tailieunhanh - Radio Frequency Identification Fundamentals and Applications, Bringing Research to Practice Part 6

Tham khảo tài liệu 'radio frequency identification fundamentals and applications, bringing research to practice part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Stochastical Model and Performance Analysis of Frequency Radio Identification 93 The calculation of the optimal frame size In the frame slotted ALOHA based RFID tag collision resolution protocols once the population of RFID tags is known or can be estimated the choice of the frame length adopted in the protocol affects the efficiency of the protocol and the latency of a collision resolution cycle. The choice of the optimal frame size should take into consideration of both the throughput of the protocol and the efficiency of RFID tag identification. The throughput of the collision resolution protocol reflects the efficient use of the air interface and is defined as e C1 t s - Ủ 1 1 S 1 Gth s s 9 where t is the RFID tag population and s refers to the frame length adopted. For eth to achieve its maximize value we need to fix t and let 0. It can be found that tn . ds when s t eth is maximinzed to be 1 i . Similarly according to the law of large number the stable maximum value of eth can be calcuated as max eth lim 1 -- e 1 10 t An alternative is to view this collision resolution process as a Poisson distribution process. The probability that t RFID tags transmit their identifiers back to the RFID reader in a time interval 0 t is in accordance with the Poisson distribution and can be calculated with P X t fc ì e ẢT 11 fc where À -. Due to that the frame slotted ALOHA based RFID tag collision resolution protocols divide an identification frame into a series of discrete data slots and each slot can be viewed as one time unit if only one RFID tag chooses the time unit to transmit its identifier no collision occurs and the RFID tag is identified successfully so the throughput of the frame slotted ALOHA based collision resolution protocol can viewed as p X 1 1 Ae and when 1 1 p is maximized to be . This also verifies that when s t the throughput of the protocol is maximized. The throughputs achieved by the frame slotted ALOHA based RFID tag collision .