SOLVING A HIDDEN NODE PROBLEM DUE TO TRANSMISSION POWER IMBALANCE
The present invention discloses an apparatus, a method and a computer program for resolving a hidden node problem in relation to handshake message transferring e.g. in WLAN networks. In one embodiment of the invention, the apparatus receiving a Clear to Send (CTS) message repeats the message after a Short Interframe Space (SIFS) time period. Stations not directly hearing the original CTS due to a low power are able to receive the repeated CTS and defer their transmissions accordingly. In another embodiment, the apparatus receiving the CTS message indicates in its Ready to Send (RTS) message that the CTS sender station has a low transmitting power. With this knowledge, the other present stations can defer their transmissions until they are sure that the data transfer between the first two stations having the RTS-CTS messaging has not been initiated or is already completed.
1 . An apparatus, which is configured to:
receive a message which message is transmitted by a first station;
indicate from the message that the first station transmits with a lower transmitting power than the apparatus, the first station deemed as a hidden node; and
transmit information comprising an indication of the hidden node, where the indication is received by at least one other station; and as a consequence to the received indication, the at least one other station is configured to defer its data transmission.
2 . The apparatus according to claim 1 , the apparatus being further configured so that the indication of the hidden node is the transmission of the first station repeated by the apparatus.
3 . The apparatus according to claim 2 , the apparatus being further configured to transmit the information with larger power than the first station.
4 . The apparatus according to claim 1 , the apparatus being further configured so that the indication of the hidden node is included in a part of a transmitted message by the apparatus.
5 . The apparatus according to claim 1 , the apparatus being further configured so that the received message comprises information of at least one of a device class, transmission power class or maximum transmitting power of the first station.
6 . The apparatus according to claim 2 , the apparatus being further configured so that the transmitted information comprises power level information comprising at least one of a device class, transmission power class or maximum transmitting power of the apparatus.
7 . The apparatus according to claim 6 , the apparatus being further configured so that in case the power level information does not match with the power of the received message, the received message is repeated by the apparatus.
8 . The apparatus according to claim 1 , wherein the message transmitted by the first station is a Clear to Send message.
9 . The apparatus according to claim 1 , wherein the transmitted information comprises a Ready to Send message.
10 . The apparatus according to claim 9 , wherein the Ready to Send message is transmitted with the same power as the repeated transmission.
11 . The apparatus according to claim 8 , wherein the data transmission is deferred for a selectable time period.
12 . The apparatus according to claim 11 , where the time period is selected as two times the Short Interframe Space plus the frame duration of the Clear to Send message.
13 . The apparatus according to claim 9 , in case a data transmission after the Ready to Send message takes place by the apparatus, the at least one other station is configured to defer its transmission until the data transmission by the apparatus is completed and acknowledged.
14 . The apparatus according to claim 1 , wherein the apparatus, the first station and the at least one other station are TV Band Devices.
15 . The apparatus according to claim 1 , wherein the apparatus, the first station and the at least one other station are part of a Wireless Local Area Network.
16 . A method, comprising:
receiving a message which message is transmitted by a first station;
indicating from the message that the first station transmits with a lower transmitting power than the apparatus, the first station deemed as a hidden node; and
transmitting information comprising an indication of the hidden node, where the indication is received by at least one other station; and as a consequence to the received indication, the at least one other station is configured to defer its data transmission.
17 . The method according to claim 16 , wherein further, the indication of the hidden node is the transmission of the first station repeated by the apparatus.
18 . A computer program comprising code adapted to perform the following steps, when executed on a data-processing system, comprising:
receiving a message which message is transmitted by a first station;
indicating from the message that the first station transmits with a lower transmitting power than the apparatus, the first station deemed as a hidden node; and
transmitting information comprising an indication of the hidden node, where the indication is received by at least one other station; and as a consequence to the received indication, the at least one other station is configured to defer its data transmission.
19 . The computer program according to claim 18 , wherein further, the indication of the hidden node is the transmission of the first station repeated by the apparatus.
20 . The computer program according to claim 18 , wherein the computer program is stored on a computer readable medium.