Source: https://patents.google.com/patent/US8971351B2/en
Timestamp: 2020-02-18 06:49:34
Document Index: 166406574

Matched Legal Cases: ['Application No. 201110124432', 'Application No. 2011', 'Application No. 2011', 'Application No. 2011', 'Application No. 2011', 'Application No. 2011', 'Application No. 2013168490']

US8971351B2 - Enhanced carrier sensing for multi-channel operation - Google Patents
US8971351B2
US8971351B2 US13/568,563 US201213568563A US8971351B2 US 8971351 B2 US8971351 B2 US 8971351B2 US 201213568563 A US201213568563 A US 201213568563A US 8971351 B2 US8971351 B2 US 8971351B2
US13/568,563
US20120300707A1 (en
2012-08-07 Priority to US13/568,563 priority patent/US8971351B2/en
2012-11-29 Publication of US20120300707A1 publication Critical patent/US20120300707A1/en
2015-03-03 Publication of US8971351B2 publication Critical patent/US8971351B2/en
In various embodiments, a multi-channel request-to-send and a multi-channel clear-to-send may be used in a wireless communications network to assure that a subsequent multi-channel communications exchange between two devices takes place only over channels that are sensed by both devices as being free.
For wireless communications networks operating under various standards, a device may sometimes transmit simultaneously over multiple channels, therefore increasing the amount of data that may be transmitted in a specified time period. Before making such a multi-channel transmission, a device may sense whether any of those narrow channels are currently busy. However, a channel that is sensed as free by the intended transmitter may be sensed as busy by the intended receiver due to the so-called hidden node problem (for example, a receiver at the edge of the current network may be able to hear signals from a device in a neighboring network that aren't strong enough to reach the transmitter of the current network). If the transmitter goes ahead and transmits because it isn't aware of that hidden node, the receiver may not be able to correctly receive the transmission due to interference from the neighboring device on any of those channels. Networks that exclusively use a single channel for communication may use a Request-to-Send/Clear-to-Send (RTS/CTS) exchange for avoiding the hidden-node problem, but in these exchanges both RTS and CTS are transmitted on a single channel. If the interfering signal is on one of the other channels that are contained in the transmission, the transmitter will not be aware of it and will transmit a signal that probably won't be received.
The term “wireless” may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that communicate data by using modulated electromagnetic radiation through a non-solid medium. A wireless device may comprise at least one antenna, at least one radio, and at least one processor, where the radio's transmitter transmits signals through the antenna that represent data and the radio's receiver receives signals through the antenna that represent data, while the processor may process the data to be transmitted and the data that has been received. The processor may also process other data which is neither transmitted nor received.
The term “network controller” (NC) is intended to mean a device that schedules and controls, at least partially, wireless communications by other devices in the network. A network controller may also be known as a base station (BS), access point (AP), central point (CP), or any other term that may arise to describe the functionality of a network controller. In a multi-channel network, a number of channels may generally be available to use for communications between devices in the network. These available channels may be specified by industry standard, by government regulations, by the limitations of the network devices themselves, or through any other feasible means. Of the available channels, the NC may select which ones may be used in a specific communication between two specific devices in the network. The NC may change this selection from time to time as it deems appropriate.
The term “mobile device” (MD) is intended to mean a device whose wireless communications are at least partially scheduled and controlled by the network controller. A mobile device may also be known as a mobile node, a STA, a subscriber station (SS), user equipment (UE), or any other term that may arise to describe the functionality of a mobile device. Mobile devices may move during such communications, but movement is not required.
The term “free channel” is intended to mean a channel that has been determined as not being in use, as sensed by the device making the determination, and therefore may be available for use by that device. In various embodiments, the determination may be made by monitoring the amount of electromagnetic energy sensed on that channel, by trying to decode data that has been encoded on that channel, or by any other feasible means that would indicate that the sensing device could use the channel for communications without a high, likelihood of interference. In some situations, when two devices are to communicate with each other, it is possible that one device may sense a channel as free but the other device will sense the channel as busy, because of their relative distances from the device that is already using that channel.
The term multi-channel request-to-send (MRTS) is intended to mean a request-to-send (RTS) that requests a reservation for multiple channels. A multi-channel clear-to-send (MCTS) is intended to mean a clear-to-send (CTS) that agrees to a reservation for one or more multiple channels in response to an MRTS. Just as an RTS/CTS exchange may be used to reserve a single channel, an MRTS/MCTS exchange may be used to reserve multiple channels for the same period of time.
In various embodiments, a first wireless device may transmit an MRTS to a second wireless device indicating which of multiple channels are sensed as free by the first device. The second device may reply with an MCTS that indicates which of those free channels are also sensed as free by the second device. After this MRTS/MCTS exchange, the first device will have a list of available channels that are sensed as free by both devices, and the hidden node problem may thereby be avoided in a subsequent multi-channel communication by using only those channels that are sensed as free by both devices.
FIG. 2 shows a flow diagram of communications between two devices, according to an embodiment of the invention. In flow diagram 200, the two devices are labeled as a requestor and a responder. Each device may transmit and receive at different times during the exchange. For this document, the device that requests the communication (by transmitting an MRTS) is called the requestor, and the device that responds to that request (by transmitting an MCTS) is called the responder. In some instances, the responder may deny the request (e.g., by not responding, by indicating no channels are free, or by any other feasible means), but the description here assumes that the responder accepts the request. In some embodiments the requestor may be an MD and the responder may be an NC, but in other embodiments those roles are reversed, and in some other embodiments both devices may be peer devices.
At 210 the requestor may sense the various channels that are available to it to determine which channels are currently free. In some embodiments this may happen during a ‘contention’ period in the network during which the devices are allowed to contend for the medium. At 220 the requestor may make a list (e.g., list A) of the channels that are currently free, and at 230 it may transmit this list to the responder in an MRTS. The list may take any feasible form, and it may be represented in the MRTS in any feasible manner. Possible formats are discussed later in more detail. In some instances, for various reasons, the requestor may limit this list to a subset of the channels that were sensed as being free. For the purposes of this description, the list of free channels is the list of channels indicated by the MRTS as being free, even if more channels could have been included in the list.
In the meantime, at 215 the responder may also sense the various channels that are available to it to determine which channels are currently free. In many instances, the ‘available channels’ will be the same for both devices, but sometimes this may not be the case. At 225 the responder may make a list (e.g., list B) of the channels that are currently free, and at 235 it may receive the MRTS that was transmitted by the requestor.
Although described as a ‘list’, the indication of which channels were sensed as free may be formatted in any feasible manner. In one embodiment, a bitmap may be used in which each available channel is represented by a bit in the bitmap, and the state of each bit indicates whether the associated channel is free or not. This bitmap may then be placed into a particular field in the MRTS and/or MCTS. Other embodiments may use any other feasible formatting technique to convey this information.
The contents of the RA field may indicate the address of the receiving device, i.e., the requestor device for whom this MCTS is intended. Since only the device addressed in the MRTS should respond with an MCTS, there may be no TA field—the receiving device may simply assume that the device responding to the MRTS is the same device that was indicated by the RA field in the MRTS. The Channel Bitmap field may contain list C, that is, the list A channels that were also sensed as being free by the responder. As before, the FCS field may contain a frame checksum value to verify that the frame as received was not corrupted.
FIG. 6 shows a communication sequence involving multiple responders, according to an embodiment of the invention. In some networks, the requestor may want to transmit data to multiple responders in the same communications sequence, and the MRTS may therefore be addressed to multiple responders. Such multiple addressing may be handled in various ways, such as but not limited to multicast addressing. To keep from interfering with each other, the responders may transmit their MCTS's at different times.
In some networks, the devices may communicate using multi-user multiple input multiple output (MU MIMO), in which different “spatial channels” may be used to transmit different signals to different devices over the same frequency channel, without interference. (In this document, the term ‘channel’ is assumed to mean a frequency channel unless specifically identified as a spatial channel.) In such cases, each spatial channel may use the techniques previously described, without concern for whether the same channels are simultaneously being used on another spatial channel.
(2 SIFSTimes)+(TXTIMEMCTS)+(PHY-RX-START Delay)+(2 slot times)
where SIFSTime is the duration of a short interframe space, TXTIMEMCTS is the time to transmit the MCTS, PHY-RX-START Delay is a required delay to wait before receiving, and the slot times are predefined. Whichever delay formula is used, it should be at least long enough to reach the Data phase. If the medium is busy after that delay period, then the device may assume the original duration period obtained from the MRTS is still valid, and not reset its NAV.
1. A method of operating in a wireless communication network comprising:
transmitting from a transmitting device to a receiver a request-to-send (RTS) that requests a reservation for multiple channels sensed as free by the transmitting device, wherein:
the RTS is formatted as a control frame that includes:
a Frame Check Sequence (FCS) field;
the RTS further indicating the channels sensed as free by the transmitting device;
receiving from the receiver a clear-to-send (CTS) indicating one or more channels sensed as free by the receiver that are a subset of the channels sensed as free by the transmitting device;
transmitting to the receiver only on the one or more channels.
2. The method of claim 1, wherein the multiple channels include a primary channel, and wherein transmitting to the receiver includes transmitting on the primary channel.
3. The method of claim 1, wherein the control frame of the RTS includes a Channel Bitmap field containing a list of the channels sensed as free by the transmitting device.
4. The method of claim 1, wherein transmitting to the receiver includes using multi-user multiple input multiple output (MU-MIMO).
5. The method of claim 1, further including sensing the multiple channels by the transmitting device to determine the channels sensed as free by the transmitting device only when the transmitting device is going to transmit.
6. A method of operating in a wireless communication network comprising:
receiving at a receiver from a transmitting device a request-to-send (RTS) that requests a reservation for multiple channels sensed as free by the transmitting device;
transmitting from the receiver a clear-to-send (CTS) that indicates one or more channels sensed as free by the receiver that are a subset of the channels sensed as free by the transmitting device, wherein the CTS is formatted as a control frame and includes:
a RA field indicating an address of the transmitting device;
receiving from the transmitting device only on the one or more channels.
7. The method of claim 6, wherein the multiple channels include a primary channel, and wherein receiving from the transmitting device includes receiving on the primary channel.
8. The method of claim 6, wherein the control frame of the CTS includes a Channel Bitmap field containing a list of the one or more channels sensed as free by the receiver.
9. The method of claim 6, wherein receiving includes receiving a multi-user multiple input multiple output (MU-MIMO) transmission.
10. The method of claim 6, further including sensing the multiple channels by the receiver to determine the one or more channels sensed as free by the receiver only after receiving the RTS.
11. A transmitting device to operate in a wireless network and including a processor, a memory, a radio and one or more antennas, the transmitting device to:
transmit to a receiver a request-to-send (RTS) that requests a reservation for multiple channels sensed as free by the transmitting device, wherein:
receive from the receiver a clear-to-send (CTS) indicating one or more channels sensed as free by the receiver that are a subset of the channels sensed as free by the transmitting device;
transmit to the receiver only on the one or more channels.
12. The transmitting device of claim 11, wherein the multiple channels include a primary channel, and wherein the transmitter is to transmit to the receiver on the primary channel.
13. The transmitting device of claim 11, wherein the control frame of the RTS includes a Channel Bitmap field containing a list of the channels sensed as free by the transmitting device.
14. The transmitting device of claim 11, wherein the transmitting device is to transmit using multi-user multiple input multiple output (MU-MIMO).
15. The transmitting device of claim 11, wherein the transmitting device is to sense the multiple channels to determine the channels sensed as free by the transmitting device only when the transmitting device is going to transmit.
16. A receiver to operate in a wireless communication network and comprising a processor, a memory, a radio and one or more antennas, the receiver to:
receive from a transmitting device a request-to-send (RTS) that requests a reservation for multiple channels sensed as free by the transmitting device;
transmit from the receiver a clear-to-send (CTS) that indicates one or more channels sensed as free by the receiver that are a subset of the channels sensed as free by the transmitting device, wherein the CTS is formatted as a control frame and includes:
receive from the transmitting device only on the one or more channels.
17. The receiver of claim 16, wherein the multiple channels include a primary channel, and wherein the receiver is to receive from the transmitting device on the primary channel.
18. The receiver of claim 16, wherein the control frame of the CTS includes a Channel Bitmap field containing a list of the one or more channels sensed as free by the receiver.
19. The receiver of claim 16, wherein the receiver is to receive a multi-user multiple input multiple output (MU-MIMO) transmission.
20. The receiver of claim 16, wherein the receiver is to sense the multiple channels to determine the one or more channels sensed as free by the receiver only after receiving the RTS.
21. A non-transitory tangible computer-readable medium storing information which, when read and executed by one or more processors, enables performance of operations including:
22. The computer-readable medium of claim 21, wherein the multiple channels include a primary channel, and wherein transmitting to the receiver includes transmitting on the primary channel.
23. The computer-readable medium of claim 21, wherein the control frame of the RTS includes a Channel Bitmap field containing a list of the channels sensed as free by the transmitting device.
24. The computer-readable medium of claim 21, wherein transmitting includes using multi-user multiple input multiple output (MU-MIMO).
25. The computer-readable medium of claim 21, wherein the operations further include sensing the multiple channels by the transmitting device to determine the channels sensed as free by the transmitting device only when the transmitting device is going to transmit.
26. A non-transitory tangible computer-readable medium storing information which, when read and executed by one or more processors, enables performance of operations including:
27. The computer-readable medium of claim 26, wherein the multiple channels include a primary channel, and wherein receiving from the transmitting device includes receiving on the primary channel.
28. The computer-readable medium of claim 26, wherein the control frame of the CTS includes a Channel Bitmap field containing a list of the one or more channels sensed as free by the receiver.
29. The computer-readable medium of claim 26, wherein receiving includes receiving a multi-user multiple input multiple output (MU-MIMO) transmission.
30. The computer-readable medium of claim 26, wherein the operations further include sensing the multiple channels by the receiver to determine the one or more channels sensed as free by the receiver only after receiving the RTS.
31. A method of operating in a wireless communication network comprising:
transmitting from a transmitting device to a receiver a request-to-send (RTS) formatted as a control frame that includes:
a Frame Check Sequence (FCS) field; and
a Channel Bitmap field containing a list of multiple channels sensed as free by the transmitting device; and
receiving from the receiver a clear-to-send (CTS).
32. The method of claim 31, wherein the multiple channels include a primary channel, and wherein transmitting to the receiver includes transmitting on the primary channel.
33. The method of claim 31, wherein transmitting includes using multi-user multiple input multiple output (MU-MIMO).
34. The method of claim 31, further including sensing the multiple channels by the transmitting device to determine the channels sensed as free by the transmitting device only when the transmitting device is going to transmit.
35. A transmitting device to operate in a wireless network and including:
a processor, a memory, a radio and one or more antennas;
the transmitting device to:
transmit to a receiver a request-to-send (RTS) formatted as a control frame that includes:
receive from the receiver a clear-to-send (CTS).
36. The transmitting device of claim 35, wherein the multiple channels include a primary channel, and wherein the transmitter is to transmit to the receiver on the primary channel.
37. The transmitting device of claim 35, wherein the transmitting device is to transmit using multi-user multiple input multiple output (MU-MIMO).
38. The transmitting device of claim 35, wherein the transmitting device is to sense the multiple channels to determine the channels sensed as free by the transmitting device only when the transmitting device is going to transmit.
39. A non-transitory tangible computer-readable medium storing information which, when read and executed by one or more processors, enables performance of operations including:
40. The computer-readable medium of claim 39, wherein the multiple channels include a primary channel, and wherein transmitting to the receiver includes transmitting on the primary channel.
41. The computer-readable medium of claim 39, wherein transmitting includes using multi-user multiple input multiple output (MU-MIMO).
42. The computer-readable medium of claim 39, wherein the operations further include sensing the multiple channels by the transmitting device to determine the channels sensed as free by the transmitting device only when the transmitting device is going to transmit.
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US13/568,563 US8971351B2 (en) 2010-03-29 2012-08-07 Enhanced carrier sensing for multi-channel operation
US14/605,662 US9503339B2 (en) 2010-03-29 2015-01-26 Enhanced carrier sensing for multi-channel operation
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US20120300707A1 US20120300707A1 (en) 2012-11-29
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US12/748,678 Active 2030-06-19 US8259745B2 (en) 2010-03-29 2010-03-29 Enhanced carrier sensing for multi-channel operation
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