Clear Channel Assessment for Duplex Transmissions in Wireless Local Area Networks

1 . A method, comprising:

receiving, at a first communication device, a first packet from a second communication device, wherein:

the first packet is addressed to the first communication device,

the first communication device and the second communication device belong to a communication network, and

the first packet spans a communication channel;

determining, at the first communication device, whether another communication network is also using the communication channel during the transmission of the first packet; and

in response to determining that another communication network is not using the communication channel during the transmission of the first packet, transmitting, by the first communication device, a second packet addressed to the second communication device, wherein the second packet is transmitted while the first communication device is receiving the first packet, and wherein the second packet is transmitted in the communication channel.

2 . The method of claim 1 , wherein determining whether another communication network is also using the communication channel during the transmission of the first packet comprises:

determining, at the first communication device, whether a network allocation vector (NAV) timer indicates that another communication network is also using the communication channel during the transmission of the first packet.

3 . The method of claim 2 , wherein determining whether another communication network is also using the communication channel during the transmission of the first packet comprises:

when the NAV timer indicates that the communication channel is busy and when the NAV timer was set in response to a transmission from a transmitter that belongs to another communication network, determining that another communication network is using the communication channel during the transmission of the first packet; and

when the NAV timer indicates that the communication channel is busy and when the NAV timer was set in response to a transmission from a transmitter that belongs to the communication network, ignoring the NAV timer.

4 . The method of claim 2 , wherein determining whether another communication network is also using the communication channel during the transmission of the first packet comprises:

when the NAV timer indicates that the communication channel is busy and when the NAY timer was set in response to a transmission from a transmitter other than the second communication device, determining that another communication network is using the communication channel during the transmission of the first packet; and

when the NAV timer indicates that the communication channel is busy and when the NAV timer was set in response to a transmission from the second communication device, ignoring the NAV timer.

5 . The method of claim 2 , wherein:

the NAV timer is a first NAV timer,

the method further comprises: maintaining a second NAY timer that indicates whether another communication device in the communication network is using the communication channel; and

wherein determining whether another communication network is also using the communication channel during the transmission of the first packet comprises ignoring the second NAY timer.

6 . The method of claim 1 , wherein determining whether another communication network is also using the communication channel during the transmission of the first packet further comprises:

measuring, at the first communication device, energy in the communication channel during a time period immediately prior to a beginning of first packet.

7 . The method of claim 6 , wherein the first packet and the second packet are transmitted during a transmit opportunity period (TXOP), wherein the communication channel is a first communication channel, and wherein the method further comprises:

receiving, at a first communication device, a third packet from the second communication device during the TXOP, wherein:

the third packet is addressed to the first communication device, and

the third packet is transmitted in a second communication channel;

determining, at the first communication device, whether another communication network is also using the communication channel during the transmission of the third packet; and

in response to determining that another communication network is not using the communication channel during the transmission of the third packet, transmitting, by the first communication device, a fourth packet addressed to the second communication device, wherein the fourth packet is transmitted while the first communication device is receiving the third packet.

8 . The method of claim 1 , wherein:

the communication channel comprises multiple sub-channels;

determining whether another communication network is also using the communication channel during the transmission of the first packet comprises determining whether another communication network is using any of the multiple sub-channels; and

transmitting the second packet is in response to determining that another communication network is not using any of the multiple sub-channels during the transmission of the first packet.

9 . The method of claim 1 , wherein:

the communication channel comprises multiple sub-channels;

determining whether another communication network is also using the communication channel during the transmission of the first packet comprises determining whether another communication network is using each of the multiple sub-channels;

transmitting the second packet is in response to determining that another communication network is using a first subset of the multiple sub-channels and is not using a second subset of the multiple sub-channels during the transmission of the first packet;

the second packet is transmitted in the second subset of the multiple sub-channels and not in the first subset of multiple sub-channels.

10 . An apparatus, comprising:

a network interface device associated with a first communication device, wherein the network interface device includes one or more integrated circuit (IC) devices configured to:

receive a first packet from a second communication device, wherein:

the first packet is addressed to the first communication device,

the first communication device and the second communication device belong to a communication network, and

the first packet spans a communication channel;

wherein the one or more IC devices are further configured to:

determine whether another communication network is also using the communication channel during the transmission of the first packet, and

in response to determining that another communication network is not using the communication channel during the transmission of the first packet, transmit a second packet addressed to the second communication device, wherein the second packet is transmitted while the first communication device is receiving the first packet, and wherein the second packet is transmitted in the communication channel.

11 . The apparatus of claim 10 , wherein:

the network interface device includes a network allocation vector (NAV) timer implemented on the one or more IC devices; and

the one or more IC devices are further configured to: determine whether the NAY timer indicates that another communication network is also using the communication channel during the transmission of the first packet.

12 . The apparatus of claim 11 , wherein the one or more IC devices are further configured to:

when the NAV timer indicates that the communication channel is busy and when the NAV timer was set in response to a transmission from a transmitter that belongs to another communication network, determine that another communication network is using the communication channel during the transmission of the first packet; and

when the NAV timer indicates that the communication channel is busy and when the NAV timer was set in response to a transmission from a transmitter that belongs to the communication network, ignore the NAV timer.

13 . The apparatus of claim 11 , wherein the one or more IC devices are further configured to:

when the NAV timer indicates that the communication channel is busy and when the NAV timer was set in response to a transmission from a transmitter other than the second communication device, determine that another communication network is using the communication channel during the transmission of the first packet; and

when the NAV timer indicates that the communication channel is busy and when the NAV timer was set in response to a transmission from the second communication device, ignore the NAV timer.

14 . The apparatus of claim 11 , wherein:

the NAV timer is a first NAV timer;

the network interface device includes a second NAV timer implemented on the one or more IC devices;

the second NAY timer indicates whether another communication device in the communication network is using the communication channel; and

the one or more IC devices are further configured to ignore the second NAY timer when determining whether another communication network is also using the communication channel during the transmission of the first packet comprises.

15 . The apparatus of claim 10 , wherein:

the network interface device comprises energy measurement circuitry implemented on the one more IC devices, the energy measurement circuitry configured to measure energy in the communication channel during a time period immediately prior to a beginning of first packet;

the one or more IC devices are further configured to determine whether another communication network is also using the communication channel during the transmission of the first packet using the measured energy in the communication channel during the time period.

16 . The apparatus of claim 15 , wherein:

the first packet and the second packet are transmitted during a transmit opportunity period (TXOP);

the communication channel is a first communication channel;

the one or more IC devices are further configured to receive a third packet from the second communication device during the TXOP;

the third packet is addressed to the first communication device;

the third packet is transmitted in a second communication channel;

the one or more IC devices are further configured to:

determine whether another communication network is also using the communication channel during the transmission of the third packet, and

in response to determining that another communication network is not using the communication channel during the transmission of the third packet, transmit a fourth packet addressed to the second communication device; and

the fourth packet is transmitted while the first communication device is receiving the third packet.

17 . The apparatus of claim 10 , wherein:

the communication channel comprises multiple sub-channels;

the one or more IC devices are further configured to:

determine whether another communication network is using any of the multiple sub-channels, and

transmit the second packet is in response to determining that another communication network is not using any of the multiple sub-channels during the transmission of the first packet.

18 . The apparatus of claim 10 , wherein:

the communication channel comprises multiple sub-channels;

the one or more IC devices are further configured to:

determine whether another communication network is using each of the multiple sub-channels, and

transmit the second packet in response to determining that another communication network is using a first subset of the multiple sub-channels and is not using a second subset of the multiple sub-channels during the transmission of the first packet; and

the second packet is transmitted in the second subset of the multiple sub-channels and not in the first subset of multiple sub-channels.

19 . The apparatus of claim 10 , wherein:

the network interface device comprises i) a media access control (MAC) processor implemented on the one or more IC devices, and ii) a physical layer (PHY) processor implemented on the one or more IC devices, and coupled to the MAC processor; and

the MAC processor is configured to:

determine whether another communication network is also using the communication channel during the transmission of the first packet, and

in response to determining that another communication network is not using the communication channel during the transmission of the first packet, prompt the PHY processor to transmit the second packet while the first communication device is receiving the first packet.

20 . The apparatus of claim 19 , further comprising:

one or more antennas coupled to the network interface device.