Traditional and Real-Time Elevator Scheduling Algorithms

The article reviews a range of elevator dispatching algorithms, outlining their principles, strengths, and limitations.

1.1 First‑Come‑First‑Serve (FCFS) schedules requests in the order they arrive, offering fairness and simplicity but performing poorly under heavy load.

1.2 Shortest Seek Time First (SSTF) selects the next request that requires the shortest travel distance, reducing average response time but causing high variance and possible starvation.

1.3 SCAN moves the elevator continuously between the top and bottom floors, serving all requests in the current direction, which improves efficiency but is non‑real‑time.

1.4 LOOK is an improvement over SCAN that reverses direction as soon as there are no further requests ahead, reducing unnecessary travel.

1.5 SATF (Shortest Access Time First) modifies SSTF by considering passenger boarding time instead of floor‑seeking time, reflecting modern elevator performance characteristics.

2.1 Earliest Deadline First (EDF) is a simple real‑time algorithm that always serves the request with the nearest deadline, though it may lead to low throughput.

2.2 SCAN‑EDF combines SCAN and EDF, using EDF to pick the next request and SCAN to resolve ties with identical deadlines.

2.3 PI (Priority Inversion) divides the request queue into high‑ and low‑priority levels, guaranteeing timely service for high‑priority requests.

2.4 FD‑SCAN (Feasible Deadline SCAN) selects the earliest‑deadline request that can be reached from the current position within its deadline, then proceeds with a SCAN sweep, though it may ignore the cost of serving other requests.

The discussion then moves to high‑level research, noting that elevator control has progressed to group‑control systems, leveraging expert systems, fuzzy logic, genetic algorithms, and fuzzy‑neural networks.

Finally, a demand analysis describes a 21‑floor building with two elevators, detailing button configurations, timing parameters (door operation, passenger loading, travel times), and special idle‑position rules.

Button functions are explained, covering internal floor selection, door open/close controls, and external up/down call buttons, including automatic door opening behavior when no button is pressed.