A computer-implemented method of determining backoff windows in a wireless computer network is disclosed. The method comprises defining, by an access point in the wireless computer network, a plurality of collision patterns related to message transmission via one or more communication channels in the wireless computer network; detecting, by the access point, occurrence of one of the plurality of collision patterns involving a group of sender nodes in the wireless computer network that have each transmitted a message to the access point and received no acknowledgement message from the access point indicating successful transmission; setting to a first length a length of a backoff window for avoiding collision in data transmission based on a size of the group of sender nodes; sending a first message to a first plurality of nodes in the wireless computer network, the first message instructing performance of backoff during the backoff window having the first length.