Unl icensed Frequency Bands

BACKG ROU N D

The present disclosu re relates generally to sol utions for improving the performance, quality and power efficiency in a radio commu nication network that uses both licensed and unl icensed frequency bands. More particularly the proposed sol ution relates to wireless nodes and corresponding methods as defined below. The disclosure also relates to a computer program and a processor-readable medi um .

The 3G PP Rel- 1 3 featu re LAA (Licensed-Assisted Access) allows LTE (Long Term Evolution) equipment to also operate in the unlicensed 5 GHz radio spectrum . The u nlicensed 5 GHz spectrum is used as a complement to the licen sed spectrum . An on-going 3G PP Rel- 1 4 work item has added U L transmissions to LAA. According ly, devices con nect in the licensed spectrum (primary cell or PCell) and use carrier aggregation to benefit from additional transmission capacity in the un licensed spect- rum , a secondary cel l or so-called SCell . Standalone LTE in unlicensed spectrum , MulteFire, is another version of unlicensed spectrum LTE and is currently under development in the MulteFire Alliance Foru m.

In u nlicensed bands, spectrum is usually opportu nistic. Recent- ly, there has been interest i n sharing the use Licensed Shared Access with Authorized shared access (ASA) . Such systems usually propose a division of rights of use, based on time of use or geographical constraints between mobile operators and an incumbent user. A typical use of this scenario is to enable use of a band that is available for licensed users in some markets, but is bei ng restricted in others because of incumbents such as radar or satellite systems. Incumbent systems can be protected around the area of deployment, while authorization for mobile infrastructure can be granted in such a way that aggregate interference from mobile systems towards the incumbent is limited to an acceptable level of noise rise or performance degradation . In LSA, the mobile operator is licensed to operate in permitted or authorized areas, and is the reasonable reg u latory approach to ASA.

In this disclosure the term "interference" is used extensively. Generally, interference should here be understood to mean that one or more commu nication resou rces being used by a first node overlap with least one communication resource that is also used by a second node; and that radio energy relating to the communication of the second node reaches the first node in such a manner that the quality of the com munication of the first node is degraded in relation to a situation where the second node had not used the least one overlapping communication resource.

An alternative method of spectru m sharing is defined for the Citizen's Broadband Radio Service (CBRS) in the United States within the 3.5 GHz band . The CBRS defi nes three tiers of sharing , with h igher tiers providing higher priority of access to spectrum than the lower ones. In general , multiple tiers of users can be defi ned, although a pragmatic choice is three tiers. The assignment of channels to different tiers and related configurations are performed by a geolocation database and policy management system known as the Spectru m Access System (SAS) . I n the CBRS, naval radar in littoral waters, and commercial Fixed Satel lite Service (FSS) compose the incumbents. The second tier consists of Priority Access Licenses (PALs) , and the third tier comprises opportun istic users known as general authorized access (GAA) users. I ncumbent radar activity in the CBRS is dynam ic, while FSS (space-to-earth) is static. The SAS is charged with protecting incumbents, and PALs. In addition , the SAS authorizes the authorization of spectrum to GAA users. Multe- Fire (M F) is a candidate Radio Access Technology (RAT) for certain classes of devices in the 3.5 GHz band, possibly for lower power indoor use. Therefore, the SAS needs to configure different aspects of the channel access and transmission parameters of the MF-based Citizen Broadband Radio Service De- vices (CBSDs), i.e., base stations in the form of E-UTRAN Node B, also known as Evolved Node B (eNBs) and their associated user equipments (UEs).

LTE uses OFDM (Orthogonal Frequency Division Modulation) in the downlink and DFT (Discrete Fourier Transform)-spread OFDM (also referred to as single-carrier FDMA (Frequency Division Multiple Access)) in the uplink. The basic LTE downlink physical resource, illustrated in Figure 1, can thus be seen as a time-frequency grid, where each resource element RE corresponds to one OFDM subcarrier Af during one OFDM symbol in- terval S. The uplink subframe has the same subcarrier spacing as the downlink and the same number of SC-FDMA symbols in the time domain as OFDM symbols in the downlink.

In the time domain, see Figure 2, LTE downlink transmissions are organized into radio frames of 10 ms, each radio frame RF consisting of ten equally-sized subframes SF0, SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 and SF9 of length T _subframe = 1 ms. Each subframe comprises two slots of duration 0.5 ms each, and the slot numbering within a frame ranges from 0 to 19. For normal cyclic prefix, one subframe consists of 14 OFDM symbols. The duration of each symbol is approximately 71.4 με.

Furthermore, the resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. A pair of two adja- cent resource blocks in time direction (1.0 ms) is known as a resource block pair. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth. Figure 3 shows an example of a downlink subframe (DLSF). Downlink transmissions are dynamically scheduled, i.e., in each subframe the base station transmits control information about which terminals data is transmitted to and upon which resource blocks the data is transmitted, in the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe and the number n = 1, 2, 3 or 4 is known as the Control Format Indicator (CFI). The downlink subframe also contains common reference symbols, which are known to the receiver and used for coherent demodulation of e.g. the control information. The reference symbols are the cell specific reference symbols (CRS) and are used to support multiple functions including fine time and frequency synchronization and channel estimation for certain transmission modes.

Uplink transmissions are dynamically scheduled, i.e., in each downlink subframe the base station transmits control information about which terminals should transmit data to the eNB in subsequent subframes, and upon which resource blocks the data is transmitted. Figure 4 exemplifies the structure of an uplink sub- frame (ULSF) in LTE. Here, the uplink resource grid contains data and uplink control information in the physical uplink channel (PUSCH), uplink control information in the physical uplink control channel (PUCCH), and various reference signals such as demodulation reference signals (DMRS) and sounding reference signals (SRS). DMRS are used for coherent demodulation of PUSCH and PUCCH data, whereas SRS is not associated with any data or control information but is generally used to estimate the uplink channel quality for purposes of frequency-selective scheduling. Note that UL DMRS and SRS are time-multiplexed into the UL subframe ULSF, and SRS are always transmitted in the last symbol of a normal UL subframe ULSF. The PUSCH DMRS is transmitted once every slot for subframes with normal cyclic prefix, and is located in the fourth and eleventh SC-FDMA symbols. From LTE Rel-11 onwards, downlink (DL) or uplink (UL) resource assignments can also be scheduled on the enhanced physical downlink control channel (EPDCCH). For Rel-8 to Rel-10 only the physical downlink control channel (PDCCH) is avail- able. Resource grants are UE specific and are indicated by scrambling the downlink control information (DCI) Cyclic Redundancy Check (CRC) with the UE-specific C-RNTI identifier.

The LTE Rel-10 standard supports bandwidths larger than 20 MHz. One important requirement on LTE Rel-10 is to assure backward compatibility with LTE Rel-8. This should also include spectrum compatibility. That would imply that an LTE Rel-10 carrier, wider than 20 MHz, should appear as a number of LTE carriers to an LTE Rel-8 terminal. Each such carrier can be referred to as a Component Carrier (CC). In particular for early LTE Rel-10 deployments it can be expected that there will be a smaller number of LTE Rel-10-capable terminals compared to many LTE legacy terminals. Therefore, it is necessary to assure an efficient use of a wide carrier also for legacy terminals, i.e. that it is possible to implement carriers where legacy terminals can be scheduled in all parts of the wideband LTE Rel-10 carrier. The straightforward way to obtain this would be by means of Carrier Aggregation (CA). CA implies that an LTE Rel-10 terminal can receive multiple CC, where the CC have, or at least the possibility to have, the same structure as a Rel-8 carrier. A CA-capable UE is assigned a primary cell (PCell) which is always activated, and one or more secondary cells (SCells) which may be activated or deactivated dynamically.

The number of aggregated CC as well as the bandwidth of the individual CC may be different for uplink and downlink. A sym- metric configuration refers to the case where the number of CCs in downlink and uplink is the same whereas an asymmetric configuration refers to the case that the number of CCs is different. It is important to note that the number of CCs configured in a cell may be different from the number of CCs seen by a ter- minal. A terminal may for example support more downlink CCs than uplink CCs, even though the cell is configured with the same number of uplink and downlink CCs.

Up to now, the spectrum used by LTE is dedicated to LTE. This has the advantage that the LTE system does not need to care about the coexistence issue and the spectrum efficiency can be maximized. However, the spectrum allocated to LTE is limited, which cannot meet the ever increasing demand for larger throughput from applications/services. Therefore, Rel-13 LAA extended LTE to exploit unlicensed spectrum in addition to li- censed spectrum. Unlicensed spectrum can, by definition, be simultaneously used by multiple different technologies. Therefore, LTE needs to consider the coexistence issue with other systems such as IEEE 802.11 (Wi-Fi). Operating LTE in the same manner in unlicensed spectrum as in licensed spectrum can serious- ly degrade the performance of Wi-Fi because Wi-Fi will not transmit once it detects that the channel is occupied.

Furthermore, one way to utilize the unlicensed spectrum reliably is to transmit essential control signals and channels on a licensed carrier. In this document, we denote a secondary cell in unlicensed spectrum as licensed-assisted access secondary cell (LAA SCell). In the case of standalone operation as in MulteFire, no licensed cell is available for uplink control signal transmissions.

In Rel-13 LAA and MF, listen-before-talk (LBT) for DL data transmissions follow a random backoff procedure similar to that of Wi-Fi, with contention window (CW) adjustments based on (hybrid automatic repeat request) HARQ (negative acknowledgement) NACK feedback. Several aspects of UL LBT are under discussion in Release 14. With regard to the framework of UL LBT, the discussion focused on the self-scheduling and cross- carrier scheduling scenarios. UL LBT imposes an additional LBT step for UL transmissions with self-scheduling, since the UL grant itself requires a DL LBT by the eNB. The UL LBT maximum CW size should then be limited to a very low value to over- come this drawback, if random backoff is adopted . Therefore, Release 1 3 LAA recommended that the U L LBT for self -scheduling should use either a single clear channel assessment (CCA) duration of at least 25 με (sim i lar to DL DRS) , or a random backoff scheme with a defer period of 25 με includi ng a defer duration of 1 6 us fol lowed by one CCA slot, and a maxi mum contention window size chosen from X= {3, 4, 5, 6, 7} . These options are also applicable for cross-carrier scheduling of UL by another unlicensed SCell . A short UL LBT procedure for the case involving cross-carrier scheduling by a licensed PCel l remai ns open for fu rther study in LAA. The other option supported i n M F is a full -fledged random backoff procedure si m ilar to that used by Wi-Fi stations.

Moreover, UL transmissions without LBT when an UL transmis- sion burst follows a DL transmission burst on that respective carrier (with a gap of at most 1 6 με between the two bursts) are allowed in Rel- 1 4 LAA and MF.

WO 201 5/1 87282 A1 discloses a solution for shared spectrum access in which multiple tiers of users are allowed to access a set of shared spectrum resources. Second tier users, which receive priority access from the first spectrum tier, transmit reserving signals over the avai lable shared channels during clear chan nel assessment (CCA) periods associated with the shared channels. Third tier users, which access the shared spectru m at a lower priority than the second tier users, attempt to syn ch ronize timi ng with second tier users when second tier user presence is detected. Third tier users will be blocked from transmission on the shared channels when the th ird tier users detect the reserving signals. Second tier users, thus, transm it on the shared chan nels with a lower likel ihood of i nterference from third tier users, and third tier users will be able to transmit on any of the shared channels when the third tier user detects a clear CCA. In the MulteFire Alliance Forum , it has been further discussed that the SAS may coordinate LBT parameters and discovery reference signal transm ission parameters across MF eNBs that share channels. The existing coexistence methods that use energy-detection (ED) based LBT do not work well in scenarios with asymmetric transmit powers. This is because the higher-power nodes cause a disproportionate level of silencing of adjacent nodes. This, in turn , reduces the spatial reuse and degrades both DL and UL network th roughput.

LTE has some existing en hanced inter-cell interference coordination (elCIC) techniques to m itigate interference between high - power macro cells and lower-power pico cells, such as almost blank subframes (ABS) and cell range expansion (CRE) . ABS is semi-statically config ured and cannot adapt dynamical ly to traffic variations. CRE is designed for enhancing cell association and mobility management for lower-power cells, and not for balancing chan nel access or i nterference mitigation to data transmissions. SUMMARY

The object of the present disclosure is therefore to offer a solution which solves, or at least mitigates the above problems.

According to a first aspect, the object is ach ieved by a method performed in a first wireless node of a wire less communication system . The first wireless node is associated with a first cell having a first cell identity. The proposed method comprises obtaining information relating to a set of wireless nodes, which use at least one overlapping communication resource that is also used by at least one second node in the first cell . The method further comprises generating a preamble containing first and second data fields. The first data field designates the first cell identity. The second data field reflects a respective identity of the wireless nodes in the set of wireless nodes which use the at least one overlapping communication resource. Additionally, the method comprises transmitting a preamble signal containing the preamble over a predefined set of resources in a shared resource structure of the wireless communication system . According to a second aspect, the object is achieved by a method performed in a second wireless node of the wireless communication system . The second wireless node is associated with a first cell having a first cell identity. The proposed method comprises measuring wireless signals from at least one other wire- less node, which is associated with a cell different from the first cell . The method further comprises generating a report identifying at least one node of the at least one other wireless node as a member of a set of wireless nodes, which use an overlapping communication resource that is also used in the first cell . More- over, the method comprises transmitting a report signal over a predefined set of resources in a shared resource structure of the wireless commu nication system . The report signal contains said report.

The first and second methods are advantageous because they reduce the risk of inter-cell i nterference considerably. At the same time, good spatial reuse is attai nable as well as a hig h throughput in the wireless communication system . Consequently, robust coexistence of multiple M F cells with asym metric transmit powers on a shared channel is possible. Furthermore, an SAS can efficiently coordinate M F-based GAA networks.

According to other aspects, the object is ach ieved by first and second wireless nodes in the wireless communication system , which operate in agreement with the first and second methods respectively. The advantages of these nodes, as well as the pre- ferred embodi ments thereof, are apparent from the discussion above with reference to the proposed wireless nodes.

According to a fu rther aspect, the object is achieved by a computer program loadable into the memory of at least one proces- sor, and includes software adapted to im plement the method proposed above when said program is ru n on at least one processor.

According to yet another aspect, the object is achieved by a pro- cessor-readable medium , having a program recorded thereon , where the program is to control at least one processor to perform the method proposed above when the prog ram is loaded into the at least one processor.

Further advantages, beneficial featu res and applications of the proposed solution will be apparent from the fol lowi ng description and the dependent claims.

BRI EF DESCRI PTION OF TH E DRAWINGS

The proposed solution is now to be explained more closely by means of preferred embodi ments, wh ich are disclosed as examples, and with reference to the attach ed drawings.

Figure 1 illustrates the LTE downl ink physical resou rce;

Figure 2 illustrates the LTE time-domain structure ;

Figure 3 exemplifies the structure of a downlink subframe in LTE ;

Figure 4 exemplifies the structure of an uplink subframe in

LTE ;

Fig ure 5 shows a system overview illustrati ng the wireless nodes of the proposed sol ution ;

Figure 6 shows a block diagram over a first wireless node according to one embodi ment;

Figure 7 shows a block diagram over a second wireless

de accordi ng to one embodiment;

Figure 8 illustrates the structure of a preamble according to one embodiment;

Figure 9 illustrates, by means of a first flow diagram , a first general method according to the proposed solution ; and

Figure 1 0 illustrates, by means of a second flow diagram , a second general method according to the proposed solution .

DETAI LED DESCRI PTION

The present disclosure proposes a solution for preamble-based coexistence in M F in order to improve performance over an E D- based LBT approach. Referring to Figures 5 and 6, we see a first wireless node 1 00 in a wireless communication system . The first wireless node 1 00 is associated with a first cell having a first cell identity CI D 1 . This means that the first wireless node 1 00 is configured to serve wireless devices that are located within the first cell . Conse- quently, the first cell represents a physical area in proximity to the first wireless node 1 00, e.g . an area surrounding the first wireless node 1 00. However, other cell configurations are equal ly well conceivable, such as sector shaped cells, where one or more antennas are arranged to cover a widening area extending from the first wireless node 100. In any case, the first wireless node 1 00 has first and second interfaces 1 1 0 and 1 20 respectively and a first processing unit 1 30.

The first interface 1 1 0 is configured to obtain information relating to a set of wireless nodes 300, 400 and 500 respectively, which use at least one overlapping commu nication resource that is also used by a second node 200 in the f irst cell . In the context, "the use of a communication resource" is understood to mean employ a particular resource element or resource block for transmitting data from one wireless node to another. For example, the first interface 1 1 0 may obtain the info rmation about the set of such potentially interfering wireless nodes 300, 400 and 500 by receiving a report signal R from a second wire- less node 200 in the wireless communication system . The report signal R, in turn , may be a radio signal that is transmitted over a predefined set of resources in a shared resource structure of the wireless commu nication system . The first processing unit 1 30 may be configured to decode the report signal R to derive the at least one wireless node as being a member of the set of wireless nodes 300. 400 and 500 which use the overlapping communication resource in the first cell .

In the first wireless node 1 00, the first processing unit 1 30 is configured to generate a preamble P containing a first data field F1 designating the first cell identity CI D 1 , see Figure 8. The preamble P, which is preferably located at a start of a first downlink frame in a new transmission opportunity for the first wireless node 1 00, also contains a second data field F2 reflecting a respec- tive identity I D300, I D400 and I D500 of the wireless nodes 300, 400 and 500 in the set of wireless nodes which use the at least one overlapping commu nication resource. In other words, the second data field F2 contains pieces of information that for eac h of the wireless nodes 300, 400 and 500 uniquely designate the identity I D300, I D400 and I D500 of the wireless nodes 300, 400 and 500 respectively in the wireless communication system . Thus, the second data field F2 constitutes a basis for identifying potentially interferi ng wireless nodes.

The second interface 1 20 is configured to transmit a preamble signal S[P] containing the preamble P. The preamble signal S[P] is transmitted over a predefined set of resources in a shared resource structure of the wireless communication system , for example operating according to MulteFire.

The first processing unit 1 30 is further configured to check if a preamble signal S[P] has been received from at least one other wireless node, say 500, via the predefined set of resources. If so, the first processing unit 130 is configured to decode the preamble signal S[P] to obtain a decoded preamble P. Then , the first processing unit 1 30 is configured to check if the first cell identity CI D 1 , i .e. its own I D, is included i n the decoded preamble P. If so, the first processing unit is configured to refrain from causing the first wireless node 1 00 to transmit on at least one shared resource in the shared resource structure of the wireless communication system duri ng a def ined period of time TDEF- Thereby, the risk of interference is reduced.

According to one embodiment, the preamble P also contains a third data field. The third data filed describes the defined period of time T _DE F during which first wireless node 1 00 ref rains from transmitting on the at least one shared resource in the shared resource structure of the wireless communication system . In the embodiment, the fi rst processing unit 1 30 is further configured to derive the defined period of time T _DE F from the decoded pre- amble P.

According to another embodiment, the first processing unit 1 30 is configured to obtain the information relating to a set of wireless nodes 300 , 400 and 500 , which use the overlapping communication resource in the first cell by: (a) receiving a report signal R from a second wireless node 200 in the wire less communication system ; and (b) decoding the report signal R to derive at least one wireless node as being a member of the set of wireless nodes 300 , 400 and 500 , which use the overlapping communication resource in the first cell . Preferably, the first processing unit 1 30 is further configured to introduce at least one measurement block in the shared resource structure of the wireless communication system of the first cell . In the measurement block, the first wireless node 1 00 refrains from transmitting signals during the measurement block. Thus, during one or more intervals corresponding to the at least one measurement block it is rendered easier for the second wireless node 200 to measure any signals from the wireless nodes 300 , 400 and 500 respectively. Further preferably, the first processing unit 1 30 is configured synchronize the at least one measurement block with an interval provided in the shared resource structure in the at least one neighbor cell to the first cell , i .e. in Figure 5, the cells having se- cond and third cell identities CI D2 and CI D3 respectively. D u ring said interval , wireless nodes 300 and 500 respectively (e.g . eNBs) in the neighbor cel ls transmit a respective reference signal configured to form a basis for measurements underlying the report signal R. Referring now to Figure 7, it is presumed that the second wireless node 200 is associated with the first cell having the first cell identity CI D 1 . In other words, the second wireless node 200 is served by the first wireless node 100. Hence, the first wireless node 1 00 may be a base station in the form of an eNB. The second wireless node 200 contai ns a second processing unit 230 and a second interface 21 0. The second processing unit 230 is configured to measure wireless signals from at least one other wireless node, in Figure 5 nodes 300, 400 and 500, which are associated with cells different from the first cell , namely CI D3 and CI D2. For example, the wireless node 300 may be a first other base station (e.g . an eNB) ; the wireless node 400 may another wireless device (e.g . a U E) that is served by said wireless node 300 ; and the wireless node 500 may be second other base station (e.g . an eNB) . Additionally, the second processing unit 230 is configured to generate a report identifying at least one node of the at least one other wireless node 300, 400 and 500 as a member of a set of wireless nodes, which use the overlapping communication resource in the first cell . An output interface 21 0 in the second wireless node 200 is configured to transmit a report sig nal R over a predefined set of resources in a shared resource structure of the wireless communication system , preferably at least to the first wireless node 1 00, where the report signal R contains said report. Thus, the report signal R may form a basis for the preamble P.

According to one embodiment, the second processing unit 230 is configured to perform the measuring of the wireless signals from the wireless node 300, 400 and/or 500 by: (i) measuring a power level of a received reference signal and/or (ii) measuring a parameter reflecting a quality a received reference signal . The parameter reflecting the quality of the received reference signal thus carries information about a quality of the wireless signal . The quality, in turn , may for example quantify an absolute amount in relation to a predefined standard, and/or indicate a relative figure or quota among the signals received. In addition thereto, or as another alternative, the second processing unit 230 may be configured to perform the measuring of the wireless signals from the wireless node 300, 400 and/or 500 by: (iii) measuring a signal strength indicated via an average total of received power observed in a predefined set of reference sym bols.

In further detail , it is noted that the embodiments of the proposed solution are applicable to MF, LAA, 3G PP New Radio (NR) , or other LTE versions based on TDD or Enhanced Interference Mitigation & Traffic Adaptation (el MTA) when deployed in a general ASA system , and possibly coordinated by one or more ASA control lers (e.g . , SAS) . The parameter configu rations performed by a SAS are general ly on a longer time scale co mpared to the actual transmission time intervals of M F, and transmissions may be conditioned on successful LBT. The channel selections and related parameter configurations may be sent di rectly from the SAS to one or more M F eNBs over a logical in terface, or may be sent to an intermediary logical controller or domai n proxy that is connected with one or more M F eNBs.

According to embodi ments of the proposed solution , the preamble signal S[P] may be encoded and modulated as follows. In order for adjacent nodes to quickly receive and decode the preamble P, the preamble P should be located at the start of the first DL subframe DLSF in a new transmission opportunity (TXOP).

There are two possibilities for the resource allocation of the preamble signal S[P] within the control region CR of a DL subframe DLSF; namely in the physical hybrid-ARQ indicator channel (PHICH) resources or in the physical downlink control channel (PDCCH) resources.

The PHICH resources are currently unused in frame structure 3 DL subframes (LAA and MF) since the UL HARQ mechanism is asynchronous.

The number of PHICH groups for normal cyclic prefix is given in the existing LTE specs by where N _g e{1/6, 1/2, 1 , 2} is given by the higher layer. As an example, if N _g = 1/6 is fixed for a 20 MHz MF cell, then 3 PHICH groups spanning a total of 36 REs across the system bandwidth would be available. Legacy PHICH adopts length-3 repetition coding for each ACK/NACK bit, followed by code spreading with an orthogonal sequence (spreading factor 4 for normal CP). Eight orthogonal sequences are available per PHICH group. Therefore, between one to eight information bits can be sent per PHICH group.

The PDCCH resources currently span between one and three OFDM symbols at the start of a DL slot for frame structure 3. As an example, the encoding and modulation structure for the MF preamble P can be based on that of the legacy PDCCH. A specific region of the PDCCH is pre-defined and pre-allocated for MF preamble transmission. All neighbor cells will check the same PDCCH search space for the preamble P. Alternatively, the preamble P is also included in UL transmis- sions. For example, this would be useful for a TXOP that starts with a burst of U L subframes ULSF or has all UL subframes ULSF. In another example, the preamble P is transmitted in U L transmissions that were not explicitly scheduled by the eNB, i .e. , autonomous UL bursts.

If the preamble P is i ncluded in a UL subframe ULSF that spans one or more UL interlaces, a candidate resource location would be the first n SC-FDMA symbols of the first UL subframe ULSF or slot at the start of an UL bu rst. As a non-l imiting example, the encoding and modulation can be based on existi ng methods uti lized on M F-sPUCCH (short PUCCH) for transmission of UCI , which make use of tai l-biting convolutional codes followed by appendage of CRC bits.

If the M F cell is operating with multiple DL CCs using CA and the PCel l is always included in each DL transmission , then the preamble may be transm itted only on the PCell . If the multi-carrier transmissions allow the absence of the PCell, then the preamble may be transmitted on any SCell.

As mentioned above, the parameters sig naled in the preamble P include the own cell identity CI D 1 (i .e. associated with the first wireless node 1 00) and a respective identity of the wireless nodes which use the at least one overlapping communication resource (i .e. the potential interferers represented by the wireless nodes 300, 400 and 500) . Preferably, the preamble P also in- eludes a defined period of time during which the first wireless node shall refrain from transmitting on at least one shared resource in the shared resource structure of the wireless commu nication system (in other words a subframe offset until end of one or more TXOPs). Consequently, the below table 1 shows a possible generic outline of the i nformation signaled in the preamble P. Parameter # of bits

Subframe offset until end 4+

of one or more TXOPs

Own cell ID 9

N neighbour cell IDs that 9N

are causing interference

Spare bits M

Total > 9(N + 1) + M + 4

Table 1

Four bits are proposed to be allocated for the signaling of the subframe offset until the end of the current TXOP, since up to 10 ms maximum channel occupancy time (MCOT) is currently allowed in the EN BRAN harmonized standard. For NR-based systems where a single TTI may occupy a fraction of 1 ms, e.g., 0.25 ms or 0.2 ms, either additional bits are needed to signal the number of upcoming subframes, or the TXOP duration time (in ms) can be signaled directly.

The physical cell ID (PCI) of the node initiating a TXOP is included so that UEs that wish to initiate an autonomous UL transmission do not necessarily back off to their own serving cell. This cell ID is also beneficial for adjacent eNBs to discover in- terference victims and initiate interference mitigation methods. If a UE is sending the preamble, it can indicate the cell ID of its serving cell. In another aspect, the preamble may transmit the cell global identifier (CGI) using 28 bits, instead of the physical cell ID. In another aspect, the neutral host network (NHN) ID or participating service provider (PSP) ID may be transmitted instead of the PCI.

The preamble includes the PCI of N strongest neighboring interfering cells, where N > 0. The selection of such interferer cells may be based on metrics such as SINR, INR, RSRP, RSSI, or RSRQ relative to a threshold at one or more served UEs or at the eNB receiver. As another non-limiting example, for a certain TXOP, an eN B can attempt to defer strongest neig hboring interfering cells to M U Es that are transmitting/receiving withi n the TXOP in which the preamble is sent. The N strongest neighbors are selected based on one or more of the metrics (e.g . SIN R, RSRP, RSRQ and/or IN R) considering measurement from the M U Es only. This mini mizes the un necessary blockage of eNBs with less interfe rence impact on the upcomi ng transm ission in the TXOP in which the preamble is sent. A n umber of spare bits are proposed to be included for future enhancements. Additional optional fields may also be transmitted using the spare bits, for example : the DL-to-UL transition point within the current TXOP,

• channel access parameters currently used, such as the con - tention window (CW) ,

HARQ NACK-to-ACK ratios of recent transmissions,

• The location and occurrence of critical periodic transmissions such as DRS and RACH ,

Channel access mechanism mode for uplink transm issions, such scheduled or autonomous. Additionally, the ti me duration or transition point can be included.

Upon successful decodi ng of a preamble P sent by an adjacent node, receiving nodes that identify their cell I D i n the list of i n terferes may be required to defer their transmissions by a cer- tain period of ti me. Examples for this period are until the end of the TXOP specified in the received preamble, or one or more MCOTs. As a non-lim iti ng example, the deferral period can be adjusted based on the load conditions, type of traffic to be served, previous performance or uplink channel access mechanism mode in the interferer cells. The receiving nodes that identify their cel l I D can also reduce transmit power, or i ncrease ED threshold, or change the operating frequency channel etc. in order to mitigate interference to the preamble transmitter. These adjustments can be together with deferring.

Apart from Reference Signal Received Power (RSRP) and Refe- rence Signal Received Quality (RSRQ), LAA already supports feedback of RSSI from UEs to their serving cell. To support the determination of strong interferers, the eNB may configure measurement periods or gaps where UEs measure strongest interferers and their corresponding PCIs. These measurement periods may be chosen to coincide with the DRS occasions of adjacent cells, if known to the eNB. Additional feedback mechanisms and signaling may be introduced to convey such reports from UEs to their serving cell. As a non-limiting example, the determination of strong interferers can be based on the measurements provi- ded by all served UEs or only the one or more UEs with worst performance in terms of data rate, SINR, etc.

In order to sum up, and with reference to the flow diagrams in Figures 9 and 10, we will now describe how the proposed solution may be executed in the first wireless node and the second wireless node respectively.

In a first step 910 of Figure 9, it is checked if information has been obtained, which information relates to a set of wireless nodes using at least one overlapping communication resource that is also used by at least one node in the own cell, i.e. the first cell. If such information has been obtained, the procedure continues to a step 920; and otherwise, the procedure loops back and stays in step 910.

In step 920, a preamble is generated, which contains a first data field designating an identity of the own cell, i.e. the first cell; and a second data field reflecting a respective identity of the wireless nodes set of wireless nodes using at least one overlapping communication resource. As explained above, the second data field may contain pieces of information that, for each of a number of wireless nodes, uniquely designate a respective identity of said nodes. Consequently, generating the preamble involves putting together information about the own cell identity and the identities of potentially interfering wireless nodes; and as- sembling this information into a standardized format.

Then, in a step 930, a preamble signal containing the preamble is transmitted over a predefined set of resources in the shared resource structure of the wireless communication system. Subsequently, the procedure loops back to step 910. In Figure 10, in a first step 1010, wireless signals are measured, which originate from at least one other wireless node that is associated with a cell different from the own cell, i.e. not the first cell. After that, in a step 1020, a report is generated, which report identifies at least one node of the at least one other node as a member of a set of wireless nodes which use an overlapping communication resource that is also used in the own cell, i.e. the first cell. Thus, analogous to the above, generating the report involves putting together information about the identities of the potentially interfering wireless nodes; and assembling this information into a standardized format.

Thereafter, in a step, 1030, a report signal is transmitted over a predefined set of resources in a shared resource structure of the wireless communication system, which report signal contains said report. Then, the procedure ends. Especially, the processing units 130 and 230 of the present wireless nodes 100 and 200 respectively may comprise one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression "processor" may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The pro- cessing circuitry may further perform data processing fu nctions for i nputting , outputting , and processing of data comprisi ng data buffering and device control fu nctions, such as cal l processin g control , user interface control , or the like. Moreover, althoug h the embodi ments of the proposed solution has described above with reference to the drawings comprise processor and processes performed in at least one processor, the solution thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for practical implementation . The prog ram may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form , or in any other form suitable for implementation . The program may either be a part of an operating system , or be a separate application . The car rier may be any entity or device capable of carrying the prog ram . For example, the carrier may comprise a storage medium , such as a Flash memory, a ROM ( Read Only Memory), for example a DVD (Digital Video/ Versatile Disk) , a CD (Compact Disc) or a semiconductor ROM , an EP ROM (Erasable Programmable Read- Only Memory) , an E EP ROM (Electrically Erasable Programmable Read-Only Memory) , or a magnetic recording medi um , for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal which may be conveyed directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the prog ram is embedded, the integrated circuit being adapted for performing , or for use in the performance of, the relevant processes.