synchronization

Abstract

According to an example aspect of the present invention, there is provided an apparatus configured to detect, over an air interface, synchronization signals from a base node of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part transmitted with a first time periodicity, and a second part transmitted with a second, lower, time periodicity, and wherein the apparatus is further caused to detect the first part based on the first time periodicity, and to detect the second part based on the second time periodicity.

Description

SYNCHRONIZATIONFIELD

[0001] The present disclosure relates to synchronization procedures in wireless communication networks.BACKGROUND

[0002] In cellular communication networks, user equipments, UEs, roam in a coverage area of the network and attach themselves to cells of the network.

[0003] To obtain dependable communication with a cell, a UE needs to synchronize itself with the cell, for example in both time and frequency domains, whereby symbol timing and frequency synchronization are obtained, so that orthogonal frequency domain multiplexing, OFDM, based communication may be conducted between the UE and the cell.

[0004] Synchronization signals may be transmitted by the cell, and detected by the UE, to achieve synchronization.SUMMARY

[0005] According to some aspects, there is provided the subject-matter of the independent claims. Some embodiments are defined in the dependent claims. The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments, examples and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0006] According to a first aspect of the present disclosure, there is provided an apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to detect, over an air interface, synchronization signals from a base node of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, whereinthe synchronization signals are organized into a first part transmitted with a first time periodicity, and a second part transmitted with a second, lower, time periodicity, and wherein the apparatus is further caused to detect the first part based on the first time periodicity, and to detect the second part based on the second time periodicity.

[0007] According to a second aspect of the present disclosure, there is provided an apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to transmit, over an air interface, synchronization signals of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part that the apparatus is caused to transmit with a first time periodicity, and a second part that the apparatus is caused to transmit with a second, lower, time periodicity.

[0008] According to a third aspect of the present disclosure, there is provided a method comprising detecting, over an air interface, synchronization signals from a base node of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part transmitted with a first time periodicity, and a second part transmitted with a second lower time periodicity, and wherein the method further comprises detecting the first part based on the first time periodicity, and detecting the second part based on the second time periodicity.

[0009] According to a fourth aspect of the present disclosure, there is provided a method comprising transmitting, over an air interface, synchronization signals of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part transmitted with a first time periodicity, and a second part transmitted with a second, lower, time periodicity.

[0010] According to a fifth aspect of the present disclosure, there is provided an apparatus comprising means for detecting, over an air interface, synchronization signals from a base node of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first parttransmitted with a first time periodicity, and a second part transmitted with a second, lower, time periodicity, and wherein the apparatus further comprises means for detecting the first part based on the first time periodicity, and detecting the second part based on the second time periodicity.

[0011] According to a sixth aspect of the present disclosure, there is provided an apparatus comprising means for transmitting, over an air interface, synchronization signals of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part transmitted by the apparatus with a first time periodicity, and a second part transmitted by the apparatus with a second, lower, time periodicity.

[0012] According to a seventh aspect of the present disclosure, there is provided a non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least detect, over an air interface, synchronization signals from a base node of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part transmitted with a first time periodicity, and a second part transmitted with a second, lower, time periodicity, and wherein the apparatus is further caused to detect the first part based on the first time periodicity, and to detect the second part based on the second time periodicity.

[0013] According to an eighth aspect of the present disclosure, there is provided a non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least transmit, over an air interface, synchronization signals of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part that computer readable instructions cause the apparatus to transmit with a first time periodicity, and a second part that the computer readable instructions cause the apparatus to transmit with a second, lower, time periodicity.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIGURE 1 illustrates an example system in accordance with at least some embodiments of the present invention;

[0015] FIGURE 2A illustrates examples of synchronization signals in accordance with the first embodiment;

[0016] FIGURE 2B is a mapping of SSS parts to PRBs in accordance with at least some embodiments of the present invention;

[0017] FIGURE 2C is a flowchart of UE behaviour in the first embodiment of the present disclosure;

[0018] FIGURE 2D illustrates synchronization signaling;

[0019] FIGURE 2E is a flowchart of UE behaviour in the second embodiment of the present disclosure;

[0020] FIGURE 3 illustrates an example apparatus capable of supporting at least some embodiments of the present invention;

[0021] FIGURE 4 illustrates signalling in accordance with at least some embodiments of the present invention, and

[0022] FIGURE 5 is a flow graph of a method in accordance with at least some embodiments of the present invention.EMBODIMENTS

[0023] Herein are disclosed synchronization mechanisms, wherein plural synchronization signals are provided from a cell to a UE. In detail, the synchronization signals are provided in two parts, which are provided with different time periodicities. Further, a secondary synchronization signal, SSS, may be provided in a first SSS part and a second SSS part, which together form the entire SSS, to enable delivery of the SSS using a lower peak-to-average power ratio, PAPR, as will be discussed herein below. Also the split of the synchronization signals into the two parts provides a lower PAPR, since the SSS isassociated with a higher PAPR than a primary synchronization signal, PSS, which may thus be provided more often than the SSS.

[0024] FIGURE 1 illustrates an example system in accordance with at least some embodiments of the present invention. This system includes base stations 130, 135 in communication with UEs, such as UE 110. A radio link connects base station 130 with UE 110. The radio link may be bidirectional, comprising an uplink, UL, to convey information from UE 110 toward base station 130, and a downlink, DL, to convey information from the base station 130 toward UE 110. A cellular communication system may comprise hundreds or thousands of base stations, of which only two are illustrated in FIGURE 1 for the sake of clarity of the illustration. The base stations may be distributed in that they comprise a centralized unit, CU, and one or more distributed unit, DU. A base station is an example of a base node.

[0025] Base station 130 is further coupled communicatively with core network node 140, which may comprise, for example, a mobility management entity, MME, or access and mobility management function, AMF. The core network node 140 may be coupled with further core network nodes, and with a network 150, which may comprise the Internet or a corporate network, for example. The system may communicate with further networks via network 150. Examples of the further core network nodes, which are not illustrated in FIGURE 1 for the sake of clarity, include gateways and subscriber information repositories. Core network nodes may be virtualized in the sense that they may run as software modules on computing substrates, such that more than one virtualized network node may run on a same computing substrate. The network may be configured to function in accordance with a suitable cellular standard such as long term evolution, LTE, fifth generation, 5G, which is also known as New Radio, NR, or sixth generation, 6G standards as defined by the the 3rdgeneration partnership project, 3GPP. To obtain interoperation, UEs attaching to the network are configured to support a same standard as the network.

[0026] Base station 130 controls, in the example of FIGURE 1 cells 130A and 130B, of which UE 110 is in the situation illustrated in FIGURE 1 attached with cell 130A, and base station 135 controls, in the example of FIGURE 1, cells 135A and 135B. The number of cells, or beams, may be in excess of what is illustrated in FIGURE 1. It is also possible that a base station has a single cell or beam. While illustrated as sector-shaped, cells of a same base station may be omnidirectional and operate on different frequencies, for example.A mobility event may comprise a switch from one beam to another beam of the same cell, or a switch from one cell to another cell. To support mobility procedures, UEs, including UE 110, are configured to conduct mobility measurements to measure signal strengths of adjacent beams and / or cells, and report results of these measurements to the network, which may then take a decision concerning a mobility event, such as a beam change or a cell switch.

[0027] Cells, such as cells 130A, 130B, 135A and 135B are configured to transmit synchronization signals, such as primary synchronization signal, PSS, and secondary synchronization signal, SSS, to enable synchronization of UEs to the frame structure of the cells, for example in connection with initial attach or mobility procedures.

[0028] In 5G, for example, the cell provides a synchronization signal block, SSB, which comprises a PSS, SSS, physical broadcast channel, PBCH and a demodulation reference signal, DMRS, for PBCH demodulation. The SSB may be provided, in 5G, using a unitary resource block of four OFDM symbols in the time domain and 20 physical resource blocks, PRBs, in the frequency domain, wherein each PRB in 5G amounts to twelve subcarriers. In 5G, the PSS is an m-sequence and the SSS is a gold sequence, which is obtained from two m-sequences of equal length using an exclusive-OR operation. The PSS and SSS of 5G are transmitted using binary phase-shift keying, BPSK, while the PBCH of 5G is transmitted using quadrature phase shift keying, QPSK. The PSS is used for acquiring time and frequency synchronization with the cell, while the SSS is used for more precise frequency synchronization, and the PBCH is used in frame and half-frame synchronization and to convey a DMRS, used for slot timing. The PBCH may also be used to convey configuration information the UE may use in accessing the cell, such as an antenna configuration, for example. Further, a physical cell identifier, PCI, is encoded into the PSS and SSS. In detail, the PCI, N^11, may be defined by N^11E{0,1, ... ,335} and A[DG {0,1,2}. PSS is an m-sequence which depends on A[Dand hence there are three possible m-sequences that may be used as the PSS in 5G. SSS is a gold- sequence which depends on bothand N^ .

[0029] Energy efficiency in cellular communication networks is of relevance in terms of both power costs and overall energy usage, as industrial use of energy also has effects on the environment. Sixth generation, 6G, networks will need to be more energy-efficient than prior systems, which may be accomplished, for example, by dynamically switchingcomponents and nodes off or to low-energy states, as well as scaling down network capacity when the demand is lower.

[0030] When transmitting a signal from a cell or a UE, a power amplifier, PA, is used. When a PA is driven beyond its normal, linear operating range, the PA will begin to generate spurious signals, the generation of which amounts to energy consumed in generating noise, and which also expands the bandwidth de facto affected by the transmission, which may cause interference onto adjacent frequency channels. The amount of spurious emissions created onto the adjacent frequency bands may be upper limited by regulation and / or 3 GPP RAN4 radio-frequency, RF, requirements. Those may include e.g. an adjacent channel leakage ratio, ACLR, requirement and a spectrum emission mask. This may be mitigated by limiting the average PA output power to avoid driving the PA beyond the linear range. When this approach is used, the peak power should not exceed the PA’s 1 dB output compression power to reduce spectral re-growth and enhance bit-error-rate, BER, performance. The error vector magnitude, EVM, a metric of modulation quality at the transmitter, will consequently be small when a sufficient back-off is used. The amount of back-off to be chosen for a modulated signal not only depends on the PAPR of the used waveform but also on the probability of PAPR peaks occurring. Backing off the power to avoid PA compression will result in lower power efficiency and thus reduced coverage for the transmitted signal. In 6G, higher frequencies beyond the sub-6 GHz frequency range 1, FR1, are foreseen to become more important, which further increases the relevance of DL energy efficiency and coverage.

[0031] The following table shows the 98th-percentile of average sample-based PAPR values for the PSS, SSS, and also for SSB symbols 1, 2 and 3 having PBCH, PBCH DMRS and SSS in 5G:

[0032] As may be seen from the table, the PSS is associated with lower PAPR than the SSS, and also than the SSS multiplexed with the PBCH. Even though the PSS is the first signal the UE searching for, the SSS, which is provided within the third symbol of the 5G SSB, is the main 5G signal to be used for primary SSB-based beam measurements, as well as for mobility measurements both in the idle and connected modes. SSS transmission involves higher PAPR with or without being multiplexed with PBCH PRBs in frequencydomain and high transmission power back-off is needed, which reduces reception quality of the SSS signal, or equivalently coverage. Especially symbol-based PAPR shows that SSS multiplexing with PBCH further increases the PAPR.

[0033] Synchronization mechanisms are herein described, which enhance synchronization signal structure to make the synchronization signals more energy-efficient to transmit, which simultaneously also improves downlink coverage. In other words, these synchronization mechanisms provide a low PAPR synchronization signal structure and transmission, for example for 6G based systems. The lowered PAPR may translate to an improved synchronization signal coverage, improved energy efficiency (which may result in reduced energy consumption), and / or reduced synchronization signal overhead in beambased cells. Downlink design in 6G for the already defined FR1 band may be OFDM-based in order to enable, for example, multi radio spectrum sharing between 5G and 6G systems. For the higher bands, such as for a 7 - 15 GHz band for 6G, a separate energy efficient structure could be considered as there are no legacy systems to coexist with.

[0034] Based on performance studies, it has been discovered that the SSB channel needs coverage enhancement in certain cases, for example in an urban 4 GHz time-division duplex, TDD scenario, or an urban 28 GHz TDD non-line-of-sight, NLOS outdoor-to-indoor scenario. Therefore, it may be concluded that the SSB channel in general would benefit from a coverage enhancement solution not only in FR1 and the over-6 GHz FR2, but also for a 6G-relevant 7 - 15 GHz band. Further motivation for improving the SSB coverage is that it allows to widen the transmit beams used to convey the synchronization signals. This will reduce the number of beams needed, and will reduce the synchronization signal overhead accordingly.

[0035] In a similar way, even if the coverage would not need to be increased, the reduced PAPR waveform is a way to use the PA(s) in a more efficient way, and therefore reduce the amount of dissipated power. Thus energy savings can be obtained by using lower PAPR signals. From the network perspective, SSB is a periodic block of signals that is periodically transmitted, thus reducing its PAPR would conserve energy in the network.

[0036] The PAPR may be sought to be reduced by providing the synchronization signals organized into a first part transmitted with a first time periodicity, and a second part transmitted with a second lower time periodicity. Further, the SSS may be provided organized into a first SSS part and a second SSS part, which together form the entire SSS,to enable delivery of the SSS using a lower PAPR than when using a gold sequence. The first and second SSS parts are low-PAPR sequences, such as m-sequences, for example.

[0037] In a first embodiment, the first part comprises the PSS, and the second part comprises the SSS and the PBCH. The first part and the second part may, in this embodiment, be provided using the same transmit beams from the base station. In the first embodiment, PSS and the second part have different time domain periodicities. For example, the PSS may be transmitted more frequently, and the higher-PAPR second part, comprising the SSS, may be transmitted less frequently than the PSS. Thus an overall lower PAPR is obtained in the first embodiment by transmitting the higher-PAPR part less frequently. Further, the PSS involves the transmission of a single symbol while the PSS, SSS and PBCH together involve four symbols, wherefore sending the shorter PSS more frequently reduces the average transmission time, which saves energy.

[0038] The second part may comprise, for example, first SSS part, for example a first m-sequence transmitted in the first symbol of the second part of the synchronization signals. Further, the second part may comprise a PBCH symbol transmitted in second symbol of the second part of the synchronization signals, a second SSS part, for example a second m- sequence, transmitted in a third symbol of the second part of the synchronization signals, and a PBCH symbol transmitted in the fourth symbol of the second part of the synchronization signals. There can also be three PBCH symbols, such as a PBCH symbol also in a fifth symbol of the second part of the synchronization signals.

[0039] The first SSS part and / or the separate second SSS part may be used as a demodulation reference signal for the PBCH. Correspondingly, the UE may be configured to assume that the SSS parts are transmitted using the same antenna port as PBCH and thus to share the same quasi co-location, QCL, characteristics, such as doppler spread, doppler shift, average delay and delay spread, and beam.

[0040] In the first embodiment, the symbols of the second part may be also differently ordered, such as the first SSS part in the first symbol, PBCH symbols in the second and third symbols, and the second SSS part in a fourth symbol of the second part of the synchronization signals. This ordering provides the UE with a larger range for the frequency offset estimation but may be having a slightly lower channel estimation performance in high speed / high doppler cases.

[0041] In the first embodiment, the bandwidth (or frequency span) of at least one of the SSS parts is at least equal to the bandwidth of the PBCH and overlapping with PBCH in frequency domain. In the first embodiment, the UE is configured to combine the full SSS information from the first SSS part and the second SSS part. Information encoded in the SSS may include, for example, physical cell ID or physical cell ID together with timing information, such as a block / beam index having PBCH. In the first embodiment, the PBCH transmissions may be transmitted using a discrete Fourier transform spread orthogonal frequency division multiplexing, DFT-s-OFDM waveform. Alternatively, the PBCH may be provided using a cyclic-prefix, CP-OFDM waveform.

[0042] In one variant of the first embodiment, diversity is used for DFT-s-OFDM based PBCH, and the first and second SSS parts are transmitted from two antenna ports using a frequency where each antenna port signal is mapped to every other subcarrier in frequency domain. In other words, port-specific SSS parts from two antenna ports may be transmitted using repetition factor 2. Furthermore, a transmit diversity mode, such as space frequency block coding, SFBC, a frequency-domain version of an Alamouti transmitter, could be used for the PBCH. Alamouti block coding with two antenna ports may be realized e.g. in the groups of two consecutive subcarriers such that the first subcarrier carries [sO, -si*] for the first and the second antenna ports (sO and si being the modulation symbols for two consecutive modulation symbols, and * being complex conjugate), and the second subcarrier carriers [si, sO*] for the first and the second antenna ports, respectively.

[0043] In a second embodiment, the first part of the synchronization signals comprises the PSS, the first SSS part and the second SSS part, and the second part of the synchronization signals comprises the PSS, two PBCH symbols and the second SSS part.

[0044] In the second embodiment, the first and second parts of the synchronization signals may be transmitted using different transmit beams of a base station, for example, the first part may be transmitted using wider beams and higher power, facilitated by lower PAPR, allowing the UE to perform timing acquisition of a cell, frequency synchronization using SSS and PSS, and cell-ID detection. The second part may then be transmitted using narrower beams of the base station and lower power.

[0045] The UE may be configured to use the transmit beam of the base station used to convey the second part of the synchronization signals to determine a transmit beam of the UE for a random access transmission. The UE may be configured to use the transmit beamof the base station used to convey the second part of the synchronization signals to determine a receive beam of the UE for a subsequent downlink transmission. A first reference signal, characterizing the transmit beam of the base station used to convey the first part of the synchronization signals, may be a quasi co-location source at least in terms of a spatial receiver parameter for a second reference signal characterizing the transmit beam of the base station used to convey the second part of the synchronization signals.

[0046] In the second embodiment, the PBCH symbols may be transmitted using a DFT-s-OFDM waveform or a CP-OFDM waveform. The transmit beams used for the second part of the synchronization signals may be used for the physical downlink control channel, PDCCH, and / or physical downlink shared channel, PDSCH, for system information block 1, SIB1, and for other common control signaling.

[0047] A quasi co-location, QCL, source, such as a beam, may be defined by the second SSS part transmitted in the same block as PBCH symbols. If the UE detects the second part of the synchronization signals first, it may acquire cell timing (FFT timing) but only a part of the physical cell ID and not yet the full physical cell ID. In this second embodiment, it may be defined that the first SSS part has less hypothesis, for example cyclic shifts, than the second SSS part and thus the UE could try different first SSS part hypotheses when demodulating and decoding PBCH - it may be assumed that PBCH is scrambled with a scrambling code that depends at least on the full physical cell ID. Alternatively, PBCH may be scrambled with a scrambling code that comprises a second SSS part index but not a first SSS part index. The first SSS part index and, hence, the missing part of the physical cell ID, would be provided in the PBCH payload or as part of the physical layer bits.

[0048] A synchronization index providing slot timing may be provided either in the second SSS part, or as part of physical layer bits, or entirely in the payload of the PBCH. The time periodicity used in transmitting the first part of the synchronization signals may be, for example, 10 or 20 milliseconds. The time periodicity used in transmitting the second part of the synchronization signals may be, for example, 40 or 80 milliseconds.

[0049] In the second embodiment, if the first and second parts of the synchronization signals would be, as a result of their time periodicities, in the same half-frame, the base station may be configured to transmit the second part of the synchronization signals and abstain from transmitting the first part of the synchronization signals. To avoid this collision,the first and second parts of the synchronization signals may be configured with a half-frame or frame level time offset so that these parts will not overlap.

[0050] In the second embodiment, alternatively to what is described above, the second part of the synchronization signals may comprise a symbol sequence of a first PBCH symbol, the first SSS part, the second SSS part, and a second PBCH symbol. A yet further alternative is a symbol sequence comprising the first SSS part, a first PBCH symbol, the second SSS part, and a second PBCH symbol, in which case the first part of the synchronization signals is the first SSS part, the PSS, and the second SSS part.

[0051] In case that there is a time offset preventing first and second parts of the synchronization signals from overlapping, the second part of the synchronization signals may comprise PSS and SSS in the form of a gold sequence constructed from two m- sequences, the first SSS part and the second SSS part, and PBCH that are multiplexed in time, or partially also in frequency as in 5G SSB.

[0052] In the second embodiment, when different-width beams are used, the required number of wider beams used for the first part, transmitted e.g. with 20 ms periodicity, may be reduced. More narrow beams, used for PBCH decoding, QCL reference for downlink data reception (e.g. PDCCH and PDSCH for SIB1, paging, other system info reception), etc. may be transmitted less frequently, as described herein above, to communicate the second part of the synchronization signals.

[0053] FIGURE 2A illustrates examples of synchronization signals in accordance with the first embodiment. There are five alternatives 201, 202, 203, 204 and 205 illustrated for the second part of the synchronization signals, the first part being only the PSS in the first embodiment. In the figure, “1” denotes the first SSS part, “2” denotes the second SSS part, and “B” denotes a PBCH symbol. Frequency is along the vertical direction and time along the horizontal direction of the figure. The PSS may be part of the block when the periodicities of the first and second parts of the synchronization signals happen to agree, that is, PSS may be transmitted in an adjacent symbol of the block, either side is possible, or transmitted separately. The length of the sequences, four units, is chosen for clarity of the illustration rather than intending to denote technical substance. In alternative 203, the first SSS part and the first PBCH symbol appear abbreviated because in this alternative, the PBCH is split into two parts with differing transmit bandwidths. The bandwidth of the firstPBCH symbol is aligned with the first SSS part, and the bandwidth of the second PBCH symbol is aligned with the second SSS part.

[0054] FIGURE 2B is a mapping of SSS parts to PRBs in accordance with at least some embodiments of the present invention. To support DFT-s-OFDM based Alamouti transmit diversity for the PBCH, the first SSS part and the second SSS parts are used to get transmit antenna port specific channel estimates, the first SSS part and the second SSS part may each be mapped to PRBs as illustrated in FIGURE 2B. In the SSS row, “1” denotes the first SSS part and “2” denotes the second SSS part. Frequency is along the horizontal line, and in the PRB row, the numbers denote PRB numbers.

[0055] FIGURE 2C is a flowchart of UE behaviour in the first embodiment of the present disclosure. UE selects the frequency band to search for PSS, for example in a 6G system. Initially, in phase 210, the UE determines a frequency band and a synchronization raster for the frequency band, for example based on a standardized synchronization raster defined for the band.

[0056] Processing advances from phase 210 to phase 220, where the UE searches for PSS around the synchronization raster points with a rough frequency offset and FFT / symbol timing estimation. By searching around the raster points it is here meant that the UE performs maximum likelihood, ML, searching using, for example, a fixed grid of frequency positions around and on each synchronization raster point to determine the rough frequency offset. Thus, for example, the UE may perform PSS detection in offsets -N x 6kHz, 0, +N x 6kHz positions relative to each synchronization raster point when assuming 30 kHz subcarrier spacing, SCS, where N could be 1 to 6 or 1 to 8, for example.

[0057] Once PSS is detected, processing advances to phase 230 where the first SSS part and the second SSS part are detected. Finally, in phase 240 the UE perform finer synchronization, determines the physical cell ID from the first SSS part and the second SSS part, and receives at least one PBCH symbol. The UE may determine slot timing from the first SSS part and the second SSS part, and layer- 1 reference signal received power, RSRP, measurement parameters for the cell and beam. More accurate frequency synchronization may be obtained by calculating a phase shift on the same subcarriers between the first SSS part and the second SSS part, for example. Further, channel estimates may be obtained for PBCH demodulation, and the UE may perform PBCH demodulation and decoding.

[0058] Turning then again to the second embodiment, in this embodiment the system transmits, for example, wider beams comprising PSS, the first SSS part and the second SSS part with 20 or 25 millisecond periodicity providing basic time and frequency synchronization, as well as physical cell ID provisioning. More narrow beams may be used to provide PBCH, yielding increased PBCH detection performance, and further time (slot, half frame and frame) and frequency synchronization, for example with a 40 or 80 millisecond periodicity.

[0059] The second embodiment may involve sending the first part of the synchronization signals with wider beams than what are used to send the second part of the synchronization signals, to limit or reduce the required number of SSBs in a cell. For that, the first part of the synchronization signals is designed to have lower output back-off, OBO, facilitating higher transmit power and in turn better coverage for the first part with a wider beam pattern that is at least on par with the coverage of other downlink transmissions using narrower beams. Such downlink transmissions may comprise, for example, PDCCH + PDSCH carrying SIB1, paging and other system information. A low OBO also means that the first part can be transmitted with maximum or near-maximum transmission power. The remaining part of the overall synchronization signals, the second part thereof, may then be transmitted using a narrower beam and a lower power, enabling the UE to estimate the narrower beam to be used for detection of PDCCH + PDSCH carrying SIB1, and, for example, for transmission of a random access message from the UE.

[0060] In FIGURE 2D, the first part of the synchronization signals are illustrated for a first five-millisecond half-frame block. In the figure, a beam used to convey the first part of the synchronization signals is assumed to have double beam width, reducing the number of required synchronization signal transmit blocks 250 by half.

[0061] The second part of the synchronization signals are illustrated in the 5thhalfframe block of FIGURE 2D. The second part is transmitted with narrower beams, requiring 8 blocks 260 to be transmitted. It should be noted that PSS and second SSS part positions in both parts of the synchronization signals remain unchanged. Assuming that existing 5G synchronization requires a four-symbol entire SSB transmitted on 8 beams with a 20 millisecond period, the SSBs occupy 8x4x2 = 64 symbols over a period of 40 millisecond. In the second embodiment of the present disclosure, on the other hand, the first part of the synchronization signals requires four beams and the second part of the synchronizationsignals is transmitted on eight beams with 40 millisecond period, the synchronization signals overall occupy 4x3 + 8x4 = 44 symbols over a period of 40 milliseconds.

[0062] FIGURE 2E is a flowchart of UE behaviour in the second embodiment of the present disclosure. In phase 270, the UE determines a frequency band and a synchronization raster for the frequency band, for example based on a standardized synchronization raster defined for the band. Processing advances to phase 272, where the UE searches for PSS around the synchronization raster points with a rough frequency offset and FFT / symbol timing estimation. By searching around the raster points it is meant that the UE performs maximum likelihood, ML, searching using, for example, a fixed grid of frequency positions around and on each synchronization raster point to determine the rough frequency offset. Thus, for example, the UE may perform PSS detection in offsets -N x 6kHz, 0, +N x 6kHz positions relative to a synchronization raster point when assuming 30 kHz subcarrier spacing, SCS, where N could be 1 to 6 or 1 to 8, for example.

[0063] Upon detection of PSS, processing advances to phase 274, where the UE searches for the second SSS part and once this is detected, the UE uses it to fine-tune the frequency synchronization initially obtained using the PSS. Subsequently, processing advances to phase 276, where the UE determines whether the symbol after PSS is the first SSS part or a first PBCH symbol.

[0064] If it is the first SSS part, processing advances to phase 278, where the UE obtains the PCI from the first and second SSS parts. In embodiments where slot timing is included in SSS, the UE obtains slot timing, partly or fully, from the first and second SSS parts. Further, more accurate frequency synchronization may be obtained by calculating a phase shift on the same subcarriers between the first and second SSS parts. Yet even further, channel estimates may be determined for PBCH demodulation and a layer- 1, LI, RSRP measurement of the cell may be obtained, for instance for use in mobility measurements.

[0065] From phase 278 processing advances to phase 280, where the UE waits for PBCH, and upon detection of a first PBCH symbol, channel estimates from the second SSS part may be used for demodulation of the PBCH. In case first SSS part index is included in the PBCH payload, the UE may determine PCI from SSS1 and SSS2 indexes. In some embodiments, slot timing is partly or fully obtained from the first SSS part and PBCH content. The type of the first part of the synchronization signals may be determined, and Ll-RSRP measurement of the beam may be obtained.

[0066] Subsequently, the UE may obtain the system information of the cell, phase 282, and estimate Doppler, time and beam parameters for further downlink channel reception, such as for PDCCH and PDSCH reception, phase 284. These parameters may be re-used from the second SSS part communication.

[0067] On the other hand, if in phase 276 the symbol after PSS is determined to be a PBCH symbol, then processing advances from phase 276 to phase 286, where the PBCH symbol is received, and the PCI is possibly determined, slot timing is estimated, and an Ll- RSRP measurement is obtained for the beam. Subsequently, phase 288, the first SSS part is sought, and when received it is used to fine-tune frequency synchronization and define an Ll-RSRP measurement for the cell. Processing advances then to phase 282 which is a decision point concerning obtaining the SI. In phase 282, whether reached from phase 280 or 288, if the SI is not obtained, then processing advances from phase 282 back to phase 272.

[0068] FIGURE 3 illustrates an example apparatus capable of supporting at least some embodiments of the present invention. Illustrated is device 300, which may comprise, for example, a mobile communication device such as UE 110 or, in applicable parts, a base station 130 of FIGURE. Comprised in device 300 is processor 310, which may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multi-core processor comprises more than one processing core. Processor 310 may comprise, in general, a control device. Processor 310 may comprise more than one processor. When processor 310 comprises more than one processor, device 300 may be a distributed device wherein processing of tasks takes place in more than one physical unit. Processor 310 may be a control device. A processing core may comprise, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Zen processing core designed by Advanced Micro Devices Corporation. A processing core or processor may be, or may comprise, at least one qubit. Processor 310 may comprise at least one Qualcomm Snapdragon and / or Intel Atom processor. Processor 310 may comprise at least one application-specific integrated circuit, ASIC. Processor 310 may comprise at least one field- programmable gate array, FPGA. Processor 310, optionally together with memory and computer instructions, may be means for performing method steps in device 300, such as detecting, accepting, using, receiving or transmitting. Processor 310 may be configured, at least in part by computer instructions, to perform actions.

[0069] A processor may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with embodiments described herein. As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in only analogue and / or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analogue and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a UE or base station, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0070] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0071] Device 300 may comprise memory 320. Memory 320 may comprise randomaccess memory and / or permanent memory. Memory 320 may comprise at least one RAM chip. Memory 320 may be a computer readable medium. Memory 320 may comprise solid- state, magnetic, optical and / or holographic memory, for example. Memory 320 may be at least in part accessible to processor 310. Memory 320 may be at least in part comprised in processor 310. Memory 320 may be means for storing information. Memory 320 may comprise computer instructions that processor 310 is configured to execute. When computer instructions configured to cause processor 310 to perform certain actions are stored in memory 320, and device 300 overall is configured to run under the direction of processor 310 using computer instructions from memory 320, processor 310 and / or its at least one processing core may be considered to be configured to perform said certain actions. Memory 320 may be at least in part external to device 300 but accessible to device 300. Memory 320 may be transitory or non-transitory. The term “non-transitory”, as used herein, is a limitationof the medium itself (that is, tangible, not a signal) as opposed to a limitation on data storage persistency (for example, RAM vs. ROM).

[0072] Device 300 may comprise a transmitter 330. Device 300 may comprise a receiver 340. Transmitter 330 and receiver 340 may be configured to transmit and receive, respectively, information in accordance with at least one cellular or non-cellular standard. Transmitter 330 may comprise more than one transmitter. Receiver 340 may comprise more than one receiver. Transmitter 330 and / or receiver 340 may be configured to operate in accordance with global system for mobile communication, GSM, wideband code division multiple access, WCDMA, 5G, long term evolution, LTE, IS-95, wireless local area network, WLAN, Ethernet and / or worldwide interoperability for microwave access, WiMAX, standards, for example.

[0073] Device 300 may comprise a near-field communication, NFC, transceiver 350. NFC transceiver 350 may support at least one NFC technology, such as NFC, Bluetooth, Wibree or similar technologies.

[0074] Device 300 may comprise user interface, UI, 360. UI 360 may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device 300 to vibrate, a speaker or a microphone. A user may be able to operate device 300 via UI 360, for example to accept incoming telephone calls, to originate telephone calls or video calls, to browse the Internet, to manage digital files stored in memory 320 or on a cloud accessible via transmitter 330 and receiver 340, or via NFC transceiver 350, and / or to play games.

[0075] Device 300 may comprise or be arranged to accept a user identity module 370. User identity module 370 may comprise, for example, a subscriber identity module, SIM, card installable in device 300. A user identity module 370 may comprise information identifying a subscription of a user of device 300. A user identity module 370 may comprise cryptographic information usable to verify the identity of a user of device 300 and / or to facilitate encryption of communicated information and billing of the user of device 300 for communication effected via device 300.

[0076] Processor 310 may be furnished with a transmitter arranged to output information from processor 310, via electrical leads internal to device 300, to other devices comprised in device 300. Such a transmitter may comprise a serial bus transmitter arrangedto, for example, output information via at least one electrical lead to memory 320 for storage therein. Alternatively to a serial bus, the transmitter may comprise a parallel bus transmitter. Likewise processor 310 may comprise a receiver arranged to receive information in processor 310, via electrical leads internal to device 300, from other devices comprised in device 300. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from receiver 340 for processing in processor 310. Alternatively to a serial bus, the receiver may comprise a parallel bus receiver.

[0077] Device 300 may comprise further devices not illustrated in FIGURE 3. For example, where device 300 comprises a smartphone, it may comprise at least one digital camera. Some devices 300 may comprise a back-facing camera and a front-facing camera, wherein the back-facing camera may be intended for digital photography and the frontfacing camera for video telephony. Device 300 may comprise a fingerprint sensor arranged to authenticate, at least in part, a user of device 300. In some embodiments, device 300 lacks at least one device described above. For example, some devices 300 may lack a NFC transceiver 350 and / or user identity module 370.

[0078] Processor 310, memory 320, transmitter 330, receiver 340, NFC transceiver 350, UI 360 and / or user identity module 370 may be interconnected by electrical leads internal to device 300 in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a master bus internal to device 300, to allow for the devices to exchange information. However, as the skilled person will appreciate, this is only one example and depending on the embodiment various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the present invention.

[0079] FIGURE 4 illustrates signalling in accordance with at least some embodiments of the present invention, in particular the first embodiment. On the vertical axes are disposed, on the left, UE 110 of FIGURE 1, and on the right, base station 130 of FIGURE 1. Time advances from the top toward the bottom.

[0080] In phase 410, base station 130 provides to UE 110 the PSS, forming the first part of the synchronization signals. Based on the PSS, the UE performs initial time and frequency synchronization with the cell, phase 420. Subsequently, in phase 430 base station 130 provides to UE 110 the second part of the synchronization signals, comprising the SSSand PBCH, the SSS being provides as the first SSS part and the second SSS part, these SSS parts being m-sequences. Following receipt of the second part of the synchronization signals, the UE completes synchronization into the cell, phase 440, enabling a subsequent transmission of a random access channel, RACH, preamble to the base station in phase 450.

[0081] FIGURE 5 is a flow graph of a method in accordance with at least some embodiments of the present invention. The phases of the illustrated method may be performed in UE 110, for example, or in a control device configured to control the functioning thereof, when installed therein.

[0082] Phase 510 comprises detecting, over an air interface, synchronization signals from a base node of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part transmitted with a first time periodicity, and a second part transmitted with a second lower time periodicity, and wherein the first part is detected based on the first time periodicity, and the second part is detected based on the second time periodicity.

[0083] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0084] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0085] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on theirpresentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0086] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0087] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0088] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

[0089] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.INDUSTRIAL APPLICABILITY

[0090] At least some embodiments of the present invention find industrial application in wireless communication.ACRONYMS LISTDMRS demodulation reference signalNLOS non-line-of-sightOBO output back-off OFDM orthogonal frequency domain multiplexingPAPR peak-to-average power ratioPSS primary synchronization signalSSS secondary synchronization signalTDD time-division duplex QCL quasi co-locationREFERENCE SIGNS LIST

Claims

CLAIMS:

1. An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to:- detect, over an air interface, synchronization signals from a base node of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part transmitted with a first time periodicity, and a second part transmitted with a second, lower, time periodicity, and wherein the apparatus is further caused to detect the first part based on the first time periodicity, and to detect the second part based on the second time periodicity.

2. The apparatus according to claim 1, wherein the first part comprises the PSS, and the second part comprises the SSS and the PBCH.

3. The apparatus according to claim 1 or 2, wherein the SSS is composed of a first SSS part and of a second SSS part transmitted as separate synchronization signals.

4. The apparatus according to claim 3, wherein the first part comprises the PSS, the first SSS part and the second SSS part, and the second part comprises the second SSS part and the PBCH.

5. The apparatus according to claim 4, wherein the second part further comprises the PSS or the first SSS part.

6. The apparatus according to claim 4 or 5, wherein the PSS, the first SSS part and the second SSS part are modulated by respective first, second and third m-sequences, and wherein first, second and third parameters used for generating the respective first, second and third m-sequences are based on a physical cell identifier.

7. The apparatus according to any of claims 1 - 5, further caused to receive the first part via a first transmit beam of the base node, and to receive the second part via a second transmit beam of the base node, the first transmit beam of the base node being different from the second transmit beam of the base node.

8. The apparatus according to any of claims 1 - 7, wherein the apparatus is further caused to receive the PBCH using discrete Fourier transform spread orthogonal frequency division multiplexing, DFT-s-OFDM.

9. The apparatus according to any of claims 1 - 8, wherein the apparatus is further caused to use at least the first part for one or more of the following:- acquiring time and frequency synchronization with the base node;- obtaining a physical cell identifier of a cell; or- cell measurements, and wherein the apparatus is further caused to use at least the second part for one or more of the following:- acquiring or adjusting time and / or frequency synchronization with the base node; or- obtaining a configuration for accessing the cell.

10. An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to:- transmit, over an air interface, synchronization signals of a network, the synchronization signals comprising at least a primary synchronization signal, PSS, a secondary synchronization signal, SSS, and a physical broadcast channel, PBCH, wherein the synchronization signals are organized into a first part that the apparatus is caused to transmit with a first time periodicity, and a second part that the apparatus is caused to transmit with a second, lower, time periodicity.

11. The apparatus according to claim 10, wherein the first part comprises the PSS, and the second part comprises the SSS and the PBCH.

12. The apparatus according to claim 10 or 11, wherein the SSS is composed of a first SSS part and of a second SSS part, and wherein the apparatus is further caused to transmit the first SSS part and the second SSS part as separate synchronization signals.

13. The apparatus according to claim 12, wherein the first part comprises the PSS, the first SSS part and the second SSS part, and the second part comprises the second SSS part and the PBCH.14 The apparatus according to claim 13, wherein the second part further comprises the PSS or the first SSS part.

15. The apparatus according to claim 13 or 14, wherein the PSS, the first SSS part and the second SSS part are modulated by respective first, second and third m-sequences, wherein the apparatus is further caused to use first, second and third parameters for generating the respective first, second and third m-sequences, and wherein the first, second and third parameters are based on a physical cell identifier.

16. The apparatus according to any of claims 10 - 15, wherein the apparatus is further caused to transmit the first part via a first transmit beam of the apparatus and to transmit the second part via a second transmit beam of the apparatus, the first transmit beam being different from the second transmit beam.

17. The apparatus according to any of claims 10 - 16, wherein the apparatus is further caused to transmit the PBCH using discrete Fourier transform spread orthogonal frequency division multiplexing, DFT-s-OFDM.

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