In this paper, the performance of HIPERLAN (HIgh PErformance Radio Local Area Networks) CAC (Channel Access Control) of ETSI (European Telecommunication Standards Institute) in Europe, as High speed wireless LAN, is analyzed mathematically. The CAC protocol of HIPERLAN is the EY-NPMA (Elimination Yield-Nonpreemptive Priority Multiple Access) in which data is transmitted after prioritization, elimination and yield phase. We analyzed channel contention phase composed of elimination and yield phase and then throughput is inspected by simulation. This result is useful to design and implement of Ad hoc wireless networks.