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`US008442473Bl
`
`US 8,442,473 Bl
`
`(10)Patent No.:
`c12) United States Patent
`
`(45)Date of Patent:
`May 14, 2013
`
`Kaukovuori et al.
`
`
`
`Al 5/2010 Pal 2010/0118923
`
`
`(54)METHODS OF RECEIVI�G AND RECEIVERS
`8/2010 Sundstrom 2010/0210272 Al et al.
`
`
`
`
`2011/0268232 Al 11/2011 Park et al. ..................... 375/344
`
`(75)Inventors:
`Jouni Kristian Kaukovuori, Vantaa
`
`(FI); AamoTapio Espoo (FI); Parssinen,
`
`
`
`Helsinki (FI)
`Antti Oskari Immonen,
`EP
`EP
`Tokyo
`(73) Assignee:
`WO
`
`Renesas Mobile Corporation,
`WO
`(JP)
`WO
`WO
`the term of this ( *) Notice: Subject to any disclaimer,
`
`
`
`
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 35 days.
`
`FOREIGN PATENT DOCUMENTS
`
`1/2010
`2 141 818 Al
`10/2011
`2 378 670 A2
`
`WO 00/11794 Al
`3/2000
`WO 2010/092167
`8/2010
`
`WO 2010/129584 Al
`11/2010
`WO 2013/024450 Al
`2/2013
`
`OTHER PUBLICATIONS
`
`(21)Appl. No.:
`13/300,004
`
`(22)Filed:Nov. 18, 2011
`
`R4-113595, 3GPP TSG RAN WG4 Meeting #59AH, Bucharest,
`
`
`
`
`
`Romania, Jun. 27-Jul. 1, 2011, ST-Ericsson/Ericsson, "Non-Con­
`
`
`
`
`tiguous Carrier Aggregation Configurations", (5 pages).
`
`(Continued)
`
`(30)
`
`
`
`
`
`Foreign Application Priority Data
`
`
`
`Primary Examiner - Nhan Le
`
`
`
`
`
`
`Nov. 17, 2011 (GB) ................................... 1119888.4
`Robert P. Michal
`
`(7 4) Attorney, Agent, or Firm - Lucas & Mercanti LLP;
`
`(2006.01)
`
`(57)
`
`ABSTRACT
`
`( 56)
`
`
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`(51)Int. Cl.
`H04B 1126
`Data transmitted via a combination of radio frequency RF
`
`
`
`(52)U.S. Cl.
`
`
`
`
`signals using carrier aggregation CA is received, each RF
`
`
`
`USPC ......... 455/334; 455/550.1; 375/324
`455/323;
`
`
`signal occupying a respective RF band, the bands being
`
`
`455/313, (58)Field of Classification Search ..................
`
`
`arranged in two groups separated in frequency by a first
`
`455/323, 324, 334, 339-341, 550.1; 375/324
`
`
`
`frequency region, the first of the two groups occupying a
`
`
`
`
`See application file for complete search history.
`
`
`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 bandpass filtered
`
`
`
`components and filtered using a second bandpass filter band­
`
`
`
`width, different from the first bandpass filter bandwidth, to
`
`
`
`
`6,356,746 Bl * 3/2002 Katayama ..................... 455/324
`
`
`give second bandpass filtered components. A reconfigurable
`
`6,785,529 B2 *
`
`
`8/2004 Ciccarelli et al. ............. 455/324
`
`
`
`receiver is configurable to a first mode to receive the combi­
`
`
`4/2009 Davidoff et al. .............. 375/350
`
`7,526,052 B2 *
`
`
`8/2010 Wakayama et al ............ 455/333
`
`7,783,275 B2 *
`
`
`nation of RF signals, and is also configurable to at least a
`7 /2003 Shi et al.
`
`2003/0138032 Al
`
`
`second mode. A filter is configured, in different modes, to use
`11/2004 Javor et al.
`
`2004/0224654 Al
`
`
`a first or a lowpass bandpass filter bandwidth.
`9/2007 Zipper
`
`2007/0211837 Al
`
`5/2008 Cleveland et al.
`
`2008/0112470 Al
`4/2010 Lee et al.
`
`2010/0104001 Al
`
`
`
`20 Claims, 18 Drawing Sheets
`
`
`
`INTEL 1025
`
`

`

`US 8,442,473 BI
`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_4CIISDPA”,(3 pages).
`3GPP TS 25.101 (see Table 7.2C), User Equipment (UE) radio trans-
`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, May31, 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 measures and carricr 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 Combined Search 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 Band Rejection.” 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 was issued in a
`related PCT Application No. PCT/IB2012/056440 (15 pages).
`
`* cited by examiner
`
`

`

`U.S. Patent
`
`May14, 2013
`
`Sheet 1 of 18
`
`US 8,442,473 B1
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`
`
` Operator A||Operator A Operator A
`
`FIG. 2
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`

`

`U.S. Patent
`
`May14, 2013
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`Sheet 2 of 18
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`US 8,442,473 B1
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`U.S. Patent
`
`May14, 2013
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`Sheet 3 of 18
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`US 8,442,473 B1
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`U.S. Patent
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`May14, 2013
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`Sheet 4 of 18
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`US 8,442,473 B1
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`May14, 2013
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`Sheet 5 of 18
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`

`US 8,442,473 Bl
`
`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 inparticular,
`but not exclusively, to non-contiguous carrier aggregation
`schemes.
`
`10
`
`15
`
`BACKGROUND
`
`
`
`Long Term Evolution (LTE) Advanced is a mobile tele-ar dc :
`
`=)
`communication standard proposed by the 3” Generation 2
`Partnership Project (3GPP) andfirst 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
`
`(ITU-R) Sector, while maintaining compatibility with legacy
`mobile communication equipment, LT;Advanced proposes
`the aggregation of multiple carrier signals in order to provide
`a higher aggregate bandwidth than would be available if
`transmitting via a single carrier signal. This technique of
`CarrierAggregation (CA) requires each utilised 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. CarrierAggregation can be used
`also in other radio communication protocols such as High
`Speed Packet Access (HSPA).
`Carrier signals are typically composed ofa carrier f[re-
`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 frequencycarrier signal bands. Contiguous radio
`frequency carrier signal bands maybe separated by guard
`bands, which are small unused sections of the frequency
`spectrumdesigned to improve the ease with whichindividual
`signals can be selected by filters at the receiver by reducing
`the likelihood of interference between signals transmitted in
`adjacent bands. Non-contiguous Carrier Aggregation com-
`prises aggregationof carrier signals that occupy non-contigu-
`ous radio frequencycarrier signal bands, and may comprise
`aggregation of clusters of one or more contiguous carrier
`signals. The non-contiguous radio frequency carrier signal
`bands are typically separated bya frequency region whichis
`not available to the operator of the network comprising the
`carrier signals, and maybe allocated to another operator. This
`situation is potentially problematic for the reception of the
`carrier signals, since there maybe signals in the frequency
`regionthat separates the non-contiguous carriers whichare at
`a higher powerlevel than the wanted carrier signals.
`A Direct Conversion Receiver
`(DCR)
`is
`typically
`employedto receive cellular radio signals, and typicallypro-
`vides an economical and powerefficient implementation of a
`receiver. A DCR uses a local oscillator placed withinthe radio
`frequency bandwidth occupied bythe signals to be received
`to directly concert the signals to baseband. Signals on the high
`side of the local oscillator are mixed to the same baseband
`
`frequency band as signals on the lowside ofthe local oscil-
`lator, and in order to separate out the high and lowside
`signals, it is necessaryto mix the signal with two components
`
`30
`
`40
`
`45
`
`60
`
`65
`
`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 lowside signals. The
`reconstructed high andlowside signals may be filtered in the
`digital domainto separate carrier signals received within the
`receiver bandwidth of the DCR.
`
`The presence ofa higher power signal in the region sepa-
`rating non-contiguous carrier clusters poses particular prob-
`lems if'a DCRis to be usedto receive a band offrequencies
`comprising non-contiguous Carrier Aggregation signals. In
`particular, since the higher powersignal is within the receiver
`bandwidth, the dynamic range ofthe 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 ofthe I] and Q channels,
`the process of reconstructing the separate high side and low
`side signals suffers from a limited degree ofcancellation of
`the image component; that is to say, some ofthe high side
`signals break through onto the reconstructed low side signals,
`and vice versa. The degree of rejection of the image signal
`maybe termedthe Image Reject Ratio (IRR). If the higher
`powersignalis a highside signal, it maycauseinterference to
`received low side signals due to the finite ]]R, and similarly if
`the higher power signal is a low side signal, it may cause
`interference to received highside 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-
`quencyregion betweenthe clusters before digitisation. Hlow-
`ever, this approachis potentially expensive and power con-
`suming, and maysuffer frominterference betweenthe closely
`spaced local oscillators.
`Itis an object ofthe invention to address at least some ofthe
`limitations of the prior art systems.
`
`SUMMARY
`
`In accordance with a first exemplary embodiment of the
`present invention, there is provided a method ofreceiving
`data transmitted via a combinationofat least a plurality of
`radio frequency signals using carrier aggregation, each radio
`frequencysignal occupying a respective band of a plurality of
`radio frequency bands, the plurality of radio frequency bands
`being arranged in two groups separated in frequency bya first
`frequencyregion, the first of the two groups occupying a
`wider frequency region than the second group, the method
`comprising:
`downconverting said plurality of radio frequencysignals
`using quadrature mixing to give inphase and quadrature com-
`ponents;
`filtering said inphase and quadrature components using a
`first bandpass filter bandwidthto give first bandpass filtered
`inphase and quadrature components; and
`filtering said inphase and quadrature components using a
`second bandpass filter bandwidth, different from the first
`bandpass filter bandwidth, to give second bandpass filtered
`inphase and quadrature components.
`In accordance with a second exemplary embodimentofthe
`present invention, there is provided a receiver for receiving
`data transmitted via a combinationofat least a plurality of
`radio frequency signals, each radio frequency signal occupy-
`
`

`

`US 8,442,473 Bl
`
`3
`ing a respective bandofa plurality of radio frequencybands,
`the plurality of radio frequency bands being arranged in two
`groups separated in frequencybya first frequencyregion, the
`first of the two groups occupying a wider frequencyregion
`than the secondgroup, 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 configured tofilter 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 embodiment of the
`presentinvention, there is provided a reconfigurable receiver
`capable of receiving data transmitted via a combination ofat
`least a plurality ofradio frequencysignals using carrier aggre-
`gation, each radio frequency signal occupying a respective
`bandofa plurality of radio frequency bands,
`the receiver being configurable to a first mode to receive
`radio signals in which theplurality of radio frequency bands
`are arranged in two groups separated in [frequencybya first
`frequency region, the first of the two groups occupying a
`wider frequencyregion than the second group, and to 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 the first
`mode, to filter said inphase and quadrature components using,
`a first bandpass filter bandwidthto givefirst bandpass filtered
`inphase and quadrature components and, in the second mode
`to filter said inphase and quadrature components usinga first
`lowpassfilter bandwidthto givefirst lowpass filtered inphase
`and quadrature components;
`at least one second filter 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 bandpassfil-
`tered inphase and quadrature components.
`Further features and advantages of the invention will be
`apparent fromthe following description ofpreferred embodi-
`ments ofthe invention, whichare given by way of example
`only.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram showingthe transmission of
`carrier aggregation signals by the radio access network of a
`first operator and transmissionofa signal fromanothera radio
`access network;
`
`FIG, 2 is amplitude-frequency diagram showingcarriers in
`a non-contiguous carrier aggregation method and a carrier
`from another operator received at a higherlevel;
`FIG. 3 is a schematic diagram showing a conventional
`direct conversionreceiver;
`FIG.4 is a diagramillustrating an effect of a finite image
`rejection ratio in a direct conversion receiver;
`VIG. 5 is a diagramillustrating reception of non-contigu-
`ous aggregated carriers in a lowII’ receiver.
`FIG.6 is a schematic diagram showing a conventional low
`IF receiver;
`
`No
`
`30
`
`Le a
`
`40
`
`45
`
`65
`
`4
`FIG.7 is a diagramillustrating 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 embodimentofthe 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
`lowside signals in an embodimentof the invention;
`FIG. 10 is a schematic diagram showing a receiver having
`twozero IF branches cach 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 embodimentofthe 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 aggregatedcarri-
`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 diagramillustrating an RF ICimple-
`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-frequencydiagram illustrating the
`recepuion ofnon-contiguous aggregated carriers, showing a
`single signal from another operator betweencarrier aggrega-
`tion clusters andthe effect ofimage frequencies in an embodi-
`ment ofthe invention;
`FIG. 19 is an amplitude-frequencydiagram illustrating the
`reception of non-contiguous aggregated carriers, showing
`two signals from another operator betweencarrier aggrega-
`tion clusters andthe effect of image frequencies in an embodi-
`mentof the invention;
`FIG.20 is an amplitude-frequencydiagramillustrating the
`reception of non-contiguous aggregated carriers, showing
`three signals from another operator between carrier aggrega-
`tion clusters andthe effect ofimage frequencies in an embodi-
`mentof the invention;
`FIG. 21 is an amplitude-frequencydiagramillustrating the
`recepuion ofnon-contiguous aggregated carriers, showing a
`different filter bandwidth used for the reception of highside
`andlowside signals in an embodiment ofthe invention;
`FIG, 22 is an amplitude-frequencydiagramillustrating the
`reception of non-contiguous aggregated carriers, showing a)
`the use of a complexfilter characteristic b) the effect of the
`complex filter characteristic shown with a digital filter char-
`acteristic superimposed and c) the combined effect of the
`complex and digital filters;
`FIG. 23 (upper part) is schematic diagram showing a
`receiver architecture having complexfilters and a digital data
`path:
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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 same I and Q mixers.
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`6
`necessary to mix the RF signal with two components of the
`local oscillator whichare in quadrature (1.e. 90 degrees out of
`phase with one another) to produce inphase(I) 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 lowpass 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 lowside signals. The reconstructed
`high and low side signals maybefiltered 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 betweenthe amplitudes and phasesof the I and Q
`now be described in 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 froma limited degree of cancel-
`lation ofthe image component, so that some ofthe high side
`access technology, as associated with E-UTRANradioaccess
`signals break throughontothe reconstructed low side signals,
`networks in LTE systems. However,it will be understood that
`and vice versa. The degree of rejection of the image signal
`this is by way of example only and that other embodiments
`maybe termed the Image Reject Ratio (IRR).
`mayinvolve wireless networks using other radio access tech-
`FIG. 4 showsthe effect of a finite image rejection ratio ina
`nologies, such as UTRAN, GERANor JEEE802.16 WiMax
`systems.
`direct conversion receiver, in the case where two bands 202,
`204 are received at approximately the same powerlevel at
`FIG. 1 shows the transmission ofradio frequencysignal
`radio frequency. As can be seen, the two bandsare mixed with
`signals 10a, 104 and 10c by the radio access network to a
`a local oscillator 206 and downconverted to a band encom-
`receiver 8. The radio frequencysignals each occupya respec-
`passing zero frequency, which may be referred to as DC
`live carrier signal band, as shownin the amplitude-frequency
`(Direct Current). In FIG.4, the highside signal 204 is shown
`diagramofFIG. 2. A carrier signal bandis the part ofthe radio
`as being downconverted to positive frequency 210, and the
`frequency spectrum occupied by a modulated radio fre-
`lowside signal 202 is shown as being downconverted to a
`quencycarrier comprising the radio frequency signal. Radio
`negative frequency 208. This is a matter of convention, and
`frequency signals 10a, 106, and 10c¢ occupy radio frequency
`bands 14a, 144 and 14cas shownin FIG.2. Data is received
`the designation of positive and negative frequencies may be
`transposed. The concept of positive and negative frequencies
`using the combinationofthe radio frequency signals 10¢, 104
`has meaning only within the complex signal domain, in which
`and 10¢, and the bands 14a, 146 and 14¢ shownin FIG. 2 ,
`signals are represented by I and Q components. A negative
`representa set ofradio [requencysignals, that maybe referred
`
`to as componentcarriers, transmitted using CarrierAggrega- frequencyhasaphasordefined by its I and Q componentsthat
`tion. It can be seen from FIG.2 that non-contiguous Carrier
`rotates in the opposite direction to the phasor of 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 frequencyregion separating bands 144 and 14c.
`Fourier Transform (I'l) or a complex digital mixer, signals
`In l'IG. 1, the radio frequency signals are sent froma first base
`originating as high side RI’ signals may be separately
`station 4, operated by Operator A. A secondbase station6,
`received from signals originating as lowside RF signals. So,
`operatedby adifferent operator, OperatorB, is situated within
`as shownin FIG. 4, data may be extracted from two received
`the area of coverage2 of the first base station 4, and transmits
`carrier signal bands, provided that the signal to noise ratio
`aradio frequencysigna] 12 that is received by the user equip-
`(SNR)is not degraded unacceptablybythe image component
`ment8. It can be seenthat the second basestationis closer to
`214 ofthe high side signal 204 thatis in the same band 208 as
`the user equipment8 than is the first base station. As a result,
`the downconverted lowside signal 202, and the image com-
`it can be seen from I'IG.2 that the radio frequencysignalis
`ponent 212 ofthe lowside 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. l’or signals
`powerlevel, as shownby the amplitude ofthe band16 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. 5 is a diagram illustrating reception of non-contigu-
`100, andfiltered bya 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 fromsaturation 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 I'IG.5, a local oscillator
`desired radio frequency (RF) band. RFsignals that are both
`306 maybe placedin the middle ofa receive banddefined 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 fromFIG.5, imagesofthe higher powerradio frequency
`downconvert the RF signals to baseband frequencies, which
`signal resulting from the finite imagerejectratio do notfall on
`are the difference between the RF and local 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-
`power radio frequencysignal.
`band ofthe low passfilters 114, 116 of the direct conversion
`l'IG. 6 is aschematic diagram showing a conventional low
`receiver. In order to distinguish between RFsignalsthat origi-
`IF receiver that maybe usedto receive the signals illustrated
`in FIG. 5. It can be seenthat the lowIF 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 Bl
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`conventional DCR receiver, as shown in FIG. 3, have been
`replaced by bandpass filters 114, 118, to filter the I and Q
`signals respectively. The band pass characteristics of the band
`pass fillers have been shown onFIG. 5, as the dashedlines
`324, 322, around the wanted component signal bands 308,
`322. It can be seen that the downconverted components 320of
`the higher power radio frequencysignal are rejected by the
`bandpassfilters in the I and Q signal paths, so that saturation
`of the A/D converter by the unfiltered downconverted com-
`ponents 320 of the higher power radio frequency signal may
`be avoided.
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`quencyonthe lowfrequencyside, 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 ofsignal to noise plus
`interference ratio measurements for each of the wanted sig-
`nals.
`
`FIG. 9 showsthatthat 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 ofsignals.
`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.
`
`A first branch is a lowIF receiver having I and Q channels,
`each of which has a bandpass filters 814, 816 with a first
`bandwidth. A second branchis also configured as a lowII
`receiver as shownin 1G. 10, and also has I and Qchannels,
`each of which has a bandpass filters 814, 816 with a second
`bandwidth, different from the first bandwidth. Afirst subset of
`downconverted radio signals may be received using thefirst
`branch, and a second subset of downconverted radio signals
`maybe received using the second branch.
`FIG. 11 is a schematic diagram showing analternative
`receiver having two branches each having different bandpass
`filters in an embodimentofthe invention, in whichasingle set
`of quadrature mixers is shared between the twobranches.
`Embodiments of the invention will now be described in
`more detail. Embodiments of the invention relate to multi-
`
`carrier wireless systems, using carrier aggregation. Operators
`may own non-contiguous allocation of spectrum; this may
`comeabout, for example, ifan operator buys another opera-
`tor’s businesses. If the spectrums happento be non-adjacent
`then the allocation is non-contiguous. Operators typically
`wishto exploit their spectrumas effectively as possible, so the
`need for non-contiguous multi-carrier systemsis increasing.
`An example of such scenario is presented in FIG. 2. In a
`scenario such