can also
determine the service option to be employed and check whether the
second base station 112 supports the determined service option. This
step is necessary since the second base static~, 112 may be a base station
3 0 of a different operator which has chosen to support different service
options. As one of ordinary skill in the art will d~le~idLr, the available
service option infr,rm~tir n may reside at either the first base station 102
19
WO 96142174 ~ PCTIUS96/05998
2~g668~ ~
or the CFSC 114. ~~nnhmling, based on the determination, the first base
station 102 will insert the data l~ ,.i,nn of the ~1~t.orm;nf~d service
option into the Additional Fields field 502 of the Extended Handoff
Direction Message 500, and will transmit the Extended Handoff
Direction Message 500 to mobile station 106. The mobile station 106
will receive the Extended Handoff Direction Message 500, and send the
data within the message to IIP 370 for u~L~ klLion. The IIP 370
interprets the data received, changes the service option based on the
data ~ a~llLdLion in the Additional Fields field 502, and alters the
receiver 303 of the mobile station 106 so as to perform a cellular handoff
in ~rrnr~l~n~ with the invention.
As one of ordinary skill in the art will a~ ciaL~, service option
change in ac~nr~l~n~e with the invention is not limited to intercell
handoff as described above. For example, service option change in
accordance with the invention may be beneficially applied to inhracell
handoffs. Referring to FIG. 1, the mobile station 106 may require a
intracell handoff because of restraints placed on the system. As an
example, capacity restraints may limit the service options supported by
a given base station 102. During times of high system capacity (peak
2 0 times during the day), the base station 102 could be designed to notsupport certain channel-time concllmin~ sen~ice options, such as group
3 facsimile. When system capacity is lessened (off peak times of the
day), the base station 102 would then allow all service options to be
~u~ Lt d. These system reshraints can be provided for in a manner
that is Lld~ Jdl~llL to the digital radio channel 108 supported by the
protocol of layer 1400.
Since no ~ ;h-1n~l tirne is required to perform the cumbersome
negotiation process of the prior art, the CDMA ~nmmnn;~tinn system
in accordance with the invention performs a service option change
3 0 without incurring an increase in the rate of dropped calls.
At~/1;tinn~lly, since all signalling occurs at layer 2 404, 406 or above, the
service option change in accordance with the invention is transparent
WO 96/42174 21 g ~68 ~ PCT/US96/05998
.~ :
to the digital radio channel 108 supported by the protocol of laye} 1400.
Finally, since the mobile station 106 does not delay in entering soft
handoff, system interference is reduced, which results in a
~u~ u~ g increase in system capacity when compared to the prior
art method of service option change.
While the invention has been particularly shown and described
with reference to a particular embodiment, it will be understood by
those skilled in the art that various changes in form and details may be
made therein without departing from the spirit and scope of the
1 0 invention.
What we claim is:
