3/.9:>.Eable Commissioner of Patents and Trademarks
`
`ington, DC 20231
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`66/6U/IIMILlllwylmllllllllltl
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`NEW PROVISIONAL APPLICATION TRANSNIITTAL LETTER
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`w,_..‘I’?
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`Transmitted herewith for filing is the Provisional Patent Application of InVentor(s):
`
`Residence:
`
`Marcos C. Tzannes
`
`12 LaEspira1
`Orinda, CA 94563
`
`Citizenship
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`United States
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`Office Address:
`
`Same as above
`
`CSCO-1008
`Cisco v. TQ Delta
`Page 1 of 7
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`

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`PATENTS
`103118-0058
`
`Transceiver Supporting Multiple Applications
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`Enclosed are the following papers required to obtain a filing date under 37 C.F.R. §l.53(c):
`
`lblb}IQ
`
`Sheets of Informal Drawings
`Pages of Specification, Drawings & Tables
`Claims
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`
`
`
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`;i33&j1"s;::‘=i§"e:‘éEiii:MfliEl:ljljlj
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`1%..
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`The following papers, if indicated by an
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`are also enclosed:
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`A Declaration and Power of Attorney
`An Assignment of the invention
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`An Information—Disclosure Statement, Form PTO-1449 and a copy of
`each cited reference
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`A Small—Entity Declaration
`A Certificate of Express Mailing, Express Mail Label No. EE8 10799905US
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`Basic Fee:
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`$150
`
`A check in the amount of $150 is enclosed to cover the Filing Fee.
`
`Please address all communications and telephone calls to the undersigned.
`
`Respectfully submitted,
`
`,&a;1Z£,l.ag‘“
`
`Gail I./eonick
`Aware, Inc.
`
`":;’£"'““’
`
`40 Middlesex Turnpike
`Bedford, MA. 01730
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`
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`21333;:21333::atiiisi2%)}:"iii.
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`Page 2 of 7
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`

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`PATENT
`1031 18-0060
`
`UNITED STATES PROVISIONAL PATENT APPLICATION
`
`0f
`
`Marcos C. Tzannes
`
`for a
`
`A METHOD FOR RANDOMIZING THE PHASE OF THE CARRIERS IN A
`
`MULTICARRIER COMMUNICATIONS SYSTEMS TO REDUCE THE PEAK
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`TO AVERAGE POWER RATIO OF THE TRANSMITTED SIGNAL
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`Page 3 of 7
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`

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`Aware Proprietary and Confidential Information
`
`Patent
`103118-0060
`
`A Method for Randomizing the Phase of the Carriers in a Multicarrier Communications Systems to
`Reduce the Peak to Average Power Ratio of the Transmitted Signal
`
`By
`
`Marcos Tzannes
`
`Background of the invention
`
`Discrete Multi-Tone (DMT) modems (a.k.a. multicarrier modems) transmit multiple individually
`modulated tones in parallel. The DMT transmitter is typically implemented by using an Inverse Fast
`Fourier Transform (IFFT) to generate the modulated waveforms (Figure 1). The resulting transmitted time
`domain signal, which is the linear combination of multiple modulated tones (carriers), can be approximated
`to have a Gaussian probability distribution. This approximation is accurate if the phase of the modulated
`tones is truly random. Since phase modulation is used to modulate signals in DMT systems, this implies
`that the transmitted data bits must be random as well. Most DMT transmitters use data scramblers for this
`reason. The scrambler, which is positioned before the IFFT modulator, will output data bits that are
`randomized in order to assure that the transmitted signal at the output of the IFFT modulator will have a
`Gaussian probability distribution. Generating a transmitted signal with a Gaussian distribution is important
`in order to transmit a signal with a low Peak to Average Power Ratio (PAR). The PAR of a signal is an
`important aspect of a system design because it effects the total power consumption and component linearity
`requirements of the system.
`
`Data bits
`
`random bits
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`IFFT
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`Scrambler
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`Modulator
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`Transmitted
`Signal
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`Figure 1: DMT modulator
`
`The problem with DMT transmitters that operate in such a manner is the inherent assumption that the phase
`of the modulated carriers is random. If for any reason the phase of the modulated carriers is not random
`then the PAR can increase greatly resulting in system with high power consumption and/or with high
`probability of clipping the transmitted signal. Examples of cases where the phases of the modulated carriers
`are not random are when:
`1)
`scramblers are not used
`2) multiple tones are used to modulate the same data bits
`3)
`the constellation maps (mapping of data bits to tone phases) used for modulation are not random
`enough.
`
`There are obviously other cases where the phase of the [FFT carriers may not be random enough to
`generate a "Gaussian distributed" transmitted signal. This invention provides a mechanism to randomize the
`phase of DMT tones for the three examples above, as well as for other cases not specified in this invention
`which require such randomization to decrease the PAR of me transmitted signal.
`
`Page 4 of 7
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`

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`Aware Proprietary and Confidential Information
`
`Patent
`103118-0060
`
`Overview of the invention
`
`This invention describes a method for randomizing the phase of DMT carriers in order to reduce the PAR
`of the transmitted signal. The phase randomization is important in cases where several modulated carriers
`may have the same phase. As mentioned in the previous section, examples of when this would occur are:
`1. The data bits being modulated are not truly random. This could occur, for example, if a scrambler is
`not being used and the data bits have a specific repetitive pattern (e. g. all zeros, or all ones)
`2. The same data bits are used to modulate multiple carriers. This would occur in cases where it was
`desired (or required) to send the same data bits on different carriers and then combine the results at the
`receiver in order to receive the bits at a lower Bit Error Rate (this is a well-known method for using
`frequency diversity to decrease the BER).
`Constellation maps do not provide a truly random phase mapping. Constellation maps are used map
`data bits to DMT carrier phases. An example of a commonly used constellation map is shown in table
`1. This one bit constellation map will provide some randomness to the phase of the DMT tones, but
`this randomness is limited since there are only two possible phase states.
`
`Data Bits
`
`Phase of DMT carrier
`
`-
`
`Table 1: one bit constellation map
`
`For the conditions mentioned above, and other conditions where the DMT carrier phases are not
`sufficiently random, this invention describes how to efficiently randomize the phase of the modulated
`carriers in order to provide a low PAR in the transmitted signal.
`
`The method for randomizing the phase of these tones is as follows:
`
`The phase of each DMT carrier is randomized by adding a different phase shift to each DMT carrier. This
`phase shift is based on a variable that is known in advance by the DMT transmitter and the receiver. This
`variable is not related to the data bits so that it is independent of the randomness of the data bits. Examples
`of such variables are the DMT carrier number, the DMT symbol (or frame) count (or superframe count),
`etc.
`
`DMT carrier number: DMT systems enumerate the carriers in ascending order in frequency. The DMT
`carrier number represents the location of a tone in frequency relative to other tones. As an example, in
`DMT ADSL systems there are 256 DMT carriers, separated by 4.3125 kHz, spanning the frequency
`bandwidth from 0 kHz to 1104 kHz. DMT carriers are numbered from 0 to 255. As an example, "DMT
`carrier number 50" represents the 50"‘ DMT carrier located at the frequency position 50*4.3 l25=2l5.625
`kHz.
`
`DMT symbol count: DMT systems often use DMT symbol (or frame) counters to synchronize the data
`transmitted between the transmitter and the receiver. DMT symbol counters are used to number DMT
`symbols in time as they are transmitted and received by DMT systems. In DMT ADSL systems there is a
`symbol counter called a "frame counter" that is synchronized between the transmitter and the receiver that
`is based on a module 68 count. This means the ADSL DMT symbol count (frame count) counts from 0 to
`68 and then repeats again from 0 to 68 and so on. The collection of 69 consecutive DMT frames is called a
`"DMT superframe" in ADSL systems. There is also an ADSL DMT "superframe counter" that is
`synchronized between the transmitter and the receiver that is based on a module 255 count of DMT
`superframes. This means the ADSL DMT superframe count counts superframes from 0 to 255 and then
`repeats again from 0 to 255 and so on.
`
`In this invention, the phases of DMT carriers are randomized by adding different phases shifts to the DMT
`carriers based on variables such as the DMT carrier number and DMT symbol count. The invention uses
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`Page 5 of 7
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`

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`Aware Proprietary and Confidential Information
`
`Patent
`103118-0060
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`equations that may contain one or several of these variables. As examples, the phase of a carrier could be
`randomized by adding a different phase shift to each ca.rrier that is based on the following equations:
`
`Example 1: (Phase shift added to carrier number N) = N*TV3, modulo 211. In this example, carrier number
`N=50 would have a phase shift added to the modulated carrier that is equal to 50*1t/3 (modulo 27:) = 2/37:.
`Carrier number N=5l would have a phase shift added to the modulated carrier that is equal to 51*7'r/3
`(modulo 271) = it. And so on.
`
`Example 2: (Phase shift added to carrier number N): (N+M)*'rr/4, modulo 27t where M is the symbol count.
`In this example, carrier number N=5O on DMT symbol count M=8 would have a phase shift added to the
`modulated carrier that is equal to (50+8)* TE/4 (modulo 2n) = rt/2. Carrier number N=50 on the next DMT
`symbol count M29 would have a phase shift added to the modulated carrier that is equal to (50+9)* 7r/4
`(modulo 271:) = 37t/4.
`
`Example 3: (Phase shift added to carrier number N): X1; * at/6, module 21:, where XN is an array of N
`pseudo-random numbers. In this example, carrier number N:5 and XN = [3, 8, l, 4, 9, 5, ...] would have a
`phase shift added to the modulated carrier that is equal to (5+9)* rr/6:7‘:/3. Carrier number N26 would have
`a phase shift added to the modulated carrier that is equal to (5+5)* TL/6=5‘rt/3.
`
`Obviously other equations are possible using other variables that are synchronized and known by both the
`transmitter and receiver. Obviously other constructions of equations are also possible. The fundamental
`principle used in this invention is to use known parameters at the transmitter and the receiver to randomize
`the phase of the tones in a multicarrier system. By using known parameters that vary over frequency (such
`as the DMT tone number) or over time (such as the symbol count) to randomize the phase of all the carriers
`transmitted DMT symbol, the transmitter and receiver can easily process the data without regard to the
`information data bit content. This invention has many advantages including the reduction of the PAR of the
`transmitted signal when the data bits being modulated are not random. As a result, another advantage of
`this invention is that it allows elimination of the data bit scrambler in DMT systems.
`
`In another embodiment of this invention, the phase scrambling is used as a method to avoid clipping of the
`transmitted DMT signal on a symbol by symbol basis. In this embodiment, if a particular DMT symbol
`clips in the time domain (i.e. one or more time domain samples are larger than the maximum allowed
`digital value), the transmitter sends a predefined signal in place of the clipped DMT transmitted signal. The
`predefined signal is the same duration in time as a DMT symbol and can be treated by the transmitter and
`the receiver as a DMT symbol as such. It simply is not based on the modulated information bits and can be
`easily detected by the receiver. When the receiver detects the predefined signal it just discards it.
`In this embodiment the phase of the DMT carriers are scrambled based on a parameter that varies over time
`(e. g. the symbol counter). As a result, at the transmitter the same information bits modulated in the DMT
`symbol following the clipped DMT symbol will produce a different time domain signal. The new DMT
`symbol will have a different phase randomization than the clipped DMT symbol because the phase of the
`DMT tones will have changed since the phase randomization parameters change over time. As a result,
`since clipping occurs infrequently, the new DMT symbol will most likely not clip as well. In the unlikely
`event the new DMT symbol does clip then once again the same predefined signal is sent by the transmitter
`instead of the clipped DMT symbol. This process continues until a DMT symbol that is not clipped is
`generated and sent. The probability of a DMT signal clipping in time depends on the PAR of the signal.
`In general, DMT systems are designed to clip very infrequently, eg. on the order of 1 clip every 1E7 time
`domain samples. Therefore it is very unlikely that consecutive DMT symbols that are phase randomized
`according to this invention will clip. If they do though, as described above, the system simply sends another
`version of the predefined signal and tries again to generate a non—clipped signal during the next DMT
`symbol period. The receiver simply looks for the predefined signal in every received DMT symbol period.
`If it detects that predefined signal pattern, the receiver discards the received DMT symbol. If it does not
`detect the signal predefined pattern it demodulates the received DMT symbol using the phase
`randomization information for that specific instance in time.
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`Page 6 of 7
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`

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`Aware Proprietary and Confidential Information
`
`Patent
`103118-0060
`
`As mentioned above the predefined signal has the same duration as a DMT symbol in order to maintain
`symbol timing between transmitter and receiver. Obviously the predefined transmitted signal can be a
`variety of different signals. It can be a known pseudo-random sequence pattern that is easily detected by the
`receiver. It can also be an "all zeros" signal, i.e. a zero voltage signal at the transmitter output (zero volts
`modulated on all the carriers). This can also be easily detected by the receiver. This also has the advantage
`that it greatly reduces the power consumption of the transmitter when this zero volt signal being
`transmitted. Obviously any other predefined, easily detected signal can be used as well.
`One important point to note is that in case where a pilot tone is used for timing recovery the predefined
`signal may contain a pilot tone in order to maintain sample phase lock during reception of the predefined
`signal.
`
`As specific example of this embodiment of the invention consider the case where the following equation is
`used to randomize the phase of each DMT carrier:
`
`Phase of carrier # N = (II:/3)* (M+N), where N is the DMT carrier number and M is the DMT symbol count.
`
`If on DMT symbol count M=5 the DMT symbol clipped in the time domain then the "all zeros" signal is
`sent instead of the current clipped DMT symbol. On the following DMT symbol period, DMT symbol
`count M=6 is used in the phase randomizing equation generating a different time domain signal. If this new
`signal is not clipped then the DMT symbol is transmitted. If this new signal is clipped then the DMT
`symbol is not transmitted and the "all zeros" signal is sent instead. The algorithm is continued in this
`manner so that only signals without clipping are transmitted.
`Another benefit of this embodiment of the invention is that it allows DMT systems to be designed with a
`lower PAR. In general DMT systems are designed to have a large PAR, on the order of 14.5 dB. This will
`result in a 1E-7 clipping probability for die time domain signal. The penalty of a high PAR is that it
`requires the implementation of an analog front end with higher power consumption and analog components
`with higher voltage linearity requirements.
`This invention allows the design of DMT systems with lower PAR because in the event a DMT symbol
`clips, the predefined signal is sent instead. As a result the DMT systems can relax the strict 1E-7
`probability of clipping requirement and lower the PAR. As an example the system could operate with a IE-
`5 probability of clipping (PAR=12.8 dB). Assuming a DMT symbol had 512 time domain samples this
`would result in one clipped DMT symbol out every 100000/512: 195 DMT symbols. Therefore 1 out of
`195 or approximately 0.5% of the time the predefined signal would be sent instead of the clipped DMT
`symbol. This 1.7 dB reduction in PAR will result in large savings in transmitter complexity in the form of
`power consumption and component linearity.
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`Page 7 of 7