Patent Description:
In a modern radio access network, radio coverage to served (mobile) terminal devices is provided in the form of a network of radio access nodes that are in some literature called base stations, Nodes B, etc. With the latest evolution versions of the cellular networks, a concept where a single access node has multiple spatially distant remote radio heads (RRH). A single access node or a RRH may serve a particular terminal device and is, thus, configured to process signals received from the terminal device. A channel estimate representing a state of a radio channel between the RRH and a terminal device may be used for various purposes, e.g. for equalization. There may be a need to transfer the channel estimate from the RRH for various signal processing tasks or applications.

Publication <CIT> discloses a distributed radio frequency communication system which includes a remote radio unit (RRU and a baseband unit (BBU) and facilitates communication between a wireless terminal and a core network. The RRU receives a radio frequency signal from a wireless terminal and convert the radio frequency signal to digital baseband samples using receiver circuitry and an analog-to-digital converter. The RRU then adaptively compresses the digital baseband samples, using adaptive compression circuitry, to create fronthaul uplink information, and sends the fronthaul uplink information over a fronthaul link to the BBU using an adaptive fronthaul protocol. The RRU also receives fronthaul downlink information over a fronthaul link from the BBU using an adaptive fronthaul protocol and generates frequency-domain samples, based on the fronthaul downlink information received. It then creates time-domain baseband samples from the frequency-domain samples and converts the time-domain baseband samples into a radio frequency signal to send to the wireless terminal.

The scope of protection sought for various embodiments is set out by the independent claims. Dependent claims define further embodiments included in the scope of protection. The exemplary embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

Embodiments are described below, by way of example only, with reference to the accompanying drawings, in which.

The following embodiments are examples.

In the following, different exemplifying embodiments will be described using, as an example of an access architecture to which the embodiments may be applied, a radio access architecture based on long term evolution advanced (LTE Advanced, LTE-A) or new radio (NR, <NUM>), without restricting the embodiments to such an architecture, however. A person skilled in the art will realize that the embodiments may also be applied to other kinds of communications networks having suitable means by adjusting parameters and procedures appropriately. Some examples of other options for suitable systems are the universal mobile telecommunications system (UMTS) radio access network (UTRAN or E-UTRAN), long term evolution (LTE, the same as E-UTRA), wireless local area network (WLAN or WiFi), worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (UWB) technology, sensor networks, mobile ad-hoc networks (MANETs) and Internet Protocol multimedia subsystems (IMS) or any combination thereof.

<FIG> shows terminal devices or user devices <NUM> and <NUM> configured to be in a wireless connection on one or more communication channels in a cell with an access node (such as (e/g)NodeB) <NUM> providing the cell. (e/g)NodeB refers to an eNodeB or a gNodeB, as defined in 3GPP specifications. The physical link from a user device to a (e/g)NodeB is called uplink or reverse link and the physical link from the (e/g)NodeB to the user device is called downlink or forward link. It should be appreciated that (e/g)NodeBs or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage.

A communications system typically comprises more than one (e/g)NodeB in which case the (e/g)NodeBs may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used not only for signalling purposes but also for routing data from one (e/g)NodeB to another. The (e/g)NodeB is a computing device configured to control the radio resources of communication system it is coupled to. The NodeB may also be referred to as a base station, an access point, an access node, or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (e/g)NodeB includes or is coupled to transceivers. From the transceivers of the (e/g)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to user devices. The antenna unit may comprise a plurality of antennas or antenna elements. The (e/g)NodeB is further connected to core network <NUM> (CN or next generation core NGC). Depending on the system, the counterpart on the CN side can be a serving gateway (S-GW, routing and forwarding user data packets), packet data network gateway (P-GW), for providing connectivity of user devices (UEs) to external packet data networks, or mobile management entity (MME), etc..

The user device may also utilise cloud.

<NUM> enables using multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. <NUM> mobile communications supports a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications (such as (massive) machine-type communications (mMTC), including vehicular safety, different sensors and real-time control. <NUM> is expected to have multiple radio interfaces, namely below <NUM>, cmWave and mmWave, and also being capable of being integrated with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and <NUM> radio interface access comes from small cells by aggregation to the LTE. In other words, <NUM> is planned to support both inter-RAT operability (such as LTE-<NUM>) and inter-RI operability (inter-radio interface operability, such as below <NUM> - cmWave, below <NUM> - cmWave - mmWave). One of the concepts considered to be used in <NUM> networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

The current architecture in LTE networks is fully distributed in the radio and typically fully centralized in the core network. The low-latency applications and services in <NUM> require to bring the content close to the radio which leads to local break out and multi-access edge computing (MEC).

The communication system is also able to communicate with other networks <NUM>, such as a public switched telephone network or the Internet, or utilize services provided by them.

Using edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head (RRH) or base station comprising radio parts. Terminology in the literature may vary but, in some literature, the RRH corresponds to the DU <NUM>. A single CU <NUM> may have multiple RRHs that are spatially remote with respect to one another, e.g. located at different geographical locations or antenna sites. <FIG> illustrates such a scenario where the CU <NUM> has three RRHs <NUM>, 105A, 105B. An interface between the CU and the RRH (or DU) is F1 interface in the <NUM> specifications. Such an arrangement enables the CU to employ, for example, spatially distributed multiple-input-multiple-output (MIMO) communications where the CU communicates with different terminal devices simultaneously over the same time-frequency resources via different RRHs. Each RRH may establish a spatial channel to one or more terminal devices served by the RRH, wherein the spatial channel may be substantially orthogonal (or at least distinguishable) with respect to one or more spatial channels formed by one or more other RRHs in the same time-frequency resources. Such a scenario may improve spectral efficiency.

It should also be understood that the distribution of functions between core network operations and base station operations may differ from that of the LTE or even be non-existent. <NUM> (or new radio, NR) networks are being designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or node B (gNB).

Possible use cases are providing service continuity for machine-to-machine (M2M) or Internet of Things (IoT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway, maritime, and/or aeronautical communications. Satellite communication may utilize geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano)satellites are deployed). The on-ground cells may be created through an on-ground relay node or by a gNB located on-ground or in a satellite.

Typically, in multilayer networks, one access node provides one kind of a cell or cells, and thus a plurality of (e/g) NodeBs are required to provide such a network structure.

<FIG> illustrates a scenario where the access node <NUM> employs multiple RRHs 105A, 105B, 105C connected to the same DU <NUM> and CU <NUM>. An interface between the RRH and the DU is called a fronthaul link in the <NUM> specifications, while an interface between the DU and the CU is an F1 interface. Signal processing tasks may be distributed between the RRH, DU and CU. The RRH may perform some low-level (physical layer) signal processing tasks such as channel estimation and equalization, the DU may perform some higher-level (physical layer and optionally link layer) signal processing tasks such as demodulation and decoding, and the CU may perform some even higher level signal processing tasks. A common term for the DU and CU is a network node in the following description. The DU and even CU may perform some signal processing tasks that require information on the radio channel between the RRH and the terminal device. The RRH estimates the channel on the basis of a reference signal received from the terminal device, and the RRH may deliver the channel estimate to the DU and even CU. However, the fronthaul and the F1 interfaces transfer great amounts of traffic, and efficient transfer of any signalling information would be beneficial.

<FIG> and illustrate embodiments of processes for transferring the channel estimate. <FIG> illustrates a process for the RRH while <FIG> illustrates a process for the network node, e.g. the DU or CU. Referring to <FIG>, the process in the radio head of the network node comprises: receiving (block <NUM>) a reference signal from a terminal device (UE) and computing a channel estimate on the basis of the reference signal; transferring (block <NUM>) the channel estimate with a first precision level to the network node over a link between the radio head and the network node, wherein the first precision level defines a first number of bits carrying the channel estimate; determining (block <NUM>) to change the precision level and, in response to said determining, transferring (block <NUM>) the channel estimate or a further channel estimate with a second precision level to the network node, wherein the second precision level defines a second number of bits carrying the channel estimate or the further channel estimate, the second number being different from the first number. If the first precision level is determined to be sufficient in block <NUM>, the process may return to block <NUM> for reception of the next reference signal and computation of a new channel estimate.

Referring to <FIG>, the process in the network node comprises: receiving (block <NUM>), from the radio head over the link between the radio head and the network node, a channel estimate with a first precision level, wherein the first precision level defines a first number of bits carrying the channel estimate; determining (block <NUM>) to change the precision level and, in response to said determining, transmitting (block <NUM>) to the radio head a message requesting transfer of the channel estimate or a further channel estimate with a second precision level, wherein the second precision level defines a second number of bits carrying the channel estimate or the further channel estimate, the second number being different from the first number; receiving (block <NUM>), from the radio head, the channel estimate or the further channel estimate with the second precision level; and using (block <NUM>) the channel estimate or the further channel estimate in signal processing.

In the embodiments of <FIG>, the channel estimates are transferred with an adaptive precision level where each precision level is bound to a determined number of bits used for defining a channel estimate. Accordingly, the number of bits needed for transferring the channel estimate varies in response to the selected precision level. When the channel estimate is transferred with the precision level needed for the signal processing in the network node, the amount of bits transferred over the link can be adapted to the need. This reduces the signalling overhead while ensuring that the precision level is sufficient for the signal processing of block <NUM>. As described in <FIG>, the network node may initiate the change of the precision level. , although some non-claimed embodiments described below configure the radio head to autonomously detect the need for changing the precision level. The embodiment of <FIG> covers both options for changing the precision level, i.e. block <NUM> may be responsive to the request received from the network node (block <NUM>) or it may be responsive to an internal event in the radio head.

In an embodiment, the first precision level and the second precision level define a number of bits per channel coefficient. In other words, the precision of channel coefficients may be scaled according to the embodiments described herein. For example, the first precision level may indicate a first fixed point number per channel coefficient while the second precision level may indicate a second, different, fixed point number per channel coefficient. When using floating point numbers, the first precision level may define a first total number of bits for the channel estimate while the second precision level may define a second, different total number of bits for the channel estimate. The available number of bits may then be distributed unevenly to define the channel coefficients. Some channel coefficients may be defined with a lower number of bits than other channel coefficients.

In an embodiment, the first precision level and the second precision level define a method for exploiting correlation between channel coefficients to compress the number of bits carrying the channel estimate or the further channel estimate. The radio head may then compress the channel estimate by using the correlation and the compression method, and the network node respectively decompresses the channel estimate or the further channel estimate by using an inverse of the compression method. For example, if the channel coefficients are highly correlated, at least some of the channel coefficients may be skipped and not transmitted. The network node may then compute the missing channel coefficients by using interpolation and the transferred channel coefficients, for example. The number of skipped channel coefficients may vary for different precision levels.

The first number of bits and the second number of bits refer to the number of payload bits used to describe the channel estimate(s). Accordingly, methods used to artificially increase redundancy to the payload bits, e.g. for the purpose of channel encoding or parity check, is not counted into the first and second number of bits. In other words, the first number of bits and second number of bits determine the precision level for the purpose of the signal processing application using the (raw) channel estimate bits in the network node.

Let us then describe some embodiments of <FIG> with reference to the signalling diagrams of <FIG>. <FIG> illustrates an embodiment where the radio head receives, from the network node, a channel estimate request indicating the second precision level and, in response to the request, to determine to change the precision level. Referring to <FIG>, the radio head may carry out block <NUM> in the above-described manner and compute the channel estimate. As described above, the channel estimate may comprise the channel coefficients representing the state of the radio channel between the terminal device and the radio head. As known in the art, the channel coefficients may be frequency-domain samples describing a frequency response of the channel, for example. The radio head may transfer the channel estimates to the network node as they are estimated, with a determined precision level.

In block <NUM>, the network node detects a need for a channel estimate, e.g. in a signal processing application such as demodulation or link adaptation (selection of a modulation and coding scheme). The network node may determine the precision level of the currently available channel estimate (e.g. the first precision level). In block <NUM>, the network node may evaluate whether the current precision level is sufficient for the signal processing application. This may be performed before or after performing the signal processing application, e.g. by the network node. The network node may have stored information on the previously used precision levels and whether or not they have been accurate enough for successful execution of the signal processing application. Accordingly, the network node is capable of evaluating in block <NUM> whether or not the current precision level has been observed as statistically sufficient for the signal processing application. Another option is to perform the signal processing application with the current precision level, evaluate the performance and, then, determine whether to perform the signal processing application again with the improved precision level. A threshold may be set on the basis of the stored information, and block <NUM> may comprise comparison between the threshold and the precision level. If the precision level is deemed not high enough in block <NUM>, the process proceeds to step <NUM> where the network node transmits to the radio head a request to change the precision level and resend the channel estimate with a higher precision level. The network node may explicitly indicate the requested precision level in step <NUM>. In response to the message, the radio head may change the precision level of the channel estimate and transmit it with the higher precision level (e.g. the second precision level) in step <NUM>. Upon receiving the channel estimate with the higher precision level, the network node may proceed with the signal processing application in block <NUM>. If the current precision level was determined to be acceptable in block <NUM>, block <NUM> may be executed without step <NUM>. Accordingly, no additional traffic to the link is caused if the current precision level is deemed suitable for the signal processing application.

In block <NUM>, the signal processing application is executed by using the channel estimate. Additionally, block <NUM> may comprise evaluating a quality of the signal processing and outputting a quality metric representing the quality. For example, in case the signal processing application is demodulating and decoding data, the quality metric may indicate whether or not the demodulation and decoding was successful. In other applications, another similar metric may be derived. In block <NUM>, the quality metric is compared with a threshold to determine whether or not the quality provided by the channel estimate was sufficient. If the quality is determined to be sufficient, the process may proceed to block <NUM> where the current precision level is maintained. Accordingly, upon receiving no contrary request, the radio head may also use the current precision level. In other words, if step <NUM> was not carried out, the original precision level is maintained. If step <NUM> was performed, the precision level agreed in step <NUM> is maintained. On the other hand, if the current precision level is not suitable, e.g. it is determined to be too low or even too high, the process may proceed to block <NUM> where the precision level is changed. Block <NUM> may comprise comparison with one threshold or two thresholds: one for determining whether quality was too low and the other for determining whether the quality was too high. Accordingly, the quality evaluation may aim to find a precision level that is just enough for meeting the quality demand. If block <NUM> is executed, the network node may transmit to the radio head a request (block <NUM>) to change the precision level and send a subsequent channel estimate with a new precision level. The network node may explicitly indicate the requested precision level in step <NUM>. In response to the message, the radio head may change the precision level of the channel estimate and transmit subsequent channel estimate(s) with the new precision level. Upon receiving the channel estimate with the new precision level, the network node may store the channel estimate in a memory for the next iteration of the process of <FIG>. Reflecting to the embodiment of <FIG>, blocks <NUM> and <NUM> may be comprised in step <NUM> and/or in step <NUM>.

The procedure of <FIG> may be used to adapt the precision level to the required precision by using the quality metric. In practice, the procedure of Figure <NUM> may use the one or multiple thresholds to determine, on the basis of the quality metric, whether to increase, retain, or decrease the precision level. When using one threshold, the procedure may gradually reduce the precision level until the precision is found not high enough, which causes the increase of the precision level. Even when using multiple thresholds, the change in block <NUM> may be incremental, e.g. one bit per channel coefficient may be added/reduced in each iteration or otherwise a determined number of bits may be added/reduced in each iteration.

In an embodiment, the network node requests the radio head to stop transfer of further channel estimates, if the quality of said signal processing is above the quality threshold and if the precision level is below a determined precision threshold. In other words, if acceptable quality is determined to be possible to reach even without the channel estimates, the network node may instruct the radio head to stop transmitting the channel estimates, thus reducing the signalling overhead in the link. Upon detecting that the quality degrades below the threshold, the network node may again request transmission of the channel estimates with the agreed precision level.

In an embodiment, the network node monitors a capacity of the link, e.g. the fronthaul link, and uses the estimated capacity as a further criterion for determining whether or not to change the precision level. In particular, the link capacity may be taken into account upon determining to increase the precision level of the channel estimate. <FIG> illustrates a signalling diagram that is modified from the procedure of <FIG>. The same reference numbers represent the same functions as in <FIG>. The network node may monitor the capacity of the link in block <NUM>. Block <NUM> may comprise evaluating the traffic load or available link capacity to determine whether or not the link can carry further traffic in the form of the channel coefficients with the increased precision level. Upon determining to increase the precision level in block <NUM> or <NUM>, the link capacity may be compared with a threshold in block <NUM>. The threshold may define a level for determining whether or not the link can carry additional signalling load caused by the increased precision level. Upon determining that the link capacity is too low to accommodate the increase in the precision level, the increase may be overruled. Upon determining that there is capacity available, the increase may be permitted and step <NUM> or <NUM> may be carried out.

A determined balancing may be used between the needs from the perspective of the quality metric and the link capacity. Different signal processing application may have different weights for the two parameters, and the weights may be incorporated into the thresholds used in blocks <NUM>, <NUM>, and <NUM>. Some application may set a higher weight to the quality while other applications may set a higher weight to the link capacity. For example, if a higher weight is given to the link capacity in a situation where the quality metric indicates a need for precision level increase while the link is congested, the precision level may actually be decreased in step <NUM>.

As described above, in a non-claimed embodiment the radio head autonomously initiates the change of the precision level. The radio head may monitor a channel quality level of the radio channel and determine to change the precision level in response to detecting a change in the monitored channel quality level. <FIG> illustrates a signalling diagram of such an embodiment. The same reference numbers as in <FIG> represent the same or substantially similar operations.

Referring to <FIG>, block <NUM> may be carried out in the above-described manner and the radio head may report the channel estimates to the network node with the determined (first) precision level. In block <NUM>, the radio head monitors the channel quality level representing a state of the radio channel. An example of a metric that is monitored in block <NUM> is a noise level of the radio channel. Upon detecting a change in the channel quality level (block <NUM>), e.g. an increase or decrease in the noise level, the radio head may initiate the change of the precision level. Accordingly, the radio head may transmit in step <NUM> a request to change the precision level and also indicate the new precision level that is proposed. In block <NUM>, the network node may determine whether or not to accept the new precision level. The decision in block <NUM> may be based on any one of the embodiments described above in connection with <FIG>. For example, the quality metric and/or the link capacity may be taken into account. Upon determining in block <NUM> that the request is acceptable, the network node may respond and acknowledge the change of the precision level (step <NUM>). Accordingly, the radio head may change the precision level and transmit the further channel estimate(s) with the agreed precision level. Upon receiving the subsequent channel estimate with the agreed new precision level, the precision level is changed in the network node as well (block <NUM>). On the other hand, upon determining not to change the precision level because of a readily sufficient quality in the signal processing or congestion in the link, for example, the network node may reject the request in step <NUM>. Accordingly, the radio head may maintain the current precision level. The radio head may also refrain from sending a new request (step <NUM>) for a determined time interval. Upon the network node detecting the need for increasing the precision level meanwhile, the procedure of <FIG> or <FIG> may be used.

In a situation where the radio head is currently not transmitting the channel estimate to the network node, the procedure of <FIG> may be modified such that the radio head requests transmission of the channel estimate upon detecting decreased channel quality in block <NUM>. Accordingly, step <NUM> may be modified to be a request to start transmitting the channel estimate with a proposed precision level. If the request is approved in step <NUM>, the radio head may start transmitting the channel estimate with the agreed precision level. In this case, the approval may include a resource allocation grant to transmit the channel estimate over the (fronthaul) link. In a similar manner, the procedure may be used by the radio head to propose to stop transmitting the channel estimate, upon detecting that the channel quality is above a determined threshold. Upon approval in step <NUM>, the radio head may stop transmitting the channel estimate.

As described above, some embodiments may be employed for transmitting the channel estimate again with a changed precision level. For that purpose, the radio head may store the channel estimate for a determined time interval called a channel estimate lifetime. The lifetime may be known to the network node. Upon expiry of the lifetime, the radio head may discard the channel estimate. The lifetime and/or other parameters for the adaptive management of the precision level may be agreed between the radio head and the network node. Such other parameters may include the compression method and the format in which the channel estimate is transferred at each precision level. These parameters enable the extraction and reconstruction of the channel estimate at the network node. The parameters may include, for example, an interpolation method defining, for each precision level, what information is needed by the network node to interpolate channel coefficients that are not transmitted in the channel estimate. For example, different precision levels may be associated with different frequency indices of channel coefficients that shall be transmitted to the network node. The parameters may include a binary format defining a format for the channel estimate and, optionally, a scaling parameter for the channel estimate. The format may indicate, for each precision level, whether the fixed point or floating-point representation is used and at which precision. The scaling factor may define, for each precision level, a value used by the network node to scale the received channel coefficient values.

Above, several examples of the signal processing applications are readily disclosed. A further example is a detection algorithm for determining whether or not the radio head is capable of receiving a signal from a particular terminal device served by another radio head of the network node. The detection procedure may be used to determine whether or not the terminal device interferes with the radio head. A reference signal of the terminal device may be known to the network node because it is served by the network node. The network node may acquire a first equalized signal representing a signal received by the radio head serving the terminal device, the first equalized signal comprising a signal received by the serving radio head from the terminal device. The network node may further acquire a second equalized signal representing a signal received by a radio head not serving the terminal device, wherein the second radio head is spatially distant from the first radio head. The network node may then cross-correlate the first equalized signal with the second equalized signal and determine, on the basis of said cross-correlating, whether or not the second equalized signal also comprises a signal received from the terminal device. This procedure may be used, for example, to determine whether or not to perform interference cancellation at the non-serving radio head in order to reduce the interference from the terminal device. A cross-correlation signal is conventionally compared with a detection threshold used as a basis for detecting whether or not the non-serving radio head receives a signal from the terminal device. This procedure may be improved by performing reverse equalization for the second equalized signal. The reverse equalization may be performed on the basis of the channel estimate received according to any one of the above-described embodiments from the non-serving radio head. The cross-correlation may then be performed between the reverse-equalized second signal and the first equalized signal. A corresponding reverse equalization may be performed for the first equalized signal as well, before the cross-correlation and obviously by using the channel estimate received from the serving radio head. The reverse equalization removes the effect of the (potentially sub-optimal) equalization by the non-serving radio head, thus improving the accuracy of the detection. However, the precision level of the channel estimate available to the network node may affect the performance of the reverse equalization. Accordingly, the quality of the detection may be evaluated according to the embodiment of <FIG> or <FIG>, for example. One quality metric may be a result of the detection: if several consecutive detections indicate either confirmed detection or non-detection of the terminal device, this constant behaviour may be deemed to indicate sufficient quality (no false alarms). On the other hand, if the detection result is sporadic, providing alternating detection and non-detection, the network node may determine that false alarms are included in the detections and that an increase in the precision level of the channel estimate is required. Another metric for determining the quality of the detection is by evaluating a result of a cross-correlation signal used as the basis for the detection. When the quality is high, even too high, a peak of the cross-correlation signal indicating the detection, is much higher than the detection threshold. In such a case, lower precision level might provide acceptable results. The difference between the detection threshold and the peak that would trigger the reduction of the precision level may be set according to the desired implementation.

<FIG> is a yet another embodiment of a procedure for using the channel estimate with an adaptive precision level, e.g. in the terminal device detection procedure described above. Referring to <FIG>, the terminal device may transmit a reference signal in step <NUM>. Upon receiving the reference signal, the radio head may perform the channel estimation (step <NUM>) and store the channel estimate for the channel estimate lifetime. The channel estimate may be a raw channel estimate comprising channel coefficients computed directly from the reference signal. For example, the reference signal may include reference symbols on selected time-frequency resources, and the raw channel estimate may have the channel coefficients only for those time-frequency resources. In order to determine the channel coefficients for the other time-frequency resources interpolation or another method may be used to span the channel estimate to those time-frequency resources not comprising the reference signal. The radio head may equalize a signal (e.g. data) received together with the reference signal in a transmission resource, e.g. a transmission time interval (TTI). Equalized symbols may be transferred to the network node in step <NUM> for demodulation and decoding in block <NUM>. Upon decoding and performing error checking via cyclic redundancy check, for example, the result of the error checking may be delivered to the radio head in step <NUM>, and the radio head may transmit an acknowledgment (ACK/NAK) to the terminal device in step <NUM>. The acknowledgment indicates whether or not the decoding was successful, thus indicating to the terminal device whether or not a retransmission is needed.

Additionally, the network node may carry out block <NUM> according to any one of the above-described embodiments to determine a precision level for the channel estimate. The decision may be based on the error checking and/or the quality of the cross-correlation as the quality metric and/or the link capacity, as described above. In step <NUM>, the network node requests the raw channel estimate with the determined precision level and receives channel coefficients of the raw channel estimate in step <NUM> with the requested precision level. Then, the network node decodes the channel estimate in block <NUM>, e.g. via interpolation or decompression in the above-described manner. The decoding may include computing channel coefficients for frequency resources (e.g. sub-carriers) for which the raw channel estimate has no channel coefficient. Thereafter, the channel estimate may be used in the signal processing application, e.g. to perform the reverse equalization for the equalized symbols received in step <NUM> in order to reinstate the channel effect into the symbols. Thereafter, the reverse-equalized symbols may be subjected to the cross-correlation.

It should be appreciated that while the embodiments described above are mainly described in the context that the radio head stores the channel estimates and transfers them to the network node, the channel estimates may equally be stored in the DU and delivered to the CU for the purpose of the signal processing application, and the DU may perform the above-described functions of the radio head.

<FIG> illustrates an embodiment of a structure of the above-mentioned functionalities of an apparatus executing the functions of the network node in the embodiments described above, e.g. the process of <FIG> or any one of embodiments thereof. As described above, the apparatus for the network node may be configured to use channel estimates in a signal processing task and to receive the channel estimates with an adaptive precision level. In an embodiment, the apparatus may be a circuitry or an electronic device realizing some embodiments of the invention in the network node. The apparatus carrying out the above-described functionalities may thus be comprised in such a device, e.g. the apparatus may comprise a circuitry such as a chip, a chipset, a processor, a micro controller, or a combination of such circuitries for the network node.

Referring to <FIG>, the apparatus may comprise a communication controller <NUM> providing the apparatus with capability of performing the above-described functions of the network node. In some embodiments, the apparatus may comprise a communication interface or communication circuitry <NUM> to communicate with RRHs connected to the network node such as the DU. The interface <NUM> may operate according to the specifications of the fronthaul interface or F1 interface of <NUM> networks, depending on the implementation of the network node. However, in some embodiments the above-described procedures may be performed by another network node of the radio access network or even the core network and, in such embodiments, the interface <NUM> may support another communication protocol. In any case, the network node may acquire the channel estimates via the interface <NUM>.

In some embodiments, the apparatus comprises a second communication interface <NUM> configured to provide the apparatus with capability of communicating towards the core network <NUM> or to the CU, depending on the implementation. In some embodiments, the communication interface <NUM> may also be used to communicate with the other network nodes via wired connections. In the context of <NUM> networks, the communication interface <NUM> may be configured for communication over an Xn interface, and/or an NG interface.

The communication controller <NUM> may comprise at least one processor or a processing circuitry. The apparatus may further comprise a memory <NUM> storing one or more computer program products <NUM> configuring the operation of said processor(s) of the apparatus. The memory <NUM> may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The memory <NUM> may further store a configuration database <NUM> storing operational configurations of the apparatus, e.g. the threshold value(s) for various comparisons described above and the precision levels and associated parameters defining the format of the channel estimate for each precision level.

The communication controller may comprise an RRC controller <NUM> configured to establish, manage, and terminate radio connections between the network node and the terminal devices connected to the network node. The RRC controller <NUM> may operate under a control of RRC functions that make the decisions of RRC actions such as the handovers. The RRC controller <NUM> may also perform the interference management described above. The interference controller may receive, as an input, the information on the coverage of terminal devices, e.g. the correlation matrix. The RRC controller may also instruct a coverage monitor circuitry <NUM> to determine the coverage areas of the terminal devices according to any one of the above-described embodiments.

The communication controller may include a signal processor <NUM> configured to carry out the above-described signal processing application <NUM> or task that requires the channel estimate, at least occasionally. For the purpose of the signal processing application, the signal processor <NUM> may comprise a precision level estimator <NUM> configured to determine the precision level required for the appropriate operation of the signal processing application. The precision level estimator <NUM> may be configured to perform the decisions in blocks <NUM>, <NUM>, and/or <NUM>, as described above. The signal processor may further comprise a quality estimator monitoring the performance of the signal processing application <NUM>, e. g by computing the quality metric in block <NUM>.

<FIG> illustrates an embodiment of a structure of the above-mentioned functionalities of an apparatus executing the functions of the radio head in the embodiments described above, e.g. the process of <FIG> or any one of embodiments thereof. As described above, the apparatus for the radio head may be configured to compute the channel estimates from reference signals received from terminal devices and to transfer the channel estimates to the network node with an adaptive precision level. In an embodiment, the apparatus may be a circuitry or an electronic device realizing some embodiments of the invention in the radio head. The apparatus carrying out the above-described functionalities may thus be comprised in such a device, e.g. the apparatus may comprise a circuitry such as a chip, a chipset, a processor, a micro controller, or a combination of such circuitries for the radio head.

Referring to <FIG>, the apparatus may comprise a communication controller <NUM> providing the apparatus with capability of performing the above-described functions of the radio head. In some embodiments, the apparatus may comprise a communication interface or communication circuitry <NUM> to communicate with network node such as the DU. The interface <NUM> may operate according to the specifications of the fronthaul interface of <NUM> networks. The apparatus may further comprise a radio communication interface <NUM> configured to provide the apparatus with capability of communicating over the radio interface with the terminal devices. The radio communication interface may comprise an antenna array, analogue radio frequency components required for the radio communications, and digital baseband signal processing components required to process received signals and to compute the channel estimates.

The communication controller <NUM> may comprise at least one processor or a processing circuitry. The apparatus may further comprise a memory <NUM> storing one or more computer program products <NUM> configuring the operation of said processor(s) of the apparatus. The memory <NUM> may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The memory <NUM> may further store a configuration database <NUM> storing operational configurations of the apparatus, e.g. the precision levels and associated parameters defining the format of the channel estimate for each precision level.

The communication controller may comprise a channel estimator circuitry <NUM> configured to compute the channel estimate. A common method is to process a reference signal received from the terminal device via the radio interface by using a known reference signal of the reference signal, thus remove the reference signal from the received signal and leaving only a signal representing the radio channel, e.g. the channel coefficients. Such a raw channel estimate may then be stored in the memory <NUM>. In some embodiments, the communication controller <NUM> may further comprise a precision level estimator <NUM> configured to monitor the channel state <NUM> and to determine when to propose a change to the precision level of the channel estimate transferred to the network node, e.g. according to the embodiment of <FIG>.

As used in this application, the term 'circuitry' refers to one or more 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 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 in <FIG> or any of the embodiments thereof may also be carried out in the form of one or more computer processes defined by one or more computer programs. A separate computer program may be provided in one or more apparatuses that execute functions of the processes described in connection with the Figures. The computer program(s) may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of 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.

Claim 1:
An apparatus (<NUM>) for a network node of a radio access network, comprising:
at least one processor; and
at least one memory (<NUM>) including computer program code, wherein the at least one memory (<NUM>) and computer program code are configured, with the at least one processor, to cause the apparatus (<NUM>) to perform the following:
receiving, from a radio head over a link between the radio head and the network node, a channel estimate with a first precision level, wherein the first precision level defines a first number of bits carrying the channel estimate;
determining that the first precision level is not suitable for a signal processing application needing the channel estimate;
determining to change the precision level and, in response to said determining, transmitting to the radio head a message requesting transfer of the channel estimate or a further channel estimate with a second precision level, wherein the second precision level defines a second number of bits carrying the channel estimate or the further channel estimate, the second number being different from the first number;
receiving, from the radio head, the channel estimate or the further channel estimate with the second precision level; and
using the channel estimate or the further channel estimate in signal processing.