Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2614—Peak power aspects
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/02—Channels characterised by the type of signal
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/02—Channels characterised by the type of signal
  • H04L5/023—Multiplexing of multicarrier modulation signals, e.g. multi-user orthogonal frequency division multiple access [OFDMA]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. Transmission Power Control [TPC] or power classes
  • H04W52/04—Transmission power control [TPC]

Definitions

• This invention generally relates to communication. More particularly, this invention relates to power control in communications.
• Wireless and wireline communication systems are well known and in widespread use. There are a variety of challenges associated with facilitating successful and reliable communications. One is managing power levels.
• Multi-carrier transmission is often used in wireline and wireless applications, for example with Discrete Multitone Transmission (DMT) for Digital Subscriber Line (DSL) techniques and Orthogonal Frequency Division Multiplexing (OFDM) for WLAN, WiMAX, DVB or the forthcoming E-UTRA wireless communications standards.
• DMT Discrete Multitone Transmission
• DSL Digital Subscriber Line
• OFDM Orthogonal Frequency Division Multiplexing
• a major drawback of multi-carrier transmissions is the high peak-to-average power ratio (PAPR) of the transmit signal.
• PAPR peak-to-average power ratio
• a high PAPR requires a large power amplifier back-off from maximum power so that the operation of the power amplifier remains approximately linear, which in turn reduces the average transmit power and the power efficiency of a particular power amplifier.
• PTS applies one rotation factor to N non- overlapping subvectors, respectively. Every subvector is characterized by multiplication with one rotation factor per OFDM symbol.
• the rotation factors are usually chosen from a discrete set of rotation factors at the unit circle, e.g. ⁇ 1 j,-l,-j ⁇ , such that transmit energy is preserved.
• Clipping causes in-band and out-of-band distortions.
• Adaptive constellation extension and tone injection cause the transmit power to vary and require specific receiver designs. Tone reservation and partial transmit sequences reduce the capacity or data rate of the transmission system.
• An exemplary method of peak-to-average power ratio (PAPR) reduction in a multiple sub-carrier communications system includes selecting a PAPR reduction method from a plurality of PAPR reduction methods dependent upon a modulation scheme in use for a set of sub-carriers. The selected PAPR reduction method is applied to the set of the sub-carriers.
• PAPR peak-to-average power ratio
• Figure 1 is a flow chart diagram summarizing an example procedure used with an embodiment of this invention.
• Figure 1 includes a flow chart diagram 20 that summarizes an example approach for reducing peak-to-average power ratio (PAPR) when composite signals are used in communications.
• This example begins at 22 where a peak in a composite signal is identified. In one example, this occurs in an over-sampled domain that approximates an analog signal because the amplifier used with the composite signal has an analog waveform.
• PAPR peak-to-average power ratio
• a PAPR reduction method is selected for at least one of the users.
• a plurality of users will have a contribution to the peak of the composite signal such that a PAPR reduction method will be useful for each corresponding set of sub-carriers.
• the modulation scheme in use on each set of sub-carriers dictates which PAPR reduction method is selected for the corresponding set of sub-carriers.
• One feature of this approach is that it takes advantage of the differing requirements associated with users that have different channel conditions.
• the PAPR reduction method of choice is a partial transmit sequence (PTS) method.
• PTS is only applied to a set of sub- carriers having a higher modulation schemes in use because the additional overhead for transmitting the information about the rotation factors is small compared to the data rate for these users.
• Every user employing 64 QAM (possibly also 16 QAM) modulation will have the OFDM symbols rotated by either one of the factors ⁇ +1J,- 1,-j ⁇ which requires 2 bits of extra information per OFDM symbol.
• all sub-carriers for a particular user are rotated with the same factor.
• control signaling overhead in additional control signaling for conveying the information about the rotation factors in such an example is relatively small.
• control signaling overhead for 16 QAM users is approximately 2/48
• control signaling overhead for 64 QAM is approximately 2/72.
• PTS has the advantage that the transmission power setting that is decided by the scheduler is not changed by the PAPR method. Furthermore, PTS does not introduce any distortion, which is particularly important for the higher modulations, since these are very sensitive towards modulation errors, which are measured by error vector magnitude (EVM).
• EVM error vector magnitude
• PAPR reduction methods that are used in some examples include clipping, adaptive constellation extension, tone reservation and tone injection. Given this description, those skilled in the art will realize which PAPR reduction method(s) will work well with a particular modulation scheme to meet the needs of their particular situation.
• [0002O]At 30 the selected PAPR reduction method is applied to the corresponding set of subcarriers. The applied PAPR reduction method(s) are intended to reduce a magnitude of the peak of the composite signal.
• At least two users have a contribution to the peak of the composite signal that warrant applying PAPR reduction to their respective sub- carriers. If the different users have different modulation schemes in use on their assigned sub-carriers at a given time, then different PAPR reduction methods are selected and used for their respective sets of sub-carriers.
• At least one and in some cases a plurality of subcarriers that are temporarily or permanently unused and do not carry any modulated data symbols, can be employed to introduce a compensation signal for lowering the PAPR.
• this technique is known as tone reservation method.
• One feature of the disclosed examples is that they allow for cost savings in communication system equipment. For example, lower PAPR implies that lower power amplifier back-off is required and the power efficiency of the power amplifier is increased. In other words, with the disclosed examples, it is possible to avoid requiring more expensive amplifiers to accommodate higher PAPR that would exist if the disclosed techniques were not employed.

Landscapes

• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Computer Networks & Wireless Communication (AREA)
• Transmitters (AREA)
• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Amplifiers (AREA)

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• 2006
  • 2006-10-03 GB GBGB0619490.6A patent/GB0619490D0/en not_active Ceased
• 2007
  • 2007-09-26 WO PCT/US2007/020787 patent/WO2008042189A1/en not_active Ceased
  • 2007-09-26 EP EP07838893A patent/EP2074783B1/en not_active Not-in-force
  • 2007-09-26 KR KR1020097006785A patent/KR101086808B1/ko not_active Expired - Fee Related
  • 2007-09-26 CN CN2007800358768A patent/CN101518009B/zh not_active Expired - Fee Related
  • 2007-09-26 JP JP2009531397A patent/JP4918139B2/ja not_active Expired - Fee Related
  • 2007-09-26 DE DE602007007972T patent/DE602007007972D1/de active Active
  • 2007-09-26 AT AT07838893T patent/ATE475248T1/de not_active IP Right Cessation

Patent Citations (2)

Non-Patent Citations (1)

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