WO2015185126A1

WO2015185126A1 - Signalling of link adaptation scheme

Info

Publication number: WO2015185126A1
Application number: PCT/EP2014/061600
Authority: WO
Inventors: Klaus Ingemann Pedersen; Beatriz SORET; Niels Jorgensen; Frank Frederiksen
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2014-06-04
Filing date: 2014-06-04
Publication date: 2015-12-10

Abstract

This document discloses a solution where a terminal device of a cellular communication system is configured to utilize a frequency-selective link adaptation scheme, wherein different link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal device.

Description

DESCRIPTION

Title SIGNALLING OF LINK ADAPTATION SCHEME

TECHNICAL FIELD

The invention relates to the field of cellular communication systems and, particularly, signalling a link adaptation scheme used in a communication link.

BACKGROUND

Cellular communication system employs link adaptation to compensate for changes in a radio channel. Link adaptation enables changing, for example, a modulation and coding scheme or a diversity scheme on the basis of measured radio channel quality between a base station and a terminal device.

BRIEF DESCRIPTION

The invention is defined by the independent claims.

Embodiments are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figure 1 is illustrates a wireless communication system to which embodiments of the invention may be applied;

Figure 2 illustrates a signalling diagram of a procedure for determining a link adaptation scheme for a terminal device according to an embodiment of the invention;

Figures 3 and 4 illustrate processes for selecting the link adaptation scheme for the terminal device according to some embodiments of the invention;

Figures 5 to 12 illustrate embodiments of frequency-selective link adaptation schemes and associated signalling between a base station and a terminal device;

Figure 13 illustrates a signalling diagram for determining a wideband link adaptation scheme for the terminal device according to an embodiment of the invention;

Figure 14 illustrates a transmitter-receiver diagram for the wideband link adaptation scheme according to an embodiment of the invention; and Figures 15 and 16 illustrate blocks diagrams of apparatuses according to some embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The following embodiments are exemplary. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may contain also features/structures that have not been specifically mentioned.

Figure 1 illustrates a wireless communication scenario to which embodiments of the invention may be applied. Referring to Figure 1 , a cellular communication system may comprise a radio access network comprising base stations disposed to provide radio coverage in a determined geographical area. The base stations may comprise macro cell base stations 102 arranged to provide terminal devices 106 with the radio coverage over a relatively large area spanning even over several square miles, for example. In densely populated hotspots where improved capacity is required, small area cell base stations 100 may be deployed to provide terminal devices 104 with high data rate services. Such small area cell base stations may be called micro cell base stations, pico cell base stations, or femto cell base stations. The small area cell base stations typically have significantly smaller coverage area than the macro base stations 102. The cellular communication system may operate according to specifications of the 3^rd Generation Partnership Project (3GPP) Long-Term Evolu- tion (LTE) Advanced or its evolution version.

Modern cellular communication systems employ link adaptation to cope with changing radio channel. Link adaptation may be carried out by changing link adaptation parameters on the basis of channel measurements. The channel measurements may comprise estimating channel path loss, a received signal strength indicator (RSSI), and/or a coherence bandwidth of the radio channel. Terminal devices may measure the channel properties, generate a channel quality indicator, and transmit the channel quality indicator to a base station for use in determining the link adaptation parameters. Additionally, the base station may make channel measurements on the basis of a pilot signal received from the terminal device. The coherence bandwidth is an indicator of a bandwidth wherein the channel properties remain substantially con- stant. Additional criteria may be used for selecting the link adaptation parameters, as described below. Link adaptation parameters may comprise a modulation scheme, e.g. phase-shift keying (PSK), amplitude-shift keying (ASK), or their combination quadrature amplitude modulation (QAM). Link adaptation parameters may comprise a channel coding scheme. A typical channel coding scheme employs convolutional channel codes. In the LTE systems, however, turbo coding may be used. At least a code rate of the channel coding may be made adaptive for the link adaptation. The code rate represents the number of error correction bits generated per one payload bit. Link adaptation parameters may comprise multi-antenna communication scheme, e.g. the number of parallel spatial streams and selection between spatial diversity and spatial multiplexing. In the spatial diversity, the same information may be transmitted in a plurality of parallel spatial streams or from a plurality of antennas, thus improving reliability of the transmission. In the spatial multiplexing, the multiple spatial streams are employed to improve the payload data rate. Accordingly, different data may be transferred to in the parallel spatial streams. Such multi-antenna transmission schemes are available when a transmitter and/or or receiver comprises multiple antennas and an appropriate spatial signal processing circuitry. For example, the LTE systems employ multiple-input-multiple-output (MIMO) communication which is an example of the multi-antenna transmission scheme where both a base station and a terminal device comprise multiple antennas and the spatial signal processing circuitries. Link adaptation affects directly the reliability and data rates so improvements in the selection of the optimal link adaptation scheme are always required.

Modern cellular communication systems are wideband systems where a large bandwidth may be scheduled to a single terminal device for the transmission of data. The scheduled resources may be indicated in terms of physical resource blocks or frequency resource blocks. Each frequency resource block has a determined bandwidth and a centre frequency and one or more frequency resource blocks may be scheduled to the terminal device at a time. The frequency resource blocks scheduled to the terminal device may be contiguous and, thus, form a continuous scheduled band for the terminal device. However, the resource blocks may be non-contiguous in which case the form a non-contiguous band fragmented into a plurality of smaller bands.

Let us now describe an embodiment of the invention for selecting and signalling link adaptation parameters with reference to Figure 2. Figure 2 illustrates a signalling diagram illustrating a method for signalling link adaptation parameters between a base station of a cellular communication system, e.g. base station 100 or 102, and a terminal device of the cellular communication system, e.g. the terminal device 104 or 106. In another embodiment, the procedure of Figure 2 may be carried out between the terminal device and an access node or, more generally, a network node. The network node may be a server computer or a host computer. For example, the server computer or the host computer may generate a virtual network through which the host computer communicates with the terminal device. In general, virtual networking may involve a process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Network virtualization may involve platform virtualization, often com- bined with resource virtualization. Network virtualization may be categorized as external virtual networking which combines many networks, or parts of networks, into the server computer or the host computer. External network virtualization is targeted to optimized network sharing. Another category is internal virtual networking which provides network-like functionality to the software containers on a single system. Virtual networking may also be used for testing the terminal device.

Referring to Figure 2, a communication link is established between the base station and the terminal device (step 200). Step 200 may comprise establishment of a control channel connection. The control channel connection may comprise a radio resource control (RRC) connection. In block 202, the base station selects a link adaptation scheme for the terminal device. The selection may be made between at least one frequency-selective link adaptation scheme 204 and a wideband link adaptation scheme 206. In the frequency-selective link adaptation scheme 204, different link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal device. In the wideband link adaptation scheme 206, the same link adaptation parameters are applied to the terminal device over all the frequency resource blocks scheduled to the terminal device. The scheduled frequency resource blocks may refer to frequency resource blocks of the same transmission time interval (TTI). In step 208, the base station transmits a control message to the terminal device. The control message comprises at least one information element indicating the selected link adaptation scheme. The terminal device acquires the control message from the base station in step 208 and stores the information on the selected scheme. The information may be used in connection with transferring data with the base station, as described next.

In block 210, the base station schedules frequency resource blocks to the terminal device. Block 210 may be executed as a result of the base station detecting availability of downlink data to be transmitted to the terminal device or as a result of receiving an uplink scheduling request from the terminal device. The base station may schedule the frequency resource blocks that form a contiguous or non-contiguous band. The base station may also determine the link adaptation parameters for the resource blocks on the basis of the link adaptation scheme selected in step 202 and on the basis of channel measurements. In step 212, the base station transmits a scheduling message to the terminal device. The scheduling message may comprises at least one information element indicating the determined plurality of frequency resource blocks and at least one information element indicating the selected link adaptation parameters the resource blocks. Upon receiving the scheduling message, the terminal device may gain knowledge of the scheduled resource blocks and associated link adaptation parameters. In block 214, the base station and the terminal device may employ the link adaptation parameters in processing of data transferred in the scheduled frequency resource blocks.

Adaptive selection of the link adaptation scheme enables better capability to adapt to varying radio channel characteristics, thus providing performance improvements.

In an embodiment, the scheduling message is a scheduling grant responding to the uplink scheduling request. In such an embodiment, the scheduling grant may indicate uplink frequency resource blocks scheduled to the terminal device. In another embodiment, the scheduling message may be a downlink scheduling grant indicating downlink frequency resource blocks scheduled to the terminal device.

In an embodiment, the control message indicating the selected link adaptation scheme is transmitted as a RRC signalling message on Layer 3.

In an embodiment, the control message indicating the selected link adap- tation scheme is transmitted as a medium access control signalling message on Layer 2. In this embodiment, the control message transferred in step 208 and the scheduling message transferred in step 212 may even be transmitted in the same message on a control channel, e.g. a physical downlink control channel (PDCCH).

In an embodiment, the scheduling message or the message mapping the selected link adaptation parameters to the frequency resource blocks may be a physical layer control message transferred on Layer 1.

In an embodiment, the base station may determine to change the link adaptation scheme, e.g. to switch from the frequency-selective scheme 204 to the wideband scheme 206. As a result, steps 202 and 208 may be reiterated.

Let us now describe some embodiments of block 202 with reference to

Figures 3 and 4. Figures 3 and 4 illustrate embodiments for making a selection be- tween the frequency-selective link adaptation scheme 204 and the wideband link adaptation scheme 206. Referring to Figure 3, the base station may estimate channel properties of a radio channel between the base station and the terminal device in block 300. Block 300 may comprise receiving channel measurement report from the terminal device and estimating the channel properties from the channel measurement report. Block 300 may comprise receiving a pilot signal from the terminal device and estimating the channel properties on the basis of properties measured from the received pilot signal. In an embodiment, block 300 comprises estimating channel coherence bandwidth. A state-of-the-art estimation algorithm may be used to estimate the coherence bandwidth, e.g. determining a range of frequencies over which the channel can be considered "flat", wherein "flat" is defined by a determined tolerance range in spectral amplitude degradation. In block 302, the estimated coherence bandwidth is compared with the bandwidth of an operating band of the terminal device. The operating band may be defined as a band from which the base station schedules the fre- quency resource blocks to the terminal device. If the coherence bandwidth is smaller than the bandwidth of the operating band, the frequency-selective link adaptation scheme may be selected and the process may proceed to block 304. If the coherence bandwidth is higher than the bandwidth of the operating band, the wideband link adaptation scheme may be selected and the process may proceed to block 306.

The embodiment of Figure 3 enables the selection of the frequency- selective link adaptation scheme in situations where the use of the same link adaptation parameters over the whole operating band would result in sub-optimal performance. On the other hand, the wideband link adaptation scheme may be employed when the coherence bandwidth is high, thus resulting in less signalling overhead.

Referring to Figure 4, the base station may select the link adaptation scheme at least partially on the basis of the number of terminal devices connected to the base station. In block 400, the number of served or connected terminal devices is determined. The determined number is then compared with a threshold in block 402. If the number of terminal devices is below the threshold, the frequency-selective link adaptation scheme may be selected (block 304). If the number of terminal devices is above the threshold, the wideband link adaptation scheme may be selected (block 306). In an embodiment, the threshold is two terminal devices. In another embodiment, the threshold is three terminal devices.

In an embodiment, the embodiments of Figures 3 and 4 may be com- bined. For example, both criteria may be need to be fulfilled to select one scheme, e.g. the number of connected terminal devices must be below the threshold and the coherence bandwidth below the bandwidth of the operating band in order to select the frequency-selective link adaptation scheme. In a further modification, the processes of Figures 3 and/or 4 may be exclusive to small area cell base stations, e.g. the base station 100 may carry out the embodiments of Figure 2, 3, and/or 4 but the macro base station 102 may not.

Let us now describe embodiments of the link adaptation schemes in greater detail with reference to Figures 5 to 14. Figures 6, 8, 10, and 12 illustrate embodiments of the frequency-selective link adaptation scheme, and Figures 5, 7, 9, and 1 1 illustrate respective signalling diagrams. Figure 14 illustrates an embodiment of the wideband link adaptation scheme, and Figure 13 illustrates a respective signalling diagram.

Referring to Figure 5, the base station makes the selection of the link adaptation scheme between the at least one frequency-selective scheme 500 and the wideband scheme 206. In this embodiment, the frequency-adaptive link adaptation scheme 500 comprises selecting separately a modulation scheme for a plurality of subsets of frequency resource blocks allocated to the terminal device and employing common channel coding and cyclic redundancy check (CRC) computation for the plurality of subsets of frequency resource blocks allocated to the terminal device. Let us assume that the base station selects the frequency-selective link adaptation scheme in step 202. In step 502, the base station transmits the control message comprising information element indication the selection of this frequency-selective link adaptation scheme 500.

In block 504, the terminal device and the base station employ the frequency-selective link adaptation scheme 500 in the transfer of data in the frequency resource blocks the base station has scheduled to the terminal device. Block 504 may comprise the base station selecting the frequency resource blocks for the terminal device, dividing the selected frequency resource blocks into a plurality of subsets, wherein each subset comprises a number of adjacent frequency resource blocks amongst the selected frequency resource blocks such that each subset defines a sin- gle consecutive sub-band amongst the frequency band between a resource block on the highest frequency block and a resource block on the lowest frequency block. Then, the link adaptation parameters may be selected separately for each subset while some link adaptation parameters may be common to all subsets. Block 504 may be carried out for uplink and/or downlink transmissions.

Figure 6 illustrates processing of link adaptation parameters in a transmitter and a receiver in block 504. As described above, the transmitter may be the base station and the receiver may be the terminal device or the transmitter may be the terminal device and the receiver may be the base station, depending on whether block 504 is performed for uplink or downlink. As described above, the CRC and the channel coding a performed jointly for all the subsets while the modulation is performed separately for each subset, thus providing capability of using different modulation schemes for each subset. Referring to Figure 6, a CRC computer 600 of the transmitter computes a common CRC sequence from data bits to be allocated to the scheduled frequency resource blocks. Then, the data bits and the CRC sequence are input to a channel encoder 602 configured to add redundancy to the input bits by executing a channel encoding algorithm. The channel encoder 600 may be a turbo encoder, for example. Then, the channel-encoded bits are divided to modulators 604, 606, 608 each associated with a different subset of frequency resource blocks. Each modulator 604 to 608 modulates the input bits with a modulation scheme that is selected separately for each modulator 604 to 608. Accordingly, the modulators 604 to 608 may each employ the same or different modulation scheme that another modulator 604 to 608, depending on the channel characteristics. Before the modulation, a rate matching may be used to select the encoded bits that are to be transmitted in a determined transmission time interval (TTI) in which the scheduled frequency resource blocks are provided. After the modulation converting the bits into amplitude/phase symbols, the selected symbols are mapped to the corresponding frequency resource blocks and transmitted to the receiver.

In the receiver, reverse operations are performed. Demodulators 610, 612, 614 demodulate the symbols acquired from the subset of frequency resource blocks after which a rate de-matching is performed. The demodulation and the rate de- matching are performed for each subset in this embodiment. Then, the rate de- matched bits from blocks 610 to 614 may be combined into a single bit stream and input to a channel decoder 616 performing common channel decoding for the subsets of frequency resource blocks. When the channel encoder 602 is the turbo encoder, the channel decoder 616 may be a turbo decoder. After the decoding, the decoded bits may be output as a single stream to a CRC decoder 618 configured to perform CRC decoding commonly for the subsets.

Figures 7 and 8 illustrate an embodiment where independent modulation, rate matching, and channel coding are performed for each subset of frequency resource blocks. The CRC is performed commonly for all the subsets. Referring to Fig- ure 7, the base station makes the selection between this frequency-selective link adaptation scheme 700 and the wideband scheme 206 and, when the frequency- selective scheme is selected, signals the control message comprising an information element indicating the frequency-selective scheme 700 to the terminal device (step 702). Then, the frequency-selective scheme may be employed in the transfer of data between the base station and the terminal device in block 704.

Referring to Figure 8, the CRC computer 600 performs the CRC sequence computation in the above-described manner in the transmitter (the base station or the terminal device). Then, the bits being transmitted are divided into a parallel streams according to the subsets of the frequency resource blocks, wherein each stream is channel encoded, rate-matched, and modulated separately in the channel encoders 800, 602, 802 and blocks 604 to 608. In the receiver (the terminal device or the base station), the respective demodulators, rate de-matchers and channel decoders 804, 616, 808 are provided separately for each stream, while the CRC decoder 618 is again common for all streams. In other words, the CRC sequence is common for all streams.

Figures 9 and 10 illustrate an embodiment where independent modulation, rate matching, channel coding, and CRC sequence computation and CRC decoding are performed for each subset of frequency resource blocks. Referring to Figure 9, the base station makes the selection between this frequency-selective link adaptation scheme 900 and the wideband scheme 206 and, when the frequency-selective scheme is selected, signals the control message comprising an information element indicating the frequency-selective scheme 900 to the terminal device (step 902). Then, the frequency-selective scheme may be employed in the transfer of data between the base station and the terminal device in block 904.

Referring to Figure 10, the data bits are divided into the parallel streams before the CRC computers 1000, 600, 1002 configured to perform the CRC sequence computation for each streams separately in the above-described manner in the transmitter (the base station or the terminal device). Accordingly, a unique CRC sequence is acquired for each parallel stream. Then, each stream is channel encoded, rate-matched, and modulated separately in the channel encoders 800, 602, 802 and blocks 604 to 608. In the receiver (the terminal device or the base station), the respective demodulators, rate de-matchers and channel decoders 804, 616, 808 are provided separately for each stream. A separate CRC decoder 1004, 618, 1006 is also provided for each stream, and the streams may be combined after the CRC check has been completed.

Above, the channel rank, i.e. the number of independent spatial streams the channel between the base station and the terminal device provides, may be used as a link adaptation parameter. In the embodiments of Figures 5 to 10, the channel rank may be used as a link adaptation parameter determined commonly for all the subsets. Figures 1 1 and 12 illustrate an embodiment where independent modulation, rate matching, channel coding, and CRC sequence computation and CRC decoding are performed for each subset of frequency resource blocks. Furthermore, a number of parallel spatial streams is determined for each subset separately. Referring to Figure 1 1 , the base station makes the selection between this frequency-selective link adaptation scheme 1 100 and the wideband scheme 206 and, when the frequency- selective scheme 1 100 is selected, signals the control message comprising an infor- mation element indicating the frequency-selective scheme 1 100 to the terminal device (step 1 102). Then, the frequency-selective scheme may be employed in the transfer of data between the base station and the terminal device in block 1 104.

Referring to Figure 12, the number of parallel spatial streams may be determined and the data bits divided into the parallel streams before the CRC computa- tions in blocks 100, 600, 1002, 1200. Now, the number of parallel streams depends on the number of subsets formed from the scheduled frequency resource blocks, as in the above embodiments, and additionally on the number of parallel spatial streams selected for each subset. In the embodiment of Figure 12, two parallel spatial streams are selected for one subset while only one spatial stream is selected for the other subsets. Accordingly, the number of formed parallel streams is four. In general, an equation for determining the number of parallel streams Ν_ω may be derived as:

Ntot = N_Si1 + N_s,2 + ... + N_S,N (1 ) where N_{s 1} represents the number of spatial streams for a first subset, N_{s 2} represents the number of spatial streams for a second subset and so on until the N^th subset, wherein N≥ 2. After the parallel streams have been formed, the CRC computation, the channel coding, the modulation and rate matching may be performed separately for each stream in the transmitter and respective reverse processing may be carried out in the receiver. An additional processing line formed by blocks 1200, 1202, 1204, 1206, 1208, 1210 may be formed for the additional spatial signal stream that is mapped to the same frequency resource blocks as the stream processed by blocks 100, 800, 604, 610, 804, 1004.

The transmitter and the receiver may further comprise a spatial signal processing circuitry before the CRC computers 1000, 1200 and after the CRC decoders 1004, 1210 that perform spatial signal processing for the plurality of spatial streams. The link adaptation parameters selected for the frequency-selective link ad- aptation scheme may define a spatial signal processing scheme, e.g. spatial multiplexing or spatial diversity.

Figures 13 and 14 illustrate an embodiment of the wideband link adaptation scheme where common modulation, rate matching, channel coding, and CRC sequence computation and CRC decoding are performed for all frequency resource blocks. Referring to Figure 13 the base station makes the selection between at least one of the above-described frequency-selective link adaptation schemes 204, 500, 700, 900, 1 100 and the wideband scheme 206 and, when the wideband scheme 206 is selected, signals the control message comprising an information element indicating the wideband scheme 206 to the terminal device (step 1302). Then, the wideband scheme may be employed in the transfer of data between the base station and the terminal device in block 1304.

Referring to Figure 14, the CRC computer 600 computes a CRC sequence from the data bits mapped to the scheduled frequency resource blocks. Simi- larly, common channel encoder 602 and modulator 606 may be employed for the data bits that are then mapped to the scheduled frequency resource blocks. From another point of view, only a single subset is then formed from the scheduled frequency resource blocks. Similarly in the receiver, a common demodulator 612, channel decoder 616, and the CRC decoder 618 are employed for all the frequency resource blocks.

With respect to all embodiments of Figures 5 to 14, the division of the frequency resource blocks into the subsets and the selection of the link adaptation parameters for each subset may be made by the base station for both uplink and downlink transmissions or by a transmitter, depending on the embodiment. With respect to the downlink transmissions, the base station may indicate the link adaptation parameters in a scheduling message indicating also the scheduled frequency resource blocks. The link adaptation parameters may be indicated per resource block or, in some embodiments, a single information element may indicate the link adaptation parameters for the subset, that is commonly to a plurality of frequency resource blocks.

An embodiment provides an apparatus comprising at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to carry out the procedures of the above-described base station or the network node. The at least one processor, the at least one memory, and the computer program code may thus be considered as an embodiment of means for executing the above-described procedures of the base station or the network node. Figure 15 illustrates a block diagram of a structure of such an apparatus. The apparatus may be comprised in the base station or the network node, e.g. the apparatus may form a chipset or a circuitry in the base station or the network node. In some embodiments, the apparatus is the base station or the network node. The apparatus com- prises a processing circuitry 10 comprising the at least one processor. The processing circuitry 10 may comprise a channel estimation circuitry 16 configured to estimate channel properties of radio channels between the base station and each terminal device connected to the base station. The channel estimation circuitry may be configured to determine the channel coherence bandwidth, as described above, and output the coherence bandwidth to a link adaptation scheme selector 18. The link adaptation scheme selector 18 may be configured to make a selection between the wideband link adaptation scheme and at least one frequency-selective link adaptation scheme. In some embodiments, the base station supports only one frequency-selective link adaptation scheme but, in other embodiments, the base station supports multiple fre- quency-selective link adaptation schemes. In such other embodiments, the base station may make the selection between the frequency-selective schemes according to a determined criterion. In an embodiment, the criterion is capabilities of the terminal device, e.g. the frequency-selective scheme is selected amongst the schemes supported by the terminal device. In another embodiment, the criterion is measured radio channel properties, e.g. certain measured properties may be mapped to certain frequency-selective link adaptation schemes. For example, different ranges of the channel quality indicator may be mapped to different frequency-selective link adaptation schemes. In another embodiment, the criterion is a quality-of-service of the terminal device, e.g. each quality-of-service (QoS) class may be mapped to a determined fre- quency-selective link adaptation scheme and at least two of the QoS classes may be mapped to different frequency-selective link adaptation schemes. In another embodiment, the criterion is a service provided to the terminal device. For example, wireless services having different traffic or reliability requirements may be mapped to different frequency-selective link adaptation schemes. Upon selecting the link adaptation scheme, the link adaptation scheme selector 18 may output a signal indicating the selected scheme to a control message generator configured to generate the control message indicating the selected scheme to the terminal device for which the scheme is selected.

The apparatus may further comprise a scheduler circuitry 14 configured to schedule frequency resource blocks in transmission time intervals to the terminal devices. The scheduler circuitry 14 may output to the control message generator infor- mation on the schedulings and the control message generator 12 may create the scheduling messages indicating the schedulings to the terminal devices on a control channel.

The processing circuitry 10 may comprise the circuitries 12 to 18 as sub- circuitries, or they may be considered as computer program modules executed by the same physical processing circuitry. The memory 20 may store one or more computer program products 24 comprising program instructions that specify the operation of the circuitries 12 to 18. The memory 20 may further store a database comprising definitions for the selection of the link adaptation scheme, for example. The apparatus may further comprise a communication interface 22 providing the apparatus with radio communication capability with the terminal devices. The communication interface 22 may comprise a radio communication circuitry enabling wireless communications and comprise a radio frequency signal processing circuitry and a baseband signal processing circuitry. The baseband signal processing circuitry may be configured to carry out the functions of the transmitter and/or the receiver, as described above in connection with Figures 6, 8, 10, 12, 14. In some embodiments, the communication interface may be connected to a remote radio head comprising at least an antenna and, in some embodiments, radio frequency signal processing in a remote location with respect to the base station. In such embodiments, the communication interface 22 may carry out only some of radio frequency signal processing or no radio frequency signal processing at all. The connection between the communication interface 22 and the remote radio head may be an analogue connection or a digital connection.

An embodiment provides another apparatus comprising at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to carry out the procedures of the above- described terminal device. The at least one processor, the at least one memory, and the computer program code may thus be considered as an embodiment of means for executing the above-described procedures of the terminal device. Figure 16 illustrates a block diagram of a structure of such an apparatus. The apparatus may be comprised in the terminal device, e.g. it may form a chipset or a circuitry in the terminal device. In some embodiments, the apparatus is the terminal device. The apparatus comprises a processing circuitry 50 comprising the at least one processor. The processing circuitry 50 may comprise a communication controller circuitry 54 configured to extract scheduling messages received from a serving base station, to determine communication resources scheduled to the terminal device, e.g. frequency resource block(s) and associated transmission time intervals, and to control the terminal device to transmit or receive data between the base station in the scheduled communication resources. The apparatus may further comprise a link adaptation parameter selector 52 configured to determine prevailing link adaptation parameters for the scheduled communication resources and to cause the terminal device to process the data transferred in the scheduled communication resources according to the prevailing link adaptation parameters. The link adaptation parameter selector 52 may determine the prevailing link adaptation scheme from the control message received from the base station that indicates whether to apply the frequency-selective or wideband link adap- tation scheme. Furthermore, the link adaptation parameter selector 52 may select the link adaptation parameters for the link adaptation scheme on the basis of the same control message or another control message received from the base station. In some embodiments where the channel is relatively stable, the link adaptation parameters may be semi-static and maintained constant over a plurality of consecutive schedul- ings. In an embodiment described above, the scheduling message indicating the resource scheduled to the terminal device indicates the link adaptation parameters, and the link adaptation parameter selector 52 may determine the link adaptation parameters used for the scheduled resources from the received scheduling message. The link adaptation parameter selector 52 may then cause the terminal device to process the data transferred in the scheduled resources according to the selected link adaptation parameters, e.g. a modulation scheme, a channel coding scheme, and whether or not to execute the above-described processes per subset of scheduled frequency resource blocks or commonly for all scheduled frequency resource blocks.

The processing circuitry 50 may comprise the circuitries 52, 54 as sub- circuitries, or they may be considered as computer program modules executed by the same physical processing circuitry. The memory 60 may store one or more computer program products 64 comprising program instructions that specify the operation of the circuitries 52, 54. The apparatus may further comprise a communication interface 62 providing the apparatus with radio communication capability with base stations of one or more cellular communication networks. The communication interface 62 may comprise a radio communication circuitry enabling wireless communications and comprise a radio frequency signal processing circuitry and a baseband signal processing circuitry. The baseband signal processing circuitry may be configured to carry out the functions of the transmitter and/or the receiver, as described above in connection with Figures 6, 8, 10, 12, 14. As used in this application, the term 'circuitry' refers to all of the following: (a) hardware-only circuit implementations such as implementations in only analog and/or digital circuitry; (b) combinations of circuits and software and/or firmware, such as (as applicable): (i) a combination of processor(s) or processor cores; or (ii) portions of processor(s)/software including digital signal processor(s), software, and at least one memory that work together to cause an apparatus to perform specific functions; and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

This definition of 'circuitry' applies to all uses of this term in this application. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor, e.g. one core of a multi-core processor, and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for example and if applicable to the particular element, a baseband integrated circuit, an application- specific integrated circuit (ASIC), and/or a field-programmable grid array (FPGA) circuit for the apparatus according to an embodiment of the invention.

The processes or methods described above in connection with Figures 2 to 14 may also be carried out in the form of one or more computer process defined by one or more computer programs. The computer program shall be considered to encompass also a module of a computer programs, e.g. the above-described processes may be carried out as a program module of a larger algorithm or a computer process. The computer program(s) may be in source code form, object code form, or in some intermediate form, and it may be stored in a carrier, which may be any entity or device capable of carrying the program. Such carriers include transitory and/or non-transitory computer media, e.g. a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package. Depending on the processing power needed, the computer program may be executed in a single electronic digital processing unit or it may be distributed amongst a number of processing units.

The present invention is applicable to cellular or mobile communication systems defined above but also to other suitable communication systems. The protocols used, the specifications of cellular communication systems, their network elements, and terminal devices develop rapidly. Such development may require extra changes to the described embodiments. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodi- ment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1 . A method comprising: establishing, in a network node, a communication link with a terminal device of a cellu- lar communication system; selecting, in the network node for the terminal device, a frequency-selective link adaptation scheme in which different link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal device; causing, in the network node, transmission of a control message to the terminal device, the control message comprising at least one information element indicating the selected frequency-selective link adaptation scheme.

2. The method of claim 1 , further comprising in the network node after selecting the frequency-selective link adaptation scheme: determining a plurality of frequency resource blocks to schedule to the terminal device; selecting different link adaptation parameters for at least two subsets formed from the plurality of frequency resource blocks; and causing transmission of a scheduling message comprising at least one information element indicating the determined plurality of frequency resource blocks and at least one information element indicating the selected link adaptation parameters for each subset.

3. The method of claim 2, further comprising in the network node in con- nection with transferring data according to the frequency-selective link adaptation scheme: determining, on the basis of channel measurements, a different modulation scheme for the at least two subsets.

4. The method of claim 2 or 3, further comprising in the network node in connection with transferring data according to the frequency-selective link adaptation scheme: performing a channel coding procedure jointly for the at least two subsets.

5. The method of any preceding claim 2 or 3, further comprising in the network node in connection with transferring data according to the frequency-selective link adaptation scheme: performing a channel coding procedure for each subset separately.

6. The method of any preceding claim 2 to 5, further comprising in the network node in connection with transferring data according to the frequency-selective link adaptation scheme: computing a cyclic redundancy check sequence jointly for the plurality of subsets, wherein a single cyclic redundancy check sequence is associated with the at least two subsets.

7. The method of any preceding claim 2 to 5, further comprising in the network node in connection with transferring data according to the frequency-selective link adaptation scheme: computing cyclic redundancy check sequences separately for the at least two subsets, wherein each of a plurality of cyclic redundancy check sequences represents a different subset.

8. The method of any preceding claim 2 to 7, further comprising in the network node in connection with transferring data according to the frequency-selective link adaptation scheme: selecting a different number of spatial transmission streams for the at least two subsets.

9. The method of any preceding claim, further comprising in the base station: determining to switch the terminal device to a wideband link adaptation scheme in which the same link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal device; and causing transmission of a control message to the terminal device, the control channel comprising at least one information element indicating the wideband link adaptation scheme.

10. A method comprising: establishing, in a terminal device of a cellular communication system, a communication link with a network node; acquiring, in the terminal device, a control message from the network node, the control message comprising at least one information element indicating a frequency- selective link adaptation scheme allocated to the terminal device, in which frequency- selective link adaptation scheme different link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal de- vice.

1 1 . The method of claim 10, further comprising in the terminal device: acquiring from the network node a scheduling message comprising at least one infor- mation element indicating a plurality of frequency resource blocks scheduled to the terminal device and at least one information element indicating different link adaptation parameters for each of at least two subsets formed from the plurality of frequency resource blocks; determining, from the link adaptation parameters allocated to each frequency resource block and processing data comprised in each frequency resource block according to the link adaptation parameters assigned to each frequency resource block.

12. The method of claim 1 1 , further comprising in the terminal device in connection with transferring data according to the frequency-selective link adaptation scheme: determining, from the received control message, a different modulation scheme for the at least two subsets.

13. The method of claim 1 1 or 12, further comprising in the terminal device in connection with transferring data according to the frequency-selective link adaptation scheme: performing a channel coding procedure jointly for the at least two subsets.

14. The method of claim 1 1 or 12, further comprising in the terminal device in connection with transferring data according to the frequency-selective link adaptation scheme: performing a channel coding procedure for each subset separately.

15. The method of any preceding claim 1 1 to 14, further comprising in the terminal device in connection with transferring data according to the frequency- selective link adaptation scheme: computing a cyclic redundancy check sequence jointly for the plurality of subsets wherein a single cyclic redundancy check sequence is associated with the at least two subsets.

16. The method of any preceding claim 1 1 to 14, further comprising in the terminal device in connection with transferring data according to the frequency- selective link adaptation scheme: computing cyclic redundancy check sequences separately for the at least two subsets, wherein each of a plurality of cyclic redundancy check sequences represents a different subset.

17. The method of any preceding claim 1 1 to 16, further comprising in the terminal device in connection with transferring data according to the frequency- selective link adaptation scheme: selecting a different number of spatial transmission streams for the at least two subsets.

18. The method of any preceding claim 1 1 to 17, further comprising in the terminal device: acquiring, in the terminal device, a second control message from the base station, the second control message comprising at least one information element indicating a wideband link adaptation scheme allocated to the terminal device, in which wideband link adaptation scheme the same link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal device.

19. An apparatus comprising:

at least one processor; and

at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to: establish a communication link with a terminal device of a cellular communication sys- tern; select for the terminal device a frequency-selective link adaptation scheme in which different link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal device; cause transmission of a control message to the terminal device, the control message comprising at least one information element indicating the selected frequency- selective link adaptation scheme.

20. The apparatus of claim 19, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform the following after selecting the frequency-selective link adaptation scheme: determine a plurality of frequency resource blocks to schedule to the terminal device; select different link adaptation parameters for at least two subsets formed from the plurality of frequency resource blocks; and cause transmission of a scheduling message comprising at least one information ele- ment indicating the determined plurality of frequency resource blocks and at least one information element indicating the selected link adaptation parameters for each subset.

21 . The apparatus of claim 20, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to determine, on the basis of channel measurements and in connection with transferring data according to the frequency-selective link adaptation scheme, a different modulation scheme for the at least two subsets.

22. The apparatus of claim 20 or 21 , wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform, in connection with transferring data according to the frequency-selective link adaptation scheme, a channel coding procedure jointly for the at least two subsets.

23. The apparatus of any preceding claim 20 or 21 , wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to performing a channel coding procedure for each subset separately in connection with transferring data according to the frequency- selective link adaptation scheme.

24. The apparatus of any preceding claim 20 to 23, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform the following in connection with transferring data according to the frequency-selective link adaptation scheme: compute a cy- die redundancy check sequence jointly for the plurality of subsets, wherein a single cyclic redundancy check sequence is associated with the at least two subsets.

25. The apparatus of any preceding claim 20 to 23, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform the following in connection with transferring data according to the frequency-selective link adaptation scheme: compute cyclic redundancy check sequences separately for the at least two subsets, wherein each of a plurality of cyclic redundancy check sequences represents a different subset.

26. The apparatus of any preceding claim 20 to 25, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to select a different number of spatial transmission streams for the at least two subsets in connection with transferring data according to the frequency-selective link adaptation scheme.

27. The apparatus of any preceding claim 19 to 26, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to: determine to switch the terminal device to a wideband link adaptation scheme in which the same link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal device; and cause transmission of a control message to the terminal device, the control channel comprising at least one information element indicating the wideband link adaptation scheme.

28. An apparatus comprising:

at least one processor; and

at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to: establish a communication link with a network node; acquire from the network node a control message of a cellular communication system, the control message comprising at least one information element indicating a frequency-selective link adaptation scheme allocated to the apparatus, in which frequency-selective link adaptation scheme different link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the apparatus.

29. The apparatus of claim 28, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to: acquire from the network node a scheduling message comprising at least one information element indicating a plurality of frequency resource blocks scheduled to the apparatus and at least one information element indicating different link adaptation parameters for each of at least two subsets formed from the plurality of frequency resource blocks; determine, from the link adaptation parameters allocated to each frequency resource block and processing data comprised in each frequency resource block according to the link adaptation parameters assigned to each frequency resource block.

30. The apparatus of claim 29, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to determine, from the received control message in connection with transferring data according to the frequency-selective link adaptation scheme, a different modulation scheme for the at least two subsets.

31. The apparatus of claim 29 or 30, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform a channel coding procedure jointly for the at least two subsets in connection with transferring data according to the frequency-selective link ad- aptation scheme.

32. The apparatus of claim 29 or 30, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform a channel coding procedure for each subset separately in connection with transferring data according to the frequency-selective link adaptation scheme.

33. The apparatus of any preceding claim 29 to 32, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform the following in connection with transferring data according to the frequency-selective link adaptation scheme: compute a cyclic redundancy check sequence jointly for the plurality of subsets wherein a single cyclic redundancy check sequence is associated with the at least two subsets.

34. The apparatus of any preceding claim 29 to 32, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform the following in connection with transferring data according to the frequency-selective link adaptation scheme: compute cyclic redundancy check sequences separately for the at least two subsets, wherein each of a plurality of cyclic redundancy check sequences represents a different subset.

35. The apparatus of any preceding claim 29 to 34, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to select a different number of spatial transmission streams for the at least two subsets in connection with transferring data according to the frequency-selective link adaptation scheme.

36. The apparatus of any preceding claim 29 to 35, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to acquire a second control message from the base station, the second control message comprising at least one information element indi- eating a wideband link adaptation scheme allocated to the apparatus, in which wideband link adaptation scheme the same link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the apparatus.

37. The apparatus of any preceding claim 19 to 36, further comprising a communication interface configured to provide the apparatus with radio communication capability.

38. An apparatus comprising means for carrying out all the steps of the method according to any preceding claim 1 to 18.

39. A computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when loaded into an apparatus, execute the method according to any preceding claim 1 to 18.

40. A computer program product embodied on a non-transitory distribution medium readable by a computer and comprising program instructions which, when loaded into the computer, execute a computer process comprising: causing a network node to establish a communication link with a terminal device of a cellular communication system; select for the terminal device a frequency-selective link adaptation scheme in which different link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal device; cause transmission of a control message to the terminal device, the control message comprising at least one information element indicating the selected frequency- selective link adaptation scheme.

41. A computer program product embodied on a non-transitory distribution medium readable by a computer and comprising program instructions which, when loaded into the computer, execute a computer process comprising: causing a terminal device of a cellular communication system to establish a commu cation link with a network node; acquire, in the terminal device, a control message from the network node, the control message comprising at least one information element indicating a frequency-selective link adaptation scheme allocated to the terminal device, in which frequency-selective link adaptation scheme different link adaptation parameters are selected for a plurality of frequency resource blocks scheduled simultaneously to the terminal device.