text:
Envoy calls on U.N. council to impose measures for failure to follow peace plan
Kofi Annan, the special envoy whose peace plan for ending the increasingly violent conflict in Syria is paralyzed and at risk of collapse, asked the U.N. Security Council on Wednesday to threaten the Syrian government and the rebels with consequences for failure to comply.
Annan made his request as new evidence emerged of fracturing in the government of President Bashar Assad, which has faced a slow but growing rash of defections and desertions. The latest was Syria's ambassador to Iraq, Nawaf Fares, who issued a statement reported by Al-Jazeera and Reuters that he had resigned and had renounced his membership in Assad's Syrian Baath Party.
"I urge all honest members of this party to follow my path because the regime has turned it to an instrument to kill people and their aspiration to freedom," Fares said in the statement from an unidentified location. There was no immediate comment from the Syrian government on the defection, the first by a Syrian ambassador since the uprising broke out in March 2011.
The Security Council has already passed two resolutions that request compliance with Annan's plan but do not carry coercive pressure. "You should insist on implementation of your decisions, and send a message to all that there will be consequences for noncompliance," Annan, who represents the U.N. and Arab League, told the council.
Annan did not specify that the council should threaten measures under Chapter 7 of its charter, which authorizes economic sanctions, and if necessary, military action, as was done in the Libyan conflict last year. But his request quickly laid bare the makings of a potential confrontation among the five permanent members of the Security Council, whose effort to speak in a unified way on the Syria conflict has often masked serious divisions.
Representatives of the United States, Britain and France said they would address Annan's request with a resolution that included Chapter 7 sanctions. But Russia and China, which have twice blocked such coercive measures, were expected to resist. Russia, the Syrian government's most important foreign supporter, circulated its own draft resolution that does not include the Chapter 7 provision.
Alexander Pankin, the ranking Russian diplomat at the Security Council, said that Annan had "asked that the council speak in a united and single voice. And there will be consequences. But consequences does not mean under a certain chapter or certain article."
Annan, who spoke to the council by video link from his Geneva office after having visited Syria, Iran and Iraq, also said that Assad was open to the idea of an interlocutor between him and the political opposition, which presumably would allow a dialogue without the two sides' having to directly talk to each other.
It was not clear whether Syria's array of anti-Assad groups, who have said they would not negotiate with Assad, would agree to such an idea.
Annan addressed the council less than two weeks before the authorization of the 300-member observer mission in Syria, assigned to monitor a cease-fire and other provisions of the plan, will expire. The observers, who are unarmed and have no enforcement authority, suspended work a month ago because the Syrian government and its armed antagonists were ignoring Annan's plan, and the rising violence had made the mission's work too dangerous.


text:
DMV to Internet-less New Yorkers: Get in Line
By Jared Chausow
By Katie Toth
By Elizabeth Flock
City Hid Facts From Feds About Rikers
By Albert Samaha
Flood Wall Street Gets Pepper Sprayed and Arrested
By Anna Merlan
By Jon Campbell
Report Sheds Light on Anti-Muslim Bias
By Jon Campbell
Rikers Island Lawsuits Over Diabetic Care
By Albert Samaha
At best, baseball has always been a metaphor for real life, and an annoying one at that; now it has actually turned into the real thing. Help! I'm trapped inside a bad metaphor and I can't get out.
It all began months ago when the mayor attempted to OK his buddy George Steinbrenner's wishes to move out of the Bronx and build a new stadium in Manhattan with taxpayer dough. However, according to the New York City Independent Budget Office, it would cost 1 billion in tax dollars to build the thing. In return, analysts estimate, new stadiums for both the Mets and the Yanks could be expected to bring an additional $5 million each year to the city in tax revenues. Heythat's not so bad. It would only take about 200 years to make up the shortfall.
The mayor sees no problem in this. It's the Yankees, after all. Peter Vallone sees a real problem with it. He figures that for a lot less money the Yankees can stay where they areinarguably the most beautiful stadium in the countryand spiff up the surroundings. The mayor's men say they can never really fix it up because it's in a dangerous area. Maybe it's dangerous when the Yanks aren't in town, but when they are, the most horrifying thing is those fat guys with "YANKS RULE" written across their naked bellies. And, of course, during playoffs, there's the ever present danger of being run over by a limo.
Anyway, hoping to stop the stadium, the City Council then created a referendum to let the voters decide how they wanted their money spent. That's when the game turned into a war. Vallone claims that to retaliate, Giuliani vetoed and/or cut the council's best proposals and programssuch as delivery of hot meals to 500 homebound elders, library and school programs, affordable senior housing, breast cancer awareness, increased day-care slots, jobs for youth, and foster-care improvement. Talk about strict!
While these cuts only amounted to one percent of the entire city budget, they were a real blow to those affectedand to the council.
To add another nail to the coffin, the mayor created a city charter referendum which wouldby lawsupersede and knock out the Yankee referendum. Whew!
In the meantime the poorwhose life-sustaining programs were being used as leveragewere forgotten in the heat of the game. And that's where the whole mess lay until last week, when the council won one the same day the Yanks lost game two. Justice Douglas McKeon ruled that the City Council had a right to ask the voters whether they wanted to pay for a new stadium in Manhattan. He also threw out the mayor's charter revision referendum, calling it a "virtual charade."
Now we have to suffer through an appeal. The smart money is betting the ruling gets overturned. Did McKeon rule with his heart and not his head? Maybe. The city charter allows revision referendums, and it includes the mayor's right to appoint a charter revision review commission. They in turn can put revisions on the ballot.
This could go on longer than the O.J. trialor at least until term limits kill off some of the players. Meanwhile, in the greater scheme of things, who really cares that George Steinbrenner wants to watch baseball in Manhattan? I can name at least 500 homebound elderly folk who are more concerned about where their next hot meal is coming from than whether George Steinbrenner parks his behind in Manhattan or the Bronx. The professional politicians should be, too.
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subset: commoncrawl


text:
Systems and methods are disclosed to adaptively pre-distort a signal prior to being used by a non-linear circuit, such as a higher power amplifier (at transmit) or a low noise amplifier (at receive). The signal is compared with a feedback signal from the non-linear circuit and a metric is calculated and minimized. The input signal is adaptively changed, such as by varying tap coefficients, until the metric is sufficiently minimized, resulting in a pre-distorted signal that is substantially linear upon passing through the non-linear circuit.
1. A pre-distortion circuit, comprising:
an adder coupled to receive a feedback signal from a non-linear power amplifier and a first signal, wherein the adder generates a difference signal between the feedback signal and the first signal, wherein the first signal is a signal to be transmitted that is time-aligned with the feedback signal;
an adaptive coefficient generator configured to receive the difference signal and a second signal, wherein the second signal is a version of the signal to be transmitted, and wherein the adaptive coefficient generator generates a set of tap coefficients; and
a timing and filter circuit configured to receive the feedback signal and the signal to be transmitted and generate the first signal and receive the tap coefficients and generate a pre-distorted output signal based on a mean square error.
2. The circuit of
3. The circuit of
4. The circuit of
5. The circuit of
6. The circuit of
7. An RF transceiver, comprising:
an adaptive pre-distortion circuit configured to receive an RF signal and a feedback signal and adaptively generate a pre-distortion signal; and
a non-linear circuit configured to receive the pre-distortion signal and provide an amplified linear output signal.
8. The RF transceiver of
9. The RF transceiver of
10. The RF transceiver of
11. The RF transceiver of
12. The RF transceiver of
an adder coupled to receive the feedback signal and a first signal, wherein the adder generates a difference signal between the feedback signal and the first signal, wherein the first signal is a signal to be transmitted that is time-aligned with the feedback signal;
an adaptive coefficient generator configured to receive the difference signal and a second signal, wherein the second signal is a version of the signal to be pre-distorted, and wherein the adaptive coefficient generator generates a set of tap coefficients; and
a timing and filter circuit configured to receive the feedback signal and the signal to be pre-distorted and generate the first signal and receive the tap coefficients and generate the pre-distortion output signal based on a mean square error.
13. The RF transceiver of
14. The RF transceiver of
15. A pre-distortion circuit, comprising:
means for receiving an input signal and a feedback signal from a non-linear circuit;
means for determining a metric between the input signal and the feedback signal;
means for adaptively changing the input signal based on minimizing the metric; and
means for generating a non-linear pre-distorted signal using the adaptively changed input signal, wherein the non-linear pre-distorted signal is input to the non-linear circuit to provide a linear output signal.
16. The pre-distortion circuit of
17. The pre-distortion circuit of
18. A method of pre-distorting an input signal, comprising:
receiving an input signal and a feedback signal from a non-linear circuit;
determining a metric between the input signal and the feedback signal;
adaptively changing the input signal based on minimizing the metric; and
generating a non-linear pre-distorted signal using the adaptively changed input signal, wherein the non-linear pre-distorted signal is input to the non-linear circuit to provide a linear output signal.
19. The method of
20. The method of
This application is a Continuation Application of U.S. patent application Ser. No. 10/704,439, filed Nov. 7, 2003. The contents are hereby incorporated by reference in their entirety.
This invention relates generally to communication systems and, more particularly, to pre-distortion circuitry for use with power amplifiers.
Many types of communication systems use a power amplifier as part of the front end of a transmitter for transmitting RF signals. In some systems, a low noise amplifier (LNA) at the front end of a receiver may be used for receiving RF signals. However, a power amplifier has non-linear distorting characteristics that can cause distortion of the information signal being amplified. The non-linear distorting characteristics of the power amplifier can impact the instantaneous amplitude and phase of the signal significantly. Furthermore, non-linearity within the RF components can introduce distortion in the signal and reduced SNR or poorer performance at the receiver. In wireless systems, non-linearity in the power amplifier at transmission can introduce intermodulation distortion which can result in spectral emissions in the adjacent channels. Typically, tight specifications in terms of spectral masks are provided by Standards Committees and/or Government bodies, which put a maximum limit to such spurious, out-of-band emissions for compliant transceivers. Therefore, it is desirable to provide a linear signal out of the power amplifier.
One type of method to linearize the power amplifier output signal is to "pre-correct" the signal being input to the amplifier, also known as pre-distortion. There are many known techniques are used to pre-correct an information signal in order to linearize the output of the amplifier. One of these techniques involves amplitude correction which produces a linear piece-wise pre-correction function which is correlated to the non-linear characteristics of the amplifier. The result is a piece-wise correction curve which approximates the ideal correction. The correction is then added to the information signal.
Pre-distortion has been almost exclusively in the baseband domain. The typical approach has been to apply a pre-distortion function at digital baseband. A relatively recent but commonly used approach has been to store the pre-distortion function as a look-up table which stores the gain and phase values as a function of the input signal envelope. The input signal is compared with the feedback signal from the power amplifier and certain metrics, such as ratio of in-band to out-of-band emission power and/or their correlation are used to adaptively map the look-up table with respect to the envelope of the input signal. Thus, the data path is simply a complex multiplication at digital baseband; the adapt-path (or feedback path) consists of a look-up table indexed by the input signal envelope and the adaptation metric is the ratio of in-band to out-of-band emission or the correlation between the feedback and the input signals. These operations are carried out at digital baseband.
However, increasing the linearity of the power amplifiers can reduce the power efficiency of the amplifiers, make them more voluminous, require more cooling equipment, and substantially increase the cost and form-factor of the transceivers. To improve the linearity of the transmission without resorting to a higher end and more expensive power amplifier, one method that has been carried out in the prior art is to perform pre-distortion on the transmitted signal before the signal is input into the power amplifier such that the pre-distortion equalizes in some sense the non-linear post-distortion of the amplifier. The pre-distortion may be carried out within an integrated circuit; however, a significant challenge has always been to be able to adaptively obtain the pre-distortion transfer function so as to be optimal in some metric. It is also desirable to have a tracking mechanism with the pre-distortion so that different temperature and aging effects are also compensated for.
Accordingly, it would be desirable to have systems and methods for performing pre-distortion in power amplifiers that overcome the disadvantages of the prior art as discussed.
According to one aspect of the present invention, adaptive pre-distortion is performed using a least-mean square (LMS) method to adaptively obtain an optimal pre-distortion transfer function in the mean square error sense. In one embodiment, a LMS-based adaptive pre-distortion circuit coupled between an input signal to be transmitted and a non-linear power amplifier compares the input signal to a feedback signal from the power amplifier. The circuit adaptively reduces the least-mean square error between the two signals using both linear and non-linear filters and various feedback signals within the circuit. The result is an approximately linear output from the power amplifier. This technique can be used with single and multi-carrier transceivers, as well as with either a power amplifier (at the transmitter) or low noise amplifier (LNA) (at the receiver). The adaptive pre-distortion can be performed in the baseband domain or purely in the RF domain, using analog continuous-time or discrete-time signal processing.
According to one embodiment, an LMS-based adaptive pre-distortion (LAPD) circuit receives an input signal to be transmitted, such as from a baseband processor and RF circuitry, and a feedback signal from a power amplifier. The LAPD circuit adaptively minimizes a metric, such as an error signal, formed by the difference between the two signals. The LAPD circuit receives the input signal through an adaptive AGC circuit. The LAPD circuit further includes a feedforward filter, an adaptive coefficient generator, a slicer, timing control circuit, and slicer output time-align circuit. An error timing align circuit within the adaptive coefficient generator may be used to time align the input signal from the adaptive AGC circuit with the error signal e(t) or equalize delays between the input signal and the error signal. The error timing align circuit may receive as an input signal a feedback tap coefficient vector c or the error signal e(t). The timing control circuit time aligns or equalizes the delays between the input signal and the feedback signal from the power amplifier to compute an error signal, which is the time difference between the two signals. This error signal is iteratively reduced until a desired signal is obtained. The output signal is then input to the non-linear power amplifier, which amplifies the signal for transmission, resulting in a linearized output signal.
The scope of the invention is defined by the claims, which are incorporated into this section by reference. A more complete understanding of embodiments of the present invention will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described briefly.
Embodiments of the present invention and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.
System 100 further includes a power coupler 110 that receives the output signal from power amplifier 108 and splits a portion of the input RF signal into the feedback path and passes the rest of the signal through to the antenna for transmission. The output signal from power coupler 110 is received by an amplitude control or controllable gain circuit 112, which then scales the signal so that the signal input into LAPD circuit 106 is within an admissible range for operation of the LAPD circuit. Controllable gain circuit 112 feeds the signal back to LAPD circuit 106 for comparing with the desired signal to be transmitted. Power coupler 110, after receiving the signal from power amplifier circuit 108, sends the signal to an antenna 114 for transmission. After adaptive pre-distortion by LAPD circuit 106, the signal from power amplifier circuit 108 is essentially linear.
Input signal x1 is received by adaptive AGC circuit 300. Feedforward filter 302 receives the output signal x1′ from adaptive AGC circuit 300 and tap coefficients from adaptive coefficient generator 304 and generates a pre-distorted signal, which is input to adder 312. The other input to adder 312 is the product 314 of the output of low pass filter block 316, and slicer output time-align circuit 310.
The feedback signal (from product 314) into adder 312 provides an iterative correction to an error signal e(t) for use by adaptive coefficient generator 304 to generate adaptive tap coefficients. The error signal, processing through adder 318, is the difference between the output of timing control circuit 308 and input signal x2 (the feedback signal from the power amplifier). As time passes, the error signal converges until a sufficiently small error signal is obtained through adaptively changing the tap coefficients.
Referring to
In one embodiment, low pass filters 602 are analog (or continuous-time) first-order low-pass filters having a transfer function
Selecting values for G and T1 depend on system requirements and include factors such as the maximum steady state mismatch of signals, time variability of the channel, amount of noise within the channel, and parasitic effects of the circuit. In one embodiment, the gain G may be set to 10 to 50 which will result in small mismatch and possibly stable operation. The time constant T1 is typically set to about 10,000 to 100,000 symbol times, in one embodiment. For very fast varying channels, T1 is much smaller. T1 is larger for channels having less temporal variations and more noise. Higher order low pass filters are also suitable for use with the present invention.
Referring back to
The controllable delay in the present invention is used to time align the input signal x1 with the feedback signal x2 from the power amplifier. As used herein, time align can also be described as equalizing the delays between two signals. In one embodiment, the ALTI circuit of the above referenced application is used to adaptively set the delay to align the signals by using the feedback signal x2(t) from the power amplifier. The ALTI block may be used to time-align the input signal to compute the distortion error signal which is the difference between the power amplifier output signal and the input signal, i.e., the time-align circuit 308 delays its output signal to compensate for delays introduced by processing of the input signal by the circuit.
The controllable delay in the present invention is used to time align the decision feedback signal, which is the signal from slicer 306, to be a symbol period delay with respect to the slicer input signal from which it is cancelled. A method of obtaining this delay in an adaptive manner is by using the FTA block, as described in the above-referenced application, which uses the tap coefficients or error signal e(t) as a control input signal.
The resulting product signals are summed in a signal summing circuit 814. The resulting sum signal is integrated in an integration circuit 816 (e.g., a low pass filter) to produce the first adaptation control signal d(t). This adaptation control signal d(t), in addition to being provided to timing interpolation parameter signal generator 806, is multiplied within multiplier circuits 818-1, 818-2 with the other adaptation control signals r(t) and 1−r(t), respectively, provided by timing interpolation parameter signal generator 806. The product signals resulting from these multiplication operations are the adaptive coefficient signals d(t)r(t) and d(t)[1−r(t)].
The resulting product signal is integrated by a signal integration circuit 826 (e.g., a low pass filter) to produce one of the adaptation control signals r(t) used by coefficient signal generator 804. This adaptation control signal r(t) is further processed by a signal complement circuit 828, in which the input signal r(t) is subtracted from a reference signal having a normalized value, with the resulting difference signal 1−r(t) serving as the other adaptation control signal used by coefficient signal generator 804. For example, if the value of the incoming signal r(t) were considered to have a normalized signal value range bounded by the values of zero and one, signal complement circuit 828 subtracts the incoming signal r(t) from the value of one to produce the output signal 1−r(t).
The above described embodiment utilizes an adaptive pre-distortion circuit with feedback circuitry and both linear and non-linear elements. By selecting the appropriate parameters for the low pass filters, the convergence of the least mean square value can be controlled to prevent coefficient drift of the adaptive tap coefficients. The continuous time iterative process results in the ability to adaptively change the tap coefficients for error minimization and provide a linear signal out of a non-linear power amplifier.
While the above description is for a single-carrier transceiver, the present invention can also be used with multi-carrier transceivers.
After adaptively generating a pre-distortion signal for each carrier, the output signals from LAPD datapath 204-1 and from LAPD datapath 204-2 are passed through bandpass filters 206-1 and 206-2, respectively. As with the single-carrier embodiment, bandpass filters 206 may be internal to or external of multi-carrier LAPD circuit 910. The output signals from bandpass filters 206-1 and 206-2 are then summed by an adder 1004 to generate a pre-distorted signal z for power amplifier 912. Due to adaptively pre-distorting input signals according to the present invention, the output of a non-linear power amplifier can be made linear with a wider range of factors, as well as at lower cost and size.
In some applications and systems, the power amplifier and/or other RF components may introduce inter-symbol interference (ISI) in addition to non-linearity. To compensate for both ISI and non-linearity effects jointly, the present invention can be modified, in part, by using a larger number of taps N′ such that N′*τ>Ts.
The above-described embodiments of the present invention are merely meant to be illustrative and not limiting. It will thus be obvious to those skilled in the art that various changes and modifications may be made without departing from this invention in its broader aspects. For example, although the multi-carrier mode is shown with two carriers, the invention can also be used with a multi-carrier transceiver having more than two carriers by modifying the above descriptions accordingly. Further, the above description has focused on continuous-time, RF domain signal processing; however, the present invention can be extended or modified for use with discrete-time signal processing architectures as well. Therefore, the appended claims encompass all such changes and modifications as fall within the true spirit and scope of this invention.
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Indians activate Asdrubal Cabrera, drop John McDonald
Jun 26, 2013, 3:45 PM EDT
Asdrubal Cabrera is back from the disabled list after missing the past three weeks with a quadriceps injury and to make room for him on the roster the Indians designated John McDonald for assignment.
Cabrera was off to a solid start before the quadriceps injury, hitting .254 with five homers and a .745 OPS to basically match his career numbers. Mike Aviles, who had been filling in as the Indians' starting shortstop, will now go back to a utility role.
McDonald was acquired from the Pirates after Cabrera went down to provide some middle infield depth. He got a grand total of eight plate appearances for the Indians and at age 38 may have to put in some time at Triple-A if he wants to continue playing in the majors.
- Detroit Michael - Jun 26, 2013 at 4:54 PM
John McDonald, age 38. Congratulations are in order for carving out a long career without (by major league standards) much batting talent.
- spursareold - Jun 26, 2013 at 5:25 PM
My best friend's sister's boyfriend's brother's girlfriend heard from this guy who knows this kid who's going with the girl who saw Ferris pass out at 31 Flavors last night. I guess it's pretty serious.
- yahmule - Jun 26, 2013 at 9:05 PM
John Hughes was underrated.
- mississippimusicman - Jun 26, 2013 at 5:33 PM
Spam much?
- mississippimusicman - Jun 26, 2013 at 5:34 PM
I always get the names John McDonald and Michael McDonald mixed up. Looks like they're both Takin' It to the Streets now, though.
- spursareold - Jun 26, 2013 at 5:38 PM
I think John's career is Minute by Minute at this point.
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So much fun
posted 7 years ago
This is another great product to get even if you are not an agility person. It can be a fun game to play and a way to give your dog extra exercise and training.
Pros: Good exercise and fun to do
Cons: None
9 of 9 people found this review helpful.
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Ace in the hole
posted 7 years ago
This was the easiest exercise to train for my dog and it was a great deal of fun for him. This is also very easy to set up.
Pros: Easy to teach and lots of fun
Cons: none
6 of 6 people found this review helpful.
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Good exercise
posted 7 years ago
Agility training is great for bored dogs. I've done a little with my dog Scout. It was awesome for his seperation anxiety. Our trainer had this equipment and it's very sturdy.
Pros: good for bored dogs
Cons: none
2 of 2 people found this review helpful.
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