1111111111111111 IIIIII IIIII 11111 1111111111 1111111111 1111111111 11111 11111 1111111111 11111111
`c19) United States
`
`
`c12) Patent Application Publication
`c10) Pub. No.: US 2009/0209256 Al
`
`
`(43) Pub. Date: Aug. 20, 2009
`
`Nakashima et al.
`
`US 20090209256Al
`
`(54)MOBILE COMMUNICATION SYSTEM,AND
`
`(86)PCT No.:
`MOBILE UNIT, BASE STATION UNIT AND
`METHOD THEREFORE
`
`§ 371 (c)(l),
`
`(2), ( 4) Date:
`
`Nov.13, 2008
`
`PCT /JP2007 /059981
`
`(76)Inventors:Daiichiro Nakashima, Chiba-shi
`
`
`(51)Int. Cl.
`
`
`(JP); Hidekazu Tsuboi, Chiba-shi
`H04W 36/00 (2009.01)
`(JP)
`H04B 17100 (2006.01)
`H04M 1100 (2006.01)
`
`
`(52)U.S. Cl. ..................... 455/436; 455/67.11; 455/67.7;
`455/561
`
`
`
`Publication Classification
`
`Correspondence Address:
`
`
`BIRCH STEWART KOLASCH & BIRCH
`POBOX747
`
`
`FALLS CHURCH, VA 22040-0747 (US)
`
`(21)Appl. No.:
`
`12/300,768
`
`
`
`(22)PCT Filed:May 15, 2007
`
`
`
`(57)
`
`ABSTRACT
`
`In mobile communication system having a plurality of mobile
`
`
`
`
`
`
`
`
`
`traits and a plurality of base station units, the system of the
`
`
`
`
`present invention is characterised in that the base station unit
`
`
`
`
`
`
`has a gap period length setting section for setting the length of
`
`
`the gap period for the mobile unit depending on the type of the
`
`
`
`
`radio access technology to be monitored by the mobile unit.
`
`cl
`
`RIIT1
`
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`1
`
`

`

`Patent Application Publication
`
`Aug. 20, 2009 Sheet 1 0f 12
`
`US 2009/0209256 A1
`
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`

`

`Patent Application Publication
`
`Aug. 20, 2009 Sheet 2 0f 12
`
`US 2009/0209256 A1
`
`FIG 2
`
`MOBILE UNIT
`
`COMMUNICATION
`
`INSTANTANEOUS OOI
`VALUE MEASUREMENT
`
`SEOTION ‘ SECTION
`CONTROL _ FEEDBACK INTERVAL
`
`SETTING SECT | UN
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`FIG.3
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`FEEDBACK INTERVAL SETTING SECTION
`
`12
`
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`
`MEMORY
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`MEAN 001 VALUE
`DERIVING SECTION
`
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`
`SYSTEM TO BE MDNITORED
`
`'
`CO! THRESHOLD VALUE
`
`MODE DECISION
`SECTION
`
`INFORMATION CONCERNING
`MOBILE COMMUNICATION
`
`FEEDBACK INTERVAL
`SETTING SECTION
`
`FEEDBACK INTERVAL
`
`3
`
`

`

`Patent Application Publication
`
`Aug. 20, 2009 Sheet 3 0f 12
`
`US 2009/0209256 A1
`
`IFIIIE Allflk
`
`
`RADIO
`ACCESS TECHNOLOGY
`
`
`
`LENGTH OF GAP PERHJD
`
`
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`
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`LENGTH OF GAP PERIOD
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`ACCESS TECHNOLOGY
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`UTRA
`
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`

`

`Patent Application Publication
`
`Aug. 20, 2009 Sheet 4 0f 12
`
`US 2009/0209256 A1
`
`LENGTH OF GAP PERIOD FUR GSM
`T20 T20 T20 T20 T20 T20
`
`
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`TIME
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`

`

`Patent Application Publication
`
`Aug. 20, 2009 Sheet 5 0f 12
`
`US 2009/0209256 A1
`
`FIG 6
`
`BASE STATION UNIT
`
`COMMUNICATION
`
`SECTION
`
`INTERVAL SETTING SECTION
`
`CONTROL
`UNIT
`
`RESOURCE ALLOCATION
`
`FIG.7
`
`RESOURCE ALLOCATION INTERVAL SETTING SECTION
`
`MEAN COI
`DERIVING SECTION
`
`INSTANTANEOUS
`COI VALUE
`
`SECTION
`
`ON] T
`
`HR
`
`ESHOLD VA
`
`LUE
`
`MODE DECISION
`SECTION
`
`INFORMATION CONCERNING
`MOBILE COMMUNICATIONS
`SYSTEM TO BE NONIIOREO
`BY MOBILE UNIT
`
`RESOURCE ALLOCATION
`INTERVAL SELECTION
`
`RESOURCE ALLOCATION INTERVAL
`
`6
`
`

`

`Patent Application Publication
`
`Aug. 20, 2009 Sheet 6 0f 12
`
`US 2009/0209256 A1
`
`ITI(Ei 5%
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`

`

`Patent Application Publication
`
`Aug. 20, 2009 Sheet 7 0f 12
`
`US 2009/0209256 A1
`
`FIG 9
`
`BASE STATION UN I T
`m
`
`5100
`
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`
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`
`8
`
`

`

`Patent Application Publication
`
`Aug. 20, 2009 Sheet 8 0f 12
`
`US 2009/0209256 A1
`
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`Patent Application Publication
`
`Aug. 20, 2009 Sheet 9 0f 12
`
`US 2009/0209256 A1
`
`BASE STATION UNIT
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`

`Patent Application Publication
`
`Aug. 20, 2009 Sheet 10 0f 12
`
`US 2009/0209256 A1
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`Patent Application Publication
`
`Aug. 20, 2009 Sheet 12 0f 12
`
`US 2009/0209256 A1
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`

`US 2009/0209256 A1
`
`Aug. 20, 2009
`
`MOBILE COMMUNICATION SYSTEM, AND
`MOBILE UNIT, BASE STATION UNIT AND
`METHOD THEREFORE
`
`TECHNICAL FIELD
`
`[0001] The present invention relates to a mobile communi-
`cation system, and a mobile unit, a base station unit and a
`mobile communication method therefore and, particularly to
`such system, and a mobile unit, a base station unit, and a
`mobile communication method adapted to provide wireless
`communication between cells to which the same frequencies
`are assigned under the same radio access technology, between
`cells to which mutually different frequencies are assigned
`under the same radio access technology, or between cells
`under mutually different radio access technologies.
`[0002]
`Priority is claimed on Japanese Patent Application
`No. 2006-136259 filed May 16, 2006, the content ofwhich is
`incorporated herein by reference.
`
`BACKGROUND ART
`
`In a cellular mobile communication system based
`[0003]
`on the same radio access technology (RAT), a number ofbase
`station units are remotely located, each of which constitutes a
`wireless communication area, thereby to provide a service
`area, wherein a mobile unit in one of the cells is allowed to
`have access to the base station unit through a radio channel.
`When the mobile unit moves from one cell to another during
`on-going conversation, the so-called handover H0 is per-
`formed to permit the communication to be continued in a
`seamless manner.
`
`[0004] There are two different types of handover, i.e., the
`intra-frequency handover (intra-freq HO) on one hand, and
`the inter-frequency handover (inter-freq HO) on the other.
`[0005]
`In addition, in a cellular mobile communication sys-
`tem based on mutually different radio access technologies,
`there is the inter-RAT handover (inter-RAT HO) performed
`when a mobile unit moves across a cell-to-cell border based
`
`on mutually different radio access technologies.
`[0006] The cell-to-cell handover under the same radio
`access technology, which may be called intra-RAT handover
`(intra-RAT H0), is in Contrast to the last-mentioned inter-
`RAT H0.
`
`[0007] Referring to FIG. 12 illustrating the handover pro-
`cessing to be performed while the mobile unit is in motion,
`base station units BSl, BS2, BS3 and BS4 are separately
`located on a two-dimensional plane. These base station units
`BSl, BS2, BS3 and BS4 provide wireless communication
`links to mobile units through carrier waves at frequencies fl,
`f2, f3 and f4, respectively; and using radio access technolo-
`gies RAT1, RAT1, RAT1 and RAT2, respectively.
`[0008] Base station units BSl, BS2, BS3 and BS4 can be in
`communication with mobile units MSl, MS2, MS4 and MSG
`located in cell c1; with mobile units MS4 and MSS located in
`cell c2, with mobile units MS2 and MS3 located in cell c3;
`and with mobile units MS6 and MS7 located in cell c4.
`
`[0009] Mobile unit MS4 in motion between cells c1 and c2
`performs the handover based on the intra-RAT—HO (and inter-
`freq-HO). Similarly, mobile unit MS2 in motion between
`cells c1 and c3 performs the handover based on the intra-RAT—
`HO (and intra-freq-HO); while mobile unit MS6 in motion
`between cells c1 and c4 performs the handover based on the
`inter-RAT—HO (and inter-freq-HO).
`
`[0010] The well-known W-CDMA (wideband-code divi-
`sion multiple access) radio access technology provided by the
`3GPP (3rd generation partnership project) has been in use for
`the third generation, cellular mobile communication systems
`as the standard radio access technology. For the W—CDMA
`system, the so-called compressed mode is provided to moni-
`tor or measure the performance ofbase station units operating
`at mutually different frequencies to provide the intra-RAT—
`HO (and inter-freq-HO) and/or inter-RAT—HO (and inter-
`freq-HO).
`[0011] Under the above-mentioned situation, the base sta-
`tion unit sets a gap period, as show in FIG. 13 (a), during
`which the data transmission through the dedicated channel
`DPCH is stopped. On the other hand, the mobile unit switches
`its frequency during the gap period, thereby to monitor the
`function of the base station unit operating at a different fre-
`quency.
`In the 3GPP, the high speed downlink packet access
`[0012]
`HSDPA to realize for downlink a high speed packet transmis-
`sion at a maximum transmission rate of 14.4 Mbps, which is
`an extension of W-CDMA wireless interface, has already
`been adopted as a technology standard (Non-Patent Docu-
`ment 2 referred to). In the adopted standard, high-speed
`downlink shared control channel HS-SCCH and high-speed
`physical downlink shared channel HS-PDSCH are addition-
`ally defined for downlink as independent channels separate
`from the above-mentioned dedicated channel to which the
`
`compressed mode is inherently applied. Similarly, high-
`speed dedicated physical control channel HS-DSPCCH is
`additionally defined for uplink.
`[0013]
`In the HSDPA, adaptive modulation and coding
`scheme AMCS is adopted, which switches, depending on
`downlink channel quality indicator CQI indicative of the
`current state of the transmission paths for the respective
`mobile units, wireless transmission parameters such as data
`modulation scheme for the shared data channel, error correc-
`tion scheme, coding rate for the error correction code, spread-
`ing factors for time/frequency domain, and the order of code-
`multiplexing of multicodes. In addition, hybrid automatic
`repeat request scheme HARQ is also adopted, under which a
`mobile unit sends the acknowledgement/negative acknowl-
`edgement ACK/NACK signals and the CQI signal hack to the
`base station unit through the dedicated control channel.
`[0014]
`FIGS. 13 (b) and 13(c) illustrate examples of packet
`signals transmitted from a base station unit to a mobile unit,
`with FIG. 13 (b) showing a shared control channel for the base
`station unit-to-mobile unit transmission and FIG. 13 (0) show-
`ing a shared data channel for the base station Unit-to-mobile
`unit transmission.
`
`In the HSDPA, a mobile unit does not have, during
`[0015]
`the time period corresponding to the gap period, those packet
`data allotted thereto which are addressed to itself, because the
`exchange of data transmission with a base station unit cannot
`be performed if the base station unit operating at a different
`frequency is to be monitored or measured. The base station
`unit is therefore adapted to send, in advance of the provision
`of the gap period, instructions to the mobile unit to stop the
`allotment of data for a shared data channel through the shared
`control channel. In response to the instructions, the mobile
`unit provides the gap period, thereby to perform the monitor-
`ing and the measurement of the base station unit operating at
`a different frequency.
`[0016] More specifically, in contrast to the situation of FIG.
`13 ((1), wherein the base station unit provides the gap period
`
`14
`
`14
`
`

`

`US 2009/0209256 A1
`
`Aug. 20, 2009
`
`by applying the data compression or the like to continuous
`data to be sent to a mobile unit, the gap period is provided in
`the case of FIGS. 13(1)) and 13(c) by preventing the allotment
`ofthe packet control signal and the packet data for the mobile
`unit to the gap period.
`[0017]
`It is to be noted here that the radio interface of
`W-CDMA- or HSDPA-based mobile communication system
`is generally referred to as universal terrestrial radio access
`UTRA.
`
`Further study is now in progress for the evolved
`[0018]
`universal terrestrial radio access EUTRA and for the evolved
`universal terrestrial radio access network EUTRAN, both for
`the third generation radio access technology.
`[0019] The orthogonal frequency division multiplexing
`access OFDMA has been proposed for providing the down-
`link for the SUTRA, while the AMOS technique has been
`applied to the OFDMA system as the EUTRA scheme (Non-
`Patent Documents 3 and 4 referred to). For the EUTRA
`scheme, the radio frame structure for the downlink transmis-
`sion and a mapping method for the radio channel have been
`proposed (Non-Patent Document 4 referred to).
`[0020]
`In regard to the intra-RAT-HO (and the intra-freq-
`HO) and/or the inter-RAT-HO (and the inter-freq HO) for the
`EUTRA/EUTRAN, an autonomous gap control method for
`autonomously providing the gap period when the instanta-
`neous CQI value becomes lower than the mean CQI value has
`been proposed as a method for controlling the gap period to
`monitor or measure a different frequency-based base station
`unit (FIG. 1 of Non-Patent Document 5 referred to).
`[0021]
`FIGS. 14(a) and 14(b) illustrate a method of con-
`trolling the gap period, which has been proposed in the past.
`In the prior-art method illustrated, the mobile unit receives the
`shared pilot channel, measures the instantaneous CQI values
`at a predetermined CQI measurement interval, and reports the
`measured CQI values to the base station unit. At the same
`time, the mobile unit averages the instantaneous CQI values
`at a predetermined interval (a system parameter) to provide
`mean CQI values, and then compare the mean CQI values
`with a CQI threshold value, which is also a system parameter.
`When the mean CQI value is lower than the CQI threshold
`value, the mobile unit sets itself in a measurement mode for
`monitoring or measuring the base station unit operating at a
`different frequency.
`[0022]
`In the measurement mode, the mobile unit stops
`receiving the signals from the base station unit currently in
`communication, thereby to provide the gap period, when the
`measured instantaneous CQI value is lower than the mean
`CQI value. Upon receipt ofthe instantaneous CQI value from
`a certain mobile unit, the base station unit provides a mean
`CQI value for that mobile unit in a manner similar to the
`calculation at the mobile unit. The base station unit then
`
`compares the mean CQI value with a CQI threshold value,
`which is a system parameter. When the mean CQI value is
`higher than the CQI threshold value, the base station unit sets
`itself at an ordinary mode, while it sets itself at a measurement
`mode when the mean CQI value is lower than the CQI thresh-
`old value. In the measurement mode, the base station unit
`stops transmission of data packets to the mobile unit currently
`in communication therewith, to provide the gap period, when
`the measured instantaneous CQI value is lower than the mean
`CQI value.
`[0023] As shown in FIG. 14 (a), the mobile unit terminates
`the gap period to resume the measurement of instantaneous
`CQI values and the report to the base station unit, after the
`
`completion of the monitoring or measurement of the base
`station unit operating at a different frequency. A similar pro-
`cessing is repeatedly performed thereafter, as shown in FIG.
`14 (b), which illustrates the successive formation of a plural-
`ity of gap periods g1 to g6.
`[0024] A next-generation mobile unit adapted to the
`EUTRA/EUTRAN is required to be operable in a plurality of
`mobile communication systems, which utilize mutually dif-
`ferent radio access technologies. More specifically, such
`next-generation, mobile unit must be operable in mobile com-
`munication systems utilizing the UTRA, GSM (global sys-
`tem for mobile communication), or other radio access tech-
`nologies, which are not specified even in the 3GPP standards.
`Such mobile communication systems may have a different
`frame length, different frame structure, and different means
`or processes for measuring the quality of signal reception at
`the mobile units. As a result, a mobile unit under control by a
`base station unit ofthe EUTRA/EUTRAN mobile communi-
`
`cation system may not always be able to set, in the inter-RAO-
`HO (and the inter-freq-HO), the length of the gap period
`which is optimum to such radio access technology, due to the
`difference in minimum required gap length for the monitoring
`or measurement of a different radio access technology-based
`base station unit. When the length of the gap period is set at a
`value longer than a minimum required gap, that results in an
`unutilized portion in the gap period, adversely affecting the
`spectral efficiency as well as the time efficiency.
`Tachikawa
`[0025] Non-Patent Document
`1: Keiji
`“W—CDMA Mobile Communication System,” ISBN4-62l-
`04894-5
`
`[0026] Non-Patent Document 2: 3GPP TR technical Report
`25.858 and HSDPA specificationirelated materials (http://
`www.3 gpp .org/ftp/Specs/html-info/25 -series.htm)
`[0027] Non-Patent Document 3: 3GPP TR (Technical
`Report) 25.913, V2.1 .0 (2005-05), Requirements for Evolved
`Universal Terrestrial Radio Access (UTRA) and Universal
`Terrestrial Radio Access Network (UTRAN). (http://www.
`3 gpp .org/ftp/Spec/html-info/25 913.htm)
`[0028] Non-Patent Document 4: 3GPP TR (Technical
`Report) 25.814, V1.0.l (2005-11), Physical Layer Aspects
`for Evolved UTRA. (http://www.3gpp.org/ftp/Specs/html-
`info/258l4.htm)
`Inc.
`[0029] Non-Patent Document 5: NTT DoCoMo,
`“Measurement for LTE Intra- and Inter-RAT Mobility,” 3GPP
`TSG RAN WG2 Meeting #50, Sophia Antipolis, France, 9-13
`Jan. 2006
`
`DISCLOSURE OF INVENTION
`
`Problem to be Solved by the Invention
`
`[0030] With a view to obviating the difficulties described
`above, it is an object of the invention to provide a mobile
`communication system, and a mobile unit, a base station unit
`and a method therefore, capable of utilizing frequency and
`time in a more efficient manner.
`
`Means for Solving the Problem
`
`[003 1] According to the present invention, there is provided
`a mobile communication, system having a plurality ofmobile
`units and a plurality of base station units, wherein the base
`station unit has a gap period setting section for setting the
`length of a gap period for a mobile unit, depending on the type
`of radio access technology to be monitored by the mobile
`unit.
`
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`
`[0032] According to one aspect of the invention, there is
`provided a mobile communication system of the type
`described above, wherein the gap period setting section ofthe
`base station unit is adapted to set the length of the gap period
`for the mobile unit, depending on the type of the radio access
`technology to be monitored and reported by the mobile unit.
`[0033] According to another aspect of the invention, there
`is provided a mobile communication system of the type
`described above, wherein the gap period setting section is
`adapted to set the lengths of a plurality of the gap periods for
`the mobile unit, depending on the types of the radio access
`technologies to be monitored by the mobile unit.
`[0034] According to the present invention, there is provided
`a mobile communication system having a plurality of mobile
`units and a plurality of base station units, wherein the base
`station unit has a gap period setting section for setting the
`length of a gap period for a mobile unit, depending on the type
`of combinations of the radio access technology to be moni-
`tored by the mobile unit and the frequency band utilized for
`the wireless communication.
`
`[0035] According to one aspect of the invention, there is
`provided a mobile communication system of the type
`described above, wherein the gap period setting section ofthe
`base station unit is adapted to set the length of the gap period
`for the mobile unit, depending on the type of the combination
`of the radio access technology monitored and reported by the
`mobile unit and the frequency band utilized for the wireless
`communication.
`
`[0036] According to another aspect of the invention, there
`is provided a mobile communication system of the type
`described above, wherein the gap period setting section ofthe
`base station unit is adapted to simultaneously set the lengths
`of a plurality of gap periods for the mobile unit, depending on
`the type of the combination of the radio access technology to
`be monitored by the mobile unit and the frequency band
`utilized for the wireless communication.
`
`[0037] According to still another aspect of the invention,
`there is provided a mobile communication system as
`described above, wherein the gap period setting section ofthe
`base station unit is adapted to set the lengths of the gap
`periods by resetting, when the base station unit receives from
`a mobile unit a reception quality indicator, a gap period of a
`length set at a longer value than the short gap length among
`the plurality of the simultaneously set gap lengths, and by
`continuously setting, when the base station unit does not
`receive within the short gap length from the mobile unit a
`reception quality indicator, a gap period set at a value longer
`than the short gap length.
`[0038] According to still another aspect of the invention,
`there is provided a mobile communication system as
`described above, wherein the mobile unit has a gap period
`setting section for setting the length of the gap period,
`depending on the type ofradio access technology to be moni-
`tored.
`
`[0039] According to still another aspect of the invention,
`there is provided a mobile communication system as
`described above, wherein the mobile unit has a gap period
`setting section for setting the length of the gap period,
`depending on the type of the combination of the radio access
`technology to be monitored and the frequency band utilized
`for the wireless communication.
`
`decision section for determining, based on the reception qual-
`ity indicator, a measurement mode for monitoring the adja-
`cent base station unit or an ordinary mode for not monitoring
`the adjacent base station unit, wherein the gap period setting
`section of the mobile unit is adapted to set the length of the
`gap period on the basis of the decision performed at the first
`mode-decision section and the reception quality indicator,
`wherein the base station unit has a second mode-decision
`
`section for determining, based on file reception quality indi-
`cator fed back from the mobile unit, whether the mobile unit
`is in the measurement mode or the ordinary mode, and
`wherein the gap period setting section at the base station unit
`sets the gap length on the basis of the decision performed at
`the second mode decision selection.
`
`[0041] According to still another aspect of the invention,
`there is provided a mobile communication system as
`described above, wherein the mobile unit has a first mode
`decision section for determining the measurement mode for
`monitoring an adjacent base station unit or the ordinary mode
`for not monitoring an adjacent base station unit, wherein the
`gap period setting section of the mobile unit is adapted to set
`the length of the gap period on the basis of the result of the
`decision performed at the first mode decision section and the
`reception quality indicator, and wherein the gap period set-
`ting section of the base station unit is adapted to set the length
`of the gap on the basis of the decision performed at the first
`mode decision section and the reception quality indicator fed
`back from the mobile unit.
`
`[0042] According to still another aspect of the invention,
`there is provided a mobile communication system as
`described above, wherein the mobile unit has a first mode
`decision section for determining, on the basis ofthe reception
`quality indicator, the measurement mode for monitoring an
`adjacent base station unit or the ordinary mode for not moni-
`toring a adjacent base station unit, wherein the gap length
`setting section ofthe mobile unit is adapted to set, on the basis
`of the decision performed at the first mode decision section
`and the reception quality indicator, the length of the gap
`period, and wherein the gap length setting section of the base
`station unit is adapted to set, based on the reception quality
`indicator fed back from the mobile unit, the length of the gap
`period.
`[0043] According to a further aspect of the invention, there
`is provided a mobile unit, wherein the mobile unit adapted to
`perform wireless communication with a base station unit has
`a gap length-setting section for setting the length of the gap
`period depending on the type of the radio access to be moni-
`tored.
`
`[0044] According to still further aspect of the invention,
`there is provided a mobile unit, wherein the mobile unit for
`performing wireless communication with a base station has a
`gap setting section for setting the length ofthe gap, depending
`on the type of combination of the radio access technology to
`be monitored and the frequency band utilized for the wireless
`communication.
`
`[0045] According to a further aspect of the invention, there
`is provided a base station unit, wherein the base station unit
`for communication with a mobile unit has a gap period setting
`section for setting the length of the gap period, depending on
`the type of radio access technology to be monitored by the
`mobile unit.
`
`[0040] According to still another aspect of the invention,
`there is provided a mobile communication system as
`described above, wherein the mobile unit has a first mode-
`
`[0046] According to still further aspect of the invention,
`there is provided a base station unit, wherein the base station
`unit for communication with the mobile unit has a gap setting
`
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`
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`
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`
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`
`section for setting the length of the gap period for the mobile
`unit, depending on the type ofcombination ofthe radio access
`technology to be monitored by the mobile unit and the fre-
`quency band utilized for the wireless communication.
`[0047] According to a further aspect of the invention, there
`is provided a mobile communication method for providing
`wireless communication between a plurality of mobile units
`and a plurality of base station units, wherein the base station
`unit is adapted to set the length of the gap period for the
`mobile units, depending on the type of radio access technol-
`ogy to be monitored by the mobile unit.
`[0048] According to still further aspect of the invention,
`there is provided a mobile communication method for pro-
`viding mobile wireless communication between a plurality of
`mobile units and a plurality of base station units, wherein the
`base station unit is adapted to set the length ofthe gap period,
`for the mobile unit, depending on the type of combination of
`the radio access technology to be monitored by the mobile
`unit and the frequency band utilized for the wireless commu-
`nication.
`
`[0049] As described above, in the present invention, the
`base station unit is adapted to set the length of the gap period
`for the mobile unit, depending on the type of radio access
`technology to be monitored by the mobile unit.
`[0050] This makes it possible for the base station unit to set
`the length of the gap period depending on the type of radio
`access technology to be monitored by the mobile unit, with
`the result that the setting of redundant gap period can be
`avoided to utilize the radio frequency spectrum more effi-
`ciently.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows an example of downlink radio frame
`[0051]
`structure for a 3GPP-based EUTRA.
`
`FIG. 2 schematically shows in blocks a mobile unit
`[0052]
`according to a first embodiment of the present invention.
`[0053]
`FIG. 3 schematically shows in blocks the structure
`of feedback interval setting section 34 (FIG. 2) in the first
`embodiment.
`
`FIG. 4A shows the relationship between the radio
`[0054]
`access technology used in the first embodiment and the length
`of the gap period.
`[0055]
`FIG. 4B shows the relationship among the radio
`access technology frequency band utilized and the length of
`the gap period.
`[0056]
`FIG. 5 shows illustration for describing the length of
`the gap period to be set by the base station unit in the first
`embodiment.
`
`FIG. 6 shows in blocks the structure of the base
`[0057]
`station unit in the first embodiment.
`
`FIG. 7 shows in blocks the structure of resource
`[0058]
`assignment interval setting section 43 (FIG. 6).
`[0059]
`FIG. 8 shows a flow chart for the processing per-
`formed at feedback interval selection unit 14 of the mobile
`unit in the first embodiment.
`
`FIG. 9 shows a flow chart for the processing per-
`[0060]
`formed at resource allocation interval selection section 24 of
`the base station unit in the first embodiment.
`
`FIG. 10 shows an illustration for describing the
`[0061]
`resource allocation interval in the second embodiment of the
`invention.
`
`FIG. 11 shows a flow chart for the processing per-
`[0062]
`formed at the resource allocation interval selection section 24
`of the base station in the second embodiment.
`
`FIG. 12 illustrates the handover processing to be
`[0063]
`performed while the mobile unit is in motion.
`[0064]
`FIG. 13 shows an example of a dedicated channel
`transmitted from the base station unit to the mobile unit.
`
`FIG. 14 shows an illustration for describing a con-
`[0065]
`ventional method of controlling the gap period.
`
`REFERENCE SYMBOLS
`
`In the drawings, reference letters/numerals BSl,
`[0066]
`BS2, BS3 and BS4 denote base station units; M81, M82,
`M84 and MSG, mobile units; 11, mean CQI value deriving
`section; 12, memory; 13, mode decision section; 14, feedback
`interval selection section; 21, mean CQI value deriving sec-
`tion; 22, memory; 23, mode decision section; 24, resource
`allocation interval selection section; 30, communication sec-
`tion; 31, timer; 32, control section; 33, instantaneous CQI
`value measuring section; 34, feedback interval selection sec-
`tion; 40, communication section; 41, timer; 42, control sec-
`tion; and 43, resource allocation interval setting section.
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`
`First Embodiment
`
`[0067] A mobile communication system according to a first
`embodiment of the invention will now be described.
`
`In FIG. 1 showing an example ofthe downlink radio
`[0068]
`signal frame structure for the