Abstract: It is especially important for slotted-ALOHA RFID to estimate tag number in order to allocate slot number optimally and maximize the efficiency The existing tag estimation methods are not accurate enough especially when tags overnumber slots What's more, their applicable ranges are quite limited A novel tag estimation method DRCTE(Derivative Reliabilities Combined Tag Estimation) is proposed Three primary estimations are obtained respectively from the rates of empty, occupy and collide slot number to the whole slot number, then their reliabilities are evaluated from the derivatives of the rates, and at last the three primary estimations are combined to get the final estimation result The proposed DRCTE algorithm not only utilizes the reliable information but also restrains unreliable information, so it is more accurate and its applicable range is larger

Key words: MAC(medium access control), slotted-ALOHA, collision, RFID, tag estimation, MRC(maximum rate combination), identification time

摘要： 时隙ALOHA是一种分时隙通信方案，对于采用了时隙ALOHA的RFID(radio frequency identification)系统，标签数目估计可以指导时隙数目的选取，有助于优化系统效率。目前的估计方法存在准确度低、估计范围小的缺点，尤其在标签数目大于时隙数目的时候估计误差很大。针对这种情况，提出一种新的导数可靠度合并的标签数目估计方法DRCTE(derivative reliabilities combined tag estimation)，该方法统计时隙ALOHA的空白时隙、独占时隙和碰撞时隙的数目，据此对标签数目做出3个初步估计；然后用3种时隙数目与总时隙数目的比值函数的导数作为初步估计的可靠度；最后用可靠度合并3个初步估计，得出最终估计结果。算法合理利用了可靠度高的信息，遏制了可靠度低的信息，具有估计精度高，估计范围大的特点。

关键词: 媒体接入控制, 时隙ALOHA, 碰撞, 射频标签, 标签数目估计, 最大比合并, 读取时间