1. A computer-implemented method of determining backoff windows in a wireless computer network, comprising: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,
wherein the method is performed using one or more processors in the access point in the wireless computer network.