Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W24/00—Supervisory, monitoring or testing arrangements
  • H04W24/02—Arrangements for optimising operational condition
• • 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]
  • H04W52/30—Transmission power control [TPC] using constraints in the total amount of available transmission power
  • H04W52/32—TPC of broadcast or control channels
  • H04W52/325—Power control of control or pilot channels
• • 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]
  • H04W52/38—TPC being performed in particular situations
  • H04W52/42—TPC being performed in particular situations in systems with time, space, frequency or polarisation diversity
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/0224—Channel estimation using sounding signals

Definitions

• the present invention generally relates to wireless communication, and in particular to channel estimation in cellular networks.
• a multiplicity of base stations may be distributed throughout a geographical area.
• Each base station communicates with user equipment (UE) devices, such as cellular phones, for example, which may move throughout the geographical area.
• UE user equipment
• pilot signals which are known to the UE and may be utilized to acquire the necessary channel information. Pilot signals may also be referred to as “reference signals” (RS), and these terms are used interchangeably throughout the following disclosure.
• a base station forming part of a cellular communications system.
• the base station includes a reference signal generator, a boost selector and a transmitter.
• the reference signal generator provides a dedicated reference signal to be transmitted over plural antennas to a dedicated user device in a cellular reception area.
• the boost selector selects a dedicated boost level that is specific for the dedicated reference signal and the transmitter transmits the dedicated reference signal boosted by its dedicated boost level to the user device.
• a first dedicated boost level applied to a first dedicated reference signal transmitted to a first dedicated user may be different than a second dedicated boost level applied to a second dedicated reference signal that is transmitted to a second dedicated user.
• the boost selector includes a boost level setter to set the boost level to generate a predetermined demodulation penalty when a transmitted signal is demodulated by the dedicated user device.
• the demodulation penalty is a function of a channel estimation processing gain plus the boost level.
• the boost selector includes a boost level setter to predefine a set of boost levels associated with modulation and coding scheme values and to select a boost level based on a currently selected modulation and coding scheme.
• the boost selector includes a boost level setter to predefine a set of boost levels and to select an appropriate boost level.
• the boost level is a downboost level.
• the cellular communications system is an LTE communications system.
• the boost level changes the power level of the dedicated reference signal with respect to a transmitted data signal.
• a method for a base station includes providing a dedicated reference signal to be transmitted over plural antennas to a dedicated user device in a cellular reception area, selecting a dedicated boost level that is specific for the dedicated reference signal and transmitting the dedicated reference signal boosted by its dedicated boost level to the user device.
• the method includes receiving a dedicated reference signal transmitted by a base station where the dedicated reference signal has been boosted by a dedicated boost level specific to the user device, determining the dedicated boost level and demodulating a data signal from the base station using the dedicated boost level and a channel estimation value.
• the determining includes estimating a channel estimate from the reference signal and inferring the boost level from a predefined demodulation penalty which is a function of a gain produced by the channel estimate plus the boost level.
• the determining includes receiving a modulation and coding scheme value and setting the boost level to a boost level associated with the received modulation and coding scheme value.
• the determining includes estimating the boost level as a function of a measured power ratio between received data signals and reference signals and selecting the boost level to be a boost level, from among a set of predefined boost levels, whose value is closest to the magnitude of the measured power ratio.
• the determining includes providing each of a set of predefined boost levels to a data demodulator and selecting the boost level which minimizes demodulation errors of the data demodulator.
• a user equipment device forming part of a cellular communications system.
• the device includes a receiver, a boost determiner and a data demodulator.
• the receiver receives a dedicated reference signal transmitted by a base station where the dedicated reference signal has been boosted by a dedicated boost level specific to the user device.
• the boost determiner determines the dedicated boost level and the data demodulator demodulates a data signal from the base station using the dedicated boost level and a channel estimation value.
• the determiner includes an estimator to estimate a channel estimate from the reference signal and an analyzer to infer the boost level from a predefined demodulation penalty which is a function of a gain produced by the channel estimate plus the boost level.
• the determiner includes a receiver to receive a modulation and coding scheme value and a boost level setter to set the boost level to a boost level associated with the received modulation and coding scheme value.
• the determiner includes an estimator to estimate the boost level as a function of a measured power ratio between received data signals and reference signals and a boost selector to select the boost level to be a boost level, from among a set of predefined boost levels, whose value is closest to the magnitude of the measured power ratio.
• the determiner includes a unit to provide each of a set of predefined boost levels to the data demodulator and a selector to select the boost level which minimizes demodulation errors of the data demodulator.
• the boost level is a downboost level.
• the cellular communications system is an LTE communications system and the boost level changes the power level of the dedicated reference signal with respect to a transmitted data signal.
• FIG. 1 is a schematic illustration of a base station configured to steer a transmitted beam towards a UE
• FIG. 2 is a schematic illustration of a base station configured to steer transmitted beams including data symbols and reference symbols toward different users in accordance with an embodiment of the invention.
• FIG. 3 is a schematic illustration of elements of a user equipment device, constructed and operative in accordance with a preferred embodiment, for demodulating the signals from the base station of Fig. 2.
• elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements. Further, where considered appropriate, similar reference numerals that are repeated among the figures indicate corresponding or analogous elements.
• Fig. 1 illustrates a base station 10 transmitting signals along a user channel 12 to a user equipment device (UE) 14.
• UE user equipment device
• the base station 10 may employ "beamforming" techniques to steer a transmitted signal along user channel 12 so that it may be best received by the intended UE (14).
• a user signal S user is transmitted through a multiplicity of antennas 16 (three antennas are shown in this example, although a different number of antennas may be used), where each copy of the signal is multiplied by a different complex valued weight W 1 (i.e. a gain factor and a phase offset) for each antenna.
• W 1 i.e. a gain factor and a phase offset
• the combination of the weights define a direction to the beam and/or a region of best reception.
• the common reference signals of LTE which are common to all UEs serviced by a base station, are generally inappropriate for channel estimation by a UE 14 receiving its data signal through beamforming, because the common reference signals are not transmitted through any beamforming weights while the UE's data signal is.
• these UEs have dedicated reference signals.
• the dedicated reference signal for each UE undergoes exactly the same beamforming weights (and consequently, the same channel conditions) as its UE's data signal, and are therefore used for the construction of the channel estimator for the beamforming mode.
• UEs operating in beamforming mode may also receive dedicated reference signals.
• Fig. 2 illustrates multiple reference signals RS transmitted through multiple antennas 16, for two exemplary users, use ⁇ and user 2 .
• Different weights may be used for different UEs; thus, Fig. 2 shows a reference signal RSuseii and a data signal S userl undergoing one set of weights optimized for user ⁇ and a reference signal RS user 2 and data signal S use r 2 undergoing another set of weights optimized for user 2 .
• Both the data signals S and the reference signals RS are transmitted through the same beamforming antennas 16; however, since user !
• Fig. 2 shows the two separately.
• user ! and user 2 may be served by different portions of the time-frequency domain, and in other cases (often known as multi-user MIMO) they may share, or partially share, the time-frequency resources.
• UEs 14 may be in particularly noisy locations and thus, channel 12 of Fig. 1 may have a high level of noise, UEs 14 may only be able to generate a poor quality channel estimation from its dedicated reference signals. This will degrade the quality of the data demodulation. In such a case, it may be desirable to "boost" (i.e.
• the power of the reference signals may increase the power of the reference signals. This may increase the signal to noise ratio of the reference signals, thereby enabling UEs 14 to calculate a more accurate channel estimate and ultimately resulting in an improved data demodulation.
• it may make sense to reduce the power (i.e. "downboosting") to the dedicated reference signals, e.g. for the purpose of reducing the interference to other UEs in the cellular network.
• downboosting may change the power level of the transmitted signal.
• the boost typically may be with respect to the power level in the data signal to be demodulated. Alternatively, it may be with respect to some other suitable, predefined power level.
• This power level may be a fixed power level, fixed by the system, or it may be a changeable power level, changed for a dedicated user device. In which case, the boost level may be the extra power over the changed power level.
• base station 10 may comprise a boost selector 20 which may select boost/downboost values G for each user.
• Base station 10 may multiply the relevant reference signal RS by the relevant boost value G (G userl for RS use ri or G User2 for RS user2 ) and may transmit the resultant signal through the antennas 16, after multiplication by the appropriate beamforming weights w.
• the UE typically needs to know the strength of the RS boost, in order to correctly scale the channel estimator to match the data signal (since the RS boost may add a scale factor to the output of the estimator).
• base station 10 may signal the magnitude of the dedicated RS boost relative to the data to the UE.
• the UE may blindly detect the RS-to-data boost.
• Fig. 3 illustrates a user equipment device 14, constructed and operative in accordance with an embodiment of the disclosure, which demodulates data in a beamforming mode with boosted reference signals.
• User equipment device 14 may comprise a receiver 28, a dedicated channel estimator 30, a boost determiner 32 and a data demodulator 34.
• Receiver 28 may be an antenna or any other device capable of receiving reference signal RS user and data signal S u s er .
• Dedicated channel estimator 30 may be any suitable channel estimator, such as a Weiner estimator described in Chapter 14 of the book OFDM and MC-CDMA for Broadband Multi-User Communications, WLANs and Broadcasting by L. Hanzo et al, John Wiley & Sons, 2003.
• Dedicated channel estimator 30 may receive the dedicated reference signal RS user and may generate an initial channel estimate h therefrom.
• Boost determiner 32 may determine the boost value.
• base station 10 may signal the UE with the boost value, in which case, boost determiner 32 of UE 14 may process the signaling to determine the boost value.
• boost determiner 32 may blindly estimate the ratio between pilot-to- data power and may determine the boost from this estimate.
• data demodulator 34 may utilize channel estimate h (produced by channel estimator 30) and boost level G (from boost determiner 32) to demodulate any incoming data signals S user - [0041]
• boost selector 20 (Fig. 2) may select the dedicated boost value G user in any suitable way in order to optimize the overall network performance.
• boost selector 20 may set the power for the dedicated reference signal (known as the "DPICH" in the LTE standard) so that some agreed upon, fixed, a-priori data demodulation penalty may be encountered, given an agreed upon channel estimator, such as estimator 30. For example, if the reference boost level is set such that the post processing channel estimation errors are 1OdB lower than the combination of noise and interference at the output of data demodulator 34, an overall data demodulation penalty of about 0.5dB will be observed. In general, for this embodiment, boost selector 20 may set the boost level such that the sum of a channel estimation processing gain plus the power boost may yield the desired a-priori known demodulation penalty.
• the dedicated reference signal known as the "DPICH" in the LTE standard
• Boost determiner 32 may infer the boost level from the known penalty.
• dedicated channel estimator 30 typically may determine post processing channel estimation errors resulting from noise samples from a plurality of dedicated reference pilots, averaged together. If these errors are different than the expected error level of 1OdB lower than the combination of noise and interference at the output of data demodulator 34, then the boost level is the cause. For example, if the post processing errors are only 3dB lower and the expected post processing errors are targeted at 1OdB below the total noise plus interference level, then the reference signal boost is 7dB. Or, if the post processing errors are 13dB lower, then the downboost is -3dB.
• boost selector 20 may have a set of predefined reference boost levels, one for each MCS, and may select the boost level based on the currently selected MCS. These boost levels, as a function of MCS, may be determined from downlink performance simulations with the DPICH reference signals.
• boost determiner 32 may determine the boost level as the boost level associated with the current MCS value.
• boost selector 20 may have a predefined set of boost levels, e.g.: 0, 3 and 6 dB, from which to select.
• Boost determiner 32 may then estimate the boost level from the measured power ratio between received data signals and reference signals, selecting the boost level to be the predefined boost level whose value is closest to the measured power ratio.
• boost determiner 32 may alternately provide each of the boost levels to data demodulator 34 and may select the boost level which minimizes demodulation errors.
• any "processing,” “computing,” “calculating,” “determining,” or similar operations refer to operations that may be performed in dedicated computing hardware, or in a generalized computer device using firmware or software.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)

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• 2009
  • 2009-03-25 US US12/410,931 patent/US8412271B2/en active Active
  • 2009-03-27 JP JP2011501317A patent/JP5282321B2/ja active Active
  • 2009-03-27 EP EP09724906.4A patent/EP2258130B1/en active Active
  • 2009-03-27 CN CN200980119579.0A patent/CN102047735B/zh active Active
  • 2009-03-27 WO PCT/IB2009/005099 patent/WO2009118635A2/en not_active Ceased
• 2013
  • 2013-03-26 US US13/850,856 patent/US9781611B2/en active Active

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