WO2019201484A1

WO2019201484A1 - 5g nr system for communication with a user terminal

Info

Publication number: WO2019201484A1
Application number: PCT/EP2019/051362
Authority: WO
Inventors: Christophe Gruet; Gil Botet; Pierre TANE; Roger Jacques
Original assignee: Kapsch CarrierCom France SAS
Current assignee: Kontron Transportation France SAS
Priority date: 2018-04-19
Filing date: 2019-01-21
Publication date: 2019-10-24
Anticipated expiration: 2020-10-19

Abstract

The invention relates to a system for communication with a user terminal according to a 5G NR standard having an OFDM structure in which synchronisation signal blocks (6n) containing the same physical cell ID are repeatedly broadcast, wherein the system (9) comprises a number of local radio equipments (12m), wherein the local radio equipments (12m) are spaced apart from each other by predetermined distances (s), wherein the coverage areas (4n) of the antennas (3n) are aligned contiguously in a chain to form an elongated radio cell (15) with said physical cell ID, wherein the system (9) is configured to broadcast each synchronisation signal block (6n) of said set (7) by at least one local radio equipment (12m) within each repetition period (8), and wherein each local radio equipment (12m) is configured to broadcast only one synchronisation signal block (6n) of said set (7).

Description

5G NR System for Communication with a User Terminal

The present invention relates to a system for communica tion with a user terminal, wherein the system is configured to communicate with the user terminal according to a 5G NR (5th Generation New Radio) standard having an OFDM (Orthogonal Fre quency Division Multiplex) structure in which a set of synchro nisation signal blocks containing the same physical cell ID (identification) is repeatedly broadcast with a predetermined repetition period, the synchronisation signal blocks of said set being broadcast successively in time, each synchronisation signal block of said set over a different antenna.

The 5G NR standard, devised by the 3GPP (3rd Generation Partnership Project) consortium, is defined in specifications 3GPP TS 38. XXX ("Series 38") and is generally also known as LTE Release 15. The term "5G NR standard" used herein covers all equivalent and subsequent standards based thereon.

In the 5G NR standard, an array of antennas with very nar row but long coverage areas is used to operate in high fre quency spectrums . These "beamforming" antennas are arranged in a circular fashion on a node to be able to communicate with user terminals in any angular directions thereof.

The 5G NR standard provides tools for the initial access of user terminals as they do not know in which coverage area of the multitude of antennas they are located. To this end, the 5G NR standard employs an OFDM structure in which a set of syn chronisation signal blocks containing the same physical cell ID is repeatedly broadcast with a predetermined repetition period, the synchronisation signal blocks of said set been broadcast successively in time, each synchronisation signal block of said set over a different antenna. In practice this means that a "sweeping" is performed over the antennas - first one antenna broadcasts one signal block, thereafter a different antenna broadcasts a different signal block, and so forth.

A user terminal located in one of the narrow coverage ar eas will receive only one signal synchronisation block and can determine its position in the OFDM structure by means of the timing and content of the signal synchronisation block. This yields an effective initial access for high frequency beamform ing systems. After receiving the synchronisation signal block, which is commonly known as the discovery phase, the user equip ment is able to acquire system information broadcast by the system and thereupon access the random access channel (RACH) to establish a bidirectional communication.

To establish a cell system covering a wider area, multiple of the above-described 5G NR cells are arranged next to each other. However, a user terminal travelling from one cell into the next is required to perform a handover procedure (a "hard handover"), which generally reduces the overall throughput and is susceptible to disconnections.

It is therefore an object of the invention to achieve a 5G NR system that overcomes the abovementioned drawbacks of the state of the art. To this end, the invention provides for a 5G NR system of the above-mentioned type, which comprises a number of local ra dio equipments that is at least equal to the number of synchro nisation signal blocks in said set, each local radio equipment having an antenna with a radio coverage area and being synchro nised with the other local radio equipments with respect to the OFDM frame structure,

wherein the local radio equipments are spaced apart from each other by predetermined distances,

wherein the coverage areas of the antennas are aligned contiguously in a chain to form an elongated radio cell with said physical cell ID,

wherein the system is configured to broadcast each syn chronisation signal block of said set by at least one local ra dio equipment within each repetition period, and

wherein each local radio equipment is configured to broad cast only one synchronisation signal block of said set.

The invention thus uses 5G NR capabilities to enhance the covered geographical area by splitting up the standard 5G NR node into separate local radio equipments, which are only fed with one synchronisation signal block, each to be broadcast at a specific time. Each local radio equipment thus only uses a part of the available OFDM structure to broadcast its synchro nisation signal block.

By spacing the local radio equipments apart from each other and arranging them in a cell-like manner, an elongated coverage area is achieved that looks exactly like a 5G NR sys- tern from the user terminal point-of-view but has a substan tially larger coverage area, thereby reducing the amount of handovers for the user terminal. When the user terminal travels through the chain from one of the chain's ends to the other, it traverses the coverage areas of all local radio equipments of the system. From the user terminal point-of-view it looks like it is going in a circle around a 5G NR node. As such, the user terminals of the system do not have to be adapted to the new cell structure as all necessary modifications are located in the (roadside) system.

Compared to the case where multiple 5G NR nodes are ar ranged in a chain-like manner, the inventive system has the ad vantage that fewer hard handovers have to be performed as long as the user terminal travels within the elongated cell. When the user terminal switches from the one coverage area to an other coverage area of two local radio equipments of the inven tive system, the highly reliable and especially fast beam switching capabilities of 5G NR are utilized such that hard handovers are avoided.

Preferably, the system comprises a baseband unit connected to all local radio equipments of the system, wherein the base band unit is configured to manage the local radio equipments. The baseband unit is an effective way to distribute the syn chronisation signal blocks to the individual local radio equip ments. The baseband unit can further determine which OFDM radio resources are to be used on which local radio equipment if one or more user terminals are located in a coverage area of the system.

Further preferably, each synchronisation signal block of said set comprises the Primary Synchronisation Signal (PSS) , Secondary Synchronisation Signal (SSS) , and Physical Broadcast Channel (PBCH) of the 5G NR standard. By means of this it is assured that all information required by the user terminal in the discovery phase is broadcast by each local radio equipment.

In this embodiment, it is further preferred if the Primary Synchronisation Signals (PSS) and Secondary Synchronisation Signals (SSS) of each synchronisation signal block of the set are the same and the Physical Broadcast Channel (PBCH) is dif ferent in each synchronisation signal block of the set and com prises a beam index. As the Primary and Secondary Synchronisa tion Signals usually encode the physical cell ID, this can be used to broadcast the same physical cell ID over the whole cell. The Physical Broadcast Channel in this case delivers, amongst others, the individual information regarding the local radio equipment, seen by the user terminal as a specific angu lar beam of a 5G NR system employing beamforming.

Compared to a conventional circular 5G NR system employing multiple antennas with beamforming, the inventive system exhib its further advantages for user terminals within the (compound) coverage area of the cell.

In one preferred embodiment, the system is configured to, after two user terminals have responded to the system which synchronisation signal block they have received, allocate the same OFDM radio resources, for uplink and/or downlink, to both user terminals if they are located within coverage areas that are not adjacent to each other. Thereby, the overall throughput of the system can be enhanced, with respect to a classical 5G NR system employing beamforming, as OFDM radio resources can be "reused" for user terminals in non-adjacent local radio equip ments .

In a second preferred embodiment, the system is configured to, after a user terminal has responded to the system that it is about to leave the coverage area of one local radio equip ment and is about to enter the coverage area of another local radio equipment, allocate the same OFDM radio resources, for uplink and/or downlink, on both of said local radio equipments for communication with the user terminal. This can be used to employ diversity schemes such as MIMO (Multiple Input Multiple Output) or MISO (Multiple Input Single Output) , for example, as this reduces the needed signal-to-noise ratio and thus enhances the throughput .

In a third preferred embodiment, the system is configured to, after a user terminals has responded to the system that it is about to leave the coverage area of one local radio equip ment and is about to enter the coverage area of another local radio equipment, allocate OFDM radio resources for downlink on the local radio equipments that the user terminal is leaving and OFDM radio resources for uplink on the local radio equip ments that the user terminal is entering. In a chain-like cell as described above, user terminals only either communicate with local radio equipments that they move away from or towards to. This can be used to reduce the Doppler shift within the system as described above. This is based on the fact that the user terminal does not adjust its internal clock after receiving a Doppler shifted communication on the downlink channel. By using the uplink channel with the local radio equipment the user ter minal moves towards to, the offset of the local clock of the user terminal is negated by the reversed relative velocity as seen by the respective local radio equipment. As a result of the reduced Doppler shift within the system, the overall commu nication quality is improved in the system, making communica tions more stable.

Preferably, the number of local radio equipments is equal to the number of synchronisation signal blocks in said set, and each local radio equipment is configured to broadcast a syn chronisation signal block of said set that is different to the synchronisation signal blocks broadcast by the other local ra dio equipments. This yields a one-to-one correspondence between synchronisation signal blocks and local radio equipments. For example, if the system broadcasts four synchronisation signal blocks, there will be four local radio equipments in the field and each local radio equipment broadcasts a different synchro nisation signal block at a different point in time with respect to the other local radio equipments.

Alternatively, the number of local radio equipments is an integer-multiple of the number of synchronisation signal blocks, and the local radio equipments are arranged in a re- peating sequence of broadcasting the different synchronisation signal blocks. This yields an n-to-one correspondence of local radio equipments to synchronisation signal blocks. For example, if the system broadcasts four synchronisation signal blocks, there will be eight, twelve, sixteen, ... local radio equipments within the chain of local radio equipments such that they re peat the scheme of broadcasting the synchronisation signal blocks, e.g., 1-2-3-4-1-2-3-4....

Especially preferably, each local radio equipment only has one antenna, which is an omni-directional antenna. This is pre ferred because the construction of the chain is made especially simple as omni-directional antennas are easy to acquire, pro gram and deploy in the field.

The invention shall now be explained in more detail below on the basis of preferred exemplary embodiments thereof with reference to the accompanying drawings in which:

Fig. 1 shows a 5G NR system of the state of the art em ploying beamforming for eight antennas with narrow coverage ar eas in a schematic top view;

Fig. 2 shows the successive broadcasting of synchronisa tion signal blocks by the node of Fig. 1 in a time-signal dia gram;

Fig. 3 shows an elongated cell according to the invention in a perspective view;

Figs. 4 and 5 show the broadcasting of synchronisation signal blocks by two different local radio equipments of the system of Fig. 3 in a time-signal diagram each; and Fig. 6 shows an extended elongated cell according to the invention with a repeating sequence of broadcasting the differ ent synchronisation signal blocks in a perspective view.

Fig. 1 shows a 5G NR system 1 according to the state of the art having a node 2 with eight antennas 3i, ..., 3_S gener ally 3_n. The antennas 3_n are operated with a very high fre quency, usually 20 to 90 GHz, such that the coverage areas 4_lt ..., 4_S generally 4_n (n = 1...N) , of the antennas 3_n are very long but narrow. During regular operation, the node 2 communicates with a user terminal 5 by means of that antenna 3_n whose cover age area 4_n overlaps the user terminal 5.

When user terminals 5 enter the "compound" coverage area created by the totality of the coverage areas 4_n of all anten nas 3_n of the node 2 for the first time, they need to receive and identify so-called synchronisation signals from the node 2 in order to have information about the OFDM structure of the communication channels used by a node 2. In order that the user terminal 5 knows in which coverage area 4_n it is located, the node 2 broadcasts synchronisation signal blocks 6_lf 6₂, ... gen erally 6_n, successively in time t, each synchronisation signal block 6_n over a different antenna 3_n as shown in Fig. 2. All successively broadcast synchronisation signal blocks 6_n to gether form a set 7 of synchronisation signal blocks 6_n, which is repeatedly broadcast with a predetermined repetition period 8. Typically, the duration of the set 7 of synchronisation sig nal blocks 6_n is 5 ms and the duration of the repetition period is 20 ms. In order for the node 2 to appear as a single cell to the user terminals 5, all antennas 3_n of the node 2 broadcast the same physical cell ID. To this end, all synchronisation signal blocks 6_n contain the same physical cell ID but a different beam index n such that the user terminal 5 knows in which cov erage area 4_n it is located. As can be seen, the node 2 peri odically sweeps through the coverage areas 4_n by successively broadcasting the synchronisation signal blocks 6_n in time t over different antennas 3_n such that it can be discovered by user terminals 5 at any angular direction to the node 2.

Fig. 3 shows a system 9 that is specifically adapted to be used for linear cellular networks. In such linear cellular net works, user terminals 5 only travel in one direction d_L or in the respective other direction d_R. For example, the system 9 can be used with trains 10 carrying user terminals 5, wherein the directions d_L, d_R of travel are defined by a track 11. Fur thermore, the system 9 could be used along a highway, tunnel, or the like. Several systems 9 can be placed next to each other to cover vast parts of the highway, tunnel, or the like as de scribed above.

The system 9 communicates with the user terminals 5 as de scribed above for the node 2 with reference to Figs. 1 and 2. As such, the system 9 communicates with the user terminals 5 according to a 5G NR standard having an OFDM structure in which a set of synchronisation signal blocks 6_n containing the same physical cell ID is repeatedly broadcast with a predetermined repetition period 8, the synchronisation signal blocks 6_n of said set 7 been broadcast successively in time t, each synchro nisation signal block 6_n of said set 7 over a different antenna 3n-

The number of synchronisation signal blocks 6_n within the set 7 is usually predetermined by the 5G NR standard, and is four synchronisation signal blocks 6_n within the repetition pe riod 8 if the system 9 uses uplink and downlink frequency bands below 3 GHz, eight synchronisation signal blocks 6_n within the repetition period 8 if the system 9 uses uplink and downlink frequency bands above 3 GHz and below 6 GHz, and so forth. The system 9 usually adopts these limitations given by the stan dard, but with slight changes to the setup of the user termi nals 5, different numbers can be chosen, too.

In contrast to the embodiment of Fig. 1, the system 9 em ploys a different physical layout. Specifically, the system 9 comprises a number of local radio equipments 12i, 12₂, ..., gen erally 12_m (m = 1...M) , which is equal to the number of synchro nisation signal blocks 6_n in the set 7 (or a multiple thereof, as will be described later) .

Each local radio equipment 12_m comprises its own antenna 3_n with radio coverage area 4_n, a support 13 on which the an tenna 3_n is mounted, and a transceiver 14. In the embodiment of Fig. 3, the antennas 3_n are omni-directional antennas. As the local radio equipments 12_m are preferably used in a linear cel lular network, the antennas 3_n could also be directional anten nas, e.g., with elliptical or eight-shaped coverage areas. Also, more than one antenna 3_n can be employed to cover a left and a right side of the local radio equipment 12_m in the linear cellular network, for example. The system 9 can also be oper ated on lower frequency bands, for example in the region of 900 MHz or between 3GHz and 6GHz so that instead of dedicated 5G antenna equipment, e.g., legacy 3G or 4G radio gear could be used for the local radio equipments 12_m and/or antennas 3_n.

The local radio equipments 12_m are spaced apart from each other by predetermined distances s, for example along said track 10. The predetermined distances s can be constant or varying between the local radio equipments 12_m of the system 9. The predetermined distance s can be at least 10 m, for example 100 - 500 m.

By spacing the local radio equipments 12_m apart from each other, the coverage areas 4_n of the antennas 3_n can be aligned contiguously in a chain to form an elongated radio cell 15 with said physical cell ID. Chain or elongated radio cell 15 means that each local radio equipment 12_m has a coverage area 4_n that adjoins or overlaps exactly two coverage areas 4_n_i, 4_n+i of dif ferent local radio equipments 12_m_i, 12_m+i of the same system 9 (except for the two outermost local radio equipments 12i, 12_M) .

This elongated radio cell 15 is especially suited for lin ear cellular networks as specified above. Many of these elon gated radio cells 15 can again be chained to each other, i.e., one outermost local radio equipment 12_m has its coverage area 4_n overlapping or adjoining the coverage area 4_n of an outer most local radio equipment 12_m of a different elongated cell 15. It can be seen that user terminals 5 have to perform a standard handover ("hard handover") when exiting one elongated cell 15 and entering another. However, as long as the user ter minals 5 travel through coverage areas 4_n of local radio equip ments 12_n of the same elongated cell 15, no hard handovers but only beam- switching according to 5G NR is performed, which is more reliable and faster than hard handovers since the same OFDM structure is used for communication.

All local radio equipments 12_m of one system 9 are managed by a common baseband unit 16. For this purpose, the baseband unit 16 is connected to all local radio equipments 12_m of the same elongated cell 15 or system 9. To employ a functional dis covery phase for an elongated cell 15 as shown in Fig. 3, each local radio equipment 12_m only broadcasts one synchronisation signal block 6_n of said set 7. For this purpose, the baseband unit 16 can feed the specific synchronisation signal block 6_n only to this local radio equipment 12_m that is going to broad cast this synchronisation signal block 6_n.

Figs. 4 and 5 show two time-signal diagrams of the first and the second local radio equipment 12i, 12₂ of Fig. 3. From Fig. 4 it can be seen that the first local radio equipment 12i only broadcasts the first synchronisation signal block 6i at a first instant in time ti, and repeatedly after the repetition period 8 described above. The second local radio equipment 12₂ of Fig. 3 only broadcasts the second synchronisation signal block 6₂ at a second instant in time t₂, repeatedly after the repetition period 8, as shown in Fig. 5. In general, the m-th local radio equipment 12_m only broadcasts the synchronisation signal block 6_n at the instant in time t_n, repeatedly with the repetition period 8.

In total, the system 9 broadcasts each synchronisation signal block 6_n of said set 7 by at least one local radio equipment 12_m within each repetition period 8.

All local radio equipments 12_m are synchronized with each other with respect to the OFDM frame structure. This can be achieved by means of the common baseband units 16 or by means of a global timing, for example delivered by GPS.

The synchronisation signal blocks 6_n of said set 7 each comprise the Primary Synchronisation Signal (PSS) , Secondary Synchronisation Signal (SSS) , and Physical Broadcast Channel (PBCH) of the 5G NR standard. PSS and SSS of each synchronisa tion signal block 6_n of the set 7 are the same and indicate the physical cell ID of the cell 15. The PBCH of each synchronisa tion signal block 6_n is different and contains a beam index in dicative of the broadcasting local radio equipment 12_m of the cell 15, amongst others.

The chain structure of the elongated cell 15 can further be utilized to enhance the throughput by optimizing interfer ences for one or more user terminals 5 travelling through the elongated cell 15. For example, in a first specific use case, when two user terminals 5 are located in coverage areas 4_n of two different local radio equipments 12_m that are not adjacent, OFDM radio resources can be re-used. Firstly, the two user ter minals 5 will indicate to the system 9 that they are in such non-adjacent coverage areas 4_n of said local radio equipments 12_m. Then the system 9, for example by means of the baseband unit 16, can allocate the same OFDM radio resources, for uplink and/or downlink, to both user terminals 5. Even though the same OFDM radio resource is used for two user terminals 5, there will be no interference because said local radio equipments 12_m are not adjacent.

In a second specific use case, a user terminal 5 will in dicate to the system 9 that it is about to leave the coverage area 4_n of one local radio equipment 12_m and is about to enter the coverage area 4_n+i of another local radio equipment 12_m+i. The system 9, for example by means of the baseband unit 16, can then allocate the same OFDM radio resource for uplink and/or downlink, on both of said local radio equipments 12_m, 12_m+i. This can be used for diversity schemes such as multiple input multiple output (MIMO) or multiple input single output (MISO) . For example, the same information can be sent on the same OFDM radio resource twice but in different representations, one by each of the local radio equipments 12_m, 12_m+i.

In another specific use case, the chain structure of the elongated cell 15 can be used to reduce the Doppler shift within the system 9. When a user terminal 5 responds to the system 9 that it is about to leave the coverage area 4_n of one local radio equipment 12_m and is about to enter the coverage area 4_n+i of another local radio equipment 12_m+i, the system 9, for example by means of the baseband unit 16, allocates OFDM radio resources for downlink on the local radio equipment 12_m that the user terminal is leaving and OFDM radio resources for uplink on the local radio equipment 12_m+i that the user terminal 5 is entering. As the user terminal 5 does not adjust its in ternal clock, the Doppler shift experienced when receiving mes sages from the downlink communication can be utilized for com pensation when sending information to the local radio equipment 12_m+i in the travelling direction.

In the embodiment of Fig. 3, the number of local radio equipments 12_m is equal to the number of synchronisation signal blocks 6_n in said set 7. Here, each local radio equipment 12_m broadcasts a synchronisation signal block 6_n of said set 7 that is different to the synchronisation signal blocks broadcast by the other local radio equipments 12_m. This means that each syn chronisation signal block 6_n is broadcast uniquely within the elongated cell 15.

Fig. 6 shows that the system 9 can also comprise a number of local radio equipments 12_m that is an integer-multiple of the number of synchronisation signal blocks 6_n. For example, there are 2, 3, 4, ... times more local radio equipments 12_m than synchronisation signal blocks 6_n to be broadcast. In this sys tem, multiple local radio equipments 12_m will broadcast the same synchronisation signal block 6_n at the same time t_n. For the user terminal 5, this does not make a difference as it sim ply thinks that it has passed through the same 5G NR node mul tiple times. The system 9, however, remembers which specific local radio equipment 12_m has received uplink data from a user terminal 5 to also transmit downlink data to this user terminal 5 via the same local radio equipment 12_m. This management can be performed by the baseband unit 16, for example.

The invention is thus not restricted to the specific em bodiments described in detail herein but encompasses all vari- ants, combinations and modifications thereof that fall within the framework within the claims.

Claims

Claims :

1. System for communication with a user terminal, wherein the system (9) is configured to communicate with the user terminal (5) according to a 5G NR standard having an OFDM structure in which a set (7) of synchronisation signal blocks (6_n) containing the same physical cell ID is repeatedly broadcast with a predetermined repetition period (8) , the syn chronisation signal blocks (6_n) of said set (7) being broadcast successively in time (t) , each synchronisation signal block (6_n) of said set (7) over a different antenna (3_n) ,

characterized in that

the system (9) comprises a number of local radio equip ments (12_m) that is at least equal to the number of synchroni sation signal blocks (6_n) in said set (7) , each local radio equipment (12_m) having an antenna (3_n) with a radio coverage area (4_n) and being synchronised with the other local radio equipments (12_m) with respect to the OFDM frame structure,

wherein the local radio equipments (12_m) are spaced apart from each other by predetermined distances (s) ,

wherein the coverage areas (4_n) of the antennas (3_n) are aligned contiguously in a chain to form an elongated radio cell (15) with said physical cell ID,

wherein the system (9) is configured to broadcast each synchronisation signal block (6_n) of said set (7) by at least one local radio equipment (12_m) within each repetition period

(8) , and wherein each local radio equipment (12_m) is configured to broadcast only one synchronisation signal block (6_n) of said set (7) .

2. System according to claim 1, characterised in that the system (9) comprises a baseband unit (15) connected to all local radio equipments (12_m) of the system (9) , wherein the baseband unit (15) is configured to manage the local radio equipments (12_m) .

3. System according to claim 1 or 2 , wherein each syn chronisation signal block (6_n) of said set (7) comprises Pri mary Synchronisation Signal, PSS, Secondary Synchronisation Signal, SSS, and Physical Broadcast Channel, PBCH, of the 5G NR standard .

4. System according to claim 3, characterised in that the Primary Synchronisation Signal, PSS, and Secondary Synchro nisation Signal, SSS, of each synchronisation signal block (6_n) of the set (7) are the same and the Physical Broadcast Channel, PBCH, is different in each synchronisation signal block (6_n) of the set and comprises a beam index.

5. System according to any one of the claims 1 to 4 , characterised in that the system (9) is configured to, after two user terminals (5) have responded to the system (9) which synchronisation signal block (6_n) they have received, allocate the same OFDM radio resources, for uplink and/or downlink, to both user terminals (5) if they are located within coverage ar eas (4_n) that are not adjacent to each other.

6. System according to any one of the claims 1 to 5 , characterised in that the system (9) is configured to, after a user terminal (5) has responded to the system (9) that it is about to leave the coverage area (4_n) of one local radio equip ment (12_m) and is about to enter the coverage area (4_n) of an other local radio equipment (12_m) , allocate the same OFDM radio resources, for uplink and/or downlink, on both of said local radio equipments (12_m) for communication with the user terminal (5) .

7. System according to any one of the claims 1 to 6 , characterised in that the system (9) is configured to, after a user terminals (5) has responded to the system (9) that it is about to leave the coverage area (4_n) of one local radio equip ment (12_m) and is about to enter the coverage area (4_n) of an other local radio equipment (12_m) , allocate OFDM radio re sources for downlink on the local radio equipments (12_m) that the user terminal (5) is leaving and OFDM radio resources for uplink on the local radio equipments (12_m) that the user termi nal (5) is entering.

8. System according to any one of the claims 1 to 7 , characterised in that the number of local radio equipments (12_m) is equal to the number of synchronisation signal blocks (6_n) in said set (7) , and

wherein each local radio equipment is configured to broad cast a synchronisation signal block (6_n) of said set (7) that is different to the synchronisation signal blocks (6_n) broad cast by the other local radio equipments (12_m) .

9. System according to any one of the claims 1 to 7 , characterised in that the number of local radio equipments (12_m) is an integer-multiple of the number of synchronisation signal blocks (6_n) , and the local radio equipments (12_m) are arranged in a repeating sequence of broadcasting the different synchronisation signal blocks (6_n) ·

10. System according to any one of the claims 1 to 9 , characterised in that each local radio equipment (12_m) only has one antenna (3_n) , which is an omni-directional antenna.