WO2008128816A1 - Beaconing information in a communication system - Google Patents

Abstract

In the disclosed wireless communication system beaconing information is communicated at least in a first part and in a second part of a data carrier entity. The first part is for carrying beaconing information in association with a first group of devices and the second part is for carrying beaconing information in association with a second group of devices.

Description

BEACONING INFORMATION IN A COMMUNICATION SYSTEM

The disclosure relates to beaconing in a communication system, and more particularly to communication of beaconing information.

A communication system can be seen as a facility that enables communication sessions between two or more entities such as communication devices, network entities and other nodes. A communication device can be understood as a device provided with appropriate communication and control capabilities for enabling use thereof for communication with others parties. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on. A communication device typically enables a user of the device to receive and transmit data via the communication system and can thus be used for accessing various applications. A communication device may also enable an unmanned entity such as an application to exploit the communication capabilities of the device.

A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standard or specification may define if a communication device is provided with a circuit switched carrier service or a packet switched carrier service or both. Communication protocols and/or parameters which shall be used for the connection are also typically defined. For example, the manner how a communication device can access a communication system and how various aspects of the communication there between shall be implemented is typically based on predefined communication protocols.

Various communication systems providing wireless communication are known. These systems are often referred to as mobile systems; although in certain systems the mobility may be restricted to substantially small areas. A mobile communication device that is configured for duplex communication is typically provided with a transceiver for enabling wireless communication with a base station of the wireless system. An example of the wireless systems is the public land mobile network (PLMN). Another example is a wireless system that is based, at least partially, on use of communication satellites. Wireless communications may also be provided by means of other types of systems, such as by means of wireless local area networks (WLAN) or short range radio or other wireless iinks. An example of the short range or local systems are wireless persona! area networks (WPANs) where the connections involve little or no infrastructure but are rather based on groups of communicating devices or stations. Thus, in a simple form a wireless communication system comprises at least two stations that are suitably configured for enabling wireless communication there between.

Local communication system such as short range communication systems may also be configured to provide high data rates. High data rates may be enabled by means of mechanism such as ultra-wide band (UWB) signalling. For various reasons, for example due to emission limits imposed by regulatory bodies, coverage radius for those systems may be limited, typically to a few meters, for example ten metres.

The local system may be connected to other networks, for example a data network and/or a telecommunication network, via an appropriate gateway arrangement.

A number of new applications may be made possible in local wireless systems, for example those employing the UWB, if the coverage radius thereof is extended. Different physical layer (PHY) modes have different operating ranges and bit rates. Extended coverage may be possible within emission masks for example by using lower bit-rate, more error-protected physical layer (PHY) modes. Such range extension, however, may impose new constraints on the system design.

In short range or local systems devices that are associated to a group may need to communicate so called beaconing information to other devices to maintain network connectivity. The beaconing information is typically included in data entities known as beacon frames. The beacon frames are needed for network maintenance in local wireless communication system such as the wireless personal area networks (WPANs). The beacon frames may need to be received by all devices belonging to the same network or group.

A transceiver of a communication device is set appropriately to enable communications. A 'term physical layer mode' is often used to refer to a combination of transceiver settings. Such transceiver settings typically include the definition of the modulation scheme and therefore its constellation size, and the channel coding error protection scheme. These determine the strength against errors. The strongest mode is a mode with better protection, typically achieved by using increased protection overhead and slower transmit rate. Beaconing may require use of the strongest of the physical layer modes. However, the strongest physical layer mode is often the less spectrum-efficient. For example, in systems that are based on time division multiple access coding (TDMA) this means that a longer time needs to be allocated for transmitting the same information. The beacon frames may sometimes need to be received by only a subset of the devices belonging to the same network or group.

Furthermore, use of lower bit rate physical layer modes (for example, 10 Mbps) may imply an increase of the operating range. This may result in larger device population in an area and therefore in beacon period length growth.

A substantially large device population may become associated with a wireless network. This may result a situation where a substantially large portion of the capacity of the network is used by the devices for beaconing. Because each device requires a certain amount of signalling capacity this may result a situation where the signalling information uses all available capacity, leaving little or even no space for any content information. This may in particular occur in wireless personal area networks and/other local systems where communication is based on so called superframes or similar. A superframe (SF) refers to a data carrier entity that may be composed by a part that is dedicated to the exchange of control signalling, typically followed by a part dedicated to data transfer. The control signalling part is an overhead and may prevent partially or even entirely transfer of data that is the intended information to be carried. Longer operating range may increase further the number of synchronized devices in short range networks. In certain dynamic beacon period mechanisms the portion of data period may then decrease as a result. This may have an disadvantageous effect on the efficiency of the system.

Furthermore, each beaconing event consumes power. A typical wireless device that is used for communication is a battery-operated one. Any saving in the time spent on accomplishing the beaconing operations would increase the lifetime of the energy-limited devices and/or result in overall energy-efficiency savings.

Various reasons, for example a need for low complexity and/or power consumption and/or capacity needs of devices, may call for low-rate requirements without the need of increased coverage. In such a case, although there may be no effects on the size of the device population, a fixed beacon information size may extend in time during transmission. The same detrimental effects on efficiency noted above may thus apply also to this case scenario, for example because the time needed to send in a low-rate scenario a similar amount of control information than in a high-rate scenario may become too long. Therefore, it may be advantageous to use a different beacon design for high-rate and low- rate scenarios. However, lower-rate devices may not be able to receive and decode, in other words, "understand", the beacons sent by higher-rate devices. Nevertheless, it may be necessary to support at least some degree of interoperability among the devices in case low-rate and high-rate devices share the same electro-magnetic resources.

It is noted that the above discussed problems are not necessarily limited to local wireless systems and/or devices employing groups and superframes but may occur in any communication environment wherein beaconing or similar signalling function may be required.

The herein described embodiments aim to address one or several of the above problems. According to an embodiment, there is provided a method in a wireless communication system, comprising communicating beaconing information in at least a first part and a second part of a data carrier entity, wherein the first part is for carrying beaconing information in association with a first group of devices and the second part is for carrying beaconing information in association with a second group of devices.

According to another embodiment, there is provided a controller for a communication device, the controller being configured to communicate beaconing information in at least two different parts of a data carrier entity depending on information of a group a communication device is associated with.

According to another embodiment, there is provided a data carrier entity that is configured to carry beaconing information, comprising at least two parts, wherein a first part is configured to carry beaconing information in association with a first group and a second part is configured to carry beaconing information in association with a second group.

A wireless communication device comprising the controller and/or otherwise adapted to use the data carrier entity and a wireless communication system comprising at least one such wireless communication device may also be provided,

In accordance with more detailed embodiments, existence of at least one device belonging to the second group of devices may be detected, and, subsequent to said detection, the second part is configured into the data carrier entity for carrying beaconing information in association with the second group of devices. Alternatively, no second part is configured, or its length is defined as being null if it is determined that only a single group of devices is present.

Information in association with a first group of devices may be communicated in a beaconing period. An extension period may be associated with the beaconing period for carrying beaconing information that is associated with a second group of devices. Configuring of the further period may comprise defining the length of the period. The length of the period may be set dynamically based on at least one of a request from at least one device and as a consequence of collisions between devices.

Communication of beaconing information may comprise communicating in at least one part beaconing information in association with one of a large population group, a seldom beaconing group, a low rate group, a high rate group, and critical devices group.

Communication of beaconing information may comprise communication of information that is associated with at least three groups of devices, wherein each group is assigned a part of the data carrier entity.

A controller role may be assigned to at least one device. The at least one controller device may provide a beaconing information hub. The at least one controller device may reserve beaconing information transmission resources. The controller role may be transferred from a device to another. The number of controller devices may be changed.

For better understanding of the present invention, reference wiil now be made by way of example to the accompanying drawings in which:

Figure 1 shows a schematic presentation of an exemplifying communication system topology where the invention may be embodied; Figure 2 shows a schematic presentation of a possible device for use in

Figure 1 system;

Figure 3 is a flowchart illustrating an embodiment;

Figure 4 shows an example of a possible data carrier entity;

Figures 5 to 10 show more detailed exemplifying embodiments; Figures 11 and 12 show schematic presentations of exemplifying communication system topologies; and

Figure 13 is a flowchart illustrating a further embodiment. An exemplifying communication system wherein the invention can be embodied is now briefly explained with reference to the topology shown in Figure 1. The communication system may be provided by a plurality of devices that may communicate with each other via wireless interfaces. An example of a wireless system is a wireless personal area network (WPAN) where the wireless connections involve little or no infrastructure but are rather based on groups of communicating devices. Thus no particular control entities may be needed.

The communication system of Figure 1 is shown to comprise three types of devices. The division is such that there are devices belonging to a first group and a second group. Also, a device is shown as belonging to both of the groups.

Before explaining in detail some exemplifying embodiments, certain general principles of a portable or mobile wireless communication device are also briefly explained with reference to Figure 2 showing a schematic partially sectioned view of a mobile wireless device 1. A portable wireless communication device can be used for communication with other stations via a wireless or radio interface. The other station may be a base station or similar wireless transmitter and/or receiver node, another portable wireless communication device or other type of a station. Each portable wireless device may have one or more radio channels open at the same time and may have communication connections with more than one other station. A mobile wireless device is typically able to move within a radio access area and also from one area to another.

The mobile device 1 of Figure 2 can be used for various tasks such as making and receiving phone calls, for receiving and sending data from at least other devices in a group of devices. Non-limiting examples of appropriate devices include a mobile station (MS), a portable computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. Further examples include control devices, for example mice and other pointers and/or actuators; audio devices, for example microphones, earphones, and loudspeakers; video devices, for example video cameras and monitors, or any combination of these or the like. The connection to other devices may be based on any appropriate wireless media. For example, the wireless device 1 may communicate over short range radio links such as those based on ultra wideband (UWB) standards, such as WiMedia, Bluetooth™ protocols and so forth. An appropriate wireless communication device is provided with required radio transmission elements and controller functions so that it is enabled to communicate wirelessly, and process control instructions it may receive and/or send. The communication occurs via an appropriate radio interface arrangement of the mobile device, typically an antenna element. The antenna may be arranged internally or externally to the device. A wireless communication device is typically also provided with at least one data processing entity 3 and at least one memory 4 for use in tasks it is designed to perform. The data processing and storage entities can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 6. The user may control the operation of the device 1 by means of a suitable user interface such as key pad 2, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 5, a speaker and a microphone are also typically provided. Furthermore, a wireless device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting externa! devices, for example hands-free equipment, thereto.

The mobile device 1 may be enabled to communicate with a number of different other devices. This is illustrated schematically in Figure 2 by the two wireless signals 11 and 21.

The wireless device or station of Figure 2 may be configured to join a group of short range devices and to communicate beaconing information with other devices in the group. In the examples described herein the beaconing information is included in appropriate data carrier entities. The data carrier entities may be provided, for example, by beacon frames.

In accordance with an embodiment devices that need to beacon less often are configured such that they do not reserve a regular beacon slot. Instead, such seldom beaconing devices may communicate the beaconing information during another period. According to an embodiment a data entity for communication of beaconing information is divided into at least two parts or sections such that beaconing information that is associated with devices in different states is communicated differently. For example, a beaconing period may be divided into sub-periods such that devices in a normal state communicate the beaconing information during a regular beaconing period and devices with lesser needs for beaconing communicate during an additional beaconing period reserved for such devices. The seldom beaconing devices may also use a contention period or organized contention less period for beaconing purposes. Thus, instead of sending beaconing information in one specific part of a data carrier entity the information can be sent in two different parts, depending, for example, on the type or class of the device the information relates to.

A flowchart in accordance with an embodiment is shown in Figure 3. At 100 a communication system comprising at least two different groups of devices is provided based on beaconing information. As shown at 102, beaconing information is communicated in at least two different parts or periods of data carriers depending on the status of a particular device, i.e. in dependence of the group it belongs to. The communication system is then managed in 104 based on the beaconing information.

In accordance with an embodiment one or more regularly beaconing devices may define the details of a period that is to be used by the less often beaconing devices. Some examples for this are described later in this specification. Also, in a network where a low number of less often beaconing devices are present, the signalling slots may be used for beaconing purposes by such devices and no regular beacon slot or additional period is needed.

In accordance with an embodiment one or more regularly beaconing devices may define details of a period that is to be used by at least one lower-rate beaconing device. Examples for this are also described later in this specification.

Use of a plurality of beaconing periods enables different beaconing schemes for different devices. For example, the additional beaconing period can be used for beaconing purposes by devices which do not need to beacon every superframe, or by devices which use lower-rate beacon transmission. The additional period may be contention based or contention free or a mixture of those. Contention- based access denotes a method by which devices can access the medium in such a way that collisions among devices are not necessarily avoided. Contentionless or contention free access then refers to an access method where there is a scheme in place for avoiding collisions. Collisions may be avoided, for example, by allocating a portion of the superframe period to a specific device in beforehand. One or more devices participating the regular beacon slots will maintain the additional period and they may also help in reporting about/for the differently beaconing devices.

In certain communication networks channel time is divided into a sequence of intervals with a similar timing structure so that that certain type of information is communicated at a certain time period. Signalling information frames of such systems are sometimes called superframes. An example of a possible superframe structure in accordance with an embodiment is shown in Figure 4. In this example a beaconing period of a superframe is divided into a plurality of sub- periods such that that at least two different beaconing periods are defined.

The exemplifying superframe of Figure 4 consists of a beacon period (BP) 30 and data transfer period (DTP) 40. The data transfer period 40 may be divided into contention based and collision-free parts. However, since the data transfer period is not of particular interest here, it will not be described in any greater detail.

The beacon period 30 is shown to consist of signalling slots (SS) 32, beacon slots (BS) 34 and an extension period (EP) 36. It is noted that although in the example of Figure 4 the extension period 36 is defined to be located at the end of the beacon period 30, this is not the only option, as will be explained later. In some embodiments the beacon period 30 may consist of only the beacon slots (BS) 34 and the extension period (EP) 36. The intra-extension period operation may be arranged for example such that beacons are sent during an extension period by giving turns to each device in that period. Back-off algorithms may also be used.

The overall control of the additional period or extension period 36 can be provided by a device that is a member of a group of devices that participate regular beacon period slots 34 and is also member of another, less often or seldom beaconing group or a lower rate group. The controlling or managing device may take care of possible reservations needed for the periods used for beaconing by the less often beaconing devices or lower rate devices. For example, the managing device may include the extension period 36 into a list of occupied beacon slots. The managing device may also act as reporter of relevant beaconing information from devices of a group to devices of another group.

In accordance with an embodiment specific information coilector (IC) devices are provided for the management purposes. These devices act as information hubs in the system. The information collector may be authorized to define the details of the extension period 36, for example the length of the extension period and the transmission order within the extension period. This, however, may not be appropriate in certain occasions where the extension period is contention based.

The one of more information collector devices may send information about devices of a sub-group in the beacons of the information collector device or in additional control messages. Such information collector role can be switched from a device to another. The switching capability may be provided together with other capabilities such as hibernation anchor capabilities. More than one information collector device can occur within a coverage range.

A specific example of an embodiment employing an extension period and at least one information collector (IC) entity will described in more detail below. A reference is made, where appropriate, to a communication system provided based on a distributed topology such as that shown in Figure 1. The exemplifying embodiment utilizes a power and resource efficient beaconing method that is suitable for energy limited devices such that beaconing information is not necessarily replicated by all associated devices in all superframes. This is faciiitated in the embodiment by a mechanisms employing at least one information collector entity or delegating device. Other communication devices in the system may rely on the presence of the information collector. For infrequent signalling information updates the devices may access the proper channel with a contention based method. In addition to that, they may optionally send short confirmation beacons to confirm that information sent by an information collector device is correct and still up-to-date. This confirmation can also serve to show that those devices are still alive and connected. An information collector mechanism described in more detail below may be particularly efficient if the content of its information in the beacon is not changing frequently.

An example will now be described with reference to a communication system where at least two sub-groups of devices are provided. As described above, a data entity configured to carry beaconing information may be divided into different parts or periods, each part being reserved for a particular sub-group of devices. A first part can be common to all devices and may hence be referred to as a part containing common signalling slots. The common signalling slots may be used, for example, to solve collisions in the beacon slot acquisition by new devices willing to join the network. A second part may then be used by a first group of devices. For example, only time-critical devices may use this part. Thus this part is referred to in this example as a critical devices sub-group (CSG). A third part may also be used for a large-population sub-group (LSG). A device may belong to any number of sub-groups. In accordance with another example, devices belonging to a high-rate devices group (HRG) may use the second part, whereas devices belonging to a low-rate devices group (LRG) may use a third part.

Devices of the critical devices sub-group may need a full or larger set of functionalities, like frequent renegotiation of channel allocation. Devices of the high-rate sub-group may in general afford to send anyway such richer information. Non-limiting examples of functionalities for critical devices sub-group devices or high-rate devices include WiMedia / multi-band Orthogonal Frequency Division Multiplexing (OFDM) alliance (MBOA) medium access control (MAC) and European Computers Manufacturer Association (ECMA) 386 medium access control (MAC). In these systems associated devices are assumed to send quantity of signalling information in their beacons. This transmission is typically done periodically. A device may even become disassociated if nothing is heard from it in a specified interval. The information to be sent includes the list of all associated devices, replicated by each associated device. Although this information is typically needed for a number of reasons, in some cases, this "overhead" may not be affordable.

Devices of the large-population sub-group can be seen as scattered devices. The scattered devices may need only a subset of the functionalities mentioned above. For example, the scattered devices may not need frequent updates of network information nor information regarding changes in channel allocation.

Devices belonging to the critical devices sub-group typically need timely delivery of beaconing information or need their information to be updated frequentiy. This may be, for example, because frequent reallocation of slots for data transfer is needed. Devices belonging to the large population sub-group typically do not need frequent updates of their beaconing information. On the other hand, the number of devices in the large population sub-group may be, as suggested by the name, typically relatively large and it is therefore important to keep their signalling traffic as limited as possible. A possibility to achieve this is described in the following example. Low-rate devices cannot send efficiently a large amount of information in beacons. In some instances the low rate devices cannot afford this at all.

Instead of having all beacons containing redundant information, as may be needed in the critical devices sub-group, no redundant information is necessarily transmitted over the channel by the large population sub-group devices. This may provide efficiency in both the usage of the radio resources and in the usage of energy. The additional effort in energy required for an information collector device may be shared among the capable devices, for example in a manner described below. The beaconing information can be collected by the information collector device. The beaconing information may be sent once at the beginning of the common signalling slots, or at least twice, depending on the application. The other devices in the large population sub-group may send regularly reduced information only. Among the information that may be sent is the acknowledgment of the correctness of the own information included in the common beacon sent by the information collector device.

A part 50 of the beaconing period 30 that is reserved for a large-population subgroup may be divided further as shown in Figure 5. At the beginning of this part one information collector (!C) beaconing slot 52 may be provided for use by the information collector device for communication of large population sub-group beaconing information. The information collector beaconing slot 52 may include all information that is successfully received by all associated large population subgroup devices. The information collector beaconing slot may optionally be sent periodically, with a given period to save energy, or in each superframe, i.e., with a period value 1. This may be used, for example, to improve reliability.

The value of the period may be defined for example by the first member of the large population sub-group. The value may optionally be changed during the lifetime of the network. The change may be provided, for example, in response to a request by at least one member of the large population sub-group or as a consequence of collisions observed by an information collector.

After information collector beacon slots 52, n contention full beacon slots (CF1 to CFn) 54 may be provided. These slots can be used aperiodically by the devices belonging to the large population sub-group. The number of contention full slots, n, may be set to be relatively small, for example 2. The value of n may be defined for example by the first member of the large population sub-group. This value may also be optionally changed during the lifetime of the network, for example upon request of at least one of the large population sub-group devices or as a consequence of collisions observed by an information collector. The devices of the large population sub-group may send their complete information in the shared contention full beacon slots. The large population subgroup devices may send their beacon slots only when the content of the carried information is changed.

Optionally a back-off algorithm may be used to set the time for the next attempt. Aperiodicity in accesses and attempts may need to be assured when selecting the time instant a contention full beacon slot is accessed. The contention scheme used for access may be based on any appropriate protocol. An example of these is the S-Aloha protocol. The duration of a contention full beacon period may be set to be smaller than the duration of the information collector beacon slot.

After the contention full beacon slots (CF), m smaller contention-less reduced beacon slots (LR1 to LRm) 56 may follow. The content of the contention-less reduced beacon slots sent by the large population sub-group devices may include a flag by which a device confirms that information sent by the information collector is correct or it may announce that this information is not correct. In the latter case, that device may correct its information in the following superframe. Additionally and/or optionally, the device may send a bitmap for correctly/erroneously received beacon slots sent by other large population subgroup devices. The number of contention-less reduced beacon slots, m, may be set to zero, i.e., the contention-less reduced beacon slots can be an optional feature. The value may be defined by the first member of the large population sub-group. The value may be optionally changed during the lifetime of the network, for example upon request of a large population sub-group device.

The duration of a contention-less reduced beacon slots (LR) 56 can be made smaller than the duration of the contention full beacon slots (CF) 54. This may have a positive impact on energy efficiency. Depending on the application and the noisiness of the environment, contention-less reduced beacon slots 56 may be completely avoided. Figure 6 shows a further example where more than one additional group is enabled. More particularly, in the example of Figure 6 a plurality of beaconing periods 60 to 62 can be reserved for large population groups.

For backward compatibility with previous versions of standard specifications, a large population sub-group beaconing period may be implemented as a reserved part in the data transfer period. In this way, the large population sub-group beaconing period may be seen by the members of the critical devices sub-group as a reserved time in their data transfer period.

Figure 7 shows a specific embodiment that may be used in connection with WiMedia medium access control (MAC). Figure 8 shows a specific embodiment that may be used in connection with WiMedia medium access control (MAC) when a plurality of additional groups is used. Similar principles may be applied with any other medium access control mechanism where only one type of regularly beaconing devices is defined.

In the embodiments of Figures 5 to 8 at least one information controller slot 52, 72 is provided in the critical group part (CSG) 70 of the beacon period 30. More particularly, common signalling slots beacon period part (CSS) 74 described above provide the beacon slots that are used as signalling slots. The so-called critical devices sub-group beacon period part (CSG) 72 is used by such devices that are always beaconing when active. The common signalling slots beacon period part and the critical group part thus form together a beacon period (BP).

In this specific example the presence of the critical group may be mandatory. The following describes how an optiona! large group period may be provided.

The information collector beacon slot (IC) may be sent as regular beacon in the beacon period. The beaconing information of the represented devices can be included in a special information element (IE). Since the duration of this slot is limited, that information may be sent, if needed to cover all related devices in the large population group, in a number of successive superframes (SF). As also shown by Figures 7 and 8, special beacon slot(s) of the large group period 76 may be located in the data transfer period (DTP) 40 rather than in the beaconing period 30, They can be made to look like reserved to all devices of the beaconing group, including those not compliant with the extension part described above. The large group part can thus be seen as used by all non-large group devices. All of those devices may not, however, use that reserved part. The large group part may well be unused by the large group devices. Instead, it may only be reserved for possible use, according to the contention based access.

A possible application scenario concerns use of low-rate devices with a less powerful error-protection channel coding scheme. This application case may enable use of devices with a lower link-layer rate than in the embodiments described with reference to Figures 5 to 8. Thus use of simpler and possibly cheaper devices may be enabled as the aim is to provide lower rate devices for lower consumption purposes and not to gain extended coverage. Nevertheless, as is for example the case with the lower-rate/longer-range scenario described above, similar issues concerning optimization of beaconing can be applied. Accordingly, other examples of possible applications include lower-rate devices

Figure 9 shows an example how the low rate devices may be used in connection with WiMedia medium access control (MAC) and coexist with higher-rate devices, for example legacy devices. Figure 10 shows another embodiment that may be used in connection with WiMedia medium access control (MAC), the difference to Figure 9 being that a plurality of additional groups is provided.

In these examples, an information collector device sends a beacon during a first group beaconing period, i.e. high-rate devices group (HRG) beaconing period 90, to reach high-rate devices group (HRG) devices, and another beacon during a second (or nth) group beaconing period, i.e. LRG beaconing period 92, to reach the devices of the second group, i.e. the devices of the low rate group (LRG). This can be utilised to enable backward compatibility with systems that enable high-rate devices only. Each of the groups may have its respective slots reserved for use by respective information controller devices. In Figures 9 and 10 such slots are provided by slots ICH 94 for the high-rate devices group (HRG) and ICL 96 for the low rate group (LRG) group.

It is noted that despite the different naming of the groups the overall general principles described above with reference to Figures 5 to 8 apply also to the examples shown in Figures 9 and 10. For example, similarly to the CSG/LSG scenario more than one lower data rate group may exist also with HRG/LRG scenario.

The following are examples of possibilities to reserve a large group period. In accordance with a possibility a private reservation mechanism is used. The private reservation mechanism is a feature of WiMedia medium access control. This method enables reservation of a portion of a data transfer period by a device for unspecified use, for example for use other than data transfer. Hard reservation is also a possibility. Hard reservation is also a feature of WiMedia medium access control. With this method, a portion of the data transfer period is reserved by a device for data transfer. The reserved portion cannot be used by other devices. In these reservation mechanisms devices that are authorised to use the reserved part (so-called owner and target devices) can also terminate the usage by exchange of specific frames. This will free the reservation for the other devices to use. By means of this the private and hard reservations can be used for protecting the large group period, provided that the large group devices do not send any terminating frames during the reserved time. A further example of the reservation methods is Alien beacon period reservation.

A plurality of distinct groups may exist in a beacon group. More than one large population sub-group, at least one for each large group, may thus also exist in the same beacon group. One information collector may be selected for each large population sub-group.

An example of the use of a plurality of information collectors is shown in Figure 11. In this exemplifying topology all devices are in mutual coverage such that two distinct large population groups and two distinct critical devices groups are present. The information controllers of the large population groups may belong to both groups. Figure 11 shows also newcomer devices that are to join the beacon group (BG).

Figure 12 shows an example of large population groups with different types of devices. Example of such an environment is a big meeting room or conference exhibition.

In accordance with a yet further embodiment, the information collector role may be handed over from a device to another. A device may be selected initially as an information collector device based on an appropriate rule. For example, a first device that is a part of a large population or low rate sub-group selects itself as the information collector for that group. When more devices join the sub-group, the device that is currently in charge of the information collector role may select another device in the large population or low rate sub-group as the new information collector device. The selection may be performed based on any appropriate rule. The current information collector may then signal to the selected device to initiate information collector role handover. The selected new device may then accept the role and maintain information collector duties so that the information from superframes is not missed following its acknowledgement. The new information collector device may keep the role or select a new device within the large population or low rate sub-group, including the former information collector device.

The selection may be based, for example, on the residual energy level of the selected device, if this information is available. Any other appropriate rule may be enforced. As a default method, a device with immediately larger (or smaller) identity number is selected. Random selection may also be used.

The number of information collectors may be increased or decreased. Appropriate signalling may be sent to increase and decrease the number of the information collectors. An increase or decrease the number of information collectors may be triggered by a change in the topological situation. For example, if an information collector does not reach all devices in a group, there may be a need to increase the number of the information collectors. Also, if more than one information collector is reporting about the same devices of a group to the same devices of another group, this may be indicative of a situation where the number of information collectors can be reduced. The decision of which devices to select may be based on random or a weight according to how long a device has been an information collector and so on.

In an embodiment shown in Figure 13 devices may perform scanning to identify and detect the presence of other groups of similar or different devices that appear into the scene. In stage 110 a device detects existence of at least one device belonging to a group of devices. Subsequent to said detection, the device may configure at 112 a second or further part into a data carrier entity for carrying beaconing information in association with the detected group of devices. This may be advantageously used for example to ensure that no additional periods are reserved when there are no additional groups.

The detection may be needed, for example, due to relative mobility of the groups. The scanning may be periodic, every now and then and/or provided in response to a predefined event. A problem is, however, that only homogeneous cases may be handled. That is, e.g. high data rate (HDR) devices may listen only for other HDR-devices, and low data rate (LDR) devices may be able to listen only for other LDR-devices. Also, it may be that a HDR-group could interfere or otherwise damage a LDR-group and vice versa.

Consider first scenario where lower-rate (LDR) devices co-exist with higher-rate devices. The LDR devices may operate autonomously and form a communication group. For example, because of mobility or for changed propagation environment, LDR devices and HDR devices may become positioned in the same coverage and/or interference area. Although the different devices may not recognize each other, they may, without proper measures, interfere with each other and possibly even hinder communications amongst the respective groups. All devices in a LDR group that are capable of function as an information controller (IC) device may perform scanning of the wireless medium. The IC capability may be declared by the relevant devices with a dedicated one-bit flag in a specific IC-information element (IC-IE), for example by marking '1C capability=TRUE\ by 1 or 0 and so on. The scanning operation may be provided in predefined intervals and/or in response to a predefined event. The purpose of the scanning is to detect the presence of a HDR-devices group.

The first device that detects at 110 a group may elect itself as the iC-device for its low rate group. This can be made known to other devices by setting a dedicated one-bit flag in its IC information element, for example 'IC.active=TRUE'. An optional (e.g., two octets) field of the IC information element can be provided as an identification (ID) of a high rate device or the group of a high rate device, e.g.,

'IC.representer=<address>\ A predefined identification (e.g., all zeros or all ones) may be provided to denote an unknown ID.

if more devices of the same lower rate group set their information controller active flag to TRUE during the same superframe, and, when applicable, if they report the same (non-"zero") value for a information controller (IC) representer, then a procedure for selection is performed. This may be done, for example, by selecting a device with the best received signal strength indicator (RSSt) from the external device (the HDR-device) to provide the information controller device, or by selecting a device with the lowest/highest device ID, or based on any other method. The elected device can keep 'IC.active=TRUE' and all other devices may then set 'IC.active=FALSE\

When the information controller device is elected, this device can negotiate and reserve in the superframe of the external group the time that is needed for the lower rate group operations. After this is done, if needed, the information controller device may perform a beaconing period (BP) relocation, i.e., a time shift of the superframe of the lower rate group. This may be done similarly to the beaconing period switch operations. In the above selection of at least one information collector device was discussed with reference to a large population or low rate sub-group. The information collector selection may be also applied to other types of groups, for example a group of critical devices or high-rate devices.

In addition, in certain occasions it may be advantageous to ensure that a critical or high-rate devices sub-group is aware of the identity of the information collector of a large population or low-rate sub-group. A way of providing this is to select as an information collector a device from the large population or low-rate sub-group that is also a member of the critical or high-rate devices sub-group. This may be advantageous in maintaining network integrity.

An information collector of a low rate group may be required to regularly beacon the principal/normal part of the beacon period used by a high-rate group. In other words, an information collector of a low rate group may also be a member of the high-rate group. Not all members of the low rate group may be able to receive beacons of the high-rate group. All members of the high-rate group can be made aware of the existence of the low-rate group and vice-versa, since the information collector is a member of both groups.

An information collector of a large group may be required to be also a device regularly beaconing in the principal/normal part of the beacon period. In other words, an information collector of a large group may also be a member of the critical group. Not all members of the critical group may be able to receive beacons of the large group, but all members of the critical group may receive the beacon of the information collector since it is also a member of that group.

A handover mechanism may be provided to enable replacement of a critical or high-rate devices sub-group device by another device. This can be achieved, for example, by a disassociation / association procedure. Alternatively, provided that timing is consistent with possible specifications concerning the hibernation that follows, the old information collector may hibernate and the new information collector may wake up or associate for the first time, and so on. in this way, fairness may be achieved with backward compatibility. Various reasons may exist for information collector handover. For example, the handover may be provided in order to be fair in view of energy consumption related to the duties of an information collector. The new information collector may be a device that was not known to other devices of the critical group.

Therefore, a possibility for performing the handover is to disassociate the old information collector from the critical group and to associate the new information collector to the critical group. Another possibility is that the devices having the role of an information collector alternate their information collector-active periods according to hibernation periods.

A possibility to obtain savings in the length of a beacon period is to allow sparsely beaconing devices to use signalling slots for their beacons. However, this may be applicable only in network where a small number of sparsely beaconing devices is present.

In accordance with an embodiment efficiency may be achieved also at local or device level by delegating the transmission of relevant information to a possibly more energy capable device. This embodiment is based on the realisation that although relevant information may be needed in each superframe, especially for devices willing to join the group, it is however irrelevant who is sending that information.

In accordance with an embodiment, if it is determined that there is no such devices requiring use of a further beaconing period, for example an extension period as described above with reference to Figure 4, then no further period needs to be configured. A possibility is to define the length of the further period to be null (0).

The embodiments may be applied, for example, to a WiMedia ultra-wideband (UWB) system and other wireless radio systems. The data carrier entity may be provided as a Wimedia superframe. Examples of applications include multicast services like earphones for speech translation, or scattered speakers for music and speech to be rapidly deployed in exhibition and conference areas, and so forth, in these applications a larger coverage than that provided by short range systems may be useful. On the other hand, bit-rate requirements may be looser in these systems than in the above examples, and thus the larger area may be obtained.

A possible use scenario may adopt opposite direction of traffic. An example of this is sensor data fusion where a single destination combines information collected from a plurality sources. In this scenario channel time access may be provided differently than what is described above.

A yet other example is limited mobility support for current wireless universal serial bus (W-USB) applications, allowing users to move farther from corresponding nodes. A possibility in here is to use a reduced bit-rate to be paid as trade-off for increased mobility.

The embodiments may be applied in various access systems, for example those based on time division multiple access (TDMA) or code division multiple access (CDMA) wherein the beaconing information may be communicated in at least two different parts of a beaconing information carrying data entity. For example, in these access systems a beacon spreading codes set may comprises at least two different sub-parts, each comprising a beacon spreading codes sub-set. In these examples each of the parts may be in the time domain in the TDMA and in the code domain in the CDMA.

The required data processing functions may be provided by means of one or more data processors. The processing facility may be provided on an appropriate platform, such as by a computer chip. The above described data processing functions of a device communication in the system may be provided by separate processors or by an integrated processor. For example, data processing may be provided in a centra! processing unit of a communication device, or distributed across several data processing modules.

An appropriately adapted computer program code product or products may be used for implementing the embodiments, when loaded on an appropriate processor, for example in a processor of the communication device and/or an external device. The program code means may, for example, perform the generation and/or interpretation of the beacon frames, selection and/or determination of suitability of a device for a role, generation of messages and so forth. The program code product for providing the operation may be stored on and provided by means of a carrier medium such as a carrier disc, card or tape. A possibility is to download the program code product to the communication device via a data network.

An advantage provided by at least some of the above described embodiments is that they allow a large number of associated devices whilst only relatively low data rates may be needed for beaconing. Efficient beaconing may be enabled in large networks, both in terms of number of associated devices and in terms of spatial extension. The embodiments may avoid the need to reserve beacon slots to all associated devices by freeing some of the active devices from sending their beacons in each signalling data entity, for example a superframe. In certain embodiments less channel time may be needed to be reserved for beaconing purposes, in some embodiments coexistence of lower-rate devices and higher- rate devices (for example provided by legacy devices) can be supported. Lower- rate devices may not need to be compatible with higher-rate devices, and yet consistent operation of the entire system may be achieved. Advantage may also be obtained in view of efficiency and/or robustness.

It is also noted herein that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention as defined in the appended claims.

Claims

Claims

1. A method in a wireless communication system, comprising: communicating beaconing information in at least a first part and a second part of a data carrier entity, wherein the first part is for carrying beaconing information in association with a first group of devices and the second part is for carrying beaconing information in association with a second group of devices.

2. A method as claimed in claim 1, comprising, before communicating beaconing information in the first and second parts, detecting existence of at least one device belonging to the second group of devices, and, subsequent to said detection, configuring the second part into the data carrier entity for carrying beaconing information in association with the second group of devices.

3. A method as claimed in claim 1 or 2, comprising: communicating in a beaconing period beaconing information in association with the first group of devices; and associating an extension period with the beaconing period for carrying beaconing information association with the second group of devices.

4. A method as claimed in claim 3, comprising configuring the extension period one of in the beaconing period and a data transfer period.

5. A method as claimed in claim 4, comprising configuring the extension period at the end of the beaconing period and at the beginning of the data transfer period.

6. A method as claimed in any of claims 3 to 5, wherein the configuring comprises defining the length of the extension period.

7. A method as claimed in any preceding claim, comprising carrying only beaconing information in the second part.

8. A method as claimed in claim 1 , further comprising, before communicating beaconing information in the first and second parts, receiving a request for use of the second part, and, controlling use of the second part for carrying beaconing information in association with the second group of devices.

9. A method as claimed in claim 8, wherein the controlling comprises defining at least one superframe and at least one period of the second part where a device associated with the second group of devices is allowed to send beaconing information.

10. A method as claimed in any preceding claim, wherein communicating beaconing information in association with the second group of devices comprises communicating beaconing information in a data transfer part of the data carrier entity.

11. A method as claimed in claim 10, wherein communicating beaconing information comprises communicating beaconing information in at least one sub- part of a beaconing period of the data carrier entity and in at least one sub-part of a data transfer period of the data carrier entity

12. A method as claimed in any preceding claim, wherein each beaconing information carrying part of the data carrier entity comprises a beacon spreading codes sub-set.

13. A method as claimed in any preceding claim, wherein communicating beaconing information comprises communicating in at least one part beaconing information in association with one of a large population group, a seldom beaconing group, a low rate group, a high rate group, and critical devices group.

14. A method as claimed in any preceding claim, comprising communicating beaconing information that is associated with at least three groups of devices, wherein each group is assigned a part of the data carrier entity.

15. A method as claimed in any preceding claim, comprising assigning a controller role to at least one device.

16. A method as claimed in claim 15, wherein the at least one controller device provides a beaconing information hub.

17. A method as claimed in claim 16, comprising communicating beaconing information between devices of at least two groups of devices and the controller device.

18. A method as claimed in any of claims 15 to 17, comprising reserving beaconing information transmission resources by the at least one controller device.

19. A method as claimed in any of claims 15 to 18, comprising transferring the controller role from a device to another.

20. A method as claimed in claim 19, comprising selecting a device for the controller role based on at least one of residual energy level of a device, received signal strength, identity number of a device, random, length of service in the controller role, information regarding group or groups a device belongs to, and fairness.

21. A method as claimed in claim 19 or 20, comprising handing the controller role from a device to another device by mean of one of disassociation / association procedure and hibernation / wake-up procedure.

22. A method as claimed in any of claims 15 to 21 , comprising changing the number of controller devices.

23. A method as claimed in any of the preceding claims, comprising communicating information generated by a controller device in a sub-part of at least one of said different parts of the data carrier entity.

24. A method as claimed in claim 23, comprising communicating beaconing information in at least one other sub-part of said at least one part of the data carrier entity, wherein the at least one other sub-part is contention based.

25. A method as claimed in claim 24, comprising communicating further information in at least one additional sub-part of said at least one part of the data carrier entity, wherein the at least one additional sub-part is contention free.

26. A method as claimed in claim 24 or 25, wherein the information carrying capacity of the at least one other sub-part and/or the additional sub-part is less than the information carrying capacity of said sub-part.

27. A method as claimed in any preceding claim, comprising changing at least one parameter associated with one of the parts.

28. A method as claimed in any preceding claim, comprising delegating transmission of information from a device to a more energy efficient device.

29. A method as claimed in any preceding claim, comprising sending beaconing information in at least one contention full part.

30. A method as claimed in claim 29, comprising setting a value for available contention full slots in said at least one part by a device in a group.

31. A method as claimed in claim 30, wherein the number of available contention full slots is set by a device belonging to a large population group.

32. A method as claimed in any preceding claim, comprising sending beaconing information in at least one contention free part.

33. A method as claimed in claim 32, comprising setting a value for available contention free slots in said at least one part by a device in a group.

34. A method as claimed in claim 1 , comprising, before communicating beaconing information, determining that only devices belonging to a single group of devices are present, and, subsequent to said determination, configuring the second part such that its length is null, or abstaining from configuring a part into the data carrier entity for carrying beaconing information in association with any other groups of devices.

35. A controller for a communication device, wherein the controller is configured to communicate beaconing information in at least two different parts of a data carrier entity depending on information of a group a communication device is associated with.

36. A controller as claimed in claim 35, wherein the controller is configured to communicate beaconing information in at least two different sub-parts of a beaconing part of the data carrier entity.

37. A controller as claimed in claim 35 or 36, wherein the controller is configured to communicate beaconing information in a data transfer part of the data carrier entity.

38. A controller as claimed in any of claims 35 to 37, wherein the controller is configured to assume a role of a beaconing controller.

39. A controller as claimed in claim 38, wherein the controller is configured to provide at least one of a beaconing information hub and allocation of beaconing information transmission resources.

40. A controller as claimed in any of claims 35 to 39, wherein the controller is configured to detect existence of at least one device belonging to a second group of devices, and, subsequent to said detection, to configure a second part into the data carrier entity for carrying beaconing information in association with the second group of devices.

41. A controller as claimed in claim 40, wherein the controller is configured to define the length of the second part.

42. A controller as claimed in claim 41 , wherein the controller is configured to dynamically define the length of the second part based on at least one of a request from at least one device and as a consequence of collisions between devices.

43. A controller as claimed in any of claims 35 to 42, wherein the controller is configured to receive a request for a second part for carrying beaconing information in association with a second group of devices and to control use of the requested second part.

44. A controller as claimed in claim 43, wherein the controller is configured to define at least one superframe and at least one period of the second part for enabling a device associated with the second group of devices to send beaconing information.

45. A wireless communication device comprising a controller as claimed in any of claims 35 to 44.

46. A data carrier entity configured to carry beaconing information, comprising at least two parts, wherein a first part is configured to carry beaconing information in association with a first group and a second part is configured to carry beaconing information in association with a second group.

47. A data carrier entity as claimed in claim 46, wherein the second part is configured to carry beaconing information in association with a group where devices require less beaconing information than devices in the other group or groups.

48. A control mechanism for a communication system, configured to use a data carrier entity as claimed in claim 46 or 47.

49. A wireless communication system comprising at least one wireless communication device as claimed in claim 45.

50. A wireless communication system as claimed in claim 49, the wireless communication system comprising a wireless personal area network.

51. A computer program comprising program code means adapted to perform any of steps of any of claims 1 to 34 when the program is run on a processor.