Wireless LAN with contention avoidance

1 . A method for communication, comprising:

associating a plurality of stations with an access point in a wireless local area network (WLAN);

selecting a station among the associated stations to transmit an uplink signal; and

transmitting an unsolicited Clear-To-Send (CTS) message from the access point to the stations specifying a time interval in which the selected station is to transmit the uplink signal.

2 . The method according to claim 1 , wherein selecting the station comprises selecting multiple stations among the associated stations to transmit respective uplink signals in alternation, and wherein transmitting the unsolicited CTS message comprises transmitting multiple, successive CTS messages specifying respective time intervals for uplink transmission by the multiple stations.

3 . The method according to claim 1 , wherein selecting the station comprises selecting the station responsively to a type of application traffic that is to be transmitted by the station.

4 . The method according to claim 3 , wherein selecting the station comprises allocating the time interval to at least one of the stations for uplink transmission of real-time traffic.

5 . The method according to claim 1 , wherein transmitting the CTS message causes all the stations receiving the CTS message other than the selected station to refrain from uplink transmission during the specified time interval.

6 . The method according to claim 1 , wherein the WLAN comprises multiple access points, and comprising receiving the uplink signal from the selected station during the specified time interval at two or more of the access points, and selecting one of the two or more of the access points to respond to the uplink signal.

7 . The method according to claim 1 , wherein selecting the station comprises selecting at least first and second stations among the associated stations to transmit uplink signals simultaneously, and

wherein transmitting the unsolicited CTS message comprises transmitting at least first and second unsolicited CTS messages from first and second access points, respectively specifying that the first and second stations are to transmit uplink signals during the specified time interval.

8 . Apparatus for communication, comprising:

an access point, which is configured to communicate with a plurality of stations in a wireless local area network (WLAN); and

an access manager, which is operative to select a station among the plurality of stations to transmit an uplink signal, and to cause the access point to transmit an unsolicited Clear-To-Send (CTS) message to the stations specifying a time interval in which the selected station is to transmit the uplink signal.

9 . The apparatus according to claim 8 , wherein the access manager is adapted to select multiple stations among the plurality of stations to transmit respective uplink signals in alternation, and to cause the access point to transmit multiple, successive CTS messages specifying respective time intervals for uplink transmission by the multiple stations.

10 . The apparatus according to claim 9 , wherein the access manager is adapted to select the station responsively to a type of application traffic that is to be transmitted by the station.

11 . The apparatus according to claim 10 , wherein the access manager is adapted to allocate the time interval to at least one of the stations for uplink transmission of real-time traffic.

12 . The apparatus according to claim 8 , wherein transmitting the CTS message causes all the stations receiving the CTS message other than the selected station to refrain from uplink transmission during the specified time interval.

13 . The apparatus according to claim 8 , wherein the WLAN comprises multiple access points, which are disposed so that two or more of the access points receive the uplink signal transmitted by the selected station, and wherein the access manager is adapted to select one of the two or more of the access points to respond to the uplink signal.

14 . The apparatus according to claim 8 , wherein the access point is one of a plurality of access points comprising at least first and second access points, and

wherein the access manager is adapted to select at least first and second stations among the associated stations to transmit uplink signals simultaneously, and to instruct at least the first and second access points to transmit first and second unsolicited CTS messages, respectively specifying that the first and second stations are to transmit uplink signals during the specified time interval.