US 8,442,473 B1
`(10) Patent No.:
`a2) United States Patent
`Kaukovuori et al.
`(45) Date of Patent:
`May 14, 2013
`
`
`US008442473B1
`
`5/2010 Pal
`2010/0118923 Al
`(54) METHODS OF RECEIVING AND RECEIVERS
`8/2010 Sundstrém etal.
`2010/0210272 Al
`T/2011 Park et abe oscscesesce 375/344
`2011/0268232 AL
`(75)
`Inventors: Jouni Kristian Kaukovuori, Vantaa
`FOREIGN PATENT DOCUMENTS
`(FI); AamoTapio Parssinen, Espoo (FD;
`2141818 Al
`1/2010
`EP
`Antti Oskari Immonen, Helsinki (FI)
`
`EP 2378670 A2=10/2011
`WO
`(73) Assignee: Renesas Mobile Corporation, Tokyo
`WO 00/11794 Al
`3/2000
`(IP)
`WO
`WO 2010/092167
`8/2010
`WO
`WO 2010/129584 Al
`11/2010
`Subject to any disclaimer, the term ofthis
`Wo
`WO 2013/024450 AT
`2/2013
`patent is extended or adjusted under 35
`OTHER PUBLICATIONS
`US.C. 154(b) by 35 days.
`R4-113595, 3GPP TSG RAN WG4 Meeting #59AH, Bucharest,
`(21) Appl. No.: 13/300,004
`Romania, Jun. 27-Jul. 1, 2011, ST-Ericsson/Ericsson, ““Non-Con-
`tiguous Carrier Aggregation Configurations”, (5 pages).
`(Continued)
`
`(22)
`
`Filed:
`
`Nov. 18, 2011
`
`(*) Notice:
`
`Foreign Application Priority Data
`(30)
`Nov. 17,2011
`(GB) ccessssssssseesssesssnseesnees 1119888.4
`(51)
`Int. Cl.
`HOAB 1/26
`(52) U.S. CL.
`USPC oo. 455/323; 455/334; 455/550.1; 375/324
`(58) Field of Classification Search .................. 455/313,
`455/323, 324, 334, 339-341, 550.1; 375/324
`See applicationfile for complete search history.
`
`(2006.01)
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`6,356,746 BL*
`3/2002 Katayama ..eeccessseceeee 455/324
`6,785,529 B2*
`8/2004 Ciccarelli et al. oc... 455/324
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`4/2009 Davidoffetal. .......... 375/350
`7,783,275 B2*
`8/2010 Wakayamaet al.
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`soaestoy ‘I eos anea
`2007/0211837 Al
`9/2007 Zipper
`2008/0112470 Al
`5/2008 Clevelandetal.
`2010/0104001 Al
`4/2010 Lee et al.
`
`Primary Examiner —Nhan Le
`(74)Attorney,Agent or Firm —Lucas & Mercanti LLP;
`
`ABSTRACT
`67)
`Data transmitted via a combination of radio frequency RF
`signals using carrier aggregation CA is received, each RF
`Signal occupying a respective RF band, the bands being
`arranged in two groups separated in frequency by a first
`frequency region, the first of the two groups occupying a
`wider frequency region than the second group. Inphase and
`quadrature components of the RF signals are filtered using a
`first bandpass filter bandwidth to give first bandpassfiltered
`componentsand filtered using a second bandpass filter band-
`width, different from the first bandpass filter bandwidth, to
`give second bandpassfiltered components. A reconfigurable
`receiver is configurable to a first mode to receive the combi-
`nation of RF signals, and is also configurable to at least a
`second mode.A filter is configured, in different modes, to use
`a first or a lowpass bandpassfilter bandwidth.
`
`20 Claims, 18 Drawing Sheets
`
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`106
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`

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`US 8,442,473 B1
`
`Page 2
`
`OTHER PUBLICATIONS
`
`R4-113494, TSG-RAN Working Group 4 (Radio) Meeting #59AH,
`Bucharest, Romania, Jun. 27-Jul. 1, 2011, ZTE,“Handling the Inter-
`ferences in the NC_GAP in NC_4CHSDPA”,(3 pages).
`3GPP TS 25.101 (see Table 7.2C), User Equipment (UE)radiotrans-
`mission and reception (FDD) Specification Detail (4 pages). Avail-
`able on-line: http://www.3gpp.org/ftp/specs/html-info/25 101 -htm,
`Feb. 21, 2012.
`Ericsson, 3 GPP TSG-RAN Meeting #51, RP-110416, Kansas City,
`Missouri, USA Mar. 15-18, 2011, “Non-contiguous 4C-HSDPA
`Operation, Core-Part, 4C Performance Part” (13 pages).
`Nokia Corporarion, 3GPP TSG-RAN Meeting #52, RP-110732,
`Bratislava, Slovakia, May 31, Jun. 3, 2011, “LTE Carrier Aggregation
`Enhancements, Core-Part, Performance” (17 pages).
`Ericsson, 3GPP TSG-RAN Meeting #60, Tdoc R4-114401, Athens,
`Greece, Aug. 22, 26, 2011, “Feedback on non contiguous carrier
`aggregation feasibility,” (2 pages).
`Renesas Electronics Europe, 3GPP TSG-RAN WG4 Meeting #58,
`RF-111965, Shanghai, China, Apr. 10-15, 2011, “Considerations on
`RSTD measuresandcarrier aggregation.” (9 pages).
`Ericsson, 3GPP TSG-RAN WG4 Meeting #61, R4-115583, San
`Francisco, California, Nov. 14-18, 2011, “Scenarios for non-continu-
`ous intra-band CA,”(7 pages).
`Non-Final Office Action dated Feb. 28, 2013 issued in a related U.S.
`Appl. No. 13/677,776 (12 pages).
`UKIPO Combined Search and Examination Report under Sections
`17 and 18(3) dated Mar. 15, 2012 issued in a related British Appli-
`cation No. GB1119887.6 (5 pages).
`
`UKIPO Combined Search and Examination Report under Sections
`17 and 18(3) dated Mar. 19, 2012 issued in a related British Appli-
`cation No. GB1119888.4 (5 pages).
`UKIPO CombinedSearch and Examination Report under Section 17
`and 18(3) dated Dec. 7, 2012 issued in a related British Application
`No. GB1219626.7 (6 pages).
`PCT Notification of Transmittal of the International Search Report
`and the Written Opinion and PCT International Search Report, PCT
`Written Opinion mailed Feb. 25, 2013 issued in a related PCT Appli-
`cation No. PCT/IB2012/056441 (15 pages).
`Pietro Andreani, et al., “A CMOSg,, *C Polyphase Filter with High
`Image BandRejection,” Solid-State Circuits Conference, 2000, Pro-
`ceedings of
`the 26 Round European,
`IEEE, pp. 272-275,
`XP03 1952366 (4 pages).
`Nokia et al., 3GPP TSG-RAN WG4 Meeting 2010 AH#4,
`R4-103677, Xi’an, China, Oct. 11-15, 2010, “Image Rejection in
`intraband carrier aggregation”(8 pages).
`Toru Kitayabu., “Concurrent Dual-Band Receiver for Spectrum
`Aggregation System,” Radio and Wireless Symposium, 2009, RWS
`2009, IEEE, Piscataway, NJ, USA, pp. 634-637 XP03 1457487 (4
`pages).
`PCT Notification of Transmittal of the International Search Report
`and the Written Opinion and PCT International Search Report, PCT
`Written Opinion mailed Mar. 13, 2013, all of which wasissued in a
`related PCT Application No. PCT/IB2012/056440 (15 pages).
`
`* cited by examiner
`
`

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`U.S. Patent
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`FIG. 5
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`Sheet 4 of 18
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`Sheet 5 of 18
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`U.S. Patent
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`Sheet 9 of 18
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`Sheet 10 of 18
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`Sheet 11 of 18
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`Sheet 12 of 18
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`Sheet 13 of 18
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`U.S. Patent
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`Sheet 14 of 18
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`U.S. Patent
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`Sheet 16 of 18
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`U.S. Patent
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` Digital
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`US 8,442,473 B1
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`1
`METHODS OF RECEIVING AND RECEIVERS
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`
`This application claims benefit under 35 U.S.C. §119(a)
`and 37 CFR 1.55 to UK Patent Application 1119888.4, filed
`on Nov. 17, 2011.
`
`TECHNICAL FIELD
`
`The present invention relates to methods of receiving and
`receivers for radio communication systems, and in particular,
`but not exclusively, to non-contiguous carrier aggregation
`schemes.
`
`BACKGROUND
`
`Long Term Evolution (LTE) Advanced is a mobile tele-
`communication standard proposed by the 3” Generation
`Partnership Project (GPP) and first standardised in 3GPP
`Release 10. In order to provide the peak bandwidth require-
`ments of a 4” Generation system as defined by the Interna-
`tional Telecommunication Union Radiocommunication
`
`frequency band as signals on the low side of the local oscil-
`lator, and in order to separate out the high and low side
`signals, it is necessary to mix the signal with two components
`
`(ITU-R)Sector, while maintaining compatibility with legacy
`mobile communication equipment, LTE Advanced proposes
`the aggregation of multiple carrier signals in order to provide
`a higher aggregate bandwidth than would beavailable if
`transmitting via a single carrier signal. This technique of
`CarrierAggregation (CA) requires eachutilised carrier signal
`to be demodulated at the receiver, whereafter the message
`data from each of the signals can be combined in order to
`reconstructthe original data. Carrier Aggregation can be used
`also in other radio communication protocols such as High
`Speed Packet Access (HSPA).
`Carrier signals are typically composed of a carrier fre-
`quency that is modulated to occupy a respective radio fre-
`quencycarrier signal band. Contiguous Carrier Aggregation
`involves aggregation of carrier signals that occupy contigu-
`ous radio frequency carrier signal bands. Contiguous radio
`frequency carrier signal bands may be separated by guard
`bands, which are small unused sections of the frequency
`spectrum designed to improvethe ease with which individual
`In accordance with a first exemplary embodimentof the
`signals can be selected byfilters at the receiver by reducing
`present invention, there is provided a method of receiving
`the likelihood of interference between signals transmitted in
`data transmitted via a combination ofat least a plurality of
`adjacent bands. Non-contiguous Carrier Aggregation com-
`radio frequency signals using carrier aggregation, each radio
`prises aggregationof carrier signals that occupy non-contigu-
`
`ous radio frequencycarrier signal bands, and may comprise frequency signal occupying a respective bandofaplurality of
`aggregation of clusters of one or more contiguous carrier
`radio frequency bands, theplurality of radio frequency bands
`
`signals. The non-contiguous radio frequency carrier signal being arranged in two groups separated in frequencybyafirst
`bandsare typically separated by a frequency region which is
`frequency region, the first of the two groups occupying a
`not available to the operator of the network comprising the
`wider frequency region than the second group, the method
`carrier signals, and may be allocated to another operator. This
`comprising:
`situation is potentially problematic for the reception of the
`downconverting said plurality of radio frequency signals
`carrier signals, since there may be signals in the frequency
`using quadrature mixing to give inphase and quadrature com-
`ponents;
`region that separates the non-contiguouscarriers whichare at
`a higher powerlevel than the wanted carrier signals.
`filtering said inphase and quadrature components using a
`A Direct Conversion Receiver
`(DCR)
`is
`typically
`first bandpass filter bandwidth to give first bandpassfiltered
`employedto receive cellular radio signals, and typically pro-
`inphase and quadrature components; and
`vides an economical and powerefficient implementation of a
`filtering said inphase and quadrature components using a
`receiver. A DCRuses a local oscillator placed within the radio
`second bandpass filter bandwidth, different from the first
`frequency bandwidth occupied by the signals to be received
`bandpass filter bandwidth, to give second bandpass filtered
`to directly concert the signals to baseband. Signals on the high
`inphase and quadrature components.
`side of the local oscillator are mixed to the same baseband
`In accordance with a second exemplary embodimentofthe
`present invention, there is provided a receiver for receiving
`data transmitted via a combination ofat least a plurality of
`radio frequency signals, each radio frequency signal occupy-
`
`2
`of the local oscillator in quadrature (i.e. 90 degrees out of
`phase with one another) to produce inphase (1) and quadrature
`(Q) signal components at baseband. The I and Q components
`are digitised separately, and may be processed digitally to
`reconstruct the separate high side and low side signals. The
`reconstructed high and low side signals maybe filtered in the
`digital domain to separate carrier signals received within the
`receiver bandwidth of the DCR.
`
`The presence of a higher powersignal in the region sepa-
`rating non-contiguouscarrier clusters poses particular prob-
`lems if a DCRis to be used to receive a band of frequencies
`comprising non-contiguous Carrier Aggregation signals. In
`particular, since the higher powersignal is within the receiver
`bandwidth, the dynamic rangeofthe receiver need to encom-
`pass the powers of the wanted carrier signals, which are
`typically received at a similar power to each other, and the
`higher power signal. This may place severe demands on the
`dynamic range of the analogue to digital converter (A/D) in
`particular. Furthermore, due to inevitable imbalances
`between the amplitudes and phases of the I and Q channels,
`the process of reconstructing the separate high side and low
`side signals suffers from a limited degree of cancellation of
`the image component; that is to say, some of the high side
`signals break through onto the reconstructed low side signals,
`and vice versa. The degree of rejection of the image signal
`may be termed the Image Reject Ratio (RR). If the higher
`powersignalis a high side signal, it may cause interference to
`received low side signals dueto the finite IIR, and similarly if
`the higher powersignal is a low side signal, it may cause
`interference to received high side signals.
`One conventional method of receiving Non-contiguous
`Carrier Aggregation signals is to provide two DCRreceiver
`stages, each having a local oscillator tuned to receive a cluster
`of contiguous carriers, and so rejecting signals in the fre-
`quency region betweenthe clusters before digitisation. How-
`ever, this approach is potentially expensive and power con-
`suming, and maysuffer from interference between the closely
`spaced local oscillators.
`Itis an object ofthe inventionto addressat least some ofthe
`limitations ofthe prior art systems.
`
`SUMMARY
`
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`US 8,442,473 B1
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`3
`ing a respective bandofa plurality of radio frequency bands,
`the plurality of radio frequency bands being arranged in two
`groups separated in frequency bya first frequency region, the
`first of the two groups occupying a wider frequency region
`than the second group, the receiver comprising:
`at least one downconverter configured to downconvert said
`plurality of radio frequency signals using quadrature mixing
`to give inphase and quadrature components;
`at least one first bandpass filter configured to filter said
`inphase and quadrature components using a first bandpass
`filter bandwidth to give first bandpass filtered inphase and
`quadrature components; and
`at least one second bandpass filter configuredto filter said
`inphase and quadrature components using a second bandpass
`filter bandwidth, different from the first bandpassfilter band-
`width, to give second bandpassfiltered inphase and quadra-
`ture components.
`In accordance with a third exemplary embodimentof the
`present invention, there is provided a reconfigurable receiver
`capable of receiving data transmitted via a combinationof at
`least a plurality ofradio frequency signals using carrier aggre-
`gation, each radio frequency signal occupying a respective
`bandof a plurality of radio frequency bands,
`the receiver being configurable to a first mode to receive
`radio signals in which the plurality of radio frequency bands
`are arranged in two groups separated in frequency bya first
`frequency region, the first of the two groups occupying a
`wider frequency region than the second group, andto at least
`a second mode,
`receiver comprising:
`at least one downconverter configured to downconvert said
`plurality of radio frequency signals using quadrature mixing
`to give inphase and quadrature components;
`at least onefirst filter arranged to be configured,in thefirst
`mode,to filter said inphase and quadrature components using
`a first bandpass filter bandwidthto give first bandpass filtered
`inphase and quadrature componentsand, in the second mode
`to filter said inphase and quadrature components using a first
`lowpassfilter bandwidthto give first lowpass filtered inphase
`and quadrature components;
`at least one secondfilter arranged to be configured, in the
`first mode,to filter said inphase and quadrature components
`using a second bandpassfilter bandwidth, different from the
`first bandpass filter bandwidth, to give second bandpass fil-
`tered inphase and quadrature components.
`Further features and advantages of the invention will be
`apparentfrom the following description ofpreferred embodi-
`ments of the invention, which are given by way of example
`only.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG.1 is a schematic diagram showing the transmission of
`carrier aggregation signals by the radio access network of a
`first operator and transmission of a signal from another a radio
`access network;
`FIG. 2 is amplitude-frequency diagram showingcarriers in
`a non-contiguous carrier aggregation method anda carrier
`from another operator received at a higherlevel;
`FIG. 3 is a schematic diagram showing a conventional
`direct conversion receiver;
`FIG.4 is a diagram illustrating an effect of a finite image
`rejection ratio in a direct conversion receiver;
`FIG. 5 is a diagram illustrating reception of non-contigu-
`ous aggregated carriers in a low IF receiver.
`FIG.6 is a schematic diagram showing a conventional low
`IF receiver;
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`4
`FIG. 7 is a diagram illustrating problems with reception of
`non-contiguous aggregated carriers in a direct conversion
`receiver;
`FIG. 8 is an amplitude-frequency diagram illustrating
`reception of non-contiguous aggregated carriers in a direct
`conversion receiver in an embodimentof the invention;
`FIG. 9 is an amplitude-frequency diagram illustrating
`reception of non-contiguous aggregated carriers in an
`receiver having different passbandfilters for the high side and
`low side signals in an embodimentofthe invention;
`FIG. 10 is a schematic diagram showing a receiver having
`twozero IF branches each having different bandpassfilters in
`an embodimentofthe invention;
`FIG. 11 is a schematic diagram showing an alternative
`receiver having two zero IF branches each having different
`bandpass filters in an embodimentof the invention;
`FIG. 12 is a diagram illustrating a conventional direct
`conversion receiver as implemented in an RFIC;
`FIG. 13 is a frequency-amplitude diagram illustrating
`problemswith reception of non-contiguous aggregated carri-
`ers ina direct conversion receiver, showing image frequencies
`at the equivalent position in RF frequency;
`FIG. 14 is a frequency-amplitude diagram illustrating a
`conventional solution for the reception of non-contiguous
`aggregated carriers, by the use of two receivers, each having
`a different local oscillator frequency;
`FIG. 15 is a schematic diagram illustrating an RF IC imple-
`mentation for the reception of non-contiguous aggregated
`carriers, by the use of two receivers, each having a separate
`RFIC and a different local oscillator frequency;
`FIG. 16 is a schematic diagram illustrating an RF IC imple-
`mentation for the reception of non-contiguous aggregated
`carriers, by the use of two receivers, each having a different
`local oscillator frequency on a single RFIC;
`FIG. 17 is an amplitude-frequency diagram illustrating
`reception of non-contiguous aggregated carriers, with a
`single signal from another operator between the wanted car-
`rier signals in an embodimentofthe invention;
`FIG.18 is an amplitude-frequency diagram illustrating the
`reception of non-contiguous aggregated carriers, showing a
`single signal from another operator between carrier aggrega-
`tion clusters and the effect ofimage frequencies in an embodi-
`mentof the invention;
`FIG. 19 is an amplitude-frequency diagram illustrating the
`reception of non-contiguous aggregated carriers, showing
`two signals from another operator between carrier aggrega-
`tion clusters and the effect ofimage frequencies in an embodi-
`mentof the invention;
`FIG.20 is an amplitude-frequency diagram illustrating the
`reception of non-contiguous aggregated carriers, showing
`three signals from another operator between carrier aggrega-
`tion clusters and the effect ofimage frequencies in an embodi-
`mentof the invention;
`FIG.21 is an amplitude-frequency diagram illustrating the
`reception of non-contiguous aggregated carriers, showing a
`different filter bandwidth used for the reception of high side
`and low side signals in an embodimentofthe invention;
`FIG.22 is an amplitude-frequency diagram illustrating the
`reception of non-contiguous aggregated carriers, showing a)
`the use of a complex filter characteristic b) the effect of the
`complexfilter characteristic shown with a digital filter char-
`acteristic superimposed and c) the combined effect of the
`complex anddigital filters;
`FIG. 23 (upper part) is schematic diagram showing a
`receiver architecture having complexfilters and a digital data
`path;
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`US 8,442,473 B1
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`DETAILED DESCRIPTION
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`FIG. 23 (lower part) is schematic diagram showing a
`receiver architecture havingrealfilters and a digital data path
`having image reject mixing;
`FIG. 24 is a schematic diagram showing a reconfigurable
`receiver having two branches, a first branch having a filter
`with a selectable low pass or band pass characteristic and a
`second branch having a band pass characteristic; and
`FIG. 25 is a schematic diagram showing an alternative
`reconfigurable receiver having two branches, a first branch
`having a filter with a selectable low pass or band pass char-
`acteristic and a second branch having a band pass character-
`istic, the two branchessharing the sameI and Q mixers.
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`necessary to mix the RF signal with two components of the
`local oscillator which are in quadrature (i.e. 90 degrees out of
`phase with one another) to produce inphase (1) and quadrature
`(Q) signal components at baseband. As shownin FIG.3, the
`local oscillator is split into 0 and -90 degree componentsin a
`splitter 108 and each componentis mixed with the incoming
`RFsignal in a respective mixer 110, 112. The I and Q com-
`ponents are separately filtered low pass filtered, and each
`filtered signal is converted to the digital domain in an Ana-
`logue to digital converter (A/D) 118, 120, to produce a data
`stream with I and Q components 122, 124. The I and Q
`components may be processed digitally to reconstruct the
`separate high side and low side signals. The reconstructed
`high andlow side signals maybe filtered in the digital domain
`to separate carrier signals received within the receiver band-
`width of the DCR. However, as already mentioned, due to
`By way of example an embodimentof the invention will
`imbalances between the amplitudes and phases of the I and Q
`now be describedin the context of a wireless communications
`channels, the process of reconstructing the separate high side
`system supporting communication using E-UTRA radio
`and low side signals suffers from a limited degree of cancel-
`lation of the image component, so that someofthe high side
`access technology, as associated with E-UTRANradio access
`signals break through onto the reconstructed low side signals,
`networks in LTE systems. However,it will be understoodthat
`and vice versa. The degree of rejection of the image signal
`this is by way of example only and that other embodiments
`may be termed the Image Reject Ratio (IRR).
`may involve wireless networks using other radio access tech-
`FIG.4 showsthe effect of a finite imagerejection ratio in a
`nologies, such as UTRAN, GERANor IEEE802.16 WiMax
`direct conversion receiver, in the case where two bands 202,
`systems.
`204 are received at approximately the same powerlevel at
`FIG. 1 showsthe transmission of radio frequency signal
`radio frequency. As can be seen, the two bands are mixed with
`signals 10a, 10 and 10c by the radio access network to a
`a local oscillator 206 and downconverted to a band encom-
`receiver 8. The radio frequency signals each occupy a respec-
`tive carrier signal band, as shownin the amplitude-frequency
`passing zero frequency, which may be referred to as DC
`
`diagram ofFIG.2.Acarrier signal bandis the part ofthe radio (Direct Current). In FIG.4, the high side signal 204 is shown
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`frequency spectrum occupied by a modulated radio fre-
`as being downconverted to positive frequency 210, and the
`quency carrier comprising the radio frequency signal. Radio
`low side signal 202 is shown as being downconverted to a
`frequency signals 10a, 105, and 10c occupy radio frequency
`negative frequency 208. This is a matter of convention, and
`bands 14a, 146 and 14c as shownin FIG.2. Data is received
`the designation of positive and negative frequencies may be
`using the combination ofthe radio frequency signals 10a, 105
`transposed. The conceptof positive and negative frequencies
`and 10c, and the bands 14a, 144 and 14c shownin FIG. 2
`has meaning only within the complex signal domain, in which
`representa set ofradio frequency signals, that may be referred
`signals are represented by I and Q components. A negative
`
`to as componentcarriers, transmitted using Carrier Aggrega- frequency hasaphasordefinedbyits I and Q componentsthat
`tion. It can be seen from FIG.2 that non-contiguous Carrier
`rotates in the opposite direction to the phasorof a positive
`Aggregation is used, since a radio frequency signal from
`frequency. By distinguishing between positive and negative
`another operator, other than the operator sending the data,is
`frequencies by signal processing, for example using a Fast
`present in a frequency region separating bands 14 and 14c.
`Fourier Transform (FFT) or a complex digital mixer, signals
`
`In FIG.1, the radio frequency signals are sent fromafirst base originating as high side RF signals may be separately
`station 4, operated by Operator A. A second basestation 6,
`received from signals originating as low side RF signals. So,
`operated by a different operator, OperatorB, is situated within
`as shownin FIG.4, data may be extracted from two received
`the area of coverage2 ofthefirst base station 4, and transmits
`carrier signal bands, provided that the signal to noise ratio
`aradio frequency signal 12 that is received by the user equip-
`(SNR) is not degraded unacceptably by the image component
`ment8. It can be seen that the second basestation is closer to
`214 of the high side signal 204that is in the same band 208 as
`the user equipment8 thanis the first base station. As a result,
`the downconverted low side signal 202, and the image com-
`it can be seen from FIG.2 that the radio frequency signal is
`ponent 212 ofthe low side signal 202 that is in the same band
`received at the user equipment 8 at a significantly higher
`210 as the downconverted high side signal 204. For signals
`powerlevel, as shown by the amplitude of the band 16 trans-
`received at approximately the same powerlevel, SNR is not
`mitted by operator B.
`usually degraded unacceptably by the finite image reject
`ratio.
`FIG. 3 is a schematic diagram showing a conventional
`
`direct conversion receiver. A signal is received by an antenna FIG.5is a diagram illustrating reception of non-contigu-
`100, andfiltered by a front endfilter 102, which removes out
`ous aggregated carriers. In this example, wanted component
`of band signals, protecting the Low Noise Amplifier (LNA)
`signal bands 302 and 302 are separated by a higher power
`104 from saturation by strong out of band signals. A local
`radio frequency signal 318, which may originate from
`oscillator 106 is typically set to a frequency in the centre of a
`another operator. As can be seen from FIG.5,a local oscillator
`desired radio frequency (RF) band. RF signals that are both
`306 maybe placed in the middle of a receive band defined by
`higher than (high side) and lower than (low side) the local
`the three component signal bands 302, 304, 318. As can be
`oscillator frequency are mixed with the local oscillator to
`seen from FIG. 5, images ofthe higher powerradio frequency
`downconvert the RF signals to baseband frequencies, which
`signal resulting from thefinite image reject ratio do notfall on
`are the difference between the RF andlocal oscillator fre-
`top of the downconverted weakersignals in this case, butfall
`quencies. These difference frequencies, for signals within an
`within the downconverted components 320 of the higher
`intended receive band, are arranged to fall within the pass-
`powerradio frequency signal.
`bandofthe low passfilters 114, 116 of the direct conversion
`FIG. 6 is a schematic diagram showing a conventional low
`receiver. In order to distinguish between RFsignalsthat origi-
`IF receiver that may be usedto receive the signals illustrated
`in FIG.5. It can be seen that the low IF receiver differs from
`nated on the high side ofthe local oscillator and RF signals
`that originated on the high side of the local oscillator, it is
`a conventional DCRreceiver in that the low passfilters of a
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`US 8,442,473 B1
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`quency on the low frequency side, it may be determinedthat
`the local oscillator offset should be set at a position that
`causes the least total interference with the wanted signals.
`This may be determined onthe basis of signal to noise plus
`interference ratio measurements for each of the wanted sig-
`nals.
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`FIG. 9 showsthat that setting of the local oscillator may be
`used in conjunction with a receiver having two bandpass filter
`characteristics 540, 538 one of which 538 is wider than the
`other 540. The bandpass characteristics may be set to be
`appropriate to receive the component signal bands in the
`respective groups of signals.
`FIG. 10 is a schematic diagram showing a receiver having
`two bandpassfilter characteristics as illustratedin FIG. 9 in an
`embodimentof the invention. The receiver has two branches.
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`conventional DCR receiver, as shown in FIG. 3, have been
`replaced by bandpass filters 114, 118, to filter the ] and Q
`signals respectively. The band pass characteristics ofthe band
`pass filters have been shown on FIG.5, as the dashed lines
`324, 322, around the wanted componentsignal bands 308,
`322. It can be seen that the downconverted components 320 of
`the higher power radio frequency signal are rejected by the
`bandpassfilters in the I and Q signalpaths, so that saturation
`of the A/D converter by the unfiltered downconverted com-
`ponents 320 of the higher powerradio frequency signal may
`be avoided.
`FIG.7 is a diagram illustrating problems with reception of
`non-contiguous aggregated carriers in a direct conversion
`receiver. This illustrates the situation shown in FIG. 2, in
`which component signals bands 524, 502, 504 in a non-
`contiguous carrier aggregation system are arranged in two
`A first branch is a low IF receiver having I and Q channels,
`groups, or clusters, the first group occupying a wider fre-
`each of which has a bandpass filters 814, 816 with a first
`quency region than the second group. A higher powersignal
`bandwidth. A second branch is also configured as a low IF
`518 is located between in a frequency region betweenthefirst
`receiver as shown in FIG. 10, and also has J and Q channels,
`group and the second group. In this case, by contrast to the
`each of which has a bandpass filters 814, 816 with a second
`situation shownin FIG.5, it can be seen that the images 528
`bandwidth,different from thefirst bandwidth.A first subset of
`ofthe higher powerradio frequency signalthat result from the
`downconverted radio signals may be received usingthefirst
`finite imagerejectratio fall directly in the same band as one of
`branch, and a second subset of downconverted radio signals
`the downconverted componentsignal bands 508. Depending
`may be received using the second branch.
`on the difference between the received power of the higher
`FIG. 11 is a schematic diagram showing an alternative
`power signal, the received po