谁能解释下802.22协议里PPD和SPD的意思？

protecting device (PD): A beaconing device that is protecting a low-power, licensed device. The PD may be either the primary protecting device (PPD) or a secondary protecting device (SPD) primary protecting device (PPD): A device that uses periodic beacons to protect its corresponding licensed device. Its protection may be extended to other licensed devices in the area (i.e., SPDs) secondary protecting device (SPD): A device that shares the responsibility of protecting its corresponding licensed device with the PPD. An SPD occasionally sends beacons for the sole purpose of communicating with the PPD next-in-line protecting device (NPD): An SPD that will become a PPD in the event that the already-existing PPD stops transmitting periodic beacon frames

我感觉PPD与SPD都是PD，是说PPD是主用户，SPD是二级用户吗？那PPD、SPD与NPD又是什么关系？

是电视塔和无线麦克风吗？ 楼主能把协议给我发一份吗，fgz02@126.com，谢谢 【 在 dongri (dongri) 的大作中提到: 】 : 认知无线电网络802.22协议中有两个概念，PPD与SPD，看了之后还是不明白这是什么Device，有谁明白的能给通俗的解释一下吗？谢谢 : 协议为这个《IEEE Standard for Information technology— Telecommunications and information exchange between systems— Local and metropolitan area networks—Specific requirements— Part 22.1/D2.0: Enhanced Protection for Low-Power, Licensed Devices Ope