CN109906591B

CN109906591B - Apparatus and method for wireless communication network synchronization

Info

Publication number: CN109906591B
Application number: CN201680090597.0A
Authority: CN
Inventors: 汪凡; 布兰尼斯拉夫·M·波波维奇; 王鹏; 富兰崛克·伯根
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2016-11-02
Filing date: 2016-11-02
Publication date: 2021-06-22
Anticipated expiration: 2036-11-02
Also published as: WO2018082768A1; CN109906591A

Abstract

A system and method for wireless communication network synchronization is described. The wireless communication system transmits an SS block including at least a primary synchronization signal, a secondary synchronization signal, and an SS block index. The user equipment receives the transmitted blocks and the user equipment can extract the signal and index from any received block. In addition to the SS block index, a beam index may be encoded into each SS block. The user equipment may respond appropriately to the received information.

Description

Apparatus and method for wireless communication network synchronization

Technical Field

The present disclosure relates to the field of wireless communications, and more particularly, to transmission of synchronization signals.

Background

Cellular radio systems rely on proper synchronization. Generally, synchronization is performed by using a synchronization signal. The base station transmits a synchronization signal which is detected by a mobile device, which may be a mobile phone, any type of user equipment, possibly also other devices comprising a wireless communication unit or similar.

Long Term Evolution (LTE) is a widely used technology for wireless communication at present. In LTE, a synchronization signal is periodically transmitted by a Base Station (BS), for example, in subframes 0 and 5 of each frame for Frequency Division Duplexing (FDD). In LTE, a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) are transmitted in different Orthogonal Frequency Division Multiplexing (OFDM) symbols. Within one period, i.e. 5ms, the PSS and SSS are each transmitted in one synchronization signal block, i.e. one OFDM symbol. The UE acquires time and frequency synchronization and cell Identity (ID) by detecting PSS and SSS.

A New Radio (NR) access technology capable of supporting a beamformed synchronization signal is currently being developed. For example, the NR base station applies a plurality of beams to a plurality of synchronization intervals of a synchronization occasion within one period. In one aspect, a network node, such as a base station, access point, or transmit receive point, may support three implementations of beamforming, which are analog beamforming, digital beamforming, and hybrid beamforming. Particularly for analog beamforming and hybrid beamforming, the maximum number of concurrent beams may be limited by the number of Radio Frequency (RF) chains. On the other hand, the number of beams employed by different network nodes may also differ from each other depending on the detailed deployment scenario and the required coverage area. It is therefore a problem to provide synchronization signals that can be transmitted using beamforming, while enabling mobile devices to acquire and track a flexible number of beamformed synchronization signals employed by a network node, and to provide efficient network node operation.

In one proposed solution, a plurality of different spatial beams are applied to the same number of synchronization signal blocks of one synchronization occasion within one period. The mapping between beams (also interpreted as beam directions or beam indices) and the synchronization signal block are one-to-one and predefined, e.g. beam 1, beam 2,. and beam N are employed in synchronization signal block 1, synchronization signal block 2,. and synchronization signal block N, respectively. The UE obtains the beam index by detecting the synchronization signal and may feed back this beam information to the network node through, for example, a random access procedure or uplink feedback.

In another proposed solution, the synchronization signal includes a PSS including a portion of the cell ID, an SSS including a remaining portion of the cell ID, and an Extended Synchronization Signal (ESS) including a synchronization signal block index, wherein each synchronization signal block is an OFDM symbol. Each PSS, SSS and ESS triplet uniquely corresponds to one beam and is frequency division multiplexed in one of a predetermined number (i.e., 14) OFDM symbols. For each OFDM symbol, PSS and SSS follow the same design as LTE, and the ESS is generated using the product of a Zadoff Chu (ZC) sequence, in which the symbol index is coded with different cyclic shifts, and a pseudo-random sequence. And the UE obtains the cell ID by detecting the PSS/SSS and obtains the synchronization interval index by detecting the ESS.

In the proposals discussed above, the network node implementation is limited. The network node needs to generate a fixed number of beams, i.e. a number equal to the synchronization interval. In some implementations, the network node may generate a different number of beams, e.g., less than or greater than the number of synchronization signal blocks, however, the network node is also required to apply beamforming in a predefined manner, which unnecessarily increases implementation constraints, as well as specification efforts.

Disclosure of Invention

A method of transmitting a synchronization signal using a flexible number of beams in one or more Synchronization Signal (SS) blocks for a predefined period, which may be an SS burst or a set of SS bursts, will be described below. A marking method of coding cell identification, interval block index, Transmission Received Point (TRP) identification and/or beam index is provided in a synchronization signal to allow a UE to perform continuous search for an appropriate transmission point by acquiring synchronization and/or beams even when the UE does not know the number of beams used at a network node. In particular, it allows a network node to transmit multiple beams in one SS block at the same time, while it also allows the network to transmit a flexible number of SS blocks in one SS burst.

In a first aspect, a network node for wireless communication comprising a processor is disclosed. The processor is configured to provide at least one SS block, wherein the at least one SS block includes at least a primary synchronization signal and a secondary synchronization signal. The processor is further configured to encode an SS block index into each of the Synchronization Signal (SS) blocks. The network node further comprises a transceiver configured to transmit the SS blocks. In some terms, the SS block may be an SS burst and, correspondingly, the SS block index may be an SS burst index.

A network node transmits a plurality of synchronization signals in a plurality of SS blocks of the same SS burst or set of SS bursts, each synchronization signal comprising at least a PSS and a SSs and possibly an ESS, wherein each synchronization signal comprises information of an SS block index. The network node may propagate in a beam-forming manner in each SS block in a proprietary manner, i.e., without restricting how the network node applies the beams in the SS blocks. In particular, the SS block index may be coded in various ways, e.g., coded in PSS by modulating ZC sequences, or coded in SSs/Extended Synchronization Signal (ESS) by reusing SSs sequences, or divided into more than one part, each part corresponding to one of PSS, SSs and possibly another part transmitted in Physical Broadcast Channel (PBCH). In addition, a different network node identity, e.g. a TRP identity, than the cell identity can be encoded in the synchronization signal, which allows the UE to synchronize to multiple TRPs within the same cell. The UE obtains an SS block index from the detected synchronization signal sequence resource. The UE may utilize the SS block index for feedback to help the eNodeB obtain associated beam information, e.g., implicitly.

In a first implementation of the first aspect, the transceiver is configured to transmit the SS blocks using a plurality of beams. Multiple beams are used to provide beamforming gain to extend the coverage of the synchronization signals in the SS block.

In a second implementation of the first aspect, the SS block further includes at least one of an additional secondary synchronization signal and physical broadcast channel information. It is advantageous to allow the SS block to include other signals besides the primary and secondary synchronization signals. It allows the network node to send other information than the information in PSS and SSS, e.g. System Frame Number (SFN).

In a third implementation form of the first aspect, the processor is configured to encode the SS block index into at least two of the primary synchronization signal, secondary synchronization signal, additional secondary synchronization signal, and physical broadcast channel information. When the SS block index is divided into a plurality of portions and included in different types of signals, respectively, the network node may freely select to which signal it is efficient to encode a portion of the SS block index. This provides further flexibility. The network node is free to choose how to split the SS block index and divide the SS block index into several parts.

In a fourth implementation of the first aspect, the number of SS blocks is from 1 to N, where N is a predefined maximum value. It is advantageous to allow the use of any number of SS blocks between 1 and a predefined maximum. This allows the network node to select a flexible number of used SS blocks, which further results in a flexible overhead of synchronization signals. In a fifth implementation of the first aspect, the processor is configured to encode the SS block index into any one of: the primary synchronization signal, wherein the processor is further configured to multiply a Zadoff Chu sequence with an additional sequence to obtain a primary synchronization signal sequence, wherein the additional sequence is used in encoding the SS block index; or the additional secondary synchronization signal, wherein the processor is configured to obtain the additional secondary synchronization signal from the same set of sequences as the secondary synchronization signal; or the secondary synchronization signal, wherein a period of the secondary synchronization signal is an integer multiple of one system frame. By encoding the SS block index in the PSS, the UE may advantageously obtain the SS block index from the PSS sequence resources without increasing the signaling overhead in the SSs. By encoding the SS block index in an additional secondary synchronization signal that reuses the same set of sequences as the SSS, it is advantageous because existing synchronization signal design/detection can be maximally exploited while additional functionality is met. By encoding the SS block index in the SSS, the UE may advantageously obtain the SS block index from the SSS sequence without increasing the signaling overhead in the PSS.

In a sixth implementation of the first aspect of the apparatus and method for wireless communication network synchronization, the processor is further configured to encode a beam index into each of the at least one SS block. In a sixth implementation of the first aspect, beam information (e.g., beam index) is encoded in the synchronization signal sequence in addition to the SS block index. The total number of beams associated with the total synchronization signal sequence is predefined. The network may use a flexible number of beams, which should not be larger than a predefined total number of beams. The UE obtains the SS block index and the beam information from the detected synchronization signal sequence. The UE may use the beam information for feedback to the network node.

In a seventh implementation form of the first aspect, the number of beam indices is encoded into the at least one SS block from 1 to M, where M is a predefined maximum value. It is advantageous to allow the use of any number of beams between 1 and a predefined maximum. This allows the network node to apply beamforming, e.g., analog/hybrid/digital beamforming, using different implementations. In particular, this allows the network node to apply concurrent transmission of multiple beams to further provide reduced control overhead or finer beam resolution.

In an eighth implementation form of the first aspect, the processor further encodes a TRP identity and a cell identity into each of the at least one SS block. Including additional network node identity related information in the SS block is advantageous because it provides the UE with the possibility to identify the network when the UE is connected to multiple TRPs in a cell.

In a second aspect of the apparatus and method for wireless communication network synchronization, a user equipment for wireless communication is provided. The user equipment includes: a transceiver configured to receive one SS block including at least a primary synchronization signal and a secondary synchronization signal; a processor configured to extract an SS block index from the received SS block.

In a first implementation of the second aspect, the user equipment is configured to extract the SS block index from the at least one received SS block by decoding any one of: the primary synchronization signal obtained from multiplying a Zadoff Chu sequence and an additional sequence, wherein the additional sequence encodes the SS block index, or an additional secondary synchronization signal obtained from the same sequence set as the secondary synchronization signal, or the secondary synchronization signal, wherein a period of the secondary synchronization signal is an integer multiple of one system frame. By encoding the SS block index in the PSS, the UE may advantageously obtain the SS block index from the PSS sequence resources without increasing the signaling overhead in the SSs. By encoding the SS block index in an additional secondary synchronization signal that reuses the same set of sequences as the SSS, it is advantageous because existing synchronization signal design/detection can be maximally exploited while satisfying additional functionality. By encoding the SS block index in the SSS, the UE may advantageously obtain the SS block index from the SSS sequence without increasing the signaling overhead in the PSS.

In a second embodiment of the second aspect, the processor is further configured to obtain any one of a beam index and a TRP identity. Including additional network node identity related information in the SS block is advantageous because it provides the UE with the possibility to identify the network when the UE is connected to multiple TRPs in a cell. In a third implementation of the second aspect, the user equipment is configured to obtain uplink transmissions from any one of the SS block index, the beam index and the TRP identity. It is advantageous to obtain the uplink transmission from the received information so that the best possible conditions can be selected for the communication between the network and the UE.

In a third aspect of an apparatus and method for wireless communication network synchronization, a method for wireless communication is disclosed. The method includes providing at least one SS block, wherein the at least one SS block includes at least a primary synchronization signal and a secondary synchronization signal; encoding an SS block index into each of the SS blocks and transmitting the at least one SS block. It is beneficial to encode an SS block index into each transmitted SS block. This will allow the UE to obtain the SS block index even if only one SS block is received at the UE.

In a first embodiment of the third aspect, the method further comprises transmitting at least one of the SS blocks using a plurality of beams. Multiple beams are used to provide beamforming gain to extend the coverage of the synchronization signals in the SS block. In a second implementation of the third aspect, the SS block further includes at least one of an additional secondary synchronization signal and a physical broadcast channel. It is advantageous to allow the SS block to include other signals besides the primary and secondary synchronization signals. It allows the network node to send other information than the information in PSS and SSS, e.g. the System Frame Number (SFN).

In a third implementation of the third aspect, the method further includes encoding the SS block index to at least two of the primary synchronization signal, secondary synchronization signal, additional secondary synchronization signal, and physical broadcast channel information. When the SS block index is divided into a plurality of portions and included in different types of signals, respectively, the network node may freely select to which signal it is efficient to encode a portion of the SS block index. This provides further flexibility.

In a fourth embodiment of the third aspect, the number of the at least one SS block is from 1 to N, where N is a predefined maximum value. It is advantageous to allow the use of any number of SS blocks between 1 and a predefined maximum. This allows the network node to select a flexible number of used SS blocks, further resulting in a flexible overhead of synchronization signals.

In a fifth implementation manner of the third aspect, the method further includes encoding the SS block index to any one of the primary synchronization signal, the additional secondary synchronization signal, or the secondary synchronization signal, wherein the method further includes: obtaining a primary synchronization signal sequence by multiplying a Zadoff Chu sequence and an additional sequence, wherein the additional sequence is used in encoding the SS block index, wherein the method further comprises obtaining the additional secondary synchronization signal from the same sequence set as the secondary synchronization signal, wherein a period of the secondary synchronization signal is an integer multiple of one system frame. By encoding the SS block index in the PSS, the UE may advantageously obtain the SS block index from the PSS sequence resources without increasing the signaling overhead in the SSs. By encoding the SS block index in an additional secondary synchronization signal that reuses the same set of sequences as the SSS, it is advantageous because existing synchronization signal design/detection can be maximally exploited while additional functionality is met. By encoding the SS block index in the SSS, the UE may advantageously obtain the SS block index from the SSS sequence without increasing the signaling overhead in the PSS.

In a sixth implementation form of the third aspect, the method further comprises encoding a beam index into each of the at least one SS block. It is beneficial for the UE to receive and use all the information received from the network. It can more efficiently utilize resources and improve the availability of the device. In a seventh implementation of the third aspect, the number of beam indices encoded into the at least one SS block is from 1 to M, where M is a predefined maximum value. It is advantageous to allow the use of a number of beams between 1 and a predefined maximum. This allows the network node to apply beamforming, e.g., analog/hybrid/digital beamforming, using different implementations. In particular, this allows the network node to apply concurrent transmission of multiple beams to further provide reduced control overhead or finer beam resolution.

In an eighth implementation of the third aspect, the method further comprises encoding a TRP identity and a network identity into each of at least one of the SS blocks. Including additional network node identity related information in the SS block is advantageous because it provides the UE with the possibility to identify the network when the UE is connected to multiple TRPs in a cell.

In a fourth aspect of the apparatus and method for wireless communication network synchronization, a method for a user equipment for wireless communication is provided. The method includes receiving an SS block, wherein the SS block includes at least a primary synchronization signal and a secondary synchronization signal, and extracting an SS block index from the received SS block. It is advantageous for the user equipment to receive transmissions where each SS block includes an SS block index. Therefore, all information required for synchronization can be acquired by receiving only one SS block.

The above disclosed apparatus and method for wireless communication network synchronization and method for wireless communication provide an efficient mechanism for providing the required synchronization information from the network side to the user equipment. It is particularly advantageous that the arrangement disclosed above is in a beamformed network, wherein a number of limitations can be removed by using the above-described aspects and implementations. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Drawings

For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

figure 1a shows a schematic diagram of a network node and a UE interacting in a wireless communication system;

fig. 1b shows an example of a method used in a wireless communication system;

fig. 1c shows an example of a method used in a wireless communication system;

figure 1d shows an example of a network node for use in a wireless communication system;

fig. 2 shows a signaling diagram of a wireless communication system;

fig. 3 shows an example of a synchronization signal;

fig. 4 shows an example of a beam-dependent SS block; and

fig. 5 shows an example of an SS block.

Detailed Description

The detailed description provided below in connection with the appended drawings is intended as a description of embodiments and is not intended to represent the only forms in which the embodiments may be constructed or utilized. However, the same or equivalent functions and structures may be accomplished by different embodiments.

In the following description, a synchronization signal block (SS block) and an SS block index (SS block index) are widely discussed. The SS block is used to carry different signals and information. The SS block index is an index of an SS block, e.g., a Synchronization Signal (SS) burst, over a period of time. For example, if an SS burst includes three SS blocks, the corresponding SS block index includes information of the three SS blocks. Other expressions used for the same purpose are, for example, synchronization signal intervals, synchronization signal occasions, synchronization symbols or the like. However, for example, the difference between the synchronization signal interval and the synchronization signal interval index corresponds to the difference described above with respect to the SS block and the SS block index.

Fig. 1a shows a wireless communication system with one base station 100 and one user equipment 108. For clarity, only one base station and user equipment are shown. Typically, wireless communication systems involve a very large number of base stations that are connected to serve a very large number of users. The base station of fig. 1a comprises signal processing circuitry 101, a beamformer 102 and two

antennas

103a, 103 b. The network connection 105 is used to connect the base station 100 to the core network 105. The signal processing circuitry comprises at least one processor 106 and at least one memory 107, which are configured to process and generate signals to be further transmitted. The processing includes several different tasks related to synchronization and synchronization signals. The beamformer 102 receives a signal comprising a synchronization signal from the signal processing circuitry 101 and provides a beamformed version to the transceiver 104, which transceiver 104 transmits a beam using the transmit

antennas

103a, 103 b. The number of antennas is not limited to two.

As shown in fig. 1a, the base station 100 is configured to transmit data to at least one user equipment 108. Specific processing of the received data and appropriate response to the received synchronization signal. The user device 108 may be a mobile phone, a smart phone, or similar device.

As shown in fig. 1b, an aspect of a method used in a wireless communication system, e.g. the base station 100 of fig. 1a or the network node 118 of fig. 1d, is disclosed. In the method, an SS block is first provided, as in step 111. In this example, the SS block index is then encoded into the SS block, as in step 112. The encoded SS block is then transmitted, as in step 113. The transmission may be in the form of beamforming. But this is not essential.

As shown in fig. 1c, another embodiment of a method for use in a wireless communication system, such as the system of fig. 1a, is disclosed. In the method, an SS block is first provided, as in step 114. In this example, the SS block index is then encoded into the SS block, as in step 115. In addition to the SS block index, the beam index is also encoded into the SS block, as in step 116. In the example of fig. 1c, the transmitting step 117 is in a beamformed form, however, even if beamformed communication is used, it is not necessary to transmit the SS blocks in a beamformed form.

Fig. 1d illustrates an aspect of a wireless communication system. In this figure, network element 118 is shown. The network element 118 includes a processor 119. A beamformer 120 is also optionally included. The network element 118 is configured to perform the method according to fig. 1 b. Optionally, the network element 118 is configured to perform the method of fig. 1 c. When performing the method of fig. 1c, a beamformer 120 is comprised in the network node 118.

Fig. 2 shows a signaling diagram of a wireless communication system. A network node 200, such as a base station, is configured to communicate with a User Equipment (UE) 201. The network node 200 sends a signal 202 comprising at least one SS block to the user equipment 201. The SS block includes a primary synchronization signal and a secondary synchronization signal. The synchronization signal block is transmitted in a beam-formed form. Each SS block also includes an SS block index. The SS block may also include a beam index.

From the received signal, the UE201 obtains downlink synchronization information and possibly preferred beam information. Further, the UE 202 is configured to indicate beam information and/or synchronization information to the network node in order to obtain preferred downlink beam information.

In the example of fig. 2, the network node 200 transmits synchronization signals using a flexible number of beams and a fixed number of synchronization signal sequence resources, each synchronization signal sequence resource being associated with a unique SS block of the fixed number of SS blocks. The UE201 obtains SS block information from the detected synchronization signal sequence resource.

The network node transmits the synchronization signal 202 using a flexible number of beams (X) in a synchronization signal burst or synchronization signal burst set comprising a flexible number (T) of SS blocks, wherein P beams are applied in each SS block, wherein 1< ═ P < ═ M and 1< ═ T < ═ N, and M and N are predefined, e.g. in a standard. The number of beams P per SS block is not necessarily known in the UE prior to initial access.

Fig. 3 provides an example of transmission of a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSs) in a set of Synchronization Signal (SS) bursts comprising a plurality of SS bursts, where each SS burst comprises a plurality of SS blocks. For PSS, SSS and possibly other signals, e.g. the common broadcast channel (PBCH), the same beam direction will be applied in one SS block. These signals in an SS block may be Time Division Multiplexed (TDM), i.e., as shown in fig. 3, or Frequency Division Multiplexed (FDM). An SS block may be an OFDM symbol, or any other predefined time interval. A Transmit Receive Point (TRP) may use P (P < ═ M) beams per SS block and T (T < ═ N) SS blocks per SS burst to achieve beamformed synchronization signals, where "nominal" denotes predefined maximum values (M and N) and "actual" denotes the value that the TRP uses according to its beamforming capability in fig. 3. Note that this includes support for single beam transmission, for example, when P ═ T ═ 1. The UE does not need to know the actual number of beams used to decode the synchronization signal and the actual number of SS blocks, since the same synchronization and cell search procedure (e.g., sliding window) can be employed. Cell search information may be obtained when an SS is detected from any SS block.

In fig. 4, the selection of the number of beams for each SS block and the number of SS blocks to achieve the same coverage is shown. The number of beams X may be equal to the number of SS blocks N, but it need not be. In one embodiment, X is equal to N. The network node may apply sequential beamforming, i.e. each beam direction corresponds to one SS block; in another embodiment, X is greater than N. This may be particularly beneficial in some implementations that allow multiple beams to be transmitted concurrently, for example, using hybrid beamforming or digital beamforming. The network node may apply concurrent transmission of a plurality of beamformed synchronization signals in at least one SS block. The concurrent transmission of multiple beamformed synchronization signals may be marked, for example, by different synchronization signal sequences. The synchronization signal sequences of the same SS block may have the same tag for SS block index and different tags for beam index. Concurrent beam transmission may be used to achieve a wider wide block angular width, thereby reducing the number of SS blocks to reduce overhead, as shown in fig. 4. Concurrent beam transmission may also be used to achieve better beam resolution over a given number of SSs, a wide beam to be transmitted in one SS block may be split into multiple concurrent narrow beams; in another embodiment, X is less than N. The network node may apply one beam direction to multiple SS blocks. This is particularly beneficial for some implementations that generate a wide beam, e.g., a network node with a limited number of antenna elements.

The above arrangement is advantageous because there is no strict limit on the number of beams used to transmit the synchronization signal, and it is not necessary to define in advance the mapping between SS blocks and beams within an SS burst or set of SS bursts.

Next, the coding of SS block indices in PSS or SSS will be explained. The SS block index is encoded in the synchronization signal sequence resource, e.g., using a processor of the base station. The synchronization signal resource is a container of SS block indexes, where one synchronization signal sequence corresponds to one index. A number of synchronization signal sequence resources are predefined in the standard, the total number of which equals the maximum number of SS blocks, i.e. N. The relationship between the N synchronization signal resources and the N SS blocks is one-to-one and predefined. The synchronization signal sequence resources may be PSS sequences, SSS sequences, or a combination of PSS and SSS sequences. The synchronization signal sequence resource may also be a PSS sequence set, an SSS sequence set, a combination of PSS and SSS sequence sets, or a combination of PSS and SSS sequence sets.

In one embodiment, the SS block index is encoded in the PSS sequence. Each synchronization signal sequence resource includes a different PSS sequence. The network transmits multiple PSS sequences in multiple SS blocks. Each PSS sequence is associated with a unique SS block. An example of an association is given in table 1. The PSS sequence may be a Zadoff-Chu sequence as defined in LTE, or any other sequence, which may or may not contain cell specific information such as cell ID.

TABLE 1 Association between synchronization Signal sequence resources and SS blocks

This is advantageous because the UE can obtain the SS block index from the PSS sequence resources without also increasing the signaling overhead in the SSs.

The PSS sequence may be generated by modulating a sequence with SS block index, e.g., by the following formula

c_S(n)＝d_u(n)b_S(nmodm),n＝0,1,...,L-1

In the equation L-tm and t and m are positive integers, d_u(n) is the nth element of an L-length ZC sequence defined in 3GPP LTE with root index μ, b_S(nmodm) is the n mod m-th element of a sequence of length m, restricted to be composed of complex numbers with the same (unity) amplitude, and derived from the SS block indices, i.e., each SS block corresponds to a unique sequence { b }_S(nmodm)}。

This is advantageous because the UE obtains cell specific information from the PSS, i.e. a part of the cell ID from the used root index μ, while also being able to obtain the SS block index. It should be noted that in this case, a set of PSS sequences is associated with one SS block, i.e. they constitute one synchronization signal resource.

In one embodiment, the SS block index is encoded in the SSs sequence. Each synchronization signal sequence resource includes a different SSS sequence. The network transmits a plurality of SSs sequences in a plurality of SS blocks. Each SSS sequence is associated with a unique SS block. The SSS sequence may be a sequence defined in LTE, or any other sequence that may contain cell-specific information such as a cell ID or any other information. This is advantageous because the UE can obtain the SS block index from the SSS sequence without increasing the signaling overhead in the PSS.

In one embodiment, the SS block index S_IDAre jointly coded in PSS and SSS. S_IDIs that

And

a function of wherein

Is coded in the PSS sequence and is,

encoded in the SSS sequence. In one embodiment, there are four SS blocks indexed by 0,1,2,3,

from the {0,1},

from {0,1}, and

this is advantageous because the indication of the SS block index can be set

And

are flexibly allocated to PSS and SSS to achieve better performance and complexity trade-off.

In fig. 5, another embodiment is disclosed. In this embodiment, each PSS is associated with one SSS (i.e., SSS1) and one additional secondary synchronization signal (i.e., SSS 2). SSS1 is used to carry cell ID as in LTE. The SSS2 indicates additional information using the same set or subset of SSS sequences. Detailed design may be found in fig. 5, where each SS block includes PSS, SSs1, SSs2 and PBCH corresponding to the same beam. In LTE, for coding of frame timing, SSS sequences for the first half frame and the second half frame are different, for example, the first half is 168 sequences and the second half is 168 sequences. Thus, the total available sequence for SSS2 is 336. This is advantageous because the SSS sequence can be reused to load additional information including SS block index and beam index. In addition, the SSS detector may be reused for SSS1 and SSS2 because they share the same set of sequences.

In another embodiment, each PSS is associated with one SSS (i.e., SSS1) or one additional secondary synchronization signal (i.e., SSS 2). The SSS2 uses a partial SSS sequence to indicate information other than SSS1, such as SS block index and/or beam index information. Specifically, SSS1 uses the first 168 sequences to carry the cell ID and is sent only in the first half of each frame. In this way, frame timing information may be obtained directly by detecting SSS 1. In addition, SSS2 uses the last 168 SSS sequences of all 336 SSS sequences and is sent only in the second half of each frame. The SSS2 sequence is selected independently of the SSS1 sequence and may be used to carry additional information. For example, assuming there are 14 SS blocks, the last 168 SSs2 sequences may be divided into 14 groups, each group containing 12 SSs2 sequences. Each group is uniquely associated with one synchronization interval and each SSS2 sequence in a group is uniquely associated with one beam index. This is advantageous because existing synchronization signal design/detection can be maximally exploited while fulfilling additional functions.

In another embodiment, the SS block index is jointly encoded in the synchronization signal sequence and the PBCH. In LTE, different SSS sequences are used in the first and second half frames. Assuming that the period of the SS increases from half a system frame to a longer value (e.g., one system frame), a different SSs sequence of the latter half frame may be reused to indicate two states of SS block index. Other remaining SS block indices may be indicated in the associated PBCH. This is advantageous because existing synchronization signal sequence designs can be reused, which will simplify implementation and standardization.

The SS block index may be transmitted in PBCH by reusing existing information bits in LTE. The problem can be adjusted when the synchronization period is further increased, for example, to several system frames. In one embodiment, the SS period is increased to 80ms, i.e., 8 frames. Then, when the PSS/SSS is detected and the SS block index is obtained, the frame index is also available within every 8 frames, which means that 3 bits are saved in the PBCH for the system frame number indication field. The saved 3 bits may be used to indicate 2 of the SS block³Without increasing PBCH overhead, 8 states. In combination with the ability of two state indications maintained by the SSS sequence, 16 states will be stored without increasing the number of synchronization signal sequences or the number of bits in the PBCH. This applies to the division of the SS block index into two parts, one in the synchronization signal and the other in the PBCH. This is advantageousBecause both the existing synchronization signal sequence design and PBCH design can be reused, implementation and standardization will be simplified.

In another embodiment, the beam information may be associated with an SS block index. The association is known at the network node but unknown to the UE. The UE feeds back the SS block index explicitly (e.g., uplink control signaling) or implicitly (e.g., selected Physical Random Access Channel (PRACH) resources). The network node may then obtain beam information from the association between the used beam and the SS block. This is because the network node contains information of which beam is used in a particular SS block indicated by the UE. This is advantageous because the network node may acquire at least part of the beam information. In the case where only one beam is employed in each SS block, all beam information can be obtained unambiguously.

In another embodiment, a network node transmits synchronization signals using a flexible number of beams X and a flexible number of synchronization signal sequence resources T, where each T is associated with a unique SS block. The total N synchronization signal sequence resources include a plurality of synchronization signal sequences, each synchronization signal sequence being associated with a beam. The N total synchronization signal sequence resources are associated with a predefined maximum number of beam indices M. The UE obtains explicit beam information from the detected synchronization signal sequence resources.

In one embodiment, a predefined maximum number of beams M is used. The beam information is encoded in the synchronization signal sequence in addition to the SS block index. The maximum number of beams M is predefined. The detailed radiation pattern of each beam depends on the implementation of the network node and is unknown at the UE. As already disclosed in the first embodiment, the number of beams X is not necessarily limited by the number of SS blocks N. The UE has no information of X before initial access. However, the UE has M information and an association of N synchronization signal sequence resources with M beam indices. For a network node, the N synchronization signal sequence resources include only sequences mapped to X beams, e.g., beam IDs {0, 1. This is advantageous because the UE may obtain the beam ID from a predefined association between the synchronization signal and the beam. The beam ID may then be fed back to the network node.

In one embodiment, N synchronization signal sequence resources are associated with M beams. One synchronization signal sequence resource is uniquely associated with one SS block index and is also associated with a beam, as shown in table 2.

TABLE 2 Association between synchronization Signal sequence resources, SS blocks and beams

Synchronization signal sequence resource index	SS block index	Beam ID
			0	0	{0,1, …, M-1} or a subset thereof
1	1	{0,1, …, M-1} or a subset thereof
			…	…	{0,1, …, M-1} or a subset thereof
N-1	N-1	{0,1, …, M-1} or a subset thereof

This is advantageous because a reduction of feedback signaling can be achieved. Since the synchronization signal sequence typically includes information for cell ID and SS block index, the total number of information states included in the synchronization signal sequence is typically greater than the number of beams. In one example, if there are 504 cell indices and 10 SS blocks, then the number of information states is 5040, and the maximum number of beams may be much smaller, e.g., M ═ 16. Therefore, the UE may use the beam ID instead of using the synchronization signal sequence index to feed back less information.

In one embodiment, the synchronization signal sequence resources include a set of SSS sequences including information for SS block index, cell ID, and beam ID. The intra-group SSS sequences associated with the synchronization signal sequence resource carry the same SS block index but have different beam IDs. The set of sequences with the same SS block index forms one synchronization signal sequence resource. The information of the SS block index may be an index selected from N values, i.e., {0,1, …, N-1 }. The information of the cell ID may be a cell index or may be a part of the cell index as in LTE. The information for the beam ID may be an index selected from M values, i.e., {0,1, …, M-1 }. This is advantageous because there is flexibility to apply to each SS block to enable the beam to reach its maximum, i.e., up to M concurrent beams.

As a special case of table 2, the beam IDs associated with the synchronization signal sequence resources may be only a subset of 0,1, …, M-1. In one embodiment, the beam IDs are classified into N groups, each of which is associated with a unique synchronization signal sequence resource. For example, by assuming N-4 and M-8, the association is shown in table 3 below.

Table 3. association between synchronization signal sequence resources, SS blocks and beams. Where N-4, M-8, and each synchronization signal sequence resource is associated with only a subset of beam IDs

In this case, the beam ID and the SS block index are commonly associated with the synchronization sequence resource. The number of beam information of the partial synchronization signal sequence can be reduced. Note that the UE needs to know this association to obtain the SS block index and beam ID from the detected synchronization signal sequence. This is advantageous because the reduced number of synchronization signal sequences can be predefined in the standard. In this embodiment, the total number of information states per synchronization signal sequence resource is reduced from 8 to 2. This allows a maximum of 2 concurrent beams per SS block. Similar to the previous embodiments with only SS block indices, beam information may be jointly encoded in the synchronization signal and PBCH to reuse LTE design.

In all described embodiments, the UE may work with multiple connections of the network, e.g. multiple beams connected to the same TRP, or multiple beams of different TRPs in the same cell (i.e. with the same cell ID), or even multiple TRPs in different cells. In particular, for UEs connected to multiple TRPs of the same cell, it is expected that the synchronization signal design may allow the UE to acquire TRP information in order to maintain multiple TRP connections. The TRP information may be encoded similarly to the previous embodiments, e.g. TRP ID in PSS, SSS, ESS, PBCH or combinations thereof.

Systems and methods for wireless communication network synchronization have been described in connection with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.

Claims

1. A network node (100) for wireless communication, comprising:

a processor (106) configured to:

providing (111) at least one synchronization signal, SS, block, wherein the SS block comprises at least a primary synchronization signal and a secondary synchronization signal;

encoding (112) the SS block index into any of:

-the primary synchronization signal, wherein the processor (106) is further configured to multiply a Zadoff Chu sequence with an additional sequence to obtain a primary synchronization signal sequence, wherein the additional sequence is used in encoding the SS block index, or

-the additional secondary synchronization signal, wherein the processor (106) is configured to obtain the additional secondary synchronization signal from the same set of sequences as the secondary synchronization signal, or

-said secondary synchronization signal, wherein the period of said secondary synchronization signal is an integer multiple of one system frame;

encoding a plurality of beam indices into each of the at least one SS block; and

a transceiver (104) configured to transmit (113) the SS block.

2. The network node (100) of claim 1, wherein the transceiver (104) is configured to transmit (115) the SS block using multiple beams.

3. The network node (100) according to claim 1 or 2, wherein the SS block further comprises at least one of an additional secondary synchronization signal and physical broadcast channel information.

4. The network node (100) according to claim 1 or 2, wherein the number of SS blocks is from 1 to N, wherein N is a predefined maximum value.

5. The network node (100) according to claim 1, wherein the number of beam indices encoded to the at least one SS block is 1 to M, wherein M is a predefined maximum value.

6. The network node (100) according to claim 1 or 2, wherein the processor (106) further encodes a transmit reception point, TRP, identity and a cell identity into each of the at least one SS block.

7. A user equipment (108) for wireless communication, comprising:

a transceiver (109) configured to receive at least one synchronization signal, SS, block comprising at least a primary synchronization signal and a secondary synchronization signal;

a processor (110) configured to:

extracting the SS block index from the at least one received SS block by decoding any of:

-obtaining said primary synchronization signal PSS resulting from multiplying a Zadoff Chu sequence and an additional sequence, wherein said additional sequence encodes said SS block index, or

-an additional secondary synchronization signal obtained from the same set of sequences as the secondary synchronization signal, or

a plurality of beam indices are extracted from the received SS block.

8. The user equipment (108) according to claim 7, wherein the processor (110) is further configured to obtain a transmission reception point, TRP, identity.

9. The user equipment (108) according to claim 8, wherein the user equipment (108) is configured to obtain uplink transmissions from any of the SS block index, the beam index and the TRP identity.

10. A method for wireless communication, comprising:

providing (111, 114) at least one synchronization signal, SS, block, wherein the at least one SS block comprises at least a primary synchronization signal and a secondary synchronization signal;

encoding the SS block index into any of:

-the primary synchronization signal, wherein the method further comprises multiplying a Zadoff Chu sequence with an additional sequence to obtain a primary synchronization signal sequence, wherein the additional sequence is used in encoding the SS block index, or

-the additional secondary synchronization signal, wherein the method further comprises obtaining the additional secondary synchronization signal from the same set of sequences as the secondary synchronization signal, or

-sending (113, 117) the SS block.

11. A method of wireless communication, comprising:

receiving at least one Synchronization Signal (SS) block, wherein the SS block comprises at least a primary synchronization signal and a secondary synchronization signal;

-said secondary synchronization signal, wherein the period of said secondary synchronization signal is an integer multiple of one system frame; and

a plurality of beam indices are extracted from the received SS block.