| This paper investigates the energy efficiency of RFID anti-collision protocols and determine their suitability in RFID-Enhanced wireless sensor networks (WSNs). We present a detailed analytical methodology and in-depth qualitative and quantitative energy analysis of Pure and Slotted Aloha anti-collision protocols and their variants. We find that Slotted Aloha variants that employ muting with early-end are the most energy efficient, but are computationally expensive. Overall, for all Aloha variants we investigated, if the offered load is very high, tag responses will cause a bottleneck at the reader. Thereby, resulting in no tags being identified and incur significant identification delays -- thus severely impacting a sensor node's battery lifetime. |