WO2019137602A1

WO2019137602A1 - Client device and methods thereof

Info

Publication number: WO2019137602A1
Application number: PCT/EP2018/050477
Authority: WO
Inventors: Bengt Lindoff; Wenquan HU; Neng Wang
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2018-01-09
Filing date: 2018-01-09
Publication date: 2019-07-18

Abstract

The invention relates to a client device (100) for a wireless communication system (500). The client device (100) determines a first phase shift between symbols of a first set of received symbols (RS1); and determine a first frequency range and a first centre frequency for a set of control channel resources based on the first phase shift and the first set of received symbols (RS1). The client device (100) further monitors the set of control channel resources in the first frequency range based on the first centre frequency. Furthermore, the invention also relates to corresponding methods and a computer program.

Description

CLIENT DEVICE AND METHODS THEREOF

Technical Field

The invention relates to a client device. Furthermore, the invention also relates to corresponding methods and a computer program.

Background

The 5G wireless communication system, also called new radio (NR), is currently being standardized. NR is targeting radio spectrum from below 1 GHz up to and above 60 GHz. To allow for such diverse radio environments not only different system bandwidths will be supported, but also different numerologies, such as different sub-carrier-spacings (SCS).

When a user equipment (UE) is switched on in a wireless communication system an initial cell search is performed to find a cell to connect to. During the initial cell search the UE will search for synchronisation signal blocks (SSBs) by scanning potential carrier frequencies. In NR, the system bandwidth may be up to 100-200 MHz, compared to 20 MHZ in Long Term Evolution (LTE). Furthermore, there may be multiple SSBs in the system bandwidth of a NR base station.

Summary

An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

The above and further objectives are solved by the subject matter of the independent claims. Further advantageous embodiments of the present invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a client device for a wireless communication system, the client device being configured to

determine a first phase shift between symbols of a first set of received symbols;

determine a first frequency range and a first centre frequency for a set of control channel resources based on the first phase shift and the first set of received symbols;

monitor the set of control channel resources in the first frequency range based on the first centre frequency.

The first frequency range can in this disclosure be understood to mean a first frequency range used to monitor a set of control channel resources and may hence also be referred to as a first monitoring frequency range. Furthermore, the first centre frequency can in this disclosure be understood to mean a first centre frequency used to monitor a set of control channel resources, and may hence also be referred to as first monitoring centre frequency.

The control channel resources may be frequency-time resource used by a control channel for transmission of control messages.

An advantage of the client device according to the first aspect is that a good trade-off between decoding complexity and decoding reliability can be achieved for monitoring the set of control channel resources. Moreover, improved initial cell search performance is possible with a client device according to the first aspect.

In an implementation form of a client device according to the first aspect, the client device is further configured to

monitor the set of control channel resources based on demodulating symbols of a second set of received symbols in the first frequency range.

The second set of received symbols can be demodulated using the first centre frequency. In addition, the set of control channel resources are resources located in the first frequency range.

An advantage with this implementation form is that the client device can demodulate the control channel associated with the control channel resources and hence decode control channel messages received on the control channel.

determine a second phase shift between at least two adjacent symbols of the second set of received symbols based on the first phase shift and the first centre frequency;

phase adjust the second set of received symbols based on the second phase shift prior to demodulating the symbols of the second set of received symbols.

An advantage with this implementation form is that the client device can more reliably decode the second set of received symbols by phase adjusting the second set of received symbols using the second phase shift. Thereby improved decoding performance is achieved. In an implementation form of a client device according to the first aspect, the client device is further configured to

determine the first centre frequency such that a resulting second phase shift between two adjacent symbols of the second set of received symbols is less than a phase shift threshold value.

An advantage with this implementation form is that the client device does not need to perform phase shift compensation for the second set of received symbols therefore making decoding in the client device less complex.

demodulate the symbols of the second set of the received symbols without phase compensation.

An advantage with this implementation form is that the client device does not need to perform phase shift compensation therefore making decoding in the client device less complex.

In an implementation form of a client device according to the first aspect, the first frequency range is asymmetrically arranged around the first centre frequency.

An advantage with this implementation form is that by selecting the first centre frequency such that the first frequency range is asymmetrically around the first centre frequency is that the client device therefore can then select a first centre frequency resulting in no or a very small second phase shift. Thereby, making decoding in the client device less complex since there will be no need to perform phase shift compensation.

determine the phase shift threshold value based on a total phase shift p over symbols of the second set of received symbols and N number of symbols in the second set of received symbols.

The total phase shift p over symbols of the second set of received symbols gives a measure of allowed phase shift and may for instance be 45 degrees. An advantage with this implementation form is that the client device then knows the how the first centre frequency should be chosen for a sufficiently small phase shift between adjacent symbols of the second set of received symbols.

In an implementation form of a client device according to the first aspect, the phase shift threshold value is given as p/N.

An advantage with this implementation form is that the client device then knows how the first centre frequency should be chosen for sufficiently small phase shift between adjacent symbols of the second set of received symbols. Further, in this implementation form a closed form expression is also given.

determine the first frequency range based on system information carried by the first set of received symbols.

An advantage with this implementation form is that the client device from the system information knows where the control channel resources are within the (gNB) system bandwidth and hence making decoding of the first set of symbols more efficient by using a receiver bandwidth according to the first frequency range.

In an implementation form of a client device according to the first aspect, the system information is a master information block.

In an implementation form of a client device according to the first aspect, the system information is received in a physical broadcast channel.

An advantage with this implementation form is that the client device knows from the physical broadcast channel where the control channel resources are within the (gNB) system bandwidth and hence making decoding of the first set of symbols more efficient by using a receiver bandwidth according to the first frequency range. In an implementation form of a client device according to the first aspect, the first frequency range is associated with remaining system information. Or in other words, the first frequency range is a frequency range in which time-frequency resources are located which carry remaining system information (RMSI).

An advantage with this implementation form is that the client device knows where the remaining system information is within the (gNB) system bandwidth.

determine the first frequency range based on a bandwidth part configured for the client device.

An advantage with this implementation form is that the client device can derive the first frequency range from the configured bandwidth part. Thereby, a low complex solution is provided for determining the first frequency range.

receive a control message from a network access node, wherein the control message indicates the bandwidth part configured for the client device.

An advantage with this implementation form is that the client device can directly derive the configured bandwidth part from the control message indicating the bandwidth part.

In an implementation form of a client device according to the first aspect, the first set of received symbols comprises synchronization signal blocks.

An advantage with this implementation form is that the client device can from the synchronization signal blocks derive information about remaining system information.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a method for a client device, the method comprises

determining a first phase shift between symbols of a first set of received symbols;

determining a first frequency range and a first centre frequency for a set of control channel resources based on the first phase shift and the first set of received symbols; monitoring the set of control channel resources in the first frequency range based on the first centre frequency.

The method according to the second aspect can be extended into implementation forms corresponding to the implementation forms of the client device according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the client device.

The advantages of the methods according to the second aspect are the same as those for the corresponding implementation forms of the client device according to the first aspect.

The invention also relates to a computer program, characterized in program code, which when run by at least one processor causes said at least one processor to execute any method according to embodiments of the present invention. Further, the invention also relates to a computer program product comprising a computer readable medium and said mentioned computer program, wherein said computer program is included in the computer readable medium, and comprises of one or more from the group: ROM (Read-Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically EPROM) and hard disk drive.

Further applications and advantages of the embodiments of the present invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different embodiments of the present invention, in which:

- Fig. 1 shows a client device according to an embodiment of the invention;

- Fig. 2 shows a method according to an embodiment of the invention;

- Fig. 3 shows a wireless communication system according to an embodiment of the invention;

- Fig. 4 shows a method according to an embodiment of the invention;

- Fig. 5 shows a section of a client device according to an embodiment of the invention;

- Fig. 6 shows determination of a first centre frequency according to an embodiment of the invention;

- Fig. 7 shows determination of a first centre frequency according to an embodiment of the invention. Detailed Description

According to the 5G/New Radio (NR) specification in TS 38.21 1 v15.0.0, the time-continuous signal s ^r,m ΐ ) on antenna port p and subcarrier spacing configuration m for orthogonal frequency division multiplexing (OFDM) symbol / in a subframe for any physical channel or physical signal except physical random access channel (PRACH) is defined by

where o £ ί < (/n^ + /v^_{p ;})r_c and m is the subcarrier spacing configuration. Furthermore, a[^r{^m) is the modulation symbol / on sub-carrier k, NRB is the number of physical resource blocks, and Nsc is the number of sub-carriers per resource block (RB). Hence, the product NRB*NSC corresponds to the next generation eNode B (gNB) fast Fourier transform (FFT) size. Furthermore, Af denotes the sub-carrier spacing, T_c is the chip duration and the ko is an offset parameter. The function exp(j^*x) in the above expression is the complex valued exponential function and hence s ^{p, )}(t) is the complex-valued baseband representation of the transmitted signal. Modulation and up-conversion to the carrier frequency fo of the complex-valued OFDM baseband signal for antenna port p and subcarrier spacing configuration m is given by

The main difference of a synchronization signal transmission between NR and LTE is that in NR the central subcarrier of a SSB will not be aligned with the up-conversion carrier frequency fo for a gNB. The carrier frequency fo is the centre frequency of the FFT spanning the entire gNB system bandwidth (BW). Typically, the gNB system bandwidth is up to 20 MHz in LTE, while for NR the system bandwidth can be up to 100-200 MHz. Furthermore, in NR there can be multiple SSBs in the gNB system bandwidth. Moreover, the SSB in NR consists of the primary synchronization signal (PSS) and the secondary synchronization signal (SSS) as well as the physical broadcast channel (PBCH), which includes the master information block (MIB). In the MIB, information such that whether a cell is allowed for initial connection or not is found as well as information about the subframe number (SFN).

The eNB centre frequency in LTE is indirectly detected using the knowledge that the PSS, SSS and PBCH always are transmitted in the central 6 RBs centred around the carrier frequency. Therefore, once a UE have determined the PSS and SSS it has also determined the centre frequency of the eNB system bandwidth, and hence the centre frequency used in the receiver FFT processing.

The NR PBCH does not contain much information, instead there will be a pointer to where the remaining system information (RMSI) control resource set (CORESET) can be found. From this pointer, the UE gets information about a frequency range where the UE should monitor the CORESET, i.e. time-frequency resources in a control channel where indication of RMSI information is sent. In the RMSI further system information is given including random access channel (RACH) parameters for initial connection setup, and information and/or pointer to other system information (OSI).

For SSB symbols in NR, the baseband signal at a gNB transmitter can be written as:

(Equation 1 ) where 0 < / < (/V_u + N_cp ^T_c,l = 0,1,2... . a_{k l} is the modulated symbol of a SSB, and wherein the SSB occupies only part of subcarriers in the system bandwidth, herein labelled as the FFT size of the SSB, i.e. NSSB. The parameter M is the offset in sub-carriers between the centre frequency of the gNB system bandwidth and the centre frequency of the SSB bandwidth.

The relationship between the frequency offset f_m, the sub-carrier offset M and the subcarrier spacing Af is given as f_m=M*Af. The lower frequency of the SSB bandwidth starts at carrier frequency according to

According to the current status of NR specification, up-conversion to the carrier frequency fo of the SSB part of the baseband signal is given by

n 2). In initial cell search in NR, a UE will search for SSBs. In principle the UE will adapt its down- conversion frequency to a hypothetical down conversion frequency f_x and adapt its receiver bandwidth to cover the SSB signal, and down-convert the received signal and trying to detect the PSS and SSS. As long as the hypothetical down conversion frequency f_x is different from the frequency fo +†M the UE will not detect the SSB and will scan for further potential carrier frequencies.

Assuming an ideal channel, the received baseband signal after down-conversion by a receiver local oscillator at frequency fo +†M, i.e. the correct carrier frequency at the UE for detecting the SSB in an OFDM symbol without cyclic prefix (CP) length, can be expressed as

where†M=MA† is an unknown subcarrier offset between the carrier frequency at the receiver and the carrier frequency at the transmitter at the initial cell search phase for a UE. Hence, upon switching on a UE and performing an initial cell search in NR, the UE will be affected by an unknown phase shift between the symbols of the SSB, where the phase shift among other things is dependent on the length of the cyclic prefix as well as the frequency offset between the gNB centre (carrier) frequency and the SSB centre frequency as can be seen from the expression in Equation 3

where / is the symbol number. It can be noted that if M=0, i.e. no frequency offset between the SSB and the gNB offset, then ph(l)=J

As mentioned above, in NR a UE need to monitor a frequency range for RMSI after PBCH detection. However, since the UE still not know the gNB centre frequency it is not known how the UE should chose reception parameters, such as local oscillator frequency and receiver bandwidth, for optimized cell search. Hence, there is a need for a client device and a method providing a solution for choosing such parameters for optimized cell search. Therefore, in the following disclosure it is presented a client device and corresponding methods providing such a solution.

Fig. 1 shows a client device 100 according to an embodiment of the invention. In the embodiment shown in Fig. 1 , the client device 100 comprises at least one processor 102, an internal or external memory 104, and a transceiver 106. The processor 102 can be coupled to the memory 104 and the transceiver 106 by communication means 108 known in the art. The client device 100 may further comprise a plurality of processors 102. The memory 104 may store program code that, when being executed, causes the processor(s) 102 of the client device 100 to performing the functions and actions described herein. The client device 100 further comprises an antenna or antenna array 1 10 coupled to the transceiver 106, which means that the client device 100 is configured for wireless communications in a wireless communication system. That the client device 100 is configured to perform certain actions should in this disclosure be understood to mean that the client device 100 comprises suitable means, such as e.g. the processor(s) 102 and the transceiver 106, configured to perform said actions.

The client device 100 herein is configured to determine a first phase shift between symbols of a first set of received symbols. The client device 100 is further configured to determine a first frequency range and a first centre frequency for a set of control channel resources based on the first phase shift and the first set of received symbols. The client device 100 is further configured to monitor the set of control channel resources in the first frequency range based on the first centre frequency.

Fig. 2 shows a flow chart of a corresponding method 200 which may be executed in a client device 100, such as the one shown in Fig. 1 . The method 200 comprises determining 202 a first phase shift between symbols of a first set of received symbols. The method 200 further comprises determining 204 a first frequency range and a first centre frequency for a set of control channel resources based on the first phase shift and the first set of received symbols. The method 200 further comprises monitoring 206 the set of control channel resources in the first frequency range based on the first centre frequency.

Fig. 3 shows a wireless communication system 500 according to an implementation. The wireless communication system 500 comprises a client device 100 and a network access node 300 configured to operate in the wireless communication system 500. For simplicity, the wireless communication system 500 shown in Fig. 3 only comprises one client device 100 and one network access node 300. However, the wireless communication system 500 may comprise any number of client devices 100 and any number of network access nodes 300 without deviating from the scope of the invention.

With reference to the wireless communication system 500 in Fig. 3 and the flow chart of Fig. 4, the client device 100 in this particular case performs an initial cell search procedure in the wireless communication system 500.

In step 402 in Fig. 4, the client device 100 during an initial search receives a first set of received symbols RS1 from the network access node 300. The client device 100 determines a first phase shift between two or more symbols of the first set of received symbols RS1 . The first set of received symbols RS1 may e.g. comprises one or more SSBs and in that case, the client device 100 detects the one or more SSBs and determines a first phase shift between the symbols of the one or more SSBs.

In step 404 in Fig. 4, the client device 100 determines a first frequency range for a set of control channel resources based on the determined first phase shift from step 402 and the first set of received symbols RS1.

The client device 100 may according to embodiments of the invention determine the first frequency range in step 404 based on system information carried by the first set of received symbols. The system information may in this case e.g. be a Master Information Block, MIB. Furthermore, the first set of received symbols may be a PBCH which implies that when the first set of received symbols comprises a SSB, the client device 100 decodes the PBCH associated with the SSB, using the first phase shift so as to phase compensate the PBCH symbols. From the decoded PBCH the client device 100 thereafter extracts system information, such as e.g. the MIB, that gives information about the first frequency range for monitoring the set of control channel resources. This information may e.g. be in the form of a pointer to where the set of control channel resources can be found. Hence, based on the information extracted from the system information, the client device 100 can determine the first frequency range for the set of control channel resources. Based on the determined first frequency range the client device 100 can derive the first centre frequency. The first centre frequency may be used by the client device 100 for demodulating, e.g. Fourier processing the mentioned set of control channel resources. In some embodiments, the client device 100 chooses the first centre frequency so that the first frequency range is symmetrically arranged around the first centre frequency. However, embodiments of the invention are not limited thereto and in other cases the client device 100 chooses the first centre frequency so that the first frequency range is asymmetrically arranged around the first centre frequency.

In embodiments of the invention the set of control channel resources for which the first frequency range is determined in step 404 may be associated with remaining system information, RMSI, e.g. time-frequency resources in a physical control channel indicating where RMSI can be found. In such embodiments, the first frequency range is hence associated with RMSI.

Moreover, in further embodiments of the invention, the client device 100 may determine the first frequency range in step 404 based on a bandwidth part configured for the client device 100. The bandwidth part configured for the client device 100 may be signalled from a network access node 300 to the client device 100 in control signalling. Therefore, as illustrated in Fig. 3, the client device 100 can be configured to receive a control message 512 from the network access node 300, wherein the control message 512 indicates the bandwidth part configured for the client device 100. In this case, the client device 100 can based on the centre frequency for the first set of received symbols and the centre frequency of the configured bandwidth part determine the first frequency range which is within the configured bandwidth part.

In step 406 in Fig. 4, the client device 100 determines a first centre frequency for the set of control channel resources based on the first frequency range determined in step 404 and the first phase shift determined in step 402.

Which method the client device 100 should use to determine the first centre frequency may be pre-configured in the client device 100, such that the client device 100 either determines the first centre frequency to be equal to the centre frequency of the first frequency range for the set of control channel resources so that a demodulation e.g. with Fourier transformation at the first centre frequency can be performed symmetric with no unnecessary time-frequency resources (not carrying RMSI) demodulated. Alternatively the client device 100 determines the first centre frequency such that no phase shift compensation is to be performed when decoding the symbols of the set of control channel resources.

Therefore, according to some embodiments the first centre frequency is determined to be equal to the centre frequency of the first frequency range for the set of control channel resources, as will be further described below with reference to Fig. 6. The first centre frequency can however according to other embodiments instead further be determined such that no phase shift compensation is performed when decoding the symbols of the set of control channel resources, as will be further described below with reference to Fig. 7.

A pre-configured method for determining the first centre frequency 100 may e.g. be based on the transceiver architecture of the client device 100. For example, if there are dedicated hardware resources configured to perform phase shift the RMSI centre frequency can be used as first centre frequency for the demodulation of the RMSI symbols as described with Fig. 6. If no such dedicated hardware resources are implemented in the client device 100, an offset centre frequency when compared to the RMSI centre frequency may be preferred as first centre frequency for the demodulation of the RMSI symbols.

However, the method for determining the first centre frequency may in embodiments be selected by the client device 100 instead of being pre-configured. The determining method may e.g. be selected based on the first frequency range for the set of control channel resources. For example, if the centre frequency for the set of control channel resources is the same as the centre frequency for the SSB, the client device 100 may select to use the centre frequency for the set of control channel resource as the first centre frequency. In this way, adaptation of the first centre frequency may be avoided and hence faster detection of the set of control channel resource is possible.

In step 408 in Fig. 4, two different processing methods may be employed by the client device 100.

In a first embodiment in step 408, a second phase shift between at least two adjacent symbols of a second set of received symbols is determined based on the first phase shift and the first centre frequency. Based on the second phase shift, the second set of received symbols are thereafter phase adjusted prior to demodulation (at the first centre frequency) of the symbols of the second set of received symbols. The client device 100 can determine the second phase shift based on the first phase shift, the first centre frequency and cyclic prefix length of the symbols of the second set of received symbols. This embodiment is explained more in detail with reference to Fig. 6 below.

In a second embodiment in step 408, the client device 100 instead determines the first centre frequency such that a resulting second phase shift between two adjacent symbols of the second set of received symbols is less than a phase shift threshold value. In this case, the client device 100 can demodulate (at the first centre frequency) the symbols of the second set of the received symbols without a second phase compensation therefore simplifying decoding. The client device 100 can determine the phase shift threshold value based on a total phase shift p over symbols of the second set of received symbols and N number of symbols in the second set of received symbols. For example, the phase shift threshold value may be given as p/N, such as 45 degrees phase shift over a span of N number of (maximum) expected symbols, i.e. phase shift threshold = 45/N degrees. A phase shift between two symbols of up to 60-70 degrees will generally not degrade performance for robust QPSK/BPSK signalling. For 16-QAM 45 degrees may give acceptable degradation. For high performance 64 QAM or 256 QAM phase shift thresholds around 15-20 may be acceptable. This embodiment is explained more in detail with reference to Fig. 7 below.

In step 410 in Fig. 4, the client device finally 100 monitors the set of control channel resources in the first frequency range based on the first centre frequency. The client device 100 can monitor the set of control channel resources based on demodulating symbols of the second set of received symbols using the first centre frequency in the first frequency range carrying the set of control channel resources. The demodulation can be performed by Fourier processing of the second set of received symbols using the first centre frequency.

In this respect according to embodiments of the invention the processor 102 of the client device 100 comprises a baseband processor 120 and a control unit 122 as shown in Fig. 5. The baseband processor 120 and the control unit 122 are each coupled to the transceiver 106. The baseband processor 120 is configured to determine a first phase shift pi as well as a first frequency range 4 and a first centre frequency fci for monitoring the set of control channel resources, such as control channel resources associated with RMSI, according to embodiments of the invention. The first phase shift pi is therefore determined based on a first set of received symbols RS1 feed from, and down converted by the tranceiver 106 after reception from the antenna 1 10. The determined first phase shift pi, the first frequency range 4 and the first centre frequency fci are sent from the baseband processor 120 to the control unit 122. The control unit 122 based on the first frequency range 4 and the first phase shift pi determines a local oscillator frequency 4o as well as possible digital down- or up-conversion frequencies fee to be adapted to the corresponding first centre frequency fci. The local oscillator frequency 4o is fed to the transceiver 106 that adapts its local oscillator frequency for RMSI monitoring based on the recived local oscillator frequency 4o- Further, the possible digital down- or up-conversion frequencies fee are fed from the control unit 122 to the baseband processor 120 since parts of the down conversion can be performed by the baseband processor 120. The transceiver 106, after having adapted its local oscillator frequency based on o, receives a radio signal S comprising one or more sets of symbols, via the antenna 1 10, and downconverts the radio signal S to a baseband signal that is processed for RMSI monitoring in the baseband processor 120 of the processor 102. The first centre frequency fci may be used in the digital baseband into a monitoring and decoding unit (not shown in Fig. 5), i.e. as centre frequencies prior to FFT or discrete Fourier transform (DFT) processing. The adaptation to the first centre frequency fci can be made in several ways. For example, the local oscillator frequency o or the oscillator frequency in a last analogue intermediate frequency (IF) mixer stage can be selected such that the output mixing frequency corresponds to the determined first centre frequency fci. In other embodiments, the intermediate frequency input to the processor 102 from the transceiver 106 may be digitally down- or up-converted to a frequency prior to monitoring the set of control channel resources according to the determined first centre frequency fci.

As previously mentioned with reference to step 408 in Fig. 4, in an embodiment the client device 100 determines the first centre frequency to be equal to the centre frequency of the first frequency range for the set of control channel resources. This embodiment will now be described in even more detail with reference to Fig. 6.

In the embodiment shown in Fig. 6, the first set of received symbols are SSBs. As previously explained a SSB comprises PSS, SSS and PBCH. The client device 100 therefore firstly detects PSS and SSS and further estimates a first phase shift f 7. Once PSS and SSS are detected, the client device 100 has also determined the cyclic prefix length NCP, as well as the sub-carrier spacing Nsc and the chip symbol time 7 c. The first phase shift f 1 corresponds to a phase shift seen by the client device 100 between two or more symbols in the SSB. Once the first phase shift f 1 has been estimated, i.e.

f 1 =2n^*M’^*Ncp/N_FFT=2^*n^*M’^*Ncp^*Af^*Tc,

where N_FFT is the FFT size used by the network access node 300, the client device 100 can determine the sub-carrier offset M’. Since the estimate of the first phase shift only gives estimates in the interval between 0 to 2p (in radians) the client device 100 cannot estimate the correct sub-carrier offset M but instead M’=M+n^*N_FFT/Ncp, where n is an integer which is unknown for the client device 100. Hence, when the centre frequency difference between a receiver (client device) and a transmitter (network access node) is M subcarriers, the corresponding phase shift between OFDM symbols is 2n*M*N_CF/N_{FF T}. The client device 100, using the first phase shift can read PBCH (since PBCH has the same centre frequency as SSS and PSS) and from the PBCH determine the first frequency range for monitoring RMSI (e.g. RMSI CORESET). Based on the frequency location of the SSB the client device 100 can determine the frequency offset between the SSB centre frequency f_m and the RMSI centre frequency 4, the frequency distance equals K sub carriers which information (i.e. K) can be detected in the PBCH. From this information, the client device 100 can determine a second phase shift f2 related to the frequency distance between the SSB and the RMSI which is a phase shift seen by the client device 100 between two or more symbols of RMSI (similarly as the case for SSB), i.e. q>2=2n^*(M’-K)^*Ncp/NFFT. As can be noted, if K=0, i.e. the RMSI centre frequency is on the same frequency as the SSB centre frequency f_m, then the second phase shift equals to the first phase shift, f2=f 7. Furthermore, if K=M’ or K=n^*M’^*N_FFr/Ncp (where n is an integer), then the second phase shift f2 between RMSI symbols will be zero, which also holds for the case K=M. The client device 100 adapts the first centre frequency to RMSI centre frequency 4, i.e. to the centre frequency of the RMSI frequency range and adapts the receiver bandwidth to be at least as wide as the RMSI frequency range. The client device 100 further starts monitoring the control channel resources within the first frequency range. In order for correct detection of the control symbols and data symbols of the second set of received symbols the client device 100 needs to phase adjust the second set of symbols using the second phase shift f2.

As previously mentioned with reference to step 408 in Fig. 4, in another embodiment the client device 100 determines the first centre frequency such that no phase shift compensation is needed when decoding the symbols of the set of control channel resources. This embodiment will now be described with reference to Fig. 7.

In the embodiment shown in Fig. 7, symbols of the first set of received symbols are SSBs. Utilizing the fact that 2p*h, where n is an integer ambiguity of the phase function, another approach for choosing a first centre frequency for monitoring and decoding RMSI (e.g. RMSI CORESET), is to select another frequency or sub-carrier distance K’ preferably close to K, such that the following condition holds for the second phase shift f2, i.e.

(p2=2n*(M’-K’)*Ncp/N_FFT=2n*(M’-K’)*Ncp*Af*Tc~2n*n (Equation 4).

If the condition in Equation 4 holds the second phase shift f2 between RMSI symbols is zero and corresponds to no phase shift in the complex plane. Hence, the client device 100 in this case does not need to perform a phase adjustment of the RMSI symbols if the client device 100 when decoding the RMSI uses a first centre frequency at distance K’from the centre frequency of SSB where K’ fulfils the condition in Equation 4. The receiver bandwidth of the client device 100 need also in this case cover the entire RMSI frequency range. However, the receiver bandwidth may, depending on the client device 100 implementation, be chosen larger than the RMSI frequency range in this case due to the offset in centre frequency and receiver filter design. It is further to be noted that this embodiment also covers the previously described case that the client device 100 chose K’such that the phase shift may not be exactly zero but smaller than a phase shift threshold value. The phase shift threshold can be chosen such that the phase shift is small, and therefore can be neglected in RMSI monitoring.

In a further embodiment the network access node 300 may have, at least partly, pre- compensated the first set of received symbols. Hence, instead of determining the first phase shift the client device 100 may directly determine the first frequency range only based on the first set of (phase pre-compensated) received symbols without performing a phase shift on these symbols. Then based on the determined first frequency range the client device 100 determines a monitoring centre frequency and the second phase shift. The second phase shift corresponds to a (radio channel) phase shift between adjacent control symbols or data symbols in the first frequency range. In some embodiments, the second phase shift can be based on at least in part on the client device 100 (such as UE) carrier (or down-conversion) frequency. In some other embodiment it may be based at least in part on the absolute frequency for one of the sub-carriers in the frequency range, for instance the centre sub-carrier (that may be offset from the carrier frequency). The second phase shift in this embodiment may be defined by a pre-defined rule in combination with the determined frequency range and first center frequency, or may also be send as a configuration from the network access node 300 in a RRC message.

The client device 100 then configures the first centre frequency and monitors the CORESET and performs phase shift compensation of symbols in the frequency range according to determined second phase shift.

To summarize, the further embodiment provides a client device 100 configured to monitor a control channel resource set (CORESET). The client device 100 is configured to determine a first frequency range the client device 100 needs to monitor the control channel resource set on. The client device is further configured to determine a first centre frequency and a second phase shift. The second phase shift corresponds to a (radio channel) phase shift between adjacent control symbols or data symbols in the first frequency range. The client device 100 is further configured to monitor signals with a centre frequency according to the determined first centre frequency. For this, the client device 100 may employ a receiver bandwidth including at least the determined first frequency range. The client device 100 is further configured to monitor the control channel resource set in the first frequency range. The monitoring of the control channel resource set in the first frequency range further comprises a phase shift compensation of symbols in the first frequency range according to the determined second phase shift. The second phase shift may be based at least in part on the client device carrier frequency. Furthermore, the first frequency range may be determined based on the reception of a BWP configuration of the client device 100 received from a network access node, e.g. in control signalling possibly using control messages. Furthermore, the first frequency range may be determined based on decoding (phase pre-compensated) symbols on a data channel (such as PBCH) associated to a set of sync signals (such as PBCH in the SSB).

The client device 100 herein, may be denoted as a user device, a User Equipment (UE), a mobile station, an internet of things (loT) device, a sensor device, a wireless terminal and/or a mobile terminal, is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UEs may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.1 1 - conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The UE may also be configured for communication in 3GPP related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth generation wireless technologies, such as New Radio.

The network access node 300 herein may also be denoted as a radio network access node, an access network access node, an access point, or a base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter,“gNB”,“gNodeB”,“eNB”, “eNodeB”,“NodeB” or“B node”, depending on the technology and terminology used. The radio network access nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network access node can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The radio network access node may also be a base station corresponding to the fifth generation (5G) wireless systems.

Furthermore, any method according to embodiments of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

Moreover, it is realized by the skilled person that embodiments of the client device 100 and the network access node 300 comprises the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the present solution. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the present solution. Especially, the processor(s) of the client device 100 and the network access node 300 may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression“processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like. Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

1. A client device (100) for a wireless communication system (500), the client device (100) being configured to

determine a first phase shift between symbols of a first set of received symbols (RS1 ); determine a first frequency range and a first centre frequency for a set of control channel resources based on the first phase shift and the first set of received symbols (RS1 );

2. The client device (100) according to claim 1 , configured to

3. The client device (100) according to claim 2, configured to

4. The client device (100) according to claim 2 or 3, configured to

determine the second phase shift based on the first phase shift, the first centre frequency and cyclic prefix length of the symbols of the second set of received symbols.

5. The client device (100) according to claim 3 or 4, configured to

6. The client device (100) according to claim 5, wherein the first frequency range is asymmetrically arranged around the first centre frequency.

7. The client device (100) according to claim 5 or 6, configured to

8. The client device (100) according to claim 7, wherein the phase shift threshold value is given as p/N.

9. The client device (100) according to any of the preceding claims, configured to

determine the first frequency range based on system information carried by the first set of received symbols (RS1 ).

10. The client device (100) according to claim 9, wherein the system information is a master information block.

1 1. The client device (100) according to claim 9 or 10, wherein the system information is received on a physical broadcast channel.

12. The client device (100) according to any of claims 9 to 1 1 , wherein the first frequency range is associated with remaining system information.

13. The client device (100) according to any of the preceding claims, configured to

determine the first frequency range based on a bandwidth part configured for the client device (100).

14. The client device (100) according to claim 13, configured to

receive a control message (512) from a network access node (300), wherein the control message (512) indicates the bandwidth part configured for the client device (100).

15. The client device (100) according to any of the preceding claims, wherein the first set of received symbols (RS1 ) comprises synchronization signal blocks.

16. A method (200) for a client device (100), the method (200) comprising

determining (202) a first phase shift between symbols of a first set of received symbols (RS1 );

determining (204) a first frequency range and a first centre frequency for a set of control channel resources based on the first phase shift and the first set of received symbols (RS1 ); monitoring (206) the set of control channel resources in the first frequency range based on the first centre frequency.

17. A computer program with a program code for performing a method according to claim 16 when the computer program runs on a computer.