I 1111111111111111 11111 1111111111 11111 111111111111111 IIIII IIIIII IIII IIII IIII
`US008964632B2
`
`c12) United States Patent
`Sorrentino et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,964,632 B2
`Feb.24,2015
`
`(54) METHODS AND ARRANGEMENTS FOR
`CHANNEL ESTIMATION
`
`(75)
`
`Inventors: Stefano Sorrentino, Solna (SE); George
`Jiingren, Stockholm (SE)
`
`(73) Assignee: Telefonaktiebolaget L M Ericsson
`(Puhl), Stockholm (SE)
`
`( *) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 199 days.
`
`(21) Appl. No.: 13/422,298
`
`(22) Filed:
`
`Mar. 16, 2012
`
`(65)
`
`Prior Publication Data
`
`US 2013/0201840Al
`
`Aug. 8, 2013
`
`Related U.S. Application Data
`
`(60) Provisional application No. 61/594,566, filed on Feb.
`3, 2012.
`
`(51)
`
`(2009.01)
`
`Int. Cl.
`H04W56/00
`(52) U.S. Cl.
`CPC ........ H04W 56/001 (2013.01); H04W 56/0095
`(2013.01)
`USPC .......................................................... 370/324
`( 58) Field of Classification Search
`USPC .......................................... 370/324, 350, 507
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`2010/0220800 Al *
`2011/0176517 Al
`2013/0028217 Al *
`
`9/2010 Erell et al.
`7/2011 Huetal.
`1/2013 Sumasu et al. ................ 370/329
`
`.................... 375/267
`
`FOREIGN PATENT DOCUMENTS
`
`WO
`
`WO 2011/125300 Al * 10/2011
`
`H04J 99/00
`
`OTHER PUBLICATIONS
`
`Sumasu et al., Machine translation copy of WO 20 l l/ 125300 Al,
`Oct. 13, 2011.*
`International Search Report issued in corresponding International
`application No. PCT/SE2013/050081, date of mailing May 22, 2013.
`Written Opinion of the International Searching Authority issued in
`corresponding International application No. PCT/SE2013/050081,
`date of mailing May 22, 2013.
`Motorola Mobility, "Scenario and Modeling Discussion for DL(cid:173)
`MIMO Enhancement," 3GPP Draft, Rl-112444, 3rd Generation
`Partnership Project (3GPP), Mobile Competence Centre, 650 Route
`des Lucioles, F-06921 Sophia-Antipolis Cedex, France, TSG RAN
`WG 1 #66, Athens, Greece, Aug. 22-26, 2011, XP050537545.
`(Continued)
`
`Primary Examiner - Hoon J Chung
`(74) Attorney, Agent, or Firm - Patent Portfolio Builders
`PLLC
`
`(57)
`
`ABSTRACT
`
`Some embodiments provide a method for channel estimation
`in a wireless device. According to the method, the wireless
`device obtains an indication that a set of antenna ports, or
`antenna port types, share at least one channel property. The
`wireless device then estimates one or more of the shared
`channel properties based at least on a first reference signal
`received from a first antenna port included in the set, or having
`a type corresponding to one of the types in the set. Further(cid:173)
`more, the wireless device performs channel estimation based
`on a second reference signal received from a second antenna
`port included in the set, or having a type corresponding to one
`of the types in the set, wherein the channel estimation is
`performed using at least the estimated channel properties.
`
`13 Claims, 12 Drawing Sheets
`
`800
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`
`Ex.1016
`APPLE INC. / Page 1 of 25
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`

`

`US 8,964,632 B2
`Page 2
`
`(56)
`
`References Cited
`
`OTHER PUBLICATIONS
`
`St-Ericsson et al., "Geographically separated antenna and impact on
`CSI estimation," 3GPP Draft, R4-120679, Geographically Separated
`Antennas v2, 3rd Generation Partnership Project (3GPP), Mobile
`Competence Centre, 650 Route des Lucioles, F-06921 Sophia(cid:173)
`Antipolis Cedex, France, TSG RAN WG4 meeting #62, Dresden,
`Germany, Feb. 6-9, 2012, XP050568289.
`Ericsson et al., "Discussion on Antenna Ports Co-location," 3GPP
`Draft, Rl-121026 Ports Colation, 3rd Generation Partnership Project
`(3GPP), Mobile Competence Centre, 650 Route des Lucioles,
`F-06921 Sophia-Antipolis Cedex, France, TSG RAN WG4, Jeju,
`Korea, Mar. 26-30, 2012, XP050599267.
`3GPP TS 36.211 Vl0.2.0 (Jun. 2011), Technical Specification; "3rd
`Generation Partnership Project; Technical Specification Group
`
`Radio Access Network; Evolved Universal Terrestrial Radio Access
`(E-UTRA); Physical Channels and Modulation (Release 10)"; 4
`Advanced LTE, 3 GPP; Jun. 2011; pp. 1-103; Valbonne, France.
`3GPP TS 36.212 Vl0.2.0 (Jun. 2011), Technical Specification; "3rd
`Generation Partnership Project; Technical Specification Group
`Radio Access Network; Evolved Universal Terrestrial Radio Access
`(E-UTRA); Multiplexing and channel coding (Release 10)"; 4
`Advanced LTE, 3 GPP; Jun. 2011; pp. 1-178; Valbonne, France.
`3GPP TS 36.213 Vl0.2.0 (Jun. 2011), Technical Specification; "3rd
`Generation Partnership Project; Technical Specification Group
`Radio Access Network; Evolved Universal Terrestrial Radio Access
`(E-UTRA); Physical layer procedures (Release 10)"; 4 Advanced
`LTE, 3 GPP; Jun. 2011; pp. 1-120; Valbonne, France.
`International Preliminary Report on Patentability in corresponding
`International Application No. PCT/SE2013/050081 mailed Jun. 3,
`2014.
`
`* cited by examiner
`
`Ex.1016
`APPLE INC. / Page 2 of 25
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`

`

`U.S. Patent
`
`Feb.24,2015
`
`Sheet 1 of 12
`
`US 8,964,632 B2
`
`ONE RESOURCE ELEMENT
`
`ONE OFDM SYMBOL INCLUDING CP
`FIG.1
`
`#9
`#1...
`#0
`◄------------------------------------------------------------~
`RADIO FRAME (TFRAME = 10 ms)
`
`FIG. 2
`
`Ex.1016
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`U.S. Patent
`
`Feb.24,2015
`
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`US 8,964,632 B2
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`
`Ex.1016
`APPLE INC. / Page 5 of 25
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`

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`U.S. Patent
`
`Feb.24,2015
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`Ex.1016
`APPLE INC. / Page 8 of 25
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`Ex.1016
`APPLE INC. / Page 9 of 25
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`Ex.1016
`APPLE INC. / Page 10 of 25
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`Ex.1016
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`

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`U.S. Patent
`
`Feb.24,2015
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`Sheet 10 of 12
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`US 8,964,632 B2
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`Feb.24,2015
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`US 8,964,632 B2
`
`1
`METHODSANDARRANGEMENTSFOR
`CHANNEL ESTIMATION
`
`RELATED APPLICATION(S)
`
`This application claims priority and benefit from U.S. Pro(cid:173)
`visional Patent Application No. 61/594,566, filed Feb. 3,
`2012, the entire teachings of which are incorporated herein by
`reference.
`
`TECHNICAL FIELD
`
`The present invention relates to methods and arrangements
`for improved channel estimation.
`
`BACKGROUND
`
`The 3rd Generation Partnership Project (3GPP) is respon(cid:173)
`sible for the standardization of the Universal Mobile Tele(cid:173)
`communication System (UMTS) and Long Term Evolution
`(LTE). The 3GPP work on LTE is also referred to as Evolved
`Universal Terrestrial Access Network (E-UTRAN). LTE is a
`technology for realizing high-speed packet-based communi(cid:173)
`cation that can reach high data rates both in the downlink and
`in the uplink, and is thought of as a next generation mobile
`communication system relative to UMTS. In order to support
`high data rates, LTE allows for a system bandwidth of 20
`MHz, or up to 100 Hz when carrier aggregation is employed.
`LTE is also able to operate in different frequency bands and
`can operate in at least Frequency Division Duplex (FDD) and
`Time Division Duplex (TDD) modes.
`LTE uses orthogonal frequency-division multiplexing
`(OFDM) in the downlink and discrete-Fourier-transform(cid:173)
`spread (DPT-spread) OFDM in the uplink. The basic LTE
`physical resource can be seen as a time-frequency grid, as 35
`illustrated in FIG. 1, where each resource element corre(cid:173)
`sponds to one subcarrier during one OFDM symbol interval
`( on a particular antenna port). There is one resource grid per
`antenna port.
`An antenna port is a "virtual" antenna, which is defined by 40
`an antenna port-specific reference signal. An antenna port is
`defined such that the channel over which a symbol on the
`antenna port is conveyed can be inferred from the channel
`over which another symbol on the same antenna port is con(cid:173)
`veyed. The signal corresponding to an antenna port may 45
`possibly be transmitted by several physical antennas, which
`may also be geographically distributed. In other words, an
`antenna port may be transmitted from one or several trans(cid:173)
`mission points. Conversely, one transmission point may
`transmit one or several antenna ports. In the following, an 50
`antenna port will be interchangeably referred to as an "RS
`port".
`In the time domain, LTE downlink transmissions are orga(cid:173)
`nized into radio frames of 10 ms, each radio frame consisting
`often equally-sized subframes ofl ms as illustrated in FIG. 2. 55
`A subframe is divided into two slots, each of 0.5 ms time
`duration.
`The resource allocation in LTE is described in terms of
`resource blocks, where a resource block corresponds to one
`slot in the time domain and 12 contiguous 15 kHz subcarriers
`in the frequency domain. Two time-consecutive resource
`blocks represent a resource block pair, which corresponds to
`the time interval upon which scheduling operates.
`Transmissions in LTE are dynamically scheduled in each
`subframe. The base station transmits downlink assignments/
`uplink grants to certain UEs via the physical downlink control
`information (Physical Downlink Control Channels, PDCCH,
`
`2
`and enhanced PDCCH, ePDCCH). The PDCCHs are trans(cid:173)
`mitted in the first OFDM symbol(s) in each subframe and
`spans more or less the whole system bandwidth. A UE that
`has decoded a downlink assignment, carried by a PDCCH,
`5 knows which resource elements in the subframe contain data
`aimed for the UE. Similarly, upon receiving an uplink grant,
`the UE knows which time/frequency resources it should
`transmit upon. In LTE downlink, data is carried by the physi(cid:173)
`cal downlink shared data link (PDSCH) and in the uplink the
`10 corresponding link is referred to as the physical uplink shared
`channel (PUSCH).
`Demodulation of received data requires estimation of the
`radio channel, which is performed using reference signals
`(RS). A reference signal comprises a collection ofreference
`15 symbols, and these reference symbols and their position in the
`time-frequency grid are known to the receiver. In LTE, cell(cid:173)
`specific reference signals (CRS) are transmitted in all down(cid:173)
`link subframes. In addition to assisting downlink channel
`estimation, they are also used for measurements, e.g. mobility
`20 measurements, performed by the UEs. As of Release 10, LTE
`also supports VE-specific RS aimed for assisting channel
`estimation for demodulation of the PDSCH, as well as RS for
`measuring the channel for the purpose of channel state infor(cid:173)
`mation (CSI) feedback from the UE. The latter are referred to
`25 as CSI-RS. CS I-RS are not transmitted in every subframe and
`they are generally sparser in time and frequency than RS used
`for demodulation. CSI-RS transmissions may occur every
`5th, 10th, 20th, 40th, or 80th subframe according to an RRC
`configured periodicity parameter and an RRC configured
`30 subframe offset.
`FIG. 3 illustrates how the mapping of physical control and
`data channels and reference signals may be done on resource
`elements within a downlink subframe. In this example, the
`PDCCHs occupy the first out of three possible OFDM sym(cid:173)
`bols, so in this particular case the mapping of data could start
`already at the second OFDM symbol. Since the CRS are
`common to all UEs in the cell, the transmission of CRS
`cannot be easily adapted to suit the needs of a particular UE.
`This is in contrast to VE-specific RS, where each UE has RS
`of its own placed in the data region of FIG. 3 as part of
`PDSCH.
`A UE operating in connected mode may be requested by
`the base station to report channel state information (CSI),
`e.g., reporting a suitable rank indicator (RI), one or more
`precoding matrix indices (PMis) and a channel quality indi(cid:173)
`cator (CQI). Other types ofCSI are also conceivable, includ-
`ing explicit channel feedback and interference covariance
`feedback. The CSI feedback assists the base station in sched(cid:173)
`uling, including deciding the subframe and RBs for the trans(cid:173)
`mission, which transmission scheme/precoder to use, and
`also provides information on a suitable user bit rate for the
`transmission (link adaptation). A detailed illustration of
`which resource elements within a resource block pair may
`potentially be occupied by VE-specific RS and CSI-RS is
`provided in FIG. 4. The CSI-RS utilizes an orthogonal cover
`code of length two to overlay two antenna ports on two
`consecutive REs. As seen, many different CSI-RS pattern are
`available. For the case of2 CSI-RS antenna ports we see that
`there are 20 different patterns within a subframe. The corre-
`60 sponding number of patterns is 10 and 5 for 4 and 8 CSI-RS
`antenna ports, respectively. For TDD, some additional CSI(cid:173)
`RS patterns are available.
`Improved support for heterogeneous network operations is
`part of the ongoing specification of 3GPP LTE Release- I 0,
`65 and further improvements are discussed in the context of new
`features for Release-I 1. In heterogeneous networks, a mix(cid:173)
`ture of cells of differently sized and overlapping coverage
`
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`US 8,964,632 B2
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`3
`areas are deployed. One example of such deployments is
`illustrated in FIG. 5, where pico cells are deployed within the
`coverage area of a macro cell. Other examples oflow power
`nodes, also referred to as points, in heterogeneous networks
`are home base stations and relays. The aim of deploying low 5
`power nodes such as pico base stations within the macro
`coverage area is to improve system capacity by means of cell
`splitting gains as well as to provide users with wide area
`experience of very high speed data access throughout the
`network. Heterogeneous deployments are in particular effec(cid:173)
`tive for covering traffic hotspots, i.e., small geographical
`areas with high user densities served by e.g., pico cells, and
`they represent an alternative deployment to denser macro
`networks.
`A classical way of deploying a network is to let different
`transmission/reception points form separate cells. That is, the
`signals transmitted from or received at a point is associated
`with a cell-id that is different from the cell-id employed for
`other nearby points. Typically, each point transmits its own
`unique signals for broadcast (PBCH) and sync signals (PSS,
`SSS).
`The mentioned classical strategy of one cell-id per point is
`depicted in FIG. 6 for a heterogeneous deployment where a
`number of low power (pico) points are placed within the
`coverage area of a higher power macro point. Similar prin(cid:173)
`ciples apply to classical macro-cellular deployments, where
`all points have similar output power and may be placed in a
`more regular fashion than what is the case for a heterogeneous
`deployment.
`An alternative to the classical deployment strategy is to 30
`instead let all the UEs within the geographical area outlined
`by the coverage of the high power macro point be served with
`signals associated with the same cell-id. In other words, from
`a UE perspective, the received signals appear to be coming
`from a single cell. This is illustrated in FIG. 7. Note that only
`one macro point is shown, other macro points would typically
`use different cell-ids ( corresponding to different cells) unless
`they are co-located at the same site, corresponding to other
`sectors of the macro site. In the latter case of several co(cid:173)
`located macro points, the same cell-id may be shared across 40
`the co-located macro-points and those pico points that corre(cid:173)
`spond to the union of the coverage areas of the macro points.
`Sync, BCH and control signals are all transmitted from the
`high power point while data can be transmitted to a UE also
`from low power points by using shared data transmissions
`(PDSCH) relying on UE specific RS. Such an approach has
`benefits for those UEs that are capable of receiving the
`PDSCH based on VE-specific RS. Those UEs that only sup(cid:173)
`port CRS for PDSCH (which is likely to at least include all
`Release 8/9 UEs for FDD) have to settle for the transmission
`from the high power point and thus will not benefit in the
`downlink from the deployment of additional low power
`points.
`The single cell-id approach is geared towards situations in
`which there is fast backhaul communication between the
`points associated to the same cell. A typical case would be a
`base station serving one or more sectors on a macro level as
`well as having fast fiber connections to remote radio units
`(RRU s) playing the role of the other points sharing the same
`cell-id. Those RRUs could represent low power points with 60
`one or more antennas each. Another example is when all the
`points have a similar power class with no single point having
`more significance than the others. The base station would
`then handle the signals from all RRUs in a similar manner.
`A clear advantage of the shared cell approach compared 65
`with the classical one is that the typically involved handover
`procedure between cells only needs to be invoked on a macro
`
`4
`basis. Another important advantage is that interference from
`CRS is greatly reduced since CRS does not have to be trans(cid:173)
`mitted from every point. There is also much greater flexibility
`in coordination and scheduling among the points.
`The concept of a point is heavily used in conjunction with
`techniques for coordinated multipoint (CoMP). In the present
`disclosure, a point ( also referred to as a "transmission point"
`and/or a "reception point") corresponds to a set of antennas
`covering essentially the same geographical area in a similar
`10 manner. Thus, a point might correspond to one of the sectors
`at a site, but it may also correspond to a site having one or
`more antennas all intending to cover a similar geographical
`area. Often, different points represent different sites. Anten-
`15 nas correspond to different points when they are sufficiently
`geographically separated and/or have antenna diagrams
`pointing in sufficiently different directions.
`Techniques for CoMP entail introducing dependencies in
`the scheduling or transmission/reception among different
`20 points, in contrast to conventional cellular systems where a
`point, from a scheduling point of view, is operated more or
`less independently from the other points. One fundamental
`property ofDL CoMP is the possibility to transmit different
`signals and/or channels from different geographical loca-
`25 tions. One of the principles guiding the design of the LTE
`system is transparency of the network to the UE. In other
`words, the UE should be able to demodulate and decode its
`intended channels without specific knowledge of scheduling
`assignments for other UEs or network deployments.
`For example, different CS I-RS patterns may be transmitted
`from ports belonging to different transmission points. Feed(cid:173)
`back based on such patterns may be exploited e.g. for point
`selection and/or for optimization of precoding weights and
`CoMP scheduling. Alternatively, the same CSI-RS pattern
`35 may be jointly transmitted by different transmission points in
`order to generate an aggregated feedback including joint spa(cid:173)
`tial information for multiple points. In any case, UEs are
`generally not aware of the geographical location from which
`each antenna port is transmitted.
`CRS are typically transmitted from a static set of points.
`Nevertheless, for certain deployments, it is possible to trans(cid:173)
`mit different CRS ports from different geographical loca(cid:173)
`tions. One application of this technique is in distributed
`deployments, where the transmit antennas belonging to the
`45 same node are deployed in a non-collocated fashion.
`DMRS or VE-specific RS are employed for demodulation
`of data channels and possibly certain control channels ( ePD(cid:173)
`CCH). Data may be transmitted from different points than
`other information (e.g. control signaling). This is one of the
`50 main drivers behind the use ofUE-specific RS, which relieves
`the UE from having to know many of the properties of the
`transmission and thus allows flexible transmission schemes
`to be used from the network side. This is referred to as trans(cid:173)
`mission transparency (with respect to the UE). A problem is,
`55 however, that the estimation accuracy ofUE-specific RS may
`not be sufficient in some situations. Furthermore, especially
`in case of Co MP and/or distributed deployments, the DMRS
`for a specific UE-might be transmitted from geographically
`separated ports.
`There is a need in the art for mechanisms for improved
`channel estimation.
`
`SUMMARY
`
`An object of some embodiments is to provide a mechanism
`for improved channel estimation, in particular in CoMP sce(cid:173)
`nar10s.
`
`Ex.1016
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`US 8,964,632 B2
`
`6
`FIG. 2 is a schematic diagram showing the LTE time(cid:173)
`domain structure.
`FIG. 3 is a schematic diagram showing an LTE downlink
`subframe.
`FIG. 4 is a schematic diagram showing possible reference
`signal patterns.
`FIG. 5 is a schematic diagram showing an example macro
`and pico cell deployment.
`FIG. 6 is a schematic diagram showing an example hetero-
`10 geneous deployment.
`FIG. 7 is a schematic diagram showing another example
`heterogeneous deployment.
`FIG. 8 is a schematic diagram illustrating a wireless com(cid:173)
`munication system.
`FIG. 9 is a flow chart showing an example method in a
`network node.
`FIG. 10 is a flow chart showing an example method in a
`wireless device.
`FIG. 11 is a flow chart showing an example method in a
`20 network node.
`FIG. 12 is a flow chart showing an example method in a
`wireless device.
`FIG. 13 is a flow chart showing an example method in a
`network node.
`FIG. 14 is schematic diagram showing an example net(cid:173)
`work.
`FIG. 15 is a block diagram showing an example network
`node.
`FIG. 16 is a block diagram showing an example wireless
`device.
`
`25
`
`5
`Some embodiments provide a method for channel estima(cid:173)
`tion in a wireless device. According to this method, the wire(cid:173)
`less device obtains an indication that a set of antenna ports, or
`antenna port types, share at least one channel property. The
`device then estimates one or more of the shared channel 5
`properties. The estimation is based at least on a first reference
`signal received from a first antenna port included in the set, or
`having a type corresponding to one of the types in the set.
`Further, the wireless device performing channel estimation
`based on a second reference signal received from a second
`antenna port included in the set, or having a type correspond(cid:173)
`ing to one of the types in the set. The channel estimation is
`performed using at least the estimated channel properties.
`In particular embodiments, the wireless device receives a
`message from the network node comprising the indication. In 15
`other embodiments, the set is determined based on a rule.
`In some embodiments, the wireless device is thus able to
`use estimated channel properties for one antenna port in the
`estimation for another antenna port, by assuming co-location
`of certain antenna ports. In a particular example, the device
`may perform joint estimation based on two or more antenna
`ports, which leads to improved estimation accuracy. In
`another example, the device may apply an estimated property
`for one port to another port in the set, which may lead to a
`faster estimation process.
`Some embodiments provide a method in a network node.
`The method comprises obtaining an indication that a set of
`antenna ports, or antenna port types, share at least one channel
`property. The network then transmitting signals correspond(cid:173)
`ing to at least two of the antenna ports in the set, or antenna 30
`ports having types comprised in the set, from the same set of
`transmission points.
`Thus, in some embodiments the network node enables the
`wireless device to perform improved channel estimation, by
`ensuring that certain antenna ports are co-located.
`Some embodiments provide a wireless device for perform(cid:173)
`ing channel estimation. The device comprises radio circuitry
`and processing circuitry. The processing circuitry further
`comprises a channel analyzer and a channel estimator. The
`processing circuitry is configured to obtain an indication that 40
`a set of antenna ports, or antenna port types, share at least one
`channel property. The channel analyzer is configured to esti(cid:173)
`mate one or more of the shared channel properties based at
`least on a first reference signal transmitted from a first antenna
`port included in the set, or having a type corresponding to one 45
`of the types in the set, wherein the first reference signal is
`received via the radio circuitry. The channel estimator is
`configured to perform channel estimation based on a second
`reference signal transmitted from a second antenna port
`included in the set, or having a type corresponding to one of 50
`the types in the set, wherein the channel estimation is per(cid:173)
`formed using at least the estimated channel properties, and
`wherein the second reference signal is received via the radio
`circuitry.
`Some embodiments provide a network node comprising 55
`radio circuitry and processing circuitry. The processing cir(cid:173)
`cuitry is configured to obtain an indication that a set of
`antenna ports, or antenna port types, share at least one channel
`property. The processing circuitry is further configured to
`transmit, via the radio circuitry, at least two of the antenna 60
`ports in the set, or antenna ports having types comprised in the
`set, from the same transmission point;
`
`DETAILED DESCRIPTION
`
`As explained above, reference signals may be transmitted
`35 from geographically separated ports. Geographical separa(cid:173)
`tion of RS ports implies that instantaneous channel coeffi(cid:173)
`cients from each port towards the UE are in general different.
`Furthermore, even the statistical properties of the channels
`for different ports and RS types may be significantly different.
`Example of such statistical properties include the SNR for
`each port, the delay spread, the Doppler spread, the received
`timing (i.e., the timing of the first significant channel tap), and
`the number of significant channel taps. In LTE, nothing can be
`assumed about the properties of the channel corresponding to
`an antenna port based on the properties of the channel of
`another antenna port. This is in fact a key part of maintaining
`transmission transparency.
`Based on the above observations, the UE needs to perform
`independent estimation for each RS port of interest for each
`RS. This may result in inadequate channel estimation quality
`for certain RS ports, leading to undesirable link and system
`performance degradation. A related problem which indirectly
`also affects the estimation accuracy is that it is not possible for
`the UEs to assume co-location ofDMRS ports with other RS
`ports, particularly in CoMP scenarios.
`Some embodiments disclosed herein provide the UE with
`selected information about RS ports grouping, in order to
`allow channel estimator implementations to exploit common
`channel properties for different RS ports and/or RS types
`within a group. The information comprises e.g. of signaling
`which reference signals may be assumed to be used in com-
`bination with each other to form a channel estimate corre(cid:173)
`sponding to a certain antenna port. Similarly but stated dif(cid:173)
`ferently, which antenna ports may be assumed to have
`65 channels that can be utilized for inferring properties of the
`channel over which symbols for the antenna port of interest is
`conveyed. That is, the UE may be signaled that it is allowed to
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram showing the LTE downlink
`physical resource.
`
`Ex.1016
`APPLE INC. / Page 17 of 25
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`

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`US 8,964,632 B2
`
`7
`assume that reference signals on some antenna ports may be
`used to assist in the channel estimation of a channel for
`another antenna port.
`The antenna ports whose channels exhibit such mutual
`dependence can be said to form a group. In practice, this
`assumption would allow the UE to assume that at least some
`statistical properties of the channels are similar over different
`antenna ports. Such information allows the UE to jointly
`estimate channel properties and to achieve increased estima(cid:173)
`tion accuracy for the corresponding channels estimates. Thus, 10
`particular embodiments enable improved channel e