Patent ID: 12250164

DETAILED DESCRIPTION

FIG.1shows a wireless communication network100in which the present invention may be used. The wireless communication network comprises a second transceiver110that is in communication with, or adapted for wireless communication with a first transceiver120. The second transceiver110has at least one antenna111through which wireless signals are sent and received. The first transceiver120has a plurality of antenna elements121,122,123through which the first transceiver120can receive wireless signals transmitted by the second transceiver110. The first transceiver120may also transmit signals towards the second transceiver110via the plurality of antenna elements, or via other not shown antenna elements. The first transceiver120further has a plurality of antenna branches124,125,126. Each antenna branch is connected to at least one of the plurality of antenna elements121,122,123. The antenna elements are only connected to one antenna branch. The antenna elements of different branches124,125,126are individually steerable. However, in case there are more than one antenna element on one antenna branch, those antenna elements on the same branch may not be mutually individually steerable. The first transceiver120further comprises an aggregate unit128to which the plurality of antenna branches124,125,126leads. When the second transceiver110transmits an analog time-domain signal, such as a reference signal from its antenna111, the signal is received at each of the plurality of antenna elements121,122,123of the first transceiver120. The analog time-domain signal arriving at each antenna elements is fed from the antenna element into the respective antenna branch where it is treated, as will be shown further below. Thereafter the signal of each antenna branch is conveyed to the common aggregate unit128in which further treatment is performed, such as a transformation from time domain into frequency domain of the combined signal. When then signals are conveyed from the plurality of antenna branches124,125,126and into the aggregate unit128, they are sent over an interface129, which may be an interface between separate ICs of the first transceiver120. Further, according to an embodiment, the first transceiver120comprises two or more ICs135,136. One or more of the antenna branches are combined in one IC. In the example ofFIG.1antenna branches124,125are combined in a first IC135and antenna branch126lies on a second IC136. The first and second ICs135,136are then connected to the aggregate unit128over the interface129.

FIG.2shows an example of a wireless communication network100in which the present invention may be used. The network100comprises a radio access network node130that is in, or is adapted for, wireless communication with a wireless communication device140. The second transceiver110ofFIG.1may be the radio access network node130and the first transceiver120ofFIG.1may be the wireless communication device140. Alternatively, the second transceiver110ofFIG.1may be the wireless communication device140and the first transceiver120may be the radio access network node130.

The wireless communication network100ofFIGS.1and2may be any kind of wireless communication network that can handle Orthogonal Frequency Division Multiplexing (OFDM) modulated signals and provide radio access to wireless devices. Example of such wireless communication networks are Long Term Evolution (LTE), LTE Advanced, Wireless Local Area Networks (WLAN), 5thgeneration wireless communication networks based on technology such as New Radio (NR), and any possible future 6thGeneration wireless communication networks.

The RAN node130may be any kind of network node that provides wireless access to a wireless device140alone or in combination with another network node. Examples of radio access network nodes130are a base station (BS), a radio BS, a base transceiver station, a BS controller, a network controller, a Node B (NB), an evolved Node B (eNB), a gNodeB (gNB), a Multi-cell/multicast Coordination Entity, a relay node, an access point (AP), a radio AP, a remote radio unit (RRU), a remote radio head (RRH) and a multi-standard BS (MSR BS).

The wireless device140may be any type of device capable of wirelessly communicating with a RAN node130using radio signals. For example, the wireless device140may be a User Equipment (UE), a machine type UE or a UE capable of machine to machine (M2M) communication, a sensor, a tablet, a mobile terminal, a smart phone, a laptop embedded equipped (LEE), a laptop mounted equipment (LME), a USB dongle, a Customer Premises Equipment (CPE) etc.

FIG.3, in conjunction withFIG.1, describes a method performed by a first transceiver120of a wireless communication network100, for handling reference signals. The first transceiver120comprises M antenna branches124,125,126, M being at least two, each antenna branch comprising an antenna element121,122,123. The method comprises receiving202, from a second transceiver110of the wireless communication network, at the antenna elements121,122,123of each of the M antenna branches124,125,126and in time domain, an OFDM modulated wideband reference signal comprising an OFDM reference signal symbol mapped to every K subcarrier frequency of at least a subset of a carrier frequency bandwidth, K being called comb factor, and at each of the M antenna branches124,125,126, sampling204the received wideband reference signal using N samples per OFDM symbol. The method further comprises, for each of the M antenna branches124,125,126, accumulating210the received, sampled wideband reference signal over at least two repetition blocks, each block having a length of N/K samples, to obtain a condensed signal with the length N/K samples, based on information on start time of the at least two repetition blocks, and for each of the M antenna branches124,125,126, conveying212the condensed signal over an interface129to an aggregate unit128for use in estimating a wireless communication channel between the second transceiver110and the first transceiver120.

The first transceiver120may be a part of a RAN node130. In this case, the second transceiver110is part of a wireless device140. Alternatively, the first transceiver120is part of a wireless device140. In this case, the second transceiver110is part of a RAN node130. An “antenna branch”124,125,126is a signal branch, i.e. a current-conducting wire or wires. The antenna element121,122,123(or elements) connected to one end of one antenna branch wirelessly receives an analog radio signal transmitted by the second transceiver. The antenna branches are electrically arranged in parallel. The analog radio signal received at the antenna element of each branch may be treated differently on the different antenna branches. An “antenna element” is the part of the antenna from which signals are sent and received. There may be only one antenna element per antenna branch, or there may be more than one antenna element in one branch, for example a sub-array of antenna elements. The antenna branches are individually controllable. That is, the antenna elements of different antenna branches are individually controllable, whereas in case there are more than one antenna element in the same antenna branch, those antenna elements of the same antenna branch are not necessarily individually controllable. This means that it is possible to control an antenna element of one antenna branch in a different way than an antenna element of another antenna branch.

A reference signal symbol is a complex scalar. A reference signal comprises a plurality of reference signal symbols which are complex scalars. The reference signal symbols are mapped to the K subcarriers so that e.g. a first reference signal symbol is mapped to subcarrier 0, a second reference signal symbol is mapped to subcarrier K−1, a third is mapped to subcarrier 2K−1 etc. Alternatively, there may be a frequency offset so that e.g. the first reference signal symbol is mapped to subcarrier 1, the second reference signal symbol is mapped to subcarrier K etc, this is called comb offset. The wideband reference signal mapped with the reference signal symbols is OFDM modulated and transformed from frequency domain to time domain before it is sent from the second transceiver. The wideband reference signal ranges in frequency over the at least subset of the carrier frequency bandwidth. The subset comprises A subcarrier frequencies. In every K of those A subcarrier frequencies, a reference signal symbol is mapped. The reference signal symbol may be the same symbol or different symbols mapped to the different subcarrier frequencies. When sending reference signal symbols OFDM modulated over each K subcarrier frequency (called K comb), the received wideband reference signal becomes repetitive with a length of N/K samples. The wideband reference signal is repetitive in that the signal sent by the second transceiver is repeated with a length of N/K samples. That is, over one OFDM symbol the signal is repeated so that the same reference signal symbol is sent K times. When the wirelessly transmitted signal is received at the antenna elements of the first transceiver, noise and interference has been added. By accumulating two or more such repetition blocks, the noise and interference can be suppressed as noise and interference are different for different repetition blocks whereas the signal looks the same for the repetition blocks.

“Accumulating the signal over at least two of the repetition blocks” may for example be to add the signal of the at least two repetition blocks to each other over the same sample, i.e. sample 1 of repetition block 1 to sample 1 of repetition block 2 etc., and take the average value at each time point. In case the reference signal symbol is not on the first subcarrier in the repetition block window, i.e. in case there is a comb offset, the phase may need to be adapted so that the two repetition blocks are comparable, i.e. sample 1 of repetition block 1 can be added to sample 1 of repetition block 2. Comb offset is well known and described in 3GPP standard NR 38.211 SRS physical signal. As the second transceiver and the first transceiver of a wireless communication network are synchronized and as the reference signal symbols are known by both the second transceiver and the first transceiver, the first transceiver may already have, or either receives, information of when the OFDM symbols are sent and received, and thereby the start time of the repetition blocks.

An “aggregate unit” is a unit of the first transceiver in which a plurality of antenna branches meet so that signals from the plurality of antenna branches can be combined into one and the same branch. “For use in estimating the wireless communication channel”, which “use” is performed in the aggregate unit, may comprise to transform the condensed signal from time domain into frequency domain, by e.g. a Fast Fourier Transform (FFT), and estimate the communication channel based on the transformed condensed signal. The estimation of the communication channel can then be used by the first transceiver for determining communication characteristics for the first transceiver transmitting towards the second transceiver, such as beamforming weights. The channel estimate may be an estimate of the communication channel between the second transceiver and the M antennas of the first transceiver based on the fast Fourier transformed condensed signal. The sampling204, accumulating210and conveying212may be performed in a part of the first transceiver120that may be called a radio unit or radio ASIC.

When mapping a reference signal symbol to each K subcarrier frequency, the wideband reference signal sent by the second transceiver becomes repetitive within an OFDM symbol with a length (N/K). As there are reference symbols spread out over a whole frequency range of at least a subset of the carrier bandwidth, the repetitive part contains the information necessary to determine the channel, as long as there is at least one reference symbol per coherence bandwidth. Further, as the parts are repetitive, they contain the same signal. The only difference between the repetitive parts at the first transceiver is that they are added with noise and interference that looks different for the different repetitive parts. Thereby, when accumulating a plurality of such repetitive parts, the noise and interference can be suppressed, and the accumulated signal would become better over the whole channel than only one repetitive part. Further, the more repetitive parts that are accumulated, the better the accumulated signal. Further, as the amount of information of the condensed signal is much lower than for the whole signal before condensation, the communication resources of the interface can be widely limited when sending only the condensed signal over the interface to the aggregate unit compared to sending the whole signal. At the same time, the repetitive signal comprises enough information for estimating the communication channel. In fact, it has turned out that no information is lost with such a condensed signal. Further, as the condensed signal is much smaller than the whole signal, the computation resources in the aggregate unit can be limited a lot compared to when the whole signal is to be handled in the aggregate unit.

According to an embodiment, the OFDM reference signal symbol is a part of a sounding reference signal (SRS), and the comb factor K=4. The reference signal symbol can be seen as a complex scalar in the SRS. To transmit an SRS signal with comb factor 4 from a UE is supported in 3GPP 38.211 Release 15, chapter 6.4.1.4 “Sounding Reference Signal”. Consequently, the described method can be implemented on a received SRS with K=4 without needing any standardization modifications.

According to another embodiment, the OFDM reference signal symbol is a part of a sounding reference signal (SRS), and the comb factor K=6, 8, 12 or 16. Tests have shown that the method works well also for higher K-factors than the one used in the standard today, i.e. K=4. Higher K-factors means more sparse insertion of reference signals, frequency-wise, which means less data to transmit compared to K=4 and therefore sparing of transmission and data resources. Further, higher K-factor means more repetition blocks over one OFDM symbol as the repetition blocks have length N/K More repetition blocks imply that a statistically better average value of the wireless channel can be achieved, i.e. lower noise and interference. Further, the length N/K of the condensed signal becomes shorter with higher K and thus the bandwidth over the interface to the aggregate unit can be lowered even more. Also, with a higher K, more wireless devices can be multiplexed on the communication channel, by giving them different time shifts. At least theoretically, K=8 signifies that 8 wireless devices can be multiplexed. However, when the number of wireless devices increases, the bandwidth needed over the interface also increases.

According to another embodiment, the received wideband reference signal is sampled204with a sampling frequency fs. Further, the comb factor K and the sampling frequency fsare selected so that the at least two repetition blocks each comprises an equal number of samples. Hereby, the accumulating of the at least two repetition blocks will become much easier, i.e. less complex, compared to if an uneven quantity of samples are to be compared. According to another embodiment, each of the at least two repetition blocks are an integer number of samples.

According to yet another embodiment, when the at least two repetition blocks comprises a first repetition block in a first OFDM symbol and a second repetition block in a second OFDM symbol, the accumulation210is compensated for a cyclic prefix of the first or second OFDM symbol so that the shift in time between the first and the second repetition block is an integer number of samples. In some cases, the accumulation210is performed for repetition blocks that belongs to more than one OFDM symbol. This means that the accumulation is performed over an OFDM symbol border between two OFDM symbols so that at least one repetition block belongs to one OFDM symbol and at least one other repetition block belongs to another OFDM symbol. When such accumulation is performed, the cyclic prefix existing at the end and/or beginning of an OFDM symbol has to be taken into consideration. This is especially of interest when the sampling frequency is selected compared to the wireless communication network base time so that the cyclic prefix becomes a real value instead of an integer value. Then a compensation is needed so that the duration between the first and second repetition block, originally mainly or only being due to the CP, becomes an integer number of samples.

According to another embodiment, the at least two repetition blocks comprises a first set of repetition blocks in a first OFDM symbol and a second set of repetition blocks in a second OFDM symbol. Further, the accumulation210is performed so that firstly the first set of repetition blocks are accumulated, and if a time between the first and the second OFDM symbol is not an integer number of samples, a fractional delay filter is applied to the second set of repetition blocks to align them with the first set of repetition blocks and thereafter the second set of repetition blocks are accumulated with the first set of repetition blocks. In other words, the second set of repetition blocks are aligned in time with the first set of repetition blocks before the second set of repetition blocks are accumulated to the already accumulated first set of repetition blocks, see also step308ofFIG.4. This is an advantageous way of doing the cyclic prefix compensation discussed above in case the distance in time between the first and second OFDM symbol is not an integer number of samples.

According to another embodiment, the method further comprises obtaining206the information on start times of the at least two repetition blocks, the information on start times comprising the N number of samples per OFDM symbol, the comb factor K and OFDM symbol start time. This control information is then used to find the start times of each of the at least two repetition blocks, in case the start times are not already known to the first transceiver. The control information may be obtained by the first transmitter from another unit of the node such as the aggregate unit, or from another node. In case the accumulation is performed in two or more OFDM symbols, the OFDM symbol start time includes start times for each OFDM symbol included in the accumulation.

According to yet another embodiment, the method further comprises obtaining208information on a comb factor frequency offset Kshift, when the OFDM reference signal symbol is not mapped on a lowest subcarrier of the at least subset of the carrier frequency bandwidth, and when performing the accumulation210, compensating for the comb factor frequency offset Kshift. The comb factor frequency offset, aka comb offset, can be compensated for by de-rotating the comb factor frequency offset. In other words, the compensation is performed by a per sample phase shift before the accumulation. The information on comb factor frequency offset may be the actual offset or it may be the per sample phase shift. The offset may refer to the phase shift to apply, in e.g. a look-up table in the first transceiver.

According to embodiments, the inventive solution comprises of one or more of the following steps:Configuring the second transceiver to transmit a reference signal on a regular K-comb over the complete, or a subset of the system bandwidth, over at least a part of L OFDM symbols, where L may be an integer of at least 1 and K is the comb factor;At the first transceiver, receiving a time domain reference signal at a first set of Mrxantenna branches. Mrxstands for M receiver antenna branches, where M is at least two. The antenna branches may have individual antenna elements, or a combination obtained using linear receive beamforming;At each of the antenna branches, sampling the time domain signal using Nrxsamples per OFDM symbol;Configuring the receive circuitry of the first transceiver, i.e. circuitry of the antenna branches, with information relating to start and length of repetition blocks;Summing the received, sampled time domain signal for each of the Mrxantennas over repetition blocks to obtain a condensed signal or length

NrxK;Conveying the condensed signal over an internal interface to an aggregate unit; andUsing, at the aggregate unit, the condensed signal for estimating a wireless communication channel between the second transceiver and the first transceiver, i.e. for precoder generation, and/or scheduling.

In the following, the steps mentioned above will be described in more detail. First, the second transceiver, which may be a wireless device, is configured to transmit a reference signal X(k), which may be an SRS or a Demodulation Reference Signal (DMRS), on a K-comb, aka comb factor K. This means that the reference signal r is mapped to every K subcarrier, perhaps with a with a given comb factor frequency offset Kshift.
X(k)=r(k),k=Kk+KshiftX(k)=0, for k not fulfilling the equation above,
where k=subcarrier index. The second transceiver will then perform OFDM modulation and obtain a wideband reference signal in time domain x(n), which is wirelessly transmitted:

x⁡(n)=α⁢∑kX⁡(k)⁢ejnk⁢2⁢πN=α⁢∑k-r⁡(k_)⁢ej⁡(K⁢k_+Kshift)⁢n⁢2⁢πN=α⁢ejKshift⁢n⁢2⁢πN⁢∑k-r⁡(k_)⁢ej⁢k_⁢nK⁢2⁢πN
Clearly, we have;

x⁡(n+N/K)=x⁡(n)⁢ejKshift⁢2⁢πK
This is a well-known property of the Discrete Fourier Transform (DFT). Observe that any cyclic prefix addition etc. is not included here.

Thereafter, the first transceiver receives the transmitted wideband time domain reference signal at its antenna elements connected to Mrxantenna branches. At each of the antenna branches, the wideband time domain signal is sampled using Nrxsamples per OFDM symbol. The received sampled signal on antenna m is denoted by
ym(n)

Then the receive circuitry of the first transceiver is configured with information relating to start and length of repetition blocks. Duration of the repetition block is typically Nrx/K aka N/K samples. Starting point nbfor repetition block b is typically

nb={nb-1+Nr⁢xK,if⁢block⁢b⁢and⁢b-1⁢in⁢same⁢symbolnb-1+Nr⁢xK+NrxC⁢P,if⁢blocks⁢⁢b⁢and⁢b-1⁢in⁢different⁢symbols,NlC⁢P⁢is⁢⁢CP⁢duration
where n0is given by the OFDM symbol position of the first sampled OFDM symbol in the sample stream, which can be derived from frame synch.

Further, the received signal for each of the Mrxantenna ports is summed over repetition blocks to obtain a condensed signal cmof length N/K, which is mathematically described according to the following

cm(n)=∑b⁢e-j⁡(b⁢mod⁢K)⁢Kshift⁢2⁢πK⁢ym(n+nb)
Potentially, a linear transformation may be applied of the signals of the antenna branches, either to the condensed signal “c” or to the sampled signal “y”, mapping from Mrxto MrxWBstreams, where WB stands for wideband. The mapping may be performed by creating MrxWBvirtual antenna branches by a linear combination of the streams from at least some of the Mrxantenna branches. By having fewer such virtual antenna branches than actual antenna branches, an additional reduction of the wideband requirement on the interface towards the aggregate unit is achieved.

Thereafter, the condensed signal is conveyed over the internal interface to an aggregate unit. The condensed signal may be buffered and transmitted with some delay to make best use of the internal interfaces. It may for examples be transmitted in downlink (DL) slots, or when a possible narrowband receiver is not used.

Further, the condensed signal is used by the aggregate unit for estimating the wireless channel and further for e.g. precoder generation, and or scheduling. This may involve the condensed signal cm(n) being transformed into frequency domain using e.g. an FFT. Then the channel estimate ĥmkmay be formed using the condensed signal cmtransformed into frequency domain. This may involve a matched filtering step, and transform processing, using e.g. a discrete cosine transform over subcarriers, and a beamspace transformation, defining the channel estimate as a selected subset of the transformed raw channel information. The channel estimate may be used to perform one or more of the following: Determine a scheduling bandwidth for a wireless device, in DL or uplink (UL); Determine precoders for DL transmission, including for Multi-User Multiple Input Multiple Output (MU-MIMO) transmission; Determine a frequency selective spatially fully sampled interference measure; Determine receive weights for an UL reception, which weights may be e.g. one or more Grid of Beams (GoB) or DFT beams, i.e. DFT-based linear phase front precoder; Determine which wireless devices to co-schedule in a slot, and determine which wireless devices that can be spatially multiplexed.

According to an embodiment, the transmitted reference signal is an SRS with comb K=4. According to another embodiment, the transmitted reference signal is an SRS with comb K=8, or K=6, or K=16, or K=12.

According to another embodiment, to avoid complex implementation solutions, it may be of interest to have the same number of samples in each KL repetition block, i.e. in each K block of each L OFDM symbols. Then the comb factor needs to be matched with the sampling frequency. New Radio (NR) standard subcarrier bandwidth is BWsc=2μ*15 kHz where μ=0 . . . 4 and relates to numerology. NR base timing assumes 2048 time samples per symbol. All frame structure events, such as symbol start, cyclic prefix etc. takes place on time based on this time quantization. The actual implementation might deviate from this sample rate based on reasons like total communication bandwidth, cost balance between high sample rate and minimum needed sample rate being the bandwidth of the information signal. It is natural to select a sampling frequency fs=Nsamp*3.84 MHz since 3.84 MHz and 15 kHz has a power of two relationship. Further, number of samples per symbol is

Ns⁢a⁢m⁢ps⁢y⁢m⁢b=fsBWs⁢c=Ns⁢a⁢m⁢p*282μ

As one example assume 100 MHz carrier bandwidth and 120 kHz numerology (μ=3). One possibility is then to select Nsampas a power of two factor and take the lowest sampling frequency above the minimum frequency 100 MHz. This means selecting:
Nsamp=25=32=>fs=122.88 MHz
Nsampsymb=210=1024

This states that the comb factor K has to be selected as a power of two K=2α. This will give a power of two number of samples in each repetition block. Another choice is to select a lower number of Nsampto minimize overhead of sampling rate Selecting:
Nsamp=30=2*3*5=>fs=115.2 MHz
Nsampsymb=3*5*26=960
opens up for a comb factor also to include factors 3 and 5. One interesting choice is to select K=12 giving one sounding subcarrier per resource block. NR standard today limits the factor to K∈{2, 4,8}. Proposal is to allow K=2α*3γ≤32 Where the upper limit is set by coherence bandwidth in radio channels.

In some cases, repetition blocks of different OFDM symbols may be accumulated, i.e. summed. In those cases, cyclic prefixes (CP) used in between symbols, i.e. between a first and a consecutive second symbol, need to be taken into account when determining where a repetition block of the second symbol starts. Note that the length of the CP is an integer number of the NR base sample time but the number of samples of the CP varies over the slot. If the second transceiver has selected another sampling frequency than the NR base sample time, e.g. the 115.2 MHz choice mentioned earlier, then the length of each CP measured in number of samples might be a real number instead of an integer. This then has to be compensated for prior to accumulating repetition blocks from different symbols. A proposed embodiment is to select a symbol starting time that compensates for an integer part of the CP for each symbol. The accumulated result for the symbol is then compensated for the fractional sample prior to accumulation between symbols. One possible way to implement this is to apply a fractional delay filter, which is shown inFIG.4and described below.

In the following, with reference toFIG.4, is a description of a hardware realization of embodiments of the present invention. As before, a transceiver is described comprising a set of antenna branches each connected to at least one antenna element, all antenna elements being arranged in e.g., an array. A typical application has number of antenna elements in the order of 100. Communication bandwidth is also typically several hundred of MHz. As a consequence, the total amount of information to and from the antenna branches to an aggregate unit is very high. This may be costly both in terms of power and manufacturing cost.

FIG.4describes a possible implementation of one single (receiver) antenna branch of the first transceiver120, in the following called a sparse sounding receiver block300. Each antenna branch will or may have a similar implementation. An assumption is that the radio architecture enables access to digitized signals received from all antennas branches or at least enough antenna branches to identify the radio channel. Input to the sparse sounding receive block300is a digitized, i.e., sampled, and channel filtered signal, hereinafter called a sampled reference signal302. The sampled reference signal is fed to a frequency offset compensator304that, in case there is a comb factor frequency offset Kshift, de-rotates the potential frequency offset. The potentially de-rotated sampled reference signal is then fed to a first accumulator306that accumulates repetition blocks within an OFDM symbol, either all repetition blocks within the symbol or a defined amount or certain blocks. Control information for performing the accumulation is symbol start time quantified to sample rate, the comb factor K and numerology, which states the number of samples per symbol. The accumulated signal is called a condensed signal. The condensed signal has length N/K. After accumulation within a symbol in the first accumulator306, and in case accumulation is to be performed for more than one OFDM symbol, that is over an OFDM symbol border, the condensed signal is fed to a fractional delay filter308. This delay filter compensates the signal for the fractional sample part of the symbol start, e.g. for the part of CP that is not an integer number of samples. This enables accumulation between symbols. Such an accumulation is then performed in a second accumulator310, after the delay filter308compensation. Control input to the delay filter308and the second accumulator310is the number of OFDM symbols over which accumulation is to be performed, Cyclic Prefix fraction and numerology, i.e., number of samples per symbol. Finally, a received sounding sequence, aka condensed signal312is delivered. Information content of the condensed signal312has the same number of samples as a repetition block, i.e. N/K. Accumulations give a processing gain in the signal quality proportional to the total number of repeated repetition blocks.

The inventors have found out that the presented implementation has many parts in common with a proposed hardware needed to perform an efficient mutual coupling antenna calibration as presented in International patent application WO2020/043310 of the same applicant. In the document, a quite different invention is present, which deals with performing efficient antenna calibration. Part of the document is a presentation of one possible hardware block to receive the calibration signal. The proposed calibration signal is very similar to a sparse sounding signal hence one embodiment of the present invention is to use a hardware block designed to both receive antenna calibration signals as well as sparse sounding signals, using the hardware block of WO2020/043310 but added with some feature to also handle the inventive sparse sounding signal.

The hardware block of WO2020/043310 is presented inFIG.5.FIG.5shows principles of reception of antenna calibration signals. Note thatFIG.5shows a set of receive branches, see “RxVi”. In the antenna calibration case, a code sequence is multiplied to the signal of each antenna branch. The code multiplication is not used for the inventive sparse sounding but the parallel blocks marked116can be used for handling also the sounding signals as presented above. In other words, the inventors have found out that by merging the decoder part114ofFIG.5with the sparse sounding receiver block ofFIG.4, a common hardware block for both functions, i.e. antenna calibration and sparse sounding reference signal handling, has been achieved. Compared toFIG.4, the block116ofFIG.5comprises the first accumulator306, the delay filter308and the second accumulator310, wherein the delay filter308and the second accumulator310are used when accumulation is performed over two or more OFDM symbols.

FIG.6shows a flow chart of control signaling within a transceiver, according to an embodiment, when the transceiver is implemented in a base station exemplified by a gNodeB. First, the gNodeB sends402a reference signal request e.g. an SRS request, to one or more UEs. The SRS request comprises an index to parameters such as time to transmit the SRS, comb factor K, comb factor frequency offset Kshift, wherein Kshift=0 means no offset, information to determine the SRS sequence, etc. A central unit of the gNodeB, which may be the aggregate unit128ofFIG.1, then combines404the SRS request with local radio information to formulate a control message to a radio unit of the gNodeB, i.e. the antenna branches. The control message to the radio unit comprises information indicating start time of each repetition block, such as integer and fraction part when to start symbol reception, comb factor K, comb factor frequency offset Kshift, Nrof samples per repetition block, N/K, or number of samples per OFDM symbol N. The central unit communicates406the control message to the Radio unit, which is on one or more integrated circuits, e.g. ASICs separate from the central unit. The radio unit performs the following408: sets up SRS receivers, once or for each slot having an SRS, receives the sounding signals sent by the one or more UEs, and accumulates sounding signals from the antennas, according to described embodiments, and sends the resulting condensed signal to the central unit. The central unit receives410the condensed signal from the radio unit and estimates the radio channel(s) between the gNodeB and the one or more UE based on the condensed signal, i.e. the accumulated sounding signal. The radio channel estimate is then used412for further processing at the central unit.

FIG.7shows an example of a wideband reference signal as it looks in time-domain when transmitted from the second transceiver110or received by the first transceiver120when an OFDM reference signal symbol is mapped to every K subcarrier frequency. In this example K=4, which means that there will be 4 repetition blocks within one OFDM symbol, as each repetition block has a length of N/K samples. The part of the signal marked with X signifies the cyclic prefix. The repetition blocks are marked with numbers. Repetition blocks 1-4 belong to a first OFDM symbol and repetition blocks 5-8 belongs to a second OFDM symbol.

FIG.8, in conjunction withFIG.1, describes a first transceiver120operable in a wireless communication system100configured for handling reference signals. The first transceiver120comprises M antenna branches124,125,126, M being at least two, each antenna branch comprising an antenna element121,122,123. The first transceiver120further comprises a processing circuitry603and a memory604. The memory contains instructions executable by said processing circuitry, whereby first transceiver120is operative for receiving, from a second transceiver110of the wireless communication network, at the antenna elements of each of the M antenna branches124,125,126and in time domain, an OFDM modulated wideband reference signal comprising an OFDM reference signal symbol mapped to every K subcarrier frequency of at least a subset of a carrier frequency bandwidth, K being called comb factor, and, at each of the M antenna branches124,125,126, sampling the received wideband reference signal using N samples per OFDM symbol, The first transceiver120is further operative for, for each of the M antenna branches124,125,126, accumulating the received, sampled wideband reference signal over at least two repetition blocks, each block having a length of N/K samples, to obtain a condensed signal with the length N/K samples, based on information on start times of the at least two repetition blocks, and, for each of the M antenna branches124,125,126) conveying the condensed signal over an interface129to an aggregate unit128for use in estimating a wireless communication channel between the second transceiver110and the first transceiver120.

According to an embodiment, the OFDM reference signal symbol is a part of a sounding reference signal, SRS, and the comb factor K=4. According to another embodiment the OFDM reference signal symbol is a part of an SRS, and the comb factor K=6, 8, 12 or 16.

According to another embodiment, the first transceiver120is operative for the sampling of the received wideband reference signal with a sampling frequency fs, and wherein the comb factor K and the sampling frequency fsare selected so that the at least two repetition blocks each comprises an equal number of samples.

According to another embodiment, the at least two repetition blocks comprise a first repetition block in a first OFDM symbol and a second repetition block in a second OFDM symbol. Further, the first transceiver is operative for, in the accumulation, compensating for a cyclic prefix of the first or second OFDM symbol so that a shift in time between the first and the second repetition block is an integer number of samples.

According to yet another embodiment, the at least two repetition blocks comprises a first set of repetition blocks in a first OFDM symbol and a second set of repetition blocks in a second OFDM symbol. Further, the first transceiver is operative for performing the accumulation so that firstly the first set of repetition blocks are accumulated, and if a time between the first and the second OFDM symbol is not an integer number of samples, a fractional delay filter is applied to the second set of repetition blocks to align them with the first set of repetition blocks and thereafter the second set of repetition blocks are accumulated with the first set of repetition blocks.

According to yet another embodiment, the first transceiver120is further operative for obtaining the information on start times of the at least two repetition blocks, the information on start times comprising the N number of samples per OFDM symbol, the comb factor K and OFDM symbol start time.

According to yet another embodiment, the first transceiver120is further operative for obtaining information on a comb factor frequency offset Kshift, when the OFDM reference signal symbol is not mapped on a lowest subcarrier of the at least subset of the carrier frequency bandwidth, and when performing the accumulation, compensating for the comb factor frequency offset Kshift.

According to other embodiments, first transceiver120may further comprise a communication unit602, which may be considered to comprise conventional means for wireless communication with the second transceiver110. The instructions executable by said processing circuitry603may be arranged as a computer program605stored e.g. in said memory604. The processing circuitry603and the memory604may be arranged in a sub-arrangement601. The sub-arrangement601may be a micro-processor and adequate software and storage therefore, a Programmable Logic Device, PLD, or other electronic component(s)/processing circuit(s) configured to perform the methods mentioned above. The processing circuitry603may comprise one or more programmable processor, application-specific integrated circuits, field programmable gate arrays or combinations of these adapted to execute instructions.

The computer program605may be arranged such that when its instructions are run in the processing circuitry, they cause the first transceiver120to perform the steps described in any of the described embodiments of the first transceiver120and its method. The computer program605may be carried by a computer program product connectable to the processing circuitry603. The computer program product may be the memory604, or at least arranged in the memory. The memory604may be realized as for example a RAM (Random-access memory), ROM (Read-Only Memory) or an EEPROM (Electrical Erasable Programmable ROM). In some embodiments, a carrier may contain the computer program605. The carrier may be one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or computer readable storage medium. The computer-readable storage medium may be e.g. a CD, DVD or flash memory, from which the program could be downloaded into the memory604. Alternatively, the computer program may be stored on a server or any other entity to which the first transceiver120has access via the communication unit602. The computer program605may then be downloaded from the server into the memory604.

Although the description above contains a plurality of specificities, these should not be construed as limiting the scope of the concept described herein but as merely providing illustrations of some exemplifying embodiments of the described concept. It will be appreciated that the scope of the presently described concept fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the presently described concept is accordingly not to be limited. Reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed hereby. Moreover, it is not necessary for an apparatus or method to address each and every problem sought to be solved by the presently described concept, for it to be encompassed hereby. In the exemplary figures, a broken line generally signifies that the feature within the broken line is optional.