Field

The invention relates to the field of wireless communications and, particularly to negotiating a channel change in a wireless network. Background

Some wireless networks may support operation on multiple communication channels but employ only a subset of channels at a time. A channel may be understood as a frequency channel, for example. Sometimes, change of an operating channel may be reasonable in terms of performance. Brief description

The invention is defined by the independent claims.

Embodiments of the invention are defined in the 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 a wireless communication scenario to which embodiments of the invention may be applied;

Figures 2A and 2B illustrate flow diagrams of processes for changing aligning operating channels of access nodes associated with a terminal device according to some embodiments of the invention;

Figure 3 illustrates a signalling diagram of changing an operating channel of an access node involved in a multipath connection according to an embodiment of the invention;

Figure 4 illustrates a flow diagram of a process for attempting to find a common operating channel for multiple access nodes according to an embodiment of the invention;

Figure 5 illustrates a signalling diagram of a procedure for changing an operating channel of an access node and considering conditions for reverting to the original operating channel according to an embodiment of the invention; and

Figures 6 and 7 illustrate block diagrams of apparatuses according to some embodiments of the invention. Description of embodiments

The following embodiments are exemplary. 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 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 access points (AP) 100 and a plurality of terminal devices (STA) 104, 106. The APs 100, 102 may be stationary access points. A general term used in this specification and encompassing both the APs and STAs is a wireless apparatus. At least one of the terminal devices 106 may have a functionality of an AP as well. Therefore, a common term encompassing both the stationary APs 100, 102 and mobile APs 106 is an access node. An access node 100, 102, 106 may be associated with a basic service set (BSS) which is a basic building block of an IEEE 802.1 1 wireless local area network (WLAN). Each access node 100, 102, 106 may represent a different BSS. The most common BSS type is an infrastructure BSS that includes a single access node together with all STAs associated with the AP. The access node may provide access to other networks, e.g. the Internet 1 10. In another embodiment, the BSSs may be connected with each other by a distribution system (DS) to form an extended service set (ESS). An independent BSS (IBSS) is formed by an ad hoc network of terminal devices without a stationary controlling access point. While embodiments of the invention are described in the context of the above- described topologies of IEEE 802.1 1 , it should be appreciated that these or other embodiments of the invention may be applicable to networks based on other specifications, e.g. WiMAX (Worldwide Interoperability for Microwave Access), UMTS LTE (Long-term Evolution for Universal Mobile Telecommunication System), mobile ad hoc networks (MANET), mesh networks, and other networks having cognitive radio features, e.g. transmission medium sensing features and adaptive capability to coexist with radio access networks based on different specifications and/or standards. Some embodiments may be applicable to networks having features under development by other IEEE task groups, e.g. 802.19 task group 1 (TG1 ).

The different access nodes 100, 102, 106 may operate at least partly on different channels, e.g. on different frequency channels. 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 η is that the primary and secondary channels are adjacent. The 802.1 1 η 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 task group 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. Different BSSs may employ different primary channels.

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.

As described above, the BSS may be represented by the access node and one or more terminal devices connected to the access node. A terminal device 102 to 1 14 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.

Embodiments described herein are applicable to a multipath scenario in which a terminal device 104 operates a plurality of parallel associations to different access nodes 100, 102, 106. The terminal device 104 may utilize the multipath scenario to provide a multipath connection to a network server or, in general, a network device via multiple different access nodes. The multipath connection may be a transport or network level connection between the terminal device 104 and the network device, and it may comprise at least two parallel radio links through different access nodes 100, 102, 106. The use of the parallel radio links may be used in order to improve data throughput. The increase in throughput may be realized with the additional capacity in the radio interface and in the backbone link between each access node and the network device to which the multipath connection is established. As a consequence, different data may be routed through different radio links and backbones between the terminal device and the network device. Such a multipath connection is supported on higher protocol layers, e.g. by a multipath real time protocol, multipath transport control protocol (TCP) and multipath universal datagram protocol (UDP) defined within Internet Engineering Task Force (IETF). IEEE 802.1 1 (WLAN/Wi-Fi) radio is one of the main candidate radios to be used with the multipath protocols. The multipath connection may be employed for an application executed in the terminal device, and the application itself may be unaware of whether or not the connection is the multipath connection. Similarly, if the application transmits and receives data from multiple sources through separate TCP sessions, the terminal may allocate different TCP sessions to different links and hide the complexity by using a protocol similar to the multipath TCP. The parallel associations may, however, be used for other purposes as well.

The WLAN radio may be enabled to associate / establish links with many access nodes. Use of multiple links is advantageous, if the associated access nodes are capable of transmitting traffic efficiently over the air interface but backbone links of the access nodes used to connect the access nodes to the Internet have a low throughput, e.g. an ADSL (asynchronous digital subscriber line) modem. In these cases, operating with multiple APs may increase the total throughput experienced by the terminal device.

When the terminal device is in an active mode with an access node, the access node may transmit data packets to the terminal device as soon as they are received at the access node. The TXOP obtaining (CSMA/CA) may cause a random access delay. The access node may also cause some delay when preparing the packets to an appropriate transmission format, e.g. when performing frame aggregation to minimize the used air transmission time and reduce signalling overhead. For a terminal device in a power save mode, the access node may not be able to transmit the data packets to the terminal device without an additional delay caused by hibernation of the terminal device. The access node may set the packets to a sleep buffer and deliver them to the terminal device during a service period triggered by the terminal device when it powers up after the hibernation.

With respect to the definition of the power-save mode, a terminal device operating in the power-save mode may be considered as hibernating or dozing. For example, the terminal device in the power-save mode may have shut down at least some of its transceiver circuitries. According to another point of view, the terminal device is not able to communicate with the access node in the power-save mode. When the terminal device awakes from the power-save mode, it powers up its transceiver circuitries and is able to communicate with the access node. The terminal device may employ the power-save mode to reduce its functions, to reduce power consumption, and to prolong battery lifetime. When the terminal device uses a multipath protocol with access nodes having different operating channels, the terminal device may operate on a single channel at a time, when not hibernating, so it may be considered to hibernate or, in other words, operate in a power save mode towards the other access nodes.

When using the multipath protocol via different access nodes, the access nodes may operate on the same channel or on different channels. When they operate on the different channels, the terminal device needs to operate on different channels with different access nodes. An embodiment of the invention provides a procedure for the terminal device to try to arrange the access nodes to operate on the same channel.

Figures 2A and 2B illustrate embodiments of such a method. Figure 2A illustrates a flow diagram of the method from the viewpoint of the terminal device, while the method of Figure 2B illustrates a flow diagram of the method from the viewpoint of the access node. However, it should be appreciated that the concept of this embodiment may be realized in networks where there are no specific terminal devices or access nodes. Therefore, the description of this embodiment encompasses communication between two apparatuses. The respective methods may be carried out as computer processes in the respective apparatuses, each 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 cause the apparatus to carry out the respective method.

Referring to Figure 2A, an apparatus creates a first radio link with a first access node operating on a first channel in block 200. In block 202, the apparatus determines to utilize the multipath connection and to create a second, parallel radio link. The reason for using the multipath connection may be an attempt to increase data throughput. In block 204, the apparatus determines a second access node operating on a second channel different from the first channel. In block 206, by the apparatus causes transmission of a channel change request message to at least one of the first access node and the second access node. The apparatus may select the access node to which to transmit the channel change request message according to a determined procedure, e.g. one of the embodiments described below. The channel change request message requests the access node to change its operating channel. In block 208, the apparatus processes a channel change response message received from the access node to which the channel change request was transmitted. The channel change response message indicates whether or not the request to change the operating channel was accepted by the access node.

The parallel use of the radio links may be understood such that the apparatus has concurrently the first radio link to the first access node and the second radio link to the second access node. The apparatus may carry out the actual data transfer concurrently such that it transfers simultaneously data over both radio links, or it may transfer data alternately such that data is transferred only over one of the links at a time.

In an embodiment, the apparatus may be configured to transmit the channel change request message after authenticating with the second access node.

Referring to Figure 2B, an apparatus receives a channel change request message requesting the apparatus to change to a first channel from a second channel on which the apparatus currently operates (block 210). In block 212, the apparatus determines whether or not to change an operating channel from the second channel to the first channel. In block 214, the apparatus causes transmission of a channel change response message to the device from which the channel change request was received. As described above, the channel change response message indicates whether or not the apparatus has accepted the request to change to the first channel. Upon determining to change the operating channel in the apparatus, the apparatus may cause change of the operating channel from the second channel to the first channel.

This embodiment provides a system where the terminal device may request an access node to change its operating channel. The terminal device may attempt to bring the access nodes of the multipath connection to a common channel in order to improve the performance of the terminal device. The terminal device may request an access node to change the channel before it has associated to the access node and/or after the association has been made. In the first case, the terminal device may choose whether or not to associate to the access node on the basis of contents of the channel change response message. If the access node rejects the channel change, the terminal device may choose not to associate to the access node and search for another access node.

When the access nodes change their operating channels based on the channel change requests from the terminal devices, the configurability of the network and the terminal throughput may be improved. When the terminal device needs not to change the channel to communicate with different access nodes, the overhead in service period handling and channel switch are reduced. This may decrease battery consumption, increase throughput, and decrease complexity for multi-access-node switching algorithms. In some hidden node scenarios, the terminal devices may have better knowledge on hidden nodes and, in such scenarios, hidden node problems may be reduced or even eliminated.

Let us now consider to procedure of Figures 2A and 2B in greater detail with reference to a signalling diagram of Figure 3. The terminal device associates to the first access node and the second access node in steps 300 and 302, respectively. Upon detecting that the first access node and the second access node operate on different channels, e.g. they have different primary channels, the terminal device may launch block 304 in which it determines a common operating channel for the access nodes. The terminal device may use the current operating channels of the access nodes as a starting point. The terminal device may determine, for example, which one of first access node and the second access node has less active associations currently. The access node with the lower number of served terminal devices is a more promising candidate for changing its operating channel. The terminal device may determine the number of associated terminal devices from frames transmitted by the access node, e.g. from the number of different recipient unicast addresses in the detected frames. Accordingly, the operating channel of the access node with a higher number of associated terminal devices may be selected as the common channel. In another embodiment, the terminal device scans the operating channels of the first access node and the second access node and selects as the common channel the operating channel having less congestion. In yet another embodiment, the terminal device considers both the number of associated terminal device and the channel congestion jointly, and selects the common operating channel on the basis of the both criteria. For example, if one of the access nodes has no associated terminal devices at the moment, the channel of the other access node may be selected as the common channel, and if both access nodes have associated terminal devices, the channel congestion may be used as the criterion. Other methods of using both the number of associated terminal devices and the channel congestion are equally possible. Other criteria may comprise at least some of the following: amount of data and type of data (voice over Internet Protocol, Internet traffic, real-time traffic, non-real-time traffic) that the access node transmits with other terminal devices; performance of the access node, e.g. the terminal device may select an access node that has a poor or the poorest performance or a low or the lowest output; an operating mode of the access nodes, e.g. an access node operating Wi-Fi direct mode preferred to change the channel over other access nodes not supporting the Wi-Fi direct mode.

Upon determining the common operating channel, the terminal device transmits the channel change request message to the access node that does not yet operate on the determined common channel (step 306). In this case, the access node is the second access node. The channel change request message may comprise at least some of the information element illustrated in Table 1 below.

Table 1

Requested Operating Class (OC) may be one octet in length and indicate a country code and a channel indexing structure of the network. The operating class may also specify a frequency band and/or bandwidth of the channel to which the terminal device requests the access node to change.

Requested channel number (Ch #) may be 1 -octet element that indicates a primary channel to which the access node is requested to change. The channel number is defined by using the channel indexing structure defined by the operating class. Together, the operating class and the channel number specify the channel to which the AP is requested to switch.

The AP Count is an unsigned integer, and a first subset of bits in the AP count may be used to indicate the total number of access nodes to which the terminal device is currently associated, while a second subset of bits in the AP count may be used to indicate the number of associated access nodes that have their primary channel on the requested channel. The access node may use this information to determine whether or not to accept the request. For example, if the number of access nodes is high, the access node may reject the request with the higher probability, e.g. when the access node serves other terminal devices. The access node may determine that the terminal device is not highly dependent on the access node so it may rather stay on its current operating channel and not cause disassociation or channel change to the other terminal devices. In another example, if the number of access nodes operating on the requested channel is high, the access node may determine with a higher probability to reject the request, particularly if it serves other terminal devices. The reasoning may be that the access node may not want to change to a congested channel. In both examples, the decision of the access node may be based on simple threshold comparison, or the access node may carry out a more comprehensive evaluation by taking into account its other associations and its current channel conditions, for example.

With respect to the AP Count, the channel change request message may comprise an information element indicating the number of mobile access nodes to which the terminal device is currently associated. A fixed access node may accept the channel change with a higher probability, if the terminal device is only associated to mobile access nodes.

The Channel Congestion may provide an assessment of the congestion or channel occupation of the requested channel. The terminal device may sense the channel through CSMA procedure, for example, and determine channel occupation characteristics on the basis of the sensing. The channel occupation may be defined in the Channel Congestion field as a percentage of time the terminal device has sensed the channel being busy. The percentage may be scaled linearly such that 0 represents 0% and 255 represents 100% occupation, as indicated by either the physical or virtual carrier sense (CS) mechanism. When more than one channel is in use for the BSS, the Channel Congestion field value may be calculated only for the primary channel. This percentage may be computed by using the following Equation:

Channel Utilization

channel busy time

= Integer |

dotllChannelUtilizationBeaconlntervals ^■ dotllBeaconPeriod x 1024. x 255 where the channel busy time may be defined as the number of microseconds during which the CS mechanism has indicated the channel to be busy, dotl I ChannelUtilizationBeaconlntervals may represent the number of consecutive beacon intervals during which the channel busy time is measured. The value of dotH ChannelUtilizationBeaconlntervals may define a periodicity of a beacon signal employed in the BSS.

The channel change request message may comprise at least one criterion used as a condition for the access node to revert to a default operating channel of the access node. The Access Delay field may indicate an access delay criterion, and it may be an unsigned integer. It may specify a maximum access delay allowed for frame transmissions from the access node, and if the access node cannot access the channel within the maximum access delay when attempting to transmit a frame, it is allowed to revert to the default operating channel. The access delay limit for the transmitted frames may be in units of 0.25 milliseconds (ms). One value of the field, e.g. value 0, may indicate that the access delay criterion is not set.

A Minimum Operation Time may be an unsigned integer in units of 10 ms. It may specify minimum operation time the access node is obliged to operate on the channel before it is allowed to revert to its default operating channel. One value of the field, e.g. value 0, may indicate that minimum operation time is not used.

The Inactivity Criterion may be an unsigned integer in units of 5 ms. It may specify a maximum time between reception of two consecutive frames from the terminal device, and if the access node does not receive a subsequent frame from the terminal device within the maximum time, it is allowed to revert to its default operating channel. One value of the field, e.g. value 0, may indicate that the Inactivity Criterion is not set.

It should be appreciated that while any one of the criteria for allowing to revert to the default channel has been met, the access node may autonomously choose whether to still stay on the channel or to revert to its default operating channel. For example, if the access node serves other terminal device on the channel, it may choose to stay on the channel until the current associations are terminated.

Upon receiving the channel change request and the requested parameters and/or criteria, the second access node processes the request in block 308. The access node may analyse the proposed parameters and criteria and determine whether or not it can accept them. If it determines that it cannot accept at least some of the proposed parameters and/or the criteria, it may choose to reject the request and, optionally, propose new parameters/criteria that it would be able to accept. The access node may propose new parameters/criteria in the channel change response message (step 310) it transmits to the terminal device. The channel change response message may comprise at least some of the following information elements illustrated in Table 2 below.

Table 2

The Response may indicate whether or not the request of the terminal device has been accepted. If the Response indicates that the request was accepted, the response message may comprise a Time to Change field (1 octet) that may indicate timing when the access node changes to the requested channel. The time may be defined as a number of beacon intervals before the channel change or by using another time unit of the network. The other fields may be omitted in case of an acceptance. If the Response indicates that the request was rejected and the access node does not propose alternative parameters/criteria, all the other fields may be omitted. If the Response indicates that the request was rejected but the access node proposes alternative parameters/criteria, one or more of the other fields may be present in the channel change response message, in addition to the Time to Change field. The other fields are similar to those already described in connection with Table 1 . The access node may propose another operating class, another channel number, and/or other criteria.

Upon receiving the channel change response message in 310, the terminal device processes the response and determines whether or not the access node accepted the channel change request. If the channel change response message comprises new parameters/criteria proposed by the access node, the terminal device may determine whether or not it accepts the newly proposed parameters/criteria. If the access node proposes another channel on which the other access node does not operate, the terminal device may need to first request for that other access node whether or not it accepts the change to the new channel. Upon determining whether or not the newly proposed parameters/criteria are acceptable, the terminal device may transmit a channel change indication frame in 312 in which the terminal device indicates whether or not it accepts the newly proposed parameters/criteria. In an embodiment, the terminal device is arranged to transmit the channel change indication frame only to accept the proposal.

The channel change indication frame may be a first advertisement to other devices that the access node is preparing to change its operating channel. Thereafter, the access node may broadcast a beacon signal, a measurement pilot signal, or another signal in which it announces its intention to change its operating channel (314). In an embodiment, the announcement of the channel change of the access node may be carried out only by the terminal device on behalf of the access node. For example, in a Wi-Fi direct mode this may be advantageous in cases where the terminal device has a better battery condition than a mobile access node.

In an embodiment, the terminal device may detect on the basis of channel sensing that a plurality of access nodes are present on the same channel and one of the access nodes consumes the channel resources. This may be determined from the traffic proportions in view of the number of associated devices of the access nodes on the same channel. The terminal device may then determine to first request the resource-consuming access node to change the channel. Let us consider a case where the terminal is associated to an infrastructure access point and a Wi-Fi direct access point, and the Wi-Fi direct access point starts to transfer a significant amount of data that uses the transmission resources of terminal devices associated to the infrastructure access point. In this case, the terminal device may request the Wi-Fi Direct AP to change to another channel.

Let us now consider that the second access node accepts the channel change request. In block 316, the access node changes to the requested channel. The access node may utilize a determined delay between the acceptance of the channel change and the actual channel change in order to allow other devices to prepare for the channel change. In block 318, the terminal device transfers data packets over the multipath connection comprising the radio links with the access nodes on the same operating channel. The access node may include a channel change information field in management or control frames it transmits or broadcasts. The channel change information may comprise relevant information on the channel change. The channel change information field may be included in beacon frames, probe response frames, association response frames, authentication response frame, advertisement service response frames, measurement pilot frames, etc. The channel change information field may have at least some of the following information elements illustrated in Table 3.

Table 3

Staying on Channel field may be set to one value (e.g. 1 ) to indicate that the access node will not change its primary channel and set to another value (e.g. 0) to indicate that the access node may change its operating channel. The terminal devices may read this field in order to determine whether or not to transmit the channel change request message to the access node. If the access node indicates that it will not change its operating channel, the terminal devices may not transmit the channel change request messages to the access node. The access node may indicate that it will not change its channel, if it has associated terminal device or if a network operator/internet service provider considers that the change of the channel will compromise the use of the network.

The Multiple Radios field may be set to one value (e.g. 1 ) to indicate that the access node has multiple radios and is, thus, capable of immediately assigning a radio to a requested channel. If the access node has only a single radio or if all its radios are already operational and cannot change their channels, the field may be set to another value (e.g.O).

The Beacon on Channels field may set to one value (e.g. 1 ) to indicate that the access node will, in case of changing its operating channel, transmit a beacon frame on its default channel and on a channel to which it changes, and it may be set to another value (e.g. 0) to indicate that the access node transmits the beacons only on its default channel. While switching the channel, the access node may change its channel completely to the new one or it could alternatively stay active on both old and new channels. In 802.1 1 networks, a Wi-Fi Direct mode supports operation on multiple channels simultaneously, wherein the access node may announce service periods for the multiple channels.

The Time to Channel Change may be set to a value that indicates duration to the channel change. The value may be a counter value that increases or decreases towards a target value specifying the timing of the channel change. The counter value may be linked to a regular time reference employed in the network, e.g. it may define a number of beacon transmissions before the access node will change its channel. One value may indicate that access node will not change its primary channel. One value, e.g. a maximum value of the field, may indicate that the access node will change its channel after the maximum number of beacons or later. It may thus indicate that the access node is supporting the channel change but is not planning the channel change at the moment.

In an embodiment, the terminal device follows a determined sequence of requests when attempting to align the operating channels of the access nodes. Figure 4 illustrates a flow diagram according to such an embodiment. Let us assume an initial situation where the terminal device has ensured that at least one of the access nodes announces that it supports the channel change. The terminal device may determine this information from the channel change information field (Table 3) transmitted by the access nodes.

Referring to Figure 1 , the terminal device may first determine that the operating channel of the second access node is most suitable in terms of lower channel congestion, lower number of terminal devices associated to the first access node, etc. As a consequence, the terminal device transmits the channel change request to the first access node in block 400. If the first access node accepts the request (with or without modified parameters/criteria) in block 402, the process ends and the requested channel is applied as the common channel. If the first access node rejects the request or proposes changes to the parameters/criteria that the terminal device cannot meet, the process proceeds to block 404. In block 404, the terminal device determines the next best channel which may be the operating channel of the first access node. The terminal device may first attempt to align the operating channels of the access nodes to a current operating channel of one of the access nodes to which the terminal device is associated. This may lower the number of required channel changes and, thus, improve the efficiency of the channel change. Therefore, the terminal device determines in block 404 to transmit the next channel change request to the second access node and request it to change to the operating channel of the first access node. If the second access node accepts the request (with or without modified parameters/criteria) in block 406, the process ends and the requested channel is applied as the common channel. Otherwise, the process proceeds to block 408. In block 408, the terminal device may search for a channel outside the operating channels of the first access node and the second access node. Upon determining such a channel, the terminal device may transmit the channel change request message to both access nodes and request them both to change to the determined channel. If both access nodes accept the request (block 410), the process ends and the requested channel is applied as the common channel. Otherwise, the process proceeds to block 412 in which the terminal device may determine to maintain the separate operating channels and communicate with the access nodes on different channels, e.g. by using the power-save mode feature.

Figure 5 illustrates a signaling diagram of an embodiment where the above-described criteria are applied when the access changes to a channel that is not its default operating channel. In general, the channel change request and the associated channel change may be temporary in the sense that the access node may eventually revert to its default operating channel, e.g. after disassociating from the terminal device, after a link failure, and/or upon meeting a criterion for reverting to the default operating channel. Referring to Figure 5, the terminal device associates to the access node in step 500. In block 502, the terminal device determines to request the access node to change its operating channel in order to align the operating channels of the access node and at least one other access node. Data may be transferred between 500 and 502, or the terminal device may request the channel change right after the completion of the association or even before the association. In block 504, the terminal device determines the parameters of the channel change, e.g. the channel to which the access node is requested to change, AP Count, channel occupation characteristics on the requested channel, etc. The terminal device may determine in block 504 at least one criterion for the access node to revert to its default operating channel (see Table 1 ). Upon determining the parameters and/or the criteria, the terminal device transmits the channel change request to the access node in step 506. The access node may process the received channel change request in block 508 in the above-described manner, either accept or reject it or accept it with modified parameters/criteria. In step 510, the access node transmits the channel change response message to the terminal device in response to the request. If the response proposes modifications to the parameters/criteria, the terminal device may further send the channel change indication message in 512. Let us assume that the channel change is negotiated successfully and, as a result, the access node changes its operating channel to the requested channel in block 514.

In block 516, the access node monitors the compliance with the criteria. If at least one of the reverting criteria is met, e.g. the access node cannot access the channel within the specified time interval, it cannot receive a frame from the terminal device within a specified time interval from the previous reception of a data packet, and/or the access node has stayed on the channel for a required minimum time interval, the access node is no longer obliged to stay on the channel and it may start a procedure to evaluate whether or not to revert to its default operating channel (block 518). The access node may consider the congestion on the channel and on its default operating channel, the number of currently associated terminal devices, etc. when determining whether or not to revert to its default operating channel.

Figure 6 illustrates an embodiment of an apparatus comprising means for carrying out the above-mentioned functionalities of the terminal device. The terminal device may comply with specifications of an IEEE 802.1 1 network or another wireless network. The terminal device may also be 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 terminal device may be or may be comprised in a computer (PC), a laptop, a tablet computer, a cellular phone, a palm computer, or any other wireless apparatus provided with radio communication capability. In another embodiment, the apparatus carrying out the above-described functionalities of the terminal device is comprised in such a wireless apparatus, e.g. the apparatus may comprise a circuitry, e.g. a chip, a processor, a micro controller, or a combination of such circuitries in the wireless apparatus.

Referring to Figure 6, the apparatus may comprise a communication controller circuitry 10 configured to control wireless communications in the wireless device. The communication controller circuitry 10 may configure the establishment, operation, and termination of connections in the apparatus, as described above. 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 the channel change request messages, channel change response messages, channel change indication messages, as described above. The control part 12 may additionally carry out channel sensing procedures in order to scan for the channel occupation characteristics. The communication controller circuitry 10 may further comprise a data part 16 that handles transmission and reception of payload data when the terminal device is associated to one or more access nodes or to one or more wireless devices.

The communication control circuitry 10 may further comprise a multipath connection controller circuitry 15. The multipath connection controller circuitry 15 may be configured to control the multipath connections in the apparatus. Upon receiving an instruction from an application executed in the apparatus to establish a connection with a network device, e.g. a server, the multipath connection controller circuitry 15 may determine whether or not to establish the connection with the network device as the multipath connection. Upon determining to establish the multipath connection, the multipath connection controller circuitry 15 may instruct the control part 12 to create an association to at least two different access nodes in parallel. The multipath connection controller circuitry 15 may have knowledge of the presence of wireless networks, and it may select the access nodes to which to associate according to a determined logic. For example, the multipath connection controller circuitry 15 may prefer to use wireless networks of different operators or internet service providers for a multipath connection. The reasoning may be that they typically have different backbone links and, thus, the probability of the throughput increase as a result of the multipath may be increased. Other types of selection logic may naturally be used. The multipath connection controller circuitry 15 may also control the association to new access nodes and disassociation from currently serving access nodes during the operation of the multipath connection. The set of associated access nodes may need to be changed as a result of mobility of the terminal device, changing radio environment, changing congestion in the serving access nodes, etc. The use of the multipath may be invisible to the application using the multipath connection, e.g. in the multipath TCP or multipath real-time protocol.

The communication control circuitry 10 may further comprise a channel change controller circuitry 14. The channel change controller circuitry 14 may be configured to monitor the operating channels of the access nodes to which the terminal device is currently associated with respect to a determined multipath connection and search for solutions to minimize the number of different channels the terminal device needs to use for the multipath connection. The channel change controller circuitry 14 may try to find a common operating channel for at least a subset of currently serving access nodes according to the principles described above. The channel change controller circuitry 14 may use as input information channel occupation characteristics acquired through channel sensing carried out by the control part 12, the number of associated terminal devices in each serving access node, availability of the access nodes to change their operating channel, etc. when determining an access node to which the transmit the channel change request and a channel to which to request the change. The channel change controller circuitry 14 may comprise a parameter/criteria selection circuitry 18 configured to determine the above-described parameters and/or the criteria to be added to the channel change request message. The parameter/criteria selection circuitry 18 may use default criteria for the access node to revert to its default operating channel, or the parameter/criteria selection circuitry 18 may determine the criteria on the basis of predetermined parameters provided in management information block (MIB) parameters by a management entity operated by an internet service provider, for example. The parameters may be stored in a memory of the apparatus.. The channel change controller circuitry 14 may also process the received channel change response messages, and cause the control part 12 to transmit the channel change indication messages.

The circuitries 12 to 18 of the communication controller circuitry 10 may be carried out by the one or more physical 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 the memory 20 that stores computer programs (software) configuring the apparatus to perform the above- described functionalities of the terminal device. The memory 20 may also store communication parameters and other information needed for the wireless communications, e.g. channel occupation characteristics and a list of detected access nodes and their operating channels. The apparatus may further comprise radio interface components 22 providing the apparatus with radio communication capabilities within one or more wireless networks. The radio interface components 22 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 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 carrying out the embodiments of the invention in the terminal device comprises 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 cause the apparatus to carry out the functionalities of the terminal device according to any one of the embodiments of Figures 2A, 3 to 5. 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 terminal device.

Figure 7 illustrates an embodiment of an apparatus comprising means for carrying out the above-mentioned functionalities of the access node. The access node may be a wireless apparatus which complies with specifications of an IEEE 802.1 1 network or another wireless network. The wireless apparatus may also be 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 wireless apparatus may be or may be comprised in a computer (PC), a laptop, a tablet computer, a cellular phone, a palm computer, a base station with routing functionalities, or any other apparatus provided with radio communication capability. In another embodiment, the apparatus carrying out the above- described functionalities of the access node is comprised in such a wireless apparatus, e.g. the apparatus may comprise a circuitry, e.g. a chip, a processor, a micro controller, or a combination of such circuitries in the wireless apparatus.

Referring to Figure 7, the apparatus may comprise a communication controller circuitry 50 configured to control wireless communications in the wireless apparatus. The communication controller circuitry 50 may comprise a control part 52 handling control signalling communication with respect to transmission, reception, and extraction of control or management frames including the channel change request messages, channel change response messages, and channel change indication messages, as described above. The communication controller circuitry 50 may further comprise a data part 56 that handles transmission and reception of payload data with devices associated to the apparatus. The communication controller circuitry 50 may further comprise channel change request processor 54 configured to process the received channel change request messages and determine whether or not to change the operating channel. The channel change request processor 54 may consider the number of terminal devices currently associated to the apparatus, the number of access nodes to which the requesting terminal device is currently associated, the channel conditions on the current operating channel of the apparatus and on the requested channel, etc. and determine whether or not to change to the requested channel. The channel change request processor 54 may also consider if at least some of the parameters/criteria proposed in the received channel change request message needs to be changed and, if so, determine new parameters/criteria. For example, the channel change request processor 54 may determine a new channel to propose on the basis of the channel occupation characteristics comprised in the channel change request message and channel occupation characteristics on other channels scanned by the apparatus itself. The channel change request processor 54 may also propose new criteria that change the conditions under which the apparatus may revert to its default operating channel. The channel change request processor 54 may control the control part 12 to transmit the channel change response message with the determined contents (see Table 2). The channel change request processor 54 may also determine the contents of the channel change information field comprised in management frames transmitted by the apparatus (see Table 3). The communication controller circuitry 50 may further comprise a performance monitor circuitry 58 configured to monitor the performance of the apparatus when it operates on the requested channel. The performance monitor circuitry 58 may compare the performance with the agreed criteria for reverting to the default operating channel. When at least criterion for reverting to the default operating channel is met, e.g. the apparatus has operated on the requested channel for the minimum time required, the performance monitor circuitry 58 may output to the channel change request processor 54 a notification which triggers the channel change request processor 54 to start considering whether or not to revert to the default operating channel.

The circuitries 52 to 58 of the communication controller circuitry 50 may be carried out by the one or more physical 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 52 to 58 or all of them.

The apparatus may further comprise the memory 60 that stores computer programs (software) configuring the apparatus to perform the above- described functionalities of the wireless apparatus, e.g. the access node. The memory 60 may also store communication parameters and other information needed for the wireless communications within a wireless network of the access point and with other wireless networks. The memory 60 may store the measurement statistics, rules for carrying out the channel changes, etc. The apparatus may further comprise radio interface components 62 providing the apparatus with radio communication capabilities within its wireless network and/or with other wireless networks. The radio interface components 62 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 further comprise a user interface enabling interaction with the user of the device. The user interface may comprise a display, a keypad or a keyboard, a loudspeaker, etc.

In an embodiment, the apparatus carrying out the embodiments of the invention in the wireless apparatus comprises 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 cause the apparatus to carry out the functionalities of the access node according to any one of the processes described above with respect to Figures 2B and 3. 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.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware-only circuit implementations such as implementations in only analog and/or digital circuitry; (b) combinations of circuits and software and/or firmware, such as (as applicable): (i) a combination of processor(s) or processor cores; or (ii) portions of processor(s)/software including digital signal processor(s), software, and at least one memory that work together to cause an apparatus to perform specific functions; and (c) 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, e.g. one core of a multi-core 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, an application-specific integrated circuit (ASIC), and/or a field-programmable grid array (FPGA) circuit for the apparatus according to an embodiment of the invention.

The processes or methods described in Figures 2A to 5 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 some sort of carrier, which may be any entity or device capable of carrying the program. Such carriers include transitory and/or non-transitory computer media, e.g. a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package. 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 systems defined above but also to other suitable systems. The protocols and specifications of wireless systems and their network elements 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.