United States Patent (19)
`Higuchi et al.
`
`73) Assignee:
`
`(54) DIVERSITY ANTENNA COMMUNICATION
`SYSTEM
`75 Inventors: Harukazu Higuchi; Yoshizo Shibano,
`both of Osaka, Japan
`Sumitomo Electric Industries, Ltd.,
`Osaka, Japan
`(21) Appl. No.: 375,669
`22 Filed:
`Jul. 5, 1989
`30
`Foreign Application Priority Data
`Jul. 6, 1988 JP
`Japan ................................ 63-68573
`Aug. 10, 1988 JP
`Japan ........................... 63-105581U
`Dec. 23, 1988 JP
`Japan ................................ 63-327041
`51) Int. C.’....................... H04B 1/44; H04B 17/02;
`HO4B 1/O6
`52 U.S. Cl. ...................................... 455/78; 455/134;
`455/277.1
`58 Field of Search ................. 455/134, 135, 140, 63,
`455/277, 133, 78,136, 100, 101
`References Cited
`U.S. PATENT DOCUMENTS
`4,035,728 7/1977 Ishikawa et al. .................... 455/134
`4,756,023 7/1988 Kojima ................................ 4S5/34
`FOREIGN PATENT DOCUMENTS
`O124319 11/1984 European Pat. Off. .
`
`56)
`
`
`
`TRANSMISSION
`DATA
`PRODUCING
`PORTION
`
`11
`45
`
`U SOO5161252A
`Patent Number:
`Date of Patent:
`
`5,161,252
`Nov. 3, 1992
`
`016733 9/1984 Japan ................................... 455/33
`59-178830 10/1984 Japan.
`1000606 8/1965 United Kingdom.
`OTHER PUBLICATIONS
`I. Yashima et al., “Development of the TV Receiver for
`Cars", IEEE Transactions on Consumer Electronics,
`vol. CE-28, No. 3, Aug. 1982, New York, pp. 437–445.
`K. Suwa et al., "Diversity improvement of Voice Sig
`nal Transmission Using Postdetection Selection Com
`bining in Land Mobile Radio", IEEE Transactions on
`Vehicular Technology, vol. VT-33, No. 3, Aug. 1984,
`New York.
`Primary Examiner-Curtis Kuntz
`Assistant Examiner-Christine K. Belzer
`Attorney, Agent, or Firm-Cushman, Darby & Cushman
`57
`ABSTRACT
`A diversity antenna communication system for mount
`ing on and use with a mobile body. The system includes
`at least two receiving systems having different propaga
`tion paths from one another. During the transmission, a
`radio wave including receiving system change-over
`timing signals therein is radiated. Upon reception, the
`change-over timing signals are extracted to control
`reception.
`
`21 Claims, 10 Drawing Sheets
`
`CHANGE-OVER-CLOCK
`PULSE PRODUCING
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 1 of 21
`
`

`

`U.S. Patent
`
`Nov. 3, 1992
`
`Sheet 1 of 10
`
`5,161,252
`
`DISTRIBUTOR
`
`RECEIVER
`
`LEVEL
`MONITOR CKT
`
`LEVEL
`MONTOR CKT
`
`LEVEL
`COMPARISON
`CKT
`
`DISTRIBUTOR
`
`FIG. 2(A)
`
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`~~ ~~ _ _ __ -- --- -**
`
`TIME
`
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`
`
`
`
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 2 of 21
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`

`

`U.S. Patent
`
`Nov. 3, 1992
`
`Sheet 2 of 10
`
`5,161,252
`
`
`
`FIG 3(A)
`
`FIG 3(B)
`
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`FIG 3(C) .
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`LEVE MONITOR
`PERIOD
`
`CHANGE-OVER
`TIMING PERIOD
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 3 of 21
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`

`U.S. Patent
`
`Nov. 3, 1992
`
`Sheet 3 of 10
`
`5,161,252
`
`
`
`
`
`
`
`
`
`NOISSIWSN\/81
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 4 of 21
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`

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`U.S. Patent
`
`Nov. 3, 1992
`
`Sheet 4 of 10
`
`5,161,252
`
`FIG. 6(A)
`
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`FIG. 6(B)
`
`FIG. 6(C)
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 5 of 21
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`

`

`U.S. Patent
`US. Patent
`
`Sheet 5 of 10
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`ERICSSON v. UNILOC
`Ex. 1026 / Page 6 of 21
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`

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`US. Patent
`
`Nov. 3, 1992
`
`Sheet 6 of 10
`
`5,161,252
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`ERICSSON V. UNILOC
`
`EX. 1026 / Page 7 of21
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`ERICSSON v. UNILOC
`Ex. 1026 / Page 7 of 21
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`

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`US. Patent
`
`Nov. 3, 1992
`
`Sheet 7 of 10
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`5,161,252
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`ERICSSON V. UNILOC
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`EX. 1026 / Page 8 of21
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`ERICSSON v. UNILOC
`Ex. 1026 / Page 8 of 21
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`

`

`U.S. Patent
`
`Nov. 3, 1992
`
`Sheet 8 of 10
`
`5,161,252
`
`
`
`FIG 11(A)
`
`FIG 11/B).
`
`FIG 11C)
`
`-
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 9 of 21
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`

`

`U.S. Patent
`
`Nov. 3, 1992
`
`Sheet 9 of 10
`
`5,161,252
`
`
`
`13
`
`MONITOR
`CKT
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`LEVEL
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`LOWER THRESHOLD
`LEVEL D
`
`FIG 13(B),
`
`FIG. 13(C)
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 10 of 21
`
`

`

`U.S. Patent
`
`Nov. 3, 1992
`
`Sheet 10 of 10
`
`5,161,252
`
`FIG 14.
`
`3d
`
`40
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`DIS
`TRIBUTOR
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`H. CUM Ud
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 11 of 21
`
`

`

`1.
`
`OVERSITY ANTENNA COMMUNICATION
`SYSTEM
`w
`
`thereof.
`
`m
`
`BACKGROUND OF THE INVENTION
`I. Field of the Invention
`The present invention relates to a diversity antenna
`communication system to be mounted on and used in
`conjunction with a mobile body. More specifically, the
`invention relates to a diversity antenna communication
`system having two or more receiving or transmitting
`systems with different propagation paths from one an
`other in which a received signal from one of the receiv
`ing systems having a higher reception level than an
`15
`other is selected for use to reduce influences of deep
`fading.
`2. Description of Prior Art
`In a signal communication between mobile bodies
`(mobile stations) which is carried out mainly with radi
`owaves modulated with digital data, a propagation path
`20
`on the ground is a multipass type propagation path, and
`therefore the envelope and phase of a radio wave fluc
`tuate randomly in accordance with the Rayleigh's dis
`tribution law and the uniform distribution law, respec
`tively, (i.e., the radio wave suffers from fading). In
`25
`order to reduce such fading, there is a diversity receiv
`ing antenna communication system in which the receiv
`ing system is changed over from one receiving antenna
`to another.
`Conventional diversity receiving antenna communi
`30
`cation systems are used primarily on a mobile body,
`and, for example, diversity systems using space, polar
`ization, arrival angles, time and frequency have been
`utilized. Of those systems, a diversity receiving antenna
`communication system using an arrival angle is best
`suited for being mounted on a ground mobile station
`(such as a vehicle, or the like) because of its compact
`ness and its ability to reduce fading in a mobile body
`which remarkably changes a traveling direction
`A diversity signal receiving apparatus employed in
`the above-described diversity antenna communication
`system is as shown in FIG.1. That is, two signal receiv
`ing antennas 1' provided for different signal propaga
`tion paths are connected to two distributors 2", respec
`45
`tively. One of the distributors 2" is connected to a signal
`receiver 3' and to a level monitor circuit 5'; whereas the
`other distributor 2 is connected to another level moni
`tor circuit 5' and to a dummy resistor 4 equivalent in
`impedance to the signal receiver 3". The two level moni
`tor circuits 5' are connected to a level comparison cir
`cuit 6'.
`The distributors 2" operate to distribute signals re
`ceived through the receiving antennas 1' to loads (the
`receiver 3' and the dummy resistor 4") and to the level
`55
`monitor circuits 5', respectively. The level monitor
`circuits 5' monitor the levels of the signal received
`through the distributors 2 (hereinafter referred to as
`"reception levels', when applicable). The level compar
`ison circuit 6' compares the reception levels monitored
`by the level monitor circuits 5' with each other for
`detection of the reversal of the reception levels, so that
`in the signal receiving system providing a higher recep
`tion level the distributor is connected to the receiver,
`and in the preceding signal receiving system the distrib
`utor is connected to the dummy resistor.
`FIG. 2 is a diagram for explaining reception levels in
`the conventional diversity signal receiving apparatus,
`
`5,161,252
`2
`and its antenna switching timing. More specifically,
`FIG. 2(A) shows an electric field strength at a signal
`receiving point, FIG. 2(B) shows the antenna switching
`timing, and FIG. 2(C) shows relationship between re
`ceived data blocks and the antenna switching timing.
`The two signal receiving antennas receive a radio
`wave from a signal transmitting station, to provided
`two reception levels (indicated by the thin solid line (a)
`and the broken line (b) in FIG. 20A)). When the recep
`tion levels are reversed (as indicated by the broken line
`(d) in FIG. 20B)), the signal receiving antenna selected
`previously is switched over to the receiving antenna
`providing the highest reception level, which provides a
`diversity field strength (as indicated by the heavy solid
`line (c) in FIG. 2(A)).
`Thus, the signal can be received through the signal
`receiving system providing the highest reception level
`at all times. Therefore, the effect of deep fading can be
`minimized.
`However, when the communication system switches
`one receiving antenna to the other, the phases before
`and after the change-over action are not continuous
`because of the difference in propagation paths. Further,
`although data which are divided into blocks of data
`signals, such as a synchronizing word, a control word,
`a talking word, and so on are transmitted continuously,
`the continuity of data, and moreover, the data itself are
`lost at the time of the change-over action as shown in
`FIG. 2(C). Therefore, to provide the lost data, it is
`necessary to retransmit.
`In addition, in the case where the difference in level
`between the input signals received by the signal receiv
`ing system are small, the frequency of switching the
`signal receiving systems is increased, and accordingly
`the probability that the data is lost by the switching of
`the signal receiving systems is increased.
`This disadvantage will be described in detail with
`reference to FIG. 3. In the case where the difference in
`level between the input (indicated by the solid line in
`FIG. 3(A) received by a signal receiving system A and
`that (indicated by the broken line in FIG. 3(A) re
`ceived by a signal receiving system B is small (hereinaf.
`ter referred to as "having substantially the same level”,
`when applicable), the frequency of reversal of the re
`ception levels is increased. A reception level determin
`ing unit detects such a frequent level reversal to output
`a signal receiving system switching signals (as shown in
`FIGS. 3(B) and 3(C). Thus, the signal receiving sys
`tems are frequently switched over to each other, with
`the result that the data is cut and lost during the switch
`ing operation.
`Furthermore, there is a problem that data transmitted
`by a mobile body is not transmitted to the called station.
`In order to transmit signals from a mobile body, a non
`directional mono-pole antenna is used. With the non
`directional antenna, data is not transmitted at some
`times because the position of the mobile body is
`changed frequently and therefore the reception level
`transmitted from the called station changes frequently.
`For a single communication, signals are transmitted
`and received between fixed stations through directional
`diversity antennas. This is to separate an aimed station
`from a plurality of stations, thereby to perform selective
`communications.
`
`5
`
`10
`
`35
`
`65
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 12 of 21
`
`

`

`15
`
`3
`SUMMARY OF THE INVENTION
`The object of the present invention is to provide a
`diversity receiving antenna communication system for
`preventing a possibility of data loss at the switching of 5
`signal receiving systems, and minimizing the failure that
`data is not transmitted to a called station.
`The foregoing object of the invention has been
`achieved by the provision of the following systems and
`apparatuses:
`10
`In the diversity antenna communication system ac
`cording to a first aspect of the present invention, a trans
`mission side transmits a radio wave having plural re
`ceiving system change-over timing signals inserted at
`the regions other than those for the data, and a recep
`tion side including plural receiving systems receives the
`radio wave, extracts the receiving system change-over
`timing signals and produces a change-over signal in
`response to the extracted receiving system change-over
`timing signals to switch one receiving system to another
`receiving system providing reception signals of maxi
`mum (high) level. As a result, a maximum reception
`level can be obtained with little loss of data because the
`receiving system change-over action occurs in the other
`periods than those for data region.
`25
`A diversity signal receiving apparatus, according to a
`second aspect of the invention, comprises: reception
`level setting means for setting the signal reception level
`of one of at least two signal receiving systems which is
`not used for actual signal reception to a lower level than
`30
`the signal reception level of the signal receiving system
`which is used for the actual signal reception, to the
`extent that deep fading can be detected; signal receiving
`system detecting means for comparing the signal recep
`tion levels of at least two signal receiving systems
`35
`whose signal reception levels have been set by the re
`ception level setting means and detecting the signal
`receiving system highest in signal reception level; and
`signal receiving system change-over means for switch
`ing the present signal receiving system over to the sig
`nal receiving system which is highest in signal reception
`level.
`A diversity signal receiving apparatus, according to a
`third aspect of the invention, comprises: signal receiv
`ing system detecting means for comparing the signal
`45
`reception levels of at least two signal receiving systems
`and detecting the alternation in highest signal reception
`level of the signal receiving systems; and signal receiv
`ing system change-over means for setting the upper
`threshold value and the lower threshold value for a
`signal reception level at the alternation in highest signal
`reception level of the signal receiving systems to the
`extent that the deep fading can be detected and switch
`ing the present signal receiving system over to the sig
`nal receiving system highest in signal reception level
`55
`when the signal reception level of the present signal
`receiving system which is used for the actual signal
`reception becomes lower than the lower threshold
`value and the signal reception level of a signal receiving
`system which is highest in signal reception level ex
`ceeds the upper threshold value.
`In a diversity antenna communication system, ac
`cording to a fourth aspect of the invention, the signal
`receiving system highest in signal reception level which
`has been selected in the system provided according to
`65
`the first aspect of the invention or in the apparatus
`provided according to the second or third aspect of the
`invention is connected to a transmitter, so that signal
`
`5,161,252
`4.
`transmission is carried out with the antenna in the signal
`receiving system highest in signal reception level.
`In a diversity antenna communication system, ac
`cording to a fifth aspect of the invention, a signal receiv
`ing system providing the lowest level in signal reception
`level of at least two signal receiving systems is inter
`rupted, and the antennas in the remaining signal receiv
`ing systems are used for signal transmission and recep
`tion.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram showing the arrangement
`of a conventional diversity signal receiving apparatus,
`FIGS. 2A, 2B, 2C and 3A, 3B, 3C are diagrams illus
`trating the signal reception levels of the conventional
`diversity signal receiving apparatus as shown in FIG. 1
`and the antenna switching timing thereof;
`FIG. 4 is a block diagram illustrating the diversity
`receiving antenna communication system, which is an
`embodiment of the present invention;
`FIGS. 5A, 5B and 5C are a diagram demonstrating
`the operation of the diversity receiving antenna com
`munication system;
`FIGS. 6A, 6B and 6C are a diagram illustrating the
`output timing of the receiving system change-over flag
`and the receiving system change-over signal over a
`predetermined period;
`FIG. 7 is a block diagram showing the arrangement
`of a diversity receiving antenna communication system,
`which is another of the invention;
`FIG. 8 is a flow chart for explaining the operation of
`the diversity antenna communication system shown in
`FIG. 7;
`FIG. 9 is one example of the circuit arrangement of
`the receiving system change-over means in the diversity
`antenna communication system of this invention;
`FIG. 10 is a block diagram showing one example of a
`diversity signal receiving apparatus, which is another
`embodiment of the invention;
`FIGS. 11A, 11B and 11C are a diagram for explaining
`the operation of the diversity signal receiving apparatus
`shown in FIG. 9;
`FIG. 12 is a block diagram showing the arrangement
`of another example of the diversity signal receiving
`apparatus according to the invention;
`FIGS. 13A, 13B and 13C are a diagram for explaining
`the operation of the diversity signal receiving apparatus
`shown in FIG. 11;
`FIG. 14 is a block diagram showing the arrangement
`of another example of the diversity signal receiving
`apparatus according to the invention; and
`FIG. 15 is a block diagram illustrating the diversity
`signal receiving apparatus of FIG. 13 which is equipped
`with a transmitter according to the invention.
`DETALED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`A preferred embodiment of the diversity receiving
`antenna communication system according to the pres
`ent invention will be described in detail with reference
`to the accompanying drawings.
`FIG. 4 shows a block diagram of a diversity receiving
`antenna communication system according to a first
`embodiment of the present invention, having a transmis
`sion side and a reception side. A transmission side com
`prises: a transmitting data producing means 1 for pro
`ducing a series of data with receiving system change
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 13 of 21
`
`

`

`5,161,252
`6
`5
`receiving system in which the maximum reception level
`over flags (f) inserted at the regions other than data
`can be obtained. Upon selection of a new receiving
`region for data blocks, such as a synchronizing word (s),
`system, the CPU 85 supplies a receiving system change
`a control word (c) (a call signal, or the like), a talking
`over signal to the receiving system change-over means
`word (w), and so on; and a transmitting antenna 2 for
`5 when the change-over clock pulse producing means 7
`radiating the produced series of data (as shown in FIG.
`produces the change-over clock pulse. In other words,
`5(A)). In this embodiment, the receiving system change
`the CPU 85 has a reception level monitoring period (as
`over flags (f) are inserted at intervals between the data
`shown by a stripe in FIG. 5(C)) for supplying a channel
`blocks. However, the receiving system change-over
`change-over signal to the multiplexer 81 and a change
`flags(f) may be disposed at any regions so far as the
`over timing period (as shown by a slant line in FIG.
`regions are not overlapped with the data region.
`10
`5(C)) for outputting a receiving system change-over
`A reception side, located on the mobile body, com
`signal with a period which is an integer multiple of the
`prises: directive antennas 3a, 3b, 3c and 3d, (each gener
`reception level monitoring period.
`ally situated at an angular interval of 90' C. and cover
`The operation of the diversity receiving antenna
`ing all directions from 0 to 360 degrees); distributors 4a,
`communication system having the above-mentioned
`4b, 4c and 4d for distributing each of the reception sig
`configuration will be described with reference to FIG.
`nais from the respective directive antennas 3a, 3b, 3c
`5, in which FIG. 5(A). shows transmission data pro
`and 3d to a receiving system change over means 5 and
`duced by the transmission data producing portion 1,
`a level comparator as described below; the receiving
`FIG. 5(B) shows a period of a change-over clock pulse,
`system change-over means 5 for selecting a channel, in
`and FIG. 5(C) shows the relationship between the re
`which the maximum reception level can be obtained
`20
`ception level monitoring period and the change-over
`from channels 5a, 5b, 5c and 5d in accordance with a
`timing period.
`receiving system change-over signal (described later); a
`A data signal radiated from the transmission data
`receiver 6 for extracting the synchronizing word (s), the
`producing means 1 includes a synchronizing word (s), a
`control word (c), the talking word (w), and the receiv
`control word (c), a talking word (w) and so on, which
`ing system change-over flags (f) from the reception
`25
`are formatted therein. Receiving system change-over
`signal supplied through the channel providing the maxi
`flags (f) are inserted, for example, between the words as
`mum reception level by the receiving system change
`shown in FIG. 5(A). A series of data signals thus con
`over means 5; a change-over clock pulse producing
`structed are transmitted through the transmitting an
`means 7 for producing a change-over clock pulse (as
`shown in FIG. 5(B)) having a period corresponding to
`tenna 2 to all the mobile bodies located within a radio
`30
`the receiving system change-over flag (f) extracted by
`wave radiation area. Control data are designated as
`either general calling data, or specified mobile body/-
`the receiver 6; and a level comparator 8 for receiving
`bodies calling data to call the appropriate mobile station
`the change-over clock pulse from the change-over
`clock pulse producing means 7, monitoring and com
`or stations.
`paring the reception levels of the respective reception
`At the mobile station side, directive antennas 3a, 3b,
`35
`3c and 3d are disposed in two directions to receive the
`signals from distributors 4a, 4b, 4c and 4d, to select one
`of the receiving systems in which the maximum recep
`radio waves. The distributors 4a, 4b, 4c and 4d distrib
`ute each reception signal to the receiving system
`tion level can be obtained, and supplying a receiving
`change-over means 5 and the level comparator 8. One
`system change-over signal (as shown in FIG. 5(C)) to
`of the reception signals distributed to the receiving
`the receiving system change-over means 5 at the input
`system change-over means 5 is applied to the receiver 6
`timing of the change-over clock pulse. Since a propaga
`through one of the channels 5a, 5b, 5c and 5d which is
`tion path is constituted by the transmitting antenna 2 to
`selected in response to the change-over means control
`the channels of the receiving system change-over means
`signal from the level comparator 8 to maximize the
`5, it is defined that the receiving systems are constituted
`reception level. The control word (c), the talking word
`by the components along this path (i.e., a transmitting
`(w), and the receiving system change-over flags (f) are
`antenna, a directive antenna, a respective distributor,
`extracted from the reception signal by the receiver 6. A
`and a respective channel). The number of the receiving
`change-over clock pulse is produced by the change
`systems may be increased or decreased.
`over clock pulse producing means 7 on the basis of the
`The level comparator 8 will be described in more
`receiving system change-over flags (f).
`detail. The level comparator 8 comprises a multiplexer
`Meanwhile, the reception signals distributed to the
`81, an amplifier 82, a demodulator 83, an A/D con
`level comparator 8 by the distributors 4a, 4b, 4c and 4d
`verter 84, a CPU 85, and a memory 86. The multiplexer
`are fed successively to the amplifier 82 through the
`81 changes over channels 81 from one to another every
`channels 81' of the multiplexer 81 at the predetermined
`predetermined period (unlike the receiving system
`period. The envelope of the reception signals is de
`change-over means 5, which only changes over to a
`55
`new channel in response to a receiving system change
`tected by the demodulator 83 and converted by the
`A/D converter 84 to digital data. The digital envelope
`over signal from the CPU 8) in accordance with a tim
`data (i.e., the reception levels) are stored in the memory
`ing signal supplied from the CPU 85 to supply one of
`86, and compared in the CPU 85 to select one of the
`the reception signals from the distributors 4a, 4b, 4c and
`receiving systems in which the maximum reception
`4d to the amplifier 82. Accordingly, the CPU 85 can
`60
`sample the reception signals from each directive an
`level can be obtained.
`Upon reception of the change-over clock pulse from
`tenna 3a, 3b, 3c and 3d, to determine which receiving
`the change-over clock pulse producing means 7, the
`system has the maximum reception level. The demodu
`CPU 85 supplies the receiving system change-over
`lator 83 envelope-detects the amplified reception signal.
`means 5 with the change-over means control signal for
`The A/D converter 84 converts the envelope-detected
`instructing a change-over from one receiving system to
`signal to a digital signal. The CPU 85 stores the digital
`another receiving system providing the reception signal
`signal (corresponding to the reception level) in the
`of the maximum reception level.
`memory 86, and then compares the signals to select the
`
`45
`
`15
`
`65
`
`ERICSSON v. UNILOC
`Ex. 1026 / Page 14 of 21
`
`

`

`15
`
`10
`
`5,161,252
`8
`7
`from the memory 86, and applies a signal to the signal
`As shown in FIG. 6, the two receiving systems can be
`receiving system change-over means 5 to select the
`compared with respect to their electric field intensity.
`signal receiving system providing the highest reception
`On inversion of reception levels A and B, the system
`will change-over from one receiving system to another
`level, and supplies an instruction signal for switching
`on the very next change-over clock pulse. As a result,
`signal reception over to signal transmission to the trans
`signal reception can be made at the maximum reception
`mission and reception change-over means 9.
`level without loss of data because the change-over ac
`The diversity antenna communication system thus
`tion occurs in the regions other than data blocks. In
`organized will be described with reference to a flow
`addition, if the receiving system change-over flags (f)
`chart shown in FIG. 8.
`are inserted at intervals between the data blocks, the
`In Step S1, the reception levels of the signal receiving
`signal reception can be made every data block.
`systems are detected, so that the antenna providing the
`Fading may be reduced by suitably setting the dura
`highest reception level is determined.
`tion and period of the receiving system change-over
`In Step S2, it is determined whether or not the an
`flag based upon a relationship with a fading period
`tenna providing the highest reception level is being used
`which, in turn, depends on the length of the block data
`for actual signal reception. When it is determined that
`and the speed of the mobile body.
`the antenna being used for actual signal reception pro
`Although the transmission efficiency is lowered in
`vides the highest reception level, then Step S1 is effected
`the above-mentioned embodiment because at least one
`again; and when it is not, in Step S3 the change-over
`1-bit receiving system change-over flag is inserted at
`data (reception level) is stored in the memory 86 until
`every interval between data, the transmission efficiency
`arrival of the change-over clock pulse.
`is superior to the case where retransmission of data is
`In Step S4, upon arrival of the change-over cock
`required. In comparison with a system in which a cor
`pulse, the antenna in signal reception is switched over to
`rection code is added to each block data, it is possible to
`the antenna providing the highest reception level, and
`shorten the length of data to further improve the trans
`the level monitoring operation in Step S1 is carried out
`mission efficiency.
`25
`again. (The operations in Steps S1 through S4 are per
`As described above, in the diversity antenna commu
`formed by the level comparison circuit 8.)
`nication system according to the present invention, a
`In Step S5, the receiver determines according to a
`radio wave having receiving system change-over tim
`block data received whether or not it is a reception
`ing signals inserted at the regions other than those for
`data. When it is determined that it is a reception data,
`data, for example, at intervals between the data is radi
`30
`then in Step S6, the data is fetched and processed, for
`ated from the transmission side. At the reception side,
`instance, into audio signals. When it is determined that
`the receiving system change-over timing signals are
`it is not a reception data, Step Ss is effected again
`extracted out of the radio wave and used to produce a
`(standby for signal reception).
`change-over clock pulse. Meanwhile, a level compara
`In Step Sn, it is determined whether or not the trans
`tor 8 is continuously monitoring the reception levels of 35
`mission and reception change-over signal generator 11
`receiving systems to discern the maximum reception
`has received the data reception acknowledge signal
`level. Upon inversion of reception levels, the level com
`(ACK) from the receiver 6, and it is determined
`parator 8 sends receiving system change-over means 5
`whether or not the operator has provided the data
`an instruction signal for switching one receiving system
`transmission request signal. When no such signals have
`to the other to obtain the maximum reception level.
`been provided, the operation in Step 5 is carried out
`This instruction is sent at a period corresponding to the
`again.
`receiving system change-over timing signals. There
`When it is determined that those signals have been
`fore, the receiving system can be changed over at peri
`provided, in Step S8 the transmission and reception
`ods other than those for the data. Accordingly, it is
`change-over signal is produced and applied to the level
`possible to prevent data from being lost at the time of 45
`comparison circuit 8, and in Step S9 with the change
`change-over of the receiving system.
`over data read out of the memory 86, the antenna pro
`FIG. 7 shows the arrangement of the diversity re
`viding the highest reception level is selected and the
`ceiving antenna communication system of another em
`reception-to-transmission and reception change-over
`bodiment of the invention. The system shown in FIG.7
`instruction signal is applied to the transmission and
`is different from that shown in FIG. 4 in that the diver
`reception change-over means 9.
`sity antennas are utilized for signal transmission and
`In Step S10, transmission data is transmitted through
`reception.
`the antenna providing the highest reception level. Upon
`In the embodiment, the signal receiving system
`completion of the transmission, Step S5 is effected again.
`change-over means 5 is connected to a transmission and
`In the above-described embodiment, the level com
`reception change-over means 9, which is connected to
`55
`parison circuit 8 detects the antenna providing the high
`the receiver 6 and to a transmitter 10, and the receiver
`est reception level on the basis of the reception levels
`6 is connected to a transmission and reception change
`over signal generator 11 which produces a data recep
`which are monitored at all times. In transmission of
`data, the transmission and reception change-over means
`tion acknowledge signal and a transmission and recep
`tion change-over signal for switching signal reception
`9 operates to connect the transmitter to the antenna thus
`60
`detected; that is, the transmission is carried out with the
`over to signal tr