IJSOO9300432B2
`
`(12) Unlted States Patent
`(10) Patent No.:
`US 9,300,432 B2
`
`Hammarwall et a].
`(45) Date of Patent:
`*Mar. 29, 2016
`
`(54) LINK QUALITY ESTIMATION AND
`APPARATUS IN A TELECOMMUNICATION
`SYSTEM
`
`USPC ........................ 370/2767278; 455/7, 24, 63.1
`See application file for complete search history.
`
`(71) Applicant: Telefonaktiebolaget L M Ericsson
`(publ), Stockholm (SE)
`
`(56)
`
`References Cited
`
`US. PATENT DOCUMENTS
`
`(72)
`
`Inventors: David Hammarwall, Vallentuna (SE);
`George Jiingren, Stockholm (SE);
`Magnus Lundevall, Sollentuna (SE)
`
`7:37:33? 3%
`
`lgggg? gittrrzléiieétaii.
`C
`.
`d
`( ont1nue )
`
`(73) Assignee: Telefonaktiebolaget L M Ericsson
`(1’11“): 30014101111613)
`
`CN
`EP
`
`FOREIGN PATENT DOCUMENTS
`101084639 A
`12/2007
`1463230 A2
`9/2004
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 484 days.
`
`d
`C t'
`( on 1nue )
`OTHER PUBLICATIONS
`
`This patent is subject to a terminal dis—
`clannen
`
`(21) Appl. No.: 13/660,158
`
`Ericsson,“CQIMeasurementMethodology”,3GPP TSGRANWGI
`#52,Feb 11,2008,pp.1-7,Agenda nen16;15,R1-080887,3rd
`Generation Partnership Project, Sorrento, Italy.
`(Continued)
`
`Filed:
`
`(22)
`(65)
`
`OCt' 25’ 2012
`Prior Publication Data
`
`Primary Examiner 7 Siming Liu
`(74) Attorney, Agent, or Firm 7 Coats & Bennett, P.L.L.C.
`
`US 2013/0064122 A1
`
`Mar. 14, 2013
`
`(57)
`
`ABSTRACT
`
`_
`_
`Related U.S.App11catlon Data
`(63) Continuation of application No. 12/866,585, filed as
`~
`~
`application No. PCT/EP2008/058217 on Jun. 26,
`2008, now Pat. No. 8,325,624.
`.
`.
`.
`.
`Prov1s1onal a13131103111011 NO- 61/027535: filed on Feb.
`11, 2008
`
`(60)
`
`(5 1)
`
`(200601)
`(200601)
`
`Int. Cl'
`H04L ”00
`H041‘ [/16
`(52) U-S- Cl-
`CPC ~~~~~~~~~~~~~ H04L 1/0034 (201301); HML [/0026
`(201301); H04L [/1607 (201301)
`(58) Field of Classification Search
`CPC
`H04L 1/0026; H04L 1/1607; H04L 1/0034
`
`Method and apparatus for enabling accurate link quality esti-
`mation of a wireless link between a sending node and a
`receiving node. Whenthe sending node receives link state
`reports romt e rece1v1ng no e, 1t est1mates t e current state
`f
`h
`d
`h
`of the wireless link. The sending node also determines a
`measurement adjusting parameter if the link state reports are
`deemed inaccurate in relation to the estimated link state,
`based on a deviation between the received link state reports
`and the estimated actual link state. The sending node then
`sends the determined measurement adjusting parameter to the
`receiving node, and the receiving node provides a link state
`report based on signal measurements adjusted by the mea-
`surement adjusting parameter. The adjusted link state report
`can thenbe used for link adaptation ofthe wireless link and/or
`for packet scheduling decisions.
`
`18 Claims, 2 Drawing Sheets
`
`100
`
`Receive regular report
`from receiving node
`
`Estimate Iink state
`
`
`
`104
`
`Link state indicate
`
`inaccurate Report?
`
`Determine PMO based on link state in relation to
`received repon and send PMO to receiving node
`
`
`i 108
`
`
`
`
`,_______________/____
`Receive PMO-adjusted report
`
`
`E Use received report
`E
`from receiving node
`5
`forlink adaptation
`5
`
`-------------------
`112
`\_§ Use PMO-adjusted report
`i
`for link adaptation
`
`SAMSUNG 1001
`
`SAMSUNG 1001
`
`1
`
`

`

`US 9,300,432 B2
`
`Page 2
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`7,301,928 B2
`7,688,798 B2
`7,783,295 B2
`
`11/2007 Nakabayashietal.
`--
`3/2010 Dottling etal.
`8/2010 Ish11 et a1.
`
`7,894,822 B2
`
`2/2011 Jonsson
`
`JP
`JP
`JP
`JP
`
`JP
`WO
`JP
`WO
`WO
`
`2005521358 A
`2005354270 A
`2006081172 A
`2006517752 A
`
`2007159054 A
`0225853 A2
`2007521750 A
`2006052448 A2
`2006065181 A1
`
`7/2005
`12/2005
`3/2006
`7/2006
`
`6/2007
`3/2002
`89007
`5/2006
`6/2006
`
`8,325,624 B2* 12/2012 Hammarwallet a1.
`2006/0057965 A1
`3/2006 Braun et a1.
`
`....... 370/252
`
`OTHER PUBLICATIONS
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`JP
`JP
`
`1589715 A1
`2004186969 A
`20041655834 A
`
`10/2005
`2/2004
`6/2004
`
`Texas Instruments, Codeword-to-Layer Mapping for E-UTRA
`MIMO, Publication, pp. 1/6-6/6, 3GPP TSG RAN WG1 48, St.
`Louis, USA, Feb. 12-16, 2007, R1-071199.
`
`* cited by examiner
`
`2
`
`

`

`US. Patent
`
`Mar. 29, 2016
`
`Sheet 1 0f2
`
`US 9,300,432 B2
`
`100
`
`Receive regular report
`from receiving node
`
`
`inaccurate Report?
`
`
`Link state indicate
`
`
`
`
`
`
` Use received report
`
`|
`' """"""""
`
`Receive PMO-adjusted report
`from receiving node
`
`for link adaptation
`
`5
`\_: Use PMO-adjusted report
`E__-_-.f9f.l_if‘.k..af‘fi‘3‘.‘"i‘.ii’.“. ......
`
`Fig. 1
`
`
`
`Fig. 2
`
`3
`
`

`

`US. Patent
`
`Mar. 29, 2016
`
`Sheet 2 0f2
`
`US 9,300,432 B2
`
`Signal Power
`IN
`(S R)
`
`300
`
`RS/data
`
`offset
`
`PMO (underestimated SINR)
`
`Measured Power (RS)
`
`PMO adjusted Power
`(more optimistic)
`
`Compensated Power (data)
`
`PMO adjusted Power
`
`Fig. 3
`
`Signal Receiving Node
`
`4023
`
`Data/RS Receiver
`
`Signal Measuring Unit
`
`402C
`
`(more pessimistic)
`
`
`PMO Determining
`
`Quality Estimating
`
`Unit
`
`I
`
`Unit
`
`Reporting Unit
`
`Fig. 4
`
`4
`
`

`

`US 9,300,432 B2
`
`1
`LINK QUALITY ESTIMATION AND
`APPARATUS IN A TELECOMMUNICATION
`SYSTEM
`
`This application is a continuation of US. application Ser.
`No. 12/866,585, filed 11 Aug. 2010, which was the National
`Stage of International Application No. PCT/EP2008/05 8217,
`filed 26 Jun. 2008, which claims benefit of US. Provisional
`Application No. 61/027,535 filed 11 Feb. 2008, the disclo-
`sures of each ofwhich are incorporated herein by reference in
`their entirety.
`
`TECHNICAL FIELD
`
`The present invention relates generally to a method and
`apparatus for optimizing wireless transmissions in a telecom-
`munication system by means of more accurate link quality
`estimation.
`
`BACKGROUND
`
`In 3GPP (3rd Generation Partnership Project), the packet-
`switched communication systems HSPA (High Speed Packet
`Access) and LTE (Long Term Evolution) have been specified
`for wireless transmission of data packets between user termi-
`nals and base stations in a cellular/mobile network. In this
`
`description, the term “base station” is used to generally rep-
`resent any network node capable of wireless communication
`with a user terminal.
`
`LTE systems generally use OFDM (Orthogonal Frequency
`Division Multiplexing) involving multiple narrow-band sub-
`carriers which are further divided into time slots to form a
`
`so-called “time-frequency grid” where each frequency/
`timeslot combination is referred to as a “Resource Element
`
`RE”. In LTE, multiple antennas can also be employed in both
`user terminals and base stations for obtaining parallel and
`spatially multiplexed data streams, e.g. according to MIMO
`(Multiple Input Multiple Output), which is well-known in the
`art. Other wireless communication systems relevant for the
`following description include WCDMA (Wideband Code
`Division Multiple Access), WiMAX, UMB (Ultra Mobile
`Broadband), GPRS (General Packet Radio Service) and GSM
`(Global System for Mobile communications).
`A base station of a cell in a wireless network may transmit
`data and control information in a physical downlink channel
`to a user terminal or “UE” (User Equipment), and a user
`terminal may likewise transmit data and control information
`in a physical uplink channel in the opposite direction to the
`base station. In this description, a physical downlink or uplink
`channel is generally referred to as a wireless link between a
`sending node and a receiving node. Further, the terms “send-
`ing node” and “receiving node” are used here merely to imply
`the direction of the wireless link considered, although these
`nodes can of course both receive and send data and messages
`in an ongoing communication. Further, the term “Resource
`Element RE” is used in this description to generally represent
`a signal bearer element that can carry a signal over a wireless
`link, without limitation to any transmission technology such
`as LTE. For example, an RE can incorporate a specific code
`and timeslot in a system using CDMA (Code Division Mul-
`tiple Access), or a specific frequency and timeslot in a system
`using TDMA (Time Division Multiple Access), and so forth.
`When two nodes in a cell communicate over a wireless link
`
`that is configured according to various link parameters, one or
`more such link parameters can be adapted to the current state
`of the link on a dynamic basis, often referred to as link
`adaptation. Such link parameters may include transmission
`
`2
`
`power, modulation schemes, encoding schemes, multiplex-
`ing schemes, and the number of parallel data streams when
`multiple antennas are used, the latter link parameter being
`called “transmission rank”. Link adaptation is used to gener-
`ally optimize transmission in order to increase capacity and
`data throughput in the network. Further, link adaptation can
`be employed for the uplink and the downlink independently,
`if applicable, since the current state of the uplink and down-
`link can be very different, e.g. due to different interference
`and when frequency and/or time are widely separated for
`uplink and downlink transmissions between the two nodes.
`To support link adaptation during an ongoing communica-
`tion between a sending node and a receiving node, either on
`the uplink or downlink, the receiving node is often required to
`measure certain link parameters and report recommended
`link parameters to the sending node, such as a recommended
`transmission rank and/or a recommended precoder matrix.
`Also, the quality of the received signal is often measured,
`typically in terms of a Signal to Interference and Noise Ratio
`SINR, e.g. separately for different parallel data streams,
`assuming that the recommended link parameters are used by
`the sending node. Based on the recommended link parameters
`and measured SINR value(s), the receiving node estimates
`so-called “Channel Quality Indicators” CQIs, e.g. one CQI
`for each coded data block (codeword), that are used together
`with the link parameters to indicate the current state of the
`link, which is reported back to the sending node. In this
`description, a reported CQI or the equivalent and/or recom-
`mended link parameters will be called a “link state report” for
`short. The sending node can then adapt one or more link
`parameters depending on the received link state report. When
`the sending node is a base station using packet switching for
`downlink transmissions, the reported Cle may also be used
`for packet scheduling decisions.
`Typically, specific known reference symbols RS are regu-
`larly transmitted over a wireless link according to a predeter-
`mined scheme to support the above link quality estimation,
`such that the receiving node is able to detect noise and inter-
`ference more easily without having to decode the received
`signal. In an OFDM-based LTE system, these RSs are trans-
`mitted from base stations in predetermined REs in the time-
`frequency grid as known by the receiving terminal.
`In general, a received signal “r” in an RE is basically
`comprised of transmitted symbols “s” as well as noise and
`interference “n”. Thus:
`
`r:Hs+n
`
`(1)
`
`Generally, r, s and n are vectors and H is a matrix, where
`“H” represents the channel response which can be derived
`from a channel estimator in the receiver. However, the noise
`and interference of a signal in an RE display different char-
`acteristics depending on whether the RE contains payload
`data, control signalling or an RS, as the interference mix
`hitting the different types of REs may typically have different
`transmission power and spatial characteristics, e.g. due to
`time and/or frequency synchronization in neighboring cells.
`The interference/noise “I” in these different signal types may
`be characterized in terms of second order statistics that can be
`
`obtained by frequently measuring the signals over time,
`although “I” can be characterized in other ways as well.
`If an RE contains an RS signal received by a user terminal,
`the terminal is able to estimate the interference/noise n:I (RS)
`ofthe RS signal since s are known symbols in this case and H
`is given by the channel estimator. If the RE contains data
`scheduled for the terminal, the interference/noise n:I(data)
`can also be estimated once the data symbols have been
`detected (i.e. decoded) by the terminal,
`s thereby being
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`5
`
`

`

`US 9,300,432 B2
`
`3
`known at that point. Similarly, the interference/noise ofan RE
`with control signalling, n:l(control), can be estimated if the
`control symbols can be detected.
`In order to obtain proper link quality estimation and to
`determine an accurate CQl and/or link parameter recommen-
`dation for a link, the receiving node needs sufficient statistics
`from measuring signals transmitted on the link. Furthermore,
`the characteristics of inter-cell interference may be signifi-
`cantly different depending on what signal type is causing the
`interference from neighboring cells, i.e. RS signals, data sig-
`nals or control signals. If payload data is transmitted over the
`link to be estimated, the receiving node should preferably
`measure the interference l(data) that hits the data signals.
`However, the measurements would then be limited to REs
`that contain data scheduled for the user terminal involved,
`which may be too scarce such that the statistic basis for
`determining the CQl is insufficient. Moreover, the data sym-
`bols must be detected and decoded, and possibly also re-
`encoded, before the interference l(data) can be properly esti-
`mated, which may impose
`substantial
`costs
`and/or
`unacceptable delays due to the data processing.
`Alternatively or additionally, the receiving node can mea-
`sure the interference l(RS) for REs containing an RS which
`may occur more frequently than the REs containing sched-
`uled data. Measuring l(RS) is also generally more reliable
`since the RS is always known to the receiving node. However,
`the interference that hits RS signals may be significantly
`different from that hitting the data signals, e. g. with respect to
`statistics. Therefore, a CQl and/or link parameter recommen-
`dation determined from l(RS) measurements may not be rep-
`resentative for a link with payload data transmission. As a
`result, the link adaptation at the sending node may not be
`optimal for data due to either too optimistic or too pessimistic
`CQl and/or link parameter recommendation from the receiv-
`ing node. Hence, ifthe measured l(RS) is significantly greater
`than the actual l(data), the CQl and/or link parameter recom-
`mendation will be based on an overestimated interference (or
`underestimated SINR) and therefore unduly pessimistic, and
`vice versa.
`
`For example, when MlMO is employed in an LTE system,
`the RE holding an RS from one antenna at the sending node
`must be empty for a neighboring antenna, which substantially
`limits the number of REs available for RS transmissions. As
`
`a result, the interference that hits REs containing an RS will
`largely come from RS transmissions in other cells due to
`reuse of the RS transmission pattern. As mentioned above,
`RSs are always transmitted from base stations according to a
`predetermined scheme and at a relatively high fixed power in
`order to be received by any terminal in the cell, whereas
`payload data is only transmitted when scheduled for a specific
`terminal. Thus, in a situation with low data traffic and/or low
`transmissionpower for data signals, l(data) is generally lower
`than l(RS).
`Furthermore, control signals are often transmitted with
`greater power than data signals, due to different power regu-
`lation. Therefore,
`the interference measured for an RE
`affected by control signal interference may be different from
`that of an RE affected by data signal interference.
`Hence, it is often difficult to obtain accurate estimates of
`the inter-cell interference that hits data transmissions, in par-
`ticular if the interference measurements are performed on RS
`transmissions, as explained above. Inaccurate estimates ofthe
`SINR may thus result in misleading Cle and non-optimal
`link parameter recommendations such as transmission rank.
`A consequence for MlMO systems is that an underestimated
`SINR may result in a too pessimistic transmission rank when
`the used link can actually support a transmission rank greater
`
`4
`
`than the recommended one. Both of these issues may well
`result in reduced throughput. On the other hand, if the SINR
`is overestimated, the link may not be able to support any
`recommended Cle (including a recommended Modulation
`and Coding Scheme MCS) and transmission rank, resulting in
`excessive decoding errors and thereby reduced throughput
`also in this case.
`
`However, the base station may monitor so-called “ACK/
`NACK signalling” from the terminal for received data blocks,
`and detect if a Block Error Rate BLER or the like is below or
`
`10
`
`above a predetermined target value. From this information,
`the base station can decide to use a more offensive or defen-
`
`sive MCS than recommended by the terminal. However, ifthe
`base station selects a transmission rank different from the
`
`recommended one, the reported CQl will be largely irrelevant
`since, in most cases, it relates directly to the transmission
`rank. Consequently, the base station would not have a proper
`basis for selecting the MCS and other link parameters for the
`different data streams.
`
`It is thus generally a problem that, in a communication with
`dynamic link adaptation, a signal sending node may receive
`inaccurate link quality estimations and/or link parameter rec-
`ommendations from a signal receiving node, such that the
`used link parameters are not optimal or appropriate for the
`actual link used in the communication.
`
`SUMMARY
`
`It is an object of the present invention to generally address
`the problems outlined above. Further, it is an object to provide
`a solution for obtaining more accurate link or channel quality
`estimation and/or transmission rank recommendations, e.g.
`to support dynamic link adaptation of a wireless link. These
`objects and others may be accomplished by a method and
`apparatus according to the attached independent claims.
`According to one aspect, a method is provided in a sending
`node for enabling accurate link quality estimation of a wire-
`less link used for transmitting signals from the sending node
`to a receiving node. In the method, at least one link state report
`is received from the receiving node, and the current state of
`the wireless link is also estimated. A measurement adjusting
`parameter is determined if the at least one received link state
`report is deemed inaccurate in relation to the estimated link
`state, based on a deviation between the received link state
`report(s) and the estimated actual link state. The determined
`measurement adjusting parameter is then sent to the receiving
`node, and a link state report is received from the receiving
`node which is based on signal measurements adjusted by the
`measurement adjusting parameter. Thereby, inaccurate link
`quality estimations and/or link parameter recommendations
`can be avoided, and the sending node is able to use optimal or
`appropriate link parameters when communicating with the
`receiving node.
`According to another aspect, an apparatus is provided in a
`sending node for enabling accurate link quality estimation of
`a wireless link used for transmitting signals from the sending
`node to a receiving node. The sending node apparatus com-
`prises a sending unit adapted to send signals to the receiving
`node over the wireless link, a report receiver adapted to
`receive link state reports from the receiving node, and a link
`state estimator adapted to estimate the current state of the
`wireless link. The sending node apparatus further comprises
`a determining unit adapted to determine a measurement
`adjusting parameter if at least one received link state report is
`deemed inaccurate in relation to the estimated link state,
`based on a deviation between the received link state report(s)
`and the estimated link state, and to send the determined mea-
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`
`

`

`US 9,300,432 B2
`
`5
`surement adjusting parameter to the receiving node. The
`report receiver is further adapted to receive a link state report
`from the receiving node which is based on signal measure-
`ments adjusted by the measurement adjusting parameter.
`Different embodiments are possible in the sending node
`method and apparatus above. In one exemplary embodiment,
`the sending unit uses the adjusted link state report for link
`adaptation of the wireless link and/or for packet scheduling
`decisions. In another exemplary embodiment, the sending
`unit sends payload data and reference symbols to the receiv-
`ing node which configures the link state reports based on
`signal measurements on the reference symbols, where the
`measurement adjusting parameter compensates for a differ-
`ence in received power or SINR between measured signals
`and data signals.
`The measurement adjusting parameter may be a Power
`Measurement Offset PMO that the receiving node uses for
`adjusting signal power or SINR measurements upon which
`the adjusted link state report is based.
`Further, the link state reports may comprise a link quality
`estimation and/or link parameter recommendation, where the
`link quality estimation may comprise a Channel Quality Indi-
`cator CQI. The link parameter recommendation may com-
`prise a preferred transmission rank specifying the number of
`parallel data streams when multiple antennas are used.
`According to further exemplary embodiments, the link
`state estimator may estimate the current state of the wireless
`link by monitoring the amount of data errors occurring over
`the wireless link as compared to a predetermined target value.
`The link state estimator may then monitor ACK/NACK mes-
`sages from the receiving node to determine whether a Block
`Error Rate BLER or equivalent parameter deviates from the
`target value. The link state estimator may also estimate the
`current state of the wireless link by monitoring the current
`traffic load in the network used.
`
`According to yet another aspect, a method is provided in a
`receiving node for enabling accurate link quality estimation
`of a wireless link used for transmitting signals from a sending
`node to the receiving node. In this method, at least one link
`state report is sent to the sending node containing a link
`quality estimation and/or link parameter recommendation.
`When a measurement adjusting parameter is received from
`the sending node, a link quality estimation and/or link param-
`eter recommendation is/are determined based on signal mea-
`surements adjusted by the received measurement adjusting
`parameter. An adjusted state report is then sent to the sending
`node containing the determined link quality estimation and/or
`link parameter recommendation.
`According to yet another aspect, an apparatus is provided
`in a receiving node for enabling accurate link quality estima-
`tion of a wireless link used for transmitting signals from a
`sending node to the receiving node. This apparatus comprises
`a signal receiving unit adapted to receive signals from the
`sending node over the wireless link, a signal measuring unit
`adapted to measure received signals, a quality estimating unit
`adapted to estimate link quality and/or determine recom-
`mended link parameters, and a reporting unit adapted to send
`link state reports to the sending node. The quality estimating
`unit is further adapted to obtain a measurement adjusting
`parameter from the sending node, and to determine a link
`quality estimation and/or link parameter recommendation
`based on signal measurements adjusted by the received mea-
`surement adjusting parameter. The reporting unit is further
`adapted to send an adjusted link state report to the sending
`node containing the determined link quality estimation and/or
`link parameter recommendation.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`Different embodiments are possible in the receiving node
`method and apparatus above. In one exemplary embodiment,
`the signal receiving unit receives payload data and reference
`symbols from the sending node, and the reporting unit con-
`figures the link state reports based on signal measurements on
`the reference symbols, where the measurement adjusting
`parameter compensates for a difference in received power or
`SINR of measured signals and data signals.
`The measurement adjusting parameter may be a Power
`Measurement Offset PMO that is used for adjusting signal
`power or SINR measurements upon which the adjusted link
`state report is based.
`Further possible features and benefits of the present inven-
`tion will be explained in the detailed description below.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention will now be explained in more detail by
`means of exemplary embodiments and with reference to the
`accompanying drawings, in which:
`FIG. 1 is a flow chart illustrating a procedure for enabling
`accurate link quality estimation as performed by a signal
`sending node, in accordance with one embodiment.
`FIG. 2 is a flow chart illustrating a procedure for enabling
`accurate link quality estimation as performed by a signal
`receiving node, in accordance with another embodiment.
`FIG. 3 is a signal power diagram illustrating different
`power levels when the present invention is used for link
`quality estimation, in accordance with yet another embodi-
`ment.
`
`FIG. 4 is a block diagram illustrating a signal sending node
`and a signal receiving node in more detail, in accordance with
`further embodiments.
`
`DETAILED DESCRIPTION
`
`The present invention can be used to avoid inaccurate link
`quality estimations and/or link parameter recommendations,
`such that a sending node is able to use optimal or appropriate
`link parameters when transmitting payload data in commu-
`nication with a receiving node. In particular, more accurate
`transmission rank recommendations can be obtained such
`
`that a sending node can utilize recommended Cle to a large
`extent, because it does not have to override the recommended
`transmission rank. In the following description, it is assumed
`that link adaptation based on link state reports is employed,
`although the present
`invention is generally not
`limited
`thereto. In addition or alternatively, accurate link quality esti-
`mation can further be useful for scheduling decisions in
`packet-switched communications.
`Briefly described, the sending node determines whether
`the reporting from the receiving node with link quality esti-
`mation and/or link parameter recommendation is accurate or
`inaccurate for the actual link used, by estimating the current
`state of the link. The link state can be estimated in different
`
`ways, e.g. by monitoring ACK/NACK messages from the
`receiving node to see how much data errors occur in the
`transmission, and/or by monitoring the current traffic situa-
`tion in the network, which will be described in more detail
`below.
`
`Ifthe estimated link state indicates that the link state report
`is inaccurate, the sending node determines a “Power Mea-
`surement Offset PMO” or other measurement adjusting
`parameter that the receiving node will use for adjusting the
`signal power or SINR measurements or other signal measure-
`ments upon which the link quality estimation and/or link
`parameter recommendation is based. The receiving node then
`
`7
`
`

`

`US 9,300,432 B2
`
`7
`sends a PMO-adjusted link state report to the sending node
`which is able to use the PMO-adjusted link state report for
`more appropriate link adaptation. Thereby, link parameters
`will be selected that are more closely adapted to the current
`link state and with consideration to what the link can actually
`support.
`The sending node may strive to configure a PMO profile
`such that the resulting link state reports from the receiving
`node becomes relevant or accurate for the estimated link state,
`e.g. by employing an iterative process of testing different
`PMO profiles. The sending node may also strive to configure
`the PMO profile such that the amount of data errors in the
`transmission does not significantly deviate from a target
`value. In general terms, the PMO is thus effectively a “mea-
`surement adjusting parameter”, and these two expressions
`can be used in this description interchangeably.
`FIG. 1 is a flow chart illustrating an exemplary procedure
`for enabling appropriate link quality estimation, as performed
`by a signal sending node in communication with a signal
`receiving node over a wireless link. The sending node may be
`a base station or the like and the receiving node may be a user
`terminal, or vice versa, and it should be noted that the terms
`sending node and receiving node merely indicate the direc-
`tion of the link under consideration. In a first step 100, a
`regular link state report is received from the receiving node
`containing a link quality estimation and/or a link parameter
`recommendation. The receiving node has thus made a link
`quality estimation in a more or less conventional manner
`based on signal measurements, e.g. measurements of signal
`power or SINR on received RSs as described above, which is
`reflected in the link state report.
`In a next step 102, the sending node estimates the current
`state of the link, which can be made in different ways. For
`example, when retransmission of data blocks based on ACK/
`NACK reports is employed in a HARQ (Hybrid Automatic
`Repeat ReQuest) process to correct any erroneously received
`data, the ACK/NACK messages from the receiving node may
`be monitored to determine whether the Block Error Rate
`
`BLER or similar parameter deviates from a predetermined
`target value. If the BLER is below the target value, it is
`assumed that the receiving node has underestimated the link
`quality in the link state report, and vice versa. ACK/NACK
`messages from other nodes may also be taken into account
`when the sending node estimates the link state. However, the
`amount of errors can be monitoring in other ways, depending
`on the technology and protocols used. Further, the current
`traflic load in the network may also be monitored, assuming
`that a high load in the area from ongoing data transmissions
`generally results in relatively high interference, and vice
`versa.
`
`It is then determined in a following step 104 whether the
`estimated link state indicates that the received link state report
`is inaccurate, i.e. misleading and not reflecting the true link
`state or quality. As described above, this may be the case when
`the receiving node measures the signal power or SINR for
`REs containing RSs instead of payload data and when the
`interference from data transmissions is relatively low, result-
`ing in a report with underestimation of the link quality with
`respect to data transmissions.
`Ifthe received link state report is determined to be accurate
`by matching the estimated link state, it can be used for rel-
`evant and appropriate link adaptation in an optional step 106
`and/or for scheduling decisions for packet-switched commu-
`nications. However, if the link state report is deemed inaccu-
`rate in relation to the estimated link state, a measurement
`adjusting parameter or PMO profile is determined based on
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`the deviation between the received link state report and the
`estimated actual link state, which is sent to the receiving node,
`in a further step 108.
`The measurement adjusting parameter or PMO profile may
`be conveyed to the receiving node by means of suitable con-
`trol signalling such as common control signalling, e. g. broad-
`cast, or dedicated control signalling, e.g. RRC (Radio
`Resource Control). It will be described in more detail later
`below how a PMO profile can be determined by the sending
`node and used by the receiving node in the case when the
`signal power in a measured channel deviates from that of a
`data channel, e.g. when REs containing RSs are being mea-
`sured.
`
`The receiving node will now use the measurement adjust-
`ing parameter or PMO profile for adjusting the signal mea-
`surements, e.g. signal power or SINR, upon which the link
`quality estimation and/or link parameter recommendation is
`based, to compensate for any underestimation or overestima-
`tion ofthe signal power or SINR or other measured parameter.
`A PMO-adjusted link state report is then received from the
`receiving node in a next step 110, containing a link quality
`estimation and/or a link parameter recommendation based on
`signal measurements, e.g. signal power or SINR, adjusted by
`the measurement adjusting parameter or PMO profile deter-
`mined and sent in step 108.
`The sending node is now able to use the PMO-adjusted link
`state report for obtaining a more appropriate link adaptation,
`in an optional final step 112. Alternatively or additionally, the
`PMO-adjusted link state report can also be used for schedul-
`ing decisions for packet-switched communications, as simi-
`lar to step 106 above. When receiving a PMO-adjusted link
`state report from the receiving node in step 110, the sending
`node may iteratively repeat steps 104, 106 and 110, as shown
`by the dashed arrow, to find out if the used PMO p