WO2017153630A1

WO2017153630A1 - Protecting transmissions in wireless network

Info

Publication number: WO2017153630A1
Application number: PCT/FI2017/050087
Authority: WO
Inventors: Enrico-Henrik Rantala; Mika Kasslin; Janne Marin; Olli Alanen; Wessam Afifi Ahmed
Original assignee: Nokia Technologies Oy
Priority date: 2016-03-10
Filing date: 2017-02-14
Publication date: 2017-09-14

Abstract

This document discloses a solution for protecting transmissions in a wireless network. According to an aspect, there is provided a method for an access node of the wireless network, comprising:determining, by an apparatus, to protect transmission of a first packet on a first sub-channel of a frequency channel; causing, by the apparatus on the basis of said determining, transmission of a second packet on a second sub-channel of the frequency channel, wherein the second sub-channel is different from the first sub-channel, and wherein said transmission of the second packet is arranged to be carried out simultaneously with said transmission of the first packet.

Description

Protecting Transmissions in Wireless Network Field

The invention relates to the field of wireless communications and, particularly, to improving reliability of communications in a wireless network. Background

Increasing demand for wireless services and higher data rates sets a requirement for efficiency of wireless networks. Increasing number of different wireless networks inevitably leads to presence of overlapping networks that operate on overlapping resources. Some collision avoidance methods have been designed for these networks but new communication methods set new requirements for improving the reliability of communications in a wireless network.

Brief description

According to an aspect, there is provided the subject matter of the independent claims.

Embodiments of the invention are defined in dependent claims.

List of drawings

Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which

Figure 1 illustrates an example of a wireless communication scenario to which embodiments of the invention may be applied;

Figure 2 illustrates a flow diagram of an embodiment for protecting narrowband transmissions in a wireless network;

Figures 3 and 4 illustrate embodiments for transmitting a data packet in an unprotected mode and in a protected mode in a wireless network;

Figure 5A and 5B illustrate some embodiments of a protection packet;

Figure 6 illustrates some embodiments of criteria for determining a need for protecting narrowband packets in a wireless network;

Figure 7 illustrates an embodiment of a process for determining transmission power for a protection packet protecting narrowband transmissions;

Figure 8 illustrates a signalling diagram for protected transmissions in a wireless network according to an embodiment of the invention;

Figure 9 illustrates use of a wideband data packet as a protection packet according to an embodiment of the invention; and Figure 10 illustrates a block diagram of an embodiment of an apparatus carrying out functions related to the narrowband communications in the wireless network.

Description of embodiments

The following embodiments are examples. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations, this does not necessarily mean that each such reference is referring to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may contain also features/structures that have not been specifically mentioned.

A general wireless communication scenario to which embodiments of the invention may be applied is illustrated in Figure 1 . Figure 1 illustrates wireless communication devices comprising an access points (AP) 100 and a plurality of wireless terminal devices (STA) 1 10, 1 12. The access point may be associated with a basic service set (BSS) which is a basic building block of an IEEE 802.1 1 -based wireless local area network (WLAN). The most common BSS type is an infrastructure BSS that includes a single AP together with all STAs associated with the AP. The AP may be a fixed AP or it may be a mobile AP. The AP 100 may also provide access to other networks, e.g. the Internet. In another embodiment, the BSS may comprise a plurality of APs to form an extended service set (ESS). In yet another embodiment, a terminal device 1 10 may establish and manage a peer-to- peer wireless network to which one or more other terminal devices 1 12 may associate. In such a case, the peer-to-peer wireless network may be established between two terminal devices and, in some embodiment, the terminal device managing the network may operate as an access node providing the other terminal device(s) with a connection to other networks, e.g. the Internet. In other embodiments, such routing functionality is not employed and the connection terminates in the terminal devices. Such a peer-to-peer network may be utilized for data sharing or gaming, for example.

The access node 100 may be connected to a network management system (NMS) 130 which may comprise an apparatus configured to maintain channel usage information of wireless networks of one or more access nodes and to configure the channel usage of the wireless networks. For example, it may arrange wireless networks located close to each other to operate on different channels and, thus, avoid interference between the networks. An example scenario is that access nodes of an enterprise are all controlled by the same NMS 130. In an embodiment, the network management system 130 is comprised in one of the access nodes, e.g. in the access node 100. In another embodiment, the network management system is realized by an apparatus different from the access nodes, e.g. by a server computer to which the access nodes may connect via a wired or wireless connection.

While embodiments of the invention are described in the context of the above-described topologies of IEEE 802.1 1 specifications, it should be appreciated that these or other embodiments of the invention may be applicable to networks based on other specifications, e.g. other versions of the IEEE 802.1 1 , WiMAX (Worldwide Interoperability for Microwave Access), UMTS LTE (Long-term Evolution for Universal Mobile Telecommunication System), LTE-Advanced, a fifth generation cellular communication system (5G), and other networks having cognitive radio features, e.g. transmission medium sensing features and adaptiveness to coexist with radio access networks based on different specifications and/or standards. Some embodiments may be applicable to networks having features defined in the IEEE 802.19.1 specification. One example of a suitable communications system is the 5G system, as mentioned above. 5G is envisaged to use multiple-input-multiple-output (MIMO) multi-antenna transmission techniques, many more base stations or nodes than current network deployments of LTE (a so- called small cell concept), including macro sites operating in co-operation with smaller local area access nodes and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates. 5G will likely be comprised of more than one radio access technology (RAT), each optimized for certain use cases and/or spectrum. One of the RATs may be a WLAN-based RAT. 5G mobile communications will have a wider range of use cases and related applications including video streaming, augmented reality, different ways of data sharing, and various forms of machine type applications, including vehicular safety, different sensors and real-time control.

IEEE 802.1 1 η specification specifies a data transmission mode that includes 20 megahertz (MHz) wide primary and secondary channels. The primary channel is used in all data transmissions with clients supporting only the 20 MHz mode and with clients supporting higher bandwidths. A further definition in 802.1 1 n is that the primary and secondary channels are adjacent. The 802.1 1 n specification also defines a mode in which a STA may, in addition to the primary channel, occupy one secondary channel which results in a maximum bandwidth of 40 MHz. IEEE 802.1 1 ac amendment extends such an operation model to provide for wider bandwidths by increasing the number of secondary channels from 1 up to 7, thus resulting in bandwidths of 20 MHz, 40 MHz, 80 MHz, and 160 MHz. A 40 MHz transmission band may be formed by two contiguous 20 MHz bands, and an 80 MHz transmission band may be formed by two contiguous 40 MHz bands. However, a 160 MHz band may be formed by two contiguous or non-contiguous 80 MHz bands. Figure 1 illustrates such a channel 150 which, in one embodiment, is a 20 MHz channel of an 802.1 1 network. The channel 150 may be a primary channel, for example.

IEEE 802.1 1 ax task group is about to specify high -efficiency wireless (HEW) networks and an evolution version of the WLAN. IEEE802.1 1 ax task group may allow narrowband transmissions on sub-channels of the above-described channels. The narrowband transmissions may be employed in at least one of downlink and uplink. With respect to the uplink, multi-user transmissions may be employed by configuring multiple STAs to transmit simultaneously on parallel subchannels of a frequency channel. With respect to the downlink, the access node may transmit packets simultaneously to a plurality of STAs on the same frequency channel, on different sub-channels. In some embodiments, the access nodes may combine sub-channels of a frequency channel to provide a STA with more bandwidth. However, the combining may be limited to sub-channels of the same frequency channel. In some cases, the narrowband transmissions may be called long-range-low-power (LRLP) transmissions. Figure 1 illustrates an example of such sub-channels 140 to 150 that may define a sub-channel structure within the channel 150. The channel may be the primary channel, or any one of the secondary channels of the wireless network. In some embodiments, the wireless network may employ dynamically either the whole channel 150 in transmissions or one or more sub-channels 140 to 150. Such frequency-adaptation may improve the efficiency of the network and allow power-savings in the terminal devices 1 10, 1 12. As illustrated by Figure 1 , the channel 150 is a frequency channel, and sub-channels 140 to 150 are frequency channels as well. In an embodiment, the channel 150 is 20 MHz wide and the number of sub-channels is 10, each being 2 Mhz wide. In another embodiment, the channel 150 is 40 MHz wide and the number of sub-channels is 8, each being 5 Mhz wide. In yet another embodiment, the sub-channels may have a different bandwidth, e.g. 10 MHz each. In an embodiment, a sub-channel is at most 10 MHz, and the frequency channel 150 comprises a plurality of such sub-channels. These are just examples. As mentioned above, the transmission band of a BSS contains the primary channel and zero or more secondary channels. The secondary channels may be used to increase data transfer capacity of a transmission opportunity (TXOP). The secondary channels may be called a secondary channel, a tertiary channel, a quaternary channel, etc. However, let us for the sake of simplicity use the secondary channel as the common term to refer also to the tertiary or quaternary channel, etc. The primary channel may be used for channel contention, and a TXOP may be gained after successful channel contention on the primary channel. Some IEEE 802.1 1 networks are based on carrier sense multiple access with collision avoidance (CSMA CA) for channel access. Some networks may employ enhanced distributed channel access (EDCA) which provides quality-of-service (QoS) enhancements to medium access control (MAC) layer. The QoS enhancements may be realized by providing a plurality of access categories (AC) for prioritizing frame transmissions. The access categories may comprise the following priority levels in the order of increasing priority: background (AC_BK), best effort (AC_BE), video streaming (AC_VI), and voice (AC_VO). A higher priority frame transmission may use a shorter contention window and a shorter arbitration inter-frame spacing (AIFS) that result in higher probability of gaining the TXOP. Furthermore, some networks may employ restricted access windows (RAW) where a reduced set of wireless devices of the wireless network may carry out channel contention. The access node may define the RAW and a group of wireless devices that are allowed to attempt the channel access within the RAW. Grouping allows partitioning of the wireless devices into groups and restricting channel access only to wireless devices belonging to a specified group at any given time period. The time period may be enabled by allocating slot duration and a number of slots in RAW access. The grouping may help to reduce contention by restricting access to the medium only to a subset of the wireless devices. The grouping may also reduce the signalling overhead.

The STA (or AP) may carry out a clear-channel assessment (CCA) procedure in order to determine whether the channel is free or busy. Upon detecting radio energy that exceeds a preset threshold on the channel, the STA may determine that the channel is busy and prevent the transmission. On the other hand, if the STA detects no radio energy exceeding the threshold on the channel during the determined time period, it may carry out the transmission. The STA may use a single threshold in the CCA procedure but, in some embodiments, a plurality of thresholds and frame detection are applied. Upon detecting a transmission on the channel, the STA may determine whether the on-going transmission is a frame header or frame payload portion. An example of the frame header is a physical layer convergence protocol (PLCP) header, while an example of the frame payload portion is a physical layer service data unit (PSDU). Then, the STA may determine a threshold for use with the detected transmission. For example, a first threshold may be applied to the frame header while a second, different threshold may be applied to the frame payload portion. The first threshold may be denoted by a carrier sensing header threshold, while the second threshold may be denoted by a carrier sensing data unit threshold. By default, the carrier sensing data unit threshold may be -62 decibels with respect to one milliwatt (dBm), while the carrier sensing header threshold may be -82 dBm. Accordingly, the STA may be more sensitive with respect to frame headers than with respect to frame payload portions. This ensures that the headers will less likely collide with other impending transmissions, while spatial reuse of the channel is encouraged for payload portions. According to another aspect, a channel may be considered busy if the STA is able to decode a PLCP header when a signal is detected with power level between -82dBm and -62dBm, and the channel may be considered busy if a signal with power level above -62dBm is detected even if the STA is not able to decode the PLCP header.

A virtual carrier sensing function is provided by the provision of a network allocation vector (NAV) which is used to reserve a channel for the duration of the TXOP. Most of the transmitted frames comprise a duration field which can be used to reserve the medium, or provide duration of the NAV protection, for the duration indicated by the value of the duration field. In practice, the NAV is a timer that indicates the amount of time the medium will be reserved. In a typical operation, the transmitting station (STA) will set the value of the duration field according to the time for which it expects to use the medium while all receiving STAs, except the intended receiver, update their NAV appropriately with the information in the duration field and count down from the NAV to zero before starting the channel contention. The virtual carrier sensing function indicates that the medium is busy when NAV is nonzero and idle when NAV is zero. The NAV may be set to protect frame transmissions. The communication devices obtain the NAV on the primary channel of the BSS.

With respect to the definition of the wireless network in the context of the present description, the wireless network may comprise a single BSS or a plurality of BSSs. According to a viewpoint, the wireless network may comprise a plurality of BSSs that have the same service set identifier (SSID) the same roaming identifier, and/or the same roaming partnership. A ternninal device 1 10, 1 12 may establish a connection with any one of the access nodes it has detected to provide a wireless connection within the neighbourhood of the terminal device. The connection establishment may include authentication in which an identity of the terminal device is established in the access node. The authentication may comprise exchanging an encryption key used in the BSS. After the authentication, the access node and the terminal device may carry out association in which the terminal device is fully registered in the BSS, e.g. by providing the terminal device with an association identifier (AID). It should be noted that in other systems terms authentication and association are not necessarily used and, therefore, the association of the terminal device to an access node should be understood broadly as establishing a connection between the terminal device and the access node such that the terminal device is in a connected state with respect to the access node and scanning for downlink frame transmissions from the access node and its own buffers for uplink frame transmissions.

The terminal devices 100, 1 12 may discover the access node 100 through a network discovery process. IEEE 802.1 1 ai task group defines principles for fast initial link setup (FILS). One aspect of the principles is to enable faster and more precise AP and network discovery. Some principles may relate to passive scanning in which a scanning device, e.g. a STA, passively scans channels for any beacon, management, or advertisement frames. Other principles may relate to active scanning in which the scanning device actively transmits a scanning request message, e.g. a Probe Request message or a generic advertisement service (GAS) request, in order to query for present APs or networks. The probe request may also set some conditions that a responding device should fulfil in order to respond to the probe request. In some embodiments, the scanning device may be called a requesting device or a requesting apparatus. Responding devices may transmit scanning response messages, e.g. Probe Response messages, in response to the scanning request message, wherein the scanning response message may contain information on the responding device, its network, and other networks. Embodiments of the scanning enhancements described herein encompass the network discovery signalling, probe request-response processes, as well as GAS request-response processes.

In many communication scenarios, the wireless network of the access node 100 is not operating alone in a given geographical area. An overlapping wireless network managed by another access node 102 may have a coverage area that overlaps with the coverage area of the access node 100. The overlapping wireless network may comprise one or more terminal devices 1 14 that are within communication range of one or more of the devices 100, 1 10, 1 12 but do not necessarily communicate with them.

When using the channel structure of Figure 1 together with the CCA mechanism or a similar channel sensing mechanism, a narrowband transmission on a single sub-channel and/or on a minority of sub-channels of the frequency channel 150 may not generate a sufficient amount of radio energy to trigger the protection from other transmissions. A narrowband transmission on a sub-channel 140 generates less radio energy with the same transmission power than a wideband transmission on the whole channel 150 in the radio transmitter. This combined with attenuation in a radio channel may cause that a sensing device may not receive a sufficient amount of radio energy from the narrowband transmission and, as a consequence, it determines that the radio channel is free and transmits a packet that collides with the narrowband transmission. For example, the terminal device 1 14 operating in a wideband mode and measuring energy on the whole frequency channel 150 may not be capable of receiving a sufficient amount of energy from a single or a few simultaneous transmissions that in combination occupy only a subset of the sub-channels 140 to 150, e.g. a minority of the sub-channels 140 to 150. Therefore, the terminal device 1 14 may attempt channel access on the frequency channel 150 that would collide with the narrowband transmissions. On the other hand, if the simultaneous narrowband transmissions occupy all the sub-channels 140 to 150 or even a majority of the sub-channels, sufficient amount of radio energy may be generated such that the terminal device 1 14 refrains from the channel access. Similar problem may exist not only in overlapping network scenarios where the terminal device 1 14 measures the radio energy received from the devices 100, 1 10, 1 12 but also within a single wireless network.

An embodiment of the invention provides a protection mechanism to protect the narrowband packets transmitted on a sub-channel of the frequency channel, e.g. on a sub-channel 140 of the frequency channel 150. Figure 2 illustrates a flow diagram of a process according to such an embodiment. Referring to Figure 2, the process comprises in an access node such as the access node 100: determining to protect transmission of a first packet on a first sub-channel of a frequency channel (block 200) and, on the basis of said determining, causing transmission of a second packet on a second sub-channel of the frequency channel, wherein the second sub-channel is different from the first sub-channel, and wherein said transmission of the second packet is arranged to be carried out simultaneously with said transmission of the first packet. A technical effect is that the frequency channel 150 thus contains more radio energy than what the first packet could induce, which improves the probability that another node sensing the frequency channel determines the channel to be busy. Accordingly, the first packet, and/or one or more subsequent packets within the same transmission opportunity, may be more reliably received at a receiver.

In an embodiment, the second packet is transmitted by the access node. In an embodiment, the access node schedules another node to transmit the second packet. The other node may be different from a node that transmits the first packet. Accordingly, the access node may instruct the other node to protect narrowband transmission of the access node or yet another node.

Figures 3 and 4 illustrate time-frequency diagrams that demonstrate the protection affected by the second packet. A vertical axis represents frequency, wherein a frequency channel is divided into a plurality of sub-channels, e.g. as described above in connection with Figure 1 . A horizontal axis represents time.

Referring to Figure 3, the protection may be triggered after a determined number of unsuccessful transmission attempts of the first packet, e.g. a data packet 300. The data packet 300 may be a downlink data packet or an uplink data packet. In the embodiment where the data packet is an uplink data packet transmitted by a terminal device, the transmission of the data packet 300 may be preceded by transmission of a triggering frame from the access node to the terminal device. The triggering frame may trigger the uplink transmission of the data packet 300 in the terminal device. The triggering frame has been omitted from the Figures for the sake of simplicity and generality.

The transmission of the data packet 300 may be followed by a period in which an acknowledgment message ACK shall be transmitted in a case where the data packet is correctly received in a receiver, e.g. in the terminal device in a case of the downlink data packet. A timeout period may define a duration for which a transmitter, e.g. the access node in the case of the downlink data packet, shall wait before carrying out a retransmission of the data packet.

Upon a determined number of unsuccessful transmissions of the data packet 300 on the sub-channel, the access node may trigger the protected transmission mode in which a protection packet 308 or a protection signal is transmitted simultaneously with the data packet 300 but on a different sub-channel of the frequency channel.

In an embodiment, the protection packet 308 is transmitted such that at least one sub-channel is provided between the protection packet 308 and the data packet 300. The at least one sub-channel may be arranged to be free from any transmissions. This arrangement may reduce interference from sidelobes of the protection signal towards the data packet. Even though a packet is configured to be transmitted on a sub-channel, a radio signal carrying the packet may contain energy on adjacent sub-channels in the form of said sidelobes, thereby potentially interfering with signals on those adjacent sub-channels.

A minimum frequency separation between the first packet and the protection packet may be determined by an estimate of an amount of tolerable inter- sub-channel interference. The access node can decide the sub-channel separation according to some constraints on the interference towards the first packet. The access node may measure an interference level in the channel, e.g. by using the CCA function. According to the amount of external interference detected in the frequency channel or on the sub-channel, the access node may decide the required separation to maintain the interference towards the first packet tolerable. A higher interference level may cause a higher frequency separation while a lower interference level may cause a lower frequency separation between the first packet and the protection packet.

As described above, the protection message 308 may improve the probability of correct reception of the data packet 300 and result in transmission of the acknowledgment message 306 under the protected mode transmission of the data packet. The duration of the protection packet 308 may extend to protect not only the transmission of the data packet 300 but also the transmission of the acknowledgment message 306, as illustrated in Figure 3.

Figure 4 illustrates an embodiment using a scheduled transmission of the protection packet 308. The schedule of the protection packet 308 may be negotiated between the access node and the terminal device, and the schedule may be defined by using a target wake time (TWT) parameters used in the 802.1 1 network to specify a specific time. Referring to Figure 4, upon determining the need to use the protected transmission for the data packet 300, the access node and the terminal device may wait for the scheduled timing of the protection packet 308 and carry out the transfer of the data packet 300 while the protection packet 308 is being transmitted. In the embodiment of Figure 4, the need for the protected transmission is determined upon unsuccessful unprotected transmission of the data packet 300. The access node and the terminal device may have negotiated beforehand that the protected transmission shall be triggered upon a determined number of failed unprotected transmissions of the data packet 300. Accordingly, upon the determined number of failed unprotected transmissions of the data packet 300 has been detected in the terminal device, the terminal device may wait for the next scheduled protected transmission opportunity. The waiting period may be defined on the basis of the negotiated TWT. During the waiting, the terminal device may refrain from channel access. Similarly, the access node may wait for the scheduled transmission of the protection packet 308 and trigger the (re)transmission of the data packet such that the data packet 300 is transmitted simultaneously with the protection packet 308. As described above, in a case where the data packet 300 is an uplink data packet, the transmission of the data packet under the protection may be triggered by the access node by transmitting the triggering frame during or before the protection of the protection packet 308. For example, the access node may transmit a first protection packet simultaneously with the triggering frame and a second, different protection packet simultaneously with the first packet and, thus, protect the both transmissions. A single protection packet long enough to cover the both transmissions may be used in other embodiments. In an embodiment where the access node transmits the triggering frame under the protection, the protection may be created by the access node by setting a NAV on the frequency channel. The access node may set the NAV by transmitting a request-to-send (RTS), a clear-to- send (CTS), or a clear-to-send-to-self packet that triggers the NAV on the frequency channel. Any other mechanism for setting the NAV may be used in other embodiments.

Above, it is described that the uplink narrowband transmission may be initiated by the access node with the triggering frame. The access node may have gathered information on an uplink transmission buffer status of the terminal devices and, thus, know the terminal device(s) having uplink data ready for transmission. In another embodiment, the terminal device may initiate the uplink narrowband transmission. In such a case, the access node may trigger the protection upon receiving a physical layer header from the terminal device and upon identifying the transmission as the narrowband transmissions. As a consequence, the remaining part of the narrowband packet may be transmitted under the protection. As in Figures 3 and 4, the protection may be triggered after a determined number of erroneous receptions of the uplink narrowband packet, another criterion may be used as well, as described below. In another embodiment, the uplink transmission may be initiated by the terminal device by transmitting a narrowband RTS message. Upon receiving the RTS, the access node may transmit a CTS to grant the uplink channel access. The CTS may be a narrowband CTS transmitted on the same sub- channel as the narrowband RTS, for example. In another embodiment, the CTS is a wideband CTS transmitted on the whole frequency channel. In yet another embodiment, the access node may transmit a wideband CTS-to-self message and the narrowband CTS. The CTS-to-self may be used to trigger NAV on the whole frequency channel, while the narrowband CTS may clear the terminal device to transmit. In connection with the transmission of the CTS, the access node may start the transmission of the protection packet such that the subsequent uplink packet transmitted by the terminal device is under the protection of the protection packet. In yet another embodiment, the terminal device may transmit a trigger packet before the first packet carrying data, for example. Reception of the trigger packet from the terminal device in the access node may cause the access node to start the transmission of the protection packet. The first packet is thus protected by the protection packet. The terminal device may start the transmission after a determined time period after transmitting the trigger packet, e.g. a short inter-frame space (SIF)S of the 802.1 1 specifications.

In an embodiment, the second packet or the protection packet is dedicated for the protection and comprises a header 500 and, in some embodiments, pseudo payload content 502 that is artificially generated sequence or virtually any carrying no information value. In an embodiment, the sequence may be known to at least one recipient of the second packet. In such an embodiment, the contents of the second packet may be used as a pilot signal or a corresponding tool for channel measurements, channel equalization, interference cancellation, etc. Figure 5A illustrates such an embodiment. The protection packet may be addressed to no recipient or it may be addressed to a transmitter of the protection packet in this embodiment.

In another embodiment, the second packet or the protection packet is a data packet comprising the header and data payload content 504. The protection packet may in this embodiment be addressed to a node of the wireless network. The node may be other than the transmitter of the protection packet. Figure 5B illustrates this embodiment. The data packet may be scheduled with the addressed node before the transmission of the data packet.

Let us now describe some embodiments of block 200, i.e. some embodiments for determining the need for the protected transmission. Above, it was described that the need for the protected transmission may be determined upon a detecting a determined number of unsuccessful transmission attempts of a packet. The packet may be a data packet carrying data content or a control or management packet carrying control or management information, respectively. The control and management packets may contain no data payload. Referring to Figure 6 illustrating an embodiment of Figure 2, the determined number of unsuccessful transmission attempts may be detected in block 604 or 612. In block 604, the packet losses are monitored and a number of packet losses may trigger the protected transmission. In block 604, the number of packet losses associated with a certain node of the wireless network may be monitored, and/or the number of packet losses of narrowband transmissions may be monitored. A packet loss may be detected in the access node by not receiving an acknowledgement message to a transmitted packet, or by a failed decoding attempt of a received packet. A threshold in terms of the number of packet losses that triggers the protected transmission may be determined according to a design of the wireless network. The threshold may be fixed or adjustable. The packet losses may be determined by monitoring a number of failed reception attempts of a received packet, and/or by monitoring a number of triggering frame transmission that resulted in no reception of a subsequent uplink packet. In the latter case, it may be assumed that the terminal device transmitted the packet but the access node was not able to detect the packet.

In block 612, retransmissions of the first packet are monitored. If a certain number of retransmission attempts of the first packet are detected, the protected transmission for the first packet may be triggered. The number of retransmission attempts triggering the protected transmission may be one or higher than one.

Regarding the other criteria for triggering the protected transmission, block 600 represents an embodiment where the protected transmission is triggered by detection of an overlapping wireless network. When the access node detects presence of at least one wireless network at least partially on the same frequency channel used by the access node, the access node may trigger the protected transmission for narrowband packets transmitted in its wireless network. In another embodiment, the number of detected overlapping wireless networks that triggers the protected transmission is higher than one, e.g. two or three.

Block 602 represents a criterion where the protected transmission for the narrowband packets is configured in a static manner. Accordingly, upon detecting a configuration parameter configuring the protection for all narrowband packets or for narrowband packets associated with a certain terminal device or devices, or a subset of terminal devices in the wireless network, the access node may trigger the protected transmission. The configuration parameter may be set in a network planning phase, e.g. when it is known that the network will operate in a dense networking environment comprising overlapping networks. In another embodiment, the configuration parameter may be set per terminal device, e.g. during an association phase of each terminal device.

Block 606 represents an embodiment where the protected transmission is set on the basis of priority of contents of the first packet. For example, high priority contents such as certain control or management packets may always be transmitted under the protection of the protection packet. Low priority contents such as data may be transmitted in an unprotected mode, or the protection may be triggered according to another embodiment of block 200. This embodiment is well applicable to the scheduled protection packet. A transmitting node may synchronize the transmission of the high priority contents with the scheduling of the protection packets such that the high priority contents are transmitted under the protection of the protection packet. Regarding the priority, application level priority may also be considered. For example, any critical or emergency data may be categorized as high priority data that should be transmitted under the protection, while another type of data may be transmitted, at least initially, without the protection.

Block 608 represents an embodiment where the protected transmission is triggered on the basis of interference measurements. Upon detecting, on the basis of the measurements, that interference level on the frequency channel is higher than a determined interference threshold, the access node may trigger the protected transmission for the first packet. When the interference level is below the threshold, the access node may choose not to carry out the protected transmission or it may trigger the protected transmission according to another embodiment of block 200. As a metric representing the interference level, the CCA function may be used a signal-to-interference-plus-noise power (SINR) ratio or a corresponding metric may be used.

Block 610 represents an embodiment where the protected transmission is set on the basis of communication quality between the access node and another node, e.g. a terminal device. The communication quality may be measured by the access node, or the access node may acquire a measurement value from the other node. A metric representing the communication quality may be a metric measured from a signal transmitted between the access node and the other node, e.g. a path loss, a received signal strength indicator (RSSI) or a reference signal reception power (RSRP). Another metric representing the communication quality may be a distance measured from locations of the nodes, e.g. from location coordinates of the nodes. A higher distance may represent lower communication quality. Upon detecting communication quality below a determined quality threshold, the access node may trigger the protected transmission. From another perspective, a distance threshold may be used. Metrics such as the RSSI, RSRP, or the path loss may equally represent distance between the nodes. If the metric represents a distance above a determined distance threshold, the protected transmission may be triggered. It should be appreciated that one, a plurality, or even all of the above- described criteria 600 to 612 may be in parallel use. Other criteria may be used additionally, or alternatively.

Let us now return to the above-described CCA or a similar collision avoidance function used in the wireless network. The collision avoidance function such as the CCA is based on measuring radio energy on the frequency channel. As described above, the narrowband transmission on a sub-channel of the frequency channel may not carry a sufficient amount of radio energy to cause a channel- sensing node to back off from channel access. With the help of the protection packet, the amount of radio energy in on the frequency channel may be increased, thus providing the protection. Figure 7 illustrates an embodiment for determining an amount of radio energy carried in the protection packet. A process of Figure 7 illustrates block 700 in which transmission power of the protection packet is determined. The transmission power is a transmission parameter that directly affects the amount of radio energy carried by the protection packet. The higher the transmission power is, the more radio energy is carried by the protection packet.

In an embodiment, the protection packet is configured to carry more radio energy than the first packet that is being protected. This effect may be realized by configuring a higher transmission power for the protection packet than for the first packet. In another embodiment, the effect may be realized by configuring a higher transmission power per unit frequency for the protection packet than for the first packet. In yet another embodiment, the effect may be realized by configuring a higher bandwidth for the protection packet than for the first packet while transmitting the protection packet with the same or even lower transmission power than the transmission power of the first packet.

Referring now to Figure 7, block 700 may be processed after block 200. Block 700 may be understood to estimate a transmission power required to provide sufficient protection for the first packet and to select, on the basis of said estimation amongst a plurality of available transmission powers, the transmission power of the protection packet.

In block 702 representing an embodiment of a criterion affecting the selection of the transmission power, an interference level is measured and used in the selection of the transmission power. The interference level affects the correct reception of the packets and, upon detecting high interference level, a high-power protection signal may be used to improve the protection. There may be provided a mapping table mapping each measured interference level to a transmission power value. The interference level may be measured as described above in connection with block 608.

Block 704 represents a criterion for selecting the transmission power on the basis of the connection or communication quality between the access node and the other node with which the first packet is transferred. The communication quality may be measured as described above in connection with block 610. A corresponding measurement value or a metric may be mapped to a transmission power value such that a lower communication quality is mapped to a higher transmission power.

Block 706 represents an embodiment where the transmission power is determined on the basis of a bandwidth of the first packet and/or a bandwidth of the protection packet. A higher bandwidth of the first packet may be considered to provide a higher amount of radio energy and, thus, a lower transmission power may be selected for the protection packet. A lower bandwidth of the first packet may be considered to provide a lower amount of radio energy and, thus, a higher transmission power may be selected for the protection packet. The transmission power of the protection packet may thus be inversely proportional to the bandwidth of the first packet. With respect to the embodiment determining the transmission power on the basis of the bandwidth of the protection packet, the bandwidth of the protection packet may first be determined, for example as described below. Then, the bandwidth may be mapped to a transmission power on the basis of a mapping table mapping different bandwidths of the protection packet to different transmission powers. The transmission power of the protection packet may be inversely proportional to the bandwidth of the protection packet. The bandwidth of the protection packet (or any other signal) is another factor affecting the amount of radio energy on the frequency channel. The transmission power together with the bandwidth may define the amount of radio energy.

A further or alternative criterion may be a number of sub-bands on the frequency channel. The number of sub-bands may set a criterion for the amount of radio energy required to trigger the protection effect. If the number of sub-bands is high, a higher transmission power is needed for a protection packet transmitted only on a single sub-channel. If the number of sub-bands is low, a low transmission power is needed for a protection packet transmitted on a single sub-channel. If the protection packet is transmitted simultaneously on a plurality of sub-channels, the total transmission power of the transmitted protection packets may be reduced to cause the protection effect, as described above. In general, the access node may be configured to estimate the transmission power for the protection packet such that the protection reaches even edges of a coverage area of the access node. Suitable transmission powers for the different bandwidths of the protection packet may be preconfigured to the access node, e.g. on the basis of measurements and testing.

As described above, the transmission power of the protection packet may be adjustable. Upon determining the transmission power for the protection packet, the process may proceed to block 202. The access node may assign the transmission power for the protection packet transmitted by itself, naturally, but it may also carry out transmission power control of another node and select the transmission power for a protection packet transmitted by the other node.

As described above, the conditions for triggering the protected transmission may be configured in the access node and in the other node such as the terminal device. In connection with Figure 4, the scheduled protection interval where the protection packet is transmitted was also described. Figure 8 illustrates a signalling diagram of an embodiment applied to the scheduled protection interval. Referring to Figure 8, the access node 100 may indicate the protection intervals to the terminal device(s) of the wireless network. Block 800 may comprise transmitting, by the access node 100, a message carrying the indication of transmission opportunities (TXOPs) that are protected by the scheduled protection packet. The message may be a broadcast message, a multicast message, a unicast message, a beacon message, or a CTS message, for example. In a case of unicast or multicast message addressed to a determined terminal device, message may be transmitted after the terminal device has been authenticated and/or associated to the access node. Upon receiving the message in step 800, the terminal device 1 10 may store the information on the protected TXOPs.

The procedure of Figure 8 follows that of Figure 4 in the sense that the protected transmission is triggered upon failed transmission attempts of the first packet. In step 802, the access node triggers uplink transmission of the first packet by transmitting a triggering frame to the terminal device 1 10. The triggering frame may be transmitted after the access node has detected that the terminal device 1 10 has uplink data ready for transmission. This detection may be based on polling the terminal device 1 10 for the presence of the uplink data. However, the uplink transmission may be initiated by the terminal device, as described above, in which case the triggering frame may be omitted. Upon receiving the triggering frame, the terminal device accesses the channel and carries out the transmission of the first packet on the sub-channel without protection (step 804). Meanwhile, the terminal device 1 14 operating in the wideband mode carries out the CCA procedure and measures radio energy from the frequency channel in preparation for channel access (block 820). Upon measuring the amount of radio energy below a threshold, the terminal device 1 14 may initiate a wideband transmission on the frequency channel and, as a consequence, on the sub-channel. As a consequence, the wideband transmission collides with the transmission of the first packet. In block 806, the access node detects erroneous reception or no reception of the first packet and, as a consequence, triggers a new uplink transmission (steps 802 and 804 below block 806). Again, the terminal device 1 14 may cause a colliding wideband transmission because of being incapable of detecting a sufficient amount of radio energy in the unprotected transmission alone. Upon the second failed reception of the first packet in the access node, the access node may determine to use the protected transmission and, as a consequence, the access node and the terminal device wait for the next scheduled protection interval in block 808. At the timing of the scheduled protection interval, the access node 100 triggers the next uplink transmission attempt of the first packet and causes the transmission of the protection packet (step 810). The next uplink transmission of the first packet is thus carried out in step 812 while the protection packet is being transmitted. As a consequence, more radio energy is now present on the frequency channel which enables the terminal device 1 14 to detect the ongoing transmission and to refrain from transmitting the wideband transmission. Therefore, the probability for correct reception of the first packet in block 814 is improved.

The use of the protection may be triggered according to any one of the embodiments described above in connection with Figure 6.

Figure 9 illustrates yet another embodiment where the protection packet 308 carries data. The data packet functioning also as the protection packet may be addressed to a wideband node operating on the whole bandwidth of the frequency channel or to a narrowband node operating on a sub-channel of the frequency channel. Depending on the node with which the data packet is transferred, the access node may schedule a narrowband transmission on a sub-band or a wideband transmission on a plurality sub-channels of the frequency channel. With respect to the narrowband transmission, the at least one sub-channel may be arranged between the sub-channels of the data packet 300 and the protection packet 308. In a case where the access node scheduled a plurality of simultaneous protection packets on different sub-channels, similar sub-channel separation may be configured by the access node. With respect to the wideband transmission, the access node may determine the bandwidth available to the data packet functioning as the protection packet 308. The bandwidth may be determined on the basis of the sub-channel occupied by the data packet 300 and the needed sub-band separation. The bandwidth may be used for transmitting data 900 while remaining bandwidth may be padded by a fixed known signal 902 that does not generate sidelobes that would interfere with the data packet 300, e.g. a sequence of zeros, ones or alternating zeros and ones. The transmitted signals may be orthogonal frequency- division multiplexing (OFDM) signals based on multi-carrier transmission so such a solution may be implemented in a straightforward manner. The padded part 902 may be arranged between the data part 900 and the protected data packet 300 in the frequency domain. A frequency separation may be arranged even between the padded part 902 and the data packet 300. The padded sub-carriers of the protection packet 308 may be indicated to a receiving wideband node such that the receiving wideband node is able to extract only data symbols and discard the padded symbols. In some embodiments, the padded symbols may be used as a pilot signal for channel measurements, for example. In such a case, the receiving node may be made aware of the sequence of the padded symbols.

Figure 10 illustrates an embodiment of a structure of the above- mentioned functionalities of the apparatus executing the process of Figure 2 or any one of the embodiments performed by the access node 100. The apparatus may be the access node 100. The apparatus may comply with specifications of an IEEE 802.1 1 network and/or another wireless network. The apparatus may be defined as a cognitive radio apparatus capable of adapting its operation to a changing radio environment, e.g. to changes in parameters of another system on the same frequency band. The apparatus may be or may be comprised in a computer (PC), a laptop, a tablet computer, a cellular phone, a palm computer, or any other apparatus provided with radio communication capability. In another embodiment, the apparatus carrying out the above-described functionalities is comprised in such a device, e.g. the apparatus may comprise a circuitry, e.g. a chip, a chipset, a processor, a micro controller, or a combination of such circuitries in any one of the above-described devices. The apparatus may be an electronic device comprising electronic circuitries for realizing the embodiments of the present invention.

Referring to Figure 10, the apparatus may comprise a communication controller circuitry 10 configured to control wireless communications in the apparatus. The communication controller circuitry 10 may configure the establishment, operation, and termination of connections or associations in the apparatus, as described above. The communication control circuitry 10 may control management of one or more wireless networks. The communication controller circuitry 10 may comprise a control part 12 handling control signalling communication with respect to transmission, reception, and extraction of control or management frames including beacon messages, request messages, response messages, scanning or probing messages, discovery messages, scheduling messages, request-to-send (RTS) messages, and clear-to-send (CTS) messages. The control part 12 may also carry out processing of headers of data frames. The communication controller circuitry 10 may further comprise a data part 16 that handles transmission and reception of payload data when the apparatus is associated to one or more other apparatuses.

The communication control circuitry 10 may further comprise a narrowband controller 14 configured to control narrowband operations in the apparatus. In an embodiment, the apparatus may support narrowband operation and wideband operation in which case the apparatus may comprise a wideband controller (not shown). The wideband operation may refer to frame transmissions on the whole frequency channel or on a plurality of frequency channels. The narrowband operation may refer to transmission of frames on a sub-channel of a frequency channel. The wideband controller may control transmissions on at least one channel of the wireless network, e.g. on the primary channel. The wideband controller may also control transmissions on a plurality of channels of the wireless network, e.g. on the primary channel and on one or more secondary channels. The narrowband controller 14 may control the operation on one or more sub-channels of a channel of the wireless network.

The channel may be considered as a channel logically identified as a channel in the wireless network. A channel may be associated with a channel identifier or a channel index identifiable via signalling in the wireless network. According to one viewpoint, a sub-carrier of a multi-carrier signal may be excluded from the definition of the sub-channel.

The narrowband controller 14 may comprise a narrowband (NB) transmission (TX) protection controller 18 configured to monitor for the need for protecting narrowband transmissions in the wireless network of the access node. The monitoring may be based on one or more of the above-described embodiments, e.g. embodiments of Figure 6. The narrowband transmission protection controller 18 may be configured to carry out the embodiment of Figure 2 or any one of its embodiments described above. The narrowband transmission protection controller 18 may thus configure the transmission of the second packet functioning as the protection packet 308.

The circuitries 12 to 18 of the communication controller circuitry 10 may be carried out by the one or more physical or electronic circuitries or processors. In practice, the different circuitries may be realized by different computer program modules. Depending on the specifications and the design of the apparatus, the apparatus may comprise some of the circuitries 12 to 18 or all of them.

The apparatus may further comprise a memory 20 that stores computer programs (software) 22 configuring the apparatus to perform the above-described functionalities. The memory 20 may also store a configuration database 24 comprising communication parameters and other information needed for the wireless communications, e.g. acquired network parameters of the wireless network, acquired performance characteristics of the wireless network, etc. In some embodiments, the narrowband transmission protection controller 18 may determine the need for the protection on the basis of measurement information stored in the configuration database.

The apparatus may further comprise radio interface components 26 providing the apparatus with radio communication capability within one or more wireless networks. The radio interface components 26 may comprise standard well- known components such as an amplifier, filter, frequency-converter, (de)modulator, and encoder/decoder circuitries and one or more antennas. The apparatus may in some embodiments further comprise a user interface enabling interaction with the user of the communication device. The user interface may comprise a display, a keypad or a keyboard, a loudspeaker, etc.

In an embodiment, the apparatus comprises at least one processor 10 and at least one memory 20 including a computer program code 22, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to carry out the functionalities of the access node according to any one of the embodiments of Figures 2 to 9. According to an aspect, when the at least one processor 10 executes the computer program code, the computer program code causes the apparatus to carry out the functionalities according to any one of the embodiments of Figures 2 to 9. According to another embodiment, the apparatus comprises the at least one processor 10 and at least one memory 20 including a computer program code 22, wherein the at least one processor 10 and the computer program code 22 perform the at least some of the functionalities of the access node according to any one of the embodiments of Figures 2 to 9. Accordingly, the at least one processor, the memory, and the computer program code form processing means for carrying out embodiments of the present invention in the access node. According to yet another embodiment, the apparatus carrying out the embodiments of the invention in the access node comprises a circuitry including at least one processor 10 and at least one memory 20 including computer program code 22. When activated, the circuitry causes the apparatus to perform the at least some of the functionalities of the access node according to any one of the embodiments of Figures 2 to 9.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analogue and/or digital circuitry, and (b) to combinations of circuits and software (and/or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of 'circuitry' applies to all uses of this term in this application. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a wireless device.

The processes or methods described in connection with Figures 2 to 9 may also be carried out in the form of a computer process defined by a computer program. The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in a transitory or a non-transitory carrier, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital processing unit or it may be distributed amongst a number of processing units.

The present invention is applicable to wireless networks defined above but also to other suitable wireless communication systems. The protocols used, the specifications of wireless networks, their network elements and terminals, develop rapidly. Such development may require extra changes to the described embodiments. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1 . A method for an access node of a wireless network, comprising: determining, by an apparatus, to protect transmission of a first packet on a first sub-channel of a frequency channel; causing, by the apparatus on the basis of said determining, transmission of a second packet on a second sub-channel of the frequency channel, wherein the second sub-channel is different from the first sub-channel, and wherein said transmission of the second packet is arranged to be carried out simultaneously with said transmission of the first packet.

2. The method of claim 1 , wherein at least one sub-channel is arranged between the first sub-channel and the second sub-channel.

3. The method of claim 1 or 2, wherein said determining to protect the transmission of the first packet is based on at least one criterion of the following criteria: detecting presence of at least one other wireless network operating on a frequency channel overlapping at least partially with said frequency channel, detecting a configuration parameter mandating the apparatus to protect the transmission of the first packet, detecting a determined number of packet losses, detecting a determined number of erroneous packet receptions, detecting that the transmission of the first packet is a retransmission attempt of the first packet, detecting high importance of contents of the first packet, detecting a determined number of lost acknowledgment messages, detecting that a measured interference level exceeds an interference threshold, and detecting that a distance between the apparatus and another node exceeds a distance threshold.

4. The method of any preceding claim, wherein the second packet is a dedicated protection packet carrying no data.

5. The method of any preceding claim 1 to 3, wherein the second packet carries data.

6. The method of any preceding claim, wherein a transmission power of the second packet is based on estimating a transmission power required to provide sufficient protection for the first packet and, selecting, on the basis of said estimation amongst a plurality of available transmission powers, said transmission power of the second packet.

7. The method of any preceding claim, wherein a bandwidth of the frequency channel is 20 Megahertz, and wherein a bandwidth of the first sub-channel is at most 10 Megahertz.

8. The method of any preceding claim, wherein the access node transmits the first packet and the second packet.

9. The method of any preceding claim 1 to 7, wherein the access node receives the first packet and transmits the second packet.

10. The method of any preceding claim 1 to 7, wherein the access node schedules another node to transmit the second packet.

1 1 . The method of any preceding claim, wherein a transmission power of the second packet is higher than a transmission power of the first packet.

12. The method of claim 1 1 , wherein the transmission power of the second packet is dependent on a number of sub-channels on the frequency channel.

13. The method of any preceding claim, wherein a bandwidth of the second packet is different from a bandwidth of the first packet.

14. The method of any preceding claim, wherein the first packet and the second packet together occupy less than a total bandwidth of the frequency channel, the method further comprising configuring, by the apparatus, no other transmissions simultaneous to the first packet and the second packet.

15. The method of any preceding claim, wherein the apparatus comprises the access node.

16. An apparatus for an access node of a wireless network, the apparatus comprising:

at least one processor; and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to: determine to protect transmission of a first packet on a first sub-channel of a frequency channel; cause, on the basis of said determining, transmission of a second packet on a second sub-channel of the frequency channel, wherein the second sub- channel is different from the first sub-channel, and wherein said transmission of the second packet is arranged to be carried out simultaneously with said transmission of the first packet.

17. The apparatus of claim 16, wherein the at least one memory and the computer program code are configured, with the at least one processor, to arrange at least one sub-channel between the first sub-channel and the second sub-channel.

18. The apparatus of claim 16 or 17, wherein the at least one memory and the computer program code are configured, with the at least one processor, to base said determining to protect the transmission of the first packet on at least one criterion of the following criteria: detecting presence of at least one other wireless network operating on a frequency channel overlapping at least partially with said frequency channel, detecting a configuration parameter mandating the apparatus to protect the transmission of the first packet, detecting a determined number of packet losses, detecting a determined number of erroneous packet receptions, detecting that the transmission of the first packet is a retransmission attempt of the first packet, detecting high importance of contents of the first packet, detecting a determined number of lost acknowledgment messages, detecting that a measured interference level exceeds an interference threshold, and detecting that a distance between the apparatus and another node exceeds a distance threshold.

19. The apparatus of any preceding claim 16 to 18, wherein the second packet is a dedicated protection packet carrying no data.

20. The apparatus of any preceding claim 16 to 18, wherein the second packet carries data.

21 . The apparatus of any preceding claim 16 to 20, wherein the at least one memory and the computer program code are configured, with the at least one processor, to determine a transmission power of the second packet based on an estimate of a transmission power required to provide sufficient protection for the first packet and to select, on the basis of said estimate amongst a plurality of available transmission powers, said transmission power of the second packet.

22. The apparatus of any preceding claim 16 to 21 , wherein a bandwidth of the frequency channel is 20 Megahertz, and wherein a bandwidth of the first subchannel is at most 10 Megahertz.

23. The apparatus of any preceding claim 16 to 22, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the access node to transmit the first packet and the second packet.

24. The apparatus of any preceding claim 16 to 22, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the access node to receive the first packet and to transmit the second packet.

25. The apparatus of any preceding claim 16 to 22, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the access node to schedule another node to transmit the second packet.

26. The apparatus of any preceding claim 16 to 25, wherein a transmission power of the second packet is higher than a transmission power of the first packet.

27. The apparatus of claim 26, wherein the at least one memory and the computer program code are configured, with the at least one processor, to select the transmission power of the second packet on a basis of a number of sub-channels on the frequency channel.

28. The apparatus of any preceding claim 16 to 27, wherein a bandwidth of the second packet is different from a bandwidth of the first packet.

29. The apparatus of any preceding claim 16 to 28, wherein the first packet and the second packet together occupy less than a total bandwidth of the frequency channel, and wherein the at least one memory and the computer program code are configured, with the at least one processor, to configure no other transmissions simultaneous to the first packet and the second packet.

30. The apparatus of any preceding claim 16 to 29, wherein the apparatus comprises the access node.

31 . The apparatus of any preceding claim 16 to 30, further comprising a communication interface providing the apparatus with radio communication capability.

32. An apparatus comprising means for carrying out all the steps of the method of any preceding claim 1 to 15.

33. A computer program product embodied on a distribution medium readable by an apparatus and comprising program instructions which, when loaded into the apparatus, execute a computer process comprising all the steps of the method according to any preceding claim 1 to 15.