Chandrashekhara Thejaswi P. S. Junshan Zhang Man-On Pun H. Vincent Poor Dong Zheng Distributed Opportunistic Scheduling With Two-Level Probing http://arxiv.org/abs/0907.2093 2009 CoRR abs/0907.2093 db/journals/corr/corr0907.html#abs-0907-2093 informal publication