(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2001/0014592 A1
`(43) Pub. Date:
`Aug. 16, 2001
`HELMS
`
`US 2001 OO14592A1
`
`(54) TRANSMITTER
`
`Publication Classification
`
`(51) Int. Cl." ....................................................... H04B 1/02
`(52) U.S. Cl. ............................ 455/91; 455/126; 455/561;
`375/296
`
`(57)
`
`ABSTRACT
`
`A transmitter for a plurality of carriers of a broad-band
`transmitting spectrum which contains a broad-band power
`amplifier encompassing the carriers for amplifying an input
`Signal into a more powerful output Signal, wherein a mea
`Suring Signal is formed from the output Signal with the aid
`of a decoupler. The transmitter further contains an adapta
`tion unit for comparing the input signals to the measuring
`Signals and for thereafter forming a correction signal. A
`predistortion of the input signal is performed in a predistor
`tion unit in the transmitter corresponding to the Setpoint
`Selections of the correction Signal.
`
`PoweR
`AMPL FR
`
`DeCouple(R
`
`Out
`
`(76) Inventor: JOCHEN HELMS, MUENCHEN
`(DE)
`Correspondence Address:
`William E. Vaughan
`Bell, Boyd & Lloyd LLC
`P.O. BOX 1135
`Chicago, IL 60690-1135 (US)
`
`(*)
`
`Notice:
`
`This is a publication of a continued pros
`ecution application (CPA) filed under 37
`CFR 1.53(d).
`(21) Appl. No.:
`09/112,269
`(22) Filed:
`Jul. 8, 1998
`
`(30)
`
`Foreign Application Priority Data
`
`Jul. 8, 1997 (DE)........................................ 1972918.2.1
`
`
`
`PRE).57orTon
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`MN
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`PETITIONERS EXHIBIT 1024
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`Patent Application Publication Aug. 16, 2001 Sheet 1 of 2
`Fig. 1
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`US 2001/0014592 A1
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`Patent Application Publication Aug. 16, 2001 Sheet 2 of 2
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`US 2001/0014592 A1
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`Fig. 3
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`US 2001/OO14592 A1
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`Aug. 16, 2001
`
`TRANSMITTER
`
`BACKGROUND OF THE INVENTION
`0001) 1. Field of the Invention
`0002 The present invention relates to a transmitter for a
`plurality of carriers of a broadband transmission spectrum.
`0003 2. Description of the Prior Art
`0004 Transmitters of the afore-mentioned type are pref
`erably utilized in radio stations within mobile radio net
`works in which a transmission of information to further
`radio Stations occurs in a plurality of carriers with the aid of
`radio-frequency Signals. These radio Stations are base Sta
`tions which are Stationary and which carry out information
`transmission to mobile Stations, for example. In a transmit
`ter, input Signals are amplified into more powerful output
`Signals and are converted into a corresponding transmitting
`frequency.
`0005 If a broad-band transmitting spectrum with a plu
`rality of carriers is amplified, linearity problems of ampli
`fication arise. In order to keep the power efficiency of the
`power amplifier within the transmitter high, the latter is
`usually operated in AB, B or C mode. However, these modes
`are distinguished by highly non-linear behavior which
`results in a poor intermodulation Suppression. Without Suit
`able linearizing processes, Such power amplifiers in trans
`mitters with a plurality of carriers are not Suitable when a
`minimal intermodulation Suppression is required.
`0006. It is generally known to amplify each carrier indi
`vidually and, thus, to maintain the linearity. The transmitter
`is then not broad-band, however, and must be correspond
`ingly frequently made available in the radio Station. In the
`carrier-specific amplification, a merging of the carriers
`occurs at the amplifier output by means of hybrids, filters or
`antennas. The individual amplification branches are shielded
`from each other by insulators. Harmonic distortions are
`Suppressed by transmitting filters.
`0007 K. J. Parson, P. B. Kenington, “The efficiency of a
`feed-forward amplifier with delay loss”, IEEE Trans. on
`Vehicular Techn., Vol.43, May 1994, pages 407-412 teaches
`to perform the linearizing of a broad-band transmitting
`spectrum for a plurality of carriers with the aid of a “feed
`forward' method. A loop of a main amplifier and an error
`amplifier is therein constructed. The error amplifier ampli
`fies only the intermodulation distortions of the main ampli
`fier, wherein Such distortions are Subsequently Subtracted
`from the output Signal of the main amplifier. The disadvan
`tages of this method are a) the necessary analog tuning
`precision in rate and phase at the Summation points, and b)
`a lower power efficiency resulting from the utilization of two
`amplifiers, from the loSS of couplers and from the loss of
`delay units. At the moment, however, this method only
`approximately achieves the intermodulation Suppressions
`required by the GSM (Global System for Mobile Commu
`nication) mobile radio System in a double loop execution.
`
`SUMMARY OF THE INVENTION
`0008. It is consequently an object of the present invention
`to propose a transmitter for a plurality of carriers of a
`broad-band transmitting spectrum which has a higher power
`efficiency. Accordingly, the transmitter of the present inven
`
`tion contains a broad-band power amplifier encompassing
`the carriers for amplifying an input signal into a more
`powerful output signal. AS Such, a measuring Signal is
`formed from the output Signal with the aid of a decoupler.
`The transmitter further contains an adaptation unit for com
`paring input signals and measuring Signals as well as for
`forming a correction signal. In a predistortion unit which
`likewise belongs to the transmitter, a predistortion of the
`input Signal is performed which corresponds to the Setpoint
`Selections of the correction Signal.
`0009 Through this linearizing of the multicarrier trans
`mitter with the aid of adaptive predistortion, the input Signal
`is predistorted to compensate for the nonlinearity of the
`Subsequent power amplifier and other units. In a broad-band
`transmitting spectrum with a plurality of carriers, inter
`modulation products arise in the modulation which can be
`Suppressed through adaptive predistortion. Additional losses
`are low and the power efficiency of the transmitter is greater
`than in a carrier-related amplification.
`0010 Unlike in modulation methods with constant enve
`lope, such as the GMSK modulation for GSM mobile radio
`networks which do not require a linear amplifier for the input
`amplification, these intermodulation products represent an
`additional problem for the transmitter in a transmitting
`Spectrum with a plurality of carriers. This problem can be
`Solved by the present invention in an economical fashion.
`0011. According to another embodiment of the present
`invention, the predistortion unit consists of carrier-related
`predistortion units which act on input signals of the indi
`vidual carriers that are Subsequently merged into the input
`Signal. Each carrier can thus be individually predistorted,
`resulting in a high degree of predistortion flexibility.
`0012. These carrier-related predistortion units are advan
`tageously constructed for digital Signal processing So that
`digitized carrier-related input Signals can be processed.
`Further analog Switching elements for predistortion are thus
`no longer needed and the correction Signal or Signals can be
`calculated easily.
`0013. According to a further embodiment of the present
`invention, the carrier-related predistortion units act on an
`in-phase component and a quadrature component of digi
`tized carrier-related input Signals. The transmitter therein
`additionally includes a digital upward conversion unit which
`converts the predistorted carrier-related input Signals into an
`intermediate frequency prior to the merging into the input
`Signal. The predistortion can thus take place in the base band
`and does not require any radio frequency components.
`0014.
`It is also advantageous to digitize the measuring
`Signal with an analog/digital converter and to feed it to the
`adaptation unit. The adaptation unit thus also can be con
`figured as a digital Signal processor. Corresponding to the
`upward conversion unit, a downward conversion unit advan
`tageously can be provided which converts the digitized
`measuring Signal into the base band for further processing in
`the adaptation unit.
`0015 The digital signal processing in the adaptation unit
`is further simplified if the measuring Signal is also converted
`into carrier-related digital measuring Signals corresponding
`to the carrier-related input signals, for example, through a
`digital downward conversion unit which is constructed in a
`carrier-related fashion. Through Such a configuration of the
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`US 2001/OO14592 A1
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`Aug. 16, 2001
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`inventive transmitter, a complete digital processing and
`predistortion is possible. This configuration also has the
`advantage that, in addition to the nonlinearity of the power
`amplifier, the nonlinearity of a few components can be
`modulated and equalized with the aid of the predistortion
`unit. The error of the feedback branch with the measuring
`Signal should be known, however.
`0016. According to a further embodiment of the present
`invention, the transmitting unit contains a storage unit for
`Storing the correction signal which is defined by the adap
`tation unit and which is utilized for a Subsequent input
`Signal. A radio transmission often occurs in radio blocks; for
`example, in TDMA (Time Division Multiple Access) access
`methods. Following the evaluation of a radio block and the
`defined nonlinearities, the correction Signal is applied to the
`Subsequent input signal; i.e., Subsequent Symbols or the
`Subsequent radio block. A constant follow-up of the predis
`tortion is thus possible.
`0.017. A storage unit can also be used for storing certain
`intermodulation products of frequencies present in the trans
`mitter. Since all frequencies present in the System (carrier
`frequencies and cycles) are known (in contrast to broad
`band receivers), the position and order of the arising inter
`modulation distortions can be calculated in advance. The
`predistortion can then be concentrated on these predictable
`intermodulation distortions. Defined intermodulation prod
`ucts can Serve the adaptation unit as adaptation criteria for
`the predistortion.
`0018 Through the transmitter portrayed, a higher power
`efficiency is achieved and, through the extensive digitizing,
`the outlay for equalization of the analog circuit is relatively
`low. The essential nonlinearities of the transmission path are
`Summarily compensated. A Splitting and thus an intensifying
`of the total demand with respect to the intermodulation
`Suppression is not necessary. The higher outlay in the digital
`Signal processing and Storage carries leSS importance due to
`the expected technological progreSS and the price decrease
`for these technologies.
`0.019
`Additional features and advantages of the present
`invention are described in, and will be apparent from, the
`Detailed Description of the Preferred Embodiments and the
`Drawings.
`
`DESCRIPTION OF THE DRAWINGS
`0020 FIG. 1 shows a block wiring diagram of the radio
`transmission between a base Station and mobile Stations.
`0021
`FIG. 2 shows a schematic representation of the
`Splitting of the broad-band spectrum.
`0022 FIG. 3 shows a block wiring diagram of a trans
`mitter.
`0023 FIG. 4 shows a detailed block wiring diagram of a
`transmitter.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`0024 FIG. 1 shows the information transmission from a
`transmitting base station BTS to mobile stations MS. The
`base Station BTS contains a transmitter which creates a
`broad-band transmission Signal. The broad-band transmis
`sion signal includes a spectrum B, for example B=1.6 MHZ,
`
`in which a plurality of carriers 1,2,..., n=8 (see FIG. 2)
`are simultaneously contained. Two mobile stations MS can
`thus be served on different carriers Simultaneously, for
`example.
`0025 FIG. 3 shows a block wiring diagram of the
`transmitter which contains a predistortion unit PD, a power
`amplifier PA, a decoupler AK and an adaptation unit AE. An
`input signal in is fed to the predistortion unit PD and to the
`adaptation unit AE. The predistortion unit PD performs a
`predistortion of the input signal in whereby setpoint Selec
`tions of a correction Signal c created by the adaptation unit
`AE are followed. The predistorted input signal is amplified
`in the power amplifier PA, whereby the distortion of the
`power amplifier PA is anticipated by the predistortion and
`equalized
`through
`corresponding
`corrections.
`L.
`Sundströzouml;m et al., “Quantization analysis and design of
`a digital predistortion linearizer for RF power amplifiers,”
`IEEE Trans. on Vehicular Technol, Vol. 45, November
`1996, pp. 707-719 teaches methods for digital correction,
`but only for a carrier frequency and without consideration of
`intermodulation disturbances.
`0026. At the output of the power amplifier PA lies an
`output signal out. From the output signal out, a measuring
`signal outm is created with the aid of the decoupler AK. The
`decoupler AK is configured as a directional coupler; for
`example, as one which decouples a Small part of the trans
`mission power.
`0027. In addition to the input signal in, the measuring
`Signal outm is evaluated in the adaptation unit AE. A
`comparison of the input Signal in with the measuring Signal
`outm is performed in the adaptation unit, the distortions are
`amplified through the power amplifier PA and the other
`components are derived therefrom. For equalization of these
`distortions, a correction Signal c is formed which is evalu
`ated by the predistortion unit PD and which sets the latter's
`predistortion.
`0028 FIG. 4 shows the transmitter in greater detail
`wherein the input signal of the transmitter consists of
`carrier-related input Signals in1, in2, .
`.
`. , inn. These
`carrier-related input signals in1 to inn are digitized. Conse
`quently, they consist of an in-phase component I and a
`quadrature component Q. The carrier-related input signals
`in1 to inn are therein allocated to the carriers 1 to n
`according to FIG. 2.
`0029. The predistortion unit PD is also constructed in a
`carrier-related fashion in carrier-related predistortion units
`PD1, PD2, ..., PDn, which process the input signals in1 to
`inn. The predistortion of the input signals in1 to inn are Set
`corresponding to the setpoint Selections of a storage unit
`LUT
`0030) Such a storage unit LUT is allocated to every
`carrier-related predistortion unit PD1, PD2, . .
`. , Pdn.
`Alternatively, it is also possible to provide a central Storage
`unit LUT. The values of the carrier-specific correction
`Signals c are Stored in the Storage unit LUT. The predistor
`tion into predistorted input signals in1, in2, . . . , inn,
`occurs according to the Setpoint Selections of the correction
`Signals c. These are further digitized signals which are
`Subsequently fed to carrier-related, digital upward conver
`Sion units DUC.
`0031. These digital upward conversion units DUC per
`form a shift to a digital intermediate frequency IF. The
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`US 2001/OO14592 A1
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`Aug. 16, 2001
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`digital data currents of the intermediate frequency IF are
`Subsequently added up to the predistorted input signal in in
`the Summation unit SUM. A Subsequent digital/analog con
`verter DAC converts the signal of the intermediate fre
`quency IF into an analog signal which is Subsequently
`modulated in an upward mixer UM and converted into the
`transmitting frequency. Upstream and downstream relative
`to the upward mixer UM, band filters (not shown) are used
`to limit the corresponding frequency band. This signal is
`Subsequently fed to the power amplifier PA which performs
`a power amplification and emits the output Signal out.
`0032. As already explained, the decoupler AK performs
`a decoupling of a measuring Signal outm from the output
`Signal out, whereby the measuring Signal outm is fed to a
`downward mixer DM which, corresponding to the upward
`converter UM, initially converts the measuring Signal outm
`into the intermediate frequency and then bandfilters the
`Signal. Band filters are advantageously utilized upstream and
`downstream relative to the downward converter. There is
`also an analog/digital conversion in an analog/digital con
`verter ADC.
`0033. The measuring signal outm is subsequently pro
`cessed by downward conversion units DDC1, DDC2, ...,
`DDCn. These downward conversion units DDC1,
`DDC2, . . . , DDCn convert Suitable intermodulation prod
`ucts, or carriers, into complex base band and make available
`carrier-related, or intermodulation-related, measuring Sig
`nals outm1 to outmn of the adaptation unit AE. Using a
`comparison of the input Signals in1 to inn and the measuring
`Signal outm1 to outmn, the adaptation unit AE calculates
`correction signals which are emitted as correction data c to
`the storage unit LUT. The correction data defined in the
`evaluation of processed Symbols of a radio block are Sub
`Sequently used in the amplification of Subsequent Symbols
`for predistortion. The correction data care optimally current
`therein.
`0034). If the bandwidth of the available components is not
`sufficient to cover the desired total bandwidth (e.g., E-GSM:
`35 MHZ), the total band is divided into partial bands. The
`block wiring diagram according to FIG. 4 then applies per
`partial band.
`0.035 Amplitude offset errors and DC offset errors are
`avoided through the utilization of digital upward and down
`ward mixers UM, DM, respectively. The adaptation is thus
`not corrupted by these errors. A very good linearity can be
`reached despite a high power efficiency through the Sum
`mary modeling of the non-linearities in the transmission
`path not only of the power amplifier PA, but also of the
`remaining components DUC, SUM, DAC and UM. Adap
`tation criteria for the predistortion are available due to the
`selection of suitable intermodulation products IP which are
`taken into consideration by the adaptation unit AE. Since the
`frequencies used in the System are known, the intermodu
`lation products IP can be prescribed ahead of time.
`0.036 Although the present invention has been described
`with reference to specific embodiments, those of skill in the
`art will recognize that changes may be made thereto without
`departing from the Spirit and Scope of the invention as Set
`forth in the hereafter appended claims.
`I claim as my invention:
`1. A transmitter for a plurality of carriers of a broad-band
`transmitting spectrum, comprising:
`
`a broad-band power amplifier encompassing the plurality
`of carriers and amplifying an input Signal into a more
`powerful output signal;
`a decoupler for forming a measuring Signal from the
`output signal received from the power amplifier;
`an adaptation unit for comparing the input Signal to the
`measuring Signal and for thereafter forming a correc
`tion signal; and
`a predistortion unit for predistorting the input Signal
`corresponding to setpoint Selections of the correction
`Signal.
`2. A transmitter as claimed in claim 1, wherein:
`the predistortion unit further comprises carrier-related
`predistortion units which act on carrier-related input
`Signals that are Subsequently merged into the input
`Signal.
`3. A transmitter as claimed in claim 2, wherein:
`the carrier-related predistortion units perform a digital
`Signal processing of digitized carrier-related input Sig
`nals.
`4. A transmitter as claimed in claims 2, wherein:
`the carrier-related predistortion units act on in-phase and
`quadrature components of digitized carrier-related
`input Signals; and
`a digital upward conversion unit converts the predistorted
`carrier-related input signals into an intermediate fre
`quency prior to the carrier-related input signals being
`merged into the input signal.
`5. A transmitter as claimed in claim 1, further comprising:
`an analog/digital converter for digitizing the measuring
`Signal.
`6. A transmitter as claimed in claim 5, further comprising:
`a digital downward conversion unit for further processing
`the digitized measuring Signal in the adaptation unit.
`7. A transmitter as claimed in claim 6, wherein:
`the digital downward conversion unit is constructed in a
`carrier-related fashion to emit carrier-related digital
`measuring Signals.
`8. A transmitter as claimed in claim 1, further comprising:
`a storage unit for Storing the correction Signal defined by
`the adaptation unit wherein the correction Signal may
`be employed for a Subsequent input Signal.
`9. A transmitter as claimed in claim 1, further comprising:
`a Storage unit for Storing intermodulation products of
`frequencies present in the transmitter.
`10. A transmitter as claimed in claim 6, wherein:
`the digital downward conversion unit is constructed in a
`fashion related to intermodulation products to emit
`digital measuring Signals which are related to inter
`modulation products.
`11. A transmitter as claimed in claim 10, wherein:
`intermodulation products defined by the adaptation unit
`are utilized as adaptation criterion.
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`PETITIONERS EXHIBIT 1024
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