Reference signal construction based on a golay sequence

Technical field

0001The present disclosure pertains to wireless communication technology, in particular in the context of reference signaling.

Background

0002In modern wireless communication systems, different kinds of reference signaling are utilised, e.g. synchronisation signaling, demodulation signaling, etc. Such reference signaling may cover a large frequency range (bandwidth), and may have to be provided under heavy load conditions. Due to its importance for facilitating efficient communication, reference signaling should be easy to identify and in particular should have good interference characteristics and/or be easy to identify.

0003Document <patcit id="pcit0001" dnum="WO2009048907A1"><text>WO 2009/048907 A1</text></patcit> discloses techniques to employ a code from a set of scrambling codes, for scrambling primary synchronization codes (PSCs), and secondary synchronization code (SSC), based on Golay complementary sequences.

Summary

0004It is an object of the present disclosure to provide approaches facilitating improved reference signaling.

0005Accordingly, there is disclosed a radio node for a wireless communication network, as defined in indepedent claim 1.

0006There is also disclosed a method for operating a radio node in a wireless communication network, as defined in independent claim 3.

0007A corresponding computer program is defined in appended independent claim 5.

0008Preferred embodiments are defined in the appended dependent claims 2, 4, and 6.

0009A Golay sequence may comprise a number N of elements. A Golay sequence may be a sequence chosen out of a pair of complementary Golay sequences. A pair of sequences may have the same number N of elements and follow the correlation conditions discussed herein. It may be considered that a Golay sequence represents a bipolar sequence (e.g., elements may have values +1 or -1). A sequence may generally comprise a number (e.g., N) of numbered elements, e.g. a(0)...a(N-1). N may be 64 or larger, and/or in particular be a multitude of 2, and/or represent a power of 2.

0010The coding may generally be based on a pair of complementary Golay sequences, e.g. comprising a first sequence and a second sequence. The correlation characteristics of such a pair are particularly suitable to be used in the context of reference signaling, e.g. reference signaling comprising two components (e.g., covering two different frequency intervals). It may be considered that the coding maps (and/or multiplex) a first component of the reference signaling to a frequency interval, and a second component of the reference signaling to the (same) frequency interval, in particular to different frequency resources within the interval. A component of reference signaling may comprise signaling, signals and/or symbols transmitted in the same time interval, e.g. subframe and/or TTI and/or similar. In some cases, a first component may represent primary synchronisation signaling, and a second component may represent secondary synchronisation signaling.

0011Generally, the coding may map first reference signaling to a first frequency range and a second reference signaling to a second frequency range. In particular, the coding may comprise and/or represent a map and/or function or relation providing such mapping. The first and second frequency ranges may be frequency intervals, which may be non-overlapping and/or neighboring (e.g., sharing a border frequency). Each frequency range may in particular represent a carrier, the first and second ranges may represent different carriers. The first reference signaling may be different reference signaling from the second reference signaling, e.g., the first reference signaling may represent primary reference signaling and the second reference signaling may represent secondary reference signaling. Alternatively, the first reference signaling may represent a first component and the second reference signaling a second component of one type of reference signaling.

0012The elements of a Golay sequence and/or the coding (and/or resources mapped to) may be determined differentially. Differentially determining an element may be such that one or more elements after the first element of a sequence is or are determined based on one or more preceding element/s. Determining may be performed by the radio node, which may comprise a corresponding determining module and/or processing circuitry. Determining may be based on identifying a first element in received signaling, and determining following elements differentially. A first element may be identified based on a received element indication, which may represent and/or indicate the first element. Differentially determining may be based on a differential mapping, which may be indicated by the element indication. The differential mapping may be available to the radio node, e.g. a memory of the radio node. Processing, in particular transmitting, reference signaling, may comprise transmitting the element indication, e.g. in the reference signaling and/or in a separate message or signal, e.g. in a broadcast or dedicated signal or message (e.g., addressed to one or more specific user equipments or terminals). In particular, the element indication may be transmitted using control signaling. Alternatively or additionally, e.g. based on the determined elements, decoding and/or encoding may be determined, e.g. differentially. Determining a signaling sequence and/or a Golay sequence, e.g. differentially determining the Golay sequence, may comprise pruning (truncating a number N of elements to a number K<N) and/or zero padding (increasing the number of elements from N to M>N by adding zeros). A radio node may be adapted to configure another radio node (e.g., a user equipment) for a coding and/or a reference signaling to be detected and/or determined, e.g. by configuring one or more Golay sequences to be used, e.g. by transmitting the element indication and/or corresponding configuration data.

0013It may be envisioned that the reference signaling may comprise synchronisation signaling, in particular primary synchronisation signaling and/or secondary synchronisation signaling. Synchronisation signaling thus may be provided in a way allowing reliable and robust identification.

0014In some variants, the reference signaling is broadcast, e.g. in a cell, in particular synchronisation signaling. Such signaling may be efficiently identified if coded as described herein. Alternatively or additionally, the reference signaling may be dedicated signaling.

0015Processing reference signaling may comprise transmitting and/or receiving the reference signaling. Radio circuitry may generally comprise one or more transmitters and/or receivers for such transmitting and/or receiving. It may be considered that the radio node comprises one or more transmitting modules and/or one or more receiving modules for such transmitting and/or receiving, which may be implemented in the processing circuitry and/or radio circuitry. Alternatively or additionally, processing may comprise encoding the coding and/or decoding the coding. In particular, processing may comprise encoding and transmitting, and/or receiving and decoding. Processing circuitry may be adapted for, and/or used for, encoding and/or decoding, and/or the radio node may comprise a corresponding encoding module and/or decoding module. Processing, in particular receiving and/or decoding) may comprise identifying the reference signaling and/or associated frequency/ies (or related interval/s), respectively associated signals and/or symbols, and/or one or more components or sequences thereof.

0016Processing reference signaling may comprise determining a signaling sequence, e.g. using a determining module and/or processing circuitry. Processing and/or determining may comprise (if receiving) detecting the reference signaling and/or (if transmitting) constructing a signaling sequence. A detector for such detecting, and/or a constructor for such constructing, may be implemented as a module and/or in processing circuitry.

0017It may generally be considered that a radio node is adapted for transmitting and receiving reference signaling as described herein, for example transmitting synchronisation signaling and receiving sounding signaling or vice versa.

0018Reference signaling may generally comprise synchronisation signaling and/or cell reference signaling and/or channel state information reference signaling and/or demodulation signaling (in particular, if the radio node is a network node), and/or pilot signaling and/or sounding signaling and/or timing signaling (in particular, if the radio node is a user equipment). It may be considered that the reference signaling is beam-finding reference signaling and/or reference signaling for cell search and/or identification and/or timing estimation. In some cases, reference signaling may represent a random access preamble, and/or cell identification signaling.

0019Reference signaling may comprise two or more components. A component may comprise one or more signals or symbols of the reference signaling. Different components may be mapped based on different Golay sequences, in particular a pair of complementary sequences. Reference signaling may comprise a number of signals or symbols associated to, or equal to, the number of elements of the Golay sequence/s the coding is based on. A signal or symbol of reference signaling may be associated to and/or transmitted in a resource element. Signaling may comprise a sequence of symbols or signals, e.g. according to the Golay sequence/s. Thus, signaling may be represented by, and/or referred to, as signaling sequence. The sequence may cover time and/or frequency resources based on, and/or coded based on, the Golay sequence/s. A signaling sequence may be based on a repeated Golay sequence.

0020Reference signaling may be OFDM (Orthogonal Frequency Division Multiplexing) signaling and/or Single-carrier and/or DFTS-OFDM (Discrete Fourier Transform Spreading-OFDM) signaling. Signals or symbols may be formed according to such signaling.

0021Coding may generally comprise and/or represent a map of signals and/or symbols of reference signaling to time and/or frequency resources. The map may be based on one or more Golay sequences, e.g. as a form of coding based on the sequence/s. A time resource may described a time interval, in particular one or more symbol time intervals and/or subframes and/or transmission time intervals (TTIs). Such a time interval may be according to a communication standard, e.g. a 3GPP 5G standard like NR (New Radio) or LTE (Long Term Evolution) evolution. A frequency resource may comprise a frequency and/or frequency interval (e.g., bandwidth), e.g. used for transmission, in particular a subcarrier or related bandwidth, or similar, like a carrier or subdivision thereof, respectively an associated bandwidth. A frequency interval may be divided into two or more subintervals, e.g. carriers. A carrier may be divided into several subintervals, e.g. subcarriers, each of which may be associated to a frequency resource (element). A subcarrier and an associated symbol time interval may be considered a resource element. A symbol time interval may be a time interval associated to a symbol of signaling. A subframe or TTI may comprise a plurality of symbols.

0022It may be considered that a coding maps, and/or that mapping comprises, each element of a Golay sequence to another time interval, e.g. symbol time interval, which may be successive for successive elements. Alternatively or additionally, a map or mapping may be such that a sequence is mapped to a frequency range comprising a plurality of subcarriers (e.g., covering one or more carriers, which may be neighboring), e.g. such that a shift in subcarriers from a preceding subcarrier is determined by the corresponding element, e.g. based on determined beginning subcarrier (the subcarriers may be represented by a numbered reference for mapping). Thus, an element of a sequence may represent a frequency or subcarrier shift. Generally, a coding may identify where on a grid of time-frequency resources the signals or symbols of the associated signaling are located.

0023A radio node may generally be considered a device or node adapted for wireless and/or radio (and/or microwave) frequency communication, and/or for communication utilising an air interface, e.g. according to a communication standard.

0024A radio node may be a network node or a user equipment or terminal. A network node may be any radio node of a wireless communication network, e.g. a base station and/or gNodeB (gNB) and/or relay node and/or micro/nano/pico/femto node and/or other node, in particular for a RAN as described herein. For an implementation of the radio node as network node. The terms user equipment (UE) and terminal may be considered to be interchangeable in the context of this disclosure. A user equipment or terminal may represent and end device for communication utilising the wireless communication network, and/or be implemented as a user equipment according to a standard. Examples of user equipments may comprise a phone like a smartphone, a personal communication device, a mobile phone or terminal, a computer, in particular laptop, a sensor or machine with radio capability (and/or adapted for the air interface), in particular for MTC (Machine-Type-Communication, sometimes also referred to M2M, Machine-To-Machine), or a vehicle adapted for wireless communication. A user equipment may be mobile or stationary.

0025A radio node may generally comprise processing circuitry and/or radio circuitry. Circuitry may comprise integrated circuitry. Processing circuitry may comprise one or more processors and/or controllers (e.g., microcontrollers), and/or ASICs (Application Specific Integrated Circuitry) and/or FPGAs (Field Programmable Gate Array), or similar. It may be considered that processing circuitry comprises, and/or is (operatively) connected or connectable to one or more memories or memory arrangements. A memory arrangement may comprise one or more memories. A memory may be adapted to store digital information. Examples for memories comprise volatile and non-volatile memory, and/or Random Access Memory (RAM), and/or Read-Only-Memory (ROM), and/or magnetic and/or optical memory, and/or flash memory, and/or harddisk memory, and/or EPROM or EEPROM (Erasable Programmable ROM or Electrically Erasable Programmable ROM). Radio circuitry may comprise one or more transmitters and/or receivers and/or transceivers (which may operate as transmitter and receiver), and/or may comprise one or more amplifiers and/or oscillators and/or filters, and/or may comprise, and/or be connected or connectable to antenna circuitry and/or one or more antennas.

0026Any one or all of the modules disclosed herein may be implemented in software and/or firmware and/or hardware. Different modules may be associated to different components of a radio node, e.g. different circuitries or different parts of a circuitry. It may be considered that a module is distributed over different components.

0027A wireless communication network may be a Radio Access Network (RAN), in particular according to a communication standard. A communication standard may in particular a standard according to 3GPP and/or 5G, e.g. according to NR or LTE Evolution.

0028There may also be considered a program product comprising instructions, the instructions causing processing circuitry to perform and/or control any one or any combination of the methods described herein. Instructions may be implemented as code.

0029A carrier medium arrangement carrying and/or storing a program product as described herein is also proposed.

Brief description of the drawings

0030The drawings are provided to illustrate the approaches and concepts described herein, and are not intended to limit their scope. They comprise: <ul id="ul0001" list-style="none"><li><figref idref="f0001">Figure 1</figref>, showing PSS and SSS as in LTE FDD release 8;</li><li><figref idref="f0002">Figure 2</figref>, showing initial cell search procedure for LTE release 8;</li><li><figref idref="f0003">Figure 3</figref>, showing detectors for PSS and SSS;</li><li><figref idref="f0004">Figure 4</figref>, showing receiver correlation with timing and frequency offset candidates,</li><li><figref idref="f0005">Figure 5</figref>, showing autocorrelations of the two complementary sequences and the sum of these autocorrelations,</li><li><figref idref="f0006">Figure 6</figref>, showing correlation with two Golay complementary sequences;</li><li><figref idref="f0007">Figure 7</figref>, showing an exemplary Golay sequence;</li><li><figref idref="f0008">Figure 8</figref>, showing autocorrelation of a repeated Golay sequence;</li><li><figref idref="f0009">Figure 9</figref>, showing an exemplary Golay sequence with timing and frequency offset candidates;</li><li><figref idref="f0010">Figure 10</figref>, showing a block based synchronization signal transmitter using DFTS-OFDM;</li><li><figref idref="f0011">Figure 11</figref>, showing a linear synchronization signal transmitter using frequency shift;</li><li><figref idref="f0012">Figure 12</figref>, showing a receiver for differential encoded sequences with block-based transmission;</li><li><figref idref="f0013">Figure 13</figref>, showing a receiver of two frequency shifted differential encoded sequences;</li><li><figref idref="f0014">Figure 14</figref>, showing pruning a differential sequence in time (before DFT);</li><li><figref idref="f0015">Figure 15</figref>, showing zero padding in time (before DFT);</li><li><figref idref="f0016">Figure 16</figref>, showing autocorrelation of a differential decoded Golay sequence with frequency and timing errors;</li><li><figref idref="f0017">Figure 17</figref>, showing an exemplary radio node;</li><li><figref idref="f0018">Figure 18</figref>, showing an exemplary method for operating a radio node; and</li><li><figref idref="f0019">Figure 19</figref>, showing a further exemplary radio node.</li></ul>

Detailed Description

0031Synchronization sequences respective associated signaling are described as example for reference signaling in the following. Herein, a radio node like a UE is referred to as a receiver receiving and decoding/detecting signaling, and a radio node like a base station or eNB (LTE base station) or gNB (NR base station) is referred to as transmitter transmitting and/or encoding.

0032When a UE is powered on, or when it moves between cells in LTE release 8, it receives and synchronizes to downlink signals in a cell search procedure. The purpose of this cell search is to identify the best cell and to achieve time and frequency synchronization to the network in downlink (i.e. from base station to UE). The Primary and Secondary Synchronization Signals (PSS and SSS) are used at cell search in the UE for LTE. Here, in the case of FDD (Frequency Division Duplexing), the PSS is transmitted in the last OFDM symbol of slots 0 and 10 within a frame and the SSS is transmitted in the OFDM symbol preceding PSS, see the illustration in <figref idref="f0001">Figure 1</figref>. In the case of TDD (Time Division Duplex), the PSS is transmitted in the third OFDM symbol of slots 3 and 13 within a frame, and the SSS is transmitted in the last OFDM symbol of slots 2 and 12, i.e., three symbols ahead of the PSS.

0033Detectors are discussed in the following. A detector may be implemented in a receiver, e.g. a user equipment or terminal. A detector may generally be adapted for detecting reference signaling. Detecting reference signaling may be considered to comprise identifying the signals or symbols belonging to a reference signaling sequence of signals or symbols.

0034A simplified initial cell search procedure is illustrated in <figref idref="f0002">Figure 2</figref>. Here the UE tries to detect PSS from which it can derive the cell identity within a cell-identity group, which consists of three different cell identities corresponding to three different PSS. In this detection, as shown in the illustration in <figref idref="f0003">Figure 3</figref>, the UE thus has to blindly search for all of these three possible cell identities. This is done by calculating a cross-correlation between received signals and the candidate PSS sequence. Here a cross-correlation is calculated in a time domain matched filter, followed by an absolute square operation.

0035The UE also achieves OFDM symbol synchronization and a coarse frequency offset estimation with an accuracy of about 1 kHz. The latter is estimated by the UE by evaluating several hypotheses of the frequency error. Many operations have to be done for each of these frequency offset hypothesis. Typically, the lowpass filter, three time domain matched filters, and three absolute square operations have to be done for each hypothesis. Then the search for peak is done over all frequency offset hypothesis and cell id groups.

0036The UE can then continue to detect SSS (coherent detection thanks for the PSS decoding) from which it acquires the physical cell id and achieves radio frame synchronization, see <figref idref="f0003">Figure 3</figref>. Here, the UE also detects if normal or extended cyclic prefix is used. If the UE is not preconfigured for either TDD or FDD, the UE can detect the duplex mode by the position in the frame of detected SSS in relation to detected PSS. Fine frequency offset estimation can be estimated by correlating PSS and SSS. Alternatively, this fine frequency offset estimation is estimated by using the Cell specific Reference Signals (CRS) which are derived from the Physical Cell Identity (PCI) encoded in the PSS/SSS. Once the UE is capable of decoding the CRSs the UE can receive and decode cell system information which contains cell configuration parameters starting with the Physical Broadcast Channel (PBCH).

0037Frequency errors can occur due to imperfect oscillators and movement of the UE relative to the base station. Typically, frequency errors up to 20 ppm (part per million) of the carrier frequency must be handled during initial cell search when receiving synchronization signals such as PSS. For a carrier frequency of 2.5 GHz, the frequency error can thus be +- 50 kHz. As mentioned earlier, this frequency error can be estimated by detecting PSS for several pre-rotations with different candidates of the frequency errors. A few illustrations of receiver cross correlations in the detector are given in <figref idref="f0004">Figure 4</figref>

0038The drawings are provided to illustrate the approaches and concepts described herein, and are not intended to limit their scope. They comprise: <ul id="ul0002" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref>, showing PSS and SSS as in LTE FDD release 8;</li><li><figref idref="f0002">Figure 2</figref>, showing initial cell search procedure for LTE release 8;</li><li><figref idref="f0003">Figure 3</figref>, showing detectors for PSS and SSS;</li></ul>

0039Figure, with frequency error candidates between +- 50 kHz, for a Zadoff-Chu sequences as used in LTE release 8. The correct frequency and timing errors are 0 Hz and 0 microseconds, respectively, in these illustrations.

0040Golay complementary sequences are discussed in the following.

0041Golay complementary sequences were introduced by Marcel Golay. These sequences are interesting for reference signaling, in particular in the context of synchronization, for at least two reasons: <ol id="ol0001" compact="compact" ol-style=""><li>1. The sum of the autocorrelations from a complementary pair is ideal</li><li>2. Low computational complexity when calculating correlations</li></ol>

0042A pair of Golay complementary sequences may be denoted as <maths num=""><img file="EP3556037B1_D0001.tif" /></maths> and <maths num=""><img file="EP3556037B1_D0002.tif" /></maths>

0043Also, the aperiodic autocorrelations of these sequences are denoted as <maths num=""><img file="EP3556037B1_D0003.tif" /></maths> and <maths num=""><img file="EP3556037B1_D0004.tif" /></maths>

0044Then the sum of these autocorrelations is a perfect "Dirac delta function" i.e. <maths num=""><img file="EP3556037B1_D0005.tif" /></maths> where δ(k) = 1 for <i>k</i> = 0 only and zero otherwise, which is illustrated in <figref idref="f0005">Figure 5</figref>. Equation 3 to 5 may be considered to define (complementary) Golay sequences.

0045A second property of Golay complementary sequences is that the computational complexity for calculating a correlation is low. A sequence diagram is given in <figref idref="f0006">Figure 6</figref> from which correlations with two complementary sequences are calculated simultaneously.

0046A Golay sequence may be used for timing synchronization as illustrated in <figref idref="f0007">Figure 7</figref>. Here <maths num=""><img file="EP3556037B1_D0006.tif" /></maths> is a 128 symbol long Golay sequence. This sequence is repeatedly transmitted 16 times within the short training field, as illustrated in <figref idref="f0007">Figure 7</figref>, followed by one transmission with changed sign. A very simple receiver, as in <figref idref="f0006">Figure 6</figref>, can be constructed in which the received signal is correlated with the known 128 samples long Golay sequence.

0047The received signal in the detector will include a few of the last samples of a transmitted Golay sequence followed by the first samples of an identical Golay sequence in most correlations. This will result in a non-ideal correlation, as illustrated in <figref idref="f0008">Figure 8</figref>.

0048A few illustrations of receiver correlations in the detector are given in <figref idref="f0009">Figure 9</figref>Figure, with frequency error candidates between +- 50 kHz, for a three different Golay sequences.

0049The use of Zadoff-Chu as in current LTE sequences as synchronization signals is very sensitive to frequency errors. The autocorrelations, both with and without frequency errors have many false peaks which cause detections for other than the true timing and frequency error. This leads to timing and frequency offsets after synchronization. This is visible in <figref idref="f0004">Figure 4</figref> as additional peaks for nonzero delays and frequency offsets. False peaks and estimation errors also occur when using a Golay sequence as the synchronization signal, as shown in <figref idref="f0009">Figure 9</figref>.

0050For a variant, it is proposed constructing a time synchronization and/or beam finding reference signal by two differentially encoded complementary sequences which are multiplexed in frequency into one time interval.

0051Reference signaling, in particular a synchronization signaling sequence, may be constructed which <ul id="ul0003" list-style="bullet" compact="compact"><li>has a detector with very low correlation peaks for non-zero delay errors</li><li>has a detector which is robust against frequency errors</li><li>has a detector with very low computational complexity</li></ul>

0052Transmitters are discussed in the following. A transmitter may in particular be implemented as, and/or as part of, radio node like a network node.

0053An illustration is given in <figref idref="f0010">Figure 10</figref> of a transmitter for the proposed method of processing (constructing) a reference signal from differential encoded Golay complementary sequences. Here two DFTs (Discrete Fourier Transform), one for each of the complementary sequences, are followed by a concatenation and an inverse FFT (Fast Fourier Transform). This construction of a DFT followed by a larger IFFT is also known as DFTS-OFDM and is block based since a block of the transmitted signal is constructed within one IFFT.

0054An alternative transmitter structure is illustrated in <figref idref="f0011">Figure 11</figref>, where an oversampling and interpolation is followed by a frequency shift, which modulates (at least) one of the differential encoded sequences such that they span different, essentially non-overlapping, frequency intervals. This transmitter is linear since all processing is done with linear processing blocks in a sample-by-sample manner.

0055The construction by DFTS-OFDM in <figref idref="f0010">Figure 10</figref> may be beneficial for base-station implementations built with an IFFT close to the antenna ports. Here, a construction with an IFFT close to the antenna ports can be a software implementation build upon all downlink signals processed with IFFTs. Also, the base station might be designed with IFFTs in hardware which is physically placed close or inside the radio equipment such that having a signal which is not processed with an IFFT would add a significant amount of extra software or hardware support.

0056The block of signal values constructed by the DFTS-OFDM in <figref idref="f0010">Figure 10</figref> is cyclic within the OFDM symbol, in contrast to the linear processing as illustrated in <figref idref="f0011">Figure 11</figref>. A receiver structure is presented next which is based on linear processing. The receiver is thus constructed for a linear signal and will have some performance loss when combined with the block based cyclic signals as compared to using a linear transmitter.

0057A receiver is discussed in the following. A receiver may in particular be implemented as, and/or as part of, a radio node like a user equipment or terminal.

0058The signals generated by the two transmitter versions are preferable decoded using corresponding matching receiver formulations; a mismatch will lead to slightly degraded performance.

0059Block-based generated signaling is discussed in the following, as an example of processing reference signaling.

0060The block-based transmitter in <figref idref="f0010">Figure 10</figref> is matched by a receiver depicted in <figref idref="f0012">Figure 12</figref>. The frequency-domain signal is separated into the two constituent DFT components and converted back to the original sequences. Differential decoding operations are followed by correlation stages with the two complementary Golay sequences. Finally, the two correlations are added before detection.

0061If several possible synchronization sequences exist, the correlation stage pairs are repeated for each such sequence, while the FFT processing complexity does not change.

0062To extract the synchronization signal contents in the frequency domain, the FFT input samples must cover the entire OFDM symbol. Since the symbol timing is not known a priori, a simple solution is to perform an FFT and repeat the processing above at several sample timing candidates, which however may be computationally expensive.

0063To remove the FFT window placement uncertainty, the approach of oversampled FFT may be used. The receiver places double-length, 2N-FFT windows in time domain (2N is an example, other FFT length longer than N work as well), with adjacent FFTs overlapping by N samples (the symbol length). That way, every second FFT window captures an entire OFDM symbol. The transmitted OFDM symbol may contain reference symbols (not shown in <figref idref="f0010">Figure 10</figref>) to estimate and remove the resulting frequency rotation, effectively restoring the proper symbol timing. This approach works particularly well if the neighboring OFDM symbols are known to not to contain the sequence.

0064Another possible variant of the receiver for the block-based signal applies the sliding window FFT approach: a full FFT is performed at an initial time, but at each subsequent sample time, only FFT (DFT) output contribution (negative contribution) due to one new input sample (due to one input sample falling outside the new DFT window) is computed, while a linearly increasing exponential factor is applied to the corrected FFT output values to account for the time shift of the previous input samples. The number of multiplications for each FFT update is O(N), more specifically proportional to the allocated subcarriers in the FFT.

0065To formulate yet another variant for the receiver, it should be noted that the transmitter operations Golay encoding→Diff encoding→DFT→IFFT create an N-sample long time-domain sequence. A matched filter may be implemented by correlating the received signal with this time-domain sequence, which provides an alternative receiver. However, the correlation complexity is higher since the Golay sequence properties are not utilized.

0066Linearly generated signaling is discussed in the following as example of determining a coding.

0067A receiver structure for the linear transmitter in <figref idref="f0011">Figure 11</figref> is illustrated in <figref idref="f0013">Figure 13</figref>, where two different bandpass filters are used to extract the different frequency allocations for the two differentially encoded Golay sequences. Again, differential decoding operations are followed by correlation stages with the two complementary Golay sequences. Finally, the two correlations are added before detection.

0068The linear receiver processing amounts to time-domain matched filtering and correlation over a sliding window in time. If several possible synchronization sequences exist, the correlation stage pairs are repeated for each such sequence and complexity is proportional to the number of sequences.

0069Detailed descriptions of some of the above processing steps for the linear transmitter and receiver realizations of <figref idref="f0010">Figure 10</figref> and <figref idref="f0013">Figure 13</figref> are given below.

0070Differential encoding is discussed in the following. Differential encoding may be seen as implementation of differentially determining elements.

0071Example Golay sequences may be denoted as: <maths num=""><img file="EP3556037B1_D0007.tif" /></maths> or <maths num=""><img file="EP3556037B1_D0008.tif" /></maths>

0072Equation (7) may represent a first Golay sequence, Equation (8) a second Golay sequence. Reference signaling may be based on one of such sequences, or on more than one. In particular, the first and second sequence may be complementary Golay sequences.

0073Differential coded Golay sequences may be defined as: <maths num=""><img file="EP3556037B1_D0009.tif" /></maths> and <maths num=""><img file="EP3556037B1_D0010.tif" /></maths> with ã(0) = 1; b̃(0) = 1 for n = 1,...., N. Other differential encoding (and corresponding decoding schemes) are also possible, e.g. utilising a constant factor, and/or referring to different preceding elements.

0074Modulation (encoding) is discussed in the following.

0075Sub-carrier mapping (mapping to frequency resources) may be formulated as rotation (with starting sub-carrier N_c), as an example of encoding or determining coding: <maths num=""><img file="EP3556037B1_D0011.tif" /></maths> and <maths num=""><img file="EP3556037B1_D0012.tif" /></maths>

0076The sub-carrier shift is typically selected as N_c = <i>N</i> + 1. Selection of larger values (than N_c = <i>N</i> + 1) may be beneficial in terms of better separation (and less interference between) the two differentially coded Golay sequences.

0077An exemplary channel is discussed in the following.

0078The radio channel is a model of the propagation from transmission (in the base station) to the receiver (in the UE). Here a simple channel model is used, equal to a constant complex scaling, delay n₀ and additive noise and interference. Within the current section, this radio channel also includes the interpolation, bandpass filters and decimations. The same model is also used both for the DFTS-OFDM in <figref idref="f0010">Figure 10</figref> and the frequency shift transmitters in <figref idref="f0011">Figure 11</figref>.

0079The two complementary sequences are modelled separately as <maths num=""><img file="EP3556037B1_D0013.tif" /></maths> and <maths num=""><img file="EP3556037B1_D0014.tif" /></maths>

0080De-rotation is discussed in the following. De-rotation may be part of decoding and/or receiving. The radio node may comprise a derotation module for such derotation, and/or may be adapted for using the processing circuitry therefor.

0081Compensate for the sub-carrier shift (or sub-carrier mapping) by <maths num=""><img file="EP3556037B1_D0015.tif" /></maths> and <maths num=""><img file="EP3556037B1_D0016.tif" /></maths>

0082Inserting (11) and (13) into (15) results in <maths num=""><img file="EP3556037B1_D0017.tif" /></maths>

0083Also, inserting (12) and (14) into (16) results in <maths num=""><img file="EP3556037B1_D0018.tif" /></maths>

0084Note that the received, de-rotated signal in (16) still has a complex exponential factor which depends on the unknown delay n₀. This complex exponential will be eliminated by the following differential decoding.

0085Differential decoding is discussed in an example in the following. Differential decoding may be part of, and/or an implementation of, differentially determining a coding.

0086The two complementary Golay sequences are differentially decoded according to <maths num=""><img file="EP3556037B1_D0019.tif" /></maths> and <maths num=""><img file="EP3556037B1_D0020.tif" /></maths>

0087Correlations are discussed in the following.

0088Correlation with the two complementary Golay sequences can be done with the receiver structure as illustrated in <figref idref="f0006">Figure 6</figref>, which corresponds to <maths num=""><img file="EP3556037B1_D0021.tif" /></maths> and <maths num=""><img file="EP3556037B1_D0022.tif" /></maths>

0089Detection is discussed in the following.

0090Detection of timing equals the delay <i>k</i>, corresponding to the largest absolute square of the sum of these correlation, i.e. <maths num=""><img file="EP3556037B1_D0023.tif" /></maths>

0091Aspects of DFTS-OFDM are discussed in the following.

0092The detection of the synchronization signals in the receiver, as illustrated in <figref idref="f0013">Figure 13</figref>, is very much simplified if the decimation is done by an integer factor. For the transmitter based on DFTS-OFDM, as illustrated in <figref idref="f0010">Figure 10</figref>, this requirement of integer decimations leads to restrictions in the relation between the length of the DFT and the length of the IFFT. Denote the size of the DFT as <i>N_DFT</i> such that <maths num=""><img file="EP3556037B1_D0024.tif" /></maths> and <maths num=""><img file="EP3556037B1_D0025.tif" /></maths>

0093Also, denote the size of the IFFT as <i>N_IFFT</i> such that <maths num=""><img file="EP3556037B1_D0026.tif" /></maths>

0094Note that the summations above are only needed over the <i>N_DFT</i> values of Ã(k) and B̃(k). The decimation in the receiver can now be expressed as <maths num=""><img file="EP3556037B1_D0027.tif" /></maths>

0095Typical examples are <i>N_DFT</i> = 64 and <i>N_IFFT</i> = 2048 such that <i>D</i> = 32.

0096From the design of Golay sequences, the length of a Golay sequence is typically <maths num=""><img file="EP3556037B1_D0028.tif" /></maths>

0097With <i>m</i> = 6, <i>k</i> = 0, <i>l</i> = 0 follows that <i>N</i> = 64.

0098However, within the differential encoding, the length of sequence "over air" increases with one such that a sequence of 64 values increase to 65 values. Two different solutions are listed below in order to achieve integer decimation: <ol id="ol0002" ol-style=""><li>1. Prune differential sequence in time (before DFT), i.e. select <i>N_DFT</i> = <i>N</i>.</li><li>2. Zero padding in time (before DFT), i.e. <i>N_DFT</i> > <i>N</i>, e.g. <i>N_DFT</i> = 2<i>N</i></li></ol>

0099An illustration of the autocorrelation of pruned differential sequences is given in <figref idref="f0014">Figure 14</figref>, and for zero padding in <figref idref="f0015">Figure 15</figref>.

0100Frequency offset is discussed in the following.

0101The detection of synchronization signals is independent of frequency offset with the use of differential encoding and decoding, a related illustration is provided in <figref idref="f0016">Figure 16</figref>. The actual frequency offset is estimated in a subsequent step using a symbol sequence (r̃_a(n) or r̃_b(n)) in a non-differentially-decoded form, using the previously detected timing alignment value.

0102Alternative multiplexing of Golay-encoded sequences is described in the following.

0103In <figref idref="f0010">Figure 10</figref>, the two constituent (or component) sequences are multiplexed side-by-side in frequency by virtue of directly stacking the DFT outputs for the two sequences. This effectively yields a signal that is a sum of two single-carrier signals.

0104In some alternative variants, the DFT outputs may be interleaved in frequency according to a regular or pseudorandom pattern, e.g. to increase robustness to fast fading in dispersive channels. The receiver in <figref idref="f0012">Figure 12</figref> is then adapted by changing the mapping of FFT outputs to DFT inputs accordingly.

0105Separate time and frequency allocations are discussed in the following.

0106In yet another variant, the sequences are separated both in time and frequency. Then the single-carrier properties could be preserved. A drawback is that sequences would need to be shorter (given same total amount of resources), so that fewer orthogonal sequences are possible. However, if only a few different sequences are needed in some scenario, this solution could be a reasonable trade-off to reduce PAPR and thereby increase coverage.

0107Generally, there may be considered a synchronization signal constructed by differential encoding of two complementary sequences, which are mapped to different frequency intervals.

0108<figref idref="f0017">Figure 17</figref> shows an exemplary radio node 100, which may be implemented as a network node or user equipment. Radio node 100 comprises processing circuitry (which may also be referred to as control circuitry) 120, which may comprise a controller connected to a memory. Any module, e.g. receiving module and/or transmitting module and/or configuring module of the radio node may be implemented in and/or executable by the processing circuitry 120. The processing circuitry is connected to control radio circuitry 122 of the radio node 100, which provides receiver and transmitter and/or transceiver functionality (e.g., comprising one or more transmitter and/or receiver and/or transceiver). An antenna circuitry 124 may be connected or connectable to radio circuitry 122 for signal reception or transmittance and/or amplification. The radio node 100 may be adapted to carry out any of the methods for operating a radio node disclosed herein; in particular, it may comprise corresponding circuitry, e.g. processing circuitry. The antenna circuitry may be connected to and/or comprise an antenna array.

0109<figref idref="f0018">Figure 18</figref> shows an exemplary method for operating a radio node. The method comprises an action RS10 of processing reference signaling based on a coding, the coding being based on a Golay sequence.

0110<figref idref="f0019">Figure 19</figref> shows an exemplary radio node. The radio node comprises a processing module RM10 for performing action RS10.

0111Receiving or transmitting on a cell or carrier may refer to receiving or transmitting utilizing a frequency (band) or spectrum associated to the cell or carrier. A cell may generally comprise and/or be defined by or for one or more carriers, in particular at least one carrier for UL communication/transmission (called UL carrier) and at least one carrier for DL communication/transmission (called DL carrier). It may be considered that a cell comprises different numbers of UL carriers and DL carriers. Alternatively or additionally, a cell may comprise at least one carrier for UL communication/transmission and DL communication/transmission, e.g., in TDD-based approaches.

0112A cell may be generally a communication cell, e.g., of a cellular or mobile or wireless communication network, provided by a node like a network node. A cell may be provided in a RAN. A serving cell may be a cell on or via which a network node (the node providing or associated to the cell, e.g., base station or eNodeB) transmits and/or may transmit data (which may be data other than broadcast data) to a user equipment, in particular control and/or user or payload data, and/or via or on which a user equipment transmits and/or may transmit data to the node; a serving cell may be a cell for or on which the user equipment is configured and/or to which it is synchronized and/or has performed an access procedure, e.g., a random access procedure, and/or in relation to which it is in a RRC_connected or RRC_idle state, e.g., in case the node and/or user equipment and/or network follow the LTE-standard. One or more carriers (e.g., uplink and/or downlink carrier/s and/or a carrier for both uplink and downlink) may be associated to a cell.

0113There is disclosed a carrier (or storage) medium arrangement carrying and/or storing at least any one of the program products described herein and/or code executable by processing and/or control circuitry, the code causing the processing and/or control circuitry to perform and/or control at least any one of the methods described herein. A carrier medium arrangement may comprise one or more carrier media. Generally, a carrier medium may be accessible and/or readable and/or receivable by processing circuitry. Storing data and/or a program product and/or code may be seen as part of carrying data and/or a program product and/or code. A carrier medium generally may comprise a guiding/transporting medium and/or a storage medium. A guiding/transporting medium may be adapted to carry and/or carry and/or store signals, in particular electromagnetic signals and/or electrical signals and/or magnetic signals and/or optical signals. A carrier medium, in particular a guiding/transporting medium, may be adapted to guide such signals to carry them. A carrier medium, in particular a guiding/transporting medium, may comprise the electromagnetic field, e.g. radio waves or microwaves, and/or optically transmissive material, e.g. glass fiber, and/or cable. A storage medium may comprise at least one of a memory, which may be volatile or non-volatile, a buffer, a cache, an optical disc, magnetic memory, flash memory, etc. Code may generally comprise instructions.

0114An uplink direction may refer to a data transfer direction from a terminal to a network node, e.g., base station and/or relay station. A downlink direction may refer to a data transfer direction from a network node, e.g., base station and/or relay node, to a terminal. UL and DL may be associated to different frequency resources, e.g., carriers and/or spectral bands. A cell may comprise at least one uplink carrier and at least one downlink carrier, which may have different frequency bands. A network node, e.g., a base station or eNodeB, may be adapted to provide and/or define and/or control one or more cells, e.g., a PCell and/or a LA cell. Cellular DL operation and/or communication of a wireless device or UE may refer to receiving transmissions in DL, in particular in cellular operation and/or from a radio node/network node/gNB/base station. Cellular UL operation of a wireless device or UE may refer to UL transmissions, in particular in cellular operation, e.g. transmitting to a network or radio node/network node/gNB/base station.

0115Configuring (e.g., with or for a configuration) a device like a UE or terminal or radio node or network node may comprise bringing the device into a state in accordance with the configuration. A device may generally configure itself, e.g. by adapting a configuration. Configuring a terminal, e.g. by a network node, may comprise transmitting a configuration or configuration data indicating a configuration to the terminal, and/or instructing the terminal, e.g. via transmission of configuration data, to adapt the configuration configured. Configuration data may for example be represented by broadcast and/or multicast and/or unicast data, and/or comprise downlink control information, e.g. DCI according to 3GPP standardization. Scheduling may comprise allocating resource/s for uplink and/or downlink transmissions, and/or transmitting configuration or scheduling data indicative thereof.

0116In this disclosure, for purposes of explanation and not limitation, specific details are set forth (such as particular network functions, processes and signaling steps) in order to provide a thorough understanding of the technique presented herein. It will be apparent to one skilled in the art that the present concepts and aspects may be practiced in other variants and variants that depart from these specific details.

0117For example, the concepts and variants are partially described in the context of Long Term Evolution (LTE) or LTE-Advanced (LTE-A) or LTE Evolution or NR mobile or wireless or cellular communications technologies; however, this does not rule out the use of the present concepts and aspects in connection with additional or alternative mobile communication technologies such as the Global System for Mobile Communications (GSM). While the following variants will partially be described with respect to certain Technical Specifications (TSs) of the Third Generation Partnership Project (3GPP), it will be appreciated that the present concepts and aspects could also be realized in connection with different Performance Management (PM) specifications.

0118Moreover, those skilled in the art will appreciate that the services, functions and steps explained herein may be implemented using software functioning in conjunction with a programmed microprocessor, or using an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP), a Field Programmable Gate Array (FPGA) or general purpose computer. It will also be appreciated that while the variants described herein are elucidated in the context of methods and devices, the concepts and aspects presented herein may also be embodied in a program product as well as in a system comprising control circuitry, e.g. a computer processor and a memory coupled to the processor, wherein the memory is encoded with one or more programs or program products that execute the services, functions and steps disclosed herein.

0119It is believed that the advantages of the approaches, aspects and variants presented herein will be fully understood from the foregoing description, and it will be apparent that various changes may be made in the form, constructions and arrangement of the exemplary aspects thereof without departing from the scope of the concepts and aspects described herein or without sacrificing all of its advantageous effects. Because the aspects presented herein can be varied in many ways, it will be recognized that any scope of protection should be defined by the scope of the claims that follow without being limited by the description.