(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2007/0104174 A1
`Nystrom et al.
`(43) Pub. Date:
`May 10, 2007
`
`US 20070 104174A1
`
`(54) METHOD AND APPARATUS FOR
`ALLOCATING A PILOT SIGNAL ADAPTED
`TO THE CHANNEL CHARACTERISTICS
`
`(76) Inventors: Johan Nystrom, Stockholm (SE); Pal
`Frenger, Vallingby (SE); Erik
`Dahlman, Bromma (SE); Svante
`Signell, Vallingby (SE); Goran Klang,
`Enskede (SE)
`Correspondence Address:
`NIXON & VANDERHYE, PC
`901 NORTH GLEBE ROAD, 11TH FLOOR
`ARLINGTON, VA 22203 (US)
`(21) Appl. No.:
`10/582.478
`(22) PCT Filed:
`Dec. 1, 2004
`(86). PCT No.:
`PCT/EPO4/53.192
`
`S 371(c)(1),
`(2), (4) Date: Jun. 12, 2006
`
`
`
`(30)
`
`Foreign Application Priority Data
`
`Dec. 12, 2003 (EP)........................................ O3104661.8
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`H04 IA00
`(52) U.S. Cl. .............................................................. 370/343
`
`ABSTRACT
`(57)
`A set of different pilot structures are designed for use in
`different environments and/or different user behaviours that
`are expected to occur in a cell. The radio conditions for a
`user are estimated. Each user is then assigned an area
`(108A-E) in resource space for its communication, which
`has a suitable pilot configuration. In one embodiment, the
`entire resource space is provided with different pilot struc
`tures in different parts (110A-D) In advance and allocation
`of resources to the users are then performed in order to
`match estimated radio conditions to the provided pilot
`structure. In another embodiment, allocation is performed
`first, and then the actual pilot structure is adapted within the
`allocated resource space area to Suit the environmental
`conditions.
`
`PROVIDEAT LEAST 2
`PILOT CONFIG.
`
`ALLOCATE WITH PILOT
`CONFIG. MATCHED TO
`RADIO COND.
`
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`Patent Application Publication May 10, 2007 Sheet 1 of 10
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`US 2007/0104174 A1
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`FREgUENCY 108B
`
`DNSILEZIZIZ
`
`DITTI IZŠZTIZ
`
`SN
`
`ÈHHHHHH-SHE`I-HHHHHHRHÈH
`
`2 2
`
`Fig. 2A
`
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`Patent Application Publication May 10, 2007 Sheet 2 of 10
`
`US 2007/0104174 A1
`
`FREgUENCY
`
`FREgUENCY
`
`Fig. 3B
`
`04
`
`O2
`
`
`
`Fig. 3A
`
`TME
`
`CODE
`
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`Patent Application Publication May 10, 2007 Sheet 3 of 10
`
`US 2007/0104174 A1
`
`
`
`PROVIDE AT LEAST 2
`PLOT CONFIG.
`
`2O2
`
`OBTAN EST.
`RADIO COND
`
`204
`
`ALLOCATE WITH PLOT
`CONFIG. MATCHED TO
`RADIO COND
`
`2O6
`
`299
`
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`Patent Application Publication May 10, 2007 Sheet 4 of 10
`
`US 2007/0104174 A1
`
`FREgUENCY 108B
`
`OA
`
`108A
`
`110D 108D
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
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`
`
`
`
`
`
`
`
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`
`
`
`
`OB
`
`5A
`
`OC
`
`FREgUENCY 108B
`
`OA
`
`108A 110D 108D
`
`N
`
`2
`N
`
`SNS
`NN
`an
`
`LIN
`
`LILIITILIS
`
`OC
`
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`Patent Application Publication May 10, 2007 Sheet 5 of 10
`
`US 2007/0104174 A1
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`p FREgUENCY 108B
`
`108C
`
`108A
`
`
`
`
`
`O8E
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`
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`N
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`a
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`2 s
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`
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`
`
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`
`SELECT RESOURCE
`AREATO ALLOCATE
`
`ADAPT PLOT CONFIG.
`N SELECTED AREA
`
`nar ---- mes------------------aa-no-ma------------
`
`TO STEP 299
`
`Fig. 8
`
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`Patent Application Publication May 10, 2007 Sheet 6 of 10
`
`US 2007/0104174 A1
`
`
`
`2OO
`
`2O3
`
`204
`
`2O7
`
`299
`
`PROVIDE RESOURCE
`SPACE WITHAT LEAST
`2 PLOT CONFIG.
`
`OBTAN EST.
`RADIO COND.
`
`SELECT RESOURCE
`SPACE MATCHED TO
`RADIO COND.
`
`Fig. 7A
`
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`Patent Application Publication May 10, 2007 Sheet 7 of 10
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`US 2007/0104174 A1
`
`2OO
`
`PROVIDE RESOURCE
`SPACE WITHAT LEAST
`2 PLOT CONFIG.
`
`2O3
`
`
`
`OBTAN EST.
`RADIO COND.
`
`204
`
`
`
`2O5
`
`209
`
`NO
`
`
`
`
`
`RESOURCE SPACE
`EXSTP
`
`YES
`
`
`
`SELECT ANY FREE
`RESOURCE SPACE
`
`
`
`
`
`SELECT RESOURCE
`SPACE MATCHED TO
`RADIO COND.
`
`2O7
`
`
`
`
`
`ADAPT PLOT CONFIG.
`IN SELECTED AREA
`
`
`
`2O
`
`299
`
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`Patent Application Publication May 10, 2007 Sheet 8 of 10
`
`US 2007/0104174 A1
`
`
`
`RADIO COND.
`PROC.
`
`-
`
`POST ON
`EST MATOR
`
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`Patent Application Publication May 10, 2007 Sheet 9 of 10
`
`US 2007/0104174 A1
`
`
`
`
`
`
`
`FREgUENCY
`
`Fig. 10
`
`OA
`
`110D
`
`S •N
`
`©III. TIÑITIITSIIFITTISI
`
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`LILIITTI T-T-T-T ITTTTTTTTTTTTTTT
`
`Fig. 11
`
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`Patent Application Publication May 10, 2007 Sheet 10 of 10
`FREgUE
`3.
`
`US 2007/0104174 A1
`
`| | | | | | `
`DF
`
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`—————— | || || ||()|
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`
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`US 2007/01 04174 A1
`
`May 10, 2007
`
`METHOD AND APPARATUS FOR ALLOCATING A
`PILOT SIGNAL ADAPTED TO THE CHANNEL
`CHARACTERISTICS
`
`TECHNICAL FIELD
`0001. The present invention relates generally to wireless
`multi-carrier communications systems and in particular to
`resource allocation and pilot signals of Such systems.
`
`BACKGROUND
`0002. In most wireless systems, e.g. GSM (Global Sys
`tem for Mobile communications), WCDMA (Wideband
`Code Division Multiple Access), WLAN (Wireless Local
`Area Network), special well known training sequences or
`pilot signals are transmitted so that the receiver can estimate
`the channel parameters sufficiently well for detection of any
`data signal, not previously known by the receiver. Several
`methods exist to do this, Some use user specific pilots and
`Some use common pilots or combinations. Some pilots are
`code spread and overlaid with user data, others have dedi
`cated time-frequency slots when pilots are transmitted. In
`any case, Some part of the available radio resources must be
`allocated for pilots resulting in overhead that cannot be used
`for data.
`0003. In single-carrier systems, such as e.g. described in
`U.S. Pat. No. 6,452.936, pilot data can be provided in certain
`time slots within a transmission frame. A shorter time
`interval between successive pilot data gives a more accurate
`channel estimation, but decreases instead the transmission
`rate. In U.S. Pat. No. 6,452.936, a particular code of the
`CDMA system is allocated to a user. A pilot density of a
`frame structure is continuously selected dependent on chan
`nel estimation information.
`0004. A multi-carrier approach has been proposed in
`wireless communications systems, in which a data stream
`typically is separated into a series of parallel data streams,
`each of which is modulated and simultaneously transmitted
`with a different frequency. An example of a multi-carrier
`system is an OFDM (Orthogonal Frequency Division Mul
`tiplexing) system. This allows a relative size of transmitted
`symbols relative to a multipath delay to be much larger
`which reduces intersymbol interference. Such a cellular
`multi-user, multi-carrier wireless communications system
`thus allows a particular user to utilise more than one carrier
`simultaneously. The allocation of one or several carriers
`depends typically on quality of service consideration, Such
`as requested transmission rate. Generally, in a multi-carrier,
`multi-user system, the resource space is used in a flexible
`manner to give each user the best possible quality at each
`time. The principles and requirements for providing channel
`estimations become in this way more complex than in a
`single-carrier system, since a continuously use of a single
`communication resource is not ensured. In a cellular multi
`user, multi-carrier wireless communications system, the
`base station must accommodate many users that each expe
`riences different channel characteristics due to fading in both
`time and frequency. Furthermore, different users travel at
`different speeds and thus experience different Doppler shifts.
`0005 Today, there are a few multi-carrier systems in use.
`However, they are not particularly designed for the difficult,
`ever changing, hard-to-predict multi-user environments that
`are envisioned for future wireless systems.
`
`0006 For example, the systems for DVB/DAB (Digital
`Video Broadcasting/Digital Audio Broadcasting) are broad
`cast systems that cannot take into account the need for
`individual users. Such systems must design their pilot struc
`ture according to the worst-case scenario So that detection
`becomes possible even under the worst possible conditions.
`Such a pilot structure gives rise to a substantial pilot
`overhead, and is indeed necessary in these worst-case sce
`narios. However, whenever the situation is better than the
`worst case, which typically is the case most of the time, the
`pilot structure is unnecessarily extensive, giving an unnec
`essary pilot overhead for most users. The pilot overhead can
`indeed be substantial. This reduces data capacity in the own
`cell and furthermore increases the interference to the neigh
`bouring cells (so called pilot pollution).
`0007 Another example of a multi-carrier system is
`WLAN (i.e. IEEE 802.11a, IEEE 802.11g). Such a system is
`designed for a limited geographical area in which the users
`are stationary or slowly moving. The design is not intended
`for conditions in which the user is moving quickly or for
`handling mobility in a multi-cellular environment.
`0008. In the published US patent application 2003/
`0215021, a communications system is disclosed, in which
`channel characteristics are determined by analysing a signal
`received over a (sub)-carrier. The determined characteristics
`are then used to divide the Sub-carriers into groups of similar
`fading characteristics. Each group is then allocated a pilot
`sub-carrier. The determined pilot allocation scheme is then
`used for future transmissions across the Sub-carrier. This
`system compensates for differences in fading characteristics
`over the carrier bandwidth, but has a disadvantage in that it
`is assumed that a sub-carrier is continuously used for one
`single user. A user has to have access to a large number of
`Sub-carriers in order to make Such a pilot allocation efficient.
`Furthermore, entire sub-carriers are allocated as pilot sub
`carriers, which occupies a large part of the available
`resource space, contributing to the pilot pollution.
`
`SUMMARY
`0009. The main problems with existing solutions are that
`pilot structures are either not at all suitable for considerably
`changing radio conditions or that they are designed for worst
`cases which in turn results in vast pilot overhead and “pilot
`pollution'.
`0010. An objective of the present invention is to provide
`methods and devices for multi-user multi-carrier wireless
`communications system, which are capable to provide all
`users with Sufficient pilots without causing unnecessary pilot
`overhead and pilot pollution. A further objective of the
`present invention is to provide such methods and devices,
`which are easy to implement within present and planned
`wireless systems.
`0011. The above objectives are achieved by methods and
`devices according to the enclosed patent claims. In general
`words, a set of different pilot structures are designed for use
`in different environments and/or different general radio
`characteristics that are expected to occur in the cell. The
`radio conditions for a user are estimated, either from direct
`measurements or from knowledge about the cell character
`istics, possibly combined with position information. Each
`user is then assigned an area in resource space for its
`communication, which has a Suitable pilot configuration. In
`
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`US 2007/01 04174 A1
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`May 10, 2007
`
`one embodiment, the entire resource space is provided with
`different pilot structures in different parts in advance and
`allocation of resources to the users are then performed in
`order to match estimated radio conditions to the provided
`pilot structure. In another embodiment, allocation is per
`formed first, and then the actual pilot structure is adapted
`within the allocated resource space area to Suit the environ
`mental conditions. Forbest performance, depending on Such
`things as frequency selectivity, time selectivity (e.g. time
`dispersion and Doppler shift), and path loss the amount of
`pilot energy should be adapted and the distance between
`pilots in the time-frequency domain needs to be changed.
`0012. The radio resource space can have different dimen
`sions. In multi-carrier systems, frequency is one dimension.
`Other dimensions that could be utilised within the present
`invention are time, code, antenna and/or spatial dimensions.
`One or several of these dimensions span the radio resource
`space, in which the present invention is applied.
`0013 By adapting the pilot structure to the environment
`or set of environments likely to occur in the cell and
`allocating these pilots to the users most likely to benefit from
`them, an overall efficiency is achieved. The amount of pilot
`overhead is then connected to the actual environments being
`accommodated. Difficult environments require more over
`head than simpler ones and hence pilot pollution is reduced
`on the average.
`BRIEF DESCRIPTION OF THE DRAWINGS
`0014. The invention, together with further objects and
`advantages thereof, may best be understood by making
`reference to the following description taken together with
`the accompanying drawings, in which:
`0.015
`FIG. 1 is a schematic illustration of a multi-user
`wireless communication system;
`0016 FIGS. 2A and 2B are illustrations of pilot structures
`in time-frequency space, and the allocation of different users
`to Subspaces;
`0017 FIG. 3A illustrates a radio resource space having a
`code dimension;
`0018 FIG. 3B is an illustration of a pilot structure in the
`frequency-code Sub-space;
`0.019
`FIG. 4 is a flow diagram illustrating an embodi
`ment of a method according to the present invention;
`0020 FIGS.5A, 5B and 6 are diagrams illustrating pilot
`structures in time-frequency space, and the allocation of
`different users to subspaces according to embodiments of the
`present invention;
`0021 FIGS. 7A and 7B are flow diagrams illustrating
`other embodiments of a method according to the present
`invention;
`0022 FIG. 8 is a flow diagram illustrating a part of a
`further embodiment of a method according to the present
`invention;
`0023 FIGS. 9A to 9C are block diagrams of downlink
`radio management devices of network nodes according to
`embodiments of the present invention;
`0024 FIG. 10 is a block diagram of uplink radio man
`agement devices of network nodes according to embodi
`ments of the present invention;
`
`0025 FIG. 11 is a diagram illustrating pilot structures in
`time-frequency space having different intensities, and the
`allocation of different users to Subspaces according to an
`embodiment of the present invention; and
`0026 FIGS. 12 and 13 are diagrams illustrating limited
`data descriptions of regular pilot structure.
`
`DETAILED DESCRIPTION
`0027. In the following description, OFDM (Orthogonal
`Frequency Division Multiplexing) systems are used for
`exemplifying the present invention. However, the present
`invention can also be applied to other multi-carrier wireless
`communications systems.
`0028. In the present disclosure, “pilots’ refer to signals
`known by a receiver and therefore used for estimation
`purposes. "Data” refers to signals not previously known by
`the receiver, typically user data, control signals or broadcast
`information.
`0029 FIG. 1 illustrates a multi-user multi-carrier wireless
`communications system 10, in this particular embodiment
`intended to be an OFDM system. Non-exclusive examples
`of other communications systems, in which the present
`invention is advantageously applicable, are IFDMA (Inter
`leaved Frequency Division Multiple Access) systems, non
`orthogonal or bi-orthogonal multi-carrier systems. A base
`station or access point 20 communicates with two mobile
`stations or user equipments 30A, 30B. There is a downlink
`connection 22A between the access point 20 and the user
`equipment 30A and an uplink connection 24A between the
`same nodes. Likewise, there is a downlink connection 22B
`between the access point 20 and the user equipment 30B and
`an uplink connection 24B between the same nodes. User
`equipment 30A is located at a relatively large distance from
`the access point 20, but the speed 32A (illustrated as an
`arrow) of the user equipment 30A is small. User equipment
`30b is located closer to the access point 20, but has a high
`speed32B (also illustrated as an arrow). The user equipment
`30A may have a relatively high need for repetitive pilots in
`the frequency dimension, since the propagation conditions
`for the different carriers may differ considerably over the
`bandwidth in case of multi-path propagation with large
`delay spread. However, the radio conditions are probably
`quite slowly varying with time due to the Small speed of user
`equipment 30A. The user equipment 30B is close to the
`access point, and a pilot on one frequency can probably be
`used for channel estimations for many neighbouring carri
`ers. However, the radio conditions are probably changing
`rapidly in time, whereby frequent pilots in time dimension
`are required.
`0030 FIG. 2A is a diagram of a time-frequency space.
`This can represent a limited portion of the entire available
`radio resource space 100 in these two dimensions. Data is
`transmitted in quantities limited in time and frequency.
`These data quantities correspond to the Small squares 104 in
`the diagram. Selected ones 102 of these data quantities
`contain pilot data and are illustrated in the diagram with
`hatching. The pilot structure is in this embodiment dispersed
`over the time-frequency space relatively uniformly. With
`this distribution, one data quantity out of 11 is occupied by
`pilot data. The useful data transmission rate is thereby
`reduced by /11. The users of the user equipments 30A and
`30B (FIG. 1) have allocated radio resources within the
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`available radio resource space 100. User equipment 30A is
`allocated the resource sub-space indicated by 108A, while
`user equipment 30B is allocated the resource sub-space
`indicated by 108B. Both users are experiencing the same
`pilot density and the uniform distribution between the fre
`quency and time dimensions.
`0031) User 30B moves fast. The time between two con
`secutive pilot messages in time dimension is 11 time slots,
`and even if information from neighbouring frequencies are
`used for channel estimation in the meantime, at least 4 time
`slots will pass between two consecutive updates. The speed
`ofuser 30B is so high that this pilot structure is not sufficient
`for an acceptable quality of service.
`0032. However, arranging the pilot structure as in FIG.
`2B will change the situation. Here, there is a new update in
`time dimension every second time slot, which will Supports
`the fast moving user equipment. Despite this increased
`density in time direction, the total amount of pilot data
`quantities is reduced somewhat. Now only one data quantity
`out of 12 comprises a pilot. The overhead has decreased
`from /11 to /12 (about 9%).
`0033. However, user equipment 30A now achieves prob
`lems. This user equipment 30A moves slowly and is of
`limited use of the frequent updating in time. However, it has
`need for more closely located pilots in frequency dimension
`instead. The pilot structure of FIG. 2B becomes very unsuit
`able for user equipment 30 A.
`0034 So far, only two dimensions, time and frequency,
`have been discussed. FIG. 3A illustrates a radio resource
`space in three dimensions, time, frequency and code. In Such
`a system, each data quantity will instead correspond to a
`small cube 104. Generalisation can be performed to higher
`order spaces, comprising e.g. antenna or space dimensions.
`In general, any radio resource space in at least two dimen
`sions, of which one is frequency, can be used with the
`present invention.
`0035 FIG. 3B illustrates a pilot pattern in a frequency
`code space for a specified time. In this example 16 different
`codes are available and also 16 different frequencies. The
`illustrated pilot pattern leads to that the pilots are transmitted
`on all frequencies during the specified time duration, how
`ever, spread out in the code dimension. One code in each
`frequency is occupied by a pilot, whereas the remaining 15
`codes are used for data transmission.
`0036) As mentioned briefly above, more generally the
`antenna or spatial dimensions could also be part of the
`resource space. One example is that different frequency
`bands are allocated to different beams of a multi-sector or
`fixed beam site. In this case, the spatial dimension is part of
`the description since different pilot patterns may be
`deployed for the different beams that overlap in the spatial
`domain. With the grouping of resources in terms of antenna
`sectors or beams the pilots allocated to different users can
`change dynamically when the user for example moves
`between sectors and the sectors have different frequency
`bands allocated to them. In Such cases, antenna or spatial
`dimension can also be used as additional dimensions in a
`total resource space.
`0037. The flow diagram of FIG. 4 illustrates the main
`steps of an embodiment of a method according to the present
`invention. The procedure starts in step 200. In step 202, a
`
`number of pilot configurations are provided, which are
`believed to suit different radio conditions appearing in the
`cell in question. At least two Such pilot configurations are
`available, i.e. they can be handled by both sides of the
`transmission connection. At least one of the pilot configu
`rations comprises sub-carriers having both pilot resources
`and data resources, i.e. resources allocated for any data not
`previously known by the receiver. Such as user data, control
`signals or broadcast information, in order to accommodate
`efficiency requests from e.g. slow-moving terminals. The
`transmitter manages the sending of pilots according to this
`configurations and the receiver is capable of performing
`channel estimation based on the at least two pilot configu
`rations. In step 204, an estimation of the radio conditions at
`the receiver is obtained. This estimation can be provided in
`many different ways. The actual radio conditions can be
`measured and evaluated. Another possibility is to assume an
`estimate from knowledge about the characteristics in the cell
`and possibly based on e.g. location and/or speed of the
`receiver relative the transmitter.
`0038. In step 206, a user is allocated resources in resource
`space, which have a pilot configuration that is matched to the
`estimated radio conditions. This matching can be performed
`in different manners, described more in detail further below.
`The procedure stops in step 299. Anyone skilled in the art
`realises that step 202 preferably is performed once, and the
`provided pilot structures can then be used for any future
`allocation of users, or re-allocation of existing users.
`0039. A few examples, using OFDM as an example
`system, will be used to visualise the effect of the present
`invention. The basic setup in FIG. 5A is assumed as follows.
`During a certain time period and seen over all frequency
`resources, the available radio resources constitute a grid of
`basic resources that can be used for data, control signaling
`or pilot signals or other signals as discussed earlier. The
`resolution in frequency dimension is one OFDM carrier and
`in time it is one OFDM symbol. Pilot symbols are as above
`depicted with hatched boxes.
`0040. The transmitter side, in this example assumed to be
`the base station, determines a number of different pilot
`patterns and assigns these pilot patterns to different parts of
`the entire radio resource space. The pilot patterns may for
`example be periodically recurring with some period or
`pseudo-randomly designed. This means that different parts
`of the radio resource space have a denser or at least differing
`pilot pattern than other parts. Each pilot pattern is intended
`to accommodate users experiencing different channel char
`acteristics.
`0041) This is illustrated in FIG. 5A. The entire radio
`resource space illustrated is divided into four rectangular
`parts, 110A-D. The resource space part 110A has a pilot
`pattern, having a dense occurrence in time dimension (every
`second OFDM symbol at certain carriers), but a more
`dispersed behaviour in the frequency dimension (only every
`sixth OFDM carrier). The resource space part 110B has a
`very diluted pilot pattern, having only one pilot in 36
`resource units, evenly spread in time and frequency dimen
`sions. The resource space part 110C is the opposite of part
`110A, with a dense pilot pattern in frequency dimension, but
`sparse in time dimension. Finally, resource space part 110D
`has a very dense pilot structure in both dimensions, com
`prising a pilot symbol in every fourth resource unit.
`
`Intel Corporation Ex. 1017
`Intel Corp v. UNM Rainforest Innovations - IPR2020-01576
`Page 14 of 19
`
`

`

`US 2007/01 04174 A1
`
`May 10, 2007
`
`0042. According to one embodiment of the invention, the
`users are now allocated to the different parts of the radio
`resource space dependent on their estimated radio condi
`tions. In other words, whenever a certain user has certain
`demands, the user is assigned resources in the resource space
`where pilots with the appropriate density can be utilised for
`channel estimation. In the situation in FIG. 5A, there are
`pilot structures suitable for typically four combinations of
`Doppler and delay spread. In part 110A, the pilot structure
`is intended for a large Doppler and low delay spread. In part
`110B, the pilot structure is intended for a low Doppler and
`low delay spread. In part 110C, the pilot structure is intended
`for a low Doppler and high delay spread. In part 110D, the
`pilot structure is intended for a high Doppler and high delay
`spread.
`0043. A first user, having radio conditions demanding a
`high density of pilots in both dimensions is allocated to the
`resource sub-space 108A within the part 110D. A second
`user, only having need for dense pilot in the time dimension
`is allocated resources in a resource sub-space 108B within
`the part 110A. A third user with very favourable radio
`conditions is allocated to a resource sub-space 108C in part
`110B. Finally, two more users, having high demands on pilot
`density are given resources in two sub-spaces 108D and
`108E, respectively in part 110D. One realises that each user
`has achieved a pilot pattern that is suited to its individual
`needs. It is beneficial, e.g. to assign resources for mobiles
`with certain fast varying channel or Doppler conditions in
`the dense parts of the pilot pattern and users with more
`slowly varying conditions in the less dense parts.
`0044) Note that the base station does not need to transmit
`all pilots at all times. Only pilots that in fact can be utilised
`by any user needs to be transmitted. If a pilot resource at
`time of transmission cannot be utilised by any data symbol
`that some user need to detect with the help of said pilot, then
`the pilot need not be transmitted. In such a way, the overall
`pilot pollution is reduced, and so is the average transmission
`power.
`0045. In FIG. 5B, a further embodiment of the present
`invention is mustrated. Assume the same situation as was
`present in FIG. 5A. Three users are occupying all resources
`in the densest part 110D. E. yet another user with need for a
`very dense pilot configuration appears, the pre-defined pilot
`configuration plan of FIG. 5A becomes insufficient. How
`ever, the new user can be allocated to a free resource
`sub-space 108F, preferably in connection with the part
`110D. This sub-space 108F had originally a pilot pattern
`according to part 110C, but when allocating the user, the
`pilot pattern is adjusted to match the demands put by the new
`user. In such a way, the original pre-determined division into
`different parts in the resource space can be adapted to the
`actual need. However, if a good initial configuration is used,
`most cases are covered and the frequency of adjustments is
`low.
`0046) Now, return to the situation of FIG. 5A. If the user
`having the allocation of sub-space 108E slows down, the
`estimated radio conditions change, and the need for pilots is
`reduced. The user can then be reallocated to another sub
`space of the resource space, having a more Suitable pilot
`configuration for the new estimated radio conditions, e.g. to
`part 110C. An alternative is to keep the allocated sub-space
`but instead change the pilot pattern to a more Suitable one for
`the new conditions.
`
`0047 The ideas of adjusting or adapting the pilot con
`figuration when needed can also be brought to the extreme
`end, where no pilot pattern at all is pre-configured for the
`different parts of the resource space. Instead, there is always
`an adjustment of pilot pattern for all users. This is schemati
`cally illustrated in FIG. 6. Here, a first user was assigned a
`sub-space 108A, without associated pre-defined pilot pat
`tern. The pilot pattern was then adjusted according to the
`actual needs as concluded from the estimated radio condi
`tions. In this case a dense pattern was selected. A second user
`was allocated to sub-space 108B and subsequently, a suit
`able pilot pattern was selected for his Sub-space. In Such a
`way, all the sub-spaces 108A-F were associated with pilot
`configurations suitable for each individual need. Sub-spaces
`not allocated to any user do not comprise any pilots in Such
`an approach. A user with certain estimated properties is thus
`allocated to use certain resources and the pilot pattern is
`designed accordingly. The result is the same as the previous
`embodiments, pilot patterns and user characteristics are
`matched.
`0048. The above embodiments can also be expressed in
`flow diagrams. In FIG. 7A, a flow diagram corresponding to
`the situation in FIG. 5A is illustrated. The resource space is
`in step 203 provided with at least two different pre-deter
`mined pilot configurations at different parts of the resource
`space. Step 204 is unchanged compared to FIG. 4. In step
`207, the matching of the radio conditions and pilot structures
`is performed by selecting a suitable resource space.
`0049. The situation in FIG. 5B is illustrated by the flow
`diagram of FIG. 7B. Also here, pre-defined pilot configu
`rations are associated with different parts of the resource
`space in step 203. In step 205, it is determined whether there
`is any available resources in parts that are suitable for the
`particular estimated radio conditions for the user to be
`allocated. If there are resources with suitable pilot structures
`available, the procedure continues to step 207, as in FIG. 7A.
`If no resource space with appropriate pilot structure is
`available, any free resource space is allocated in step 209,
`however, preferably in the vicinity of the part having a
`suitable pilot pattern. In step 210, the pilot configuration is
`adapted within the selected resource Sub-space to match the
`estimated radio conditions.
`0050. The embodiment illustrated in FIG. 6 can similarly
`be illustrated by the part flow diagram of FIG.8. Here, the
`step 206 in FIG. 4 is described in more detail. In step 208,
`an area is selected as a resource Sub-space for the user. In
`step 210, the pilot configuration in the selected area is
`adapted to the need connected to the estimated radio con
`ditions of the user. Note the similarities between FIG