In this paper, we propose a cross-layer design of packet level cooperation for wireless LANs that support rate adaptation. While keeping compatibility with legacy wireless LANs, distributed control of multi-hop packet transmission is enabled without pre-negotiation of routing or pairing. These features are provided by prioritization scheme based on IEEE 802.11e EDCF in which we set the parameters according to the measured link condition at each terminal. Relaying packets with high transmission rate makes much efficient use of radio resource, and it leads not only to improve performance of the total system, but also to overcome the fairness issue known in rate adaptation, where the terminals with good link conditions cannot gain enough resource because of the time consumed by low data rate transmission. These advantages are confirmed through computer simulations considering packet error rate at each transmission which is assumed by receiving power calculated from the distance between source, relay, and destination terminals. Furthermore, we also discuss about the fairness between cooperation-enabled and legacy terminals when they coexist in the same system, in order to make gradual deployment feasible.