The rapid increase of wireless LAN (WLAN) deployments in enterprises and public places will likely cause frequent geographical coverage overlap among different domains. This work presents a radio resource broker (RRB) architecture that ensures fair allocation of radio resources across domains. The RRB keeps track of each provider's resource usage, and enforces fair resource allocation across providers by limiting the number of available channels or introducing network-initiated load balancing. We derive an empirical workload model based on measurements from a university-campus environment, and then use it to evaluate our approach with simulated dynamic radio resource usage. The simulation results demonstrate that channel compensation and load balancing are effective for redistributing radio resources fairly over a long time span, and that load balancing also performs well over a short span.