United States Patent [191
`Yamaura et al.
`
`lllllllllllllllllIlllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`US005321721A
`[11] Patent Number:
`5,321,721
`[45] Date of Patent:
`Jun. 14, 1994
`
`[54]
`
`[75]
`
`SPREAD SPECTRUM COMMUNICATION
`SYSTEM AND TRANSMITTER-RECEIVER
`Tomoya Yamaura; Katsuya
`Inventors:
`Yamamoto, both of Kanagawa; Jun
`Iwasaki, Tokyo; Etsumi Fujita,
`Chiba, all of Japan
`Assignee:
`Sony Corporation, Tokyo, Japan
`[73]
`Appl. No.: 942,708
`[21]
`Filed:
`Sep. 9, 1992
`[22]
`Foreign Application Priority Data
`[30]
`Sep. 13, 1991 [JP]
`Japan ................................ .. 3-234608
`Sep. 13, 1991 [JP]
`Japan .................... .. 3-234619
`Jun. 26, 1992 [JP]
`Japan ................................ .. 4-169676
`_
`‘
`
`.................... " HMB
`,37O/l 18,
`. ........................................ ..
`.
`.
`[58] Field of Search
`375/1_ 370/109 118
`"""""""""" "
`’37O/18 go 841
`_
`’
`’
`References Cited
`U.S. PATENT DOCUMENTS
`4,550,399 10/1985 Caron .................................. .. 370/80
`5,128,959 7/1992 Brukert ................................. .. 375/1
`
`[56]
`
`Primary Examiner—Gilberto Barron, Jr.
`Attorney, Agent, or Firm-Jerry A. Miller
`
`ABSTRACT
`[57]
`A spread spectrum communication system for perform
`ing spread spectrum communication by superimposing
`a pseudo noise signal on a transmitted signal. The sys
`tem comprises traf?c detecting means for detecting the
`traf?c of the transmitted signal, and means for changing
`the clock frequency of the pseudo noise signal in accor
`dance with the output from the traf?c detecting means.
`The system may alternatively comprise transmission
`quality determining means for determining thetransmis
`sion quality of the received signal, and means for chang
`ing the clock frequency of the pseudo noise signailgn
`accordance with the transmission quality determine y
`the transmission quality determining means. In opera
`tion’ the Sys‘em offers improved S/N ratios where mm
`?c is high or transmission quality is low, saves power
`where traffic is low or transmission quality is high, and
`ensures large margins of power control precision for
`mobile stations near the upper limit of the system’s line
`capacity.
`
`6 Claims, 27 Drawing Sheets
`
`v ~30
`{129
`SHAR'ilNqé
`UNIT
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`SPREAD CODE
`GENERATOR
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`CODE CLOCK RATE
`CONTROL INFORMATION
`GENERATOR
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`
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`SPECTRUM
`MODULATOR
`
`psK
`
`-—-—ENCODER
`MODULATOR
`
`CLOCK RATE CHANGE
`INFORMATION
`comsmme UNIT
`
`‘in-(t )
`
`ERIC-1008
`Ericsson v IV
`Page 1 of 39
`
`

`
`US. Patent
`
`June 14,1994
`
`Sheet 1 ‘of 27
`
`5,321,721
`
`F l G .
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`l
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`202
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`FIG. 2B
`
`ERIC-1008 / Page 2 of 39
`
`

`
`US. Patent
`
`June 14, 1994
`
`Sheet '2 of 27
`
`FIG.3A
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`ERIC-1008 / Page 3 of 39
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`

`
`US. Patent
`
`June 14, 1994
`
`Sheet 3 of 27
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`5,321,721
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`ERIC-1008 / Page 4 of 39
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`

`
`US. Patent
`
`June 14,1994 '
`
`Sheet 4 of 27
`
`5,321,721
`
`NARROW BAND
`INTERFERENCE SIGNAL
`COMPONENT
`SPECTRUM SIGNAL
`COMPONENT
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`
`ERIC-1008 / Page 5 of 39
`
`

`
`US. Patent
`
`June 14, 1994
`
`Sheet 5 of 27
`
`5,321,721
`
`NO
`
`F I G. 6A
`WHITE NOISE SIGNAL
`I COMPONENT
`SPECTRUM SIGNAL
`COMPONENT
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`flc
`28p
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`BPSK SIGNAL COMPONENT
`WHITE NOISE SIGNAL
`{ COMPONENT
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`FIG.6C
`
`BPSK SIGNAL COMPONENT
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`
`'
`
`__________
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`NO
`
`ERIC-1008 / Page 6 of 39
`
`

`
`US. Patent
`
`June 14, 1994
`
`Sheet 6 of 27
`
`5,321,721
`
`FIG.7
`
`22
`
`ERIC-1008 / Page 7 of 39
`
`

`
`U.S. Patent
`
`June 14, 1994
`
`7
`
`Sheet TM 27
`
`FIG.8A
`
`SPREAD SPECTRUM SIGNAL
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`.
`
`I
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`FIG.8C
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`‘ SPREAD SPECTRUM SIGNAL
`
`280
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`
`ERIC-1008 / Page 8 of 39
`
`

`
`US. Patent
`
`June 14, 1994
`
`Sheet 8 of 27
`
`5,321,721
`
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`ERIC-1008 / Page 9 of 39
`
`

`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 9 of 27
`
`5,321,721
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`ERIC-1008 / Page 10 of 39
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`

`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 10 of 27
`
`5,321,721
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`ERIC-1008 I Page 11 of 39
`
`ERIC-1008 / Page 11 of 39
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`
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`
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`
`
`

`
`US. Patent
`
`June 14, 1994
`
`Sheet 11 of 27
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`5,321,721
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`ERIC-1008 / Page 12 of 39
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`

`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 12 of 27
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`5,321,721
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`ERIC-1008 I Page 13 of 39
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`ERIC-1008 / Page 13 of 39
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`
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`

`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 13 of 27
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`5,321,721
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`ERIC-1008 I Page 14 of 39
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`ERIC-1008 / Page 14 of 39
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`ERIC-1008 I Page 15 of 39
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`ERIC-1008 / Page 15 of 39
`
`
`

`
`US. Patent
`
`June 14, 1994
`
`Sheet 15 of 27
`
`5,321,721
`
`FIG. I6
`
`_ _ _ _ _
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`ERIC-1008 / Page 16 of 39
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`

`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 16 of 27
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`5,321,721
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`ERIC-1008 I Page 17 of 39
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`ERIC-1008 / Page 17 of 39
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`
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`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 17 of 27
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`5,321,721
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`ERIC-1008 I Page 18 of 39
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`ERIC-1008 / Page 18 of 39
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`
`US. Patent
`
`June 14,1994
`
`Sheet 18 of 27
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`5,321,721
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`ERIC-1008 / Page 19 of 39
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`
`US. Patent
`
`June 14, 1994
`
`Sheet 19. of 27
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`5,321,721
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`FIG.2O
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`ERIC-1008 / Page 20 of 39
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`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 20 of 27
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`5,321,721
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`ERIC-1008 I Page 21 of 39
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`ERIC-1008 / Page 21 of 39
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`

`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 21 of 27
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`5,321,721
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`ERIC-1008 / Page 22 of 39
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`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 22 of 27
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`5,321,721
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`ERIC-1OO8V I Page 23 of 39
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`ERIC-1008 / Page 23 of 39
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`ERIC-1008 / Page 24 of 39
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`ERIC-1008 I Page 25 of 39
`
`ERIC-1008 / Page 25 of 39
`
`
`
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`ERIC-1008 I Page 26 of 39
`
`ERIC-1008 / Page 26 of 39
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`ERIC-1008 I Page 27 of 39
`
`ERIC-1008 / Page 27 of 39
`
`
`
`
`
`

`
`U.S. Patent
`
`June 14, 1994
`
`Sheet 27 of 27
`
`5,321,721
`
`F|G.28
`
`
`
`BITERRORRATE
`
`Eb /No [dB].
`
`ERIC-1008 I Page 28 of 39
`
`ERIC-1008 / Page 28 of 39
`
`

`
`1
`
`5,321,721
`
`SPREAD SPECTRUM COMMUNICATION
`SYSTEM AND TRANSMITTER-RECEIVER
`
`BACKGROUND OF THE INVENTION
`
`l. Field of the Invention:
`The present invention relates to a spread spectrum
`communication system and a transmitter-receiver based
`on CDMA (code division multiple access) and, more
`particularly, to a spread spectrum communication sys-
`tem and a transmitter-receiver capable of adaptively
`changing the power level of transmitted signals.
`2. Description of the Related Art:
`The spread spectrum communication system works
`in principle as follows: The transmitter of the system
`modulates (spreads) by pseudo noise (PN) a carrier that
`carries data. The receiver subjects the received carrier
`to a PN—coded correlation (reverse spread) process, the
`PN being generated by an encoder structurally identical
`to the one used by the transmitter. The PN-code corre-
`lation process is followed by base band demodulation
`that restores the transmitted data. Under this spread
`spectrum communication scheme, the density of power
`per unit frequency is low. This means that a minor
`increase in noise level accompanying a higher traffic,
`insignificant for other kinds of communication, can lead
`to a degenerated S/N (signal-to-noise) ratio with the
`spread spectrum communication system. The raised
`noise level hampers efforts to communicate using a
`desired signal under the spread spectrum communica-
`tion scheme.
`
`One prior art solution to the above problem is to
`widen the frequency band of spread spectrum signals
`while lowering the power density per unit frequency.
`This requires enhancing the clock rate of the transmit-
`ter, which means greater power dissipation. In that
`case, even if traffic is low, the clock rate remains unnec-
`essarily high reflecting the increased power consump-
`tion.
`FIG. 1 is a block diagram of a modulating portion in
`a transmitter for use with a conventional direct spread
`spectrum communication system. In FIG. 1, a carrier
`generator 201 generates a carrier fc for input to a PSK
`(phase shift keying) modulator 202. The PSK modula-
`tor 202 subjects the carrier fc to bi-phase shift keying
`modulation using a transmitted signal (binary coded
`signal) d(t) from an input
`terminal 203. The PSK-
`modulated signal from the PSK modulator 202 is sup-
`plied to a spread spectrum modulator 204. The spread
`spectrum modulator 204 is fed with a spread signal p(t)
`from a PN generator 205 that generates a PN (pseudo
`noise) code sequence. Using the spread signal p(t), the
`modulator 204 subjects the PSK-modulated signal to
`spread spectrum modulation.
`.
`FIG. 2A is a view of a typical change in the transmit-
`ted signal d(t) used by the modulation portion of FIG. 1.
`FIG. 2B is a view of a frequency spectrum of the PSK-
`modulated signal output by the PSK modulator 202 in
`FIG. 1. In FIG. 2A, Td is the period of the transmitted
`signal d(t). The frequency band width Bd is given as
`Bd=l/Td
`
`5
`
`10
`
`15
`
`20
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`25
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`30
`
`35
`
`45
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`50
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`55
`
`FIG. 3A is a view of a typical change in the spread
`signal p(t) from the PN generator 205. FIG. 3B is a view
`of a frequency spectrum of the spread spectrum signal
`output by the spread spectrum modulator 204. In FIG;
`3A, Tp is the period of the spread signal p(t). As shown
`
`65
`
`2
`in FIGS. 3A and 3B, the period Tp of the spread signal
`p(t) changes fast over short time with respect to the
`period Td of the transmitted signal d(t). This causes the
`spread spectrum modulator 204 to spread the frequency
`spectrum over a wide band (frequency band width
`Bp = l/Tp).
`FIG. 4 is a block diagram of a demodulating portion
`of a receiver for use with the direct spread spectrum
`communication system of FIG. 1. in FIG. 4, the spread
`spectrum signal received by an antenna or the like, not
`shown, and admitted through a terminal 211 enters a
`band-pass filter (BPF) 212. The band-pass filter 212
`retains only those components of the signal which con-
`stitute the necessary band and discards the rest.
`Past the band-pass filter 212, the spread spectrum
`signal goes into a reverse spread device 213 illustra-
`tively made of a multiplier. For its reverse spread opera-
`tion,
`the reverse spread device 213 is fed by a PN
`(pseudo noise) generator 214 with a signal p(t)’ identical
`to the above-mentioned spread signal p(t). In this case,
`the signal p(t)’ from the PN generator 214 is so con-
`trolled as to coincide in phase with the spread signal
`p(t). That is, the relation
`
`p(t)-P(1)'=P(t)2=1
`
`should hold.
`
`The output signal from the reverse spread device 213
`goes to a band-pass filter 215 whose center frequency is
`fc and whose passing band is 2 Bd. The band-pass filter
`215 extracts a PSK-modulated signal from the signal
`received. The PSK-modulated signal is supplied to and
`demodulated by a PSK demodulator 216. As a result,
`the original signal d(t) is tapped from an output terminal
`217. Spread spectrum communication, as outlined, is a
`communication method whereby a frequency spectrum
`is spread over a wide band for communications that
`ensure security and privacy with high immunity to
`interference.
`
`To keep the spread spectrum communication system
`normally operational requires conventionally that the
`receiving power of the base station remain constant
`over the communication channels connected to subor-
`dinate mobile stations. It is thus necessary to, keep con-
`stant the transmitting power of each mobile station as it
`communicates with the base station while moving
`under varying external conditions. Theoretical calcula-
`tions put the precision of transmitting power control to
`within 0.5 dB in the vicinity of the upper limit of the
`system’s circuit capacity. In practice, that kind of preci-
`sion is difficult to achieve. This has been a major prob-
`lem with spread spectrum communication systems
`based on CDMA (code division multiple access).
`FIG. SA is a view of a frequency spectrum of the
`signal sent from the input terminal 211 to the band-pass
`filter 212 in FIG. 4. FIG. 5B is a view of a frequency
`spectrum of the signal sent from the reverse spread
`device 213 to the band-pass filter 215 in FIG. 4. FIG. 5C
`is a view of a frequency spectrum of the signal sent from
`the band-pass filter 215 to the PSK demodulator 216 in
`FIG. 4. In FIG. 5A, the spread spectrum signal with a
`band width of 2 Bp mixes with a narrow band interfer-
`ence component. If the power of the signal in FIG. 5A
`is denoted by PR and that of the interference wave by
`P1, the signal-to-interference wave power ratio (S/I),4 is
`given as
`
`(s/nA=pr/P}
`
`ERIC-1008 I Page 29 of 39
`
`ERIC-1008 / Page 29 of 39
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`

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`3
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`5,321,721
`
`In FIG. 5B, a reverse relationship of what is given in
`FIG. 5A holds. That is, the signal passes through the
`band-pass filter 215 having a band width of 2 Bd. The
`result is shown in FIG. 5C. In this case, the signal-to-
`interference wave power ratio (S/I)c is given as
`
`(5/1): = (Pr/PIXBP/BU’)
`= (S/1)A(3P/34')
`= (S/DAG
`
`where, G stands for a process gain (G=Bp/Bd). As
`indicated, subjecting the input signal to spread spectrum
`modulation improves the signal-to-interference wave
`power ratio from (S/I),4 to (S/l)c, i.e., by the amount of
`G. Thus the spread spectrum communication scheme
`enhances the immunity to the adverse effects of interfer-
`ence signal components.
`Consider the case where white noise is involved, with
`no narrow band interference signal component present.
`In this case, as above, the spectrum patterns of the re-
`spective signals in FIG. 4 appear as depicted in FIGS.
`6A, 6B and 6C. The signal-to-noise ratio (S/N),1 of the
`signal in FIG. 6A is given as
`
`(S/N),4 = Pr/(Na-2Bp)
`
`10
`
`15
`
`20
`
`25
`
`where, No is the power of the white noise signal com-
`ponent. Likewise, the signal-to-noise ratio (S/N)cof the
`signal in FIG. 6C is given as
`
`30
`
`(S/N),4 = Pr/(No - 213:?)
`= (5/N)a(BP/317')
`= (S/MAG
`
`The case above thus yields the same result as that of the
`case where the narrow band interference signal compo-
`nent is involved as depicted in FIG. 5.
`In the case of communication within one system
`whose terminals utilize the same PN code, a given ter-
`minal regards the communication done by any other
`terminal as a noise similar to the white noise. That is,
`when one terminal transmits its signal at a raised power
`level, the terminal not only dissipates more power than
`before but also interferes with the communication of
`other terminals. Communication carried out under
`schemes other than the spread spectrum communication
`constitutes a component approximating the narrow
`band interference signal component. In any case, higher
`levels of traffic lead to the increase in the noise indi-
`cated by the shaded portions in FIGS. 5C and 6C. This
`is a significant impediment to the normal execution of
`communication.
`
`One prior art solution to the above impediment is to
`enlarge the band width Bp of the spread spectrum signal
`so as to increase the process gain G. This requires boost-
`ing the clock rate for reverse spread operation through
`multiplication of the spread signal p(t)’ in FIG. 4. The
`solution results in more power dissipation of which the
`level turns out to be disproportionately high where the
`process gain G need not be very high.
`SUMMARY OF THE INVENTION
`
`It is therefore an object of the present invention to
`provide a spread spectrum communication system and a
`transmitter-receiver which offer improved S/N ratios
`
`35
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`45
`
`50
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`55
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`65
`
`4
`where traffic is high or transmission quality is low, and
`which save power where traffic is low or transmission
`quality is high.
`It is another object of the invention to provide a
`spread spectrum communication system and a transmit-
`ter-receiver which ensure large margins of power con-
`trol precision for mobile stations in the vicinity of the
`upper limit of the system’s line capacity.
`It is a further object of the invention to provide a
`spread spectrum communication system and a transmit-
`ter-receiver which keep the transmitting power in-
`volved at appropriate levels.
`In carrying out the invention and according to a first
`aspect thereof, there is provided a spread spectrum
`communication system for performing spread spectrum
`communication by superimposing a pseudo noise signal
`on a transmitted signal, the spread spectrum communi-
`cation system comprising: traffic detecting means for
`detecting the traffic of the transmitted signal; and means
`for changing the clock frequency of the pseudo noise
`signal in accordance with the output_from the traffic
`detecting means.
`According to a second aspect of the invention, there
`is provided a spread spectrum communication system
`for performing spread spectrum communication by
`superimposing a pseudo noise signal on a transmitted
`signal,
`the spread spectrum communication system
`comprising: transmission quality determining means for
`determining the transmission quality of a received sig-
`nal; and means for changing the clock frequency of the ‘
`pseudo noise signal in accordance with the transmission
`quality determined by the transmission quality deter-
`mining means.
`According to a third aspect of the invention, there is
`provided a spread spectrum transmitter-receiver for
`superimposing a pseudo noise signal on a transmitted
`signal and for receiving the transmitted signal contain-
`ing the superimposed pseudo noise signal, the spread
`spectrum transmitter-receiver comprising: transmission
`quality determining means for determining the transmis-
`sion quality of a received signal; means for controlling
`the clock rate of the pseudo noise signal in accordance
`with the transmission quality determined by the trans-
`mission quality determining means; and means for com-
`bining information about the changed clock rate with
`the transmitted signal.
`According to a fourth aspect of the invention, there is
`provided a spread spectrum transmitter-receiver for
`superimposing a pseudo noise signal on a transmitted
`signal and for receiving the transmitted signal contain-
`ing the superimposed pseudo noise signal, the spread
`spectrum transmitter-receiver comprising:
`traffic de-
`tecting means for detecting the traffic of the transmitted
`signal; means for controlling the clock rate of the
`pseudo noise signal in accordance with the output from
`the traffic detecting means; and means for combining
`information about
`the changed clock rate with the
`transmitted signal.
`According to a fifth aspect of the invention, there is
`provided a spread spectrum transmitter-receiver com-
`prising:
`transmission quality determining means for
`determining the quality of a received signal from the
`other spread spectrum transmitter-receiver; control
`data generating means for generating clock control data
`for controlling the clock rate of a pseudo noise signal
`from the other spread spectrum transmitter-receiver in
`accordance with the transmission quality determined by
`
`ERIC-1008 I Page 30 of 39
`
`ERIC-1008 / Page 30 of 39
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`

`
`5,321,721
`
`5
`the transmission quality determining means; data com-
`bining means for combining with a transmitted signal
`the clock control data generated by the control data
`generating means; and a band-pass filter circuit for con-
`trolling a passing band in accordance with the changed
`clock rate of the pseudo noise signal in the received
`signal from the other spread spectrum transmitter-
`receiver.
`
`According to a sixth aspect of the invention, there is
`provided a spread spectrum transmitter-receiver com-
`prising: traffic detecting means for detecting the traffic
`of a received signal from the other spread spectrum
`transmitter-receiver; control data generating means for
`generating clock control data for controlling the clock
`rate of a pseudo noise signal from the other spread
`spectrum transmitter-receiver in accordance with the
`output from the traffic detecting means; data combining
`means for combining with a transmitted signal the clock
`control data generated by the control data generating
`means; and a band-pass filter circuit for controlling a
`passing band in accordance with the changed clock rate
`of the pseudo noise signal in the received signal from
`the other spread spectrum transmitter-receiver.
`According to a seventh aspect of the invention, there
`is provided a spread spectrum transmitter-receiver sys-
`tem comprising: a second spread spectrum transmitter-
`receiver having transmission quality determining means
`for determining the transmission quality of a received
`signal from a first spread spectrum transmitter-receiver,
`control data generating means for generating clock
`control data for controlling the clock rate of a pseudo
`noise signal from the first spread spectrum transmitter-
`receiver in accordance with the transmission quality
`determined by the transmission quality determining
`means, and data combining means for combining with a
`transmitted signal the clock control data generated by
`the control data generating means; and the first spread
`spectrum transmitter-receiver having data extracting
`means for extracting the clock control data from a re-
`ceived signal from the second spread spectrum trans-
`mitter-receiver, and clock control means for controlling
`the clock rate of the pseudo noise signal in accordance
`with the clock control data extracted by the data ex-
`tracting means.
`According to an eighth aspect of the invention, there
`is provided a spread spectrum transmitter-receiver sys-
`tem comprising: a second spread spectrum transmitter-
`receiver having traffic detecting means for detecting
`the traffic of a received signal from a first spread spec-
`trum transmitter-receiver, control data generating
`means for generating clock control data for controlling
`the clock rate of a pseudo noise signal from the first
`spread spectrum transmitter-receiver
`in accordance
`with the output from‘ the traffic detecting means, and
`data combining means for combining with a transmitted
`signal the clock control data generated by the control
`data generating means; and the first spread spectrum
`transmitter-receiver having data extracting means for
`. extracting the clock control data from a received signal
`fromthe second spread spectrum transmitter-receiver,
`and clock control means for controlling the clock rate
`of the pseudo noise signal in accordance with the clock
`control data extracted by the data extracting means.
`According to a ninth aspect of the invention, there is
`provided a spread spectrum communication system for
`performing spread spectrum communication by super-
`imposing a pseudo noise signal on a transmitted signal,
`the spread spectrum communication system compris-
`
`10
`
`15
`
`20
`
`25
`
`30
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`35
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`45
`
`50
`
`55
`
`65
`
`6
`ing: traffic detecting mean for detecting the traffic of
`the transmitted signal; and means for changing the
`clock frequency of the transmitted signal in accordance
`with the output from the traffic detecting means.
`According to a tenth aspect of the invention, there is
`provided a spread spectrum communication system for
`performing spread spectrum communication by super-
`imposing a pseudo noise signal on a transmitted signal,
`the spread spectrum communication system compris-
`ing: transmission quality determining means for deter-
`mining the transmission quality of a received signal; and
`means for changing the clock frequency of the transmit-
`ted signal in accordance with the transmission quality
`determined by the transmission quality determining
`means.
`
`According to an eleventh aspect of the invention,
`there is provided a spread spectrum transmitter-
`receiver for superimposing a pseudo noise signal on a
`transmitted signal and for receiving the transmitted
`signal containing the superimposed pseudo noise signal,
`the spread spectrum transmitter-receiver comprising:
`transmission quality determining means for determining
`the transmission quality of a received signal; means for
`controlling the clock rate of the transmitted signal in
`accordance with the transmission quality determined by
`the transmission quality determining means; and means
`for combining information about the changed clock rate
`with the transmitted signal.
`According to a-twelfth aspect of the invention, there
`is provided a spread spectrum transmitter-receiver for
`superimposing a pseudo noise signal on a transmitted
`signal and for receiving the transmitted signal contain-
`ing the superimposed pseudo noise signal, the spread
`spectrum transmitter-receiver comprising:
`traffic de-
`tecting means for detecting the traffic of the transmitted
`signal; means for controlling the clock rate of the trans-
`mitted signal in accordance with the output from the
`traffic detecting means; and means for combining infor-
`mation about the changed clock rate with the transmit-
`ted signal.
`According to a thirteenth aspect of the invention,
`there is provided a spread spectrum transmitter-
`receiver system comprising: a first spread spectrum
`transmitter-receiver having transmission quality deter-
`mining means for determining the transmission quality
`of a received signal, control data generating means for
`generating clock control data for controlling the clock
`rate of a transmitted signal in accordance with the trans-
`mission quality determined by the transmission quality
`determining means, and data combining means for com-
`bining with the transmitted signal the clock control data
`generated by the control data generating means; and a
`second spread spectrum transmitter-receiver having
`data extracting means for extracting the clock control
`data from the received signal, and clock control means
`for controlling the clock rate of the transmitted signal in
`accordance with the clock control data extracted by the
`data extracting means.
`According to a fourteenth aspect of the invention,
`there is provided a transmitter-receiver comprising: loss
`estimating means for estimating losses over a propaga-
`tion path in accordance with a received signal; and
`power control means
`for controlling transmitting
`power in accordance with the result of estimation by
`the loss estimating means.
`The above and other objects, features and advantages
`of the present invention and the manner of realizing
`them will become more apparent, and the invention
`
`ERIC-1008 I Page 31 of 39
`
`ERIC-1008 / Page 31 of 39
`
`

`
`7
`itself will best be understood from a study of the follow-
`ing description and appended claims with reference to
`the attached drawings showing some preferred embodi-
`ments of the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a modulating portion in
`a transmitter for use with a conventional direct spread
`spectrum communication system;
`FIG. 2A is a view of a typical change in a transmitted
`signal used by the modulation portion of FIG. 1;
`FIG. 2B is a view of a frequency spectrum of a PSH-
`modulated signal output by a PSK modulator in the
`setup of FIG. 1;
`FIG. 3A is a view of a typical change in a spread
`signal from a PN generator in the setup of FIG. 1;
`FIG. 3B is a view of a frequency spectrum of a spread
`spectrum signal output by a spread spectrum modulator
`in the setup of FIG. 1;
`FIG. 4 is a block diagram of a demodulating portion
`of a receiver for use with the direct spread spectrum
`communication system of FIG. 1;
`FIG. 5A is a view of a frequency spectrum of a signal
`used in the setup of FIG. 4;
`FIG. 5B is a view of a frequency spectrum of another
`signal used in the setup of FIG. 4;
`FIG. 5C is a View of a frequency spectrum of another
`signal used in the setup of FIG. 4;
`FIG. 6A is a view of a frequency spectrum of another
`signal used in the setup of FIG. 4;
`FIG. 6B is a view of a frequency spectrum of another
`signal used in the setup of FIG. 4;
`FIG. 6C is a view of a frequency spectrum of another
`signal used in the setup of FIG. 4;
`FIG. 7 is a block diagram of a spread spectrum com-
`munication system practiced as a first embodiment of
`the invention;
`FIG. 8A is a view of a spectrum distribu