Downlink synchronization method of a user device to a 5G cellular network and associated user device

Abstract

Downlink Synchronization Method of User Equipment to a 5G Cellular Network and Associated User Equipment. The downlink synchronization method (100) of user equipment to a 5G cellular network comprises: - a receiving step (105); - a first frequency-time synchronization step (110), comprising first estimates of a frequency gap (DF1) and a time gap (DT1) between the transmitted and received signals (S) and a determination of a first component (N_PSS) of the cell number (N_cell) by autocorrelation and cross-correlation; and - a second frequency-time synchronization step (120), comprising second estimates of the frequency gap (DF2) and the time gap (DT2) by autocorrelation and cross-correlation, taking into account the first component (N_PSS). The second estimates are more accurate than the first estimates. Figure for the abstract: Figure 3

Description

Title of the invention: Downlink synchronization method of a user device to a 5G cellular network and associated user device

[0001] The present invention relates to a downlink synchronization method of a user device to a 5G cellular network.

[0002] It also relates to user equipment configured to implement such a process.

[0003] The article "Synchronization Procedure in 5GNR Systems" (A. Omri, M. Shaqfeh, A. Ali and H. Alnuweiri, in IEEE Access, vol. 7, pp. 41286-41295, 2019) is a reference concerning the downlink synchronization procedure of a user device to a 5G cellular network according to the 5G standard of the 3GPP (3rd Generation Partnership Project) consortium. This article describes, in particular, the sequence of operations to be performed by a user device to retrieve the cell identity of a base station and to decode the physical broadcast channel.

[0004] We also know from document EP 0 665 665 B1 an algorithm enabling a modem to synchronize with a digital data transmitter while being robust to interference thanks to spatial or space-time processing.

[0005] However, applying the processing proposed by document EP 0 665 665 B1 to the synchronization procedure of user equipment to the 5G cellular network would require a very large number of correlations for each of the primary synchronization sequences, secondary synchronization sequences, and demodulation reference symbols of the physical broadcast channel potentially emitted by the base station, which is not feasible for user equipment within a reasonable timeframe for the application. Therefore, the downlink synchronization methods to a 5G network currently implemented by user equipment are not robust to interference.

[0006] The aim of the invention is then to propose a downlink synchronization method from a user device to a 5G cellular network that is more robust to interference.

[0007] To this end, the invention relates to a downlink synchronization method of a user device to a 5G cellular network, comprising:

[0008] - a step of receiving a signal emitted by a base station, the signal emitted comprising at least one synchronization signal block belonging to a burst of synchronization signal blocks emitted by the base station and identified within the burst by a block index, the base station belonging to a cell characterized by a cell number, the cell number being a function of a first component on which a primary synchronization sequence of the synchronization block depends and a second component on which a secondary synchronization sequence of the synchronization block depends, the synchronization block further comprising data from a physical broadcast channel;

[0009] - a first step of synchronization in frequency and time, during wherein a first estimate of a frequency difference between the signal emitted by the base station and a signal received by the user equipment during the reception stage, a first estimate of a time difference between the signal emitted by the base station and the received signal, and a determination of the first component of the cell number are performed by autocorrelation of a first portion of the received signal and cross-correlation of the first portion of the received signal with a first set of reference sequences, the first portion of the received signal comprising at least one of the primary synchronization sequences of the received signal and the first set of reference sequences comprising a reference signal for each of the primary synchronization sequences to be tested; and

[0010] - a second step of synchronization in frequency and time, during in which a second estimate of the frequency gap and a second estimate of the time gap are made by autocorrelation of a second portion of received signal and cross-correlation of the second portion of received signal with a second set of reference sequences after correction of the second portion of received signal using the first estimates of the frequency and time gaps, the primary synchronization sequence being fixed, the second estimates being made taking into account the first component determined during the first time and frequency synchronization step, the second estimates of the frequency gap and the time gap being more accurate than the first estimates of the frequency gap and the time gap respectively.

[0011] Thanks to the invention, the number of correlations to be performed is significantly reduced by dividing the process into two successive steps of increasing precision. In particular, the first synchronization step provides information about the signal that makes it possible to reduce the search field during the second synchronization step. Thus, the process can be carried out with the computing capabilities of user equipment in a time frame consistent with the application, and allows the user equipment to synchronize with a 5G network base station even in the presence of interference.

[0012] According to other advantageous aspects of the invention, the synchronization method comprises one or more of the following features, taken individually or in all technically possible combinations:

[0013] - the second frequency and time synchronization step comprises a sub- filtering step, during which the second corrected portion of the received signal is filtered, so as to limit the second portion of the received signal to the primary and secondary synchronization sequences;

[0014] - the received signal is a multi-channel signal and the method includes a step of recombination and demodulation, during which: • a third portion of the received signal is corrected using the second estimates of the frequency and time deviations, the third portion of the received signal including at least one synchronization block; • a spatial or spatio-temporal filter is calculated by autocorrelation of the third portion of the corrected received signal and cross-correlation of the third portion of the corrected received signal with a reference signal, belonging to the second set of reference sequences and having been retained during the second step of frequency and time synchronization; • the third corrected portion of the received signal is recombined into a single-channel received signal portion using the spatial or spatiotemporal filter; and • the single-channel received signal portion is demodulated, providing received orthogonal frequency distribution symbols;

[0015] - the method further comprises a sequence estimation step of secondary synchronization, in which a determination of the second component of the cell number is carried out by correlation of the received orthogonal frequency division symbols or of the multi-channel received signal portion with a third set of reference sequences, the third set of reference sequences comprising secondary synchronization sequences to be tested, the primary synchronization sequence being fixed;

[0016] - the second portion of the received signal comprises at least the sequence of secondary synchronization of the received signal and the second set of reference sequences includes a reference signal for each of the secondary synchronization sequences to be tested, and the second frequency and time synchronization step further includes the determination of a value for the second component of the cell number;

[0017] - the method further includes a step of determining the cell number in function of the first component and the second component;

[0018] - the method further comprises a step of determining the block index by correlating at least a part of the received orthogonal frequency distribution symbols with a set of reference symbols, corresponding to the block indices to be tested;

[0019] - the method further comprises a channel equalization and demodulation step of physical dissemination, during which: • the physical broadcast channel is estimated from the received orthogonal frequency distribution symbols, knowing the block index within the burst and the cell number; • a single-channel frequency equalization of the orthogonal frequency distribution symbols is performed using the estimated physical diffusion channel, providing equalized symbols from the physical diffusion channel; and • the equalized symbols of the physical broadcast channel are demodulated, providing the logarithm of a likelihood ratio for each bit of a codeword, corresponding to the master information block contained in the physical broadcast channel data;

[0020] - the method further comprises a channel equalization and demodulation step of physical dissemination, during which: • the multi-way physical diffusion channel and a spatial autocorrelation of noise and interference is estimated from a fourth portion of the received signal, corrected using the second estimates of the frequency and time gaps, knowing the block index within the burst and the cell number, the fourth portion of the received signal including at least one synchronization block; • Frequency equalization of the fourth portion of the received signal is performed by a minimum root mean square error-interference rejection combination equalizer, known as MMSE-IRC type, providing equalized symbols of the physical broadcast channel; and • the equalized symbols of the physical broadcast channel are demodulated, providing the logarithm of a likelihood ratio for each bit of a codeword, corresponding to the master information block contained in the physical broadcast channel data;

[0021] - the process further comprises a recombination and decoding step of physical broadcast channel data during which the master information block is decoded from the logarithms of the codeword likelihood ratios, providing parameters to complete the synchronization of user equipment 3 to the 5G cellular network.

[0022] The invention also relates to user equipment intended to be connected to a 5G cellular network configured to implement a synchronization method as defined above.

[0023] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0024] [Fig-1] [Fig.1] is a schematic diagram of an initial access procedure for a user equipment to a base station according to the 5G standard of the 3GPP consortium;

[0025] [Fig.2] [Fig.2] is a diagram of a synchronization block emitted by a station of based on the 5G standard of the 3GPP consortium;

[0026] [Fig.3] [Fig.3] is a block diagram of a synchronization method according to the invention;

[0027] [Fig.4] [Fig.4] is a block diagram of a first synchronization step in frequency and time of the synchronization process according to the invention;

[0028] [Fig.5] [Fig.5] is a block diagram of a second synchronization step in frequency and time of the synchronization process according to a first implementation of the invention;

[0029] [Fig.6] [Fig.6] is a block diagram of a second synchronization step in frequency and time of the synchronization process according to a second implementation of the invention;

[0030] [Fig.7] [Fig.7] is a block diagram of a recombination step and demodulation of the synchronization process according to the invention;

[0031] [Fig.8] [Fig.8] is a block diagram of a primary synchronization sequence estimation step of the synchronization process according to the first implementation of the invention;

[0032] [Fig.9] [Fig.9] is a block diagram of a step in determining the block index of the synchronization method according to the invention;

[0033] [Fig. 10] [Fig. 10] is a block diagram of an equalization and demodulation step of the synchronization process according to a first example of the invention;

[0034] [Fig. 11] [Fig. 11] is a block diagram of an equalization and demodulation step of the synchronization process according to a second embodiment of the invention.

[0035] In [Fig. 1], a user device 3 is intended to connect to a cellular radio communication network following the 5th Generation - New Radio (5G-NR - New Radio) standard of the 3GPP (3rd Generation Partnership Project) consortium. This is, for example, a commercial civilian network or another network based on this standard.

[0036] The network comprises base stations 1, one of which is shown in [Fig. 1]. Each base station 1 belongs to a cell, which is an area of ​​space covered by one or more base stations 1, and characterized by a cell number N_cell. The cell number N_cell is a function of a first component N_PSS and a second component N_SSS.

[0037] Base station 1 periodically transmits bursts of SSB synchronization blocks. A burst comprises one or more SSB synchronization blocks. The different SSB synchronization blocks of a burst can be transmitted in distinct directions as directional beams, or in the same direction by means of a respective omnidirectional antenna. The bursts are broadcast to user equipment via a physical broadcast channel.

[0038] Each SSB synchronization block is identified within the burst 5 that contains it by a block index i_SSB. According to version 18 of the 3GPP standard, an SSB synchronization block, shown in [Fig. 2], occupies 4 orthogonal frequency-division multiplexing (OFDM) modulation symbols in time, shown on the x-axis of [Fig. 2], and occupies 240 subcarriers, shown on the y-axis of [Fig. 2]. An SSB synchronization block comprises a primary PSS synchronization sequence, a secondary SSS synchronization sequence, a DMRS demodulation reference sequence for the physical broadcast channel, and PBCH physical broadcast channel data. The PBCH physical broadcast channel data allows the transmission of a 32-bit information block through 432 quadrature phase-modulated symbols (QPSK modulation) encoded with a polar code.The Physical Broadcast Channel (PBCH) data contains the message of a 24-bit Logical Broadcast Channel (BCH) and 8 bits of information about the cell's timing configuration and System Information Blocks (SSBs). Within the BCH, 23 bits correspond to the Master Information Block (MIB), which provides information about the cell's OFDM grid configuration (frequency resolution, system frame number, etc.), a cell saturation level (cellBarred; this indicator signals if the cell can no longer accept a user), and other information necessary for user equipment to synchronize with the cell, track System Information Blocks (SIBs), and initiate a connection request. These concepts are detailed in the 3GPP 5G NR standard technical specifications, TS38.331.

[0039] The primary PSS synchronization sequence depends on the first component N_PSS of the cell number N_cell. In the mathematical expressions that follow, the first component N_PSS is denoted by . The primary PSS synchronization sequence is an m-sequence defined by:

[0040] dPSS(n) = l-2xPSS(m)

[0041] where: (n+43N ( ^)mod 127 avec = 126 ' et

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049] - XpS^îj is a binary sequence obtained by a shift register with linear feedback, where: x PSS (i + 7) = (x PSS (i+4)+x PSS U))mod 2, And x PSS (6:0) = [ 1,1, 1,0,1,1, 0]. The PSS primary synchronization sequences occupy symbol 0 of an SSB synchronization block, and they are allocated to subcarriers k = 56 + n for n = 0, ..., 126, relative to the start of an SSB synchronization block. There are three possible PSS primary synchronization sequences. The secondary synchronization sequence SSS depends on the second component N_SSS of the cell number N_cell. In the mathematical expressions that follow, the second component N_SSS is denoted by . The secondary synchronization sequence SSS is a product of two m-sequences, defined by: dsss^ = [l-2xSSSfo(^o)][l-2xsssA(^i)]z Or : m0 = (n+15^] +5A^mod 127 (n+ [ A / ÿ^mod 112] )mod 127 with n = 0.....126. - the binary sequences (a, b) are obtained using registers with linear feedback lag, with: x ss ^0(i+7) = (x S s S ,o(ï+4) +x ss^0(ï) )mod 2 x ssso (6:O) = [0,0, 0,0, 0,0,1], • x SSSJ (i+7) = (x sssl (i+1)+x sssl (i) )mod 2 x sssl (6:0) = [0,0, 0,0, 0,0,1]. Secondary synchronization sequences (SSS) occupy symbol 2 of an SSB synchronization block; they are allocated to subcarriers k = 56 + n for n = 0, ..., 126, relative to the beginning of the SSB synchronization block. There are 1008 possible secondary synchronization sequences (SSS), but 336 for a given primary synchronization sequence (PSS). The DMRS demodulation reference sequence includes quadrature phased kung fu (QPSK) modulation symbols, defined by: r DMRs( in ^ [ (l-2c(2zn) ) + j( l-2c(2m +1) ) ], m= 0, ..., 143

[0050] where c(n) = (x1(n+Nc) + x / n + Nc))mod 2 , with : N c =1600, x1(n + 31) = (x^n+3) +x1(n) )mod 2 x2(n+31) = (x2(n+ 3) + x2(n+2) + x2(n+1) + x2(n) )mod 2 ^(0) = 1, • ^(n) = 0, pourn= L 30.

[0051] The register X} ( H ) is initialized such that „ _ ^30 , ., and in the case of the ^init 2jj-QX2^ i physical distribution channel, Cùüt = 2 1 '( Îssb +1 ) ( [ 1 + 1 ) + 2 6 ( 1ssb+ 1 ) + ( N^ 2 mod 4) , where iSSB is a parameter that depends on the burst 5 configuration and The block index I_SSB is the cell number N_cell. The sequence of The DMRS demodulation reference occupies 60 subcarriers on symbols 1 and 3 of the SSB synchronization block, with subcarrier indices k = 0 + V, ..., 2, 36 + V, and 24 subcarriers on symbol 2, with k = 0 + v, 44 + v, 192 + v, 236 + v , and v = mod 4 - The sequence m) is associated with these resources in ascending order of subcarrier indices first, and then of symbols. We denote 'c the number of possibilities for the DMRS demodulation reference sequence for a given PSS-SSS sequence pair.

[0052] Thus, there are 3*336*Nÿgp, or 10087^^ possible configurations of the SSB synchronization block.

[0053] The data for the PBCH physical broadcast channel comprises a master information block MIB and is scrambled with a sequence dependent on the block index I_SSB. Symbols 1 and 3 of the SSB synchronization block each have 240 subcarriers allocated for the physical broadcast channel (including the DMRS demodulation reference sequence), and symbol 2 has 96 subcarriers (including the DMRS demodulation reference sequence). The PBCH physical broadcast channel data is associated with all of these resources, except those already occupied by the DMRS demodulation reference sequence.

[0054] The number of SSB synchronization blocks in a 5-bit burst is limited to 4 for carrier frequencies up to 3 GHz, to 8 for 3-6 GHz, and to 64 for frequencies above 6 GHz. The periodicity of this transmission can range from 5 ms to 160 ms. The 5-bit burst is always limited to a 5 ms window in the first or second half of a 10 ms radio frame. The arrangement of the SSB synchronization blocks in a 5-bit burst depends on the subcarrier spacing and the carrier frequency.

[0055] An initial access procedure for user equipment 3 to the network is shown in [Fig. 1]. This access procedure takes place in two stages. First, a downlink synchronization allows user equipment 3 to synchronize with broadcast signals from base station 1. The broadcast signals include, in particular, bursts 5 of SSB synchronization signal blocks. Once synchronized, user equipment 3 can listen for system information, including a random access channel resource configuration 7. Second, an uplink synchronization, through, among other things, the random access channel 7, including an exchange 9 of messages, allows base station 1 to acquire more information about user equipment 3 in order to allocate resources to it.According to this access procedure, the connection 11 between base station 1 and user equipment 3 is established.

[0056] The present invention relates to the processing carried out by the user equipment 3 during the downlink synchronization phase, the objective of which is to decode the master MIB information block.

[0057] To do this, the user equipment 3 includes a downlink synchronization unit 48.

[0058] The downlink synchronization unit 48 includes a receive module 58 and a time and frequency synchronization module 60. Preferably, the downlink synchronization unit 48 further includes an OFDM recombination and demodulation module 62, a secondary synchronization sequence estimation module 64, a cell number determination module 66, a block index determination module 68, an equalization and demodulation module 70 and a recombination and decoding module 72.

[0059] The receiving module 58 is configured to receive a signal emitted by the base station 1.

[0060] The time and frequency synchronization module 60 is configured to perform a first and second estimation of the frequency and time differences between the signal emitted by the base station and a signal received S by user equipment 3, as well as to estimate the first component N_PSS of the cell number N_cell.

[0061] The recombination and demodulation module 62 is configured to recombine the received multi-channel signal S into a single-channel signal and to demodulate OFDM signals.

[0062] The secondary synchronization sequence estimation module 64 is configured to determine the second component N_SSS of the cell number N_cell.

[0063] The cell number determination module 66 is configured to determine the cell number N_cell based on the first component N_PSS and the second component N_SSS.

[0064] The block index determination module 68 is configured to determine the block index i_SSB of the SSB synchronization block within burst 5.

[0065] The equalization and demodulation module 70 is configured to estimate the physical broadcast channel and to demodulate equalized symbols obtained using the estimated physical broadcast channel.

[0066] The recombination and decoding module 72 is configured to decode the master MIB information block.

[0067] The details of the operations performed by each of the receiving module 58, synchronizing module 60, OFDM recombination and demodulation module 62, secondary sequence estimation module 64, cell number determination module 66, block index determination module 68, equalization and demodulation module 70 and recombination and decoding module 72 are described later in the description, in particular during the description of the steps of the downlink synchronization process according to the invention.

[0068] In the example of [Fig.1], the downlink synchronization unit 48 includes an information processing unit 50 formed for example of a memory 52 and a processor 54 associated with the memory 52.

[0069] In the example of [Fig.1], the receiving module 58, the synchronizing module 60, the recombination and demodulation module 62, the estimation module 64, the cell number determination module 66, the block index determination module 68, the equalization and demodulation module 70, and the recombination and decoding module 72 are each implemented as software, or a software block, executable by the processor 54. The memory 52 of the downlink synchronizing unit 48 is then capable of storing receiving software, time and frequency synchronization software, OFDM recombination and demodulation software, secondary synchronization sequence estimation software, cell number determination software, block index determination software, equalization and demodulation software, and recombination and decoding software. The processor 54 is then capable of running each of the aforementioned software programs.

[0070] In an alternative not shown, the receiving module 58, the synchronizing module 60, the OFDM recombination and demodulation module 62, the secondary sequence estimation module 64, the cell number determination module 66, the block index determination module 68, the equalization and demodulation module 70, and the recombination and decoding module 72 are each implemented as a programmable logic component, such as an FPGA (Field Programmable Gate Array), or as a dedicated integrated circuit, such as an ASIC (Application-Specific Integrated Circuit).

[0071] When the downlink synchronization unit 48 is implemented in the form of one or more software programs, i.e., in the form of a computer program, it is also capable of being stored on a computer-readable medium (not shown). A computer-readable medium is, for example, a medium capable of storing electronic instructions and being connected to a bus of a computer system. For example, a readable medium is an optical disc, a magneto-optical disc, a ROM, a RAM, any type of non-volatile memory (e.g., EPROM, EEPROM, FLASH, NVRAM), a magnetic card, or an optical card. A computer program comprising software instructions is then stored on the readable medium.

[0072] When the downlink synchronization unit 48 further includes one or more receiving antennas 56, configured to receive at least partially the signal emitted by the base station 1. The number of antenna(s) 56 is denoted N.

[0073] Upstream of the initial access, the user equipment 3 considers, for example, that a burst 5 of SSB synchronization blocks is emitted every 20 ms.

[0074] A method 100 enabling user equipment 3 to synchronize downlink to the network, implemented by the downlink synchronization unit 48, is shown in [Fig.3] and described in the rest of the description.

[0075] The method 100 comprises a reception step 105, a first time and frequency synchronization step 110 and a second time and frequency synchronization step 120. Advantageously, it further comprises an OFDM recombination and demodulation step 130, a cell number determination step 150, a physical broadcast channel equalization and demodulation step 170 and a physical broadcast channel recombination and decoding step 180.

[0076] The invention is expressed in two preferred implementations and two preferred embodiment examples, which are detailed in the following description. Each preferred embodiment example can be implemented with either of the two preferred implementations. According to the second implementation of the invention, the method 100 further comprises, compared to the first implementation, a secondary synchronization sequence estimation step. 140. On [Fig.3], the dotted lines correspond to the steps and links which are present only in one or the other of the implementations or in one or the other of the examples of embodiment of the invention.

[0077] The reception step 105 is implemented by the receiving module 58. During this reception step 105, the antenna(s) 56 receive at least partially the signal emitted by the base station 1. The received signal S is called the signal received by the receiving antenna(s) 56. The received signal S corresponds to the emitted signal modified by the physical broadcast channel and by the presence of interference.

[0078] The received signal S comprises a useful part, called the useful signal, and an interfering part, called the interfering signal.

[0079] The received signal S, through a multipath propagation channel, in the presence of interference, noise and time and frequency deviations with the signal emitted s(t) by base station 1, is written in baseband:

[0080] t ) = ( t ) s( t- At- ts, f H(f ' ( t)■

[0081] with: - nr = 1, ..., Nrx an index of antenna 56 of the receiver, - Regarding the time lag, - Af the frequency shift, { / &',(()}„„ of the path gains of the useful signal channel, - {Ts, n} has the channel path delays of the useful signal, - J t ) 1 of the channel path gains of the signal interfere, - | Tj delays in signal channel paths interfere, - NL the maximum number of paths of the useful signal channels and interfere, - i(t) the interfering signal, - W^nKt) an additive Gaussian noise.

[0082] After correcting the time and frequency offsets, the signal p(nj( f + Aù ) Q-jZHkft can be filtered to limit interference and noise in the SSB signal band, then the OFDM signals can be demodulated, after which we find an equivalent model in the frequency domain, with a single input and multiple outputs:

[0083] rkJ=hsMakJ+hiMikj+wkJ,

[0084] where:

[0085]

[0086]

[0087]

[0088]

[0089] - ct SOnt are Nrx 1 multi-channel reception vectors, respectively for the useful signal and the interfering signal, - &k,l is the symbol at the jth OFDM symbol and jth - WkJ is an additive Gaussian noise with zero mean and matrix of covariance. It is assumed that the interference îkj behaves in frequency as noise with zero mean and variance (7?) and with a spatial signature RiXj = E[h. ' and on the occupied subcarriers the useful signal satisfies E[|awl2 j = q-2. We can assume without loss of generality that the useful signal can have an average power cr2 which varies with k et7, according to the power allocation policy in transmission. We set ^k,I = ^kj To group the interference and noise terms, which has a spatial covariance matrix Ra)ikJ = + The method 100 allows user equipment 3 to synchronize in downlink to the network even in the presence of significant interference, i.e. when 1. The first frequency and time synchronization step 110, shown more precisely in [Fig. 4], is implemented by the synchronization module 60. This step consists of providing an initial estimate of the frequency offset DF1 and an initial estimate of the time offset DTI between the signal transmitted by base station 1 and the received signal S, as well as determining the first component N_PSS of the cell number N_cell. This first synchronization step is performed considering only the primary synchronization sequence PSS of the SSB synchronization block.Indeed, since there are only 3 possible PSS sequences, and the PSS sequence is identical on each SSB block of burst 5, using an interference-robust synchronization algorithm by correlation on the PSS sequence only is less computationally expensive than the same interference-robust synchronization algorithm on all possible PSS sequence - SSS sequence pairs. Prior to step 110, a coarse synchronization time horizon 15 and coarse Doppler cells 19 are fixed. The coarse synchronization time horizon 15 consists of Ngy^ch* samples. The coarse Doppler cells 19 have an Afr resolution and number ND. These parameters are called "coarse" in contrast to a fine synchronization time horizon 21, which is shorter than the coarse synchronization time horizon 19, and fine Doppler cells. 23 finer than the coarse Doppler boxes 19, used during the second frequency and time synchronization step 120. Similarly, a burst configuration hypothesis 17 5 is chosen prior to step 110.

[0090] Optionally, step 110 includes a substep 111 of subsampling the received signal S at the rate of the PS S sequence. This reduces the complexity of step 110 and is possible because the signal bandwidth of the PSS sequence is smaller than the signal bandwidth of the SSB block.

[0091] We then consider a first portion of the received signal, which we denote rn-. The first portion of the received signal corresponds to the received signal S, denoted sampled at a rhythm Fe at least equal to the band of the PSS sequence signal. Thus, the first portion of the received signal includes at least the primary PSS synchronization sequence of the received signal S. Due to the frequency offset of the received signal S relative to the signal transmitted by base station 1, the PSS sequence is probably not centered on the carrier, but resampling allows the out-of-band signal to be folded back onto the band corresponding to F e.

[0092] In the case of spatial synchronization, we have:

[0093] [ ^1) (np. ^NRX)( npe ]T,

[0094] which is a vector of size Nr% * 1-

[0095] In the case of spatio-temporal synchronization, we have an extended vector:

[0096] which is a vector of size Npx^ST 1 oa ^ST is a horizon length spatio-temporal and is^ is a spatio-temporal spacing step. The case of a spatial treatment is deduced from the spatio-temporal case by taking a spatio-temporal horizon length LST = 1.

[0097] Step 110 includes a substep 112 for estimating a primary autocorrelation matrix of the first portion of the received signal, expressed by:

[0098] £ =_l_yNref H xref ^n]=i2 n+m1 n+ni

[0099] on the coarse synchronization time horizon 15, where Nref is the length of the synchronization sequence in number of samples.

[0100] The primary autocorrelation matrix is ​​then inverted in a substep 113 of autocorrelation matrix inversion.

[0101] For each possible PSS sequence, therefore for each possible value of the first component N_PSS, denoted , we denote £ A / '2) ) a reference signal ID V ' IDJ generated based on hypothesis 17 of burst configuration 5. We note () 'C s^na^ of reference sampled at the same rate as rn. We obtain

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] thus a first set of reference sequences, including the reference signal for each of the PSS primary synchronization sequences to be tested. Step 110 includes a substep 114 for estimating primary cross-correlation vectors of the first portion of the received signal with the first set of reference sequences. The primary cross-correlation vectors are written as: where nd Nd is an index associated with the coarse Doppler boxes 19. K- - 2 , 2 Then, in substep 115 of the criterion calculation, a primary synchronization criterion is calculated from the inverted primary correlation matrix and the primary cross-correlation vectors. The primary synchronization criterion is expressed as: ) — ^"xdjik During substep 116 of optimum search, an optimum of the primary synchronization criterion is sought for the coarse Doppler ND cases 19, the samples of the coarse synchronization time horizon 15 and the three possible PSS sequences. In the case of a spatial synchronization criterion, one can simply search for the maximum, and it is possible to use a minimum threshold to reject weak peaks of the primary synchronization criterion, in order to target a certain probability of false alarm. In the spatiotemporal case, it may be preferable to work on the detection of a rising edge on a sliding window, for example, of the order of size of the cyclic prefix. Knowledge of the coarse Doppler box 19 optimizing the primary synchronization criterion provides the first estimate of the frequency shift DF1, knowledge of the sample of the time horizon of coarse synchronization 15 optimizing the primary synchronization criterion provides the first estimate of the frequency shift DF1, and knowledge of the PSS sequence optimizing the primary synchronization criterion provides the first component N_PSS of the cell number N_cell. According to hypothesis 17 of burst configuration 5, and knowing a priori the directivity of the beams emitted by base station 1, it is sometimes possible to use the PSS sequence of several SSB blocks to perform these correlations. In this case, the accuracy of the estimation of the time offset DTI and the frequency offset DF1 is significantly improved, but at the cost of introducing ambiguities in the frequency of the primary synchronization criterion. These can nevertheless be managed by prior knowledge of the positions of the PSS sequences during sub-step 116 of optimum search.

[0111] The second frequency and time synchronization step 120 is also implemented by the synchronization module 60. Alternatively, the second synchronization step 120 is implemented by another synchronization module, not shown, separate from the synchronization module 60. This step aims to provide a second estimate of the frequency offset DF2 and a second estimate of the time offset DT2, the second estimates of the frequency offset DF2 and the time offset DT2 being more accurate than the first estimates of the frequency offset DF1 and the time offset DTI, respectively. In other words, the first estimates of the frequency offset DF1 and DTI are coarse estimates, while the second estimates of the frequency offset DF2 and the time offset DT2 are fine estimates.

[0112] The second frequency and time synchronization step 120 is similar to the first frequency and time synchronization step 110, except that it involves a second portion of received signal and a second set of reference sequences, the primary synchronization sequence PSS being fixed. The second step 120 also involves a shorter fine synchronization time horizon 21 than the coarse synchronization time horizon 19 and finer Doppler cells 23 than the coarse Doppler cells 19. In particular, the fine Doppler cells 23 result from a finer frequency segmentation than the coarse Doppler cells 19. The amount of calculation to be performed in steps 110 and 120 is thus reduced compared to a solution that would require performing correlations from the outset on each pair of PSS sequences - SSS sequences, on the fine synchronization time horizon 21 and the fine Doppler cells 23..

[0113] The second synchronization step 120 is divided into a first variant corresponding to the first implementation of the invention, and respectively a second variant corresponding to the second implementation, the second synchronization step 120 being then noted 120A according to the first variant, and respectively 120B according to the second variant.

[0114] According to the first embodiment corresponding to the first implementation of the invention, the second synchronization step 120A is shown in [Fig. 5]. It comprises a substep 121A for compensating the frequency synchronization error, consisting of correcting the second portion of the received signal using the first estimate of the frequency deviation DF1, and a substep 122A for compensating the time synchronization error, consisting of correcting the second portion of signal received using the first estimate of the DTI time difference.

[0115] The second portion of the received signal thus corrected is advantageously filtered during a filtering substep 123A, in order to limit the band of the received signal to that of the primary PSS and secondary SSS sequences, and to reject out-of-band noise and interference.

[0116] A secondary autocorrelation matrix is ​​calculated during a substep 124A, corresponding to the autocorrelation of the second portion of the received signal corrected and filtered over the fine synchronization time horizon 21.

[0117] The secondary autocorrelation matrix is ​​then inverted in a substep 125A of autocorrelation matrix inversion.

[0118] In parallel, step 120A includes a substep 126A for estimating secondary cross-correlation vectors, by correlating the second portion of the received signal with the second set of reference sequences, the first PSS synchronization sequence being fixed by means of estimating the first N_PSS component determined in the first synchronization step 110. The estimation of the secondary cross-correlation vectors is carried out on the fine Doppler squares 23.

[0119] Analogously to the criterion calculation substep 115 and optimum search substep 116 of step 110, step 120A includes a secondary synchronization criterion calculation substep 127A and an optimum search substep 128A on each of the fine Doppler squares 23 and samples of the fine synchronization time horizon 21, providing the second estimates of the frequency offset DF2 and the time offset DT2.

[0120] According to the second variant corresponding to the second implementation of the invention, the second synchronization step 120B shown in [Fig. 6] comprises substeps 121B to 128B analogous to substeps 121A to 128A of the first implementation of the invention. Only the differences with respect to this implementation are described below.

[0121] According to the second implementation of the invention, the second portion of the received signal comprises at least one of the secondary synchronization sequences (SSS) of the received signal, and the second set of reference sequences used in the secondary cross-correlation vector estimation substep 126B comprises a reference signal for each of the secondary synchronization sequences (SSS) to be tested 25, the primary synchronization sequence (PSS) being fixed. In the worst case, there are 336 SSS sequences to be tested 25. However, if the user equipment 3 has prior knowledge of the possible values ​​for the cell identity N_cell, the number of SSS sequences to be tested 25 is less than 336.

[0122] The optimum search substep 128B is further carried out on each of the SSS sequences to be tested 25 and knowledge of the SSS sequence optimizing the secondary synchronization criterion provides the second component N_SSS of the cell number N_cell.

[0123] The amount of computation performed during the second step 120 is greater in the second implementation than in the first implementation of the invention. Indeed, in the second step 120A of the first implementation, the number of PSS sequence pairs tested is less than the number of PSS sequence pairs tested in the second step 120B of the second implementation, which includes all the SSS sequences likely to be present in the transmitted signal, thus eliminating the uncertainty regarding the SSS sequence actually present in the transmitted signal. For this reason, the first implementation is chosen when the user equipment 3 has limited computing power, preventing the implementation of the second implementation within a reasonable timeframe for the application in question.

[0124] The recombination and demodulation step 130 is implemented by the recombination and demodulation module 62. The received signal S is generally a multi-channel signal. The recombination and demodulation step 130 then aims to recombine the received multi-channel signal S into a received single-channel signal by means of a spatial or spatio-temporal filter, in order to facilitate the estimation of the other unknown parameters of the SSB synchronization block, and to demodulate the received signal S, which is modulated by orthogonal frequency division, known as OFDM modulation, according to the 5G standard of the 3GPP consortium.

[0125] The recombination and demodulation step 130 is performed on a third portion of the received signal, comprising at least one SSB synchronization block. The third portion of the received signal is corrected using the second frequency deviation estimate DF2 in a substep 131 and using the second time deviation estimate DT2 in a substep 132, before being filtered in a substep 133.

[0126] The recombination and demodulation step 130 then includes a substep 134 for estimating a tertiary autocorrelation matrix of the third corrected and filtered received signal portion, and a substep 135 for estimating tertiary autocorrelation vectors between the third corrected and filtered received signal portion and the reference signal of the second set of reference sequences selected during the optimization search substep 128A or 128B of the second time- and frequency-synchronization step 120. In other words, the cross-correlation is calculated between the third corrected and filtered received signal portion and the reference signal of the second set of reference sequences that optimized the criterion secondary synchronization during the second time and frequency synchronization step 120. The sub-steps of estimating a tertiary autocorrelation matrix 134 and estimating tertiary autocorrelation vectors 135 allow us to obtain correlation parameters over the entire third portion of the received signal, therefore over the entire band of the SSB synchronization block.

[0127] The tertiary autocorrelation matrix Rxx and the tertiary autocorrelation vectors rxd are then used in a substep 136 of calculating a spatially or spatiotemporally adapted filter _ A-1 W — K xx r xd

[0128] Then, during a substep 137 of spatiotemporal filtering and demodulation, the third corrected received signal portion is recombined into a single-channel received signal portion, using the spatially or spatiotemporally matched filter. In particular, the single-channel received signal is written as rB = wHrn. During this same substep 137 of spatiotemporal filtering and demodulation, the single-channel received signal portion is demodulated, providing received orthogonal frequency division symbols SYM_OFDM. More precisely, the demodulation consists of obtaining resource elements p Q^i+w, where i is a subcarrier index in OFDM modulation, where 1 is a symbol index in OFDM modulation, is the equivalent physical diffusion channel after recombination, and is the residual noise and interference after recombination. In cases where spatial or spatiotemporal filtering succeeds in rejecting all significant interference paths, essentially has only a noise component; otherwise, it will continue to have a strong interference component. This step assumes that over the duration of an SSB block, the signal correlation properties evolve slowly enough to maintain the same behavior across the OFDM modulation symbols of the SSB block, which should be largely verified after the second frequency synchronization.

[0129] In the first implementation of the invention, the secondary synchronization sequence estimation step 140, implemented by the secondary sequence estimation module 64, makes it possible to determine the second component N_SSS of the cell number N_cell, which was not determined during the second time and frequency synchronization step 120.

[0130] This secondary synchronization sequence estimation step 140, shown in [Fig. 8], includes a substep 141 of correlating the received orthogonal frequency division symbols SYM_OFDM or the multichannel received signal portion with a third set of reference sequences, the third set of reference sequences comprising the synchronization sequences Secondary SSS to be tested 25 and generated based on hypothesis 17 of burst configuration 5, the primary PSS synchronization sequence being fixed. A tertiary correlation criterion is calculated, defined by:

[0131] csss(Nw) = A- ùuu ' 1U * _L zi / / V çeg -^^2—~ —0—uûu \ i JJ 1U * I

[0132] where: - is the index of the DMRS demodulation sequence symbols corresponding to the NSSB possibilities considered in configuration hypothesis 17 - dsss(& ^ID -^ / ¾) eSt s^cluence SSS for fixed to the value detected during the first step 110, - N / p varies with the SSS sequences to be tested 25.

[0133] The secondary synchronization sequence estimation step 140 further includes a substep for finding the maximum of the tertiary correlation criterion 142 on each of the secondary synchronization sequences SSS to be tested 25, the primary synchronization sequence PSS being fixed. Knowledge of the secondary synchronization sequence SSS that maximizes the correlation criterion provides the second component N_SSS of the cell number N_cell.

[0134] Knowing the first N_PSS component and the second N_SSS component of the cell number, the cell number determination step 150, implemented by the cell number determination module 66, allows the cell number N_cell to be determined based on the first N_PSS component and the second N_SSS component by applying the function linking the cell number N_cell to the first N_PSS component and then to the second N_SSS component. According to the 3GPP consortium's 5G standard, this function is written as 3? / ^ +Af® •

[0135] The block index determination step 160, shown in [Fig.9], is implemented by the block index determination module 68. The objective is to find the block index i_SSB of the SSB synchronization block within burst 5.

[0136] For this purpose, the block index determination step 160 includes a substep 161 of correlation of at least a part of the received orthogonal frequency distribution symbols SYM_OFDM, corresponding to the DMRS demodulation reference symbols, with a set of reference symbols, corresponding to the i_SSB block indices to be tested.

[0137] More precisely, y = mod 4 is calculated to find indices of the OFDM subcarriers and symbols to which the DMRS is allocated. A quaternary correlation criterion (ssb) is defined as a function of the block index. I_SSS. The value of cell number N_cell is fixed to the previously determined value. The expression of the quaternary correlation criterion depends on the number of SSB synchronization blocks considered in the synchronization process. For example, if only one SSB synchronization block is considered, then the quaternary correlation criterion is expressed as:

[0138] CDMRS(iSSB) = ^sb)

[0139] The quaternary correlation criterion is evaluated for each value of the block index I_SSB to be tested, and the value optimizing the quaternary correlation criterion provides the block index I_SSB of the received signal S considered.

[0140] The equalization and demodulation step of the physical broadcast channel 170 is implemented by the equalization and demodulation module 70. It consists of providing likelihood ratios for each bit of the master MIB information block.

[0141] According to the first example of the invention, the equalization and demodulation step 170A, represented in [Fig. 10], performs for this purpose an estimation of the physical diffusion channel from the received orthogonal frequency distribution symbols SYM_0FDM.

[0142] In particular, the equalization and demodulation step 170A includes a substep 171A for estimating the single-channel equivalent physical diffusion channel 27 and the variance of the noise and residual interference 29. This estimation is carried out from the received orthogonal frequency distribution symbols SYM_OFDM, knowing the block index i_SSB within the burst and the cell number N_cell.

[0143] For example, substep 171A performs a least-squares channel estimation on the DMRS demodulation reference sequences and the SSS sequences, and then performs a two-dimensional interpolation of this estimation on all k subcarriers and symbols covering the data bandwidth of the PBCH physical broadcast channel. Alternatively, denoising methods could be used, by calculating the time impulse response huj, where n is a time-sample index, applying an inverse Fourier transform for each symbol 7, and truncating the impulse response to minimize the noise contribution. The variance of the equivalent noise 27 can also be estimated on these truncated samples, as well as on the subcarriers not carrying data. The frequency equalizer is then calculated after frequency conversion.

[0144] The frequency equalizer thus estimated is then used in a single-channel frequency equalization substep 172A of the orthogonal frequency distribution symbols SYM_OFDM, providing equalized symbols of the physical diffusion channel 31 and a variance of the equivalent post-equalization noise 33. The symbols equalized from the physical broadcast channel 31 are symbols according to a quadrature phase modulation, called QPSK modulation.

[0145] The equalized symbols of the physical broadcast channel 31 are then demodulated in a QPSK demodulation substep 173A, providing the logarithm of an LLR likelihood ratio, called the log-LLR likelihood ratio, for each of the 864 bits of a codeword corresponding to the master MIB information block.

[0146] According to the second embodiment of the invention, the equalization and demodulation step of the physical broadcast channel 170B, shown in [Fig. 11], performs the estimation of the physical broadcast channel from the received multi-channel signal S. More precisely, the processing is carried out on a fourth portion of the received signal S, comprising at least one SSB synchronization block.

[0147] The equalization and demodulation step 170B includes a substep 17IB for frequency deviation correction from the second frequency deviation estimate DF2, a substep 172B for time deviation correction from the second time deviation estimate DT2 and a filtering substep 173B.

[0148] The fourth portion of the received signal thus corrected and filtered is then jointly processed by spatial or spatio-temporal filtering and equalized, all in the frequency domain.

[0149] The multi-way equivalent physical diffusion channel estimation substep 174B performs an estimation of a noise and interference covariance matrix 60 and an estimation of the single-way equivalent physical diffusion channel 37 by a minimum root mean square error-interference rejection combination equalizer, known as MMSE-IRC type.

[0150] If we assume that the noise and interference covariance matrix remains constant across all subcarriers, then spatial processing alone against interference is preferably performed. If, on the contrary, we assume that the noise and interference covariance matrix changes with the subcarriers, then spatiotemporal processing against interference is preferably performed. For the spatiotemporal case, since the number of symbols in the PBCH physical broadcast channel data is insufficient to accurately estimate the noise and interference covariance matrix for each subcarrier, the 240 subcarriers carrying the PBCH physical broadcast channel data are advantageously divided into groups of 47 subcarriers to estimate a noise and interference covariance matrix for each group.

[0151] The equalization and demodulation step 170B then includes a substep 176B of frequency equalization of the fourth portion of the received signal by means of the estimated MMSE-IRC equalizer, providing equalized symbols of the broadcast channel physics 31 and a variance of the equivalent post-equalization noise 33. Spatial or spatio-temporal filtering is carried out jointly with frequency equalization during substep 176B.

[0152] The equalized symbols of the physical broadcast channel 31 are then demodulated in a QPSK demodulation substep 173B, providing the logarithm of an LLR likelihood ratio, called the log-LLR likelihood ratio, for each of the 864 bits of the codeword corresponding to the master information block MIB.

[0153] In configurations where the number of SSB synchronization blocks in burst 5 is less than 64 (particularly for carrier frequencies below 6 GHz), the PBCH physical broadcast channel data on the different SSB blocks is identical. In this case, several SSB blocks are advantageously equalized and demodulated, and their log-likelihood ratios (LLRs) are combined, thereby refining the decoding of the master information block (MIB).

[0154] In both examples of the invention, the recombination and decoding step of the physical broadcast channel 180 is implemented by the recombination and decoding module 72. During this substep 180, the master information block MIB is decoded from the log-likelihood ratios LLR, providing a transmitted frame index, a subcarrier offset of the SSB synchronization block relative to the rest of a resource grid, i.e., the set of subcarriers 1 and symbols k, information on physical control channels, and information on physical data channels. These parameters allow the user equipment 3 to be synchronized with the network.

[0155] The recombination and decoding step of the physical broadcast channel 180 is the final step of the downlink synchronization process of the user equipment 3.

[0156] Any feature described above for an implementation, example or variant may also be implemented for the implementations, examples and variants described above, as far as technically possible.

Claims

1. Demands Method (100) of downlink synchronization of a user equipment (3) to a 5G cellular network, comprising: - a step (105) of receiving a signal emitted by a base station (1), the emitted signal comprising at least one synchronization signal block (SSB) belonging to a burst (5) of synchronization signal blocks (SSB) emitted by the base station (1) and identified within the burst (5) by a block index (i_SSB), the base station (1) belonging to a cell characterized by a cell number (N_cell), the cell number being a function of a first component (N_PSS) on which depends a primary synchronization sequence (PSS) of the synchronization block (SSB) and a second component (N_SSS) on which depends a secondary synchronization sequence (SSS) of the synchronization block (SSB), the synchronization block (SSB) further comprising data from a physical broadcast channel (PBCH); characterized in that the method (100) further comprises: - a first frequency and time synchronization step (110), during which a first estimation of a frequency gap (DF1) between the signal emitted by the base station and a signal received (S) by the user equipment (1) during the reception step (105), a first estimation of a time gap (DTI) between the signal emitted by the base station (1) and the received signal (S) and a determination of the first component (N_PSS) of the cell number (N_cell) are carried out by autocorrelation of a first portion of the received signal and cross-correlation of the first portion of the received signal with a first set of reference sequences,the first portion of the received signal comprising at least one of the primary synchronization sequences (PSS) of the received signal (S) and the first set of reference sequences comprising a reference signal for each of the primary synchronization sequences (PSS) to be tested; and, - a second frequency and time synchronization step (120, 120A, 120B), during which a second frequency gap estimate (DF2) and a second time gap estimate (DT2) are performed by autocorrelation of a second portion of the received signal and cross-correlation of the second portion of signal received with a second set of reference sequences after correction of the second portion of received signal using the first estimates of frequency deviation (DF1) and time deviation (DTI), the primary synchronization sequence (PSS) being fixed, the second estimates being made taking into account the first component (N_PSS) determined during the first step (110) of time and frequency synchronization, the second estimates of frequency deviation (DF2) and time deviation (DT2) being more accurate than the first estimates of frequency deviation (DF1) and time deviation (DTI) respectively.

2. A method (100) according to claim 1, wherein the second frequency and time synchronization step (120, 120A, 120B) comprises a filtering substep (123A, 123B), during which the corrected second received signal portion is filtered, so as to limit the second received signal portion to the primary (PSS) and secondary (SSS) synchronization sequences.

3. A method (100) according to claim 1 or 2, wherein the received signal (S) is a multi-channel signal and wherein the method (100) comprises a recombination and demodulation step (130), during which: - a third portion of the received signal is corrected using the second estimates of the frequency (DF2) and time (DT2) deviations, the third portion of the received signal comprising at least one synchronization block (SSB); - a spatial or spatio-temporal filter is calculated by autocorrelation of the corrected third portion of the received signal and cross-correlation of the corrected third portion of the received signal with a reference signal, belonging to the second set of reference sequences and having been retained during the second frequency and time synchronization step (120); - the corrected third portion of the received signal is recombined into a single-channel received signal portion using the spatial or spatio-temporal filter;and - the single-channel received signal portion is demodulated, providing received orthogonal frequency division symbols (SYM_OFDM).;

4. A method (100) according to claim 3, further comprising a step (140) of secondary synchronization sequence estimation, in which a determination of the second component (N_SSS) of the cell number (N_cell) is carried out by correlation of the received orthogonal frequency division symbols (SYM_OFDM) or of the multi-channel received signal portion with a third set of reference sequences, the third set of reference sequences comprising secondary synchronization sequences (SSS) to be tested, the primary synchronization sequence (PSS) being fixed.

5. Method (100) according to any one of claims 1 to 3, wherein the second received signal portion comprises at least the secondary synchronization sequence (SSS) of the received signal (S) and the second set of reference sequences comprises a reference signal for each of the secondary synchronization sequences (SSS) to be tested, and wherein the second frequency-time synchronization step (120, 120B) further comprises the determination of a value of the second component (N_SSS) of the cell number (N_cell).

6. Method (100) according to any one of claims 4 or 5, further comprising a step (150) of determining the cell number (N_cell) as a function of the first component (N_PSS) and the second component (N_SSS).

7. Method (100) according to claims 3 and 6, further comprising a step (160) of determining the block index (i_SSB) by correlation of at least a part of the received orthogonal frequency distribution symbols (SYM_OFDM) with a set of reference symbols, corresponding to the block indices (i_SSB) to be tested.

8. A method (100) according to claim 7, further comprising a step (170A) of equalizing and demodulating the physical broadcast channel, in which: - the physical broadcast channel is estimated from the received orthogonal frequency division symbols (SYM_OFDM), knowing the block index (i_SSB) within the burst (5) and the cell number (N_cell); - a single-channel frequency equalization of the orthogonal frequency division symbols (SYM_OFDM) is performed using the estimated physical broadcast channel, providing equalized symbols of the physical broadcast channel (31); and - the equalized symbols of the physical broadcast channel (31) are demodulated, providing the logarithm of a likelihood ratio (LLR) for each bit of a codeword, corresponding to the master information block (MIB) contained in the physical broadcast channel (PBCH) data.

9. A method (100) according to claim 7, further comprising a step (170B) of equalization and demodulation of the physical broadcast channel, during which: - the multi-way physical broadcast channel and a spatial autocorrelation of noise and interference are estimated from a fourth portion of the received signal (S), corrected using the second estimates of the frequency (DF2) and time (DT2) deviations, knowing the block index (i_SSB) within the burst (5) and the cell number (N_cell), the fourth portion of the received signal (S) comprising at least one synchronization block (SSB); - a frequency equalization of the fourth portion of the received signal is performed by a minimum root mean square error-interference rejection combination equalizer, referred to as MMSE-IRC type, providing equalized symbols of the physical broadcast channel;and - the equalized symbols of the physical broadcast channel are demodulated, providing the logarithm of a likelihood ratio (LLR) for each bit of a codeword, corresponding to the master information block (MIB) contained in the physical broadcast channel (PBCH) data.;

10. A method (100) according to claim 8 or 9, further comprising a step (180) of recombination and decoding of the physical broadcast channel (PBCH) data during which the master information block (MIB) is decoded from the logarithms of the likelihood ratios (LLR) of the codeword, providing parameters to complete the synchronization of the user equipment 3 to the 5G cellular network.

11. User equipment (3) intended to be connected to a 5G cellular network, characterized in that it is configured to implement a method (100) according to one of the preceding claims.

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