Abstract: A method and an arrangement for detecting a collision in a communication network, such as a WLAN, on which data are sent in frames of variable lengths separated by inter-frame spaces, each frame including a header and a data payload field where the header includes information of the length of the frame, is provided. The method comprises the steps of estimating a noise level (41; 41-42) of a frame, the header of which being read by a receiver, preferably using constellation error measurement, comparing the estimated noise level with a reference noise level value, and detecting a collision with another weaker frame depending on the outcome of the comparison.

Abstract: A method and a system for transmitting secret data in a communication network are provided. An arbitrary data sequence, which lacks information required for performing channel estimation, is sent to a terminal over a transmission medium. A data sequence, which is identical with the data sequence as it was received by the terminal after having been distorted by the transmission medium is sent back on an identifiable channel. The inverse of the transfer function of the transmission medium is calculated based on the data sequence as transmitted to the terminal, and the data sequence as received from the terminal. Finally, a secret data sequence multiplied with the inverse of the transfer function to compensate for the distortions introduced by the transmission medium is sent to the terminal over the transmission medium, thereby enabling the terminal, but disabling an eavesdropper, to deduce the secret data sequence.

Abstract: In a packet-based communication network a central control unit indicates its presence on the first channel by in addition to data traffic transmits regular beacons with a specified time interval, and upon detecting radar signals on a first channel the central control unit transmits a channel switch message and immediately switches to a second channel and resumes data traffic on that second channel, thereafter repeatedly transmitting a channel switch message on the first channel and a beacon on the second channel by switching back to the first channel to transmit second channel switch messages (either contained in beacons or separately) and switching back to the second channel to transmit regular beacons for each permissible beacon transmission time slot, until as many devices as possible associated with the central control unit has followed to the second channel.

Abstract: In a transmission system which makes use of frequency translated signals, said system having a plurality of lines, a method for reducing crosstalk induced on a signal on a first line of said plurality of lines by a signal on a second line of said plurality of lines, comprising estimating a complex coupling factor for the crosstalk, which when multiplied by the signal on the second line estimates the induced crosstalk; and subtracting the estimated induced crosstalk from the signal on the first line. The invention comprises an approximation method for multiplying the complex coupling factor by the signal on the second line that operates on the signal on the second line through pre-rotation, scaling and multiplication by a complex number according to the coupling factor, said complex number being chosen from a bank of predetermined complex numbers so as to obtain the best approximation possible.