WO2012060781A1

WO2012060781A1 - Communication devices in a network and method for controlling a communication device

Info

Publication number: WO2012060781A1
Application number: PCT/SG2011/000390
Authority: WO
Inventors: Haiguang Wang; Jaya Shankar Pathmasuntharam; Zhongding Lei
Original assignee: Agency For Science, Technology And Research
Priority date: 2010-11-02
Filing date: 2011-11-02
Publication date: 2012-05-10

Abstract

The present invention is directed to a communication device for a network, the communication device comprising a message generating circuit configured to generate a message for sending to each of a plurality of communication devices in the network, wherein the message comprises a Media Access Control address associated with the plurality of communication devices, and a transmitter configured to send the message to each of the plurality of communication devices. The present invention is also directed to a communication device for a network, the communication device comprising a receiver configured to receive a message comprising a Media Access Control address associated with a plurality of communication devices in the network, a determining unit configured to determine whether the communication device is part of the plurality of communication devices, and a processor configured to process the message as a message addressed to the communication device if it is determined that the communication device is part of the plurality of communication devices. Methods for controlling a communication device are also disclosed.

Description

Communication Devices in a Network and Method for Controlling a

Communication Device

Cross-Reference To Related Application

[0001] This application makes reference to and claims the benefit of priority of an application for "Data Transmission Protection Scheme for IEEE 802.11 MU-MIMO Downlink" filed on November 2, 2010 with the Intellectual Property Office of Singapore, and there duly assigned application number 201008069-5. The content of said application filed on November 2, 2010 is incorporated herein by reference for all purposes, including an incorporation of any element or part of the description, claims or drawings not contained herein and referred to in Rule 20.5(a) of the PCT, pursuant to Rule 4.18 of the PCT.

Technical Field

[0002] Various embodiments generally relate to the field of communication devices in a network and methods for controlling a communication device.

Background

[0003] The IEEE 802.11 communication standard has been widely used for short range wireless network access. It is a complementary technology to the wired Local Area Network (LAN). However, compared to the wired communication, there are more challenges when using the wireless technology. For example, hidden terminal may be one such challenge. To solve this problem, the 802.1 1 communication standard uses Carrier Sensing Multiple Access / Collision Avoidance (CSMA/CA) to avoid collision. Request- to-Send (RTS) and Clear-to-Send (CTS) are used for media reservation. Nodes within the transmission range of source or destination are not allowed to transmit before the current transmission finished.

[0004] Figure 1 illustrates a basic view of the IEEE 802.11 technology in terms of (a) its topology and (b) its timeline transmission activities. The exemplary IEEE 802.11 network 100 of Figure 1(a) comprises a number of communication devices which may be a source (SRC) 102, a destination (DEST) 104 and others 106, such as a plurality of communication devices. The SRC 102 may send out a Request-to-Send (RTS) message or signal or packet 108. This RTS message 108 may be received by communication devices located within an area 112. As the DEST 104 is one of these communication devices within the area 1 12, it will send a reply Clear-to-Send (CTS) message or signal or packet 1 10. This CTS message 1 10 may be received by communication devices located within an area 114. As the SRC 102 is located within the area 114, the CTS message 1 10 is received by the SRC 102. The SRC 102 can then reserve channel time for data transmission with the DEST 104. As the others 106 are not responsive to the RTS message 108, they will not reply any CTS messages to the SRC 102. Therefore, no data transmission is performed between the SRC 102 and the others 106.

[0005] Figure 1(b) shows various transmission activities in the exemplary IEEE 802.11 network 100 of Figure 1(a) with respect to time 116. Time increases from left to right. In a Distributed Coordinate Functioning (DCF) protocol, the SRC 102 senses the status of the wireless medium or channel before transmitting. If the channel is continuously idle for DCF Interframe Space (DIFS) 120 duration, only then it is supposed to transmit a frame, in this case, containing the RTS message 108. If the channel is busy during the DIFS interval, the SRC 102 will defer its transmission (not shown in Figure 1(b)).

[0006] Upon receiving the RTS message 108, the DEST 104 waits for a Short Interframe Space (SIFS) 122 before acknowledging with the CTS message 110. After receiving CTS, the SRC 102 waits for a SIFS 122 and then sends data 124 to the DEST 104. Once the data 124 is received, the DEST 104 waits for a SIFS 122 before sending an acknowledgement (ACK) frame 126.

[0007] As for the others 106 when the RTS message 108 is received, the others 106 located within the area 1 12 will commence a Network Allocation Vector (NAV), in this case, a NAV (RTS) 128. The NAV is virtual carrier sensing mechanism used with wireless network protocols such as IEEE 802.11. The virtual carrier sensing is a logical abstraction which limits the need for physical carrier sensing at the air interface in order to save power. The NAV can be seen as a counter, which counts down to zero at a uniform rate. When the counter is zero, the virtual carrier sensing indication is that the medium is idle and when nonzero, the indication is busy. In a similar way, when the others 106 located in the area 114 receive the CTS message 110, they will also activate a NAV (CTS) 130. Once data transmission between the SRC 102 and the DEST 104 are completed with acknowledgement (ACK) 126, the NAV (RTS) 128 and the NAV (CTS) 130 counts down to zero and the others 106 will be released to carry out carrier sensing.

[0008] An on-going IEEE 802.1 lac or equivalent standard focuses on applying Multi- User Multi-Input- Multi-Output (MU-MIMO) technology in 802.1 1 based communication technology.

[0009] With the MU-MIMO technology, an 802.11 access point (AP) can send data to a few stations at the same time. With this technology, one of the challenges is the way of protecting data transmission over the IEEE 802.1 lac MU-MIMO downlink as the traditional RTS/CTS scheme cannot provide a complete protection over the transmission.

[0010] Assuming that there are two IEEE 802.11 networks. As shown in Figure 2, an access point (AP) 200 supports IEEE 802.1 lac technology. It has three stations, STA1 202, STA2 204 and STA3 206 attached to it. When the AP 200 wants to transmit data to STA1 202, STA2 204 and STA3 206 simultaneously with 802.1 lac MU-MIMO technology via a MU-MIMO downlink 208, an area 208 shown in Figure 2 is to be completely protected. That is, for stations 202, 204, 206 in the area defined by an outer boundary 310, either an RTS or CTS message, or both should be received.

[0011] On the other hand, Figure 3 shows an area 300 protected by a traditional single RTS 302/CTS 304 message. This protected area 300 is established by the RTS protection range 306 and the CTS protection range 308. It is observed that there are areas 310 which are not protected, as line-shaded in Figure 3. If a station STA4 312 is located in the unprotected areas 310 and if the STA4 312 is sending a signal 314 out to, for example, a different access point (AP2) 316, the signal 314 may also be received by a ST A3 318 which is located within the protected area 300. Collision 320 may also occur. Therefore, a scheme with more complete protection is necessary, especially when the data packets are long.

[0012] An alternative method to protect data transmission from collision on 802.1 1 systems is to use a CTS-to-Self scheme as illustrated in Figure 4, where an API 400 will send a CTS message 402 when it needs to send downlink packets 404 without receiving a RTS message first. However, this method can only provide protection within the coverage of the AP as defined by an area of CTS-to Self protection range 406. That is to say, for example, if a station STA4 408 is located outside the protected area 406 and if the STA4 408 is sending a signal 410 out to, for example, a different access point (AP2) 412, the signal 410 may also be received by a STA3 414 which is located within the protected area 406. Further, the drawback of such a protection is that it takes a longer time to transmit the same amount of data; thereby reducing the effective throughput.

[0013] Comparing to the full protection required as shown in Figure 2, the protection range provided by the CTS-to-Self scheme as described in Figure 4 is limited and also, it can only help in ACK protection instead of data transmission. This is because even if the CTS-to-Self scheme may collide with other transmissions, the data transmission proceeds as scheduled as seen between the STA3 414 and the STA4 408 of Figure 4. In contrast, the RTS/CTS protection for example, as described in Figure 3, data transmission will not proceed as scheduled when RTS or CTS is not transmitted or received properly.

[0014] In the scheme of Figure 3, the protected area is also less than the required complete protection area as seen in Figure 2. However, it is larger than the area protected by the CTS-to-Self scheme of Figure 4. An important point is that RTS/CTS can filter out part of potential collision in data transmission part. When they are not transmitted or received properly by the source or destination, data packet will not be transmitted. Instead, the source waits for future opportunity to do RTS/CTS transaction again.

[0015] In yet another scheme, the scheme uses single RTS multiple CTS method. As the name implies, after the AP sends out a RTS message, desired reception stations may send back CTS messages either sequentially or simultaneously. Figure 5 and Figure 6 show the two possible way of CTS transmission of sending CTS packets sequentially or simultaneously, respectively. In Figures 5 and 6, time increases from left to right. Sending multiple CTS packets back sequentially is easier in design and implementation.

[0016] More specifically in Figure 5, the SIFS may also include reduced interframe space (RIFS) 500. Further, just prior to the data frames 502, a legacy signal (L-SIG) 504 followed by a high throughput signal field (HT-SIG) 506 are provided. The HT-SIG 506 is used to carry information required to interpret the high throughput packet formats. The acknowledgement (ACK) frames may be block acknowledgements (BA) for example, BA1 508, BA2 510 and BA3 512 of Figure 5.

[0017] More specifically in Figure 6, each of the intervals between the RTS message 600 and the CTS message 602 is based on an interframe space (xIFS) time 604.

[0018] The drawback with the schemes of Figures 5 and 6 is that these schemes typically require modifying the RTS packet format by including the Media Access Control (MAC) addresses of multiple stations. This often leads to compatibility issue as legacy stations cannot decode the RTS packet with multiple receiving addresses. Although multi-cast MAC address can be used for address multiple stations, the way of allocating the multicast MAC address and the way of assigning them are yet to be defined. In addition, overheads could be an issue when multiple CTS messages are sent back unnecessarily. Despite the reduction in overheads in time for schemes where CTS packets are sent simultaneously, addressing multiple stations remains nonetheless unsolved. In addition, simultaneous sending of CTS packets also requires precise time synchronization among stations.

[0019] As described above, the IEEE 802.1 lac defines a new technology for the data transmission with Wireless Local Area Networks (WLAN). Different from a traditional WLAN technology, MU-MIMO technology is applied in the design and multiple data packets are allowed to transmit to multiple stations simultaneously. This feature makes the transmission protection provided by traditional RTS/CTS schemes incomplete.

[0020] Thus, there is a need to provide a communication device and a method of controlling a communication device seeking to address at least the problems above so as to make the system more reliable and more efficient in data transmission. Summary of the Invention

[0021] In a first aspect, the present invention relates to a communication device for a network, the communication device comprising a message generating circuit configured to generate a message for sending to each of a plurality of communication devices in the network, wherein the message comprises a Media Access Control address associated with the plurality of communication devices, and a transmitter configured to send the message to each of the plurality of communication devices.

[0022] According to a second aspect, the present invention relates to a method for controlling a communication device in a network, the method comprising generating a message for sending to each of a plurality of communication devices in the network, wherein the message comprises a Media Access Control address associated with the plurality of communication devices, and sending the message to each of the plurality of communication devices.

[0023] In accordance to a third aspect, the present invention also relates to a communication device for a network, the communication device comprising a receiver configured to receive a message comprising a Media Access Control address associated with a plurality of communication devices in the network, a determining unit configured to determine whether the communication device is part of the plurality of communication devices, and a processor configured to process the message as a message addressed to the communication device if it is determined that the communication device is part of the plurality of communication devices.

[0024] According to a fourth aspect, the present invention relates to a method for controlling a communication device in a network, the method comprising receiving a message comprising a Media Access Control address associated with a plurality of communication devices in the network, determining whether the communication device is part of the plurality of communication devices, and processing the message as a message addressed to the communication device if it is determined that the communication device is part of the plurality of communication devices. Brief Description of the Drawings

[0025] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:

[0026] Figure 1 shows a schematic view of the IEEE 802.11 technology in terms of (a) its topology and (b) its timeline transmission activities;

[0027] Figure 2 shows a schematic topological view of a complete protection required for MU-MIMO downlink;

[0028] Figure 3 shows a schematic topological view of an area protected by single RTS/CTS scheme;

[0029] Figure 4 shows a schematic topological view of a protection range achieved with CTS-to-Self messages;

[0030] Figure 5 shows a schematic timeline-based view of transmission activities of a single RTS with multiple CTS being sent sequentially;

[0031] Figure 6 shows a schematic timeline-based view of transmission activities of a single RTS with multiple CTS being sent simultaneously;

[0032] Figure 7 shows a schematic block diagram of a communication device, in accordance to various embodiments;

[0033] Figure 8 shows a representation of a RTS packet format, in accordance to various embodiments;

[0034] Figure 9 shows a representation of a CTS packet format, in accordance to various embodiments;

[0035] Figure 10 shows a representation of a RTS-to-Self format, in accordance to various embodiments;

[0036] Figure 11 shows a schematic block diagram of a communication device, in accordance to various embodiments; [0037] Figure 12 shows a schematic topological view of an example of an AP detecting conflict between Group ID and MAC address, in accordance to various embodiments;

[0038] Figure 13 shows a schematic topological view of another example of an AP detecting conflict between Group ID and MAC address, in accordance to various embodiments;

[0039] Figure 14 shows a schematic topological view of an example of an AP using a group ID directly as a group MAC address, in accordance to various embodiments;

[0040] Figure 15 shows a schematic topological view of an example of handling a lost CTS message, in accordance to various embodiments;

[0041] Figure 16 shows a schematic block diagram of a method of controlling a communication device in a network, in accordance to various embodiments;

[0042] Figure 17 shows a schematic block diagram of a communication device, in accordance to various embodiments;

[0043] Figure 18 shows a schematic block diagram of a communication device, in accordance to various embodiments; and

[0044] Figure 19 shows a schematic block diagram of a method of controlling a communication device in a network, in accordance to various embodiments.

Detailed Description

[0045] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, and logical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. [0046] In order that the invention may be readily understood and put into practical effect, particular embodiments will now be described by way of examples and not limitations, and with reference to the figures.

[0047] In a first aspect, a communication device for a network is provided as shown in Figure 7. In Figure 7, the communication device 700 comprises a message generating circuit 702 configured to generate a message for sending to each of a plurality of communication devices in the network, wherein the message comprises a Media Access Control address associated with the plurality of communication devices; and a transmitter 704 configured to send the message to each of the plurality of communication devices.

[0048] In the context of various embodiments, the term "associated with" may refer to having a link to or establishing a relationship with. For example, "associated with" may be interchangably referred as "assigned to", or "having", or "belong to", or "allocated to".

[0049] As used herein, the term "Media Access Control address" abbreviated as MAC address refers to a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies including Ethernet. MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model.

[0050] The term "communication device" may for example refer to a machine that assists data transmission, that is sending and/or receiving data information. A communication device may be, for example but not limited to, a station, or a base station, or a substation, or an access point, or a modem, a cable, or a port. In some embodiments, the communication device 700 may comprise an access point of a wireless communication network. The plurality of communication devices may be referred to as a plurality of stations.

[0051] As used herein, the term "network" refers to a communication network or a wireless communication network. For example, the network may be a IEEE 802 network.

[0052] In the context of various embodiments, the term "message" generally refers to a short information sent from one entity to at least another one entity. A message may be a packet or a cluster. [0053] In various embodiments, prior to data transmission, a media reservation may be established between a communication device 700, for example, an access point and its targeted plurality of communication devices, for example, a plurality of stations. The communication device 700 may generate and send a message to the plurality of communication devices to initiate the media reservation. Any of the plurality of communication devices may also initiate the media reservation by generating and sending a message to the communication device 700. An identifier or a multicast identifier such as a Media Access Control address may be appended in the message so that a communication device or a station receiving the message can check whether it is associated with this address, for example, whether it is of the same address. If so, the message may be meant for this communication device as a recipient and the recipient may check the rest of the message and react to it accordingly. If the communication device or the station is not associated with the address, it may mean that this communication device or station may not be an intended recipient and it may not react to the message. The message may contain requests and information that is necessary for at least establishing, maintaining and terminating the communication link.

[0054] In accordance to various embodiments, the message may indicate that the communication device is ready to send data to each of the plurality of communication devices in the network. For example, the message may a Request-to-Send message.

[0055] Figure 8 shows a Request-to-Send (RTS) packet format. In Figure 8, a RTS packet format 800 comprises an about 16 μβ preamble 802, followed by an about 10 μβ Physical Layer Convergence Procedure (PLCP) frame 804, a typically 20-octet RTS Media Access Control (MAC) frame 806, followed by a typically 6-bit tail 808 and a pad or padding field 810 for proving proper spacing. The RTS MAC frame 806 comprises a 2-octet frame control (FC) 812, a 2-octet duration ID 814, a 6-octet receiver address (RA) 816, a 6-octet transmitter or send address (TA) 818 and a 4-octet frame check sequence (FCS) 820.

[0056] Group addressing with pre-allocated MAC Address from IEEE MAC Address Space according to one embodiment is provided. To address multiple stations with a single MAC address, the simplest scheme is to assign a group MAC address and notify the stations within the group about the assignment. Then this address is used in the RTS message. When receiving an RTS message with a group address, the stations in the group can react, for example, to send or not to send a Clear-to-Send (CTS) message, based on their respective configurations.

[0057] For example, on one hand, a group MAC address may only be assigned to one group of stations associated with an access point (AP). On the other hand, the same group MAC address may be assigned to groups under a different AP if the stations in those groups have both the group MAC address and a transmitter address. A station should only reply to a RTS message with a group MAC address sent by the AP it associates with. Therefore, a group can be uniquely identified by a group MAC address and the MAC address of the AP who assigns this group MAC address to it.

[0058] In obtaining and allocating the MAC address, the Institute of Electrical and Electronic Engineering (IEEE) assigns a MAC address at a price of about S$550 for each block of 4096 MAC addresses. A company or an individual may purchase and allow the AP produced/owned to use the MAC address for group communication. With this method, an AP sends group MAC address information to the stations when they are included into a certain group. Therefore, different manufacturer or individual may have to pay for the MAC address.

[0059] To reduce the cost of address purchasing and signaling exchanging, an improved way is to allocate some MAC addresses from the IEEE MAC address space and share them among all the producers. This not only saves the cost for MAC addresses purchasing, but also reduce the number of MAC address used for communication.

[0060] In various embodiments, the message may comprise a group address corresponding to the Media Access Control address. The group address may be derived from a physical layer group address or may be assigned by an authoritative body such as the IEEE. For example, the group address may comprise a group ID. In various embodiments, the Media Access Control address may be mapped to the group ID.

[0061] The physical layer refers to the first layer of the Open Systems Interconnection model (OSI model), which is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communication system in terms of abstraction layers. Similar communication functions are grouped into logical layers.

[0062] In IEEE 802.1 lac PHY (physcial) layer, there is a group ID for use to identify the potential multiple reception stations for the current transmission at the physical layer. To reduce signaling overhead for a group MAC address assignment, a static mapping may be setup between the group ID and the MAC address. For example, the group ID 0x00 corresponds to a reserved group MAC address OxabcdOO, 0x01 corresponds to OxadcdOl and so on. As used herein, the addresses are in HEX representations. A group MAC address may be allocated automatically or pre-allocated during the negotiation of the group ID for the physical layer. This simplifies the implementation.

[0063] In an example, an access point (AP) may transmit a RTS message with a group MAC address/group ID to the network and one or several stations belong to the group can send back a CTS message based on a predefined schedule. This way to a single RTS message and multiple CTS messages are transmitted to protect the data transmission on the IEEE 802.1 lac MU-MIMO downlink. This scheme provides an improved protection over the data transmission and an improved efficiency since not every station is required to send back a CTS message and therefore relieves a medium's or a channel's bandwidth for other data transmission.

[0064] In various embodiments, the message may comprise a Clear-to-Send (CTS) message. Figure 9 shows a representation of a CTS packet format. The CTS packet format 900 comprises an about 16 μβ preamble 902, followed by an about 10 μβ PLCP frame 904, a typically 14-octet CTS MAC frame 906, followed by a typically 6-bit tail 908 and a pad or padding field 910 for proving proper spacing. The CTS MAC frame 906 comprises a 2-octet FC 912, a 2-octet duration ID 914, a 6-octet RA 916, and a 4-octet FCS 918.

[0065] For example, an AP may also send a CTS message with a group MAC address for acknowledgement (ACK) protection. Stations that are not in the group can give up the decoding of the following data packet.

[0066] Besides reserving a MAC address for group communication at the 802.1 lac MAC layer, the group ID may be used to directly for addressing in a RTS packet. In cases where some devices may have MAC addresses that are the same as group IDs such that the devices associate to an AP cannot differentiate whether the MAC address in a RTS message is for uni-cast or for multicast (or interchangably referred to as group communication), various embodiments provide the Media Access Control address of the communication device 700 being comprised in a receiver address field of the message. The group address may be comprised in a transmitter address field of the message.

[0067] This way, addressing multiple stations in a RTS message without changing the RTS packet format is achieved. Compatibility with legacy or incumbent stations can also be maintained. For example, it may be used by a 802.1 lac AP to address multiple stations in the RTS message.

[0068] For example, an AP may skip certain group ID and use other group IDs in group assignment. However, in case there is a station in Ad Hoc Mode but not associated to the AP, it may receive a RTS message with a group ID which is the same its own MAC address. If the station in Ad Hoc mode sends back a CTS message, then collision may happen. To avoid this from occurring, a RTS-to-Self scheme is used instead of a normal RTS scheme to allow multiple CTS messages be sent back from the stations. With this scheme, the RA field 1000 in the RTS message 1002 is set to the MAC address of the AP 1004 and the TA field 1006 of the RTS packet 1002 is set to group ID 1008 as illustrated in Figure 10 showing a representation of the format of the RTS-to-Self message.

[0069] For the stations associate to this AP, they will know that the RTS message 1002 is sent to a group of stations and the stations in the group may send back a CTS message to the AP. For the station with MAC address the same as group ID, it will not send back a CTS message when receiving RTS-to-Self messages, for example, similar to the RTS message 1002 as it is not the intended receiver.

[0070] In various embodiments, the message may request each communication device of the plurality of communication devices to transmit a response message indicating that the respective communication device of the plurality of communication devices is ready to receive the data. In one embodiment, the respective communication device of the plurality of communication devices may refer to one or more of the plurality of communication devices. [0071] In other embodiments, the message may be transmitted according to a communication protocol according to which the plurality of communication devices transmit respective response messages in response to the message, wherein each of the response messages indicates that the respective communication device of the plurality of communication devices is ready to receive the data.

[0072] The communication protocol may be, for example but not limited to, IEEE 802 protocol or IEEE 802.1 1 protocol or IEEE 802.1 lac protocol. The response message may be a Clear-to-Send message. In some embodiments, for each of the plurality of the communication devices, each Clear-to-Send message may be sent one after another in sequence. This allows for balancing the overhead and protection. In other embodiments, for each of the plurality of the communication devices, the Clear-to-Send messages may be sent simultaneously.

[0073] In various embodiments as seen in Figure 1 1, the communication device 700 may further comprise a receiver 1100 configured to receive a message sent by any communication device in the network.

[0074] The communication device 700 may further comprise a determining unit 1102 for determining collision if the message received by the receiver is a Request-to-Send message with a transmitter address being the same as the Media Access Control address, the Request-to-Send message being sent by any communication device that is not associated with the Media Access Control address, or if the message received by the receiver 1 100 is a Clear-to-Send message sent by one of the plurality of communication devices associated with the Media Access Control address, wherein the Clear-to-Send message being sent is not in response to a Request-to-Send message sent by the communication device 700. In response to the determining unit determining collision, the message generating circuit 702 may be configured to generate a message for sending to each of the plurality of communication devices in the network, wherein the message comprises a different Media Access Control address associated with the plurality of communication devices. In various embodiments, the different Media Access Control address may be any Media Access Control address that is not the same as the Media Access Control address previously used or currently being used. [0075] For example, in the event that the station (with a MAC address equivalent to an existing group ID) sends a RTS message to an AP, the AP can detect the conflict by receiving a RTS message from the station directly or receiving a CTS message from stations belonging to the group when no RTS message with a group address has been transmitted.

[0076] Figure 12 and Figure 13 show the scenario of the group ID and MAC address conflict detection.

[0077] In the scenario of Figure 12, an API 1200 receives a RTS message 1202 with a TA address that is the same as a group ID sent by STA4 1204, which is not associated with the plurality of communication devices, such as the STAl 1206, STA2 1208, and STA3 1210. The API 1200 can therefore detect collision of group ID and MAC address. A new (different) group ID will then be assigned to the group of STAl 1206, STA2 1208, and STA3 1210.

[0078] In the scenario of Figure 13, a STA3 1300 receives a RTS message 1302 with a TA address that is same as a group ID sent by STA4 1304, which is not associated with the plurality of communication devices, such as the STAl 1306, STA2 1308, and STA3 1300. The STA3 1300 then sends a CTS message to a API 1310. The API 1310 then detects a collision of group ID and MAC address. A new (different) group ID will then be assigned to the group of STAl 1306, STA2 1308, and STA3 1300.

[0079] To ensure the detection of an unassociated station with a MAC address equivalent to a group ID, every station in the group is to send a CTS message back to facilitate the detection.

[0080] In IEEE 802.1 lac, when stations receive transmission from an AP, if it is not included in a group ID, which is placed at the beginning of a frame at the PHY layer, the stations can stop the processing of the following part of frame. Similarly, for a RTS message with the group ID, the stations that are not include in the group can idle based on the NAV duration information contained in the RTS packet.

[0081] In various embodiments, the message received by the receiver 1 100 (as seen in Figure 11) may be a notification signal sent by one of the plurality of communication devices, wherein the notification signal indicates whether a Clear-to-Send message is to be sent upon receiving a Request-to-Send message comprising the Media Access Control address.

[0082] For example, given there are multiple stations within one group, the transmission of a CTS message may not be necessary if communications on the same channel from nearby APs and their station are rare. Therefore, the station can send a notification signal to notify the AP that it is not going to send a CTS message when receiving a RTS message to the group it belongs to. When situation changes, it may send a notification signal to indicate that a CTS message will be generated when receiving a RTS message for the group. Acknowledgement may be sent for confirmation of the change. The AP should derive the duration value for NAV when sending a RTS message based on the number of CTS messages expected. As used above, the term "notification signal" may be in the form of a message or a flag.

[0083] In various embodiments, the message may be sent to each of the plurality of communication devices to establish a communication link for data transmission between the communication device 700 and the plurality of communication devices.

[0084] In various embodiments, the communication device 700 as shown in Figure 1 1 may further comprise a transmitter 1104 configured to transmit the data after a predetermined time period after the transmission of the message. The transmitter 1104 may be configured to transmit the data to the plurality of communication devices using MIMO.

[0085] In other embodiments, the transmitter 1 104 may be configured to transmit different data to be sent to different communication devices of the plurality of communication devices in parallel. The data may be transmitted according to a communication protocol requesting the plurality of communication devices to acknowledge receipt of the data. The communication protocol may be as defined above.

[0086] Various embodiments and examples for group addressing in a RTS message allows an 802.1 lac AP to receive multiple CTS messages by sending one RTS message, and is compatible with legacy 802.11 stations. It also helps in energy saving because when stations receiving a RTS message with a group MAC address, if they are not in the group, they can stop listening to the channel until transmission activity ends. [0087] For selective CTS transmission, whether a CTS message is necessary for a given station depends on the environment. It only transmits when it senses that other 802.11 networks on the same channel are nearby and packet loss is non-negligible. Stations are allowed to send in messages to indicate whether a CTS message is necessary. When sending a RTS message, the AP checks the number of CTS messages required to send back and then set the duration value in the RTS packet accordingly. In the event that a station not belonging to the same group to be addressed by the AP (or more generally referred to as a non-station) indicates that a CTS message is necessary, the AP may either establish a RTS meassge (or a RTS-to-Self message) or a CTS-to-Self message for protection. A group address can also be put in a CTS-to-Self message.

[0088] There is provided a way for a RTS message to send out a group address so that stations under the AP will send back a CTS message based on a predefined schedule.

[0089] For example, as described above, there are two approaches for addressing the group of stations. They are simple to implement, and advantageously save signaling exchange for group addressing, and compatible with legacy system.

[0090] A first approach reserves a block for a MAC address from the IEEE 802 MAC address. The group address assignment is done through signaling exchange between an AP and its related (or associated) stations. When receiving a RTS message with a group MAC address, the stations know whether a CTS message should be sent back and when the CTS message should be sent back. A group ID of the IEEE 802.1 lac PHY layer and the group MAC address may be used. That is, for each group ID defined in the 802.1 lac PHY layer, a MAC address will be assigned to group.

[0091] A second approach uses the group ID as a group MAC address. By placing the MAC address of an AP into the receiving address and the group ID into the transmitting address, the stations know which group the RTS message is sent to and a CTS message may sent back based on the signaling information exchanged among the stations. If there are stations with MAC addresses are the same as the group ID, then either the AP gives up the group ID or only using the traditional single RTS/CTS scheme for protection.

[0092] Figure 14 shows a schematic topological view of an example illustrating an AP using a group ID directly as a group MAC address, in accordance to various embodiments. In Figure 14, an API 1400 sends a RTS message 1402 with a group ID as a group MAC address. As the STA1 1404, the STA2 1406 and the STA3 1408 being associated with the group ID, in this case being the group MAC address, MU-MIMO downlink 1410 is established between the API 1400 and these stations 1404, 1406, 1408. Although the STA4 1412 is located near the STA3 1408 and within an area which the RTS message can reach, the STA4 1412 being associated with a different AP2 1414 does not respond to the RTS message and no MU-MIMO is established between the STA4 1412 and the API 1400.

[0093] In the event that a CTS message is lost due to channel corruption or unable to receive at the target duration, the data packet to the station may be excluded from the transmission as illustrated in Figure 15. An API 1500 in Figure 5 establishes a RTS protection range 1502. The STA1 1504 and the STA2 1506 receiving the RTS message, each responds with a CTS message 1508, 1510. The STA1 1504 further has a CTS protection range 1512 which encompasses the STA2 1506. In the example, the CTS message of STA3 1514 is lost. The API may exclude data transmission to the STA3 1514. However, on the other hand, if the API 1500 proceeds with the MU-MIMO downlink 1516 with the ST A3 1514, the ST A3 1514 may at the same time receive a message from a STA4 1518, which is located outside the protected area and the message may be for a different AP2 1520, thus collision may occur in transmission 1522.

[0094] In a second aspect, a method for controlling a communication device in a network is provided as shown in Figure 16. The method 1600 comprises generating a message for sending to each of a plurality of communication devices in the network 1602, wherein the message comprises a Media Access Control address associated with the plurality of communication devices; and sending the message to each of the plurality of communication devices 1604.

[0095] In various embodiments, the generating the message 1602 may comprise generating a message indicating readiness to send data to each of the plurality of communication devices in the network. The sending the message 1604 may comprise transmitting the message according to a communication protocol according to which the plurality of communication devices transmit respective response messages in response to the message, wherein each of the response messages indicates that the respective communication device of the plurality of communication devices is ready to receive the data. The response messages may be sent by the plurality of communication devices simultaneously.

[0096] In a third aspect, a communication device for a network is provided as illustrated in Figure 17. The communication device 1700 comprises a receiver 1702 configured to receive a message comprising a Media Access Control address associated with a plurality of communication devices in the network; a determining unit 1704 configured to determine whether the communication device 1700 is part of the plurality of communication devices; and a processor 1706 configured to process the message as a message addressed to the communication device 1700 if it is determined that the communication device 1700 is part of the plurality of communication devices.

[0097] In the context of various embodiments, the phrase "the communication device is part of the plurality of communication devices" may refer to the communication device 1700 having an address which is associated with, or corresponds to, or is the same as the address of the plurality of communication devices.

[0098] In various embodiments, the determining unit 1704 may determine collision if the message is a Request- to- Send message with a transmitter address being the same as the Media Access Control address associated with the plurality of communication devices, wherein the Request-to-Send message is sent by any communication device that is not associated with the Media Access Control address, or if the message is a Clear-to-Send message sent by one of the plurality of communication devices associated with the Media Access Control address, wherein the Clear-to-Send message being sent is not in response to a Request-to-Send message sent by a communication device associated with the Media Access Control address.

[0099] In various embodiments as seen in Figure 18, the communication device 1700 may further comprise a message generating circuit 1800 configured to generate a message for sending to each of the plurality of communication devices in the network, wherein in response to determining collision, the message comprises a different Media Access Control address associated with the plurality of communication devices. [00100] In a fourth aspect, a method for controlling a communication device in a network is provided as shown in Figure 19. The method 1900 comprises receiving a message comprising a Media Access Control address associated with a plurality of communication devices in the network 1902, determining whether the communication device is part of the plurality of communication devices 1904, and processing the message as a message addressed to the communication device if it is determined that the communication device is part of the plurality of communication devices 1906.

[00101] In various embodiments, the method 1900 may further comprise determining collision if the message is a Request-to-Send message with a transmitter address being the same as a Media Access Control address associated with a plurality of communication devices, wherein the Request-to-Send message is sent by any communication device that is not associated with the Media Access Control address, or if the message is a Clear-to- Send message sent by one of the plurality of communication devices associated with the Media Access Control address, wherein the Clear-to-Send message being sent is not in response to a Request-to-Send message sent by a communication device associated with the Media Access Control address.

[00102] The method may further comprise generating a message for sending to each of the plurality of communication devices in the network in response to determining collision, wherein the message comprises a different Media Access Control address associated with the plurality of communication devices.

[00103] In the context of various embodiments, the term "about" or "approximately" as applied to a numeric value encompasses the exact value and a variance of +/- 5% of the value.

[00104] The phrase "at least substantially" may include "exactly" and a variance of +/- 5% thereof. As an example and not limitation, the phrase "A is at least substantially the same as B" may encompass embodiments where A is exactly the same as B, or where A may be within a variance of +/- 5%, for example of a value, of B, or vice versa.

[00105] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

1. A communication device for a network, the communication device comprising:

a message generating circuit configured to generate a message for sending to each of a plurality of communication devices in the network, wherein the message comprises a Media Access Control address associated with the plurality of communication devices; and

a transmitter configured to send the message to each of the plurality of communication devices.

2. The communication device as claimed in claim 1, wherein the message indicates that the communication device is ready to send data to each of the plurality of communication devices in the network.

3. The communication device as claimed in claim 2, wherein the message is a Request-to-Send message.

4. The communication device as claimed in claim 2 or 3, wherein the message comprises a group address corresponding to the Media Access Control address.

5. The communication device as claimed in claim 4, wherein the group address is derived from a physical layer group address or is assigned by an authoritative body such as the IEEE.

6. The communication device as claimed in claim 4 or 5, wherein the Media Access Control address of the communication device is comprised in a receiver address field of the message.

7. The communication device as claimed in claim 6, wherein the group address is comprised in a transmitter address field of the message.

8. The communication device as claimed in any one of claims 2 to 7, wherein the message requests each communication device of the plurality of communication devices to transmit a response message indicating that the respective communication device of the plurality of communication devices is ready to receive the data.

9. The communication device as claimed in any one of claims 2 to 7, wherein the message is transmitted according to a communication protocol according to which the plurality of communication devices transmit respective response messages in response to the message, wherein each of the response messages indicates that the respective communication device of the plurality of communication devices is ready to receive the data.

10. The communication device as claimed in claim 8 or 9, wherein the response message is a Clear-to-Send message.

11. The communication device as claimed in claim 10, wherein for each of the plurality of the communication devices, each Clear-to-Send message is sent one after another in sequence.

12. The communication device as claimed in claim 10, wherein for each of the plurality of the communication devices, the Clear-to-Send messages are sent simultaneously.

13. The communication device as claimed in any one of claims 1 to 12, further comprising a receiver configured to receive a message sent by any communication device in the network.

14. The communication device as claimed in claim 13, further comprising a determining unit for determining collision if the message received by the receiver is a Request-to-Send message with a transmitter address being the same as the Media Access Control address, the Request-to-Send message being sent by any communication device that is not associated with the Media Access Control address, or if the message received by the receiver is a Clear-to-Send message sent by one of the plurality of communication devices associated with the Media Access Control address, wherein the Clear-to-Send message being sent is not in response to a Request-to-Send message sent by the communication device.

15. The communication device as claimed in claim 14, wherein in response to the determining unit determining collision, the message generating circuit is configured to generate a message for sending to each of the plurality of communication devices in the network, wherein the message comprises a different Media Access Control address associated with the plurality of communication devices.

16. The communication device as claimed in claim 13, wherein the message received by the receiver is a notification signal sent by one of the plurality of communication devices, wherein the notification signal indicates whether a Clear-to-Send message is to be sent upon receiving a Request-to-Send message comprising the Media Access Control address.

17. The communication device as claimed in claim 1, wherein the message is a Clear-to-Send message.

18. The communication device as claimed in any one of claims 1 to 17, wherein the message is sent to each of the plurality of communication devices to reserve a wireless media for data transmission between the communication device and the plurality of communication devices.

19. The communication device as claimed in any one of claims 2 to 18, further comprising a transmitter configured to transmit the data after a predetermined time period after the transmission of the message.

20. The communication device as claimed in claim 19, wherein the transmitter is configured to transmit the data to the plurality of communication devices using MIMO.

21. The communication device as claimed in claim 19 or 20, wherein the transmitter is configured to transmit different data to be sent to different communication devices of the plurality of communication devices in parallel.

22. The communication device as claimed in any one of claims 19 to 21, wherein the data is transmitted according to a communication protocol requesting the plurality of communication devices to acknowledge receipt of the data.

23. The communication device as claimed in any one of claims 1 to 22, wherein the communication device is an access point of a wireless communication network.

24. A method for controlling a communication device in a network, the method comprising:

generating a message for sending to each of a plurality of communication devices in the network, wherein the message comprises a Media Access Control address associated with the plurality of communication devices; and

sending the message to each of the plurality of communication devices.

25. The method as claimed in claim 24, wherein generating the message comprises generating a message indicating readiness to send data to each of the plurality of communication devices in the network.

26. The method as claimed in claim 24 or 25, wherein sending the message comprises transmitting the message according to a communication protocol according to which the plurality of communication devices transmit respective response messages in response to the message, wherein each of the response messages indicates that the respective communication device of the plurality of communication devices is ready to receive the data.

27. The method as claimed in claim 26, wherein the response messages are sent by the plurality of communication devices simultaneously.

28. A communication device for a network, the communication device comprising:

a receiver configured to receive a message comprising a Media Access Control address associated with a plurality of communication devices in the network;

a determining unit configured to determine whether the communication device is part of the plurality of communication devices; and

a processor configured to process the message as a message addressed to the communication device if it is determined that the communication device is part of the plurality of communication devices.

29. The communication device as claimed in claim 28, wherein the determining unit determines collision if the message is a Request-to-Send message with a transmitter address being the same as the Media Access Control address associated with the plurality of communication devices, wherein the Request-to-Send message is sent by any communication device that is not associated with the Media Access Control address, or if the message is a Clear-to-Send message sent by one of the plurality of communication devices associated with the Media Access Control address, wherein the Clear-to-Send message being sent is not in response to a Request-to-Send message sent by a communication device associated with the Media Access Control address.

30. The communication device as claimed in claim 29, further comprising a message generating circuit configured to generate a message for sending to each of the plurality of communication devices in the network, wherein in response to determining collision, the message comprises a different Media Access Control address associated with the plurality of communication devices.

31. A method for controlling a communication device in a network, the method comprising:

receiving a message comprising a Media Access Control address associated with a plurality of communication devices in the network;

determining whether the communication device is part of the plurality of communication devices; and

processing the message as a message addressed to the communication device if it is determined that the communication device is part of the plurality of communication devices.

32. The method as claimed in claim 31, further comprising determining collision if the message is a Request-to-Send message with a transmitter address being the same as a Media Access Control address associated with a plurality of communication devices, wherein the Request-to-Send message is sent by any communication device that is not associated with the Media Access Control address, or if the message is a Clear-to- Send message sent by one of the plurality of communication devices associated with the Media Access Control address, wherein the Clear-to-Send message being sent is not in response to a Request-to-Send message sent by a communication device associated with the Media Access Control address.

33. The method as claimed in claim 32, further comprising generating a message for sending to each of the plurality of communication devices in the network in response to determining collision, wherein the message comprises a different Media Access Control address associated with the plurality of communication devices.