JP2003514444A - Reduction of PAR (Peak to Average Power Ratio) by Randomizing Carrier Phase in Multicarrier Communication - Google Patents

Abstract

(57) Summary A system and method for scrambling the phase characteristics of a carrier signal will be described. Scrambling the phase characteristics of each carrier signal includes associating a value with each carrier signal and calculating a phase displacement of each carrier signal based on the value associated with the carrier signal. Such a value is determined independently of any input bit value carried by the carrier signal. The phase shift calculated for each carrier signal is combined with the phase characteristics of the plurality of carrier signals to substantially scramble the phase characteristics of the carrier signals. The bits of the input signal are modulated onto the carrier signal having the substantially scrambled phase characteristic to generate a transmitted signal having a reduced peak-to-average power ratio (PAR).

Description

Detailed Description of the Invention

[0001]

[Display of related applications]

This specification is co-pending and incorporated by reference in its entirety 199
Claim the benefit of filing date of US provisional patent application No. 60 / 164,543 filed Nov. 10, 1997, entitled "Time Diversity Method for Improving Data Rate in Multi-Carrier System", entitled "Time Diversity Method".

[0002]

FIELD OF THE INVENTION

The present invention relates to a communication system using multicarrier modulation. In particular, the present invention relates to a multicarrier communication system that reduces the peak-to-average power ratio of transmitted signals.

[0003]

BACKGROUND OF THE INVENTION

In conventional multi-carrier communication, a transmitter communicates over a communication channel by using multi-channel modulation or separate multi-tone transform (DMT). Carrier signals (carriers) or sub-channels located within the usable frequency band of the communication channel are the symbols (ie, blocks) of the system for transmission.
(symbol transmission) Modulated at rate. The input signal including the input data bits is transmitted to a DMT transmitter such as a DMT modem. Such DMT transmitters typically use an Inverse Fast Fourier Transform (IFFT) to modulate the phase characteristic, ie the phase and amplitude of the carrier signal, to produce a time domain signal, ie the transmitted signal representing the input signal. To do. The DMT transmitter transmits the transmission signal obtained by linearly combining a plurality of carriers to a DMT receiver via a communication channel.

Since the phase and amplitude obtained as a result of arbitrary order conversion of input data bits include transmission information, the phase and amplitude of the carrier signal of the DMT transmission signal are considered to be random. So if the modulated data bits are random, then
Such a DMT transmission signal can be regarded as having a Gaussian probability distribution.
A DMT transmitter to scramble the input data bits before they are modulated to ensure that the transmitted data bits are random and that modulating these bits produces a Gaussian probability distribution. The bit scrambler is often used in.

By assigning an appropriate transmission power to a carrier or sub-channel, the system can exhibit desired performance. Further, in order to transmit a transmission signal having a low peak-to-average value ratio (PAR), that is, a peak-to-average value power ratio, it is necessary to generate a transmission signal having a Gaussian probability distribution. The PAR of a transmission signal is an instantaneous peak value (that is, maximum amplitude) of the signal specifications (for example, voltage, current, phase, frequency, power) with respect to a time average value of the signal specifications. DM
In the T system, the PAR of the transmitted signal is determined by the probability of the random transmitted signal reaching a certain peak voltage during a time interval required for a certain number of symbols. Let us assume that the PAR of the transmitted signal transmitted from the DMT transmitter is 14.5 dB, which is equivalent to having a possibility of clipping of 1E-7, for example. Since the PAR of the signal affects the total power consumption of the communication system and the component linearity condition of the system, the PAR of the transmission signal transmitted / received in the DMT communication system should be important in designing the DMT communication system. It is a matter.

If the phase of the modulated carrier is not random, the PAR may be increased significantly. The following are examples of cases where the phase of the modulated carrier is not random. In such cases, no bit scramblers are used, multiple carrier signals are used to modulate the same input data bits, and mapping of the input data bits to the phase of the carrier signal used for modulation ( The constellation map, which is a mapping, is not sufficiently random (i.e., a data bit value of 0 corresponds to a 90 degree phase characteristic of the DMT carrier signal, and a data bit value of 0 corresponds to -9 of the DMT carrier signal.
(This corresponds to a phase characteristic of 0 degree). However, the increased PAR increases the power consumption of the system and / or increases the likelihood that the transmitted signal will be clipped. Therefore, what is needed is a system and method that can efficiently convert a modulated carrier signal to provide low PAR for the transmitted signal.

[0007]

[Outline of the Invention]

The present invention relates to systems and methods for scrambling the phase characteristics of a modulated carrier signal in a transmitted signal. In one aspect, a value is associated with each carrier signal. The phase shift is calculated for each carrier signal based on the value associated with each carrier signal. Such a value is determined independently of any input bit value carried by the carrier signal. The phase shift calculated for each carrier signal is combined with the phase characteristics of the carrier signals to substantially scramble the phase characteristics of the plurality of carrier signals.

In an embodiment, an input bitstream is generated on the carrier signal having the substantially scrambled phase characteristic to produce a transmitted signal having a reduced peak-to-average power ratio (PAR). Is modulated. The value is obtained from predetermined parameters such as a random number generator, the number of carriers, the number of DMT symbol counts, the number of superframes, and the number of hyperframes. In another embodiment, a predetermined transmission signal is transmitted when the amplitude of the transmission signal exceeds a certain level.

In another aspect, the invention features a method of associating a value with each carrier signal. The value is determined independently of any input bit value carried by the carrier signal. The phase displacement of each carrier signal is calculated based on the value associated with the carrier signal. The transmitted signal is demodulated using the phase shift calculated for each carrier signal.

In another aspect, the invention relates to a system with a phase scrambler that calculates a phase shift for each carrier signal based on associated values. Further, the phase scrambler substantially scrambles the phase characteristics of the plurality of carrier signals, and thus combines the phase displacement calculated for each carrier signal and the phase characteristics of the carrier signal. In one embodiment, a modulator has the substantially scrambled phase characteristic to communicate with the phase-phase scrambler and generate a transmitted signal with a reduced peak-to-average power ratio (PAR). Modulate the bits of the input signal onto the carrier signal.

[0011]

DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a separate multitone (communicating with a remote transceiver 14 via a communication channel 18 by using a communication signal 38 having a plurality of carrier signals.
Digital Subscriber Line (DSL) communication system 2 including DMT transceiver 10
Is shown. Such a DMT transceiver 10 includes DMT transmitters 22 and D
An MT receiver 26 is provided. The remote transceiver 14 comprises a transmitter 30 and a receiver 34. Although separate multitone modulation is described herein, the principles of the present invention are not limited to these, and quadrature multiple amplitude modulation (OQA).
M), DWMT (discrete wavelet multitone) modulation, and orthogonal frequency division multiplexing (OFDM).

Communication channel 18 provides a downstream communication path from DMT transmitter 22 to remote receiver 34 and an upstream communication path from remote transmitter 30 to DMT receiver 26. In one embodiment, the communication channel 18 is a twisted pair of telephone subscriber lines. In another embodiment, the communication channel 18 is a quad cable consisting of two pairs of fiber optic lines, twisted lines, or one of the star quad cables, the Dieselhorst-Martin quad. ) It may be a cable or the like. In the case of a wireless communication system, the transceivers 10, 14 are wireless modems and a communication channel 18
Is the air through which the transmitted signal 38 is transmitted between the transceivers 10, 14.

As an example only, the DMT transmitter 22 shown in FIG. 1 includes a quadrature amplitude modulation (QAM) encoder 42, a modulator 46, a bit allocation table (BAT) 44, and a phase scrambler 66. The DMT transmitter 22 may include a bit scrambler 74 as described below. The remote transmitter 30 of the remote transceiver 14 comprises the same parts as the DMT transmitter 22. In this embodiment, the DMT
Although details of the transmitter 22 are described, the inventive concept can also be applied to receivers 34, 36 that include similar components to the DMT transmitter 22, but in that case the reverse function is reversed. Run in order.

The QAM encoder 42 has one input end for receiving the input serial data bitstream 54 and the bitstream 5 by the QAM encoder 42.
4 has a plurality of parallel outputs for transmitting the QAM symbols 58 generated by 4 in FIG. Typically, the QAM encoder 42 maps the input serial bitstream 54 in the time domain into parallel QAM symbols 58 in the frequency domain. In particular, the QAM encoder 42 uses the input serial bit stream 5
4 to N quadrature amplitude modulation (QAM) constellation points 58, or QAM symbols 58. Here, N represents the number of carrier signals generated by the modulator 46. The BAT 44 is in communication with the QAM encoder 42 to identify the number of bits carried by each carrier signal. QA
The M symbol 58 represents the amplitude and phase characteristics of each carrier signal.

Modulator 46 provides functions for DMT modulation and also transforms QAM symbols 58 into DMT symbols 70, each composed of multiple time domain samples. The modulator 46 modulates each carrier signal with a different QAM symbol 58. As a result of such modulation, the carrier signal becomes QAM symbol 5
8 based, ie, having phase and amplitude characteristics based on the input bitstream 54. In particular, the modulator 46 transforms the QAM symbol 58 into a transmitted signal 38 composed of a series of DMT symbols 70, and thus an inverse fast Fourier transform (
IFFT) is used. The modulator 46 converts the QAM symbol 58 into the DMT symbol 70 by modulating the carrier signal. In another embodiment, the modulator 4
6 transforms the QAM symbol 58 into a DMT symbol 70 using the Inverse Separation Fourier Transform (IDFT). In one embodiment, the transmit signal 38 includes pilot tones during reception of the transmit signal 38 to provide a reference signal for coherent demodulation of the carrier signal at the remote receiver 34.

Modulator 46 also includes a phase scrambler 66 that combines the calculated phase shift for each QAM modulated carrier signal with the phase characteristics of that carrier signal. Combining the phase shift and the phase characteristic according to the principles of the present invention substantially scrambles the phase characteristic of the carrier signal in the transmitted signal 38. By scrambling the phase characteristics of the carrier signal, the resulting transmitted signal 38 will have a substantially minimized peak-to-average value ratio (PAR). The phase scrambler 66 may be a part of the modulator 46 or may be provided outside thereof. Other embodiments of phase scrambler 66 include, but are not limited to, software programs stored in local memory that execute on modulator 46, mathematical functions and A digital signal processor (DSP) or the like capable of executing the algorithm is included. Similarly, the remote receiver 34 also includes the DMT transmitter 2
The two transceiver 10 is provided with a phase scrambler 66 'used for demodulating a carrier signal whose phase characteristic is already adjusted by the phase scrambler 66.

To calculate the phase shift of each carrier signal, the phase scrambler 66 associates one or more values with that carrier signal. The phase scrambler 66 determines each value of the carrier signal separately from the QAM symbol 58, that is, independently of the bit value modulated on the carrier signal. The actual value that the phase scrambler 66 associates with each carrier signal is the pseudo-random number generat.
or, pseudo-RNG), number of DMT carriers, number of DMT symbol counts, DMT
It can be obtained from one or more predetermined parameters such as the superframe count, the DMT hyperframe count, and the like. At the DMT transmitter 22 and remote receiver 34, the same technique is used so that the values associated with a given carrier signal can be detected on both sides of the communication channel 18 regardless of the technique used to produce each value. Used.

Next, since the phase scrambler 66 calculates the phase displacement of the carrier signal,
The predetermined equation is solved by using the value associated with the carrier signal as an input that influences the result of the equation. Any equation that is suitable for calculating the phase displacement can be used for calculating the phase displacement. If the equation is not affected by the bit values of the input serial bitstream 54, then the calculated phase displacement is also independent of such bit values.

In one embodiment (shown in phantom), the DMT transmitter 22 comprises a bit scrambler 74 that receives the input serial bitstream 54 and outputs substantially modulated data bits 76. There is. The substantially modulated bits 76 are then passed to the QAM encoder 42. When the bit scrambler 74 is included in the DMT transmitter 22, the operation of the phase scrambler 66 makes it more certain that the transmitted signal 38 has a Gaussian probability distribution, thereby substantially minimizing PAR.

FIG. 2 illustrates an embodiment of a process used in a DMT transmitter 22 to adjust the phase characteristics of each carrier signal and combine such carrier signals to produce a transmitted signal 38. The DMT transmitter 22 produces a value associated with the carrier signal (step 100). Both the DMT transmitter 22 and the remote receiver 34 must be aware of the value associated with the carrier signal, as that value is used to modify the phase characteristics of the carrier signal. Either the DMT transmitter 22 and the remote receiver 34 get the associated values independently, or one informs the other of the associated values. For example, in one embodiment, the DMT transmitter 22 includes a pseudo-random number generator (pseudo-RNG).
, And then transmit the generated value to the remote receiver 34. In other embodiments, the remote receiver 3 uses the same pseudo-random number generator (pseudo-RNG) and the same seed that the transmitter used (ie, the pseudo-random number generator of the transmitter is , Generate the same series of random numbers as the pseudo-random number generator of the receiver).

In another embodiment, DMT transmitter 22 and remote receiver 34 are each
A symbol counter can be maintained for counting DMT symbols. DM
The T transmitter 22 transmits the DMT symbol and increases its symbol count when the remote receiver 34 receives it. As a result, when both the DMT transmitter 22 and the remote receiver 34 use the symbol count as the value for calculating the phase shift, both the DMT transmitter 22 and the remote receiver 34 have a DM value for which the value is specific.
It is associated with a T symbol and "knows" that it is accompanied by each carrier signal of that DMT symbol.

Values can also be obtained from other types of predetermined parameters. For example, when the predetermined parameter is the number of DMT carriers, the value associated with a specific carrier signal is the number of carriers of the signal in the DMT signal. The number of carrier signals represents the position of the frequency of the carrier signal with respect to the frequencies of other carrier signals in the DMT symbol. For example, in one embodiment, DSL communication system 2 provides 256 carrier signals, each divided at a frequency of 4.3125 KHz, having a frequency band extending from 0 kHz to 1104 kHz. Here, the DMT transmitter 22 numbers from 0 to 255.
Therefore, "50 DMT carriers" is 215.625 kHz (that is,
It indicates that it is the 51st DMT carrier signal located at the frequency of 51 × 4.3125 kHz).

Again, both the DMT transmitter 22 and the remote receiver 34 have the same predetermined parameter (here, the number of DMT carriers) in order to create a value--carrier signal association. ) Is used, the DMT transmitter 22 and the remote receiver 34 can know the value associated with the carrier signal. In other embodiments (as exemplified above with the pseudo-random number generator of the transmitter), the DMT transmitter 22 sends the value to the remote receiver 34 (or vice versa) via the communication channel 18. Can be sent.

In other embodiments, other predetermined parameters associated with the counting of symbols can be used. An example of such a predetermined parameter is 69 DMs.
There is a superframe counter that increments every T symbols. A typical example of implementing a super frame counter is modulo 68 for symbol count.
To perform a modulo 68 operation on the symbol count. As another example, the DMT transmitter 22 may maintain a hyperframe counter to count hyperframes. A typical example of implementing a hyperframe count is to perform a modulo 255 operation on a superframe count. Thus, the hyperframe count is incremented by 1 each time the superframe count reaches 255.

As a result, some predetermined parameters appear to produce values that vary from carrier signal to carrier signal. For example, when the predetermined parameter is the number of DMT carriers, the value changes based on the frequency of the carrier signal. As another example, a pseudo-random number generator generates new random numbers for each carrier signal.

The other predetermined parameters generate values that change for each DMT symbol 70. For example, if the predetermined parameter is a symbol count, a superframe count, or a hyperframe count, the numerical position of the DMT symbol 70 in the associated symbol, superframe or hyperframe (numerical position).
ition) changes the value. Certain parameters such as pseudo-random number generators, symbol counts, superframe counts, and superframes are also known as time-varying parameters. The value to be substituted into the equation for calculating the phase shift of the given carrier signal is given by one or a combination of predetermined parameters.

In one embodiment, on a DMT symbol 70 by DMT is used to avoid clipping of the transmitted signal 38 on the DMT symbol 70.
symbol 70 basis) Phase scrambling is used. In this embodiment, DM
The T transmitter 22 uses a value based on a time-varying predetermined parameter, such as a symbol count, to calculate the phase shift. It will be appreciated that the principles of the present invention may be practiced with other types of predetermined parameters that vary with respect to the carrier signal. As described above, the transceivers 10 and 14 may exchange their values with each other in order to synchronize the modulation and demodulation of the carrier signal (step 110).

Next, the DMT transmitter 22 calculates the phase displacement used to adjust the phase characteristic of each carrier signal (step 115). The amount of phase displacement combined with the phase characteristics of each QAM-modulated carrier signal will vary depending on the equation used and one or more values associated with the carrier signal.

Next, the DMT transmitter 22 combines the phase shift calculated for each carrier signal with the phase characteristic of the carrier signal (step 120). By scrambling the phase characteristics of the carrier signal, the phase scrambler 66 reduces the combined PAR of the plurality of carrier signals (related to the unscrambled phase characteristics), that is, the PAR of the transmitted signal 38. The following three examples of phase changes, PS # 1 to PS # 3
Shows the method used by the phase scrambler 66 to couple the calculated phase displacement to the phase characteristics of each carrier signal.

Phase Displacement Example # 1 Phase displacement example # 1 is carrier number N by Nxπ / 3, modulo (mod) 2π.
Is the same as adjusting the phase characteristics of the QAM-modulated signal associated with the. In this example, when the carrier number N is 50, the carrier signal has a phase displacement obtained by adding 50 × π / 3 (mod2π) = 2 / 3π to its phase characteristic. When the carrier number N is 51, the carrier signal has a phase displacement obtained by adding 51 × π / 3 (mod2π) = π to the phase characteristic. When the carrier number N is 0, no phase displacement is added to the phase characteristic of the carrier signal.

Phase Displacement Example # 2 Phase Displacement Example # 2 is the same as adjusting the phase characteristics of the QAM-modulated signal associated with carrier number N by (N + M) × π / 4, modulo 2π. That is, M is the symbol count number. In this example, assuming that the carrier number N is 50 and the DMT symbol count M is 8, the carrier signal has (50 + 8) × π / 4 (mod2π) = π / 2 added to its phase characteristic. Will have a phase shift. If the carrier number N is 50 and the DMT symbol count M is 9, the carrier signal has
50 + 9) xπ / 4 (mod2π) = 3π / 4 will be added.

Phase Displacement Example # 3 Phase Displacement Example # 3 adjusts the phase characteristics of the QAM-modulated signal associated with carrier number N by (X _N ) xπ / 6, modulo 2π. Same thing. Here, X _N is a set of N pseudo random numbers. In this example, assuming that the carrier number N is 5 and X _N is [3, 8, 1, 4, 9, 5, ...], the carrier signal has a phase characteristic of (9 ) Xπ / 6 (mod2π) = π / 3
To have a phase characteristic. (Note that 9 is the fifth value of X _N ). If the carrier number N is 6, the carrier signal has a phase displacement obtained by adding (5) × π / 6 (mod2π) = 5π / 3 to the phase characteristic.

Phase displacement example # 3 may use additional and / or alternative phase shifting techniques by phase scrambler 66, and PS # 1, PS # 2 and PS # 3
It is understood that this is merely an example illustrating the principles of the invention. next,
The DMT transmitter 22 combines the carrier signals to form the transmitted signal 38 (step 130). If such a transmitted signal has not been clipped as described below, DMT transmitter 22 then transmits the transmitted signal 38 to remote receiver 34 (step 160).

Clipping of Transmit Signal By the transmit signal 38 having a high voltage peak value (ie, high PAR), D
Non-linear distortion can be induced in the MT transmitter 22 and the communication channel 18. An example of the non-linear distortion of the transmission signal 38 that can occur in this way is amplitude limitation (that is, clipping) of the transmission signal 38. For example, the DMT symbol 70
A particular DMT symbol 70 is capped to be in the time domain if one or more of the time domain samples therein is greater than the maximum digital value allowed for the DMT 70. In a multi-carrier communication system, when clipping occurs, the transmitted signal 38 will not accurately represent the input serial data bit signal 54.

In one embodiment, the DSL communication system 2 clips the transmission signal 38 by one DMT symbol 70 by DMT symbol 70 b.
asis) Avoid. The DMT transmitter 22 detects clipping of the transmitted signal 38 (step 140). If a particular DMT symbol 70 is capped to be in the time domain to produce a clipped transmit signal 38, then D
The MT transmitter 22 replaces the predetermined transmit signal 78 in place of the clipped transmit signal 38 (step 150).

The predetermined transmission signal 78 has the same time interval (eg, 250 milliseconds) as the DMT 70 to maintain the timing of the symbols between the DMT transmitter 22 and the remote receiver 34. The predetermined transmission signal 78 is the input serial data bit signal 5
4 is a pattern of bit values that is not generated (separately) based on 4 but is identified by the remote receiver 34 as an alternative signal. In one embodiment, the predetermined transmitted signal 78 is a known pseudo-random sequence pattern that is easily detected by the remote receiver 34. In another embodiment, the predetermined transmit signal 78 is an "all zero" signal that is a zero voltage signal (ie, zero volts modulated onto all carrier signals) created at the output of the DMT transmitter 22. is there. In addition to simple detection by remote receiver 34, the use of a zero volt signal reduces the power consumption of DMT transmitter 22. Also, in order to provide a reference signal for coherent demodulation of the carrier signal at the remote receiver 34 during reception of the predetermined transmission signal 78, the predetermined transmission signal 7
8 contains pilot tones.

After the remote receiver 34 receives the transmitted signal 38, the remote receiver 34 transmits the transmitted signal 3
8 is the same as the predetermined transmission signal 78. In one embodiment, if the remote receiver 34 recognizes that it is the same as the transmitted signal 78, then the remote receiver 34
Ignores (ie discards) the transmitted signal 78.

Following the transmission of the predetermined transmission signal 78, the phase scrambler 66 changes the phase characteristic of the QAM-modulated carrier signal (based on one of the predetermined parameters that changes over time) (step 120). For example, assume that the set of QAM symbols 58 produces a DMT symbol 70 with multiple time domain samples, one of which is greater than the maximum digital value allowed for the DMT symbol 70. Therefore, when a transmission is made to the remote receiver 34, the DMT transmitter 22 will instead transmit a predetermined transmit signal 78, since the transmit signal 38 will be clipped.

After transmitting the predetermined transmission signal 78, the DMT transmitter 22 attempts to transmit again the bit value that caused the transmission signal 38 to be clipped in the next DMT symbol 70 ′. In the present embodiment, the phase displacement is performed based on the value that changes with the passage of time, so the phase displacement calculated for the next DMT symbol 70 ′ has been clipped before calculated for the DMT symbol 70. Not the one with the time domain. Such different phase shifts combine with the phase characteristic of the modulated carrier signal to create a carrier signal of the next DMT symbol 70 'that has a different phase characteristic than the carrier signal of the DMT symbol 70 with clipped time domain. To be done.

The DMT communication system 2 occasionally generates a communication signal 38 that performs clipping (eg, about once every 10 ⁷ time domain samples 70). However, if the next DMT symbol 70 'contains even one time-domain sample that performs clipping, the predetermined transmission signal 78 is retransmitted to the remote receiver 34 instead of the clipped transmission signal 38. (Step 150). The clipped time domain samples may be on the same or different carrier signal as the previously clipped DMT symbol 70. The DMT transmitter 22 receives the next DMT symbol 7 which is not clipped by itself.
The predetermined transmission signal 78 is continuously transmitted until 0'is generated. When the DMT transmitter 22 generates an unclipped DMT symbol 70 ', the DMT transmitter 22
Transmits the transmission signal 38 to the remote receiver 34 (step 160). The transmission probability that the transmission signal 38 corresponding to the DMT symbol 70 is clipped in the time domain is determined based on the PAR of the transmission signal 38.

For example, the following example phase shift, PST # 4, is a method used by the phase scrambler 66 to combine different moving displacements into the phase characteristics of each carrier signal in order to avoid clipping of the transmitted signal 38. Is shown.

Phase Displacement Example # 4 Phase displacement example # 4 (PS # 4) is carrier number N according to π / 3x, mod2π.
Is the same as adjusting the phase characteristics of the QAM-modulated signal associated with the. Here, M is the count number of DMT symbols. In this example, when the DMT symbol 70 is clipped when the DMT symbol count number is 5,
The predetermined transmission signal 78 is transmitted instead of the transmission signal 38 that is currently clipped. The QAM symbols 58 used to generate both the DMT symbols 70 and 70 'are the same, but after the duration of the DMT symbols, the DMT count M will be 6, so that for the next DMT symbol 70'. A different set of time domain samples is generated at.

If this different set of time domain samples (and therefore transmit signal 38) is not clipped, DMT transmitter 22 transmits transmit signal 38. If one of the time domain samples in the different set of time domain samples 70 (and thus the transmitted signal 38) is clipped, the DMT transmitter 22 retransmits the predetermined transmitted signal 78. Processing continues until DMT symbol 70 is generated without clipped time domain samples. In some embodiments, after generating the predetermined number of clipped DMT symbols 70 ′, the transmitter 22 may use the unclipped DMT symbols for the characteristic set of QAM symbols 58.
Stop trying to generate symbol 70 '. At this time, the transmitter 22 can transmit either the most recently generated clipped DMT symbol 70 ′ or the predetermined transmission signal 78.

When the DMT symbol 70 is clipped, the predetermined transmission signal 78 is transmitted instead of the transmission signal 38, so that the PAR of the DSL communication system 2 is reduced.
For example, in the DMT communication system 2 in which the clipping probability of the time domain transmission signal 38 is usually 10 ⁻⁷ , the clipping probability is 10 ⁻⁵ and the lower limit is 1.
It operates at a low PAR of 2.8 dB (compared to 14.5 dB). 10 ^- Operating in ⁵ Kuripppingu probability, DMT symbol 70 is presumed to have 512 time domain samples 70, DMT transmitter 22, ¹⁰ 5/5
For every 12 or 195 DMT symbols 70, 1 clipped D
Experience the MT symbol. As a result, a predetermined (no data-carrying) transmission signal 78 is transmitted once on average for every 195 DMT symbols. By increasing the clipping probability up to 10 ⁻⁵ , the loop put is about 0.5% (
1/195), but the PAR of the transmitted signal 38 is reduced by 1.7 dB, which reduces transmitter complexity in the form of power consumption and component linearity.

While the invention has been shown and described with reference to certain preferred embodiments, various modifications in form and detail are intended to be within the spirit and scope of the invention as defined by the following claims. Those skilled in the art will appreciate that what can be done without departing from the above. For example, although the invention has been described in the present specification using DSL, various types of DSL such as ADSL, VDSL, SDSL, and HD are used.
It will be appreciated that SL, HDSL2 or SHDSL can also be used. The principle of the invention is that any combination of applications carried over a DSL system (
It goes without saying that it also applies to work from home, video conferencing, high speed internet access, video on demand, etc.

[Brief description of drawings]

The invention is specified in detail by the appended claims. Not only the advantages of the present invention described above, but further advantages of the present invention can be better understood by referring to the following description in connection with the accompanying drawings.

FIG. 1 shows a DMT (deiscrete multitone modulat) communicating with a remote transceiver.
FIG. 1 is a block diagram of one embodiment of a digital subscriber line communication system that includes a phase scrambler that includes an (i.

FIG. 2 is a flow diagram of one embodiment of a process for scrambling the phase characteristics of a carrier signal in a transmitted signal.

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Claims (39)

[Claims] 1. Communicating with a second transceiver using a transmit signal comprising a plurality of carrier signals for modulating an input bitstream, each carrier signal having a phase characteristic associated with the input bitstream. A method of scrambling the phase characteristics of the carrier signal in a multi-carrier modulation system comprising: a first transceiver for performing, independent of each carrier signal and any input bit value carried by the carrier signal. The step of associating with the value determined by the step of calculating the phase shift of each carrier signal based on the value associated with the carrier signal, and the phase characteristic of the plurality of carrier signals being substantially Said phase displacement calculated for each carrier signal to scramble And a step of combining the phase characteristics of the carrier signal. 2. The method of claim 1, further comprising a reduced peak-to-average power ratio (PA
R), modulating the bits of the input bitstream onto the carrier signal having the substantially scrambled phase characteristic to produce a transmitted signal having R). 3. The method of claim 1, further comprising the step of independently obtaining at each transceiver the value associated with each carrier signal. 4. The method of claim 1, further comprising the step of transmitting the value associated with each carrier signal from one transceiver to another transceiver. 5. The method of claim 1, further comprising maintaining synchronization between transceivers using the values associated with each carrier signal. 6.   The method of claim 1, wherein the value changes with each carrier signal,   Characterized by. 7. The method of claim 1, wherein the value changes with each DMT symbol. 8.   The method of claim 1, wherein the value is derived from a predetermined parameter,   Characterized by. 9.   The method according to claim 8, wherein the predetermined parameter is the number of carriers.   Characterized by. 10. The method according to claim 8, wherein the predetermined parameter is a symbol count number (s).
ymbol count). 11. The method according to claim 8, wherein the predetermined parameter is a hyperframe count. 12. The method according to claim 8, wherein the predetermined parameter is a superframe count. 13. The method of claim 1, further comprising scrambling the bits of the input bitstream. 14. The method according to claim 1, further comprising the step of transmitting a predetermined transmission signal when the amplitude of the transmission signal exceeds a certain level. 15. The method of claim 14, wherein the predetermined transmission signal comprises a predetermined pattern of bits. 16. The method of claim 14, wherein the predetermined transmitted signal comprises pilot tones. 17. The method of claim 16, wherein the pilot tones are used to maintain synchronization timing between the first transceiver and the second transceiver. 18. The method of claim 15, wherein each bit value in the bits of the predetermined pattern is zero. 19. The method of claim 15, wherein the bits of the predetermined pattern are pseudo-random sequence patterns. 20. A plurality of carrier signals for modulating an input bit stream, communicates with the second transceiver by using the transmission signals each carrier signal with one having a phase characteristic with an input bit stream A method for scrambling the phase characteristic of the carrier signal in a multi-carrier modulation system comprising a first transceiver, the method comprising: independently determining each carrier signal and any input bit value carried by the carrier signal. Associated value, calculating a phase displacement of each carrier signal based on the value associated with the carrier signal, and using the phase displacement calculated for each carrier signal And a step of demodulating a transmission signal. 21. The method of claim 20, further comprising, in each transceiver, independently obtaining the value associated with each carrier signal. 22. The method of claim 20, further comprising the step of transmitting the value associated with each carrier signal from one transceiver to another transceiver. 23. The method of claim 20, further comprising maintaining synchronization between transceivers using the values associated with each carrier signal. 24. The method of claim 20, wherein the value changes with each carrier signal. 25. The method of claim 20, wherein the value changes with each DMT symbol. 26. The method of claim 20, wherein the value is obtained from a predetermined parameter. 27. The method according to claim 26, wherein the predetermined parameter is the number of carriers. 28. The method of claim 26, wherein the predetermined parameter is the number of symbols counted.
(symbol count), characterized by. 29. The method of claim 26, wherein the predetermined parameter is a hyperframe count. 30. The method of claim 26, wherein the predetermined parameter is a superframe count. 31. The method of claim 20, further comprising the step of receiving a predetermined transmission if the amplitude of the transmission signal exceeds a certain level. 32. The method of claim 31, wherein the predetermined transmission signal comprises a predetermined pattern of bits. 33. The method of claim 31, wherein the predetermined transmitted signal comprises a pilot tone. 34. The method of claim 33, wherein the pilot tones are used to maintain synchronization timing between the first transceiver and the second transceiver. 35. The method of claim 32, wherein each bit value in the bits of the predetermined pattern is zero. 36. The method of claim 32, wherein the bits of the predetermined pattern are pseudo-random sequence patterns. 37. A transceiver that communicates via a communication channel using a transmission signal comprising a plurality of carrier signals, each carrier signal having a phase characteristic, each transceiver being based on a value associated with the carrier signal. A phase scramble for calculating a phase shift of a carrier signal and combining the phase shift calculated for each carrier signal with the phase shift of the carrier signal so as to substantially scramble the phase shift of the plurality of carrier signals. It is characterized by having a blur. 38. The transceiver of claim 37, further comprising: a modulator in communication with the phase and phase scrambler for producing a transmit signal with a reduced peak-to-average power ratio (PAR). What modulates the bit of an input signal on the carrier signal which has a substantially scrambled phase characteristic, What was provided. 39. A method of communicating over a communication channel in a multi-carrier modulation system, the series of DMTs each having a bit value pattern over the communication channel.
Receiving a transmission signal composed of symbols, comparing the bit value pattern of each received DMT symbol with a predetermined bit value pattern, the bit value pattern of the DMT symbol matches the predetermined bit value pattern In this case, a step of discarding one of the received DMT symbols in the series of DMT symbols and demodulating the DMT symbol if the received DMT symbols do not match is provided.