GB2507099A

GB2507099A - Performing noise shaping of a transmitter's DAC to reduce the quantisation noise in a receiver band

Info

Publication number: GB2507099A
Application number: GB201218807A
Authority: GB
Inventors: Markus Nentwig; Christian Jung; Maarit Inka Susanna Melvasalo
Original assignee: Renesas Mobile Corp
Current assignee: Renesas Electronics Corp
Priority date: 2012-10-19
Filing date: 2012-10-19
Publication date: 2014-04-23
Also published as: GB201218807D0

Abstract

This application concerns reduction in transmit leakage in radio transceivers and in particular to noise shaping to reduce quantization noise. A noise shaper 500 is provided upstream of a digital to analogue converter (DAC) 502 of a transceivers transmit branch. The noise shaper reduces the effect of quantization noise on a reception band of the transceivers receiver. The noise shaper is configured on the basis of at least one piece of frequency information. In a preferred embodiment the noise shaper includes a digital filter 504 which is configured to reduce quantisation noise over a notch. The centre frequency of the notch may be selecting based on the centre frequencies of the transmit and receive bands of the transceiver, and the bandwidth of the notch may be selected on the basis of the sum of the transmit and receive bandwidths. The noise shaper may include a quantizer, and its filter may be a loop filter.

Description

METHOD AND APPARATUS FOR REDUCING INTERFERENCE

TECHNICAL FIELD

Examples described in the present application relate generally to radio transmitters and receivers and means for reducing noise in frill-duplex devices.

Examples described in the present application also relate to radio access networks, such as Universal Mobile Telecommunication System (UMTS), Universal Terrestrial Radio Access Network (UTRAN), a Long Term Evolution (LTE) network called Evolved UTRAN (E-UTRAN), and an LTE advanced network.

BACKGROUND

In a radio access network (RAN) a base station, or an evolved Node B (eNB) in LTE, assigns radio resources to a user equipment (UE. In time division systems the radio resources are short time periods, such as 1 ms. These periods are termed time slots, frames, or radio frequencies. Thus, the base station assigns a certain time slot or certain a radio frequency to the UE to be used in a downlink transmission or in an uplink transmission. It is also possible to define the radio resources in regard to time and frequency. A duplex communication system is a point-to-point system composed of two devices that are able to communicate in both directions simultaneously. A telephone is an example of a duplex device. The duplex communication system provides a two-way communication channel between the devices. A term duplexing refers to mediating pair wise communication between more than one pair of devices. The duplexing enables a number of devices to use simultaneously the same communication channel. Time division duplex TDD) and frequency division duplex (FDD) are known techniques for sharing the communication channel. A half-duplex system allows communication in both directions, but only one direction at a time. Conversely, a ftill-duplex system allows the communication simultaneously in the both directions.

FIGURE 1 shows a mobile wireless device 100, such as a mobile phone, comprising a wireless transceiver 110. Transceiver 110 processes a data stream from a modem chipset 112 that processes voice information from microphone 114 during a phone call. A transmitter 116 converts the data stream to a radio frequency signal that is coupled by a duplex filter 118 to an antenna 120 fbr transmission to abase station (not shown in the figure). Antenna 120 also receives a signal from the base station and iscoupledviaduplexfllter ll8toareceiver 124. Thesignalishandledasadigital data stream in modem chipset 112 and output via a speaker 126. Mobile wireless device 100 may communicate with the base station using the FDD radio stand ath. In FDD, transmitter 116 and receiver 124 operate simultaneously on different frequencies that are separated by duplex filter 118.

Due to technical limitations, a part of the signal energy originated from transmitter 116 couples to the input of receiver 124 through an unwanted coupling path 130. These technical limitations relate, for example, to duplex filter 118 or the implementation of transmitter 116. The coupled signal energy at a receive frequency of receiver 124 interferes the signal reception in receiver 124 and may lead to dropping of the phone call, tbr example.

Transmitter 116 may comprise a quadrature path 140, where a signal to be transmitted is first converted from digital to analog in a digital-to-analog converter (DAC) 142 and then filtered in a low-pass fllterl44 and upconverted to a radio frequency in a mixer 146 using a local oscillator signal from a synthesizer 148. After the upconversion to the radio frequency, the signal to be transmitted is amplified by a power amplifier 150.

DAC 142 uscs a givcn number of bits at a given sampling rate, rcsulting in a quantization noise component The quantization noise component is upconverted to radio frequency along with the signal to be transmitted, and it is coupled through unwanted coupling path 130 to the input of receiver 124, where it appears as a part of the unwanted coupled signal energy, or in other words, interference to receiver 124.

The exemplary transmitter 116 shown in FIG. I comprises an envelope path 152. A digital signal processor 154 provides an envelope signal to envelope path 152. The envelope signal is converted to analog by digital-to-analog converter (DAC) 156, ifitered in a low-pass filter 162, and connected to an envelope modulator 15%.

Envelope modulator 158 dynamically controls the supply voltage of power amplifier 150. The purpose of envelope path 152 is to reduce the power consumption of transceiver 110. Envelope path 152 makes possible to operate power amplifier 150 at the smallest possible supply voltage that is required at any instant in time. Envelope path 152 and quadrature path 140 may form, for example, a polar transmitter architecture, an envelope tracking transmitter architecture, or an average power tracking transmitter architecture. A quantization noise component originated from DAC 156 is modulated by power amplifier 150 causing at least some interference in receiver 124.

FIGURE 2 illustrates power spectral densities of a transmitted signal 201 and a received signal 202. Transmitted signal 201 is originated from antenna 120 of FIG. 1 and the received signal 202 is simultaneuosly received via antenna 120. As shown in FIG. 1, a quantization noise component is coupled to the input of receiver 124 through unwanted coupling path 130 and then the component is upconverted around the frequency of the transmitted signal 201. The upconversion "extends" transmitted signal 201. Due to this "extension" 203 transmitted signal 201 partly overlaps received signal 202. Overlap 204, which is marked with vertical lines, causes interference to the reception of received signal 202.

The prior art includes solutions for reducing quantization noise caused by a DAC, such as DAC 142 or DAC 156. The quantization noise can be reduced by increasing the sampling rate or bitwidth of the DAC. The DAC may further move the quantization noise to frequencies above the bandwidth of the analog signal after which the quantization noise is removed by an analog low-pass filter, such as low-pass filter 162. One prior art solution is described in a document of H. Huang, J. Bao, and L. Zhang, A MASH-controlled multilevel power converter for high-efficiency 1ff transmitters, IEEE transactions on power electronics, vol. 26, No 4, Apr 2011.

Noise shaping, as known in the art, is a technique to move the quantization noise of a DAC to frequencies above the bandwidth of the analog signal.

Disadvantages of this technique are a) the need for a high oversampling ratio and b) a substantial increase in the overall level of the quantization noise, especially on high frequencies. This quantization noise at the high frequencies puts additional demands on low-pass filters 144 and 162. The quantization noise is difficult to handle on an envelope path, as the bandwidth of the analog signal is typically at least three times wider in the envelope path than the corresponding bandwidth in the quadrature path.

Quadraturc path 140 and envclope path 152 in FIG. I arc examples of these paths.

SUMMARY

The above described disadvantages of the noise shaping can be reduced or mitigated by a preferred embodiment of the present invention. Thus, aims of a preferred embodiment of the invention are that a) the high oversampling ratio is not needed andb) the quantization noise is remarkably reduced, especially on high frequencies.

One aspect of the present invention concerns a method of reducing interference in a receiver, the method comprising: determining at least one piece of frequency information; and configuring on the basis of the at least one piece of frequency information a noise shaper to make, on a transmission signal path, a reduction to a quantization noise component so that the reduction actualizes on a reception bandwidth of the receiver, wherein an output of the noise shaper is converted by a digital-to-analog converter into an analog signal and the analog signal is used for generating a transmit signal.

In one embodiment of the method, the determining comprises determining a center frequency of a receive signal; and determining a center frequency of the transmit signal.

In one embodiment of the method, the determining further comprises: calculating a notch frequency based on at least an absolute value of a difference between the center frequency of the transmit signal and the center frequency of the receive signal.

In one embodiment of the method, the configuring comprises: adjusting a filter of the noise shaper.

In one embodiment of the method, the adjusting comprises: setting the filter to cut noise at the notch frequency.

In one embodiment of the method, the adjusting is performed once after which the filter is non-adjustable.

In one embodiment of the method, the reduction is a substantial reduction of a power spectral density of the quantization noise component.

In one embodiment of the method, the adjusting comprises: using the at least one piece of frequency information as a search key for retrieving at least one coefficient from a data storage; and inputting the at least one coefficient into the filter.

In one embodiment of the method, the determining comprises: determining a radio band.

In one embodiment of the method, the determining comprises: determining a bandwidth of a receive signal; and determining a bandwidth of the transmit signal.

In one embodiment of the method, the adjusting comprises: calculating a notch bandwidth based on at least a sum of the bandwidth of the transmit signal and the bandwidth of the receive signal; and setting the filter to cut noise at the notch bandwidth.

In one embodiment of the method, the adjusting comprises: changing at least one coefficient of the filter.

In one embodiment of the method, the transmission signal path is one of the following paths: a quadrature path, an envelope path.

One aspect of the present invention concerns an apparatus comprising: at least a filter, wherein at least the filter causes the apparatus to perform the following: modifying a digital signal on the basis of at least one piece of frequency information to make, on a transmission signal path, a reduction to a quantization noise component so that the reduction actualizes on a reception bandwidth of a receiver, wherein an output of thc apparatus is converted by a digital-to-analog converter into an analog signal and the analog signal is used for generating a transmit signal.

In one embodiment of the apparatus, the filter is non-adjustable.

In one embodiment of the apparatus, the filter is adjustable and the apparatus thrther comprises: a processing system arranged to cause the apparatus to control the filter by determining the at least one piece of frequency information, wherein the at least one piece of frequency information effects to operation of the filter.

The processing system may comprise at least one processor; and at least one memory including computer program code.

In one embodiment of the apparatus, the determining comprises: determining a center frequency of a receive signal; and determining a center frequency of the transmit signal.

In one embodiment of the apparatus, the apparatus performs: calculating a notch frequency based on at least an absolute value of a difference between the center frequency of the transmit signal and the center frequency of the receive signal; and setting the filter to cut noise at the notch frequency.

In one embodiment of the apparatus, the reduction is a substantial reduction of a power spectral density of the quantization noise component.

In one embodiment of the apparatus, the apparatus adjusts the filter by: using the at least one piece of frequency information as a search key for retrieving at least one coefficient from a data storage; and inputting the at least one coefficient into the filter.

In one embodiment of the apparatus, the determining comprises: determining a radio band.

In one embodiment of the apparatus, the determining comprises: determining a bandwidth of a receive signal; and determining a bandwidth of the transmit signal.

In one embodiment of the apparatus, the apparatus performs: calculating a notch bandwidth based on at least a sum of the bandwidth of the transmit signal and the bandwidth of the receive signal; and setting the filter to cut noise at the notch bandwidth.

In one embodiment of the apparatus, the apparatus adjusts the filter by changing at least one coefficient of the filter.

In one embodiment of the apparatus, the apparatus comprises a noise shaper and wherein the noise shaper comprises the filter and the digital-to-analog converter.

In one embodiment of the apparatus, the transmission signal path is one of the following paths: a quadrature path, an envelope path.

One aspect of the present invention concerns a computer readable medium comprising a set of instructions, which, when executed in a device comprising at least a receiver and a noise shaper causes the device to perform the method aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of examples and embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which: FIGURE 1 shows an example ofa wireless mobile dcvice comprising a transceiver; FIGURE 2 shows a quantization noise component in a transmitted signal that partly overlaps a received signal; FIGURE 3A illustrates a method of reducing interference at a receiver; FIGURE 3B shows four optional substeps of the method; FIGURE 3C shows one optional substep of the method; FIGURE 4A shows a filter design problem and a solution to it; FIGURE 4B shows an example of coefficients; FIGURE 5 shows an example of a noise shaper and a DAC; FIGURE 6 shows an apparatus of reducing interference at a receiver;

DETAILED DESCRIPTON

In the following a receive signal is termed a signal received be a receiver.

The receiver is, for example, receiver 116 in FIG. 1. Correspondingly a transmit signal is a signal transmitted from a transmitter. The transmitter is, for example, transmitter 124 in FIG. 1.

FIGURE 3A illustrates a method of reducing interference at a receiver.

The method performs the following: determining 301 at least one piece of frequency information and configuring 302, on the basis of the at least one piece of frequency information, a noise shaper to make a reduction to a quantization noise component so that the reduction actualizes on a reception bandwidth of the receiver. In more detail, the reduction to the quantization noise component is made on a transmission signal

S

path. On this transmission signal path an output of the noise shaper is converted by a digital-to-analog converter into an analog signal and the analog signal is used for generating a transmit signal.

The method of FIG. 3A causes the reduction to the quantization noise component assuming that a digital signal output by the noise shaper is converted by a digital-to-analog converter into an analog signal and the analog signal is used for generating a transmit signal. An input of the method is a digital signal, for example, a digital signal from digital signal processor 154 and the transmission signal path is, for example, envelope path 152. When performing the method on envelope path 152, the noise shaper is located between DSP 154 and DAC 156 or the noise shaper comprises DAC 156. The noise shaper comprises at least a filter.

The filter of the noise shaper is either adjustable or non-adjustable. When the filter is non-adjustable the operation of the noise shaper does not change, i.e. the filter filters always the same frequencies. Correspondingly, when the filter is adjustable the operation of the noise shaper changes each time when the filter is adjusted.

FIGURE 3B shows four optional substeps of the method. Tn more detail, determining 301 may comprise 1-4 of substeps referred by 310, 312, 314, and 316. In a first embodiment determining 301 comprises substeps 310 and 312 and in a second embodiment determining 301 comprises substeps 314 and 316. In all embodiments the order of the substeps may be freely chosen without departing from the invention.

The substcp(s) may be performed as response to an impulse or a trigger event. The impulse or the trigger event is, for example, that the receiver switches to a certain band or a bandwidth mode. The method aims to continuously protect the receiver from the interference caused by the quantization noise component.

In one embodiment determining 301 comprises: determining 310 a center frequency of a receive signal. The receive signal is, for example, the signal received through antenna 120 in FIG. 1.

In one embodiment determining 301 comprises: determining 312 a center frequency of a transmit signal. The transmit signal is, for example, the signal transmitted through antenna 120.

In one embodiment determining 301 comprises: determining 314 a bandwidth of the receive signal and determining 316 a bandwidth of the transmit signal.

Theperformance orderofsubsteps 310,312,314, and/or316 maybe differentthaninFlG.3B.

FIGURE 3C shows an optional substep 320 which fbllows substeps 310- 316. hone embodiment of the method, configuring 302 comprises adjusting 320 the filter of the noise shaper so that the noise shaper causes a reduction to a quantization noise component.

In some embodiments, adjusting 320 comprises retrieving coefficients from a data storage and inputting the coefficients into the filter of the noise shaper.

The data storage is, for example, a coefficient table. The retrieving may mean in practice that at least one of the following piece of information is used as an index of table: an operating band of the transceiver, the center frequency of the transmit signal, the center frequency of the receive signal, the bandwidth of the transmit signal, or the bandwidth of the receive signal.

The method of HG. 3A relates generally to a frequency response and a stopband. The frequency response is a quantitative measure of an output spectrum of the transmission signal path. The stopband is a band of frequencies, between specified limits, through which a system does not allow signals to pass, or the attenuation is above a certain level. Regarding to the method of FIG. 3A, the system is the transmission signal path and the certain level is a valuc of thc frcqucncy rcsponsc.

Generally speaking, the method provides a substantial reduction of a quantization noise component on the reception bandwidth of the receiver. The substantial reduction ofthe power spectral density of the quantization noise component may appear, for example, as a lowpass frequency response or a bandstop frequency response on the power spectral density. A stopband in a bandstop frequency response may be referred to as a notch. Alternatively, it can be said that the method enables!bcusing a reduction of a quantization noise component on the stopband.

In one embodiment, detemining 301 comprises determining a radio band.

The radio band is, fix example, "band I" defined by 3GPP (third generation partnership project). This identifier, "band I", can be used as a search key when retrieving coefficients from the table.

Instead of using the coefficient table, the filter can be adjusted in another way. In one embodiment of the method of FIG. 3A, adjusting 320 comprises solving a fiher design problem so that two requirements are fulfilled. The first requirement is that a frequency response of the stopband is centered at a difference frequency of the center frequency of the received signal and the center frequency of the transmitted signal. The second requirement is that the width of the stopband substantially equals a sum of the determined bandwidth of the transmitted signal and the determined bandwidth of the received signal. Fulfilling of these requirements is described in the following figure. Methods for solving the filter design problem are known in the art.

FIGURE 4A shows the filter design problem and one solution of the problem. In one embodiment, determining 310 and determining 312 result in that the center frequencies the receive signal and the transmit signal arc used in a calculation of a notch frequencyfv. As illustrated in FIG. 4A, the notch frequency 401 is located in the middle of the notch. The calculation of the notch frequency is based on at least an absolute value of a difference between the center frequency of the transmit signal and the center frequency of the receive signal. When the center frequency of the transmit signal is marked withR and the center frequency of the receive signal is marked withfR, the notch frequency can be calculated: fv frx -fRx which can be considered as a basic formula off, without any constants or variables.

A constant or variable can be used, for example, as a muhiplier in the calculation of f7. When J7 is calculated, the filter is set to cut noise atf A bandwidth is the difference between the upper and lower frequencies in a continuous set of frequencies.

A notch bandwidth BW400 can be defined through its upper frequency and lower frequency. Alternatively, notch bandwidth SW 400 can be understood as a width of the notch. In one embodiment, notch bandwidth 400 is a constant. In another embodiment notch bandwidth 400 is calculated. Tn this embodiment, determining 314 and determining 316 result in the center frequencies that are used in the calculation of a notch bandwidth BW. The calculation of the notch bandwidth is based on at least a sum of the bandwidth of the transmit signal and the bandwidth of the receive signal.

When the bandwidth of the transmit signal is marked with BW and the bandwidth of thc rcceive signal is marked with BW}, the notch bandwidth can be calculatcd which is a basic formula ofBf'V. One or more constants or variables can be added into this basic foimula, if they result in such a bandwidth value that improves the operation of the filter. When BW is calculated, the filter is set to cut noise in a frequency span with bandwidth BW centered at/v. Frequency response 402 is a curve which includes thc notch on the reception bandwidth of the receiver. Due to the notch, the quantization noise component on the reception bandwidth of the receiver is reduced and the reduction of the quantization noise component reduces the interference in the receiver.

FIGURE 4B shows an example of coefficients 404. A noise shaper can be configured with coefficients 404, i.e. with 1', c, c2, c3, and e4 after which the noise shaper focuses a notch as shown in FIG. 4A. In more detail, when a quantization noise component is converted to a radio frequency, the reduction of the quantization noise component appears at notch frequency range occupied by the receive signal and has a bandwidth BW.

In one embodiment, the filter is a FIR filter, designed for example using methods of "M. Lang: Algorithms for the Constrained Design of Digital Filters with Arbitrary Magnitude and Phase Responses, doctoral dissertation, Technische Universitat Wien, June 1999", and normalized by dividing the impulse response by the first sample of the impulse response.

FIGURE 5 shows an example of noise shaper 500 and a DAC 502. Noise shaper 500 comprises a filter 504, a quantizer 550, a subtraction block 552, and an addition block 554. Noise shaper 500 is configured with input parameters which are in this example coefficients 506. Coefficients 506 are obtained, for example, from bus shown in FIG. 1. In one embodiment of the method adjusting 320 comprises changing at least one coefficient of the filter.

In one embodiment, the coefficients are obtained from a coefficient table or some other data storage, for example, 1', c1, c2, c3 and c4 as shown in Fig. 4B.

The noise shaper, such as noise shaper 500, can be utilized in the method of FIG 3A in various transmission signal paths. In one embodiment, noise shaper 500 is placed on quadrature path 140. In another embodiment, noise shaper 500 is placed on envelope path 152.

FIGURE 6 illustrates apparatus 601 for reducing interference at a receiver.

Apparatus 601 comprises at least a filter 602 that causes apparatus 601 to perform the following: modifying a digital signal 603 on the basis of at least one piece of frequency information 604 to make, on a transmission signal path, a reduction to a quantization noise component so that the reduction actualizes on a reception bandwidth of thc receivcr. In morc detail, the reduction to the quantization noise component actualizes when an output 605 of the apparatus 601 is converted by a digital-to-analog converter 606 into an analog signal 607 and analog signal 607 is used for generating a transmit signal. In one embodiment, filter 602 is a non-adjustable filterwhich is configuredby performing the methodof FIG. 3A. The performing of the method may comprise actions described in FIGs. 3B, 3C, 4A and/or 4B. The at least one piece of frequency information 604 is shortly termed "input data". A computation part 610 comprises a processor 612, a memory 613 with a computer program code 614. The computation part 610 reads input data 604, computes it, and outputs "control data" 615. In one embodiment, apparatus 601 comprises computation part 610. The center frequencies of the transmit signal and a receive signal are examples of input data 604 and the notch frequency/v is an example of control data 615.

When filter 602 is non-adjustable, filter 602 is configured (once) with control data 615, after which filter 602 is usable in noise shaping. In this embodiment, computation part 610 is a tool that is utilized when filter 602 is manufactured and arranged to cut noise. When apparatus 601 comprises non-adjustable filter 602, in one embodiment of the apparatus the at least one piece of frequency information comprises: a notch frequency, a notch bandwidth, or both of them; and the filter is arranged to cut noise at the notch frequency, at the notch bandwidth, or at both of them.

In another embodiment, filter 602 is adjustable. Then the at least one piece of frequency information, i.e. input data 604, have various values in different instants in time. The embodiment can be understood so that the method of FIG. 3A and/or actions described in FIGs. 3B, 3C, 4A, 4B are performed a number of times to (re)adjust filter 602. In one embodiment, the method of FIG. 3A is used when either the transmit signal frequency or the receive signal frequency changes. In one embodiment, the change of either of the signals is commanded by a base station. This command is received in the transceiver e.g. via a radio link. Thus, the command of the base station, or some other action, triggers apparatus 601 to perform the method of FIG. 3A andior actions described in FIGs. 3B, 3C, 4A, 4B. In response to the triggering, apparatus 601 reads input data 604 and computes control data 615. When filter 602 is adjustable the computation of the control data 615 requires that apparatus 601 comprises, or is coupled to, computation part 610. Conversely, when filter 602 is non-adjustable, apparatus 601 or the transceiver does not need to comprise computation part 610.

A center frequency of the receive signal and a center frequency of the transmit signal are examples of input data 604. In one embodiment, these center frequencies are stored as numeric values in a memory of the transceiver, for example, in memory 613. In the method of FIG. 3A "determining 301 the at least one piece of frequency information" may be a simple action, such as retrieving correct numeric values from memory 613. If the retrieved numeric value is not usable as such, a conversion of the numeric value, or some other kind of computation, may be needed.

When the center frequencies are finally determined the apparatus 601 calculates, in one embodiment, the notch frequency by using at least an absolute value of a difference between the center frequency of the transmit signal and the center frequency of the receive signal. After that apparatus 601 sets filter 602 to cut noise at the notch frequency.

Thus, in one embodiment of the apparatus, input data 604 comprises numeric values of at least the center frequency of the receive signal and the center frequency of the transmit signal. In addition, input data 604 may include numeric values of the bandwidth of the receive signal and the bandwidth of the transmit signal.

Apparatus 601 computes input data 604 with computation part 610 and outputs control data 615. Control data 615 may include numeric values. Alternatively, control data 615 is a signal. Nevertheless, control data 615 results in that filter 602 cuts noise in a wanted maimer. The wanted manner is, for example, that the noise is cut at the notch frequency.

In one embodiment, input data 604 is such piece/pieces of frequency information which is/arc uscd as a search key for retrieving at least one coefficient from data storage. The data storage is, for example, a table stored in memory 613. The at least one coefficient retrieved from the data storage is then input into the filter.

As mentioned in the above, computation part 610 reads input data 604 and computes control data 615 for filter 602. The following list shows examples of input data 604 and control data 615: -input data 604 discloses the center frequency of the receive signal and the center frequency of the transmit signal; and control data 615 discloses (or results in) the notch frequency -input data 604 further discloses the bandwidth of the receive signal and the bandwidth of the transmit signal; and control data 615 further discloses (or results in) the notch bandwidth -input data 604 discloses such piece of frequency information on the basis of which computation part 610 computes control data 615 so that control data 615 discloses (or results in) a certain bandwidth input data 604 discloses apiece of frequency information that is used as a search key for retrieving at least one coefficient, and the at least one coefficient is used as control data 615.

In one embodiment, apparatus 601 controls with computation part 610 the operation of a noise shaper, wherein the noise shaper comprises at least filter 602. In onc embodiment, the noise shaper further comprises digital-to-analog converter 606.

Apparatus 601 can be utilized, for example, in transceiver 110. When the apparatus 601 is utilized in transceiver 110, digital signal 603 is from DSP 154 and digital-to-analog converter 609 is either DAC 142 (on the quadrature path) or DAC 156 (on the envelope path). Apparatus 601 may be a separated component in the transceiver, but if needed, its functionality could also be implemented in modem ehipset 112.

The present invention may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. The hardware may be, for example, a filter, a chip, a modem, or some other apparatus which includes or is coupled to at least memory and at least one processor. The application logic, software or instruction set is maintained on any one ofvarious conventional computer-readable media. In the context of this document, a "computer-readable medium" may be any media or means that contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. A computer-readable medium may comprise a computer-readable storage medium that may be any media or means that contain or store the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer.

When not otherwise mentioned, "one embodiment" in the above refers to "one embodiment of the present invention". The exemplary embodiments can store information relating to various processes described herein. This information can be stored in one or more memories, such as a hard disk, optical disk, magneto-optical disk, RAM, and the 111cc.

All or a portion of the exemplary embodiments can be conveniently implemented using one or more general purpose processors, microprocessors, digital signal processors, micro-controllers, and the like, programmed according to the teachings of the exemplary embodiments of the present invention, as will be appreciated by those skilled in the computer and/or software art(s). Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the exemplary embodiments, as will be appreciated by those skilled in the software art. In addition, the exemplary embodiments can be implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as will be appreciated by those skilled in the electrical art(s). Thus, the exemplary embodiments are not limited to any specific combination of hardware and/or software.

Stored on any one or on a combination of computer readable media, the exemplary embodiments of the present invention can include software for controlling the components of the exemplary embodiments, for driving the components of the exemplary embodiments, for enabling the components of the exemplary embodiments to interact with a human user, and the like. Such software can include, but is not limited to, device drivers, firmware, operating systems, development tools, applications software, and the like. Such computer readable media further can include the computer program of an embodiment of the present invention for performing all or a portion (if processing is distributed) of the processing performed in implementing the present invention. Computer code devices of the exemplary embodiments of the present invention can include any suitable interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLL5), Java classes and applets, complete executable programs, Common Object Request Broker Architecture (CORBA) objects, and the like.

The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention arc envisaged. It is to be understood that any feature described in relation to anyone embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

Claims: 1. A method of reducing interference in a receiver, the method comprising: determining at least one piece of frequency information; and configuring on the basis of the at least one piece of frequency information a noise shaper to make, on a transmission signal path, a reduction to a quantization noise component so that the reduction actualizes on a reception bandwidth of the receiver, wherein an output of the noise shaper is converted by a digital-to-analog converter into an analog signal and the analog signal is used for generating a transmit signal.
2. The method according to claim 1, wherein the determining comprises: determining a center frequency of a receive signal; and determining a center frequency of the transmit signal.
3. The method according to claim 2, wherein the determining frirther comprises: calculating a notch frequency based on at least an absolute value of a difference between the center frequency of the transmit signal and the center frequency of the receive signal.
4. The method according to claim 1, wherein the configuring comprises: adjusting a filter of the noise shaper.
5. The method according to claim 4, wherein the adjusting comprises: setting the filter to cut noise at the notch frequency.
6. The method according to claim 4 or 5, wherein the adjusting is performed once after which the filter is non-adjustable.
7. The mcthod according to any prcccding claim, whercin thc rcduction is a substantial reduction of a power spectral density of the quantization noise component.
8. The method according to any of claims 4 to 6, wherein the adjusting comprises: using thc at least one piece of frequency information as a search key for retrieving at least one coefficient from a data storage; and inputting the at least one coefficient into the filter.
9. The method according to claim 1, wherein the determining comprises: determining a radio band.
10. The method according to claim 1, wherein the determining comprises: determining a bandwidth of a receive signal; and determining a bandwidth of the transmit signal.
11. The method according to claims 4 and 10, wherein the adjusting comprises: calculating a notch bandwidth based on at least a sum of the bandwidth of the transmit signal and the bandwidth of the receive signal; and setting the filter to cut noise at the notch bandwidth.
12. The method according to claim 4, the adjusting comprises: changing at least one coefficient of the filter.
13. The method according to any preceding claim, wherein the transmission signal path is one of the following paths: a quadrature path, an envelope path.
14. An apparatus comprising: at least a filter, wherein at least the filter causes the apparatus to perform the following: modifying a digital signal on the basis of at least one piece of frequency information to make, on a transmission signal path, a reduction to a quantization noise component so that the reduction actualizes on a reception bandwidth of a receiver, wherein an output of the apparatus is converted by a digital-to-analog converter into an analog signal and the analog signal is used for generating a transmit signal.
15. The apparatus according to claim 14, wherein the filter is non-adjustable.
16. The apparatus according to claim 14, wherein the filter is adjustable and wherein the apparatus further comprises: a processing system arranged to cause the apparatus to control the filter by determining the at least one piece of frequency information, wherein the at least one piece of frequency information affects operation of the filter.
17. The apparatus according to claim 16, wherein the determining comprises: determining a center frequency of a receive signal; and determining a center frequency of the transmit signal.
18. The apparatus according to claim 17, wherein the apparatus performs: calculating a notch frequency based on at least an absolute value of a difference between the center frequency of the transmit signal and the center frequency of the receive signal; and setting the filter to cut noise at the notch frequency.
19. The apparatus of any of claims 14 to 18, wherein the reduction is a substantial reduction of a power spectral density of the quantization noise component.
20. The apparatus according to claim 14 or claim 16, wherein the apparatus adjusts the filter by: using the at least one piece of frequency information as a search key for retrieving at least one coefficient from a data storage; and inputting the at least one coefficient into the filter.
21. The apparatus according to claim 16, wherein the determining comprises: determining a radio band.
22. The apparatus according to claim 16, wherein the determining comprises: determining a bandwidth of a receive signal; and determining a bandwidth of the transmit signal.
23. The apparatus according to claim 22, wherein the apparatus performs: calculating a notch bandwidth based on at least a sum of the bandwidth of thc transmit signal and thc bandwidth of the rcccivc signal; and setting the filter to cut noise at the notch bandwidth.
24. The apparatus according to claim 16, wherein the apparatus adjusts the filter by changing at least one coefficient of the filter.
25. The apparatus according to any of claims 14 to 24, wherein the apparatus comprises a noise shaper and wherein the noise shaper comprises the filter and the digital-to-analog converter.
26. The apparatus according to any of claims claim 14 to 25, wherein the transmission signal path is one of the following paths: a quadrature path, an envelope path.
27. A computer readable medium comprising a set of instructions, which, when executed in a device comprising at least a receiver and a noise shaper causes the device to perform the method of any of claims I to 13.