WO2011071428A1 - Estimation de charge dans une communication sans fil - Google Patents

Estimation de charge dans une communication sans fil Download PDF

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Publication number
WO2011071428A1
WO2011071428A1 PCT/SE2009/051397 SE2009051397W WO2011071428A1 WO 2011071428 A1 WO2011071428 A1 WO 2011071428A1 SE 2009051397 W SE2009051397 W SE 2009051397W WO 2011071428 A1 WO2011071428 A1 WO 2011071428A1
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WO
WIPO (PCT)
Prior art keywords
user
users
noise
noise floor
interference
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PCT/SE2009/051397
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English (en)
Inventor
Karl Torbjörn WIGREN
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Telefonaktiebolaget Lm Ericsson (Publ)
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Application filed by Telefonaktiebolaget Lm Ericsson (Publ) filed Critical Telefonaktiebolaget Lm Ericsson (Publ)
Priority to PCT/SE2009/051397 priority Critical patent/WO2011071428A1/fr
Priority to US13/514,009 priority patent/US8665937B2/en
Priority to EP09852110.7A priority patent/EP2510630B1/fr
Priority to CN200980162809.1A priority patent/CN102656812B/zh
Publication of WO2011071428A1 publication Critical patent/WO2011071428A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/711—Interference-related aspects the interference being multi-path interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • H04B17/318—Received signal strength
    • H04B17/327—Received signal code power [RSCP]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/20—Monitoring; Testing of receivers
    • H04B17/26—Monitoring; Testing of receivers using historical data, averaging values or statistics
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • H04B17/345—Interference values
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
    • H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
    • H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
    • H04B2201/7097—Direct sequence modulation interference
    • H04B2201/709718—Determine interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
    • H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
    • H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
    • H04B2201/7097—Direct sequence modulation interference
    • H04B2201/709727—GRAKE type RAKE receivers

Definitions

  • the present invention relates in general to methods and devices for estimation of power-related quantities in cellular communications systems and in particular to such methods and devices in cellular communications systems using interference whitening.
  • WCDMA Wideband Code Division Multiple Access
  • WCDMA Wideband Code Division Multiple Access
  • the enhanced uplink of the WCDMA system is one ingredient in the mobile broadband solution of WCDMA.
  • the load needs to be kept below a certain level. This follows since the majority of uplink user channels, at least in WCDMA, are subject to power control. This power control aims at keeping the received power level of each channel at a certain signal to interference ratio (SIR), in order to be able to meet specific service requirements.
  • SIR signal to interference ratio
  • the Radio Base Station tries to keep each channel at its specific preferred SIR value, it may happen that an additional user, or bursty data traffic of an existing user, raises the interference level, thereby momentarily reducing the SIR for the other users.
  • the response of the RBS is to command a power increase to all other users, something that increases the interference even more. Normally this process remains stable below a certain load level. In case a high capacity channel would suddenly appear, the raise in the interference becomes large and the risk for instability, a so called power rush, increases. It is thus a necessity to schedule high capacity uplink channels, like the enhanced uplink (EUL) channel in WCDMA, so that one can insure that instability is avoided. In order to do so, the momentary load must be estimated in the RBS or any node connected thereto. This enables the assessment of the capacity margin that is left to the instability point.
  • EUL enhanced uplink
  • a minimum value of a power quantity preferably a difference between the instantaneous total received wideband power and the instantaneous sum of powers of all links used in the same cell, is used as an estimate of an upper limit of the thermal noise floor, based on which a noise rise measure can be estimated.
  • An optimal and soft algorithm for noise rise estimation based on a similar basic idea of minimum values is disclosed in the published international patent application WO 2007/024166.
  • interference cancellation is being introduced in WCDMA.
  • a conventional procedure to perform IC is summarized by the following steps.
  • a channel model of the interferer to be cancelled is estimated. This does not cause any additional operations, since this channel model is anyway needed.
  • the transmitted signal of the interferer to be cancelled is also decoded. This is also anyway needed.
  • a replica of the received signal of the interferer to be cancelled is then created, by use of the channel model and the decoded signal. This replica may e.g. be reconstructed as an IQ chip stream.
  • the replica of the interfering signal is subsequently subtracted from the received signal of the user to be decoded, thereby hopefully reducing the remaining power of the interferer to very low power levels.
  • Another approach to limit the effect of interference is to use some kind of interference whitening approaches, such as GRAKE, GRAKE+ or chip equalizer.
  • the codes not used by the present user u may be used in order to estimate the covariance matrix R u .
  • the load estimations have to be performed taking the interference whitening of the GRAKE+ into account.
  • the thermal noise floor is changed in the same manner as the interference reduction obtained by the GRAKE+ process, and can no longer be treated as constant after interference whitening.
  • a treatment analogue of WO 2008/097145 can therefore not be used for achieving a noise rise estimation, the reason being that WO 2008/097145 requires the noise floor to be constant. There is thus a problem of using the created reduced interference, since no reliable noise rise estimation is available. Similar problems are present for systems utilizing GRAKE, where sub-blocks of the covariance matrix of (1) are used.
  • An object of the present invention is thus to provide methods and arrangements for providing reliable noise rise estimations in wireless communication systems using interference whitening methods, such as the GRAKE+ or the chip equalizer receivers.
  • a method for noise rise estimation in a wireless communication system comprises receiving of radio signals intended for a plurality of users.
  • An interference whitening is performed on the received radio signals based on one of GRAKE, GRAKE+ and chip equalizer with respect to a first user of the plurality of users.
  • a useful signal power for the first user after the interference whitening is determined for a plurality of time instances.
  • a first user noise floor compensation factor is derived based on combining weights for the first user used in the interference whitening.
  • a probability distribution for a compensated useful signal power for the first user is estimated from at least the determined useful signal power for the first user and the first user noise floor compensation factor.
  • a conditional probability distribution of a noise floor measure is computed based on at least the determined useful signal power for the first user and the first user noise floor compensation factor.
  • a noise rise measure for the first user is then calculated based at least on the compensated useful signal power for the first user and the conditional probability distribution of a noise floor measure.
  • an arrangement for noise rise estimation in a wireless communication system comprises a digital receiver and an interference whitener connected to the digital receiver.
  • the interference whitener is based on one of GRAKE, GRAKE+ and chip equalizer.
  • the interference whitener is arranged for providing interference whitening for a plurality of users at an output.
  • the arrangement further comprises a processor connected to the output from the interference whitener.
  • the processor is arranged for determining a useful signal power for a first user for a plurality of time instances and arranged for deriving a first user noise floor compensation factor based on combining weights for the first user used in the interference whitening.
  • the processor is further arranged for estimating a probability distribution for a compensated useful signal power for the first user from at least the determined useful signal power for the first user and the first user noise floor compensation factor and arranged for computing a conditional probability distribution of a noise floor measure based on at least the determined useful signal power for the first user and the first user noise floor compensation factor.
  • the processor is also arranged for calculating a noise rise measure for the first user, based at least on the probability distribution for the compensated useful signal power for the first user and the conditional probability distribution of a noise floor measure.
  • a base station of a wireless communication system comprises an arrangement for noise rise estimation according to the second aspect.
  • One advantage with the present invention is that the reduced interference levels achieved by GRAKE+ or chip equalizer can be fully utilized to increase the total available capacity of a wireless communication system.
  • the invention will thus be beneficial for throughput, capacity and coverage gains associated with new types of IC receiver structures when implemented.
  • FIG. 1 is a schematic illustration of a wireless communication system
  • FIG. 2 is a schematic illustration of a noise rise estimation arrangement
  • FIG. 3 is a schematic illustration of a receiver chain including a noise rise arrangement
  • FIG. 4 is a schematic illustration of a receiver chain including interference cancellation and a noise rise arrangement
  • FIG. 5 is a block scheme of an embodiment of a noise rise estimation arrangement according to the present invention.
  • FIG. 6 is a flow diagram of an embodiment of a method according to the present invention.
  • Fig. 1 illustrates a schematic view of an embodiment of such a wireless communication system 150.
  • a radio base station 160 communicates via its antenna/ antennas 39 with a multitude of user equipments (UE) 170 situated within a cell 151 of the wireless communication system 150.
  • Radio signals transmitted from the RBS 160 to the UEs 170 are denoted as downlink signals 181
  • radio signals transmitted from the UEs 170 to the RBS 160 are denoted as uplink signals 180.
  • This invention mainly considers the uplink signals, whereby arrangements for noise rise estimation typically are provided in the RBS 160.
  • the RBS 160 also receives interfering signals 182, 183.
  • N(t) is the thermal noise level as measured at the antenna connector.
  • the thermal noise level at the antenna connector is essentially time invariant and if any variations in time occur, they are generally small and slow. It remains to define what is meant with RTWP(t) .
  • the definition used here is simply the total wideband power:
  • RTWPit ⁇ P k ⁇ t)+ I N ⁇ t)+ N(t), (3)
  • I N (t) denotes the power as received from neighbour cells ( N ) of the communication system.
  • the major difficulty of any RoT estimation algorithm is to separate the thermal noise power from the interference from neighbour cells.
  • Another specific problem that needs to be addressed when determining the load is that the signal reference points are, by definition, at the antenna connector.
  • the measurements are however obtained after the analogue signal conditioning chain, in the digital receiver.
  • the analogue signal conditioning chain does introduce a scale factor error of about 1 dB (1- sigma) that is difficult to compensate for. Fortunately, all powers of (3) are equally affected by the scale factor error so when (2) is calculated, the scale factor error is cancelled as
  • Fig. 2 An embodiment of the RoT estimation algorithm currently in use is depicted in Fig. 2. It is described in detail in the published international patent application WO 2007/024166.
  • the algorithm estimates the RoT, as given by (2).
  • the main problem solved by the estimation algorithm is the accurate estimation of the thermal noise floor N(t) . This is based on the assumption of that the experienced noise floor varies in time only very slowly, which enables the use of estimation algorithms. Since it is not possible to obtain exact estimates of this quantity due to the neighbour cell interference, the estimator therefore applies an approximation, by consideration of the soft minimum as computed over a relative long window in time.
  • an arrangement 1 10 for noise rise estimation in a wireless communication system is supplied with RTWP measurements 120.
  • the RTWP measurements 120 are used in a Kalman filter 1 12 to produce filtered estimates 122 of the RTWP as well as probability density functions 124 of the RTWP.
  • These probability density functions 124 are provided to a noise floor estimator 1 14, in which noise floor estimates 128 are provided with knowledge of a prior noise floor distribution 126.
  • the noise floor estimator 1 14 operates preferably with a sliding window algorithm.
  • the noise floor estimates 128 and the filtered estimates 122 of the RTWP are provided to a noise rise determiner 1 16, producing an output of a noise rise measure, in this embodiment a RoT value 130. It is, as noted above, important to understand that this estimation relies on the fact that the noise floor is essentially constant over very long periods of time (disregarding the small temperature drift) .
  • the sliding window algorithm of the above section has the disadvantage of requiring a large amount of storage memory. This becomes particularly troublesome in case a large number of instances of the algorithm are needed, as may be the case when IC is introduced in the uplink.
  • a recursive algorithm was disclosed in the published international patent application WO 2007/0055626. That algorithm reduces the memory requirements of the sliding window scheme discussed above at least by a factor of 100.
  • the algorithms referred to in the sections concerning sliding window and recursive algorithms further above build on pre-configured information of the approximate level on the thermal noise power floor, and thereby indirectly on the RTWP and RSEPS power levels.
  • this pre-configuration may be erroneous or the conditions may have changed due to e.g. faulty hardware or external disturbances from e.g. radar stations. This may cause large but relatively slow variations of the levels of the thermal noise floor, the RTWP and the RSEPS. The consequence is a reduced performance of the algorithms described the sections concerning sliding window and recursive algorithms, which is due to a misaligned power quantization grid.
  • WO2008/041895 discloses means for adaptation and integration of a slowly varying power scale factor into the algorithms of sliding window and the recursive algorithms. Similar adaptation can be also be employed within the present invention. It is stressed that the invention of WO2008/041895 has nothing to do with interference whitening.
  • Fig. 3 schematically illustrates the arrangement 1 10 for noise rise estimation in relation to the receiver chain.
  • An antenna 100 receives electromagnetic signals and gives rise to a received analogue signal 101, which is provided to a digital receiver 102.
  • the digital receiver 102 provides a stream of digital signals 103 representative to the analogue signals, however, as mentioned above modified with a certain scale factor.
  • a measurement unit 109 is connected to the stream of digital signals 103 and performs measurements of received total wideband powers 120, which are handed on to the arrangement 1 10 for noise rise estimation.
  • FIG. 4 The stream of digital signals 103 is provided to an interference canceller 104, where signals not intended for a particular user are removed.
  • An interference cancelled digital signal 105 intended for a particular user is provided as output.
  • load estimation can be applied also to such interference cancelled digital signal 105, where the measured RTWP measure refers to the digital signal after interference cancelling.
  • the RoT estimation algorithms are still applicable in this case, since a constant noise power level is estimated.
  • the objects of the present invention are achieved by the development of optimal filtering algorithms that have a number of properties.
  • the RTWP (received total wideband power), as defined after G-rake+ whitening IC processing, is integrated into a new time variable extended Kalman filter based front end of the thermal noise floor and RoT estimator.
  • the RSEPS Receiveived scheduled EUL power share, i.e. the scheduled traffic in the enhanced uplink
  • G-rake+ whitening IC processing is integrated into the new time variable extended Kalman filter based front end of the thermal noise floor and RoT estimator.
  • the procedures take account for the fast time varying scale factor effects caused by G-rake+ interference whitening, in the new front end.
  • optimal filtering of said RTWP and RSEPS defined after G-rake+ processing, is provided in order to suppress measurement disturbances and enhance the performance.
  • the present invention provides solutions where load estimations reflect the reduced interference experienced by users exploiting interference whitening receivers.
  • the load of a particular single user exploiting GRAKE, GRAKE+ or the chip equalizer can be estimated.
  • a load estimation for the whole cell can be obtained based on such single user load estimation.
  • the present invention disclosure is focused on GRAKE+. However, also systems using GRAKE or chip equalizers can be configured in a similar manner.
  • the load estimations that reflect the reduced interference experienced by users exploiting interference whitening receivers can be obtained by estimating the received signal and exploiting results from the GRAKE process by matrix- vector operations in order to scale the noise floor estimate, obtained based on the non-interference-whitened signals, to the influence of the interference whitening process.
  • Such operations require quite large computational power, which is why such a solution may be inappropriate for applications with limited available computational power.
  • only computation of inner products may be necessary, which limits the required computational complexity significantly, possibly of the order of at least ten times.
  • the thermal noise power floor must be estimated from RTWP before interference whitening processing, e.g. G-rake+ processing, the estimated thermal noise power floor may suffer from a raised level, which also reduces the performance of the RoT, estimated after G-rake+ interference whitening.
  • the present invention provides further processing of signal quantities obtained by prior art approaches, and utilizes algorithms that enable thermal noise floor estimation and RoT estimation after interference whitening. This provides for optimal filtering of the signal quantities allowing for further suppression of measurement noise affecting the signal quantities.
  • the performance of thermal noise floor and RoT estimation for G-rake+ whitening IC receivers is thus enhanced.
  • the invention discloses means for load estimation in terms of RoT accounting directly for the interference whitening gains of the G-rake+ receiver. Performance is optimized, since the invention allows for optimal filtering and noise suppression of RTWP and RSEPS measurements at the so called sufficient statistics signal point of the G-rake+ receiver, i.e. after interference whitening gains have materialized.
  • the invention provides novel means to integrate and compensate for fast time varying scale factor variations that is an inherent effect of the G- rake + interference whitening processing.
  • One main scope is to develop and disclose procedures for code power estimation per user, capturing the effect of interference whitening. Furthermore, procedures for code power to interference ratio estimation per user, capturing the effect of interference whitening should also be provided. Also RoT estimation or other noise rise measures per user, capturing the effect of interference whitening is calculated.
  • the present approach uses the estimation at the point where the "sufficient statistics" (the performance metric) used for decoding is available.
  • Sufficient statistics refers to the exact knowledge of the probability distribution functions of a stochastic process, over time.
  • a Gaussian stochastic process is e.g. completely defined by its mean value and covariance matrix, both as a function of time - no other information is needed to write down the probability distribution functions of said Gaussian stochastic process.
  • G-rake + receiver such a sufficient statistics is available after interference whitening as discussed further below.
  • the arrangement 10 for noise rise estimation comprises a digital receiver 12, an interference whitener 14 and a processor 20.
  • the digital receiver 12 is connected to an antenna 39 for reception of a received analogue signal 40 representing electromagnetic signals received at the antenna 39.
  • the interference whitener 14 is connected to the digital receiver 12 for receiving digital signals 42 therefrom.
  • the digital receiver 12 and the interference whitener 14 are integrated as one unit, or rather that the interference whitener 14 is a part of the digital receiver 12, whereby the connection between them has to be regarded as an internal or logical connection.
  • the interference whitener 14 is generally based on one of GRAKE, GRAKE+ and the chip equalizer, and in this particular embodiment on GRAKE+.
  • the interference whitener 14 is intended for providing interference whitening for a plurality of users at an output, providing interference whitened digital signals 44.
  • the processor 20 is connected to the output from the interference whitener 14.
  • the processor 20 has a power meter 28 that is connected to be responsive to interference whitened digital signals 44 output from the interference whitener 14.
  • the power meter 28 determines a useful signal power ",f + 56 for each user of the plurality of users as defined after the interference whitening. Such determination is performed for a plurality of time instances, in order to enable a subsequent filtering process
  • combining weights w tt are obtained, see e.g. equation (1).
  • These combining weights w u 50 are supplied to a compensation factor calculating section 26 of the processor 20.
  • the compensation factor calculating section 26 is arranged for deriving a user noise floor compensation factor 52 based on combining weights for that user used in the interference whitening.
  • the noise floor compensation factor K U 52 for a user u is preferably derived as the product of a conjugate transpose of the combining weights w u 50 and the combining weights w u 50 themselves if an approximation for white noise power floor can be accepted. This is the case in the illustrated embodiment.
  • the noise floor compensation factor K U 52 for the user u is derived as the trace of the product of a conjugate transpose of the combining weights w u 50, a thermal noise covariance matrix representing the correlation due to the spectral shape of the whole wideband channel and the combining weights w u 50 themselves divided by the trace of the covariance matrix.
  • the thermal noise covariance matrix representing the correlation due to the spectral shape of the whole wideband channel is also obtainable from the interference whitening process.
  • the processor 20 preferably comprises a selector 24, connected to the output of the compensation factor calculating section 26 and the power meter 28, thus receiving the noise floor compensation factor K U 52 for each user u and respective useful signal power S t ⁇ 56 for each user u .
  • the selector 24 is arranged for selecting a first user from the plurality of users based on interference situation after interference whitening. The first user is going to be used as a model user for calculating a noise rise measure that in some respect is representative for the entire system.
  • the selector 24 is arranged for performing a selection of the first user as the user of the plurality of users having a worst interference situation after interference whitening.
  • the processor is arranged for determining a respective useful signal power for the plurality of users after the interference whitening for a plurality of time instances for deriving a respective user noise floor compensation factor for the plurality of users based on combining weights for the plurality of users used in the interference whitening, a quantity expressing an interference situation based on these factors can be used for the selection.
  • the selection of the first user is performed by selecting that user of the plurality of users that has the largest ratio between the respective useful signal power and the respective user noise floor compensation factor.
  • other users can be selected. For instance, a user corresponding to a certain percentile of the distribution of an interference measure of all users can be used. A noise rise measure for such a user can then not be used for any user without risking instability. However, by compensating such a noise rise measure with a predetermined factor, a reasonably safe maximum noise rise measure can be obtained. This approach can be useful in situations where e.g. a single user has a considerably worse interference situation than all other users and thereby influences the maximum noise rise measure too much.
  • more than one user can be selected for be used during the noise rise determination procedure. This is discussed further below.
  • the processor 20 further comprises a noise rise estimator 22.
  • the noise rise estimator 22 in turn comprises an extended Kalman filter 30 that is arranged for estimating a probability distribution for a compensated useful signal power for the first user S u pdf 64.
  • the selected first user u 54 is provided from the selector 24.
  • the extended Kalman filter 30 is provided with the determined useful signal power for the users, and by the input 54 from the selector 24, the determined useful signal power 56 for the first user can be distinguished.
  • the extended Kalman filter 30 is provided with the user noise floor compensation factors 52, and also by the input 54 from the selector 24, the first user noise floor compensation factor can be distinguished.
  • the probability distribution for a compensated useful signal power is estimated by use of a model taking the fast varying noise floor level into account by use of the first user noise floor compensation factor.
  • An example of such an extended Kalman filtering is described more in detail below.
  • a time invariant or at least slowly varying quantity is regained as an estimation quantity.
  • the processor 20 and in the present embodiment, the noise rise estimator 22 comprises a noise floor estimator 32.
  • the noise floor estimator 32 is arranged for computing a conditional probability distribution of a noise floor measure based on at least the determined useful signal power for the first user and the first user noise floor compensation factor.
  • the noise floor estimator 32 is in this embodiment provided with knowledge of a prior noise floor distribution
  • the processor 20, and in the present embodiment, the noise rise estimator 22 comprises further a noise rise determiner 34.
  • the noise rise determiner 34 connected to the outputs from the extended Kalman filter 30 and the noise floor estimator 32 and has therefore access to the noise floor N u 62 for the first user and a probability distribution for a compensated useful signal power for the first user S u pdf 64.
  • the noise rise determiner 34 is thus arranged for calculating a noise rise measure NR U 66 for the first user, based at least on the compensated useful signal power for the first user S u pdf 64 and the conditional probability distribution of a noise floor measure N u 62 for the first user.
  • the different functionalities of the processor 20 are illustrated as separate part units. However, anyone skilled in the art realises that the functionalities can be configured and realised in different manners, separately or integrated, fully or partly. The part units associated with the different functionalities should therefore only be considered as separate units concerning their functionality.
  • the arrangement 10 for noise rise estimation may in an alternative embodiment be further arranged for defining a system noise rise measure, if the noise rise measure NR U 66 for the first user cannot be used directly as a system noise rise measure.
  • a system noise rise measure There are a number of different possibilities.
  • One alternative, as was indicated further above is to select a user that has not the worst interference situation to achieve the noise rise measure NR U 66.
  • Such a noise rise measure NR tl 66 then has to be modified to fit as a general system noise rise measure. If, for instance, a first user is selected having a compensation factor that corresponds to the 75% percentile of the distribution of all user compensation factors, then the noise rise measure NR U 66 for this user can be modified according to a typical distribution of user noise rise measures to obtain a relevant system noise rise measure.
  • noise rise measures NR U 66 can be determined for more than one user at a time, and the final system noise rise measure can be determined from an evaluation of the spread of the different individual noise rise measures NR 66.
  • the selection of the first user is preferably made relatively frequently, since the interference situation may vary quite rapidly. If it is required that a worst case user is selected at all instances, the selection is preferably made for each sampling occasion. The operation of the extended Kalman filter 30 may then require a longer sampling time than the time between changes of worst user. In such a situation, it may be beneficial if at least the extended Kalman filtering is performed for more than one user at a time, preferably all users, and that the selection of the first user is made in connection with the actual noise rise determination.
  • a flow diagram of an embodiment of a method according to the present invention begins in step 200.
  • radio signals intended for a plurality of users are received at a plurality of time instances.
  • An interference whitening is performed on the received radio signals in step 212.
  • This interference whitening based on one of GRAKE, GRAKE+ and chip equalizer.
  • the interference whitening is performed with respect to at least a first user of the plurality of users.
  • the interference whitening is performed with respect to a plurality of users and most preferably for all users.
  • a first user noise floor compensation factor is derived based on combining weights for the first user used in the interference whitening.
  • the noise floor compensation factors are obtained as described in connection with Fig. 5.
  • noise floor compensation factors for a plurality of users are derived, and most preferably for all users.
  • the steps 214 and 216 are basically independent of each other and may therefore be performed in any order or partly or entirely concurrently.
  • a probability distribution for a compensated useful signal power for said first user is estimated from at least the determined useful signal power for the first user and the first user noise floor compensation factor. This may also be performed for a plurality of users.
  • a conditional probability distribution of a noise floor measure is computed in step 220 based on at least the determined useful signal power for the first user and the first user noise floor compensation factor. This step may also be performed for a plurality of users.
  • a noise rise measure for the first user is calculated based at least on the compensated useful signal power for the first user and the conditional probability distribution of a noise floor measure. The process is ended in step 299.
  • the selection of the first user is made for a purpose.
  • an interference whitening on the received radio signals based on one of GRAKE, GRAKE+ and chip equalizer is performed with respect to respective ones of the plurality of users.
  • a respective useful signal power for the plurality of users after the interference whitening is determining for a plurality of time instances.
  • the first user is then selected from the plurality of users based on the interference situation after interference whitening.
  • the selection of the first user is made as the user of the plurality of users having a worst interference situation after interference whitening.
  • the interference situation may be diagnosed by evaluating a ratio between the respective useful signal power and the respective user noise floor compensation factor.
  • a respective user noise floor compensation factor for the plurality of users is derived based on combining weights for the plurality of users used in the interference whitening. The user having the largest ratio between the respective useful signal power and the respective user noise floor compensation factor is then selected as the first user.
  • Another possibility, also briefly indicated above, is to calculate a respective noise rise measure for at least a number of the plurality of users.
  • the respective noise rise measures are then combined into a system noise rise measure. This then requires that the performance of the interference whitening, the determination of a useful signal power, the deriving of a user noise floor compensation factor, the estimating of a probability distribution for a compensated useful signal power, the computing of a conditional probability distribution of a noise floor measure and the calculation of a noise rise factor have to be performed with respect to each respective user.
  • the sliding window algorithm is based on processing of RTWP.
  • the received scheduled enhanced uplink power constitutes a part of the sum of the code powers.
  • the enhanced uplink transmissions may have properties of high and even load on the transmission power.
  • voice transmissions are typically instead very bursty in their nature. Even at high voice transmission loads, there are instances, where the instantaneous contribution to the total power of a cell is low. This means that an estimate of an appropriate noise floor is probable if only voice transmissions are present.
  • a power quantity that would be very suitable for estimating the noise floor is a difference between the received total wideband power and the received scheduled enhanced uplink power. Such a power quantity will have contributions that typically are either very small or of a bursty character, which means that low values, in the vicinity of the true noise floor, are fairly probable. This principle was used in the published International patent application WO2008/097145 to estimate a noise floor for systems without interference whitening.
  • the RSEPS power is thereby determined after an interference whitening process for a plurality of time instances.
  • the processor is thereby further arranged for determining a RSEPS power after the interference whitening for a plurality of time instances.
  • the estimating of a probability distribution and the computing of a conditional probability distribution are then further based on the determined RSEPS power.
  • the processor is further arranged for performing the estimating and the computing further based on the determined RSEPS power.
  • Equations (7) and (8) have two main implications; one indicating how power measurements can be done and one indicating the scale factor problem which is addressed below.
  • S° is the useful code signal power for the user u after interference whitening
  • l k * is the code interference signal power for the user u after interference whitening
  • N° is the code noise floor power for the user u after interference whitening.
  • WHITE NOISE POWER FLOOR The idea here is to rely on the thermal noise power floor estimation algorithm used in prior art methods, to estimate the thermal noise power floor before any GRAKE+ processing. A main problem then arises since the thermal noise is scaled by w )( when the sufficient statistics is evaluated. This means that the thermal noise power level will no longer appear constant.
  • the computation of the compensation factor only requires an additional inner product for each user.
  • N G+ N 0 tr(vv»R N w u ).
  • the code power to interference ratio is:
  • the (C/l)° + quantity is typically not directly available. It can however be directly related to SINR which is estimated in the ASIC. This is performed as: i( / G+ — ⁇ u.EDPCCH ⁇ * ⁇ u.DPDCH ' W u, codes u.EDPDCH ) ⁇ JJ ⁇ J ⁇ C+ — Pu.effective gJ ⁇ J ⁇ e+ (25) ⁇ I J ri l err? u nr? "
  • SINR is defined as (25). It is understood by anyone skilled in the art that also other code power to interference ratio measures can be used to calculate C/I and/ or SINR in order to provide a similar quantity.
  • a first combining method is to average scale factor compensated user powers.
  • the scale factor compensation is needed to equalize the importance of the different users.
  • averaging does not necessarily capture the situation for users with severe interference situations, close to causing power rushes, averaging is probably not the preferred approach.
  • the RoT estimator operates on power samples with TTI rate - for the scheduler in the WCDMA uplink this corresponds to either 2 ms or 10 ms.
  • the quantities above therefore needs to be filtered and combined to TTI rate estimates. It is hence, for generality, assumed that the following filtered estimates are produced by this step:
  • RTWP Z ⁇ (fewML, ) ( 34 )
  • K G+ (t) P G+ (t 11 - T)(C G+ (t) (c G+ (t)P G+ (tit- T C g+ (t)J + R G+ (t)) "1
  • the quantities introduced by the filter iterations (37) are as follows, t is the time, T is the TTI sampling period, G+ (t
  • A(t) is the systems matrix, B(t) is the control gain matrix.
  • C G+ (t) denotes the linearized measurement matrix (linearization of the nonlinear measurement equation c(x G+ (t)) around the most current state prediction, this motivating the superscript)
  • K G+ (t) denotes the time variable Kalman gain matrix
  • R G+ (t) denotes the measurement covariance matrix
  • R j (t) denotes the system noise covariance matrix.
  • y G+ (t) denotes the available power measurements after the IC gain has materialized and u(t) is the control signal (not used here). It can be noted that j (t) and R G+ (t) are often used as tuning variables of the filter.
  • the bandwidth of the filter is controlled by the matrix quotient of R t (t) and R G+ ( f ) ⁇
  • the filter is initialized by providing initial values to G+ (t ⁇ t - T) and P G+ (t
  • G+ denotes that the quantity is valid after the IC gain of G-rake+ has materialized.
  • a two state model needs to be introduced.
  • the selection of states is, as usual, arbitrary. However, one natural choice is to use one state that describes the RSEPS and one state that describes "the rest" of the power, here denoted the residual power. It should be noted that in case the objective is limited to the estimation of a noise floor measure, it is possible to use a one state model.
  • the states are defined to be the powers after scale factor compensation, with the scale factor compensation being modeled by the generalized output equation defined below.
  • the measurement equation becomes nonlinear.
  • the states are defined to be scale factor compensated powers, i.e. powers before G-rake+, and since the measurements are taken after G-rake+, the measurement equation need to express the effect of G-rake+ by a multiplication of the relevant scale factor discussed above.
  • the discussion is also limited to the use of the maximum combining principle for the IC gains.
  • the nonlinear measurement model is hence given by:
  • xi* EPSPowei . (t) denotes the true power of the RSEPS quantity
  • e ⁇ EPSPowerl (t) denotes the corresponding measurement uncertainty
  • XR e + sid , ia! ⁇ t) denotes the true residual power
  • e ⁇ p (t) denotes the measurement uncertainty of the RTWP measurement
  • q RSEPS (.) is the quantization function of the RSEPS measurement.
  • the RTWP measurement is similarly defined,
  • RTWP G+ ''— 1 (t) q Rmp (10 log 10 (x ⁇ ⁇ )+ x PSPower (f )+ (f )))+ 3 ⁇ )
  • the corresponding measurement covariance matrix becomes:
  • the IC scale factor compensation will be automatically handled by the Kalman filter because of the definition of the states and measurement equations. Specifically this means that the estimated residual power can be used for noise floor estimation in the sub-sequent processing steps. This is not discussed here though.
  • ASICs application specific integrated circuits
  • ASICS may be equipped with dedicated accelerators e.g. for TURBO decoding, matrix operations and similar. This is facilitated by the fact that ASICS can be programmed to perform different tasks, exploiting a variety of such hardware accelerator resources. Similar advantages may be obtained by using digital signal processors.
  • dedicated processing means for load estimation is implemented by an application specific integrated circuit and/ or a digital signal processor.
  • At least a part of the functionality of the processor as illustrated in Fig. 5 is implemented by at least one of an Application Specific Integrated Circuit (ASIC) and a Digital Signal Processor (DSP).
  • ASIC Application Specific Integrated Circuit
  • DSP Digital Signal Processor
  • the embodiment presents ASIC implementation of at least a subset of the above described functionality.
  • RSEPS Received Scheduled Enhanced dedicated channel Power Share RTWP - Received Total Wideband Power

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Quality & Reliability (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Noise Elimination (AREA)

Abstract

La présente invention se rapporte à un procédé permettant une estimation d'une augmentation de bruit dans un système de communication sans fil. Ledit procédé consiste à : recevoir (210) des signaux radio; effectuer un blanchiment d'interférence (212); déterminer (214) une puissance de signal utile pour un premier utilisateur après le blanchiment d'interférence pour une pluralité de circonstances temporelles; puis dériver (216) un facteur de compensation de bruit de fond de premier utilisateur sur la base de poids combinés pour le premier utilisateur utilisés dans le blanchiment d'interférence; estimer (218) une distribution de probabilité pour une puissance de signal utile compensée pour le premier utilisateur; calculer (220) une distribution de probabilité conditionnelle d'une mesure de bruit de fond; calculer (222) ensuite une mesure d'augmentation de bruit pour le premier utilisateur sur la base au moins de la puissance de signal utile compensée pour le premier utilisateur et de la distribution de probabilité conditionnelle d'une mesure de bruit de fond.
PCT/SE2009/051397 2009-12-10 2009-12-10 Estimation de charge dans une communication sans fil WO2011071428A1 (fr)

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US13/514,009 US8665937B2 (en) 2009-12-10 2009-12-10 Load estimation in wireless communication
EP09852110.7A EP2510630B1 (fr) 2009-12-10 2009-12-10 Estimation de charge dans une communication sans fil
CN200980162809.1A CN102656812B (zh) 2009-12-10 2009-12-10 无线通信中的负载估计

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