Related Applications

[0001] This application claims the benefit of provisional patent application serial number 62/455,270, filed February 6, 2017, the disclosure of which is hereby incorporated herein by reference in its entirety.

Technical Field

[0002] Synchronization sequence, Zadoff-Chu (ZC), autocorrelation, cross- correlation, address space

Background

[0003] When a User Equipment device (UE) is powered on, wakes from a low-power state, or when it moves between cells in Long Term Evolution (LTE) Release 8 and later, it receives and synchronizes to downlink signals in a cell search procedure. The purpose of this cell search is to identify the best cell and to achieve time and frequency synchronization to the network in downlink (i.e., from the base station to the UE).

[0004] Synchronization sequences preferably possess "good" auto and cross-correlation properties to minimize missed detection (i.e., where a transmitted synchronization signal is not detected) and false alarm (i.e., where a UE detects a synchronization signal based on a sequence which was not transmitted) probability and provide good time/frequency offset estimates. In LTE Third Generation Partnership Project (3GPP) Technical Specification (TS) 36.21 1 , the preamble sequences are generated from cyclic shifts of one or several root Zadoff-Chu (ZC) sequences. Basically, there are a number of available sequences for the UE to select for use for random access in one cell. For example, in an LTE system there are 64 sequences that can be used for random access. Each time the UE is about to do the random access, one sequence out of the 64 sequences is selected. A collision will occur if several UEs select the same sequence, and such a collision could result in random access failure for some or all UEs. Thus, the probability that multiple UEs choose the same sequence should be low. The larger the number of different available sequences, the smaller the probability of random access failure due to collision.

[0005] Typically, for a length-N resource allocation (i.e., a resource

allocation in which a length-N sequence fits), (near-)perfect cross-correlation properties can be guaranteed for N sequences. In some cases, limiting the address space size to N may be limiting for system design and some

degradation of cross-correlation performance may be acceptable if the address space can be increased.

[0006] It turns out that such expansion - letting a larger set of structured sequences coexist in the same resources - is not always trivial and can lead to a dramatic degradation of the cross-correlation properties. For example, while cross-correlation properties of N M-sequences generated from a given primitive polynomial are excellent, mixing multiple polynomials may lead to sequence pairs with unacceptably high cross-correlation values.

[0007] One example of sequence construction that attempts to increase the address space is the ZCxM design in Huawei et al., "R1 -1700034: RACH preamble design for NR," 3GPP TSG-RAN WG1 NR Ad Hoc Meeting, Spokane, USA, January 16-20, 201 7 (hereinafter "R1 -1700034"). In addition to the traditional single dimension of N-1 ZC root sequences, the sequence proposed in R1 -1700034 includes a second dimension of N time shifts of a chosen M- sequence. The total address space is then roughly N ² , instead of N for traditional ZC- or M-sequences.

[0008] The resulting cross-correlation performance of the new sequence is shown in Figures 1 and 2. Figure 1 indicates that cross-correlation between different M-sequence shifts is uniform and low if the same ZC root is used, and becomes larger and random for different roots. Similarly, Figure 2 illustrates that cross-correlation between two ZC roots with the same M-sequence shift superimposed resembles the classical ZC-only cross-correlation. However, when different M-sequence shifts are applied, the cross-correlation also becomes random and uneven.

[0009] While increasing the address space by expanded synchronization sequence designs is attractive from a system design viewpoint, the degraded cross-correlation properties negatively affect detection performance. For example, larger and uneven cross-correlation peaks worsen at least the false alarm probability of the resulting signaling scheme and may also affect missed detection if detection parameters are adjusted to control the false alarm degradation.

Summary

[0010] Systems and methods are disclosed for determining and configuring synchronization sequences for entities in a wireless network from different sets of synchronization sequences depending on, e.g., network conditions and/or number of wireless devices. In some embodiments, a method of operation of a network node in a wireless network comprises determining an operation mode for the wireless network or a part of the wireless network and determining, from at least two possible sets of synchronization sequences, based on the operation mode, a synchronization sequence set to be used by a plurality of entities in the wireless network or the part of the wireless network. In some embodiments, the at least two possible sets of synchronization sequences comprise a first set of synchronization sequences comprising a first number of synchronization sequences and a second set of synchronization sequences comprising a second number of synchronization sequences, wherein the second number is less than the first number. In some embodiments, the second set of synchronization sequences is a subset of the first set of synchronization sequences. In this manner, the first set of synchronization sequences can be used when a large number of synchronization sequences is needed; otherwise, the smaller second set of synchronization sequences can be used, which improves synchronization sequence detection. [0011] In some embodiments, a default allocation for the plurality of entities is to use the first set of synchronization sequences. In some other

embodiments, a default allocation for the plurality of entities is to use the second set of synchronization sequences.

[0012] In some embodiments, determining the operation mode for the wireless network or the part of the wireless network comprises determining the operation mode for the wireless network or the part of the wireless network based on a number of unique synchronization sequences that need to be supported. Further, in some embodiments, determining the operation mode for the wireless network or the part of the wireless network based on the number of unique synchronization sequences that need to be supported comprises determining the number of unique synchronization sequences that need to be supported based on node deployment in the wireless network or the part of the wireless network node density in the wireless network or the part of the wireless network, propagation conditions in the wireless network or the part of the wireless network, antenna array sizes used in the wireless network or the part of the wireless network, and number of current or statistical wireless devices in the wireless network or the part of the wireless device.

[0013] In some embodiments, determining the synchronization sequence set to be used comprises selecting the first set of synchronization sequences if the number of unique synchronization sequences that need to be supported is greater than a threshold. In some embodiments, determining the

synchronization sequence set to be used comprises selecting the second set of synchronization sequences if the number of unique synchronization sequences that need to be supported is less than a threshold.

[0014] In some embodiments, the first set of synchronization sequences is a ZCxM sequence set that uses cyclic versions of an M-sequence as different cover extensions of a set of cyclic-shifted Zadoff-Chu (ZC) sequences. In some embodiments, the second set of synchronization sequences is a subset of the ZCxM sequence set. In some embodiments, the subset of the ZCxM sequence set is a subset using ZC roots only without multiplication with any M-sequence. In some other embodiments, the subset of the ZCxM sequence set is a subset using a fixed M-sequence and a range of ZC roots. In some other embodiments, the subset of the ZCxM sequence set is: a subset of the ZCxM sequence set that uses a fixed M-sequence and a range of ZC roots, a subset using a fixed ZC root and a range of M-sequence shifts, and a subset using M-sequence shifts only.

[0015] In some embodiments, the first set of synchronization sequences mixes multiple sequences comprising one or more M-sequences, one or more Gold sequences, and/or one or more Barker sequences. In some

embodiments, the second set of synchronization sequences is a subset of the first set of synchronization sequences.

[0016] In some embodiments, the method further comprises determining per- entity allocations for the plurality of entities, respectively, from the

synchronization sequence set and configuring the plurality of entities in accordance with the per-entity allocations.

[0017] Embodiments of a network node for a wireless network are also disclosed. In some embodiments, a network node for a wireless network is adapted to determine an operation mode for the wireless network or a part of the wireless network and determine, from at least two possible sets of synchronization sequences based on the operation mode, a synchronization sequence set to be used by a plurality of entities in the wireless network or the part of the wireless network.

[0018] In some embodiments, a network node for a wireless network comprises a network interface and/or at least one radio unit, at least one processor, and memory. The memory stores instructions executable by the at least one processor whereby the network node is operable to determine an operation mode for the wireless network or a part of the wireless network and determine, from at least two possible sets of synchronization sequences based on the operation mode, a synchronization sequence set to be used by a plurality of entities in the wireless network or the part of the wireless network.

[0019] In some embodiments, a network node for a wireless network comprises a first determining module operable to determine an operation mode for the wireless network or a part of the wireless network and a second determining module operable to determine, from at least two possible sets of synchronization sequences based on the operation mode, a synchronization sequence set to be used by a plurality of entities in the wireless network or the part of the wireless network.

[0020] Embodiments of a method of operation of a wireless network for synchronization sequence selection are also disclosed. In some embodiments, the method comprises determining a number of required synchronization sequences based on one or both of network conditions and a number of wireless devices in the wireless network and selecting a synchronization sequence set from at least two possible sets with different sequence set size/performance trade-offs based on the number of required synchronization sequences. In some embodiments, the method further comprises determining an allocation of the synchronization sequence set to individual entities in the wireless network and configuring the entities with the sequences according to the allocation.

[0021] Embodiments of a method of operation of a wireless device in a wireless network are also disclosed. In some embodiments, a method of operation of a wireless device in a wireless network comprises receiving, from a network node in the wireless network, a configuration to use one or more synchronization sequences, the one or more synchronization sequences being from one of at least two sets of synchronization sequences and utilizing at least one of the one or more synchronization sequences.

[0022] In some embodiments, the at least two sets of synchronization sequences comprise a first set of synchronization sequences comprising a first number of synchronization sequences and a second set of synchronization sequences comprising a second number of synchronization sequences, wherein the second number is less than the first number. In some

embodiments, the second set of synchronization sequences is a subset of the first set of synchronization sequences. [0023] In some embodiments, the one of the at least two sets of synchronization sequences varies based on an operation mode of the wireless network or a part of the wireless network in which the wireless device is located. In some embodiments, the operation mode for the wireless network or the part of the wireless network is based on a number of unique

synchronization sequences that need to be supported. In some embodiments, the number of unique synchronization sequences that need to be supported is based on node deployment in the wireless network or the part of the wireless network, node density in the wireless network or the part of the wireless network, propagation conditions in the wireless network or the part of the wireless network, antenna array sizes used in the wireless network or the part of the wireless network, and number of current or statistical wireless devices in the wireless network or the part of the wireless device.

[0024] In some embodiments, the first set of synchronization sequences is a ZCxM sequence set that uses cyclic versions of an M-sequence as different cover extensions of a set of cyclic-shifted ZC sequences. In some embodiments, a default allocation for the wireless device is to use the first set of

synchronization sequences. In some other embodiments, a default allocation for the wireless device is to use the second set of synchronization sequences.

[0025] In some embodiments, the second set of synchronization sequences is a subset of the ZCxM sequence set. In some embodiments, the subset of the ZCxM sequence set is a subset using ZC roots only without multiplication with any M-sequence. In some other embodiments, the subset of the ZCxM sequence set is a subset using a fixed M-sequence and a range of ZC roots. In some other embodiments, the subset of the ZCxM sequence set is: a subset of the ZCxM sequence set that uses a fixed M-sequence and a range of ZC roots, a subset using a fixed ZC root and a range of M-sequence shifts, and a subset using M-sequence shifts only.

[0026] In some embodiments, the first set of synchronization sequences mixes multiple sequences comprising one or more M-sequences, one or more Gold sequences, and/or one or more Barker sequences. In some embodiments, the second set of synchronization sequences is a subset of the first set of synchronization sequences.

[0027] Embodiments of a wireless device for a wireless network are also disclosed. In some embodiments, a wireless device for a wireless network is adapted to receive, from a network node in the wireless network, a

configuration to use one or more synchronization sequences, the one or more synchronization sequences being from one of at least two sets of

synchronization sequences. The wireless device is further adapted to utilize at least one of the one or more synchronization sequences.

[0028] In some embodiments, a wireless device for a wireless network comprises one or more transceivers and circuitry operable to cause the wireless device to: receive, from a network node in the wireless network, a configuration to use one or more synchronization sequences, the one or more synchronization sequences being from one of at least two sets of

synchronization sequences and utilize at least one of the one or more synchronization sequences.

[0029] In some embodiments, a wireless device for a wireless network comprises a receiving module and a utilizing module. The receiving module is operable to receive, from a network node in the wireless network, a

configuration to use one or more synchronization sequences, the one or more synchronization sequences being from one of at least two sets of

synchronization sequences. The utilizing module is operable to utilize at least one of the one or more synchronization sequences.

Brief Description of the Drawings

[0030] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0031] Figure 1 illustrates cross-correlations with 21 M-sequence shifts, nine Zadoff-Chu (ZC) sequence shifts, and two ZC roots; [0032] Figure 2 illustrates cross-correlations with 126 ZC roots and two shifts of an M-sequence;

[0033] Figure 3 illustrates one example of a wireless system (e.g., a cellular communications network) in which embodiments of the present disclosure may be implemented;

[0034] Figure 4 is a flow chart that illustrates the operation of a network node according to some embodiments of the present disclosure;

[0035] Figure 5 illustrates examples of synchronization sequence sets for different modes;

[0036] Figure 6 is a flow chart that illustrates the operation of a wireless device according to some embodiments of the present disclosure;

[0037] Figures 7 and 8 illustrate example embodiments of a wireless device; and

[0038] Figures 9 through 1 1 illustrate example embodiments of a network node.

Detailed Description

[0039] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0040] Radio Node: As used herein, a "radio node" is either a radio access node or a wireless device.

[0041] Radio Access Node: As used herein, a "radio access node" or "radio network node" is any node in a radio access network of a cellular

communications network that operates to wirelessly transmit and/or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., a New Radio (NR) base station (gNB) in a Third Generation Partnership Project (3GPP) Fifth Generation (5G) NR network or an enhanced or evolved Node B (eNB) in a 3GPP Long Term Evolution (LTE) network), a high- power or macro base station, a low-power base station (e.g., a micro base station, a pico base station, a home eNB, or the like), and a relay node.

[0042] Core Network Node: As used herein, a "core network node" is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a Packet Data Network Gateway (P- GW), a Service Capability Exposure Function (SCEF), or the like.

[0043] Wireless Device: As used herein, a "wireless device" is any type of device that has access to (i.e., is served by) a cellular communications network by wirelessly transmitting and/or receiving signals to a radio access node(s). Some examples of a wireless device include, but are not limited to, a User Equipment device (UE) in a 3GPP network and a Machine Type Communication (MTC) device.

[0044] Network Node: As used herein, a "network node" is any node that is either part of the radio access network or the core network of a cellular communications network/system.

[0045] Note that the description given herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system.

[0046] Note that, in the description herein, reference may be made to the term "cell;" however, particularly with respect to 5G NR concepts, beams may be used instead of cells and, as such, it is important to note that the concepts described herein are equally applicable to both cells and beams. Other terms like sectors, nodes, and Transmit/Receive Points (TRPs) may also be used interchangeably.

[0047] According to embodiments of the present disclosure, a set of synchronization sequences allocated to UEs and/or TRPs and/or beams and/or cells is configured (e.g., dynamically) based on the required number of sequences to support in a respective usage scenario. [0048] In some embodiments, a full expanded (e.g., size-N ² ) address space (i.e., a full expanded set of synchronization sequences) is invoked only when a required number of synchronization sequences is "high" (e.g., greater than a predefined or configurable threshold). This is the case, e.g., when there are so many entities (cells, TRPs, beams, and/or UEs) that require unique

synchronization sequences in a given system neighborhood (i.e., in a particular geographic area within a coverage area of the respective network) that the original, limited-size (size-N) address space (i.e., an original or non-expanded set of synchronization sequences) is insufficient. In case the limited-size address space is sufficient, only original, low cross-correlation sequences are allocated to, e.g., UEs and/or TRPs and/or beams and/or cells, depending on the particular implementation.

[0049] In some embodiments, the set of synchronization sequences allocated is configured for either a "few-UEs mode" or a "many-UEs mode." Using the example of the ZCxM design for Physical Random Access Channel (PRACH) preamble disclosed in Huawei et al., "R1 -1700034: RACH preamble design for NR," 3GPP TSG-RAN WG1 NR Ad Hoc Meeting, Spokane, USA, January 16-20, 2017 (hereinafter "R1 -1700034"), in the few-UEs mode, each TRP/cell is allocated one root and a subset of shifts, or one shift and a subset of roots. (Alternatively, the M-sequence component could be omitted). In the many-UEs mode, the sequence allocation includes both multiple M-sequence shifts and multiple Zadoff-Chu (ZC) roots. Note that, in the baseline (state of the art) solution, the size-N ² address space is always made available, e.g., each TRP or cell has one ZC root sequence and all M-sequence shifts available, or one shift and all roots.

[0050] In systems and deployments where expanded synchronization signal design needs to be used to obtain a sufficient address space (e.g., in some areas of the network (e.g., to handle dense deployment regions or hotspots with many UEs)), the embodiments of the present disclosure improve

synchronization detection performance in other areas of the network by allowing better-performing, optimal synchronization sequence sets to be used in those areas.

[0051] Figure 3 illustrates one example of a wireless system 10 (e.g., a cellular communications network such as, for example, a 3GPP 5G or NR network) in which embodiments of the present disclosure may be implemented. As illustrated, a number of wireless devices 12 (e.g., UEs) wirelessly transmit signals to and receive signals from radio access nodes 14 (e.g., gNBs), each serving one or more cells 16. The radio access nodes 14 are connected to a core network 18. The core network 18 includes one or more core network nodes 19 (e.g., MMEs, Serving Gateways (S-GWs), and/or the like).

[0052] Figure 4 is a flow chart that illustrates the operation of a network node (e.g., a radio access node 14 or a core network node 19) (i.e., the operation of a control entity implemented in a network node) according to some embodiments of the present disclosure. In the embodiments described herein, there are two possible sets of sequences, which are referred to herein as a full extended set of sequences and a normal non-extended set of sequences. The non-extended set of sequences is a subset of the extended set of sequences or another set of sequences that is structurally related to the extended set and has good cross- correlation properties with respect to the extended set (e.g., version of the extended set where one of the component sequences is removed). The network node determines whether to allocate the full extended set of sequences or the normal non-extended set of sequences based on one or more criteria.

[0053] In some embodiments, the full extended set of sequences is a ZCxM sequence set as defined in R1 -1700034. As described in R1 -1700034, the ZCxM sequence set Z uses cyclic versions of an M-sequence as different cover extensions of original, limited-size LTE quasi-orthogonal sequences S, and can be written mathematically as: where ^{is tne set of} original cyclic-shifted ZC sequences, in which each sequence is written as

s _u (k) = ^ ^+/) « ^i+/)+1)/2 , k = 0, 1,...,N _ZC - 1

where

- W _Nzc = _e - ^j2* ' ^Nzc is a root of unity with j = !

N _zc = 2 ^m - 1 is the sequence length with m>\

- the index u represents different ZC roots which should be chosen such that u and N _zc are respective primes. If N _zc is a prime, then u = X-,N _zc -l.

- the index 1 = 0, N _CJ ,2N _cs ,- - -≤(N _zc -l) represents cyclic shifts of a root ZC sequence with cyclic shift gap N _cs .

• and T _h = {w(k + is a cover extension of the original set S obtained by multiplying all sequences in S with a common M-sequence cyclic-shifted by h . A binary M-sequence can be defined as

-i

w(k) = (- l) ^Tr(a > , ΤΓ{Χ) =∑Χ ² ' , & = 0, l,...,2 ^ffl -l

z=o

where « is a primitive element of the Galois field GF(2 ^m ) .

[0054] Note, however, that the ZCxM sequence set Z is only one example of the full extended sequence set. Many other design options can be designed according to the same principles, e.g., mixing multiple M-sequences, Gold sequences, Barker sequences, and other synchronization sequences. Extended sequences can be formed according to, e.g., principles {M1 -sequence x M2- sequence}, {Goldl sequence x Gold2 sequence}, and {M-sequence x Gold sequence}, etc.

[0055] In some embodiments, the normal, or non-extended, set of sequences is the sequence set S (i.e., the set of original cyclic-shifted ZC sequences).

[0056] As illustrated, the network node determines an operation mode (step 100). In some embodiments, a set of possible operation modes includes a few- entities (e.g., few UEs and/or TRPs and/or cells and/or beams) operation mode and a many-entities (e.g., a many UEs and/or TRPs and/or cells and/or beams) operation mode. For example, if the number of entities in the network or a defined part of the network is greater than a predefined or configured threshold, then the many-entities mode is selected; conversely, if the number of entities in the network or a defined part of the network is less than the same or a different predefined or configured threshold, then the few-entities mode is selected.

[0057] More specifically, in step 100, the network node (i.e., the control entity implemented in the network node) analyzes the network, or a part of the network, regarding the number of unique sequences that needs to be supported. This may be based on, e.g., node deployments, node density and propagation conditions, antenna array sizes, and the number of wireless devices 12 (e.g., UEs) (current or statistical) in the relevant part(s) of the network. Depending on the number of unique sequences required, the few- entities or many-entities operating mode is selected.

[0058] Note that in some cases, e.g. initial access, statistical data (recent minutes, or past long-term statistics for the given time of day) can be used to determine the number of wireless devices 12 in the relevant part(s) of the network since the instantaneous exact number may be unknown. In other scenarios, e.g. mobility measurement and target cell access in handover scenarios, the network knows the number of wireless devices 12 currently in the relevant part(s) of the network or the handover process. In any case, some statistical averaging may be performed since mode switching (e.g., switching between the few-entities mode and the many-entities mode) is preferably performed infrequently, at the time scale of, e.g., at least tens of minutes or hours.

[0059] In some embodiments, the mode may be determined based on wireless device density (e.g., cell density, beam density, TRP density, and/or wireless device density). For example, the mode may be determined in step 100 based on the number of TRPs and/or the number of cells and/or the number of beams per unit area (e.g., in the case of Primary Synchronization Signal (PSS)) or the number of wireless devices per TRP or cell group, per TRP or cell, per beam, etc., in the order of likelihood. However, if the mode is selected independently in different regions or parts of the network, e.g., a set of TRPs served by the same node (e.g., baseband unit), the density in this particular region may be used as the relevant information for determining the mode.

[0060] In some embodiments, determining the mode is a question of (1 ) how many sequences the non-expanded set supports and (2) how many wireless devices there are in the system - or trying to access the system - that need unique sequences. (1 ) is given by the signal design and is known ahead of time. (2) may be determined by, e.g., statistics (e.g., historical access volumes at the same period during the day/week). Alternatively, the instantaneous (recent) access volumes may be used. In that case, if the number of actually utilized sequences is robustly lower than the non-expanded set size, the latter may be invoked. If it exceeds a heuristic robustness threshold, e.g. the rate of PRACH failures due to sequence collisions, the expanded set is employed.

[0061] The network node determines the sequence (sub)set to use based on the determined operation mode (step 102). In some embodiments, the full extended set of sequences may be utilized when in the many-entities mode, as determined in step 100. A subset of the full extended sequence set (i.e., the normal non-extended set) is used when in the few-entities mode, as determined in step 100. With respect to the normal non-extended set, in some

embodiments, the normal non-extended set is a subset of the full extended set of sequences where only one of the component sequences is varying, or where one of the component sequences is removed. This is elaborated upon below.

[0062] Note that while steps 100 and 102 are described above in terms of the operation mode, steps 100 and 102 can also be described as follows. In step 100, the operation mode is determined. In some embodiments, this can also be described as determining a number of required synchronization sequences, e.g., based on network conditions and/or the number of wireless devices in the wireless network or the relevant part of the wireless network. Step 102 can then be described as, in some embodiments, selecting a synchronization sequence set from at least two possible sets with different sequence set sizes and/or performance trade-offs based on the number of required synchronization sequences.

[0063] The remaining steps of Figure 4 are optional, as indicated by the dashed boxes. Optionally, the network node divides the total set of available sequences (as determined in step 102) among the entities (UEs and/or TRPs and/or cells and/or beams), preferably according to some systematic structure (step 1 04). For example, one entity (e.g., a cell) is allocated a set of sequences where one of the sequences is constant in the many-entities mode, or a contiguous subset of the optimal, single-component sequence set.

[0064] Optionally, the network node allocates the sequences to the entities and configures the entities for operation using the allocated sequences via control signaling protocols, similar to legacy solutions (step 106). For example, the PRACH preamble sequence allocation to the UE is achieved via initial System Information (SI) in Master Information Block (MIB) or the Physical Broadcasting Channel (PBCH) or Remaining Minimum SI (RMSI) transmission, mobility measurement signals via node-to-UE Radio Resource Control (RRC) signaling, while the control entity may inform other network nodes via node-to- node RRC signaling. Thereafter, the various entities use the allocated and configured sequences for, e.g., synchronization/detection/measurements.

[0065] In some embodiments, the default allocation may be to use many- entity sequence sets to all UEs and/or TRPs and/or cells and/or beams as the starting point. By applying the process of Figure 4, step 102 may amount to identifying UE, TRP, cell, or beam groups for which the large set is

unnecessary, e.g., due to sparse cell deployment or a small number of UEs in the system. Those groups are then allocated few-entities subsets and the UEs, TRPs, cells, or beams are allocated sections of the subset as described below.

[0066] In other embodiments, few-entities and optimal-cross-correlation sets are assumed to be used in the network by default. According to the process of Figure 4, step 102 identifies UE, TRP, cell, or beam groups for which large sets are required, e.g., due to dense cell deployment where the UE can hear many cells at a time, or a large number of UEs in the system. Those groups are then allocated many-entities subsets.

[0067] The sequence set for few-entities mode may be a subset of the full extended sequence set for the many-entities mode or a separate set of sequences.

[0068] Using the example of ZCxM design, the few-entities mode sequence set selection can be depicted as shown in Figure 5. The full set of hashed circles represents the full extended synchronization sequence set for the many- entities mode. Each circle corresponds to a length-N sequence. The following subsets of the full extended synchronization sequence set can be defined as sequence sets for the few-entities mode:

• A first subset type subset in which a fixed M-sequence and a range of ZC roots is selected as the few-entities subset.

• A second subset type that corresponds to omitting multiplication with the M-sequence altogether, which is equivalent to assuming a trivial, all-ones M-sequence that is near-orthogonal with all other M-sequence primitive polynomials and shifts. This may be the preferred selection scheme due to best cross-correlation properties within the set.

• A third subset type that corresponds to selecting a fixed ZC root and a range of M-sequence shifts as the subset.

• A fourth subset type that corresponds to M-sequences only.

[0069] The selected subset can then be allocated to multiple UEs and/or TRPs and/or cells and/or beams so that each entity is allowed to use a predetermined number of subset elements, e.g., certain ZC roots or M- sequence shifts. In Figure 5, this corresponds to allocating sections of the selected row/column to each UE and/or TRP and/or cell and/or beam.

[0070] For small cells, the delays of the sequences can be assumed to be zero such that the cross-correlations between sequences are only evaluated without delays between sequences. In one embodiment, one M-sequence and one set of several different root sequences of ZC are allocated for all the UEs within one cell. This corresponds to the first 1 26 indices in Figure 2. Here, ZC sequences are known to have very good cross-correlation properties and correspond to one column in Figure 5. Different cells can have different M- sequences. However, received signal strength from UEs in other cells are lower (in average) as compared to signals from UEs within the same cell. Due to these power reductions, having low cross-correlations between cells is not as important as low cross-correlations between sequences from UEs within the cell or a TRP.

[0071] In another embodiment, one M-sequence and one set of several different root sequences of ZC are allocated for all the UEs within one beam. The spatial separations between the UEs in the different beams will improve detection in terms of false detections between the beams. This is because received signal strength from UEs in other beams are lower (in average) as compared to signals from UEs within the same beam.

[0072] While Figure 4 is a flow chart that illustrates the operation of a network node, Figure 6 illustrates the corresponding operation of a wireless device 12 according to embodiments of the present disclosure. As discussed above, the network node determines a per-entity allocation for each of multiple entities in the wireless network and configures those entities. Those entities may include other network nodes (e.g., a radio access node(s) 14) and wireless devices 12. In this regard, a wireless device 12 receives a configuration from a network node to use one or more synchronization sequences, where the one or more synchronization sequences are from one of at least two sets of synchronization sequences as described above (step 200). The wireless device 12 utilizes at least one of the one or more synchronization sequences with which it is configured (step 202). For example, if the synchronization sequences are synchronization sequences used as Random Access Channel (RACH) preambles, the wireless device 12 selects and uses one of the configured synchronization sequences for

transmission of a corresponding RACH preamble when performing random access, as will be appreciated by one of ordinary skill in the art. A RACH preamble is only one example use of the configured synchronization sequence(s). Many other examples for both downlink and uplink scenarios are disclosed herein.

[0073] The embodiments described herein are applicable to both downlink and uplink synchronization sequences.

[0074] For example, in the uplink PRACH preamble design context it enhances the performance and usability of the PRACH preamble design proposed in Ericsson, "R1 -1700298: NR PRACH Design," 3GPP TSG-RAN WG1 NR adhoc, Spokane, USA, January 16-20, 2017 (hereinafter "R1 -1700298"). That design achieves various performance advantages by using repeated transmission of a short uplink sequence. Due to the length of the short symbols, the address space (the number of unique sequences) is shorter than the design used in LTE. The natural address space is sufficient in many cases, but possibly not all. By applying the present disclosure, the fraction of the network where lower-performing sequences are used is limited.

[0075] Other examples of using embodiments of the present disclosure in the uplink are for sounding, channel estimation, or mobility measurement signals or other signals where large sets of near-orthogonal signals are employed.

[0076] Some examples of applying embodiments of the present disclosure in the downlink may be the cell synchronization signal (PSS / Secondary

Synchronization Signal (SSS) in LTE) or mobility measurement signals (Mobility Reference Signals (MRSs) in NR). Such signals may need to be unique per individual nodes/cells/TRPs/beams, or in some embodiments additionally per individual UEs.

[0077] The sequence set selection according to the present disclosure may be static or long-term, based on node deployments, antenna array sizes, and long-term statistics of the number of UEs in the parts of the network.

Alternatively, the selection may be dynamic, e.g., responsive to the time-varying presence of UEs in the system.

[0078] Different parts (regions/areas, neighborhoods, node clusters, TRP groups) of the network may use different operating modes and different sequences set types. At the boundaries of such regions, the different types of sequences can still be separated since their cross-correlation properties are acceptable (although they may be suboptimal).

[0079] Embodiments of the present disclosure have been described using the ZCxM sequence design as an example. However, many other design options can be designed according to the same principles - mixing multiple M- sequences, Gold sequences, Barker sequences, and other synchronization sequences. Extended sequences can be formed according to principles {M1 - sequence x M2-sequence}, {Goldl sequence x Gold2 sequence}, and {M- sequence x Gold sequence}, etc.

[0080] Embodiments of the present disclosure are also applicable when multiple component sequences are used to create a composite sequence with larger address space, e.g., by using the available sequences to send two shorter sequences. For example, assume that the baseline design is to transmit one length-63 M-sequence in 63 resource elements. To expand the address space, two length-31 M-sequences can be transmitted instead, yielding a product address space of 961 . However, detection performance of the expanded design is not as good as the original single sequence. This example provides an alternative example of address space - performance trade-off and a sequence set selection opportunity to prioritize one or the other, depending on network conditions.

[0081] Figure 7 is a schematic block diagram of the wireless device 12 (e.g., UE) according to some embodiments of the present disclosure. As illustrated, the wireless device 12 includes circuitry 20 comprising one or more processors 22 (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), Digital Signal Processors (DSPs), and/or the like) and memory 24. The wireless device 12 also includes one or more transceivers 26 each including one or more

transmitters 28 and one or more receivers 30 coupled to one or more antennas 32. In some embodiments, the functionality of the wireless device 12 described above may be implemented in hardware (e.g., via hardware within the circuitry 20 and/or within the processor(s) 22) or be implemented in a combination of hardware and software (e.g., fully or partially implemented in software that is, e.g., stored in the memory 24 and executed by the processor(s) 22).

[0082] In some embodiments, a computer program including instructions which, when executed by the at least one processor 22, causes the at least one processor 22 to carry out at least some of the functionality of the wireless device 12 according to any of the embodiments described herein is provided. In some embodiments, a carrier containing the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

[0083] Figure 8 is a schematic block diagram of the wireless device 12 (e.g., UE) according to some other embodiments of the present disclosure. The wireless device 12 includes one or more modules 34, each of which is

implemented in software. The module(s) 34 provide the functionality of the wireless device 12 described herein. For instance, the modules 34 include, in some embodiments, a receiving module operable to receive a configuration from the network node as described above with respect to, e.g., step 200 of Figure 6 and a utilizing module operable to use at least one of the two configured synchronization sequences as described above with respect to, e.g., step 202 of Figure 6.

[0084] Figure 9 is a schematic block diagram of a network node 36 (e.g., a radio access node 14 such as, for example, a gNB or a network node such as a core network node 19) according to some embodiments of the present disclosure. As illustrated, the network node 36 includes a control system 38 that includes circuitry comprising one or more processors 40 (e.g., CPUs, ASICs, DSPs, FPGAs, and/or the like) and memory 42. The control system 38 also includes a network interface 44. In embodiments in which the network node 36 is a radio access node 14, the network node 36 also includes one or more radio units 46 that each include one or more transmitters 48 and one or more receivers 50 coupled to one or more antennas 52. In some embodiments, the functionality of the network node 36 (e.g., the functionality of the radio access node 14) described above may be fully or partially implemented in software that is, e.g., stored in the memory 42 and executed by the processor(s) 40.

[0085] Figure 10 is a schematic block diagram that illustrates a virtualized embodiment of the network node 36 (e.g., the radio access node 14 or core network node 19) according to some embodiments of the present disclosure. As used herein, a "virtualized" network node 36 is a network node 36 in which at least a portion of the functionality of the network node 36 is implemented as a virtual component (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, the network node 36 optionally includes the control system 38, as described with respect to Figure 9. In addition, if the network node 36 is the radio access node 14, the network node 36 also includes the one or more radio units 46, as described with respect to Figure 9. The control system 38 (if present) is connected to one or more processing nodes 54 coupled to or included as part of a network(s) 56 via the network interface 44. Alternatively, if the control system 38 is not present, the one or more radio units 46 (if present) are connected to the one or more processing nodes 54 via a network interface(s). Alternatively, all of the functionality of the network node 36 described herein may be implemented in the processing nodes 54 (i.e., the network node 36 does not include the control system 38 or the radio unit(s) 46). Each processing node 54 includes one or more processors 58 (e.g., CPUs, ASICs, DSPs, FPGAs, and/or the like), memory 60, and a network interface 62.

[0086] In this example, functions 64 of the network node 36 described herein are implemented at the one or more processing nodes 54 or distributed across the control system 38 (if present) and the one or more processing nodes 54 in any desired manner. In some particular embodiments, some or all of the functions 64 of the network node 36 described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 54. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) 54 and the control system 38 (if present) or alternatively the radio unit(s) 46 (if present) is used in order to carry out at least some of the desired functions. Notably, in some embodiments, the control system 38 may not be included, in which case the radio unit(s) 46 (if present) communicates directly with the processing node(s) 54 via an appropriate network interface(s).

[0087] In some particular embodiments, higher layer functionality (e.g., layer 3 and up and possibly some of layer 2 of the protocol stack) of the network node 36 may be implemented at the processing node(s) 54 as virtual components (i.e., implemented "in the cloud") whereas lower layer functionality (e.g., layer 1 and possibly some of layer 2 of the protocol stack) may be implemented in the radio unit(s) 46 and possibly the control system 38.

[0088] In some embodiments, a computer program including instructions which, when executed by the at least one processor 40, 58, causes the at least one processor 40, 58 to carry out the functionality of the network node 36 or a processing node 54 according to any of the embodiments described herein is provided. In some embodiments, a carrier containing the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as the memory 42, 60).

[0089] Figure 1 1 is a schematic block diagram of the network node 36 (e.g., the radio access node 14 or a core network node 19) according to some other embodiments of the present disclosure. The network node 36 includes one or more modules 66, each of which is implemented in software. The module(s) 66 provide the functionality of the network node 36 described herein. In some embodiments, the module(s) 66 may comprise, for example, a first determining module operable to perform the function of step 100 of Figure 4, a second determining module operable to perform the function of step 102 of Figure 4, a third determining module (optional) operable to perform the function of step 104 of Figure 4, and an allocating and configuring module (optional) operable to perform the function of step 106 of Figure 4.

[0090] While not being limited thereto, some example embodiments of the present disclosure are provided below. [0091] Embodiment 1 : A method in a wireless network (10) for synchronization sequence selection, comprising: determining a number of required synchronization sequences based on one or both of network

conditions and a number of wireless devices (12) in the wireless network (10); and selecting a synchronization sequence set from at least two possible sets with different sequence set size/performance trade-offs based on the number of required synchronization sequences.

[0092] Embodiment 2: The method of embodiment 1 further comprising determining an allocation of the synchronization sequence set to individual entities in the wireless network (10); and configuring the entities with the sequences according to the allocation.

[0093] Embodiment 3: A method of operation of a network node (14, 19) in a wireless network (10), comprising: determining (100) an operation mode for the wireless network (10) or a part of the wireless network (10); and

determining (102), from at least two possible sets of synchronization sequences based on the operation mode, a synchronization sequence set to be used by a plurality of entities in the wireless network (10) or the part of the wireless network (10).

[0094] Embodiment 4: The method of embodiment 3 wherein the at least two possible sets of synchronization sequences comprise: a first set of synchronization sequences comprising a first number of synchronization sequences; and a second set of synchronization sequences comprising a second number of synchronization sequences, wherein the second number is less than the first number.

[0095] Embodiment 5: The method of embodiment 4 wherein determining (100) the operation mode for the wireless network (10) or the part of the wireless network (10) comprises determining (1 00) the operation mode for the wireless network (10) or the part of the wireless network (10) based on a number of unique synchronization sequences that need to be supported.

[0096] Embodiment 6: The method of embodiment 5 wherein determining (100) the operation mode for the wireless network (10) or the part of the wireless network (1 0) based on the number of unique synchronization

sequences that need to be supported comprises determining the number of unique synchronization sequences that need to be supported based on node deployment in the wireless network (1 0) or the part of the wireless network (10), node density in the wireless network (10) or the part of the wireless network (10), propagation conditions in the wireless network (10) or the part of the wireless network (10), antenna array sizes used in the wireless network (10) or the part of the wireless network (10), and number of current or statistical wireless devices (12) in the wireless network (10) or the part of the wireless device (10).

[0097] Embodiment 7: The method of embodiment 6 wherein determining (102) the synchronization sequence set to be used comprises selecting the first set of synchronization sequences if the number of unique synchronization sequences that need to be supported is greater than a threshold.

[0098] Embodiment 8: The method of embodiment 6 or 7 wherein

determining (102) the synchronization sequence set to be used comprises selecting the second set of synchronization sequences if the number of unique synchronization sequences that need to be supported is less than a threshold.

[0099] Embodiment 9: The method of any one of embodiments 4 to 8 wherein the first set of synchronization sequences is a ZCxM sequence set that uses cyclic versions of an M-sequence as different cover extensions of a set of cyclic-shifted ZC sequences.

[0100] Embodiment 10: The method of embodiment 9 wherein the second set of synchronization sequences is a subset of the ZCxM sequence set.

[0101] Embodiment 1 1 : The method of embodiment 10 wherein the subset of the ZCxM sequence set is: a subset of the ZCxM sequence set that uses a fixed M-sequence and a range of ZC roots, a subset using ZC roots only, a subset using a fixed ZC root and a range of M-sequence shifts, and a subset using M- sequence shifts only.

[0102] Embodiment 12: The method of any one of embodiments 4 to 8 wherein the first set of synchronization sequences mixes multiple sequences comprising one or more M-sequences, one or more Gold sequences, and/or one or more Barker sequences.

[0103] Embodiment 13: The method of embodiment 12 wherein the second set of synchronization sequences is a subset of the first set of synchronization sequences.

[0104] Embodiment 14: A network node (14, 19, 36) for a wireless network (10) adapted to perform the method of any one of embodiments 1 to 13.

[0105] Embodiment 15: A network node (14, 19, 36) for a wireless network (10), comprising: a network interface (44, 62) and/or at least one radio unit (46); at least one processor (40, 58); and memory (42, 60) storing instructions executable by the at least one processor (40, 58) whereby the network node (14, 19, 36) is operable to perform the method of any one of embodiments 1 to 13.

[0106] Embodiment 16: A network node (14, 19, 36) for a wireless network (10), comprising: one or more modules (66) operable to perform the method of any one of embodiments 1 to 13.

[0107] The following acronyms are used throughout this disclosure.

3GPP Third Generation Partnership Project

5G Fifth Generation

ASIC Application Specific Integrated Circuit

CPU Central Processing Unit

DSP Digital Signal Processor

eNB Enhanced or Evolved Node B

FPGA Field Programmable Gate Array

gNB New Radio Base Station

LTE Long Term Evolution

MIB Master Information Block

MME Mobility Management Entity

MRS Mobility Reference Signal

MTC Machine Type Communication

NR New Radio PBCH Physical Broadcasting Channel

P-GW Packet Data Network Gateway

PRACH Physical Random Access Channel

PSS Primary Synchronization Signal

RACH Random Access Channel

RRC Radio Resource Control

SCEF Service Capability Exposure Function

S-GW Serving Gateway

SI System Information

SSS Secondary Synchronization Signal

TRP Transmit/Receive Point

TS Technical Specification

UE User Equipment

ZC Zadoff-Chu

[0108] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.