PEGASIS

PEGASIS (Power-Efficient GAthering in Sensor Information Systems) is a protocol designed for energy-efficient communication in wireless sensor networks. Proposed in 2002 as an evolution of cluster-based approaches, PEGASIS organizes sensor nodes into a linear chain so that each node communicates only with a close neighbor. Data are aggregated along the chain and a designated chain leader transmits the fused information to the base station; leadership is rotated to balance energy consumption.

Operation typically involves two phases: chain formation and data transmission. Chain formation is commonly performed with a greedy algorithm that links nodes based on proximity. During each reporting round, nodes receive data from one neighbor, fuse it with their own reading, and pass the aggregated packet along the chain toward the current leader. The leader then sends the final packet to the sink.

PEGASIS advantages include reduced total transmissions, lower per-round energy use compared with flat or cluster-only schemes, and extended network lifetime in many scenarios. Limitations include increased end-to-end delay because of sequential forwarding, reliance on node positional knowledge for efficient chain construction, potential unequal energy depletion if chain length or leader duties are imbalanced, and sensitivity to node failures and mobility. Variants and extensions—such as multi-chain PEGASIS, hierarchical designs, and localized chain formation—address scalability, delay, and robustness. PEGASIS is commonly cited in research on routing strategies and energy management for static, dense wireless sensor deployments.