`
`
`
`[J800844247SBI
`
`(12) United States Patent
`Kaukovuori et a].
`
`[10) Patent No.:
`
`(45) Date of Patent:
`
`US 8,442,473 Bl
`May 14, 2013
`
`(54) METHODS OF RECEIVING AND RECEIVERS
`
`(75)
`
`Inventors: Jeuni Kristian Kaukovuori.V’aiitaa
`(1’1); Aamu’l‘apio Parssinen, Espoo (1:1):
`Antti Oskari Immenen, I--Ielsinkj (til)
`
`(73) Assignee: Renesas Mobile Corporation. Tokyo
`(JP)
`
`( "‘ ) Notice:
`
`Subject to any disclaimer. the term ofthis
`patent is extended or adjusted under 35
`U.S.(_‘. 154(1)) by 35 days.
`
`(21) Appl.No.: 131300.004
`
`(22)
`
`Filed:
`
`Nov. 18., 2011
`
`ZOIUI'OII8923 Al
`2010-“021021’2 Al
`201150268232 A1
`
`I’al
`5:"2010
`832010 Sundstriim eta].
`1]."2011 Parketal.
`
`375-344
`
`FOREIGN PATENT DOCUMENTS
`2 [41818 Al
`1.-"2010
`2 3T8 620 AZ
`|0-"2(il I
`W0 00.-"l 1794 AI
`3e'2000
`Wt.) 2010309216”?
`82010
`W0 2010;129:384 A]
`|.-"20l0
`W0 201 320 244 50 AI
`2.-"2013
`
`|
`
`EP
`lil’
`W0
`W0
`W0
`W0
`
`OTHER PUBLICATIONS
`
`R4-ll3595. 3(11’1’ 'I'SU RAN WG-4 Meeting #59AI'I. Bucharest.
`Romania. Jun. 27-Jul.
`l. 20] l. S‘1'-1'iricssom"l£ricsson. “Non-Con-
`Iiguous Carrier Aggregal ion Configuralions". (5 pages).
`
`((..‘onlinued)
`
`(30)
`
`Foreign Application Priority Data
`
`Nov. 17. 201]
`
`(GB)
`
`11198884
`
`Primary Examiner — Nlian Le
`(74) Attorney. Agent. or Firm — Lucas & Mercanti LLP;
`Robert P. Michal
`
`(2006.01)
`
`(51)
`
`(52)
`
`Int. Cl.
`11043 ”26
`[1.8. (II.
`4551323;455F334;45555011375824
`USPC
`(58) Field ofClassification Search
`455813,
`455823. 324. 334. 339—341. 550.]: 375824
`See application file for complete search history.
`
`[57)
`
`ABSTRACT
`
`Data transmitted via a combination of radio frequency RF
`signals using carrier aggregation CA is received, each R1"
`signal occupying a respective R1: 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. lnphase 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
`give second bandpass filtered components. A reconfigurable
`receiver is configurable to a first mode to receive the combi-
`nation ot' 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 iowpass bandpass filter bandwidth.
`
`20 Claims, 18 Drawing Sheets
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5.356.746 Bl ‘“
`6385.529 132 "‘
`7.526.052 B2 *
`”1.783.275 B2 *
`2003-0138032 Al
`200490224654 Al
`2007302 I 1837 Al
`2008-"01 124m A1
`201050104001 Al
`
`455E324
`
`455x324
`.. 3755350
`
`4555333
`
`Tit-“”2002 Kalayama
`8:“2004 Ciccarclli of al.
`4300‘) Davidot't‘ct al.
`832010 Wakaymna ct a].
`7.52003 Shi et al.
`1 l.-'2004 Javor et al.
`932007 Zipper
`5.9008 Cleveland et al.
`4.52010 I_ee el al.
`
`
`
`
`
`INTEL 1125
`
`INTEL 1125
`
`
`
`US 8,442,473 B1
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`Page 2
`
`OTHER PUBLICATIONS
`
`R4-l 13494. TSG-RAN Working Group 4 (Radio) Meeting #SQAH.
`Bucharest. Romania. Jun. 27-Jul. 1. 201 LZTE. “Handling the Inte -
`ferences in the NC .GAP in NC 4CHSDPA". (3 pages).
`3GPPTSZS.101(see'[able 7.3C). UserEquipment (U15)ra.dio trans-
`mission and reception (I‘DD) Specification Detail (4 pages). Avail-
`able on-line: http:t'twwfigppnrgfflp’specs.-'html-info.-'25 101 .hLm.
`Feb. 21. 2012.
`Ericsson. 3 OPP TSG-RAN Meeting #51. RP-l 10416. Kansas City.
`Missouri. USA Mar. 15-18. 201 I. “Non-contiguous 4C-HSDPA
`Operation. Core-Part. 4C Performance Part" ( 13 pages).
`Nokia Corporation. 3GPP TSG~RAN Meeting #52. RP~| 10732.
`Bratislava. Slovakia, May 3 1. Jun. 3. 2011.“LTE Carrier Aggregation
`Enhancements. Core—Part. Performance” ( 17 pages).
`Ericsson. 3GP? TSG—RAN Meeting. #60. Tdoe R4—] 14401. Athens1
`Greece. Aug. 22. 26. 2011. “Feedback on non contiguous carrier
`aggregation feasibility." (2 pages).
`Renesas Electronics Europe. 3GPP TSG-RAN WG4 Meeting #58.
`RF-l | 1965. Shanghai. China. Apr. 10-15. 201 l. “Considerations on
`RSTD measures and carrier aggregation.“ (9 pages).
`El‘icsson. 3GPP 'l'SG-RAN WG4 Meeting #61. R4-115583. San
`Francisco. California. Nov. 14-18. 201 1."Seenarios fornon-contimt-
`ous inlra-band CA.” (7 pages).
`Non-Final Office Action dated Feb. 28. 2013 issued in a related US.
`App]. No. 131677.776 (12 pages).
`UKJPO Combined Search and Examination Report under Sections
`17 and [8(3) dated Mar. 15. 2012 issued in a related British Appli-
`cation No. (3131 | 19887.6 (5 pages).
`
`UKIPO Combined Search and Examination Repon under Sections
`17 and [813) dated Mar. 19. 2012 issued in a related British Appli-
`cation No. GB1119888.4(5 pages).
`UKlPO Combined Search and Examination Report under Section 17
`and 18(3) dated Dec. '1. 2012 issued in a related British Application
`No. GBI2196263‘ (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-"1820121056441 (15 pages).
`Pietro Andreani. e1 31.. “A CMOS gm «1‘. Polyphase Filter with High
`Image Band Rejection." Solid—State Circuits Conference. 2000. Pro~
`eeedings of
`the 26 Round European.
`IFEE. pp.
`272—275.
`XPO31952366 (4 pages).
`Nokia et al.. 301’? ’l‘SG-RAN W04 Meeting 2010 AHM.
`R4-1036'f'1'. 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. 634433? XP03145748? ('4
`pages}
`PCT Notification ofTransmittaI of the [nternational 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-"IB20 121056440 (15 pages).
`
`* cited by examiner
`
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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 3? (II-‘R 1.55 to UK Patent Application 1 I 19888.4, filed
`on Nov. 1?. 2011.
`
`TECHNICAL FIELD
`
`10
`
`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.
`
`ISAC KG ROU N I)
`
`long Term I-ivolution UTE) Advanced is a mobile tele-
`commiutication standard proposed by the 3"" Generation
`Partnership Project (3GPP) 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
`'felcconnnuification Union Radiocommunication
`
`[lTU-R) Sector. while maintaining compatibility with legacy
`mobile communication equipment. [.TE Advanced proposes
`the aggregation ofmultiplc 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. whereafier the message
`data from each of the signals can be combined in order to
`reconstruct the original data. CarricrAggregation 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~
`quency carrier 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 improve the ease with which individual
`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 corn-
`prises aggregation ofcarrier signals that occupy non-contigu-
`ous radio frequency carrier 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 by a frequency region which is
`not available to the operator of the network comprising the
`carrier signals, and may be allocated to another operator. This
`situation is potentially problematic for the reception of the
`carrier signals, since there may be signals in the frequency
`region that separates the non—contiguous carriers which are at
`a higher power level than the wanted carrier signals.
`A Direct Conversion Receiver
`(DCR)
`is
`typically
`employed to receive cellular radio signals, and typically pro-
`vides an economical and power efficient implementation of a
`receiver. A DCR uses a local oscillator placed within the radio
`frequency bandwidth occupied by the 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 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
`
`3o
`
`40
`
`45
`
`50
`
`55
`
`60
`
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`
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`
`ofthe local oscillator in quadrature (i.e. 90 degrees out of
`phase with one another) to produce inpha se (I) and quadrature
`(Q) signal components at baseband. The l 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 may be filtered in the
`digital domain to 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 DC R is to be used to receive a band of frequencies
`comprising non-contiguous Carrier Aggregation signals. In
`particular. since the higher power signal 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 (AD) in
`particular. Furthermore. due
`to
`inevitable imbalances
`between the amplitudes and phases of the I and Q cllaiuiels.
`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 tenned the Image Reject Ratio (IRR). If the higher
`power signal is a high side signal. it may cause interference to
`received low side signals due to the finite HR, and similarly if
`the higher power signal 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 DCR receiver
`stages. each having a local oscillator tuned to receive a cluster
`of contiguous carriers, and so rejecting signals in the fre-
`quency region between the clusters before digitisation. How-
`ever. this approach is potentially expensive and power con—
`suming. and may suffer from interference between the closely
`spaced local oscillators.
`It is an object of the 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 of receiving
`data transmitted via a combination of at least a plurality of
`radio frequency signals using carrier aggregation. each radio
`frequency signal 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 by a first
`frequency region, the first of the two groups occupying a
`wider frequency region than the second group, the method
`comprising:
`downconverting said plurality of radio frequency signals
`using quadrature mixing to give inphase and quadrature com-
`ponents:
`filtering said inphase and quadrature components using a
`first bandpass filter bandwidth to 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 embodiment of the
`present invention, there is provided a receiver for receiving
`data transmitted via a combination of at least a plurality of
`radio frequency signals. each radio frequency signal occupy-
`
`
`
`3
`
`4
`
`US 8,442,473 B]
`
`ing a respective band ofa plurality of radio frequency bands,
`the plurality of radio frequency 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. 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 to filter said
`inphase and quadrature components using a second bandpass
`filter bandwidth. different from the first bandpass filter band-
`width. to give second bandpass filtered inphase and quadra-
`ture components.
`In accordance with a third exemplary embodiment of the
`present invention. there is provided a reconfigurable receiver
`capable ofreceiving data transmitted via a combination ofat
`least a plurality ofradio frequency signals using carrier aggre—
`gation. each radio frequency signal occupying a respective
`band of 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 by a first
`frequency region, the first of the two groups occupying a
`wider frequency region titan 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 one first filter arranged to be configured. in the first
`mode. to filter said inphase and quadrature components using
`a first bandpass filter bandwidth to give first bandpass filtered
`inphase and quadrature components and. in the second mode
`to filter said inphase and quadrature components using a first
`lowpass filter bandwidth to give first 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 bandpass filter 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
`apparent from the following description of preferred 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 showing carriers in
`a non‘contiguous carrier aggregation method and a carrier
`from another operator received at a higher level;
`FIG. 3 is a schematic diagram showing a conventional
`direct conversion receiver;
`
`FIG. 4 is a diagram illustrating an effect ofa 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;
`
`10
`
`3t]
`
`4t]
`
`45
`
`50
`
`55
`
`60
`
`65
`
`FIG. '7 is a diagram illustrating problems with reception of
`non-contiguous aggregated carriers in a direct conversion
`receiver:
`
`FIG. 8 is an amplitude-irequency diagram illustrating
`reception of non-contiguous aggregated carriers in a direct
`conversion receiver in an embodiment of the invention;
`FIG. 9 is an amplitude-frequency diagram illustrating
`reception of non-contiguous aggregated carriers in an
`receiver having different passband filters for the high side and
`low side signals in an embodiment of the invention:
`FIG. 10 is a schematic diagram showing a receiver having
`two zero IF branches each having difl'erent bandpass filters in
`an embodiment of the invention;
`FIG. 11 is a schematic diagram showing an alternative
`receiver having two zero 11" branches each having different
`bandpass filters in an embodiment of the invention:
`FIG. 12 is a diagram illustrating a conventional direct
`conversion receiver as implemented in an RF I(..‘:
`FIG. 13 is a frequency-amplitude diagram illustrating
`problems with reception of non—contiguous aggregated carri—
`ers in a direct conversion receiver. showing image frequencies
`at the equivalent pesition in RF frequency;
`FIG. 14 is a frequency-amplitude diagram illustrating a
`conventional solution for the reception of non-contiguous
`aggregated can-lets, 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
`RF I(? and a different local oscillator frequency:
`FIG. 16 is a schematic diagram illustrating an RF lC imple-
`mentation for the reception of non-contiguous aggregated
`carriers. by the use of two rmeivers. each having a different
`local oscillator frequency on a single RFIC;
`F IG. 17 is an amplitude-frequency diagram illustrating
`reception of noncontiguous aggregated carriers. with a
`single signal from another operator between the wanted car-
`rier signals in an embodiment of the 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 elfect ofimage frequencies in an embodi—
`ment of 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 ofi mage frequencies in an embodi -
`ment of the invention:
`FIG. 20 is an amplitude—irequency 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-
`ment ofthe 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 embodiment of the 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
`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 complex filters and a digital data
`path;
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`FIG. 23 (lower part) is schematic diagram showing a
`receiver architecture having real filters 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 branches sharing the same I and Q mixers.
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`DIETAIIJ 3]) DESCRIPTION
`
`By way of example an embodiment of the invention will
`now be described in the context ol’a wireless communications
`system supporting communication using E-UTRA radio
`access technology, as associated with E~UTRAN radio access
`networks in LTE systems. However. it will be understood that
`this is by way of example only and that other embodiments
`may involve wireless networks using other radio access tech«
`nologies. such as UTRAN. GERAN or IEEE802.16 WiMax
`systems.
`FIG. 1 shows the transmission of radio frequency signal
`signals Illa. 105 and 106 by the radio access network to a
`receiver 8. The radio frequency signals each occupy a respec-
`tive carrier sigal band. as shown in the amplitude-frequency
`diagram ofFIG. 2. A carrier signal band is the part ofthe radio
`freqttency spectrum occupied by a modulated radio fre-
`quency carrier comprising the radio frequency signal. Radio
`frequency signals 10a. 10b. and 100 occupy radio frequency
`bands 14:). 14b and 14c as shown in FIG. 2. Data is received
`using the combination ofthe radio frequency signals 100. 10!;
`and 106. and the bands 14a, 14b and 14c shown in FIG. 2
`rep resent a set ofradio frequency signals, that may be referred
`to as component carriers, transmitted using Carrier Aggrega-
`tion. It can be seen from FIG. 2 that non-contiguous Carrier
`Aggregation is used. since a radio frequency signal from
`another operator, other than the operator sending the data, is
`present in a frequency region separating bzmds 14b and 140.
`In FIG. I. the radio frequency signals are sent from a first base
`station 4. operated by Operator A. A second base station 6,
`operated by a different operator. Operator B. is situated within
`the area of coverage 2 of the first base station 4. and transmits
`a radio frequency signal 12 that is received by the user equip-
`ment 8. It can be seen that the second base station is closer to
`
`the user equipment 8 than is the first base station. As a result.
`it can be seen from FIG. 2 that the radio frequency signal is
`received at the user equipment 8 at a significantly higher
`power level. as shown by the amplitude of the band 16 trans—
`mitted by operator [3.
`FIG. 3 is a schematic diagram showing a conventional
`direct conversion receiver. A signal is received by an antenna
`100. and filtered by a front end filter 102. which removes out
`of band signals. protecting the Low Noise Amplifier (LNA)
`104 from saturation by strong out of band signals. A local
`Oscillator 106 is typically set to a frequency in the centre ofa
`desired radio frequency (RF) band. RI" signals that are both
`higher than (high side) and lower than (low side) the local
`oscillator frequency are mixed with the local oscillator to
`downconvert the RF signals to baseband frequencies. which
`are the difference between the RF and local oscillator fre-
`
`quencies. These ditTerence frequencies. for signals within an
`intended receive band. are arranged to fall within the pass-
`band of the low pass filters 114. 116 of the direct conversion
`receiver. In order to distinguish between RF signals that origi—
`nated on the high side of the local oscillator amd RI" signals
`that originated on the high side of the local oscillator, it is
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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 (I) and quadrature
`(Q) signal components at baseband. As shown in FIG. 3. the
`local oscillator is split into 0 and —90 degree components in a
`splitter 108 and each component is mixed with the incoming
`RF signal 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 (AID) 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 and low side signals may be filtered in the digital domain
`to separate carrier signals received within the receiver band-
`width of the DCR. However. as already mentioned, due to
`imbalances between the amplitudes and phases ofthe I and Q
`channels. the process ofreconstructing the separate high side
`and low side signals suffers from a limited degree ofcancel-
`lation of the image component. so that 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 (IRR).
`FIG. 4 shows the effect ofa finite image rejection ratio in a
`direct conversion receiver. in the case where two bands 202.
`204 are received at approximately the same power level at
`radio frequency. As can be seen. the two bands are mixed with
`a local oscillator 206 and downconverted to a band encom-
`passing zero frequency, which may be referred to as DC
`(Direct Current). In FIG. 4, the high side signal 204 is shown
`as being downconverted to positive frequency 21!}, and the
`low side signal 202 is shown as being downconverted to a
`negative frequency 208. This is a matter of convention. and
`the designation of positive and negative frequencies may be
`transposed. The concept of positive and negative frequencies
`has meaning only within the complex signal domain. in which
`signals are represented by I and Q components. A negative
`frequency has a phasor defined by its l and Q components that
`rotates in the opposite direction to the phasor of a positive
`frequency. By distinguishing between positive and negative
`frequencies by signal processing, for example using a Fast
`Fourier Transform (FFT) or a complex digital mixer, signals
`originating as high side RF signals may be separately
`received from signals originating as low side RF signals. So,
`as shown in FIG. 4. data may be extracted from two received
`carrier signal bands. provided that the signal to noise ratio
`(SNR) is not degraded unacceptably by the image component
`2 14 of the high side signal 204 that is in the same band 208 as
`the downconverted low side signal 202. and the image com-
`ponent 212 of the low side signal 202 that is in the same band
`210 as the downconverted high side signal 204. For signals
`received at approximately the same power level, SNR is not
`usually degraded unacceptably by the finite image reject
`ratio.
`
`FIG. 5 is a diagram illustrating reception of non-contigu-
`ous aggregated carriers. In this cxatnple. wanted component
`signal bands 302 and 302 are separated by a higher power
`radio frequency signal 318. which may originate front
`another operator. As can be seen from FIG. 5, a local oscillator
`306 may be placed in the middle ofa receive band defined by
`the three component signal bands 302. 304. 318. As can be
`seen from FIG. 5, images ofthe higher power radio frequency
`signal resulting from the finite image reject ratio do not fall on
`top of the downconverted weaker signals in this case. but fall
`within the downconverted components 320 of the higher
`power radio frequency signal.
`FIG. 6 is a schematic diagram showing a conventional low
`IF receiver that may be used to receive the signals illustrated
`in FIG. 5. It can be seen that the low IF receiver differs from
`a conventional DCR receiver in that the low pass filters of a
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`quency on the low frequency side, it may be determined that
`the local oscillator olfset should be set at a position that
`causes the least total interference with the wanted signals.
`This may be determined on the basis of signal to noise plus
`interference ratio measurements for each of the wanted sig-
`nals.
`FIG. 9 shows that that setting ofthe local oscillator may be
`used in conjunction with a receiver having two bandpass filter
`characteristics 540, 538 one of which 538 is wider titan 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 bandpass filtercharacteristics as illustrated in FIG. 9 in an
`embodiment ofthe invention. The receiver has two branches.
`
`A first branch is a low IF receiver having I and Q channels,
`each of which has a bandpass filters 814. 816 with a first
`bandwidth. A second branch is also configured as a low IF
`receiver as shown in FIG. 10, and also has I and Q channels.
`each of which has a bandpass filters 814, 816 with a second
`bandwidth, different from the first bandwidth. A first subset of
`downconverted radio signals may be received using the first
`branch. and a second subset of downconverted radio signals
`may be received using the second branch.
`FIG. 11 is a schematic diagram showing an alternative
`receiver having two branches each having different bandpass
`filters in an embodiment ofthe invention. in which a single set
`ofquadraturc mixers is shared between the two branches.
`[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
`come about, for example, if an operator buys another opera-
`tor’s businesses. If the spectrums happen to be non-adjacent
`then the allocation is non-contiguous. Operators typically
`wish to exploit their spectrum as effectively as possible, so the
`need for non-contiguous multi-carrier systems is increasing.
`An example of such scenario is presented in FIG. 2. In a
`scenario such as that illustrated in FIG. 2. there may be a
`problem with single receiver chain architecture in that it may
`not be known or guaranteed a priori what is allocated in the
`gap between the two non-contiguous carriers.
`'I‘ypically,
`another operator’s licensed spectrum may be present in the
`gap. Furthermore.
`it cannot be guaranteed that the other
`operator‘s signal. that is to say deployed spectrum. is not
`si