WO2020114598A1

WO2020114598A1 - Synchronous channel access mechanism in unlicensed spectrum

Info

Publication number: WO2020114598A1
Application number: PCT/EP2018/083798
Authority: WO
Inventors: Claudio Rosa; Frank Frederiksen
Original assignee: Nokia Technologies Oy
Priority date: 2018-12-06
Filing date: 2018-12-06
Publication date: 2020-06-11

Abstract

It is provided an apparatus, comprising means for monitoring configured to monitor if a request to provide a response message on a channel ina time slot is received; means for instructing configured to instruct a reception device to provide the response message on the channel in the time slot if the request is received.

Description

Synchronous channel access mechanism in unlicensed spectrum

Field of the invention

The present invention relates to access to an unlicensed spectrum by a terminal of a synchronous network (such as 3GPP network).

Abbreviations

3GPP 3^rd Generation Partnership Project

4G / 5G 4^th / 5^th Generation

BS Base Station

CTS Clear-To-Send

D2D Device-to-device (communication)

DL Downlink

eNB evolved NodeB (base Station in 4G)

gNB Base Station in 5G/NR

LAA License Assisted Access

LBT Listen-Before-talk

LTE Long Term Evolution

NR New Radio (air interface standard of 5G systems)

NR-U New radio unlicensed

OCC Orthogonal Cover Code

OFDM Orthogonal Frequency Division Multiplexing

RSSI Received Signal Strength Indicator

RTS Ready-To-Send

Rx Receive

TA Timing Advance

Tx Transmit

UE User Equipment

UL Uplink

WiFi Wireless Fidelity

Background of the invention Listen-before-talk (LBT) is one of the most commonly used co-existence mechanisms in unlicensed spectrum. LBT is a contention-based protocol that allows many devices to use the same radio channel without pre-coordination. Transmission by a device on the radio channel is conditional on the device sensing the channel as idle. A device is only allowed to occupy the channel for a limited duration of time.

Traditional LBT cannot overcome the so-called hidden node problem. The hidden-node problem occurs when the transmitter (performing LBT) is not able to detect transmission by an interfering (at the receiver) node. The Ready-to-Send/Clear-to-Send (RTS/CTS) mechanism is used in WiFi to combat the hidden-node problem. With RTS/CTS, the transmitter first sends an RTS message to the receiver. The receiver then performs LBT, and in case the channel is idle, it sends back a CTS message. Upon receiving the CTS message, the transmitter can then start data transmission on the medium towards the receiver. Other devices that detect a CTS message will backoff their transmissions.

Solutions which are based on RTS/CTS mechanism have been discussed and proposed for 3GPP-based access to unlicensed spectrum, though they were not agreed in either LAA or MulteFire. However, since the hidden-node problem is expected to become more relevant with beamformed operation, there is some probability that solutions targeted at solving the hidden- node problem may be considered as a relevant optimization of NR-U in future releases.

Lots of prior art exist on the RTS/CTS procedure - including some documents describing how RTS/CTS could be used to solve the so-called exposed node problem. The exposed node problem occurs when two transmitters are in (LBT) range of each other, while the corresponding receivers are not in range of the interfering transmitter. In this case, a device hearing the RTS from a neighbour transmitter but no CTS may be allowed to transmit.

Summary of the invention

It is an object of the present invention to improve the prior art.

According to a first aspect of the invention, there is provided an apparatus, comprising means for requesting configured to request one or more first reception devices by respective first requests to provide a respective first response message on a channel in a first time slot; means for inhibiting configured to inhibit a transmit device to transmit any signal on the channel in a response time window, wherein the response time window includes at least the first time slot; means for monitoring configured to monitor, for each of the one or more first reception devices, if the respective first response message is received on the channel; means for instructing configured to instruct the transmit device to transmit a respective signal to at least one of the one or more first reception devices on the channel if the first response message of the at least one of the one or more first reception devices is received on the channel, wherein, for each of the at least one of the one or more first reception devices, the respective signal is different from the respective first request.

According to a second aspect of the invention, there is provided an apparatus, comprising means for monitoring configured to monitor if a request to provide a response message on a channel in a time slot is received; means for instructing configured to instruct a reception device to provide the response message on the channel in the time slot if the request is received.

According to a third aspect of the invention, there is provided a method, comprising requesting one or more first reception devices by respective first requests to provide a respective first response message on a channel in a first time slot; inhibiting a transmit device to transmit any signal on the channel in a response time window, wherein the response time window includes at least the first time slot; monitoring, for each of the one or more first reception devices, if the respective first response message is received on the channel; instructing the transmit device to transmit a respective signal to at least one of the one or more first reception devices on the channel if the first response message of the at least one of the one or more first reception devices is received on the channel, wherein,

for each of the at least one of the one or more first reception devices, the respective signal is different from the respective first request.

According to a fourth aspect of the invention, there is provided a method, comprising monitoring if a request to provide a response message on a channel in a time slot is received; instructing a reception device to provide the response message on the channel in the time slot if the request is received.

Each of the methods of the third and fourth aspects may be a method of synchronous access.

According to a fifth aspect of the invention, there is provided a computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method according to any of the third and fourth aspects. The computer program product may be embodied as a computer-readable medium or directly loadable into a computer.

According to some example embodiments of the invention, at least one of the following advantages may be achieved:

• the hidden node problem is overcome;

• plural UEs may be scheduled at once for the unlicensed band;

• signalling effort is reduced;

• coexistence with conventional LBT mechanism is possible.

It is to be understood that any of the above modifications can be applied singly or in combination to the respective aspects to which they refer, unless they are explicitly stated as excluding alternatives.

Brief description of the drawings

Further details, features, objects, and advantages are apparent from the following detailed description of the preferred example embodiments of the present invention which is to be taken in conjunction with the appended drawings, wherein:

Fig. 1 shows a timing diagram according to an example embodiment of the invention;

Fig. 2 shows an apparatus according to an example embodiment of the invention;

Fig. 3 shows a method according to an example embodiment of the invention;

Fig. 4 shows an apparatus according to an example embodiment of the invention;

Fig. 5 shows a method according to an example embodiment of the invention; and

Fig. 6 shows an apparatus according to an example embodiment of the invention.

Detailed description of certain example embodiments

Herein below, certain example embodiments of the present invention are described in detail with reference to the accompanying drawings, wherein the features of the example embodiments can be freely combined with each other unless otherwise described. However, it is to be expressly understood that the description of certain example embodiments is given by way of example only, and that it is by no way intended to be understood as limiting the invention to the disclosed details. Moreover, it is to be understood that the apparatus is configured to perform the corresponding method, although in some cases only the apparatus or only the method are described.

RTS/CTS mechanism presents some challenges when operating in a synchronous communication system (such as a 3GPP system, e.g. NR) and/or in the presence of timing advance. Basically, in the synchronous communication system, time is divided into time slots. Accordingly, a device receiving RTS in DL may reply by CTS only in a time slot foreseen for transmission in UL. This may result in some time (larger than the receiver processing time) elapsing from the time instant one device receives the RTS in DL, and the time instant when it can start transmission of the CTS message in UL (potentially, the CTS message may be sent only after successful LBT). This has the main disadvantage that other systems (i.e. WiFi) with shorter Short Interframe Space (i.e. the time required to process a received frame and to respond with a response frame) may gain access to the channel between the RTS and CTS even if there is no hidden-node problem.

Moreover, the RTS/CTS procedure is mainly designed for point-to-point communication (RTS/CTS frames include the receiver and the transmitter address). Therefore, it is a relatively spectral inefficient solution in point-to-multipoint communication - especially in the cases where only a subset of the receivers need to operate in RTS/CTS mode, while the other receivers may operate in LBT without RTS/CTS.

Some example embodiments of the invention solve the problem of RTS/CTS mechanism with coarser time granularity of synchronous radio communication systems - including operation using timing advanced (i.e. considering the delay between the transmission time of a signal and the reception time of the signal). Also, some example embodiments provide optimizations to the RTS/CTS mechanism to make it more efficient in case of point-to-multipoint transmissions (and potentially even point-to-selected-multipoint transmissions). These optimizations may be applied e.g. in WiFi.

According to some example embodiments of the invention, gNB provides a pre-indication signal signature (“request”) that allows a UE or a group of UEs to unambiguously detect that they are scheduled for transmission on a channel (such as a channel of an unlicensed spectrum). However, the request may or may not comprise any information on the scheduling grant. In effect, such a signature would correspond to a“UE (UE-group) specific RTS signal”. The signature may allow a UE to instantly detect whether it is targeted for transmission of a response message. The prior art does not provide a transmission of a“request” message targeting a group of UEs. The grouping may be based on previous configuration by the network. The request may be send on the channel or on a different resource such as in a control channel of the synchronous network (e.g. 3GPP network).

Upon detection of the pre-indication signal signature, the corresponding receiving devices (UEs) may transmit a (delayed) response message (CTS) using pre-configured time/frequency/code resources at a time slot of the synchronous network. The time slot may be predefined (e.g. by standardization), or the pre-indication signal signature may comprise a corresponding indication. In some example embodiments, the time slot when to transmit the delayed response message is determined at the UE based on DL signaling (e.g. information contained in a physical downlink control channel such as the common physical downlink control channel). The time slot may include part of the Timing Advance (TA) window of the UEs operating in request-response mode. The time slot may be indicated relative to the time of the pre-indication signal signature (taking into account the timing advance). For example, it may be indicated as“the first (or second) time slot for TX in UL after receipt of the pre indication signal signature”)

There are different options to multiplex the response messages in case multiple UEs (a group of UEs) are addressed with one pre-indication signal signature:

o Block-interleaved OFDM may be used to multiplex response signatures/messages from different devices in the same time resources (Frequency Division Multiplexing, using interlaced structure);

o UEs may transmit their response messages on the same time and frequency resource, but using different signatures (codes) (i.e. Code Division Multiplexing);

o Time Division Multiplexing is also an option. However it has some limitations as it may require LBT before the transmission of the response message. In this case, the response message from one UE may be blocked by the transmission of the response message from another UE.

After transmission of the UE (UE group) specific pre-indication signal signature, the eNB may continue transmission until the (pre-)configured time slot for the transmission of the response message (CTS). That is, other UEs (i.e. UEs not configured to operate in request- response mode) can still be scheduled by and receive signals (such as data) from the gNB, while the UEs in request-response mode do not receive the DL transmission, since they are preparing the response to the pre-indication signal signature for the gNB. In some example embodiments of the invention, the gNB performs partial bandwidth or frequency interlaced transmission during the timing advance window to allow the UEs in request-response mode to perform measurements on (parts of) the radio channel without interference from the scheduling gNB.

Upon detection of the response message(s) from one or several of the UEs addressed with the previously transmitted request message (pre-indication signal signature), the gNB can start scheduling transmission of signals (e.g. data) to/from the corresponding UEs. In detail, if plural UEs (a group of UEs) are addressed, according to some example embodiments of the invention, gNB may transmit signals (e.g. data) to all or a subset of those addressed UEs from which gNB received the response message. In some example embodiments of the invention, gNB may transmit signals (e.g. data) to all or a subset of the addressed UEs if gNB received the response messages from all the addressed UEs.

In some example embodiments of the invention, the UE performs LBT before the transmission of the response message, in which case the transmission of the response message is conditional on the channel being measured as idle.

In some example embodiments of the invention, the UE does not perform LBT before the transmission of the response message. In these example embodiments, if the channel is occupied, the gNB may not be able to decode the response message and, thus, may not transmit signals (data) for the respective UE.

In some further embodiments, the UE may perform multiple LBT attempts prior to providing the response message. This may allow a delaying access to the radio channel for a UE. Such delayed response may happen on corresponding pre-configured resources as mentioned before.

Whether or not the UE performs LBT before transmitting the response message may be preconfigured in the UE, configured by the network (e.g. at initial access to the network), or configured by the pre-indication signal signature.

In some example embodiments of the invention, each UE will perform the above described method of receiving the request (pre-indication signal signature) and replying by a delayed response message. I.e., the UEs are preconfigured for operation in request-response mode. In some example embodiments of the invention, the network may decide whether or not a UE operates in request-response mode. Such a decision may be based on UE-reported RSSI measurements, or other measurements that may help determining if the hidden node problem likely exist (e.g. if the UE is at the cell’s edge). UE may be configured by control signalling from gNB, e.g. at initial attach. In some example embodiments, the UE may consider receiving the pre-indication signal signature as a configuration in the request-response mode.

Correspondingly, the resources for receiving the request and transmitting the response message may be standardized or configured by the network, e.g. by some control signalling.

An example implementation according to some embodiments of the invention with two UEs (UE#2 and UE#3) configured to operate in request-response mode and one UE (UE#1 ) not configured to operate in request-response mode (e.g. operating LBT without request- response) is illustrated in Fig. 1 . The number of UE(s) configured (or not configured) to operate in request-response mode is generally arbitrary and not limited by the example of Fig. 1 .

As shown in the uppermost row Fig. 1 , first, the gNB sends a pre-indication signal signature (request message) towards a group of UEs configured to operate in request-response mode. The transmission of such pre-indication signal signature may be preceded by LBT procedure at the gNB (indicated as“LBT” in Fig. 1 ). Typically, this LBT procedure may be a Cat4 LBT procedure that implements both random backoff and a variable contention window size, as it is typically performed at the gNB / access point before a DL transmission. This LBT procedure is not mandatory.

After that, the gNB may continue occupying the channel (medium) by transmitting data towards at least one of the UEs not configured to operate in request-response mode (here: UE#1 ). This transmission of data from gNB to UE#1 may continue until a pre-figured time slot where the UEs (UE#2, UE#3) configured to operate in request-response mode are supposed to transmit their response message. More in detail, UE#1 receives data from gNB during the time between the request and the time slot configured for reception of the response message (or until a time shortly before the time slot in order to take into account LBT by the UE#1 and UE#2 and/or their timing advances). In Fig. 1 , the reception of data is indicated by boxes with a dashed lined frame, as shown in the 2^nd row of Fig. 1 for UE#1 . Note that gNB may transmit but need not transmit data to gNB#1 in the time between request and response.

The receivers (UE#2, UE#3) configured in request-response mode may perform the LBT procedure, and in case the channel is idle, transmit their (delayed) response at the configured time slot using pre-configured time, frequency and/or code resources (see the 3^rd and 4^th rows of Fig. 1 ).

In some example embodiments, UEs do not perform LBT prior to transmission of the response message, and transmit the response message regardless of whether the channel is idle, as explained above.

The gNB listens for the responses from the UEs configured to operate in request-response mode. If the response is received (see dashed lined box in the 1^st row of Fig. 1 ), the gNB may start to transmit signals (e.g. data) towards the corresponding UE(s). Transmission of signals (e.g. data) towards the UEs configured to operate in request-response and to send the response message may be preceded by additional LBT at the gNB (not shown in Fig. 1 , this additional LBT is not mandatory).

The format (e.g. interlaces, cyclic shifts, OCC etc.) and/or content of the request and response messages may be standardized so that they are detectable by other devices (e.g. neighbor gNBs) operating on the same channel. In case of frequency/code division multiplexing of response messages from multiple UEs, the allowed formats may be limited to minimize the number of decoding attempts needed by other devices. In some example embodiments, a gNB provides information on the resources used for the request and response messages to one or more of its neighbor gNBs (of the same network) (e.g. over X2/Xn interface) to limit the number of decoding attempts at the neighbor gNBs. Thus, the neighbor gNBs may backoff their transmissions if they detect a request message and/or a corresponding response message.

In some example embodiments of the invention, a partial frequency or frequency interlace transmission towards non-request-response UEs is used. In such example embodiments, LBT by the request-response UEs is only performed on those frequency resources that are not used for transmissions towards the non-request-response UEs. The goal is to improve spectrum efficiency such that the serving base station can still serve some DL traffic towards some UEs on part(s) of the spectrum, while some other UE can listen for interference on the non-used resources. In such example embodiments, the request-response UEs may perform LBT while transmissions towards the non-request-response UEs are still ongoing

Fig. 2 shows an apparatus according to an example embodiment of the invention. The apparatus may be a transmit device (e.g. base station such as a gNB) or an element thereof. Fig. 3 shows a method according to an example embodiment of the invention. The apparatus according to Fig. 2 may perform the method of Fig. 3 but is not limited to this method. The method of Fig. 3 may be performed by the apparatus of Fig. 2 but is not limited to being performed by this apparatus.

The apparatus comprises means for means for requesting 10, means for inhibiting 20, means for monitoring 30, and means for instructing 40. The means for means for requesting 10, means for inhibiting 20, means for monitoring 30, and means for instructing 40 may be a requesting means, inhibiting means, monitoring means, and instructing means, respectively. The means for means for requesting 10, means for inhibiting 20, means for monitoring 30, and means for instructing 40 may be a requestor, inhibitor, monitor, and instructor, respectively. The means for requesting 10, means for inhibiting 20, means for monitoring 30, and means for instructing 40 may be a requesting processor, inhibiting processor, monitoring processor, and instructing processor, respectively.

The means for requesting 10 requests one or more first reception devices to provide a respective response message on a channel in a time slot (S10).

The means for inhibiting 20 inhibits a transmit device to transmit any signal on the channel in a response time window (S20). The response time window includes at least the time slot.

The means for monitoring 30 monitors, for each of the one or more first reception devices, if the respective response message is received on the channel (S30). Preferably, the means for monitoring 30 monitors only during the response time window.

If the response message of at least one of the one or more first reception devices is received on the channel (S30 =“yes”), the means for instructing 40 instructs the transmit device to transmit a respective signal to the at least one of the one or more first reception devices on the channel (S40). Preferably, if the response message of the at least one of the one or more first reception devices is not received on the channel (S30 =“no”), the means for instructing 40 does not instruct the transmit device to transmit a respective signal to the at least one of the one or more first reception devices on the channel. The respective signal may comprise data. The respective signal is different from the respective request requested by the means for requesting 10.

Fig. 4 shows an apparatus according to an example embodiment of the invention. The apparatus may be a reception device (e.g. terminal such as a UE) or an element thereof. Fig. 5 shows a method according to an example embodiment of the invention. The apparatus according to Fig. 4 may perform the method of Fig. 5 but is not limited to this method. The method of Fig. 5 may be performed by the apparatus of Fig. 4 but is not limited to being performed by this apparatus.

The apparatus comprises means for monitoring 1 10 and means for instructing 120. The means for means for monitoring 1 10 and means for instructing 120 may be a monitoring means and instructing means, respectively. The means for means for monitoring 1 10 and means for instructing 120 may be a monitor and instructor, respectively. The means for monitoring 1 10 and means for instructing 120 may be a monitoring processor and instructing processor, respectively.

The means for monitoring 1 10 monitors if a request to provide a response message on a channel in a time slot is received (S1 10). If the request is received (S1 10 =“yes”), the means for instructing 120 instructs a reception device to provide the response message on the channel in the time slot (S120).

Fig. 6 shows an apparatus according to an example embodiment of the invention. The apparatus comprises at least one processor 810, at least one memory 820 including computer program code, and the at least one processor 810, with the at least one memory 820 and the computer program code, being arranged to cause the apparatus to at least perform at least one of the methods according to Figs. 3 and 5 and related description.

Some example embodiments of the invention are described where the transmitter (also denoted as transmit device) (base station, e.g. gNB) transmits the request in DL, and a receiver (also denoted as reception device) (terminal, e.g. UE) receives the request and replies by a response in UL. However, the invention is not limited to such configurations. According to some example embodiments of the invention, the transmit device (terminal, e.g. UE) may send the request in UL, and the reception device (base station, e.g. gNB) receives the request and replies by a response in DL. According to some example embodiments of the invention, both the transmit device and reception device may be terminals (e.g. UEs in D2D communication).

Some example embodiments of the invention are described which are based on a 3GPP network (e.g. NR) using LAA. However, the invention is not limited to NR. It may be applied to any generation (3G, 4G, 5G, etc.) of 3GPP networks. However, the invention is not limited to 3GPP networks. It may be applied to other radio networks, too. A UE is an example of a terminal. However, the terminal (UE) may be any device capable to connect to the (3GPP) radio network via the channel such as a MTC device, a D2X device etc., and to the unlicensed spectrum.

A cell may be represented by the base station (e.g. gNB, eNB, etc.) serving the cell. The base station (cell) may be connected to an antenna (array) serving the cell by a Remote Radio Head. A base station may be realized as a combination of a central unit (one or plural base stations) and a distributed unit (one per base station). The central unit may be employed in the cloud.

One piece of information may be transmitted in one or plural messages from one entity to another entity. Each of these messages may comprise further (different) pieces of information.

Names of network elements, protocols, and methods are based on current standards. In other versions or other technologies, the names of these network elements and/or protocols and/or methods may be different, as long as they provide a corresponding functionality.

If not otherwise stated or otherwise made clear from the context, the statement that two entities are different means that they perform different functions. It does not necessarily mean that they are based on different hardware. That is, each of the entities described in the present description may be based on a different hardware, or some or all of the entities may be based on the same hardware. It does not necessarily mean that they are based on different software. That is, each of the entities described in the present description may be based on different software, or some or all of the entities may be based on the same software. Each of the entities described in the present description may be embodied in the cloud.

According to the above description, it should thus be apparent that example embodiments of the present invention provide, for example, a terminal (such as a UE), or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product(s). According to the above description, it should thus be apparent that example embodiments of the present invention provide, for example, a base station (e.g. gNB or eNB), or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product(s). Implementations of any of the above described blocks, apparatuses, systems, techniques or methods include, as non-limiting examples, implementations as hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It is to be understood that what is described above is what is presently considered the preferred example embodiments of the present invention. However, it should be noted that the description of the preferred example embodiments is given by way of example only and that various modifications may be made without departing from the scope of the invention as defined by the appended claims.

Claims

Claims:

1 . Apparatus, comprising

means for requesting configured to request one or more first reception devices by respective first requests to provide a respective first response message on a channel in a first time slot;

means for inhibiting configured to inhibit a transmit device to transmit any signal on the channel in a response time window, wherein the response time window includes at least the first time slot;

means for monitoring configured to monitor, for each of the one or more first reception devices, if the respective first response message is received on the channel;

means for instructing configured to instruct the transmit device to transmit a respective signal to at least one of the one or more first reception devices on the channel if the first response message of the at least one of the one or more first reception devices is received on the channel, wherein,

2. The apparatus according to claim 1 , further comprising

means for prohibiting configured to prohibit the transmit device, for each of the one or more first reception devices, to transmit the respective signal to the respective first reception device if the respective first response message is not received on the channel.

3. The apparatus according to any of claims 1 to 2, wherein

the means for inhibiting is configured to inhibit the transmit device to transmit a signal to a second reception device different from each of the one or more first reception devices at a request time when the one or more first reception devices are requested to provide the one or more first response messages.

4. The apparatus according to claim 3, further comprising

means for allowing configured to allow the transmit device to transmit the signal to the second reception device after the request time and before the response time window starts.

5. The apparatus according to any of claims 1 to 4, further comprising means for deciding configured to decide if a third reception device is one of the one or more first reception devices based on a measurement result received from the third reception device;

means for configuring configured to configure the third reception device to provide the respective first response message in the first time slot if it is decided that the third reception device is one of the one or more first reception devices.

6. The apparatus according to any of claims 1 to 5, further comprising

means for informing configured to inform a first neighbor base station on at least one of

• a first resource on which the respective first request is transmitted to at least one of the one or more first reception devices; and

• a first format of at least one of the one or more first response messages.

7. The apparatus according to any of claims 1 to 6, further comprising

first means for checking configured to check if an information on a second resource used by a second neighbor base station for transmitting a second request is available, wherein the second request requests to provide a second response message on the channel in a second time slot;

first means for intercepting configured to intercept if the second neighbor base station transmits the second request on the second resource if the information on the second resource is available;

first means for delaying configured to delay a first transmission on the channel if the second neighbor base station transmits the second request on the second resource.

8. The apparatus according to any of claims 1 to 7, further comprising

second means for checking configured to check if an information on a second format of a third response message used in responding to a third request from a third neighbor base station is available, wherein the third request requests to provide the third response message on the channel in a third time slot;

second means for intercepting configured to intercept if the third response message having the second format is provided if the information on the second format is available; second means for delaying configured to delay a second transmission on the channel if the third response message having the second format is provided.

9. The apparatus according to any of claims 1 to 8, wherein the first time slot is determined based on an operation of a synchronous network on which the one or more first reception devices communicate.

10. The apparatus according to any of claims 1 to 9, further comprising

means for forbidding configured to forbid the means for instructing to instruct the transmit device to transmit the respective signal to the at least one of the one or more first reception devices if at least one of the first response messages from the one or more reception devices is not received.

1 1. Apparatus, comprising

means for monitoring configured to monitor if a request to provide a response message on a channel in a time slot is received;

means for instructing configured to instruct a reception device to provide the response message on the channel in the time slot if the request is received.

12. The apparatus according to claim 1 1 , further comprising

means for listening configured to listen if the channel is free;

means for inhibiting configured to inhibit the instructing of the reception device if the channel is not free.

13. The apparatus according to any of claims 1 1 and 12, further comprising

means for supervising configured to supervise if a signal for the reception device is received on the channel, wherein the signal is different from the request;

means for prohibiting configured to prohibit the supervising before the time slot.

14. The apparatus according to any of claims 1 1 to 13, further comprising

means for checking configured to check if the reception device is configured to provide the response message on the channel in the time slot;

means for forbidding configured to forbid the means for instructing to instruct the reception device to provide the response message on the channel in the time slot if the reception device is not configured to provide the response message on the channel in the time slot.

15. The apparatus according to any of claims 1 1 to 14, wherein the time slot is determined based on an operation of a synchronous network on which the reception device communicates.

16. The apparatus according to any of claims 1 1 to 15, wherein

the means for instructing is configured to instruct the reception device on a resource out of a set of resources configured for transmission by the reception device.

17. The apparatus according to claim 16, wherein the resource comprises at least one of a time, a frequency, and a code.

18. The apparatus according to any of claims 1 1 to 17, wherein a format of the response message is predefined.

19. Method, comprising

requesting one or more first reception devices by respective first requests to provide a respective first response message on a channel in a first time slot;

inhibiting a transmit device to transmit any signal on the channel in a response time window, wherein the response time window includes at least the first time slot;

monitoring, for each of the one or more first reception devices, if the respective first response message is received on the channel;

instructing the transmit device to transmit a respective signal to at least one of the one or more first reception devices on the channel if the first response message of the at least one of the one or more first reception devices is received on the channel, wherein,

20. The method according to claim 19, further comprising

prohibiting the transmit device, for each of the one or more first reception devices, to transmit the respective signal to the respective first reception device if the respective first response message is not received on the channel.

21. The method according to any of claims 19 to 20, further comprising

inhibiting the transmit device to transmit a signal to a second reception device different from each of the one or more first reception devices at a request time when the one or more first reception devices are requested to provide the one or more first response messages.

22. The method according to claim 21 , further comprising allowing the transmit device to transmit the signal to the second reception device after the request time and before the response time window starts.

23. The method according to any of claims 19 to 22, further comprising

deciding if a third reception device is one of the one or more first reception devices based on a measurement result received from the third reception device;

configuring the third reception device to provide the respective first response message in the first time slot if it is decided that the third reception device is one of the one or more first reception devices.

24. The method according to any of claims 19 to 23, further comprising

informing a first neighbor base station on at least one of

• a first format of at least one of the one or more first response messages.

25. The method according to any of claims 19 to 24, further comprising

checking if an information on a second resource used by a second neighbor base station for transmitting a second request is available, wherein the second request requests to provide a second response message on the channel in a second time slot;

intercepting if the second neighbor base station transmits the second request on the second resource if the information on the second resource is available;

delaying a first transmission on the channel if the second neighbor base station transmits the second request on the second resource.

26. The method according to any of claims 19 to 25, further comprising

checking if an information on a second format of a third response message used in responding to a third request from a third neighbor base station is available, wherein the third request requests to provide the third response message on the channel in a third time slot; intercepting if the third response message having the second format is provided if the information on the second format is available;

delaying a second transmission on the channel if the third response message having the second format is provided.

27. The method according to any of claims 19 to 26, wherein the first time slot is determined based on an operation of a synchronous network on which the one or more first reception devices communicate.

28. The method according to any of claims 19 to 27, further comprising

forbidding the instructing of the transmit device to transmit the respective signal to the at least one of the one or more first reception devices if at least one of the first response messages from the one or more reception devices is not received.

29. Method, comprising

monitoring if a request to provide a response message on a channel in a time slot is received;

instructing a reception device to provide the response message on the channel in the time slot if the request is received.

30. The method according to claim 29, further comprising

listening if the channel is free;

inhibiting the instructing of the reception device if the channel is not free.

31. The method according to any of claims 29 and 30, further comprising

supervising if a signal for the reception device is received on the channel, wherein the signal is different from the request;

prohibiting the supervising before the time slot.

32. The method according to any of claims 29 to 31 , further comprising

checking if the reception device is configured to provide the response message on the channel in the time slot;

forbidding the instructing of the reception device to provide the response message on the channel in the time slot if the reception device is not configured to provide the response message on the channel in the time slot.

33. The method according to any of claims 29 to 32, wherein the time slot is determined based on an operation of a synchronous network on which the reception device communicates.

34. The method according to any of claims 29 to 33, further comprising instructing the reception device on a resource out of a set of resources configured for transmission by the reception device.

35. The method according to claim 34, wherein the resource comprises at least one of a time, a frequency, and a code.

36. The method according to any of claims 29 to 35, wherein a format of the response is predefined.

37. A computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method according to any of claims 19 to 36.

38. The computer program product according to claim 37, embodied as a computer-readable medium or directly loadable into a computer.