Beam-scan time indicator

Description

TECHNICAL FIELD [0001] The invention relates to the transmission of synchronization signals, especially so-called beam-searching. In particular, the invention relates to methods for providing synchronization using sequences transmitted at different time points. The invention also relates to corresponding computer devices and programs.

STATE OF THE ART [0002] The 3rd Generation Partnership Project, 3GPP, is responsible for the standardization of the Universal Mobile Telecommunication System, UMTS, and Long Term Evolution, LTE. 3GPP's LTE work is also called Evolved Universal Terrestrial Access Network, E-UTRAN. LTE is a technology for the implementation of fast packet communication that achieves high transmission speeds on both downlink and uplink and is the next generation of mobile communication system in relation to UMTS. To support high transfer rates, LTE covers bandwidths between 20 MHz and 100 MHz if carrier aggregation is used. LTE is also able to work in other frequency bands and can work in at least FDD (Frequency Division Duplex) and TDD (Time Division Duplex) modes.

[0003] When a User Equipment (UE) wants to connect to a wireless communication system, for example after turning on the power or after waking up after a prolonged sleep period, it goes through an initial access procedure. The first step of this procedure is typical and the UE searches for and detects a synchronization signal containing synchronization sequences that are regularly broadcast by access nodes. network access node (AN), which are also called base stations or network nodes. It should be remembered that the synchronization signal is not clearly used in the technique. In this description, the term synchronization signal is used to describe all synchronization sequences that are regularly broadcast by access nodes. In other words, the synchronization signal is the sum of periodically repeated sequences. The synchronization signal allows the UE to adapt to the network in terms of time and frequency, i.e. it learns where the time boundaries between the symbols lie (e.g., OFDM symbols) and ensures that it uses, with limited tolerance, the same carrier frequency as the network. This type of adaptation in time and frequency is crucial for subsequent communication. In LTE, one synchronization sequence may be sufficient for the UE to adapt, but in some cases, the UE will require several synchronization sequences. The use of several synchronization sequences is not a problem because the synchronization sequences are regularly retransmitted. After successful adaptation, the UE may listen to additional information from the network, e.g. so-called system information and / or responding to a network request, often, often referred to as a physical random access channel message or a PRACH physical random access channel message. The UE typically cannot send a switch-on request at any time, as this would disturb other transmissions on the system, and instead should send them at a predetermined time interval after receiving the synchronization signal. The UE usually also knows in which time interval after the synchronization signal it can expect to find additional information (if they appear), limiting the complexity of searching and detecting additional information.

[0004] WO2015 / 147717 discloses a random access method (RA) of a wireless device to an access node / network node (NN), where the node uses high gain beam forming. WO2015 / 080646 discloses a method of synchronizing WD to NN in a high frequency scenario in which beam forming is used for communication.

[0005] In some systems, the UE may not respond directly to a network inclusion request, but instead may only request the network to send additional system information or only send an uplink (UL) synchronization signal to obtain UL synchronization (in systems with significant propagation delay, downlink synchronization (DL) does not automatically guarantee UL synchronization). Generally speaking, in the following any UL signaling in response to a DL synchronization signal (including but not limited to a network connection request, additional system information request or UL synchronization signal) will be called a UL signal.

[0006] A procedure similar to the pre-access procedure can also be performed when the UE wants to perform the handover, i.e. it is already connected to the system, but wants to connect to another network node, AN.

[0007] Future systems are expected to benefit greatly from forming a narrow beam of high gain that will allow high speed transmission range also to very remote users and / or in higher frequency bands that realistically are not possible for normal wide sector beams that have less antenna gain.

[0008] In order that the pre-access procedure is not a limiting factor in such systems, the synchronization signal will usually have to use narrow high gain beams. This means that the AN will usually need to send the synchronization signal several times in different directions to provide coverage in the geographical area served by the access node, AN. For typical antenna configurations, designed for next generation communication systems, sometimes called 5G systems, a narrow beam may cover only a small part of the entire geographical area (e.g. 1%) at a time, and as a consequence, beam transmission in any required direction, one or several directions at the same time may take a long time.

[0009] AN can in principle, depending on the hardware configuration, send the synchronization signal in many directions simultaneously, but taking into account the maximum total AN output power, this type of simultaneous transmission will take place at the cost of proportional power reduction per beam, i.e. it will effectively reduce range. This can be compensated by oversizing the equipment, for example, excessive total output power is available, but this increases the cost of such equipment. The procedure of sequential beam transfer in all required directions is called beam scanning or beam scanning. "Required directions" means all directions in which coverage is required.

[0010] The UE may listen to any of a plurality of synchronization signal transmissions during the beam search, and the network will not know which UE has heard. This means that if the UE is to send a network access request, e.g. using PRACH, at a specified time after listening to the synchronization beam transmission, which is a typical random access request procedure, the network must listen to the UL signal at many time instances in a given direction and / or the UE must send its UL signal at many time instances. In addition, this means that the UE must listen to any information necessary for accessing the system, e.g. system information in multiple instances of time and / or 2

The network needs to send additional information at different time instances. All of these cases translate into insufficient use of radio resources. In particular, this is because a node can usually only listen to a limited number of signals at a time, and in TDD half-duplex systems (the normal choice for future wireless communication systems), the node cannot send any signals while listening.

[0011] The article "Directional Cell Search for Millimeter Wave Cellular Systems" by C. Nicolas Barati et al. concerns the problem of beam-based synchronization signal detection by the mobile terminal. The authors propose a base station for periodic transmission of synchronization signals in random directions to scan the angular space and a detection algorithm based on the maximum probability in which a mobile device can detect the strongest direction is proposed.

[0012] However, known references do not relate to the common problem of AN transmitting transmission signals using beam forming, detection by the mobile terminal of such beams, and transmission of system access requests, e.g., RACH requests, and AN detecting such attempts from the terminal. SUMMARY OF THE INVENTION [0013] The object of the invention is to provide methods and devices that allow to alleviate, reduce or eliminate one or several of the above deficiencies in the prior art and disadvantages in a single or joint manner. [0014] Aspects of the invention are defined in the claims.

DESCRIPTION OF THE FIGURES [0015] Aspects will become clearer from the following, more detailed description of the embodiments, as shown in the accompanying drawings, in which the same numbers refer to the same parts in different views. Figures are not necessarily to scale, but emphasis is given to illustrating the embodiments.

Fig. 1 shows a network node transmitting in different directions and two wireless devices receiving different beams;

Fig. 2 shows an exemplary configuration of a wireless device according to some embodiments;

Fig. 3 shows an exemplary configuration of the network node according to some embodiments;

Fig. 4 is a diagram showing embodiments of method steps at a network node;

Fig. 5 is a diagram showing embodiments of the method steps in a wireless device;

Fig. 6 shows the PSS and SSS cage and time domain window structure for FDD;

Fig. 7 shows an example of the PRACH configuration transmitted via SIB 2;

Fig. 8 shows the structure of PBCH in LTE. The figure at the bottom is an enlargement of one sub-frame, indicated by the thick square in the figure.

Fig. 9 shows an example of a downlink synchronization signal in the form of a set of synchronization sequences with a countdown indicator (countdown field);

Fig. 10 shows a synchronization signal.

DETAILED DESCRIPTION [0016] Aspects of the invention will be further described below with reference to the attached figures. The apparatus and methods disclosed herein can be performed in a variety of ways that should not be limited to

EP 3 369 275 B1 to the preferred embodiments of the invention described herein. The same numbers in the figures apply to the same elements.

[0017] The terminology used herein is for the purpose of describing specific aspects of the invention only and is not intended to limit the invention. The singular used here also includes the plural, unless the context otherwise requires.

[0018] The access node, AN, radio access node and network node are used interchangeably throughout the description.

[0019] The synchronization signal is a predefined signal that allows the receiving device (its master clock) to adapt to the network in terms of time and / or frequency, i.e. learns where the time limits lie between the symbols (e.g. OFDM symbols) and ensures that the receiver uses, with limited tolerance, the same carrier frequency as the transmitter. This type of time and frequency adaptation is crucial for digital radio communication.

[0020] As described in the prior art section, it is expected that future systems will greatly benefit from high beam narrow beam formation. By using beam forming, a wireless device communicating with the network node by beam forming will not know when to listen or send to the network node, i.e. when the beam is facing the wireless device. In fig. 1 an example of a network node 20 transmitting several directional beams 1, 2, 3, 4 during beam searching and two receiving wireless devices 10a, 10b is shown.

[0021] Beam scanning may serve a purpose other than just time and frequency synchronization; in particular, searching can also be used to determine the best beam direction for data transmission to the new UE. In such cases, the beam may contain certain information that uniquely identifies the synchronization beam in such a way that the UE can report to the AN which beam has been best received. In this case, the best beam can be characterized by several alternative means, for example the one received at the highest power, the highest signal-to-noise ratio, the shortest arrival time (indicating the nearest AN) or the first exceeded power threshold. It can be seen as a kind of spatial synchronization. For simplicity, in this case, time and frequency synchronization signals as well as beam identification will be commonly referred to as synchronization signals that contain synchronization sequences.

[0022] In LTE, the synchronization signals will include synchronization sequences, i.e., predefined sequences of complete symbols that are repeated in predefined patterns. Each synchronization sequence informs the receiving device about the event, for example a random access window.

[0023] If the synchronization signal containing the synchronization sequences is transmitted during beam scanning, the synchronization sequences will be repeated in each of the beams 1, 2, 3, 4. Usually, the beams and thus the synchronization sequences will be transmitted at different points in time, i.e. synchronization sequences are time dependent. This type of synchronization sequence shifted in the description is called "time-dependent" and / or "time-shifted".

[0024] Fig. 1 shows that wireless device 10a will receive a second transmission 2 and wireless device 10b will receive a fourth transmission 4 of a time dependent synchronization sequence 4 at different points in time. In LTE, the random access window time depends on sequence time 4

This means that the network node must listen for random access requests in a plurality of time windows corresponding to different beams.

[0025] In the description, it has been proposed to include in each synchronization sequence transmitted from a network node a time indication that indicates to a wireless device or user equipment, UE 10, when, for example, listening for additional information and / or sending an uplink signal. The time indication, according to some aspects, will be an integer indicating the number of OFDM symbols until the transmission of the additional signal and / or the uplink signal occurs. For example, if one beam direction is transmitted in each OFDM symbol, the time indication number will be in each subsequent beam one smaller than that of the previous beam, and thus may be called a countdown indicator or countdown field.

[0026] The invention includes several embodiments detailing how the time indication can be efficiently coded by signals transmitted in synchronization sequences. According to some aspects, a method is proposed in which a predefined mapping of the synchronization sequence index to a time indicator is present, i.e. by detecting which synchronization sequence from among the set of predefined possible synchronization sequences that have been sent, the receiver can infer the time indication value.

[0027] Figs. 2 and 3 show examples of a wireless device 10 and a network node that may use some of the below discussed embodiments of an example node. The network node is e.g. eNodeB. As shown in the figures, wireless device 10 and network node 20 may include a radio communication interface 11, 21 configured to receive and transmit any form of communication or control signals on the network. It should be remembered that the 11.21 radio communication interface may consist of many units or systems of transceiver, reception and / or transmission. In addition, it should be remembered that the radio communication interface 11, 21 can be in the form of any input / output communication port known in the art. The radio interface 11, 21 may include an RF circuit and a baseband processing circuit (not shown). In addition, the network node 20 may include a network communication interface 23 configured to exchange any form of communication or control signals with the main network and / or other network nodes. Network communication is usually called a forward link.

[0028] Wireless device 10 and network node 20 may further include at least one memory unit or system 14, 24, which may be connected to the radio communication interface 11, 21. Memory 14, 24 may be configured to store received or transmitted data and / or implemented program instructions. Memory 14, 24 can also be configured to store any form of beam forming information, reference signals and / or data or feedback. Memory 14, 24 may be any type of computer readable memory and may be a type of non-persistent and / or permanent memory. According to some aspects, the invention relates to a computer program comprising computer program code or instruction sets that, when implemented in a wireless device, cause the first wireless device to perform any aspect of the operation of the exemplary node described below. According to some aspects, the invention relates to a computer program comprising computer program code or instruction sets that, when implemented at a network node, cause the network node to perform any aspect of the operations of the exemplary node described below.

[0029] The wireless device 10 and the network node 20 may additionally comprise a controller or processing system 12, 22, respectively. The processing system 12, 22 may be any type of computing unit, e.g. a microprocessor, a digital signal processor signal processor - DSP), FPGA (field programmable gate array) or ASIC (application specific integrated circuit) or any other form of system. It should be remembered that the processing unit need not be provided in the form of a single unit, but may be in the form of any number of units or systems. The processing system is further adapted to implement all aspects of the method in the above or below network node.

[0030] Figs. 4 and 5 show the concept of the proposed technique implemented in the wireless device 10 in Fig. 2 and in the network node 20 in Fig. 3.

[0031] It should be remembered that Figures 4 and 5 cover several operations, which are represented by a solid line, and several operations, which are represented by a broken line. The operations enclosed by the solid line are operations that are included in the broader embodiment. The operations that are contained by the dashed line are embodiments that may be part of or are further operations that may be performed outside of operations closed by a solid line. Remember that operations do not have to be carried out in order. In addition, it should be remembered that not all of the operations need to be carried out. Sample operations can be performed in any appropriate order and in any combination.

[0032] The invention provides a method of using a network node to transfer synchronization sequences and synchronization signal to one or more receiving wireless devices, see Fig. 4. The method includes determining S2 of multiple synchronization sequences in such a way that each synchronization sequence includes a corresponding time indication. In other words, the synchronization sequences are not only repeated at different points in time, instead, the time-dependent version of the synchronization signal is selected or determined to differ. Thus, the time-dependent versions include additional information that defines the actual time of the event. Thus, all of the time-dependent versions of the synchronization signal refer to the same point in time, i.e. event time, for example random access pane. This means that the synchronization sequences are similar or the same in some respects because they relate to the same event. Thus, the actual sequence of complex numbers that is transmitted may vary as described below. Thus, using the proposed technique, each synchronization sequence makes it possible to determine the time of the event in the receiving wireless device. According to some aspects, synchronization sequences are a code word, e.g., they use Reed-Muller code.

[0033] The method further includes transmitting S3 synchronization sequences to one or several wireless devices at different points in time. Synchronization sequences, which are parts of the synchronization signal, are sent at different points in time to one or more wireless devices. In other words, synchronization sequences that relate to the same event are sent at different points in time. The network node processing circuit 22 is configured to determine the S2 of multiple synchronization sequences and to transfer S3, via the communication interface 21, the synchronization sequence to one or more wireless devices. According to some aspects, the processing system includes a designating element 222 for determining a synchronization sequence and a transmitter 223 for transmitting a synchronization sequence.

[0034] According to some aspects, many synchronization sequences are versions dependent on the time of the synchronization signal relating to one particular event. Providing dependent on 6

In time synchronization sequences, the fact that beam scanning transmits signals at different times can be compensated. By providing a time indication in each synchronization sequence, the wireless device is notified of the time of the event so that it can react appropriately. In a system that uses beam search, the time indication provides a way to synchronize the wireless device relative to the network node. An event is, for example, a situation in which a network node listens for a system access request from a wireless device. In this particular example, the wireless device uses a time indication to determine when to send the system access request. The wireless device does not then need to send its UL signal at multiple instances of time. It does not have to listen for additional information necessary to gain access to the system, e.g. system information at multiple time instances and / or the network does not need to send additional information at different time instances. The time display is described below with examples.

[0035] The time of the event cannot always be predetermined. Thus, according to some aspects, the method further includes determining S1 of the event time. The processing node 22 of the network node is configured to determine S1 time. In addition to some aspects, the processing system includes a designator 221 for determining time. Time is used to provide time indication in multiple synchronization sequences. To determine the time of the event, one must determine the time between the synchronization sequence transmission and the event. Another example is determining the absolute time of an event expressed by means of a reference clock. Examples will be discussed in detail below.

[0036] As can be seen in Fig. 1, synchronization sequences, according to some aspects, are transmitted in different directions. Thus, wireless devices positioned in different directions relative to the network node receive synchronization sequences that were sent in different directions, e.g., 2 and 4 in Fig. 1. Wireless devices may then use a time indication to synchronize the event with the network node. Different directions mean in this case different spatial directions from the network node, as can be seen in Fig. 1. Transmission in different directions is accomplished with the help of so-called beam forming using co-located antennas, also called antenna systems. According to some aspects, the transmission of synchronization sequences is beam search. Ie. synchronization sequences are sent in several directions, at successive points in time, from the network node. The network thus uses the formation of a narrow beam of high gain, which will allow the range of high speed transmission also to very distant users, which realistically looking are not possible in the case of normal wide sector beams, which have less antenna gain.

[0037] Sending in different directions or at different times, the time indications must be properly defined. According to some aspects, the time indications depend on the transmission time and the respective synchronization sequence. In other words, the time indication depends on the transmission time. According to some aspects, the time indication includes a length of time from the time of transmission. When the time indication depends on the transmission time, it is easy for the wireless device to determine when the event time occurred. According to some aspects, the time display depends on the reference clock; for example, a reference clock on a network node. By using the reference clock, you can accurately determine the time by referring to the reference clock. The reference clock is the clock that both the wireless device and the network node have access to. According to some aspects, 7

The time indication is an indication of the current time with respect to the cage structure, e.g. the number of OFDM symbols from the start of the current super frame, from which the wireless device can acquire time, to the point intended for additional information and / or link signal in up.

[0038] According to some aspects, the time indication is a pseudo-random number that is used once and removed until all sequences in the current signal are completed. The wireless device may have been previously equipped with a translation method to translate pseudo-ice numbers into time indications. One possible implementation of the embodiment is the use of a sequence of predetermined states of a linear feedback recorder with a known initial state.

[0039] There are several examples of events in which the invention may be useful. According to some aspects, the event is the reserved time window during which a wireless device can transmit. Ie. event is the time the network node listens for an uplink, UL signal from the wireless device. Thus, the wireless device is informed when it is possible to transfer to a network node. According to some aspects, the reserved time window is a random access window (RA). Thus, the wireless device is informed when to send a random access message. For example, an event defines the beginning of a RA window or the beginning of another activity.

[0040] According to some aspects, time is the start time of the reserved time window, which may be useful, for example, in the event that the event is a rather long time window, the length of which is variable, but has been transmitted by other means.

[0041] According to some aspects, different time indications are transmitted in different synchronization sequences to reduce uplink congestion. Such different time indications and their respective synchronizations are usually sent from the network node in different directions. Thus, time indications can refer to different points in time, which allows the use of different RA windows. In this way, wireless devices that are set in different directions relative to the network nodes will use different RA windows. This approach can be useful when many wireless devices are within range of a network node, i.e. many devices can receive synchronization signals. The detection of synchronization signals by many devices is also accompanied by the fact that many devices will send a random access signal. The threat associated with too many simultaneous RA transmissions, for example, when a network node cannot receive them all properly, is reduced by directional separation of devices into at least two transmitting groups in different RA windows. This is an adaptable option that allows you to control the compensation of Random Access resource reservations against congestion.

[0042] According to some aspects, time slots for additional information and / or uplink signal do not occur periodically, but the carrier decisions are made dynamically by the network based on the demand for traffic and / or behavior of other wireless devices.

[0043] In LTE, the network transmits Primary and Secondary Synchronization Sequences (PSS / SSS) from a known frequency allocation (6 central blocks of downlink frequency band resources) in potentially known time domain windows from point view of both OFDM symbol and sub-frames. In other words, the EU knows that the PSS / SSS are in OFDM symbol No. 6 and No. 5 (in the case of normal CP) respectively repeated in sub-box 0 and sub-box 5. After

Upon detecting both PSS and SSS, the UE is synchronized with DL from both the OFDM symbol and sub-frame perspective. This is shown in Fig. 6.

[0044] In addition to synchronization, the UE detects the physical cell identity (PCI) that is encoded in PSS / SS. On this basis, the UE is able to use cell-specific reference signals (CRS) to estimate the channel and decode system information that contains the most basic information that the UE should know before attempting to access to the system. This information is provided in something called the master information block (MIB) and system information block (SIB).

[0045] The physical channel by which this information is transmitted varies depending on the block. For example, main information blocks, MIB, are sent using the PBCH (Physical Broadcast Channel) channel, while other SIBs are transmitted on the PDSCH (Physical Downlink Shared Channel) channel so that they can be flexibly scheduled in other parts frequency bands. The structure of PBCH in LTE is shown in Figure 8.

[0046] To be able to enter the system, the UE must start a random access procedure. It is started by sending random access admission using a physical random access channel, PRACH. PRACH can be multiplexed on the uplink band using the physical uplink control channel (PUCCH) also used to send reports on the status of the channel, acknowledgments and / or scheduling requests.

[0047] Before the UE can send random access, it must retrieve information on how PRACH is multiplexed in the UL band. This is communicated in SIB2 in the prach IE Configuration Index, which includes from 0 to 63 and includes, among others Parameters (details can be found in TS 36.211, version 11.2.0): Introduction format, sub-frame sequence number and sub-frame number.

[0048] The configuration index generally indicates which time domain resources in PUCCH, the UE should send random access admission (i.e., on PRACH). Fig. 7 shows some examples of the configuration of a given intro format. Details of this can be found in TS 36.211 (chapter 5.7.1), version 11.2.0. [0049] In summary, in LTE, the UE must decode all useful data from SIB2 (after providing DL synchronization and being able to perform channel evaluation) to obtain the necessary information to send a system access request. This is based on the fact that information is sent in all directions from well-defined time domain structures (OFDM symbols, sub-frames, radio frames, etc.).

[0050] Another example relates to the case in which the event is the time of the next transmission from the network node. In other words, the event is the time the wireless device listens for the next transmission from the network node. This allows the wireless device to perform more efficiently because it does not have to listen to the transmission at other times than the time defined in the synchronization sequence.

[0051] According to some aspects, the mapping from the synchronization signal index to time is transmitted by means of system information that can be received by another method, for example used in LTE or by the system control plane access concept (SCP) ). In the case of LTE, the SIB2 message may include mapping between the synchronization sequence subject to beam forming and the allocation of time - the frequency at which the UL request signal should be sent and / or where additional information can be expected. In the case of the SCP access concept, information on this type of mapping can be provided on the basis of 9

EP 3 369 275 B1 to the access information table (AIT) followed by the system signature sequence (SSI). The UL system request signal in this context may be, for example, PRACH admission, request for the next system information to be sent, or a synchronization message without the main meaning of the above layer.

[0052] In one embodiment, "system information" may include system bandwidth information and / or other information similar to the information contained in system information in LTE, especially in the content of MIB, SIB1 and SIB2, for example, the system frame number and information about the restriction.

[0053] There are several possible ways to provide a time indication. According to some aspects, the time indications are encoded in a synchronization sequence. In other words, the time indication is coded by default. Then, for example, the system may have many different predefined synchronization sequences, and each synchronization sequence will have an index associated with it. The synchronization sequences themselves can have any structure; typically, the sequences can be optimized to have good automatic and cross-correlation properties and good Euclidean or Hamming properties. Each such type of index then corresponds to a time indication according to a predetermined mapping and will be called a computing index mapping. Generally, multiple sequence / sync indexes may correspond to the same time indication.

[0054] This is particularly useful in one variant of the proposed technique in which multiple beams are sent simultaneously from a single network node or from multiple network nodes because one would want the wireless device to be able to distinguish between different beams (e.g. future reporting to the network), still receiving the same (or different) time indication. It can be seen that the synchronization sequence thus defined will correspond to the index coding. One example of this type of variant is a network node that sends two beams (called a and b) simultaneously in different directions. However, for some reason, he just wants to listen in one direction at a time. Thus, the access node wants to make sure that the UE in different directions respond at different points in time.

[0055] Thus, according to a variant of the invention, it proposes a method of using a network node to transfer synchronization sequences and a synchronization signal to one or several receiving wireless devices. The method includes determining a plurality of synchronization sequences in such a way that each synchronization sequence includes a corresponding time indication, wherein each synchronization sequence allows determining the corresponding (or the same) event time on the receiving device; and sending synchronization sequences to one or more wireless devices, at least partly at the same point in time, but in different directions.

[0056] Another example of this variant is that the network node may send one beam in direction a and the other in direction b. However, for any reason, the UE may only send in one direction at a time that is known by the access node. Next, the access node wants to make sure that the UE can respond in one direction at a time.

Returning to Fig. 4. According to some aspects of the method, each of the synchronization sequences is determined to include a synchronization sequence from a set of different synchronization sequences and wherein each different synchronization sequence in the set is mapped to a respective point in time or time. . E.g. the time indication corresponds to the signal index 10

A synchronization device from which the receiving wireless device may infer a time indication value. When different synchronization sequences are sent in different directions, and when they are different, i.e. different, the receiving wireless device may infer a time indication value. In other words, the time indication is implied in different synchronization sequences. Another example is that the synchronization sequence is mapped to time using an index. Please note that many different sequence indexes may be mapped to the same time indication. Then, it is possible to determine the time by looking at the index in a table, for example.

[0058] According to some aspects, in the case of implicit coding, many different synchronization sequences may correspond to a different frequency-shifted version of the same base synchronization sequence, e.g., transmitting the same synchronization sequence on different subcarriers in different time windows. The frequency at which the sequence is transmitted can be mapped to the time indication.

[0059] According to some aspects, the uplink signal may be sent on a physical random access channel, PRACH, wherein the uplink signal may be, e.g., a random access preface or an uplink synchronization channel, USS, wherein the uplink signal may be e.g. synchronization sequence / uplink signal.

Preferred Embodiments [0060] In one embodiment of the invention, the downlink synchronization signals (sequences) are indexed in such a way that the indices form successive series of numbers. This can be described in the system information or even standardized. By assembling the set of downlink synchronization signals in the case of the above, not preconfigured scenarios, the access node selects a set of downlink synchronization signals whose indexes will form subsequent series of numbers. Downlink synchronization signals are transmitted in order in such a way that the respective indexes will form successive decreasing series of numbers. At a point in time when the uplink signal, e.g. a system access request, e.g. a random access request, is to be sent, a series of index numbers, indicated by potential downlink synchronization signal transmission, should reach a number in which the specified number of least significant bits is zero. This type of downlink synchronization signal may be referred to as the downlink sync signal and its index as the end of file index. The term "potential transmission" refers in this case to the downlink synchronization signal, simply because it is not certain that it is being transmitted. If the network node wants the sync bundle transmission set to terminate earlier by the uplink signal, then a decreasing series of indexes will be disturbed before it reaches the end-of-set index.

[0061] Thanks to this principle, each downlink synchronization sequence, due to its index, will indicate to the wireless device the exact time distance from transmission of the downlink synchronization sequence to the transmission of the uplink signal, i.e. will serve as a countdown indicator. For example, if the format of the end of index file is defined as the index ending in 0000, the sets of downlink synchronization sequences may consist of 8 downlink synchronization sequences with a series of binary index (assuming 8 bit sequences) 01010111, 01010110, 01010101, 01010100, 01010011,01010010, 01010001,01010000 (i.e. decimal 87, 86, 85, 84, 83, 82, 81.80), see the last 8 indexes in Fig. 9. In another example, in which the downlink synchronization sequences are not transmitted because a longer time is required for the uplink signal, there may be downlink synchronization sequences with the indices 01011001,01011000, 01010111,01010110, 01010101,01010100, 11

EP 3 369 275 B1

01010011, 01010010 (i.e. decimal 89, 88, 87, 86, 85, 84, 83, 82). The second example is shown in Fig. 9 showing a point in time for an uplink signal that has been defined for occurrence, designated as TUSS (where USS is an uplink signal) after (hypothetical / potential) transmission of the end of the link synchronization sequence down the end of the set. An example of an UL signal may be an uplink synchronization signal (e.g. uplink synchronization signal - USS), system access request or any other solution. In Fig. 9, each box represents a mobility reference signal (MRS) with a specific index, where MRS is in this case the downlink synchronization sequence and the uplink synchronization channel USS ), uplink signal. The left vertical arrow indicates the hypothetical MRS transmission of the end of the set, while the right vertical arrow indicates the point in time for the uplink signal defined so that TUSS occurs.

[0062] In another embodiment, according to some aspects, each transmission beam consists of at least two parts, one part that serves as a training sequence (pilot / reference / synchronization), e.g. a predefined sequence, e.g. QPSK modulated symbols or ZadoffaChu sequence that allows a wireless device to synchronize, detect beam and perform channel estimation, and one part that includes a time indication encoded with the appropriate channel code, e.g., Reed-Muller code. The two parts can be separated, for example, using different but usually adjacent time and / or frequency resources. FIG. 10 is an example of a synchronization signal in which each OFDM symbol consists of two parts separated in time, nA and nB, where n is the number of the OFDM symbol. The horizontal axis is the OFDM symbol number and the vertical axis is the frequency.

[0063] As already mentioned, the time indication may be coded in the synchronization sequence by default. A variant of this approach may be to allow each beam to consist of two or more parts, separated in time and / or frequency, where both parts consist of some type of synchronization sequence, but where the two synchronization sequences are not the same. [0064] For example, the synchronization sequence in one part may be the same for many beam directions and / or time instances, while the sequence in another part may be different for different beam directions and / or time instances. This type of arrangement can be useful to reduce computational complexity in a wireless device. For the first part, only a few possible synchronization sequences may be required in the system, limiting the search space, and thus the computational complexity in the wireless device, while in the second part, more synchronization sequences can be used in the system, while still maintaining the complexity of the wireless device at a medium level because the wireless device already has a fairly good channel estimate from the first part.

[0065] According to some aspects, some of the beam directions are repeated two or more times, e.g., to allow the receiver to perform a scan of the receiving beam, but at different counting index values.

[0066] According to some aspects, the invention also relates to a computer program comprising a computer program code which, when implemented in a programmable network node controller, causes the network node to implement the methods described above and below. In other words, the invention also relates to a computer readable storage medium comprising a stored computer program that, when implemented in a programmable network node controller, causes the network node to implement the methods described above and below.

[0067] The invention provides a suitable method in a wireless device, which will now be described with reference to Fig. 5. The invention provides a method used in a wireless device 10 to receive one or more synchronization sequences of a synchronization signal. The method includes monitoring the S11 synchronization sequence spectrum. Spectrum monitoring in this case means receiving a radio signal and based on the received signal, and possibly additional assumptions about e.g. noise and interference levels, estimating for one or several predefined synchronization sequences a measure of quality, e.g. the probability that it has been transmitted. This type of quality measure can usually be based on a matched filter approach in which the received signal is correlated with each of one or more predefined synchronization sequences, e.g. random access entries. Typically, monitoring continues until a match is found, i.e., until the correlation exceeds a certain threshold.

[0068] When the first synchronization sequence is detected, the method includes obtaining S12, analyzing the content of the detected first synchronization sequence, a time indication defining the event time. In the description of the network node, many examples are given about how time indication can be included.

[0069] The wireless device processing system 12 is configured to monitor S11, using the communication system 11, the spectrum and obtaining S12, a time indication. According to some aspects, the processing system includes a monitoring unit 121 for monitoring and an obtaining element 122 for obtaining a time indication. The time indication has been included in the synchronization sequence by the transmitting network node.

[0070] Accordingly, the wireless device is notified of the time of the event so that it can respond appropriately. Accordingly, this, for example, means that the wireless device does not then need to transmit its uplink, UL signal at multiple time instances. It does not have to, for example, listen for additional information necessary to access the system, e.g. system information at multiple time instances and / or the network does not need to send additional information at different time instances.

[0071] According to some aspects, in system implementations in which a network node provides a wireless device with a list of beam identifiers or sequential indexes to be monitored, the provided index for a given beam may include (1) the initial part of the full index sequence and (2) the number of hypotheses countdown, i.e. clock value. The wireless device may then add clock bits to the starting portion of the sequence to create the complete sequence and recall the corresponding reference sequence, which will then be searched for in the received signal.

[0072] As described above, many synchronization sequences, according to some aspects, are time dependent versions of a synchronization signal relating to one particular event. Analyzing the content of the detected first synchronization sequence includes, for example, decoding the first synchronization sequence and time indication search.

[0073] Depending on the position of the wireless device 10, the wireless device may receive more than one synchronization sequence. According to some aspects, the method comprises receiving S11b a second synchronization sequence, wherein the first and second synchronization sequences define the same time. In the example, when the time indication is a relative time from the transmission time, the relative time is different in the synchronization sequence, but the time that the indications define is the same. According to some aspects, it is sufficient for a wireless device to receive one signal 13

However, there may be a case where it requires several of them to provide reasonable assurance. According to some aspects, the network node has transmitted to the wireless device how the device should handle this situation. An example is that the network node has forwarded to the network device that it will repeat the synchronization sequence N times, in each beam direction, with the same sequence each time, except for the countdown field, which is reduced by 1 for each repetition to indicate which of the repetitions is. According to some aspects, the time indications are relative times in relation to the transmission time and the corresponding synchronization sequence. When the time indication depends on the transmission time, it is easy for the wireless device to determine when the event time occurred. Synchronization sequences may thus include different time indications but define the same time. This is useful, for example, if the event is an event that occurs simultaneously for all wireless devices in all directions from the network node. As described in the method of the network node, the time indications, according to some aspects, are relative to the reference clock or the event is the time of the reserved time window at which the wireless device can transmit. According to some aspects, the reserved time window is a random access window. The specificity of these examples was discussed earlier.

[0074] According to some aspects, the method comprises performing S13 transceiver operations at a time defined by a time indication. In other words, the wireless device receives and / or transmits during a defined synchronization sequence.

[0075] Processing system 12 is configured to perform S13 multiple synchronization sequences. In addition to some aspects, the processing system includes a designator 123 for determining time. The transceiver operation involves, for example, sending random access intro in the indicated time window. According to some aspects, the event is the time during which the wireless device must listen to the next transmission from the network node. Thus, the wireless device does not need to listen for any additional information at multiple time instances.

[0076] As also said earlier, discussing the method of the network node, the time indications, according to some aspects, are encoded in synchronization sequences and wherein the analysis includes decoding the synchronization sequence. If the time indication is encoded in a synchronization sequence, then the wireless device may have to decode the synchronization sequence to detect the time of the event.

[0077] According to some aspects, the wireless device monitors the spectrum for several different synchronization sequences, and wherein each different synchronization sequence is mapped to a respective point in time or time. Since the wireless device does not initially know which direction it is in relation to the network node, and thus what transmission of the synchronization sequence it can receive, it monitors the spectrum of several possible transmissions. Each of the separate synchronization sequences provides a point in time or time of event. If different synchronization sequences are mapped to different events, then the simple detection of a specific sequence (or admission) informs the wireless device about where, e.g. to send a random access request.

[0078] As described above, this type of time is either relative to another state or absolute. According to some aspects, each synchronization sequence is mapped to time using an index, while obtaining 12 involves obtaining time using an index. 14

EP 3 369 275 B1

Please note that many different sequence indexes may be mapped to the same time indication. Then, it is possible to determine the time by looking at the index in a table, for example. Thus, time defines the time of the event.

[0079] According to some aspects, the invention also relates to a computer program comprising a computer program code which, when implemented in a programmable wireless device controller, causes the wireless device to implement the methods described above and below. In other words, the invention also relates to a computer readable storage medium comprising a stored computer program which, when implemented in a programmable wireless device controller, causes the wireless device to implement the methods described above and below.

[0080] The above description refers to a wireless device that should synchronize with the network of network nodes, but the same techniques can be used in other situations regarding synchronization and / or beam search, for example a newly launched network node that must synchronize with existing network nodes (or even a wireless device) in the network, especially in networks using forward links. This description also applies to the initial device-to-device synchronization, D2D. Thus, the techniques described above can in many cases be used equally when the "uplink" is replaced by the "downlink" and vice versa. In addition, the above description focuses on initial access, but similar techniques can be used to synchronize and / or find beams in e.g. forwarding situations.

[0081] The above description mainly relates to joint synchronization and beam finding, but the techniques also relate to situations where only beam search is necessary, for example because synchronization has already been provided earlier by other means.

[0082] The above description often mentions, as an example, OFDM. However, the techniques described here also apply to many OFDM variants as well as many other multiplexing schemes, including e.g. DFT spread OFDM, filtered OFDM, FBMC (filter-bank multicarrier), SC-FDMA (single-carrier frequency -division multiple access), etc. These techniques also apply to other types of RAT, TDMA, CDMA, etc.

[0083] The value of the detected countdown indicator may be somehow embedded in the uplink response (e.g., system access request) from the UE. This can be useful to help the network determine which beam the EU has heard.

[0084] The invention translates into a significant reduction of resource allocation traffic. There is a reduction in the demand for uplink resources compared to providing a steady time between the downlink synchronization signal and the uplink signal. A downlink signaling restriction is obtained compared to sending detailed system configuration (system information) in all downlink beams. The time indication contained in the synchronization sequences is a very flexible way of indicating the appropriate time for the uplink signal. Thanks to this approach, the system can configure how often uplink signals are allowed, e.g. in the form of packet random access using e.g. PRACH. This method is in opposition to providing a fixed (or semi-static) configuration of time intervals for uplink access (PRACH). The network node may choose whether multiple beams and wireless devices or UEs received the same time indication to conserve uplink resources, or whether other beams and UEs should be configured to separate uplink time intervals to reduce congestion.

[0085] The benefits may be particularly evident in systems that use analog beamforming at the network node and / or in the wireless device. There are several reasons for this, and only one example is provided: An analog beamformer will typically use digitally controlled phase shift elements to define the beam configuration, and the shape of the resulting pattern will depend on the specific phase selected for the antenna elements or antenna ports. Thus, a beam pattern with many major projections can be marked with the same time indication for several directions, making uplink signals from different directions coincide with the same time indication value. This type of uplink signal may result from random access signals from one or more wireless devices in any privileged position.

[0086] In the context of the invention, the terms "wireless terminal" or "wireless device" include any terminal that is able to wirelessly communicate with another device and optionally with a wireless network node, transmitting and / or receiving wireless signals. Thus, the term "wireless terminal" includes, but is not limited to: user equipment, e.g. UE LTE, mobile terminal, stationary or mobile wireless device for machine-to-machine communication, integrated or embedded wireless card, externally connected wireless card, hardware key, etc. In the description, the term "user equipment" is sometimes used to cite various examples execution. However, it should not be construed as limiting because the concepts presented here are equally applicable to other wireless nodes. Thus, whenever the term "user equipment" or "UE" is used in the description, it should be viewed as including any of the above-described wireless terminals.

[0087] Aspects of the invention have been described with reference to figures, e.g., block diagrams and / or working diagrams. It should be remembered that several units in the figures, e.g. block diagram blocks and combinations of units in the figures, can be implemented by means of computer program instructions, which instructions can be saved in computer readable memory and loaded into a computer or other programmable data processing apparatus. Such computer program instructions can be sent to a personal computer processor, dedicated computer and / or other data processing equipment to create a machine that, on the basis of instructions implemented by the computer processor and / or other data processing equipment, provides a means of implementing the function / activities described in block diagrams and / or work diagrams or blocks.

[0088] In some implementations and according to some aspects of the invention, the functions or steps marked in blocks may appear out of order indicated in the operational illustrations. For example, two blocks shown sequentially can be implemented substantially in parallel, and sometimes blocks can be implemented in the reverse order, depending on the functions / activities performed. In addition, the functions or steps marked in blocks may according to some aspects of the invention be implemented in a continuous loop.

[0089] In the figures and description, exemplary aspects of the invention are disclosed. However, many changes and modifications can be made to these aspects without substantially departing from the principles of the invention. Thus, the invention should be seen as illustrative rather than limiting and not limited to the specific aspects discussed above. Accordingly, despite the fact that some concepts were used, they were used only in a generic and descriptive sense, and not for the purpose of limitation.

[0090] A description of the embodiments provided herein is provided for illustrative purposes. The description is not exhaustive or restricting the embodiments to the specific form disclosed herein, and many modifications and changes are possible in the light of the above information or resulting from the implementation of various alternatives 16

EP 3 369 275 B1 to the illustrated embodiments. The examples discussed here have been selected and described to explain the principles and nature of the various embodiments and their practical application, to enable those skilled in the art to use the embodiments in various ways and using various modifications to suit the particular intended application. The functions of the embodiments described herein can be combined in all possible combinations of methods, apparatuses, modules, systems and computer program products. Please note that the examples presented here can be implemented in any combination thereof.

[0091] It is to be remembered that the term "comprising" does not necessarily exclude the presence of other elements or steps in addition to those mentioned, but the singular notions do not exclude the presence of many such elements. In addition, it should be remembered that any reference signs do not limit the scope of the claims, that the embodiments can be implemented at least partially by means of both hardware and software, and that several "measures", "units" or "devices" may be represented by the same unit hardware.

[0092] The various embodiments described herein are provided in the general context of method steps or processes that may be implemented in one aspect by a computer program product embedded in a computer readable medium, including instructions implemented by a computer, e.g., program code, implemented by computers in network environments. The computer-readable medium can be a removable or permanent storage device, including but not limited to Read Only Memory (ROM), Random Access Memory (RAM), compact disc, DVD, etc. Generally, program modules include processes, programs, objects, components and data structures etc. that perform specific tasks or implement specific partial types of data. Computer-implemented instructions, related data structures, and program modules represent examples of program code for implementing the steps of the methods disclosed herein. A specific sequence of this type of executed instructions or related data structures represents examples of appropriate actions for implementing the functions described in such steps or processes.

[0093] In the figures and description, embodiments are disclosed. However, embodiments can be changed or modified in various ways. Accordingly, despite the fact that some terms have been used, they have been used only in a generic and descriptive sense, and not for the purpose of limitation, and the scope of the invention is defined in the following claims.