Methods and devices for “shaping” a slope of the phase component of ofdm data symbols in order to decrease an accumulation of phase error are provided. By way of example, a method includes receiving an incoming data signal via a processor of a transmitter. The method further includes computing 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 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.
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18. A method, comprising: receiving an incoming orthogonal frequency division multiplexing (ofdm) signal data signal via a processor of a transmitter; deriving a phase component of the ofdm signal via the processor of an electronic device the transmitter, wherein the ofdm signal comprises N number of subcarriers; deriving a slope mi of the phase component; adjusting the slope mi of the phase component based at least in part on a periodicity of the phase component, wherein adjusting the slope mi comprises reducing or substantially eliminating an error of the phase component; combining the phase component and an amplitude component to generate a polar form ofdm transmission signal; and transmitting the polar form ofdm transmission signal via the transmitter.
10. An electronic device, comprising:
a transmitter, comprising:
a polar modulator device configured to:
receive a first signal comprising orthogonal frequency division multiplexing (ofdm) data symbols encoded according to in-phase/quadrature (I/Q) vectors;
adjust 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 or substantially eliminating an error of the phase component;
combine an amplitude component of the first signal and the phase component into a polar coordinate transmission signal; and
an amplifier configured to generate an electromagnetic signal based on the polar coordinate transmission signal for transmission.
1. A method, comprising: receiving an incoming data signal via a processor of a transmitter, wherein the data signal comprises an in-phase (I) component and a quadrature (Q) component; computing 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; and 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 or substantially eliminating an error of the phase component; recombining an amplitude component and the phase component into a polar coordinate transmission signal following the adjustment of the value of the slope; and transmitting the polar coordinate transmission signal via the transmitter.
2. The method of
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
8. The method of
9. The method of
11. The electronic device of
12. The electronic device of
13. The electronic device of
14. The electronic device of
15. The electronic device of
16. The electronic device of
17. The electronic device of
19. The method of
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.
20. The method of
21. The method of
22. The method of
23. The method of
25. The method of
εrφ(T)=φ(T)−φcmd(T)=∫0Tferror(fcmd(t))·dt≈α·∫0Tfcmd(t)·dt=0. |
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.
Transmitters and receivers are commonly included in various electronic devices, and particularly, portable electronic devices such as, for example, phones (e.g., mobile and cellular phones, cordless phones, personal assistance devices), computers (e.g., laptops, tablet computers), internet connectivity routers (e.g., Wi-Fi routers or modems), radios, televisions, or any of various other stationary or handheld devices. One type of transmitter, known as a wireless transmitter, may be used to generate a wireless signal to be transmitted by way of an antenna coupled to the transmitter. Specifically, the wireless transmitter is generally used to wirelessly communicate data over a network channel or other medium (e.g., air) to one or more receiving devices.
The wireless transmitters may generally include subcomponents such as, for example, an oscillator, a modulator, one or more filters, and a power amplifier. Furthermore certain data modulation techniques that may be implemented by wireless transmitters may include a modulation of in-phase (I)/quadrature (Q) time samples of a signal into amplitude and phase signals. However, because certain wireless transmitters may also utilize phase information to modulate the frequency of one or more oscillators included within the wireless transmitters, the output signal, and, by extension, the information to be transmitted may become distorted. It may be useful to provide more advanced and improved wireless transmitters.
A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below.
Various embodiments of the present disclosure may be useful in “shaping” a slope of the phase component of orthogonal frequency division multiplexing (OFDM) data symbols in order to decrease an accumulation of phase error. By way of example, a method includes receiving an incoming data signal via a processor of a transmitter. The method further includes computing 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 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 refinements of the features noted above may exist in relation to various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, 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 disclosure 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.
The patent or application file 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 this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:
One or more specific embodiments of the present disclosure will be described below. These described embodiments are only examples of the presently disclosed techniques. Additionally, 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. Additionally, 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 relates to techniques for increasing frequency modulation accuracy in orthogonal frequency division multiplexing (OFDM) polar transmitters. For example, the present techniques may include providing a technique to “shape” the phase of OFDM signal symbols in order to decrease an accumulation of phase error between OFDM symbols that may become apparent due to, for example, the translation of an initial calculated frequency command word (FCW) to the frequency of an oscillator of the OFDM polar transmitter. The present techniques may further include a method to detect the offset between the OFDM polar transmitter and a receiver. For example, the frequency offset may be estimated by finding the phase difference between identical samples of a specific training field for carrier frequency offset estimation. Indeed, the present techniques of preventing phase error accumulation may be particularly useful for transmission standards which apply carrier frequency offset estimation algorithms, which may, for example, be based on phase difference between successive symbols.
With the foregoing in mind, a general description of suitable electronic devices that may employ polar transmitters and are useful in “shaping” a slope of the phase component of OFDM data symbols in order to decrease an accumulation of phase error will be provided below. Turning first to
By way of example, the electronic device 10 may represent a block diagram of the notebook computer depicted in
In the electronic device 10 of
In certain embodiments, the display 18 may be a liquid crystal display (LCD), which may allow users to view images generated on the electronic device 10. In some embodiments, the display 18 may include a touch screen, which may allow users to interact with a user interface of the electronic device 10. Furthermore, it should be appreciated 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., pressing a button to increase or decrease a volume level). The I/O interface 24 may enable electronic device 10 to interface with various other electronic devices, as may the network interfaces 26. The network interfaces 26 may include, for example, interfaces for a personal area network (PAN), such as a Bluetooth network, for a local area network (LAN) or wireless local area network (WLAN), such as an 802.11x Wi-Fi network, and/or for a wide area network (WAN), such as a 3rd generation (3G) cellular network, 4th generation (4G) cellular network, or long term evolution (LTE) cellular network. The network interface 26 may also include interfaces for, for example, broadband fixed wireless access networks (WiMAX), mobile broadband Wireless networks (mobile WiMAX), asynchronous digital subscriber lines (e.g., ADSL, VDSL), digital video broadcasting-terrestrial (DVB-T) and its extension DVB Handheld (DVB-H), ultra Wideband (UWB), alternating current (AC) power lines, and so forth.
In certain embodiments, to allow the electronic device 10 to communicate over the aforementioned wireless networks (e.g., Wi-Fi, WiMAX, mobile WiMAX, 4G, LTE, and so forth), the electronic device 10 may include a transceiver 28. The transceiver 28 may include any circuitry that may be useful in both wirelessly receiving and wirelessly transmitting 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 into a single unit, or, in other embodiments, the transceiver 28 may include a transmitter separate from the receiver. For example, as noted above, the 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, and 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 modulation technique or scheme in which a transmission channel may be divided into a number of orthogonal subcarriers or subchannels to increase data transmission efficiency. Further, in some embodiments, the transceiver 28 may be integrated as part of the network interfaces 26. As further illustrated, the electronic device 10 may include a power source 29. The power source 29 may include any suitable source of power, such as a rechargeable lithium polymer (Li-poly) battery and/or an alternating current (AC) power converter.
In certain embodiments, the electronic device 10 may take the form of a computer, a portable electronic device, a wearable electronic device, or other type of electronic device. Such computers may include computers that are generally portable (such as laptop, notebook, and tablet computers) as well as computers that are generally used in one place (such as conventional desktop computers, workstations and/or servers). In certain embodiments, the electronic device 10 in the form of a computer may be a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, or Mac Pro® available from Apple Inc. By way of example, the electronic device 10, taking the form of a notebook computer 30A, is illustrated in
The handheld device 30B may include an enclosure 36 to protect interior components from physical damage and to shield them from electromagnetic interference. The enclosure 36 may surround the display 18, which may display indicator icons 39. The indicator icons 38 may indicate, among other things, a cellular signal strength, Bluetooth connection, and/or battery life. The I/O interfaces 24 may open through the enclosure 36 and may include, for example, an I/O port for a hard wired connection for charging and/or content manipulation using a standard connector and protocol, such as the Lightning connector provided by Apple Inc., a universal service bus (USB), or other similar connector and protocol.
User input structures 42, in combination with the display 18, may allow a user to control the handheld device 30B. For example, the input structure 40 may activate or deactivate the handheld device 30B, the input structure 42 may navigate user interface to a home screen, a user-configurable application screen, and/or activate a voice-recognition feature of the handheld device 30B, the input structures 42 may provide volume control, or may toggle between vibrate and ring modes. The input structures 42 may also include a microphone may obtain a user's voice for various voice-related features, and a speaker may enable audio playback and/or certain phone capabilities. The input structures 42 may also include a headphone input may provide a connection to external speakers and/or headphones.
Turning to
Similarly,
In certain embodiments, as previously noted above, each embodiment (e.g., notebook computer 30A, handheld device 30B, computer 30C, and wearable electronic device 30D) of the electronic device 10 may include a transceiver 28, which may include an orthogonal frequency division multiplexing (OFDM) polar transmitter (e.g., WLAN OFDM polar transmitter). Indeed, as will be further appreciated, the polar transmitter may include a modulator (e.g., digital signal processor (DSP), coordinate rotation digital computer (CORDIC) processor) that may be used to translate the information of an incoming in-phase/quadrature (I/Q) component signal (e.g., Cartesian coordinate representation of an incoming data signal) into respective polar amplitude and phase signals (e.g., polar coordinate representation of the an incoming data signal). Specifically, as will be further appreciated, the polar modulator of the transmitter may generate a translated polar phase component in which the slope of the phase component may be attenuated and/or substantially annulled to generate a periodic phase component in which any phase error accumulation between the individual OFDM data symbols may be reduced or substantially eliminated.
With the foregoing in mind,
For example, in certain embodiments, the polar modulator 46 may include a digital signal processor (DSP), a coordinate rotation digital computer (CORDIC), or other processing device that may be used to process and preprocess the individual Cartesian represented data symbols (e.g., OFDM symbols) into polar coordinate amplitude and phase components.
As further depicted in
In some embodiments, because the transmitter 44 (e.g., OFDM polar transmitter) may utilize phase information to modulate (e.g., directly or indirectly) the frequency of, for example, the oscillator 50, an inherent constraint on the modulation accuracy may be experienced due to the accuracy of the translation from, for example, a digital frequency command word (FCW) to an actual electromagnetic signal at the RF frequency. Thus, in one embodiment, for example, the frequency of the output (e.g., fout) of the HPA 54 may be generally expressed as:
fout=fcarrier+fcmd+ferror(fcmd) equation (1).
In equation (1), fcmd may represent, for example, a frequency command word (FCW) (e.g., which may include frequency multiplication ratio). Similarly, ferror(fcmd) may include the frequency error, and, in one embodiment, may include a linear function of the FCW fcmd. For example, the linear error function of the of the FCW fcmd (e.g., ferror(fcmd)) may be generally expressed as:
ferror(fcmd)≈α·fcmd equation (2).
Accordingly, as will be further appreciated, the polar modulator 46 may deduce based on, for example, equations (1) and (2) that an accumulation of phase error between OFDM data symbols may be prevented when each transmitted OFDM data symbol includes a periodic phase. Thus, based on equation (2), the phase error accumulated during a symbol duration (T) may be generally expressed as:
Thus, as will be further appreciated, it may be useful provide a technique to “shape” (e.g., adjust) the phase of the OFDM data symbols in order to decrease an accumulation of phase error between the individual OFDM data symbols that may become apparent in the frequency (e.g., fout) of the output signal of the HPA 54 and also at a receiver that may receive the output signal.
Referring now to
In equation (4), x(t) may represent, for example, a time-domain function (e.g., continuous time signal) of one or more OFDM data symbols included within an OFDM data signal. Specifically, an OFDM data signal may include a physical layer convergence procedure (PLCP) protocol data unit (PPDU) frame format, which may include approximately 52 subcarriers per symbol for data transmission. In equation (4), fk may represent the central frequency of the kth subcarrier or tone (e.g., k is the order of the 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 a total numbers of tones or subcarriers, and may be a function of a period Ts of the time-domain function x(t). As noted above, the term Xk may represent the complex coefficients (e.g., complex amplitude) of, for example, transmitted bits of the data symbols (e.g., OFDM data symbols).
In certain embodiments, the polynomial roots calculation block 60 may then transform the signal 58 (e.g., continuous signal x(t) of equation (4)) from the time-domain into the Z-domain to characterize the signal 58 in terms of the roots of the function, or more specifically, the poles and zeroes of the signal 58. For example, the Z-domain representation of the signal 58 (e.g., continuous signal x(t) of equation (4)) may be expressed as:
In certain embodiments, once the polynomial roots calculation block 60 transforms the signal 58 (e.g., continuous signal x(t) of equation (2)) from the time-domain into the Z-domain, the polynomial roots calculation block 60 may then calculate the zeroes of the signal 58 (e.g., the Z-domain representation of the continuous signal x(t) of equation (4)) based on, for example, the fundamental theorem of algebra. Thus, the Z-domain representation x(z) of the signal 58 may be then expressed as:
As illustrated in equation (6), the terms {am} and {bm} may represent, for example, the zeros of the Z-domain representation x(z) (e.g., corresponding to the continuous signal x(t) of equation (2)) inside and outside of the unit circle (e.g., where
and graphically represented as a circle in the real and imaginary plane having a radius of approximately 1), respectively. In other embodiments, the polynomial roots calculation block 60 may calculate the zeroes {am} and {bm} of the Z-domain representation x(z)(e.g., equation (4)) by, for example, generating a companion matrix of the Z-domain representation x(z)(e.g., equation (4)) through QR factorization.
In certain embodiments, once the polynomial roots calculation block 60 calculate the zeroes {am} and {bm}, the polynomial roots calculation block 60 may then pass the zeroes {am} and {bm} to the Fourier series calculation block 62. The Fourier series calculation block 62 may then utilize the zeroes {am} and {bm} to calculate the Fourier coefficients corresponding to each of the k subcarriers of the OFDM signal. Specifically, the Fourier series calculation block 62 may first calculate the logarithm of the of the Z-domain representation x(z)(e.g., equation (4)), which may be expressed as:
Then, performing a power series expansion of the terms Σm=1M
In certain embodiments, as may be appreciated from equation (8), the polar modulator 46 may derive that the phase component of a given OFDM data symbol may become periodic with a period Ts when the term representing the slope of the phase
becomes a value of approximately 0, or, more aptly, when the slope term
Mi and/or
becomes a value of 0
Thus, the polar modulator 46 (e.g., DSP, CORDIC) may generate a translated polar phase component in which the slope Mi and/or slope term
of the phase component may be attenuated or substantially annulled. In this way, the polar modulator 46 may generate a periodic phase component in which any phase error accumulation between the individual OFDM data symbols based on, for example, carrier frequency offset (CFO) (e.g., ferror) and/or the translation of the calculated FCW fcmd (e.g., ferror(fcmd)) into the output frequency (e.g., fout) may be reduced or substantially eliminated. That is, the polar modulator 46 may “shape” the slope
of the phase component of the individual OFDM data symbols in order to reduce or substantially eliminate the accumulation of phase error between the individual OFDM data symbols that may otherwise become distorted when the output frequency signal is received, for example, at a receiver in communication with the transmitter 44.
Furthermore, in certain embodiments, due to the fact that the transmitter 44 may be sensitive to frequency errors, the frequency offset (e.g., ferror) may be also estimated by determining the phase difference between identical samples or subcarriers of a specific training field (e.g., legacy long training field (L-LTF)) of, for example, the PPDU of the OFDM signal Ts seconds apart, as expressed by:
In equation (9), Sout [n] may represent, for example, a discrete-time output signal (e.g., at the output of the amplifier 54), while S*out[n−NFTT] may represent, for example, a complex conjugate of the discrete-time output signal time shifted by NFTT. As may be appreciated, when the transmitter 44 experiences distortion (e.g., CFO or Doppler shift) in the translation of the calculated FCW fcmd (e.g., ferror(fcmd)) into the output frequency (e.g., fout), the linear slope of the phase of a given OFDM data symbol (e.g., unwrapped phase) may not be periodic, and may thus allow distortion to be translated into frequency offset. However, because the presently disclosed techniques may ensure periodicity in the phase component of each of the training field OFDM data symbols by attenuating or substantially annulling the slope of the phase of the individual OFDM data symbols, the overall OFDM data transmission may be substantially more robust and accurate. As further illustrated in
For example,
Turning now to
The phase difference value may be also provided to a mixer 76 to multiply the phase difference value by a generated DCO period normalization value. A phase detector 78 may then sum these various phase values, and generate a total phase signal (e.g., φn[k]) to provide to a loop filter 80. The summed phase signal may be then 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) before being modulated or tuned once more via a DCO 84 to generate a carrier frequency signal. In one embodiment, as further illustrated, the carrier frequency signal may be fed back to the phase detector 78 via an oscillator phase accumulator 86 and a sampler 88, and may thus allow the DCO gain normalization block 82 to constantly adjust the summed phase signal. The carrier frequency signal may be then passed to a digital phase accumulator (DPA) 90 to generate an RF signal for transmission.
Turning now to
The process 100 may then continue with the polar modulator 46 computing (block 104) one or more roots of a phase component of the data signal. For example, as discussed above with respect to
becomes a value of 0, or when
The process 100 may then conclude with the polar modulator 46 adjusting (block 108) a slope of the phase component based on the period to reduce or eliminate an error of the phase component of the OFDM data symbols. For example, the polar modulator 46 may “shape” the slope of the phase component, such that the slope is characterized by
of the individual OFDM data symbols in order to reduce or eliminate any accumulation of phase error between the individual OFDM data symbols that may otherwise become distorted when the output frequency signal (e.g., fout) is received, for example, at a receiver in communication with the transmitter 44.
The specific embodiments described above have been shown by way of example, and 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.
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