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WO1998005127A1 - Linearizing the transmitter of a mobile station - Google Patents

Linearizing the transmitter of a mobile station Download PDF

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Publication number
WO1998005127A1
WO1998005127A1 PCT/FI1997/000460 FI9700460W WO9805127A1 WO 1998005127 A1 WO1998005127 A1 WO 1998005127A1 FI 9700460 W FI9700460 W FI 9700460W WO 9805127 A1 WO9805127 A1 WO 9805127A1
Authority
WO
WIPO (PCT)
Prior art keywords
signal
branch
converting
converter
feedback
Prior art date
Application number
PCT/FI1997/000460
Other languages
French (fr)
Inventor
Mikko Huttunen
Original Assignee
Nokia Telecommunications Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nokia Telecommunications Oy filed Critical Nokia Telecommunications Oy
Priority to AU35447/97A priority Critical patent/AU3544797A/en
Publication of WO1998005127A1 publication Critical patent/WO1998005127A1/en

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/32—Modifications of amplifiers to reduce non-linear distortion
    • H03F1/3241—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits
    • H03F1/3247—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits using feedback acting on predistortion circuits
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/24—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/02—Transmitters
    • H04B1/04—Circuits
    • H04B2001/0408—Circuits with power amplifiers
    • H04B2001/0433—Circuits with power amplifiers with linearisation using feedback

Definitions

  • the invention relates to an arrangement for linearizing the transmitter in a mobile station comprising: a digital signal processor for processing signals, a receiving branch comprising one or more mixers for down- converting a received signal from a radio frequency to an intermediate frequency, one or more intermediate frequency filters responsive to said mixers for filtering said down-converted signal, an A/D converter responsive to said intermediate frequency filter for converting the received signal into digital form and for forwarding said signal converted into digital form into said digital signal processor, a transmitting branch comprising a D/A converter for converting a digital transmission signal into analog form, a modulator for modulating the signal into a radio frequency, a power amplifier for amplifying the transmission signal, a feedback branch comprising attenuating means for attenuating a feedback signal, down-converting means for down-converting an attenuated signal, filtering means for filtering the down-converted signal, whereby said arrangement comprises: first switching means for directing the signal of the feedback branch to the A/D converter of the receiving branch for linearizing the signal of the transmitting
  • TETRA Trans European Trunked RAdio
  • ⁇ /4-DQPSK ⁇ /4-shifted Differential Quadrature Phase Shift Keying
  • IM InterModulation
  • the PCT publication WO 92/08297 discloses an apparatus and method for linearizing the gain of a nonlinear power amplifier in a digital TDM transceiver.
  • the transfer function of the power amplifier describes a relationship between the input signal and the output signal of the power amplifier.
  • the output signal is selectively demodulated with existing receiver elements, during the transmit timeslot of a TDMA time frame.
  • An inverse transfer function is determined from the nominal gain of the power amplifier and the actual transfer function.
  • a correction value, corresponding to the transfer function and its inverse, is determined in a vector table.
  • the correction value is multiplied with the input signal resulting in an adjusted input signal.
  • the amplified adjusted input signal produces a varied output signal that is linear relative to the input signal.
  • a trunked PMR system in which different user groups share same radio channels, has strict requirements regarding adjacent channel interference caused by a transmitter.
  • adjacent channel interference caused by a transmitter.
  • the adjacent channel attenuation is required to be -70dBc.
  • the invention is applicable for use in radio telephone systems with a digital radio path.
  • a digital radio telephone system is described in the ETSI standard ETS 300 392-2: March 1996, Radio Equipment and Systems (RES); Trans-European Trunked RAdio (TETRA); Voice plus Data (V+D); Part 2: Air Interface (Al), ETSI, 583 p.
  • Page 46 of this TETRA standard sets forth an attenuation requirement of -60 dBc, which requires good linearity of the transmitter according to the TETRA standard, in addition, this requirement is considerably stricter than the approximately -25 dB required in the D-AMPS (Digital Advanced Mobile Phone Service) and JDC (Japanese Digital Cellular) systems.
  • nonlinearities of an amplifier were known in advance, it would be possible to form inverse functions of the nonlinearities, and use them to convert the input signal, whereby the nonlinearities wound be cancelled.
  • the properties of the amplifier do not, however, remain the same but vary due to aging, warming up, and according to the radio channel and transmit power used.
  • the amplifiers have individual differences. Need exists for linearization methods that must in an adaptive way be capable of adapting to changing conditions. Development work has been targeted into a number of different linearizing methods, and three of them have been found to possess qualities suitable for practical radio systems. These methods are feedforward, cartesian feedback and a predistorter.
  • FIG. 1 shows a block diagram of the prior art transmitting and feedback branches.
  • the signal to be transmitted is radio frequency modulated in an RF modulator 102, after which it is amplified in a power amplifier 110, from which the signal is applied further to an antenna 103 for transmission.
  • the signal applied to the antenna 103 is at the same time fed to a feedback branch 104 which is employed when linearizing the transmitter of a mobile station.
  • the feedback branch supplies the signal to a down-conversion and filtering unit 106 where the feedback signal is down-converted and filtered as desired. Following the down-conversion and filtering 106, the down-converted and filtered signal is fed to the A/D converter of the feedback branch, in which the signal is converted to a form suitable for a digital signal processor 108.
  • the digital signal processor 108 processes the feedback signal in a desired, prior art, way.
  • the feedback signal processed in the digital signal processor 108 influences the linearization of the entire transmitter so that the transmission from the transmitter may be kept linear more easily.
  • the processed signal and other signals to be transmitted are applied from the digital signal processor 108 to a D/A converter 109 where they are converted into continuous analog signals which are processed by the RF modulator 102. From the RF modulator onward, the apparatus operates as described above.
  • FIG. 2 is a block diagram illustration of the prior art receiving branch RX.
  • the received signal is first intermediate frequency filtered in a intermediate frequency filter 201 , from which the filtered signal is applied to an
  • A/D converter 202 after which the signal is applied to a digital signal processor which converts the received signal into a form acceptable to the mobile station and its user.
  • the present invention relates to linearizing the transmitter of a mobile station by means of feedback, in particular.
  • This new type of an arrangement for linearizing the mobile station transmission in the mobile station is achieved with the arrangement according to the invention, which is characterized by comprising: second switching means for controlling the operating frequency of said A/D converter so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch or for A/D converting the feedback signal of the feedback branch and for applying the converted signal to said digital signal processor for linearizing the signal of the transmitting branch.
  • the invention further relates to a mobile station which comprises: a digital signal processor for processing signals, a receiving branch comprising one or more mixers for down- converting a received signal from a radio frequency to an intermediate frequency, one or more intermediate frequency filters responsive to said mixers for filtering said down-converted signal, an A/D converter responsive to said intermediate frequency filter for converting the received signal into digital form and for supplying said signal converted into digital form into said digital signal processor, a transmitting branch comprising a D/A converter for converting a digital transmission signal into analog form, a modulator for modulating the signal into a radio frequency, a power amplifier for amplifying the transmission signal, a feedback branch comprising attenuating means for attenuating a feedback signal, down-converting means for down-converting an attenuated signal, filtering means for filtering the down-converted signal, whereby said mobile station comprises: first switching means for supplying the signal of the feedback branch to the A/D converter of the receiving branch for linearizing the signal of the transmitting branch.
  • the mobile station according to the invention is characterized by further comprising: second switching means for controlling the operating frequency of said A/D converter so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch or for A/D converting the feedback signal of the feedback branch and for applying the converted signal to said digital signal processor for linearizing the signal of the transmitting branch.
  • the invention further relates to a method for linearizing a mobile station transmission in a mobile station comprising: a digital signal processor for processing signals, a receiving branch comprising one or more mixers for down- converting a received signal from a radio frequency to an intermediate frequency, one or more intermediate frequency filters responsive to said mixers for filtering said down-converted signal, an A/D converter responsive to said intermediate frequency filter for converting the received signal into digital form and for forwarding said signal converted into digital form into said digital signal processor, a transmitting branch comprising a D/A converter for converting a digital transmission signal into analog form, a modulator for modulating the signal into a radio frequency, a power amplifier for amplifying the transmission signal, a feedback branch comprising attenuating means for attenuating a feedback signal, down-converting means for down-converting the attenuated signal, filtering means for filtering the down-converted signal, whereby said method comprises the following steps: applying the signal of the feedback branch to the A/D converter of the receiving branch, converting the signal of
  • the method according to the invention is characterized by comprising the following steps: controlling the operating frequency of said A D converter so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch or for A/D converting the feedback signal of the feedback branch and for feeding the converted signal to said digital signal processor for linearizing the signal of the transmitting branch.
  • the invention relates to an arrangement, mobile station and method, in which the aim is to utilize the parts in the receiving branch of the transceiver in predistortion-based linearizing of the transmitter.
  • the invention relates to utilizing the A/D converter of the receiving branch in the feedback branch of the transceiver in the mobile station, and the necessary control functions by means of which it is possible to use flexibly the receiving branch A/D converter in converting the feedback branch signals into digital form.
  • the invention is based on the idea of using as efficiently as possible the existing parts of the handheld phone, thus reducing unnecessary duplication of the hardware.
  • Such an inventive solution provides the advantage that a separate
  • Analog to Digital (A/D) converter is not required for linearizing the transmitter.
  • the hardware of the mobile station becomes simpler. Further, it is possible to save both space, an important feature in handheld phones, and money.
  • the hardware of the mobile phone becomes simpler as the invention reduces the number of components needed in the phone, and consequently also its price. Further still, the designing of the mobile station will become considerably easier because there is no need for a new A/D converter interface to the digital signal processor.
  • Figure 1 shows a block diagram of the prior art transmitting and feedback branch
  • Figure 2 shows a block diagram of the prior art receiving branch
  • Figure 3 shows a block diagram of the mobile station according to the invention
  • FIG. 4 shows a block diagram according to the solution of the invention.
  • Figure 1 shows a block diagram of the prior art transmit and feedback branch. Figure 1 has been described in connection with describing the prior art.
  • FIG. 2 shows a block diagram of the prior art receiving branch.
  • Figure 2 has been described in connection with describing the prior art.
  • Figure 3 shows a block diagram of the mobile station according to the invention.
  • the network infrastructure comprises e.g. base stations, switching exchanges, databases DB, and other data equipments.
  • the figure shows a typical radio unit 500 communicating in the mobile communication system, such as a subscriber-operated mobile phone, a mobile station or a subscriber station.
  • the function of the transceiver unit (TX/RX) 501 is to match onto the radio channel employed on any one occasion, by means of which the mobile station communicates with the network infrastructure.
  • An antenna 502 is connected to the ⁇ transceiver 501 , the antenna having connection to the radio path RP.
  • radio frequencies between the range 60-1000 MHz VHF and UHF bands
  • other frequencies can also be used.
  • the user interface 505 comprises an electroacoustic transducing means, typically a loudspeaker 506 and a microphone 507, and possibly buttons relating to beginning, ending and dialling a call.
  • Mobile stations used in a trunked system may also contain a push to talk (PTT) button which must be kept pressed down for the duration of the speaking turn.
  • PTT push to talk
  • a controller 503 The purpose of a controller 503 is to control the operation of the radio unit.
  • the controller 503 is connected to the user interface 505, from which it obtains impulses relating to, for example, the call initiation and termination. Through the user interface 505, the controller 503 may also provide the user with voice/sound or visual symbols relating to the operation of the mobile phone or the mobile radio system.
  • the controller 503 is connected to the transceiver TX/RX 501.
  • the channel employed by the transceiver is determined by the controller 503, meaning that the transceiver 501 tunes onto a channel, i.e. radio frequency and an appropriate time slot, determined by the controller 503.
  • the transceiver 501 is also switched on controlled by the controller 503.
  • the controller 503 receives and transmits signalling messages by means of the transceiver 501.
  • the inventive mobile station, i.e. the radio unit 500 may be used for example in a radio system comprising a radio network with at least one base station and subscriber stations as well as possibly one or more repeater stations and databases DB.
  • said radio unit comprises a transceiver unit 501 for receiving transmissions from other radio units or base stations and for transmitting signals to said other radio units or base stations, a control unit 503 for controlling the functions of the radio unit, and a user interface 505.
  • the mobile station 500 further comprises a digital signal processor DSP for processing signals.
  • the signal processor may be placed in connection with the transceiver 501 Tx/Rx of the mobile station, but it may also be placed elsewhere in the mobile station 500.
  • the transceiver may also have other parts 510, for example a receiving branch, a transmitting branch, and a feedback branch. The operation and contents of these are described in closer detail with the description of Figure 4.
  • FIG. 4 is a block diagram illustration of the solution according to the invention.
  • the arrangement for linearizing the transmission of a mobile station, and correspondingly the mobile' station according to the invention comprise: a digital signal processor DSP, 313 for processing signals, a receiving branch RX which comprises one or more mixers 317 for down-converting the signal received at the antenna 305 from a radio frequency to an intermediate frequency, one or more intermediate frequency filters 318 responsive to said mixers for filtering said down-converted signal, an A/D converter 312 A/D responsive to said intermediate frequency filter for converting the received signal into digital form and for applying said signal converted into digital form to said digital signal processor 313 DSP.
  • DSP digital signal processor
  • RX which comprises one or more mixers 317 for down-converting the signal received at the antenna 305 from a radio frequency to an intermediate frequency, one or more intermediate frequency filters 318 responsive to said mixers for filtering said down-converted signal, an A/D converter 312 A/D responsive to said intermediate frequency filter for converting the received signal into digital form
  • the arrangement and the mobile station according to the invention further comprise a transmission branch TX comprising a D/A converter 315 D/A for converting the digital transmission signal into analog form, a modulator 303 for modulating the signal into a radio frequency, and a power amplifier 304 for amplifying the signal to be transmitted.
  • a transmission branch TX comprising a D/A converter 315 D/A for converting the digital transmission signal into analog form, a modulator 303 for modulating the signal into a radio frequency, and a power amplifier 304 for amplifying the signal to be transmitted.
  • the arrangement and the mobile station according to the invention further comprise a feedback branch 307 comprising attenuation means 308 for attenuating a feedback signal, down-converting means 309 for down-converting an attenuated signal, and filtering means 310 for filtering the down-converted signal.
  • the filtering means may be relatively wideband.
  • the arrangement and receiver of the invention are characterized by the mobile station comprising first switching means 311 for directing the signal of the feedback branch 307 to the A/D converter 312, 202 ( Figure 2) of the receiving branch RX for linearizing the transmitting branch TX signal.
  • the signal to the transmitting branch TX of the feedback branch 307 is directed to the A/D converter 312 (202, Figure 2) of the receiving branch RX, whereby a separate A/D converter is not required for linearizing the transmitting branch TX.
  • the signal of the feedback branch 307 must bypass the intermediate frequency filter 318 of the receiving branch RX for the sampling branch signal to have as little distortion as possible.
  • the purpose of the analog filtering is to remove from the intermediate frequency signal the image frequencies formed as a mixing product.
  • the first switching means 311 connect to the A/D converter 312 either the signal of the receiving branch RX or the output of the power amplifier 304 via the feedback branch 307.
  • the arrangement and mobile station according to the invention are characterized by comprising second switching means 319 for controlling the operating frequency of said A/D converter 312 so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch RX or for A/D converting the signal of the feedback branch 307 and for feeding the converted signal to said digital signal processor DSP 313 in order to linearize the signal of the transmitting branch TX.
  • a clock i.e. a sampling frequency suited for any one occasion is connected to the A/D converter 312.
  • a clock i.e. a sampling frequency suited for any one occasion is connected to the A/D converter 312.
  • A/D converting the signal of the receiving branch RX e.g. 162 kHz 320 is suitable.
  • A/D converting the signal of the feedback branch 307 e.g. 288 kHz 321 is suitable.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Transmitters (AREA)

Abstract

An arrangement, mobile station and method for linearizing the transmitter in a mobile station, which comprises: a digital signal processor (DSP), a receiving branch (RX) comprising one or more mixers (317), one or more intermediate frequency filters (318) responsive to said mixers (317) for filtering the down-converted signal, an A/D converter (312) responsive to the intermediate frequency filter (318). The arrangement further comprises a transmitting branch (TX) comprising a D/A converter (315), a modulator (303), and a power amplifier (304). The arrangement further comprises a feedback branch (307) comprising attenuating means (308) for attenuating a feedback signal, down-converting means (309) for down-converting an attenuated signal, and filtering means (310) for filtering the down-converted signal. In the arrangement, the first switching means (311) direct the signal of the feedback branch (307) to the A/D converter (312) of the receiving branch (RX) for linearizing the signal of the transmitting branch (TX).

Description

LINEARIZING THE TRANSMITTER OF A MOBILE STATION
This application is based on the Finnish patent application Fl- 963031 , filed on July 31 , 1996, which is incorporated hereinto by reference.
FIELD OF THE INVENTION
The invention relates to an arrangement for linearizing the transmitter in a mobile station comprising: a digital signal processor for processing signals, a receiving branch comprising one or more mixers for down- converting a received signal from a radio frequency to an intermediate frequency, one or more intermediate frequency filters responsive to said mixers for filtering said down-converted signal, an A/D converter responsive to said intermediate frequency filter for converting the received signal into digital form and for forwarding said signal converted into digital form into said digital signal processor, a transmitting branch comprising a D/A converter for converting a digital transmission signal into analog form, a modulator for modulating the signal into a radio frequency, a power amplifier for amplifying the transmission signal, a feedback branch comprising attenuating means for attenuating a feedback signal, down-converting means for down-converting an attenuated signal, filtering means for filtering the down-converted signal, whereby said arrangement comprises: first switching means for directing the signal of the feedback branch to the A/D converter of the receiving branch for linearizing the signal of the transmitting branch.
BACKGROUND OF THE INVENTION
The scarcity of radio frequencies leads to a need to use spectrum efficient modulation methods in new radio systems. In Europe, a new radio system standard has been developed for PMR users, called TETRA (Trans European Trunked RAdio). As the modulation method of the TETRA system, π/4-DQPSK (π/4-shifted Differential Quadrature Phase Shift Keying) has been chosen. From the transmitter point of view, a drawback of the modulation method is the variation in the amplitude of the envelope of the RF signal. In a non-linear amplifier, such a variation causes InterModulation (IM). Intermodulation products (below, IM products) spread the spectrum of the transmitted signal, and thus tend to reduce the benefits of using a linear modulation method. The IM products cannot be filtered as they form very close to the desired signal. With constant amplitude modulation methods, spectrum spreading does not occur, and consequently the signal may be amplified by a nonlinear amplifier.
The PCT publication WO 92/08297 (Cahill) discloses an apparatus and method for linearizing the gain of a nonlinear power amplifier in a digital TDM transceiver. The transfer function of the power amplifier describes a relationship between the input signal and the output signal of the power amplifier. The output signal is selectively demodulated with existing receiver elements, during the transmit timeslot of a TDMA time frame. An inverse transfer function is determined from the nominal gain of the power amplifier and the actual transfer function. A correction value, corresponding to the transfer function and its inverse, is determined in a vector table. The correction value is multiplied with the input signal resulting in an adjusted input signal. The amplified adjusted input signal produces a varied output signal that is linear relative to the input signal.
A trunked PMR system, in which different user groups share same radio channels, has strict requirements regarding adjacent channel interference caused by a transmitter. For example, in the present standard for an analog PMR system, determined by the British Department of Trade and Industry publications "MPT 1327, January 1988, Revised and reprinted November 1991 , A Signalling Standard for Trunked Private Land Mobile Radio Systems, Radiocommunications Agency" and "MPT 1343, January 1988, Revised and reprinted September 1991 , Performance Specification, Radiocommunications Agency", the adjacent channel attenuation is required to be -70dBc.
The invention is applicable for use in radio telephone systems with a digital radio path. A digital radio telephone system is described in the ETSI standard ETS 300 392-2: March 1996, Radio Equipment and Systems (RES); Trans-European Trunked RAdio (TETRA); Voice plus Data (V+D); Part 2: Air Interface (Al), ETSI, 583 p. Page 46 of this TETRA standard sets forth an attenuation requirement of -60 dBc, which requires good linearity of the transmitter according to the TETRA standard, in addition, this requirement is considerably stricter than the approximately -25 dB required in the D-AMPS (Digital Advanced Mobile Phone Service) and JDC (Japanese Digital Cellular) systems.
In a power amplifier, good linearity is only achieved with poor efficiency. However, the efficiency of portable devices should be as high as possible for the operation time to be adequate and in order not to waste battery capacity. Further, at least relatively good efficiency is required of the power amplifiers at base stations to avoid cooling problems. The achieving of adequate efficiency and linearity calls for linearizing the transmitter. Recently, a number of different kinds of linearizing methods have been developed. These may be classified into methods employing an open loop and those employing negative feedback.
If the nonlinearities of an amplifier were known in advance, it would be possible to form inverse functions of the nonlinearities, and use them to convert the input signal, whereby the nonlinearities wound be cancelled. The properties of the amplifier do not, however, remain the same but vary due to aging, warming up, and according to the radio channel and transmit power used. In addition, the amplifiers have individual differences. Need exists for linearization methods that must in an adaptive way be capable of adapting to changing conditions. Development work has been targeted into a number of different linearizing methods, and three of them have been found to possess qualities suitable for practical radio systems. These methods are feedforward, cartesian feedback and a predistorter.
In predistortion solutions, the prior art solutions have a separate A/D converter used exclusively for linearizing.
Further, previous feedback solutions have an A/D converter in both the transmitting and the receiving branches.
Figure 1 shows a block diagram of the prior art transmitting and feedback branches. The signal to be transmitted is radio frequency modulated in an RF modulator 102, after which it is amplified in a power amplifier 110, from which the signal is applied further to an antenna 103 for transmission. The signal applied to the antenna 103 is at the same time fed to a feedback branch 104 which is employed when linearizing the transmitter of a mobile station. The feedback branch supplies the signal to a down-conversion and filtering unit 106 where the feedback signal is down-converted and filtered as desired. Following the down-conversion and filtering 106, the down-converted and filtered signal is fed to the A/D converter of the feedback branch, in which the signal is converted to a form suitable for a digital signal processor 108. The digital signal processor 108 processes the feedback signal in a desired, prior art, way. The feedback signal processed in the digital signal processor 108 influences the linearization of the entire transmitter so that the transmission from the transmitter may be kept linear more easily. The processed signal and other signals to be transmitted are applied from the digital signal processor 108 to a D/A converter 109 where they are converted into continuous analog signals which are processed by the RF modulator 102. From the RF modulator onward, the apparatus operates as described above.
Figure 2 is a block diagram illustration of the prior art receiving branch RX. The received signal is first intermediate frequency filtered in a intermediate frequency filter 201 , from which the filtered signal is applied to an
A/D converter 202, after which the signal is applied to a digital signal processor which converts the received signal into a form acceptable to the mobile station and its user.
It should be noted that the prior art solutions have an A/D converter in the receiving branch (RX) and a dedicated A/D converter in the feedback branch, and in addition both of these have an interface to the digital signal processor.
BRIEF DESCRIPTION OF THE INVENTION
The present invention relates to linearizing the transmitter of a mobile station by means of feedback, in particular.
It is the object of the invention to carry out an arrangement and a mobile station in which it is possible to implement, more advantageously than in the prior art solutions, the linearizing of the mobile station transmitter by means of a feedback solution.
This new type of an arrangement for linearizing the mobile station transmission in the mobile station is achieved with the arrangement according to the invention, which is characterized by comprising: second switching means for controlling the operating frequency of said A/D converter so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch or for A/D converting the feedback signal of the feedback branch and for applying the converted signal to said digital signal processor for linearizing the signal of the transmitting branch. The invention further relates to a mobile station which comprises: a digital signal processor for processing signals, a receiving branch comprising one or more mixers for down- converting a received signal from a radio frequency to an intermediate frequency, one or more intermediate frequency filters responsive to said mixers for filtering said down-converted signal, an A/D converter responsive to said intermediate frequency filter for converting the received signal into digital form and for supplying said signal converted into digital form into said digital signal processor, a transmitting branch comprising a D/A converter for converting a digital transmission signal into analog form, a modulator for modulating the signal into a radio frequency, a power amplifier for amplifying the transmission signal, a feedback branch comprising attenuating means for attenuating a feedback signal, down-converting means for down-converting an attenuated signal, filtering means for filtering the down-converted signal, whereby said mobile station comprises: first switching means for supplying the signal of the feedback branch to the A/D converter of the receiving branch for linearizing the signal of the transmitting branch.
The mobile station according to the invention is characterized by further comprising: second switching means for controlling the operating frequency of said A/D converter so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch or for A/D converting the feedback signal of the feedback branch and for applying the converted signal to said digital signal processor for linearizing the signal of the transmitting branch.
The invention further relates to a method for linearizing a mobile station transmission in a mobile station comprising: a digital signal processor for processing signals, a receiving branch comprising one or more mixers for down- converting a received signal from a radio frequency to an intermediate frequency, one or more intermediate frequency filters responsive to said mixers for filtering said down-converted signal, an A/D converter responsive to said intermediate frequency filter for converting the received signal into digital form and for forwarding said signal converted into digital form into said digital signal processor, a transmitting branch comprising a D/A converter for converting a digital transmission signal into analog form, a modulator for modulating the signal into a radio frequency, a power amplifier for amplifying the transmission signal, a feedback branch comprising attenuating means for attenuating a feedback signal, down-converting means for down-converting the attenuated signal, filtering means for filtering the down-converted signal, whereby said method comprises the following steps: applying the signal of the feedback branch to the A/D converter of the receiving branch, converting the signal of the feedback branch into digital form in the A D converter of the receiving branch, and passing the A/D converted signal into said digital signal processor for linearizing the transmission from the transmission branch.
The method according to the invention is characterized by comprising the following steps: controlling the operating frequency of said A D converter so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch or for A/D converting the feedback signal of the feedback branch and for feeding the converted signal to said digital signal processor for linearizing the signal of the transmitting branch.
Hence, the invention relates to an arrangement, mobile station and method, in which the aim is to utilize the parts in the receiving branch of the transceiver in predistortion-based linearizing of the transmitter. In particular, the invention relates to utilizing the A/D converter of the receiving branch in the feedback branch of the transceiver in the mobile station, and the necessary control functions by means of which it is possible to use flexibly the receiving branch A/D converter in converting the feedback branch signals into digital form.
The invention is based on the idea of using as efficiently as possible the existing parts of the handheld phone, thus reducing unnecessary duplication of the hardware. Such an inventive solution provides the advantage that a separate
Analog to Digital (A/D) converter is not required for linearizing the transmitter. By means of the invention, the hardware of the mobile station becomes simpler. Further, it is possible to save both space, an important feature in handheld phones, and money.
The hardware of the mobile phone becomes simpler as the invention reduces the number of components needed in the phone, and consequently also its price. Further still, the designing of the mobile station will become considerably easier because there is no need for a new A/D converter interface to the digital signal processor.
LIST OF DRAWINGS In the following, the invention will be described in greater detail with reference to the accompanying drawings, in which
Figure 1 shows a block diagram of the prior art transmitting and feedback branch,
Figure 2 shows a block diagram of the prior art receiving branch, Figure 3 shows a block diagram of the mobile station according to the invention, and
Figure 4 shows a block diagram according to the solution of the invention.
DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a block diagram of the prior art transmit and feedback branch. Figure 1 has been described in connection with describing the prior art.
Figure 2 shows a block diagram of the prior art receiving branch. Figure 2 has been described in connection with describing the prior art. Figure 3 shows a block diagram of the mobile station according to the invention. In Figure 3, the network infrastructure (INFRA) 600 of the mobile communication system is shown. The network infrastructure comprises e.g. base stations, switching exchanges, databases DB, and other data equipments. The figure shows a typical radio unit 500 communicating in the mobile communication system, such as a subscriber-operated mobile phone, a mobile station or a subscriber station. The function of the transceiver unit (TX/RX) 501 is to match onto the radio channel employed on any one occasion, by means of which the mobile station communicates with the network infrastructure. An antenna 502 is connected to the<transceiver 501 , the antenna having connection to the radio path RP. Usually, radio frequencies between the range 60-1000 MHz (VHF and UHF bands) are used, although other frequencies can also be used.
The user interface 505 comprises an electroacoustic transducing means, typically a loudspeaker 506 and a microphone 507, and possibly buttons relating to beginning, ending and dialling a call. Mobile stations used in a trunked system may also contain a push to talk (PTT) button which must be kept pressed down for the duration of the speaking turn.
The purpose of a controller 503 is to control the operation of the radio unit. The controller 503 is connected to the user interface 505, from which it obtains impulses relating to, for example, the call initiation and termination. Through the user interface 505, the controller 503 may also provide the user with voice/sound or visual symbols relating to the operation of the mobile phone or the mobile radio system.
The controller 503 is connected to the transceiver TX/RX 501. The channel employed by the transceiver is determined by the controller 503, meaning that the transceiver 501 tunes onto a channel, i.e. radio frequency and an appropriate time slot, determined by the controller 503. The transceiver 501 is also switched on controlled by the controller 503. The controller 503 receives and transmits signalling messages by means of the transceiver 501. The inventive mobile station, i.e. the radio unit 500 may be used for example in a radio system comprising a radio network with at least one base station and subscriber stations as well as possibly one or more repeater stations and databases DB. In such a case, said radio unit comprises a transceiver unit 501 for receiving transmissions from other radio units or base stations and for transmitting signals to said other radio units or base stations, a control unit 503 for controlling the functions of the radio unit, and a user interface 505.
The mobile station 500 according to the invention further comprises a digital signal processor DSP for processing signals. The signal processor may be placed in connection with the transceiver 501 Tx/Rx of the mobile station, but it may also be placed elsewhere in the mobile station 500. The transceiver may also have other parts 510, for example a receiving branch, a transmitting branch, and a feedback branch. The operation and contents of these are described in closer detail with the description of Figure 4.
Figure 4 is a block diagram illustration of the solution according to the invention. The arrangement for linearizing the transmission of a mobile station, and correspondingly the mobile' station according to the invention, comprise: a digital signal processor DSP, 313 for processing signals, a receiving branch RX which comprises one or more mixers 317 for down-converting the signal received at the antenna 305 from a radio frequency to an intermediate frequency, one or more intermediate frequency filters 318 responsive to said mixers for filtering said down-converted signal, an A/D converter 312 A/D responsive to said intermediate frequency filter for converting the received signal into digital form and for applying said signal converted into digital form to said digital signal processor 313 DSP.
The arrangement and the mobile station according to the invention further comprise a transmission branch TX comprising a D/A converter 315 D/A for converting the digital transmission signal into analog form, a modulator 303 for modulating the signal into a radio frequency, and a power amplifier 304 for amplifying the signal to be transmitted.
The arrangement and the mobile station according to the invention further comprise a feedback branch 307 comprising attenuation means 308 for attenuating a feedback signal, down-converting means 309 for down-converting an attenuated signal, and filtering means 310 for filtering the down-converted signal. The filtering means may be relatively wideband.
The arrangement and receiver of the invention are characterized by the mobile station comprising first switching means 311 for directing the signal of the feedback branch 307 to the A/D converter 312, 202 (Figure 2) of the receiving branch RX for linearizing the transmitting branch TX signal.
By means of the first switching means 311 , the signal to the transmitting branch TX of the feedback branch 307 is directed to the A/D converter 312 (202, Figure 2) of the receiving branch RX, whereby a separate A/D converter is not required for linearizing the transmitting branch TX. This is possible because the A/D converter 312, 202 of the receiving branch RX is not used simultaneously with transmission. The signal of the feedback branch 307 must bypass the intermediate frequency filter 318 of the receiving branch RX for the sampling branch signal to have as little distortion as possible. The purpose of the analog filtering is to remove from the intermediate frequency signal the image frequencies formed as a mixing product. The first switching means 311 connect to the A/D converter 312 either the signal of the receiving branch RX or the output of the power amplifier 304 via the feedback branch 307. The arrangement and mobile station according to the invention are characterized by comprising second switching means 319 for controlling the operating frequency of said A/D converter 312 so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch RX or for A/D converting the signal of the feedback branch 307 and for feeding the converted signal to said digital signal processor DSP 313 in order to linearize the signal of the transmitting branch TX.
Thus, by means of the second switching means 319, a clock i.e. a sampling frequency suited for any one occasion is connected to the A/D converter 312. For A/D converting the signal of the receiving branch RX, e.g. 162 kHz 320 is suitable. Correspondingly, for A/D converting the signal of the feedback branch 307, e.g. 288 kHz 321 is suitable.
The drawings and the description related thereto are only intended to illustrate the idea of the invention. In details, the arrangement, mobile station and method according to the invention may vary within the scope of the claims. Although the invention is described above mainly in connection with mobile stations, the invention is applicable to other kinds of radio transmitters/receivers as well.

Claims

1. An arrangement (Figure 4) for linearizing the transmitter in a mobile station (500) comprising: a digital signal processor (313, DSP) for processing signals, a receiving branch (RX) comprising one or more mixers (317) for down-converting a received signal from a radio frequency to an intermediate frequency, one or more intermediate frequency filters (318) responsive to said mixers (317) for filtering said down-converted signal, an A/D converter (312, A/D) responsive to said intermediate frequency filter (318) for converting the received signal into digital form and for forwarding said signal converted into digital form into said digital signal processor (313, DSP), a transmitting branch (TX) comprising a D/A converter (315) for converting a digital transmission signal into analog form, a modulator (303) for modulating the signal into a radio frequency, a power amplifier (304) for amplifying the transmission signal, a feedback branch (307) comprising attenuating means (308) for attenuating a feedback signal, down-converting means (309) for down-converting an attenuated signal, filtering means (310) for filtering the down-converted signal, whereby said arrangement comprises: first switching means (311) for directing the signal of the feedback branch (307) to the A/D converter (312) of the receiving branch (RX) for linearizing the signal of the transmitting branch (TX), c h a r a c t e r i z e d by said arrangement further comprising: second switching means (319) for controlling the operating frequency of said A/D converter (312) so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch (RX) or for A/D converting the feedback signal of the feedback branch (307) and for applying the converted signal to said digital signal processor (DSP, 313) for linearizing the signal of the transmitting branch (TX).
2. A mobile station (Figures 3 and 4), comprising a digital signal processor (313, DSP) for processing signals, a receiving branch (RX) comprising one or more mixers (317) for down-converting a received signal from a radio frequency to an intermediate frequency, one or more intermediate frequency filters (318) responsive to said mixers (317) for filtering said down-converted signal, an A/D converter (312, A/D) responsive to said intermediate frequency filter (318) for converting the received signal into digital form and for forwarding said signal converted into digital form into said digital signal processor (313, DSP), a transmitting branch (TX) comprising a D/A converter (315) for converting a digital transmission signal into analog form, a modulator (303) for modulating the signal into a radio frequency, a power amplifier (304) for amplifying the transmission signal, a feedback branch (307) comprising attenuating means (308) for attenuating a feedback signal, down-converting means (309) for down-converting an attenuated signal, filtering means (310) for filtering the down-converted signal, whereby said mobile station (Figure 4) comprises: first switching means (311) for directing the signal of the feedback branch (307) to the A/D converter (312, A/D) of the receiving branch (RX) for linearizing the signal of the transmitting branch (TX), c h a r a c t e r i z e d by said mobile station further comprising: second switching means (319) for controlling the operating frequency of said A/D converter (312, A/D) so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch (RX) or for A/D converting the feedback signal of the feedback branch (307) and for applying the converted signal to said digital signal processor (DSP, 313) for linearizing the signal of the transmitting branch (TX).
3. A method for linearizing the transmission of a mobile station
(Figure 4) in a mobile station (500) comprising a digital signal processor (313, DSP) for processing signals, a receiving branch (RX) comprising one or more mixers (317) for down-converting a received signal from a radio frequency to an intermediate frequency, one or more intermediate frequency filters (318) responsive to said mixers (317) for filtering said down-converted signal, an A/D converter (312, A D) responsive to said intermediate frequency filter (318) for converting the received signal into digital form and for forwarding said signal converted into digital form into said digital signal processor (313, DSP), a transmitting branch (TX) comprising a D/A converter (314) for converting a digital transmission signal into analog form, a modulator (303) for modulating the signal into a radio frequency, a power amplifier (304) for amplifying the transmission signal, a feedback branch (307) comprising attenuating means (308) for attenuating a feedback signal, down-converting means (309) for down-converting an attenuated signal, filtering means (310) for filtering the down-converted signal, whereby said method comprises the following steps: applying (311) the signal of the feedback branch (307) to the A/D converter (312, A/D) of the receiving branch (RX), converting the signal of the feedback branch (307) into digital form in the A/D converter (312, A/D) bf the receiving branch (RX), and passing the A/D converted signal into said digital signal processor (313, DSP) for linearizing the transmission from the transmission branch (TX), characterized by further comprising the following steps: controlling the operating frequency of said A/D converter so that the frequency is alternatively suitable for A/D converting the signal of the receiving branch (RX) or for AD converting the signal of the feedback branch (307) and for feeding the converted signal to said digital signal processor (DSP, 313) for linearizing the signal of the transmitting branch (TX).
PCT/FI1997/000460 1996-07-31 1997-07-29 Linearizing the transmitter of a mobile station WO1998005127A1 (en)

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FI963031 1996-07-31
FI963031A FI963031A7 (en) 1996-07-31 1996-07-31 Linearization of a mobile station transmitter

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Cited By (5)

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Publication number Priority date Publication date Assignee Title
WO2001063791A3 (en) * 2000-02-23 2004-02-26 Scient Generics Ltd Transmitter and receiver circuit
EP1437826A1 (en) 2002-12-30 2004-07-14 Nokia Corporation Linearisation of amplified feedback distortion
WO2005086442A1 (en) * 2004-03-08 2005-09-15 Huawei Technologies Co., Ltd. Multi-carrier receiver and method for multi-carrier signal receiving
DE102008052747A1 (en) 2008-10-22 2010-04-29 Beiersdorf Ag Antiperspirant stick without volatile carrier oils
WO2016027134A1 (en) * 2014-08-22 2016-02-25 Telefonaktiebolaget L M Ericsson (Publ) Feedback transmitter and receiver sharing

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WO1992008279A2 (en) * 1990-10-25 1992-05-14 Rosemount Inc. Transmitter with multifunction adjustment
GB2283629A (en) * 1993-10-26 1995-05-10 Motorola Ltd Splatter-reduced training for adaptive pre-distortion or cartesian feedback linearizers

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Publication number Priority date Publication date Assignee Title
WO1992008279A2 (en) * 1990-10-25 1992-05-14 Rosemount Inc. Transmitter with multifunction adjustment
GB2283629A (en) * 1993-10-26 1995-05-10 Motorola Ltd Splatter-reduced training for adaptive pre-distortion or cartesian feedback linearizers

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001063791A3 (en) * 2000-02-23 2004-02-26 Scient Generics Ltd Transmitter and receiver circuit
EP1437826A1 (en) 2002-12-30 2004-07-14 Nokia Corporation Linearisation of amplified feedback distortion
WO2005086442A1 (en) * 2004-03-08 2005-09-15 Huawei Technologies Co., Ltd. Multi-carrier receiver and method for multi-carrier signal receiving
DE102008052747A1 (en) 2008-10-22 2010-04-29 Beiersdorf Ag Antiperspirant stick without volatile carrier oils
WO2016027134A1 (en) * 2014-08-22 2016-02-25 Telefonaktiebolaget L M Ericsson (Publ) Feedback transmitter and receiver sharing

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AU3544797A (en) 1998-02-20
FI963031A7 (en) 1998-02-01

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