CN107005520B

CN107005520B - Apparatus and method for phase shaping of orthogonal frequency division multiplexing signals

Info

Publication number: CN107005520B
Application number: CN201580064954.1A
Authority: CN
Inventors: Z·阿贡
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2014-12-15
Filing date: 2015-11-04
Publication date: 2020-03-13
Anticipated expiration: 2035-11-04
Also published as: CN107005520A; WO2016099684A1; US9270509B1

Abstract

The present invention provides methods and apparatus for "shaping" the slope of the phase component of an OFDM data symbol to reduce phase error accumulation. By way of example, the method 100 includes receiving an incoming data signal via the processor 12 of the transmitter 28. The method 100 further includes calculating one or more roots of a first function representing a phase component of the data signal, calculating a second function representing the phase component based on the one or more roots, deriving a periodicity of the phase component based on the second function, and deriving a slope value of the phase component based at least in part on the periodicity of the phase component to reduce or eliminate an error of the phase component.

Description

Apparatus and method for phase shaping of orthogonal frequency division multiplexing signals

Background

The present disclosure relates generally to polar transmitters, and more particularly to polar transmitters included within electronic devices.

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

The transmitter and receiver are commonly included in a variety of electronic devices, particularly in portable electronic devices such as, for example, telephones (e.g., mobile and cellular telephones, cordless telephones, personal assistant devices), computers (e.g., laptops, tablets), internet connection routers (e.g., Wi-Fi routers or modems), radios, televisions, or any of a variety of other fixed or handheld devices. One type of transmitter known as a wireless transceiver may be used to generate wireless signals that are transmitted via an antenna coupled to the transmitter. In particular, wireless transmitters are commonly used to wirelessly transmit data over a network channel or other medium (e.g., air) to one or more receiving devices.

A wireless transmitter may generally include subcomponents such as, for example, an oscillator, a modulator, one or more filters and a power amplifier. Moreover, certain data modulation techniques that may be implemented by a wireless transmitter may include modulating in-phase (I)/quadrature (Q) time samples of a signal into an amplitude signal and a phase signal. However, because some wireless transmitters may also use phase information to modulate the frequency of one or more oscillators included within the wireless transmitter, the signal is output, and by extension, the information to be transmitted may become distorted. It may be useful to provide more advanced improved wireless transmitters.

Disclosure of Invention

The following sets forth a summary of certain embodiments disclosed herein. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these particular embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, the present disclosure may encompass a variety of aspects that may not be set forth below.

Various embodiments of the present disclosure may be used to "shape" the slope of the phase component of an Orthogonal Frequency Division Multiplexed (OFDM) data symbol in order to reduce the accumulation of phase errors. By way of example, a method includes receiving, via a processor of a transmitter, an incoming data signal. The method also includes calculating one or more roots of a first function representing a phase component of the data signal, calculating a second function representing the phase component based on the one or more roots, deriving a periodicity of the phase component based on the second function, and deriving a value of a slope of the phase component based at least in part on the periodicity of the phase component to reduce or eliminate an error of the phase component.

Various modifications to the above-described features may be possible in relation to various aspects of the present invention. Other features may also be added to these various aspects. These refinements and additional features may exist individually or in any combination. For example, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present invention alone or in any combination. The brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of embodiments of the present disclosure without limitation to the claimed subject matter.

Drawings

This patent or patent application document contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the office upon request and payment of the necessary fee.

Various aspects of the disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

fig. 1 is a schematic block diagram of an electronic device including a transceiver, according to an embodiment;

FIG. 2 is a perspective view of a notebook computer representing an embodiment of the electronic device of FIG. 1;

FIG. 3 is a front view of a handheld device showing another embodiment of the electronic device of FIG. 1;

FIG. 4 is a front view of a desktop computer showing another embodiment of the electronic device of FIG. 1;

FIG. 5 is a front and side view of a wearable electronic device representing another embodiment of the electronic device of FIG. 1;

fig. 6 is a block diagram of a transceiver included within the electronic device of fig. 1 that includes a transmitter, according to an embodiment;

fig. 7 is a block diagram of a polar modulator included as part of the transmitter of fig. 6, in accordance with an embodiment;

fig. 8 is a dot diagram illustrating one example of a periodic phase component signal, according to an embodiment;

fig. 9 is a block diagram of a frequency synthesizer included as part of the transceiver of fig. 6, according to an embodiment;

fig. 10 is a flow diagram illustrating one embodiment of a process that may be used to "shape" the slope of the phase component of an OFDM data symbol in order to reduce the accumulation of phase errors, according to an embodiment; and is

Fig. 11 is a plot showing the variation of the performance of a phase slope "shaped" WLAN OFDM data signal according to error, according to an embodiment.

Detailed Description

One or more specific embodiments of the present disclosure will be described below. These described embodiments are merely examples of the presently disclosed technology. Moreover, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Furthermore, it should be understood that references to "one embodiment" or "an embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

Embodiments of the present disclosure generally relate to techniques for improving frequency modulation accuracy in Orthogonal Frequency Division Multiplexing (OFDM) polar transmitters. For example, techniques of the present disclosure may include providing a technique for "shaping" the phase of OFDM signal symbols in order to reduce the accumulation of phase errors between OFDM symbols that may become apparent, for example, due to the initial calculated Frequency Command Word (FCW) being converted to the frequency of the oscillator of the OFDM polar transmitter. The techniques of this disclosure may also include a method for detecting an offset between an OFDM polar transmitter and a receiver. For example, the frequency offset may be estimated by finding the phase difference between the same samples of a particular training field used for carrier frequency offset estimation. Indeed, the techniques of the present disclosure to prevent phase error accumulation may be particularly useful for transmission standards that apply carrier frequency offset estimation algorithms, for example, which may be based on phase differences between consecutive symbols.

In view of the foregoing, a general description of suitable electronics that may employ a polar transmitter and that may be used to "shape" the slope of the phase component of an OFDM data symbol in order to reduce the accumulation of phase errors will be provided below. Turning first to fig. 1, an electronic device 10 according to an embodiment of the present disclosure may include, among other things, one or more processors 12, a memory 14, a non-volatile storage 16, a display 18, an input structure 22, an input/output (I/O) interface 24, a network interface 26, a transceiver 28, and a power supply 29. The various functional blocks shown in fig. 1 may include hardware elements (including circuitry), software elements (including computer code stored on a computer-readable medium), or a combination of both hardware and software elements. It should be noted that fig. 1 is merely one example of a particular implementation and is intended to illustrate the types of components that may be present in electronic device 10.

By way of example, the electronic device 10 may represent a block diagram of a laptop computer shown in fig. 2, a handheld device shown in fig. 3, a desktop computer shown in fig. 4, a wearable electronic device shown in fig. 5, or the like. It should be noted that the one or more processors 12 and/or other data processing circuitry may be referred to herein generally as "data processing circuitry". Such data processing circuitry may be embodied in whole or in part as software, firmware, hardware, or any combination thereof. Further, the data processing circuitry may be a single processing module that is included, or may be incorporated in whole or in part into any of the other elements within electronic device 10.

In the electronic device 10 of fig. 1, one or more processors 12 and/or other data processing circuitry may be operatively coupled with the memory 14 and the non-volatile memory 16 to execute various algorithms. Such programs or instructions executed by the one or more processors 12 may be stored in any suitable article of manufacture including one or more tangible computer-readable media, such as memory 14 and non-volatile storage 16, that at least collectively store the instructions or routines. Memory 14 and non-volatile storage 16 may comprise any suitable article of manufacture for storing data and executable instructions, such as random access memory, read-only memory, rewritable flash memory, hard drives, and optical disks. Additionally, programs (e.g., operating systems) encoded on such computer program products may also include instructions that are executable by the one or more processors 12 to enable the electronic device 10 to provide various functionality.

In some embodiments, display 18 may be a Liquid Crystal Display (LCD) that may allow a user to view images generated on electronic device 10. In some embodiments, display 18 may include a touch screen that may allow a user to interact with a user interface of electronic device 10. Further, it should be understood that in some embodiments, the display 18 may include one or more Organic Light Emitting Diode (OLED) displays, or some combination of LCD panels and OLED panels.

The input structures 22 of the electronic device 10 may enable a user to interact with the electronic device 10 (e.g., press a button to increase or decrease a volume level). Just as with the network interface 26, the I/O interface 24 may enable the electronic device 10 to interact with various other electronic devices. The network interface 26 may, for example, include interfaces for the following networks: a Personal Area Network (PAN) such as a bluetooth network, a Local Area Network (LAN) or a Wireless Local Area Network (WLAN) such as an 802.11x Wi-Fi network, and/or a Wide Area Network (WAN) such as a third generation (3G) cellular network, a fourth generation (4G) cellular network or a Long Term Evolution (LTE) cellular network. The network interface 26 may also include, for example, interfaces for: broadband fixed wireless access network (WiMAX), mobile broadband wireless network (mobile WiMAX), asynchronous digital subscriber line (e.g., ADSL, VDSL), digital video terrestrial broadcast (DVB-T) and its extended DVB handheld device (DVB-H), Ultra Wideband (UWB), Alternating Current (AC) power line, and the like.

In some embodiments, to allow electronic device 10 to communicate over the aforementioned wireless networks (e.g., Wi-Fi, WiMAX, Mobile WiMAX, 4G, LTE, etc.), electronic device 10 may include transceiver 28. Transceiver 28 may include any circuitry that may be used to wirelessly receive signals and wirelessly transmit signals (e.g., data signals). Indeed, in some embodiments, as will be further appreciated, the transceiver 28 may include a transmitter and a receiver combined as a single unit, or in other embodiments, the transceiver 28 may include a transmitter separate from a receiver. For example, as described above, transceiver 28 may transmit and receive OFDM signals (e.g., OFDM data symbols) to support data communication in wireless applications such as, for example, PAN networks (e.g., bluetooth), WLAN networks (e.g., 802.11x Wi-Fi), WAN networks (e.g., 3G, 4G, or LTE cellular networks), WiMAX networks, mobile WiMAX networks, ADSL and VDSL networks, DVB-T and DVB-H networks, UWB networks, and so forth. As used herein, "Orthogonal Frequency Division Multiplexing (OFDM)" may refer to a modulation technique or scheme by which a transmission channel may be divided into multiple orthogonal subcarriers or subchannels to improve the efficiency of data transmission. Additionally, in some embodiments, the transceiver 28 may be integrated as part of the network interface 26. As further shown, the electronic device 10 may include a power source 29. Power supply 29 may include any suitable power source, such as a rechargeable lithium polymer (Li-poly) battery and/or an Alternating Current (AC) power converter.

In some embodiments, the electronic device 10 may take the form of a computer, portable electronic device, wearable electronic device, or other type of electronic device. Such computers may include computers that are generally portable (e.g., laptops, notebooks, and tablets) as well as computers that are generally used in one location (e.g., conventional desktop computers, workstations, and/or servers). In certain embodiments, the electronic device 10 in the form of a computer may be available from appleInc

The model number,

Pro model, MacBook

The model number,

The model number,

mini model or Mac

The model number. By way of example, an electronic device 10 in the form of a laptop computer 30A is shown in fig. 2 according to one embodiment of the present disclosure. The illustrated computer 30A may include a housing or casing 32, the display 18, the input structures 22, and ports for the I/O interfaces 24. In one embodiment, input structures 22 (such as a keyboard and/or touchpad) may be used to interact with computer 30A, such as to launch, control, or operate a GUI or application running on computer 30A. For example, a keyboard and/or touchpad may allow a user to navigate a user interface or application interface displayed on display 18.

Fig. 3 illustrates a front view of a handheld device 30B that represents one embodiment of the electronic device 10. Handheld device 30B may represent, for example, a cellular telephone, a media player, a personal data manager, a handheld game platform, or any combination of such devices. For example, handheld device 30B may be a tablet-sized implementation of electronic device 10, which may be, for example, available from Apple Inc

The model number.

Handheld device 30B may include an enclosure 36 for protecting internal components from physical damage and shielding the internal components from electromagnetic interference. The housing 36 may enclose the display 18 which may display an indicator icon 39. The indicator icon 38 may indicate, among other things, cell phone signal strength, bluetooth connection, and/or battery life. The I/O interface 24 may pass openly through the housing 36 and may include, for example, I/O ports for hardwired connections for charging and/or content manipulation using standard connectors and protocols, such as a lightning connector provided by Apple inc.

User input structures 42 in conjunction with display 18 may allow a user to control handheld device 30B. For example, the input structure 40 may activate or deactivate the handheld device 30B, the input structure 42 may navigate a user interface to a home screen and user configurable application screen, and/or activate a voice recognition feature of the handheld device 30B, the input structure 42 may provide volume control or may toggle between a vibrate mode and a ringer mode. Input structures 42 may also include a microphone to obtain a user's voice for various voice-related features, and a speaker that may enable audio playback and/or certain telephony functions. The input structure 42 may also include a headphone input that may provide a connection to an external speaker and/or headphones.

Returning to FIG. 4, computer 30C may represent another embodiment of electronic device 10 of FIG. 1. The computer 30C may be any computer, such as a desktop, server, or laptop computer, but may also include a standalone media player or video game console. For example, computer 30C may be Apple Inc

Or other similar device. It should be noted that the computer 30C may also represent a Personal Computer (PC) of another manufacturer. A similar housing 36 may be provided to protect and enclose the internal components of the computer 30C, such as the dual-layer display 18. In certain embodiments, a user of computer 30C may interact with computer 30C using a variety of peripheral input devices, such as a keyboard 22 or mouse 38, which may be connected to computer 30C via a wired I/O interface and/or a wireless I/O interface 24.

Similarly, FIG. 5 illustrates another embodiment of the electronic device 10 of FIG. 1 that may be configured to perform using the techniques described hereinAn operative wearable electronic device 30D. For example, the wearable electronic device 30D, which may include a wristband 43, may be an Apple of Apple inc

However, in other embodiments, wearable electronic device 30D may include any wearable electronic device such as, for example, a wearable motion monitoring device (e.g., a pedometer, an accelerometer, a heart rhythm monitor), or other device of another manufacturer. The display 18 of the wearable electronic device 30D may include a touch screen (e.g., an LCD, an OLED display, an Active Matrix Organic Light Emitting Diode (AMOLED) display, etc.) that may allow a user to interact with a user interface of the wearable electronic device 30D.

In certain embodiments, as described above, each embodiment of the electronic device 10 (e.g., the laptop 30A, the handheld device 30B, the computer 30C, and the wearable electronic device 30D) may include a transceiver 28, which may include an Orthogonal Frequency Division Multiplexing (OFDM) polar transmitter (e.g., a WLAN OFDM polar transmitter). Indeed, as will be further appreciated, the polar transmitter may include a modulator (e.g., a Digital Signal Processor (DSP), coordinate rotation digital computer (CORDIC) processor) operable to convert information of an incoming in-phase/quadrature (I/Q) component signal (e.g., a cartesian coordinate representation of an incoming data signal) into a corresponding polar amplitude and phase signal (e.g., a polar coordinate representation of an incoming data signal). In particular, as will be further appreciated, the polar modulator of the transmitter may generate a switched polar phase component, wherein the slope of the phase component may be attenuated and/or substantially eliminated to generate a periodic phase component in which any phase error accumulation between individual OFDM data symbols may be reduced or substantially eliminated.

In view of the above, fig. 6 shows a transmitter 44 that may be included as part of the transceiver 28. Although not shown, it should be understood that the transceiver 28 may also include a receiver that may be coupled to the transmitter 44. As shown, the transmitter 44 may receive a signal 45 that may be modulated via a polar modulator 46. In certain embodiments, the transmitter 44 may receive a cartesian coordinate representation of the signal 45, which may include data symbols encoded according to, for example, quadrature in-phase (I) and quadrature (Q) vectors. Thus, when an I/Q signal is converted to an electromagnetic wave (e.g., a Radio Frequency (RF) signal, a microwave signal, a millimeter wave signal), the conversion is generally linear since the I/Q may be band limited. In some embodiments, however, polar modulator 46 may be used to convert the I/Q vector components of signal 45 into a polar coordinate representation of signal 45, where the OFDM data symbols may be encoded according to a magnitude component and a phase component, as shown.

For example, in certain embodiments, the polar modulator 46 may include a Digital Signal Processor (DSP), coordinate rotation digital computer (CORDIC), or other processing device that may be used to process and pre-process the respective cartesian representation of the data symbols (e.g., OFDM symbols) into polar coordinate magnitude and phase components.

As shown in fig. 6, transmitter 44 may also include digital-to-analog converters (DACs) 48A and 48B that may be used to convert (e.g., sample) the polar magnitude and phase components of signal 45 into digital signal components. As further shown, the phase component signal may then be passed to a mixer 52, which may be used to mix (e.g., up-convert or down-convert) the frequency of the polar phase component signal with the frequency of a Local Oscillator (LO)50 to generate, for example, a Radio Frequency (RF) (e.g., f)_{Output of}) The signal is used for transmission. In one embodiment, the polar magnitude component signal may be passed through an amplifier 56 (e.g., an envelope amplifier) that may be used to track and adjust the envelope of the polar magnitude component signal. Finally, the polar magnitude component signal and the polar phase component signal may each be passed to a high-power amplifier (HPA)54 to generate electromagnetic signals at RF frequencies (e.g., Radio Frequency (RF) signals, microwave signals, millimeter-wave signals) for transmission (e.g., via an antenna coupled to transmitter 44).

In some embodiments, because transmitter 44 (e.g., an OFDM polar transmitter) may utilize phase information to modulate (e.g., directly or indirectly) a frequency such as oscillator 50, due to the fact that, for example, from a digital Frequency Command Word (FCW) to an RF frequencyThe accuracy of the conversion of the electromagnetic signal may experience inherent constraints on the accuracy of the modulation. Thus, for example, in one embodiment, the output (e.g., f) of HPA54_{Output of}) Can be generally expressed as:

f_{output of}＝f_{Carrier wave}+f_cmd+f_{Error of the measurement}(f_cmd) Equation (1).

In the formula (1), f_cmdMay represent, for example, a Frequency Command Word (FCW) (e.g., which may include a multiple frequency). Similarly, f_{Error of the measurement}(f_cmd) May include frequency error and, in one embodiment, may include FCWf_cmdIs a linear function of (a). For example, FCWf_cmdLinear error function (e.g. f)_{Error of the measurement}(f_cmd) Can be generally expressed as:

f_{error of the measurement}(f_cmd)≈α·f_cmdEquation (2).

Thus, as will be further appreciated, the polar modulator 46 may infer that accumulation of phase errors between OFDM data symbols may be prevented when each transmitted OFDM data symbol includes a periodic phase based on, for example, equation (1) and equation (2). Thus, based on equation (2), the phase error accumulated during the symbol duration (T) can be expressed generally as:

d_tequation (3) is 0.

Thus, as will be further appreciated, it would be useful to provide a technique to "shape" (e.g., adjust) the phase of the OFDM data symbols in order to reduce the frequency (e.g., f) of the output signal at HPA54_{Output of}) And also the accumulation of phase errors between the various OFDM data symbols that may become apparent at a receiver that may receive the output signal.

Referring now to fig. 7, a plurality of calculation blocks (e.g., calculation blocks 60, 62, 64, and 66) may be provided that may be used to "shape" (e.g., adjust) the phase of OFDM data symbols in order to reduce the accumulation of phase errors between OFDM data symbolsAnd (4) adding. In certain implementations, the calculation blocks 60, 62, 64, and 66 may each comprise a software system, a hardware system, or some combination of software and hardware that may be implemented as part of the polar modulator 54 (e.g., DSP, CORDIC). For example, during operation, a frequency domain (e.g., frequency dependent) signal 58 (e.g., { X })_k}) may be provided to polynomial root computation block 60. In one embodiment, the frequency domain signal 58 (e.g., { X })_k} may comprise, for example, complex fourier coefficients of an OFDM data symbol or signal representation of a stream of OFDM data symbols. The polynomial root computation block 60, in conjunction with a fourier coefficient computation block 62 and a Fast Fourier Transform (FFT) and/or Inverse Fast Fourier Transform (IFFT) block 64, may be used to compute a fourier series representation of the magnitude and phase components. For example, in one embodiment, signal 58 (e.g., { X })_k}) may be expressed as:

in equation (4), x (t) may represent, for example, a time-domain function (e.g., a continuous-time signal) of one or more OFDM data symbols included within an OFDM data signal. In particular, the OFDM data signal may include a Physical Layer Convergence Procedure (PLCP) protocol data unit (PPDU) frame format, which may include approximately 52 subcarriers for each symbol used for data transmission. In the formula (4), f_kMay represent the center frequency of the kth subcarrier or tone (e.g., k is the order of subcarriers of the time domain function x (T)) of the time domain function x (T) representing one or more OFDM data symbols, and N may represent the total number of tones or subcarriers, and may be the period T of the time domain function x (T)_sAs a function of (c). Item X, as described above_kMay represent complex coefficients (e.g., complex magnitudes), such as transmitted bits, of a data symbol (e.g., an OFDM data symbol).

In certain embodiments, polynomial root computation block 60 may then transform signal 58 (e.g., continuous signal x (t) of equation (4)) from the time domain to the Z domain to characterize signal 58, or more particularly, the poles and zeros of signal 58, by the roots of the function. For example, the Z-domain representation of signal 58 (e.g., the continuous signal x (t) of equation (4)) may be expressed as:

in certain embodiments, once the polynomial root computation block 60 transforms a signal (e.g., the continuous signal x (t) of equation (2)) from the time domain into the Z domain, the polynomial root computation block 60 may then compute the zero point of the signal 58 (e.g., the Z-domain representation of the continuous signal x (t) of equation (4)) based on, for example, algebraic basic theorem. Thus, the Z-domain representation x (Z) of signal 58 can then be expressed as:

as shown in equation (6), the term { a }_mAnd { b }and_mMay respectively represent, for example, unit circles (e.g., therein)

And graphically represented as circles of radius about 1 in the real and imaginary planes) and the inside and outside Z-domain represents the zero point of x (Z) (e.g., the continuous signal x (t) corresponding to equation (2)). In other implementations, the polynomial root computation block 60 may compute the zero point { a ] of the Z-domain representation x (Z) (e.g., equation (4)) by generating an adjoint matrix of the Z-domain representation x (Z) (e.g., equation (4)) via QR factorization, for example_mAnd { b }and_m}。

In some embodiments, once the zero point a is calculated by the polynomial root calculation block 60_mAnd { b }and_mThe polynomial root computation block 60 may then zero the zero points a_mAnd { b }and_mIt is passed to a fourier series calculation block 62. The Fourier series calculation block 62 may then utilize the zero point { a }_mAnd { b }and_mCalculates fourier coefficients corresponding to each of k subcarriers of the OFDM signal. In particular, the fourier series computation block 62 may first compute the logarithm of the Z-domain representation x (Z) (e.g., equation (4)), which may be expressed as:

then the term of equation (7) is executed

And

the FFT block 68 may then generate the in-phase component based on, for example, the logarithm of the Z-domain representation x (Z) (e.g., equation (5)). In particular, FFT and/or IFFT blocks 64 may be used to perform one or more Fast Fourier Transforms (FFTs) and/or Inverse Fast Fourier Transforms (IFFTs) to, for example, compute one or more Discrete Fourier Transforms (DFT) and/or Inverse Discrete Fourier Transforms (IDFTs) on signals 58. For example, based on equation (7), FFT and/or IFFT block 64 may generate the following expression for the phase component:

in some embodiments, as can be appreciated from equation (8), the polar modulator 46 may derive a term that when representing the slope of the phase (e.g., such as

) Becomes a value of about 0 or more appropriately when the slope term (e.g., when

When and/or

Becomes a value of 0 (e.g., when

And/or

Time), the phase component of a given OFDM data symbol may become periodic with a period T_s. Thus, the polar modulator 46 (e.g., DSP, CORDIC) mayGenerating a converted polar phase component, wherein the slope M of the phase component_iAnd/or slope term

May be attenuated or substantially eliminated. In this way, polar modulator 46 may generate a periodic phase component based on, for example, a Carrier Frequency Offset (CFO) (e.g., f)_{Error of the measurement}) And/or the calculated FCW f_cmd(e.g. f)_{Error of the measurement}(f_cmd) Conversion to an output frequency (e.g. f)_{Output of}) Any phase error accumulation between the various OFDM data symbols of (a) may be reduced or substantially eliminated. That is, the polar modulator 46 may "shape" (e.g., adjust the slope or iteratively adjust the slope such that the slope is adjusted) the slope of the phase component of each OFDM data symbol

And/or

) In order to reduce or substantially eliminate the accumulation of phase errors between individual OFDM data symbols that may otherwise become distorted when the output frequency signal is received, e.g., at a receiver in communication with the transmitter 44.

Further, in some embodiments, since transmitter 44 may be sensitive to frequency errors, frequency offset (e.g., f)_{Error of the measurement}) Also by determining, for example, T_sThe phase difference between the same samples or subcarriers of a particular training field (e.g., the legacy long training field (L-LTF)) of a PPDU of a second-separated OFDM signal is estimated as follows:

in formula (9), S_{Output of}[n]May represent, for example, a discrete-time output signal (e.g., at the output of amplifier 54), and S_{Output of}[n-N_FTT]May represent, for example, an offset of N_FTTThe complex conjugate of the discrete-time output signal. As can be appreciated, when the transmitter is in use44 at the calculated FCW f_cmd(e.g. f)_{Error of the measurement}(f_cmd) Conversion to output frequency (e.g. f)_{Output of}) When experiencing distortion (e.g., CFO or doppler shift), the linear slope of the phase (e.g., unwrapped phase) for a given OFDM data symbol may not be periodic, thus possibly causing the distortion to be translated into a frequency offset. However, because the techniques disclosed herein may ensure periodicity of the phase component of each of the training field OFDM data symbols by attenuating or substantially nulling the slope of the phase of the individual OFDM data symbols, the overall OFDM data transmission may be significantly more robust and accurate. As further shown in FIG. 7, the logarithm of the magnitude component (e.g., { log | a })_n| and) and phase components (e.g., of

) May then each be passed to a base-2 logarithmic sum and window block 66 to, for example, equalize or limit the logarithm of the magnitude component (e.g., { log | a })_n| and) and phase components (e.g., of

) And generates a time-domain transformed phase component (e.g.

) And magnitude component (e.g. a)_n) To be recombined and transmitted.

For example, fig. 8 shows a phase diagram 67, which shows a periodic phase component signal 68. In particular, in one embodiment, the phase component signal 68 as shown may comprise a discrete time signal, which may correspond to the phase component signal expressed in equation (8) above. As further shown, any slope of the phase component signal 68 is attenuated or substantially nullified using one or more available bins within the OFDM symbol spectrum, and thus the phase component signal 68 is depicted as periodic. Phase diagram 67 also shows the elimination of any phase error accumulation between OFDM symbols by "shaping" the slope of phase component signal 68 to generate periodic phase component signal 68 using the teachings herein.

Turning now to FIG. 9, there is shownA frequency synthesizer 69 may be included in some embodiments as part of the polar modulator 46 of the transmitter 44. In other embodiments, frequency synthesizer 69 may be included as part of the phase path (e.g., phase branch) of transmitter 44. In particular, in certain embodiments, frequency synthesizer 69 may comprise, for example, a 2-point direct frequency modulation frequency synthesizer, which may be used to perform FCW (e.g., f)_cmd) And a carrier frequency (e.g. f)_{Carrier wave}) Thus compensating for CFO (e.g. f)_{Error of the measurement}) For example, during operation, the data signal 58 may be provided to the pulse filter 70 to filter the signal 58. Similarly, FCW (e.g., f)_cmd) The input may be provided to a Reference Phase Accumulator (RPA)72, which may also receive a reference frequency input (e.g., f via a time To Digital Converter (TDC) 74)_ref). The TDC 74 may be used, for example, to generate one or more clock and reference frequency inputs (e.g., f) representative of the synthesizer 69_ref) And provides the value of the phase difference to RPA 72.

The phase difference value may also be provided to the mixer 76 to multiply the phase difference value by the generated DCO period normalization value. Phase detector 78 may then sum the individual phase values and generate a total phase signal (e.g.

) To be provided to the loop filter 80. The summed phase signal may then be passed to a Digitally Controlled Oscillator (DCO) gain normalization block 82 to, for example, modulate or tune the summed phase signal (e.g., shape the slope of the summed phase signal), and then be modulated or tuned again via the DCO 84 to generate a carrier frequency signal. In one embodiment, as further shown, the carrier frequency signal may be fed back to phase detector 78 via oscillator phase accumulator 86 and sampler 88, thus allowing DCO gain normalization block 82 to continuously adjust the summed phase signal. The carrier frequency signal may then be passed to a Digital Phase Accumulator (DPA)90 to generate an RF signal for transmission.

Turning now to FIG. 10, a flow diagram is shown illustrating one embodiment of a process 100The process 100 is used to "shape" (e.g., adjust) the slope of the phase component of an OFDM data symbol to reduce the likelihood of being at the output frequency (e.g., f) due to, for example, the use of the polar modulator 46 included within the transceiver 28 shown in fig. 1_{Output of}) The phase error accumulation between the individual OFDM data symbols becomes significant. Process 100 may include code or instructions stored in a non-transitory machine readable medium (e.g., memory 14) and executed, for example, by the one or more processors 12 and/or polar modulator 46 included within system 10 and shown in fig. 6. The process 100 may begin with the polar modulator 46 receiving (block 102) a cartesian representation of a data signal. For example, polar modulator 46 may receive signal 45 which may include a cartesian coordinate representation of OFDM data symbols encoded according to orthogonal I/Q vectors, for example.

The process 100 may then continue with the polar modulator 46 calculating (block 104) one or more roots of the phase component of the data signal. For example, as described above with reference to fig. 7, the polar modulator 46 may calculate the zero point of the phase component. The process 100 may then continue with the polar modulator 46 determining (block 106) the period of the phase component based on the calculated root (e.g., zero). Specifically, as previously described, the polar modulator 46 may derive a term that is indicative of the slope of the phase (e.g., as

) Becomes a value of 0 or when

And/or

The phase component of a given OFDM data symbol may become periodic and have a period T_s. The process 100 may then end with the polar modulator 46 adjusting (block 108) the slope of the phase component based on the period to reduce or eliminate error in the phase component of the OFDM data symbol. For example, the polar modulator 46 may "shape" the slope of the phase component such that the slope is formed by the slope of each OFDM data symbol

Characterised so as to reduce or eliminate otherwise at the output frequency (e.g. f)_{Output of}) Such as any phase error accumulation between the various OFDM data symbols that may become distorted when received at a receiver in communication with the transmitter 44.

FIG. 11 shows a graph 110 demonstrating the phase slope shaping technique disclosed herein at K without use_DCOEstimating the change in the performance of the WLAN OFDM data signal 112 in error percentage according to the error (e.g., Error Vector Magnitude (EVM)), at K when using the OFDM data symbol phase slope shaping techniques disclosed herein_DCOThe performance of the WLAN OFDM data signal 114 in estimating the error percentage varies according to the EVM. As shown, the WLAN OFDM data signal 112 may experience substantial distortion (e.g., as shown by a sharp rise), for example, due to frequency offset errors (e.g., f) that may be caused by tuning inconsistencies and/or doppler shift or shifts in the carrier frequency signal(s)_{Error of the measurement}). On the other hand, by shaping or adjusting the slope of the phase component as described herein, any phase error accumulation between the various OFDM data symbols may be reduced or eliminated, as illustrated by the substantially linear WLAN OFDM data signal 114.

While specific embodiments have been described above by way of example, it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.

Claims

1. A method for reducing phase error, comprising:

receiving, via a processor of a transmitter, an incoming data signal, wherein the data signal comprises an in-phase (I) component and a quadrature (Q) component;

calculating one or more roots of a first function representing a phase component of the data signal;

computing a second function representing the phase component based at least in part on the one or more roots;

deriving a periodicity of the phase component based at least in part on the second function;

adjusting a value of a slope of the phase component based at least in part on the periodicity of the phase component, wherein adjusting the value of the slope comprises reducing an error of the phase component;

recombining a magnitude component and the phase component into a polar coordinate transmission signal after said adjusting the value of the slope; and

sending the polar coordinate transmission signal via the transmitter.

2. The method of claim 1, wherein receiving the incoming data signal comprises receiving a cartesian coordinate representation of the data signal.

3. The method of claim 1, wherein receiving the incoming data signal comprises receiving a plurality of Orthogonal Frequency Division Multiplexing (OFDM) data symbols.

4. The method of claim 1, wherein computing the one or more roots of the first function comprises computing one or more zeros of the first function in the frequency domain.

5. The method of claim 1, wherein adjusting the value of the slope comprises adjusting the value of the slope to be equal to a total number of subcarriers N of the data signal divided by 2, and wherein N is greater than 0.

6. The method of claim 1, wherein adjusting the value of the slope comprises generating a periodic phase signal component.

7. The method of claim 1, wherein adjusting the value of the slope comprises adjusting a value of a slope for each of a plurality of Orthogonal Frequency Division Multiplexing (OFDM) data symbols.

8. The method of claim 1, wherein adjusting the value of the slope comprises adjusting the value of the slope to attenuate the slope.

9. The method of claim 1, wherein adjusting the value of the slope comprises reducing a Carrier Frequency Offset (CFO) as the error.

10. An electronic device, comprising:

a processor; and

a memory having instructions stored thereon that, when executed by the processor, cause the processor to perform the method of any of claims 1-9.

11. A non-transitory machine readable medium having instructions stored thereon, which when executed by a processor, cause the processor to perform the method of any of claims 1-9.

12. An apparatus comprising means for performing the method of any of claims 1-9.

13. An electronic device, comprising:

a transmitter, the transmitter comprising:

a polar modulator device configured to:

receiving a first signal comprising Orthogonal Frequency Division Multiplexing (OFDM) data symbols encoded according to an in-phase/quadrature (I/Q) vector;

adjusting a slope of a phase component of the first signal based at least in part on a periodicity of the phase component, wherein adjusting the slope of the phase component comprises reducing an error of the phase component;

combining a magnitude component and the phase component of the first signal into a polar coordinate transmission signal; and

an amplifier configured to generate an electromagnetic signal for transmission based on the polar coordinate transmission signal.

14. The electronic device of claim 13, wherein the second signal comprises a Physical Layer Convergence Procedure (PLCP) protocol data unit (PPDU) frame format having approximately 52 subcarriers, and wherein the OFDM data symbols are stored into a first subset of the approximately 52 subcarriers.

15. The electronic device of claim 14, wherein the second subset of the approximately 52 subcarriers comprises a preamble of a PPDU frame format, and wherein the preamble comprises a plurality of long legacy training field (L-LTF) symbols and a plurality of short legacy training field (S-LTF) symbols.

16. The electronic device of claim 15, wherein the polar modulator device is configured to adjust the slope of the phase component by adjusting a slope of each of the plurality of L-LTF symbols.

17. The electronic device of claim 13, wherein the polar modulator device is configured to adjust the slope of the phase component by increasing the periodicity of the phase component.

18. The electronic device of claim 13, wherein the polar modulator device is configured to adjust a slope of a phase component of each of the OFDM data symbols.

19. The electronic device of claim 18, wherein the polar modulator device is configured to adjust the slope of the phase component of each of the OFDM data symbols to reduce accumulation of phase error components between each of the OFDM data symbols.

20. The electronic device of claim 13, wherein the polar modulator device is configured to adjust the value of the slope to reduce an offset error generated between a Frequency Command Word (FCW) and a carrier frequency as a phase error.

21. A method for reducing phase error, comprising:

receiving, via a processor of a transmitter, an incoming Orthogonal Frequency Division Multiplexing (OFDM) signal data signal;

deriving, via the processor of the transmitter, a phase component of the OFDM signal, wherein the OFDM signal includes N subcarriers;

deriving a slope M of the phase component_i；

Adjusting the slope M of the phase component based at least in part on a periodicity of the phase component_iWherein the slope M is adjusted_iIncluding reducing the error of the phase component;

combining the phase and magnitude components to generate a polar form OFDM transmission signal; and

sending the polar form OFDM transmission signal via the transmitter.

22. The method of claim 21, wherein deriving the slope of the phase component comprises deriving a slope

And wherein N comprises a total number of subcarriers of the OFDM signal and i comprises a discrete time interval of the OFDM signal, and wherein the total number of subcarriers is greater than 0.

23. The method of claim 21, wherein deriving the phase component of the OFDM signal comprises deriving a phase component for each of a plurality of OFDM symbols encoded within the OFDM signal.

24. The method of claim 21, wherein deriving the phase component of the OFDM signal comprises deriving a phase component expressed as:

25. the method of claim 24, wherein adjusting the slope of the phase component comprises adjusting the slope to a value

26. The method of claim 24, wherein adjusting the slope of the phase component comprises adjusting the slope to a value

27. A method according to claim 21, comprising deriving a magnitude component of the OFDM signal.

28. The method of claim 21, wherein deriving the slope of the phase component comprises deriving a periodic phase component error, and wherein the periodic phase component error is expressed as follows:

29. an electronic device, comprising:

a processor; and

a memory having instructions stored thereon that, when executed by the processor, cause the processor to perform the method of any of claims 21-28.

30. A non-transitory machine readable medium having instructions stored thereon, which when executed by a processor, cause the processor to perform the method of any of claims 21-28.

31. An apparatus comprising means for performing the method of any of claims 21-28.