View source for Self-organized time-division multiple access

'''Self-organized time-division multiple access''' ('''STDMA''' or '''SOTDMA''') is a channel access method designed by [[Håkan Lans]],<ref name=patent>{{cite patent
 | country = US
 | number = 5506587
 | status = patent
 | title =  Position indicating system
 | gdate = 1996-04-09
 | fdate = 1993-12-23 
 | pridate = 1991-07-01
 | inventor = Lans, Håkan
 | invent1 = Lans, Håkan
 | assign1 = GP&C Systems International AB
}}</ref> based on [[time-division multiplexing]].

The term "self-organized" describes the manner in which time slots are assigned to users. [[Time-division multiple access]] (TDMA) divides a channel into [[Frame (telecommunications)|frames]], which furthermore are subdivided into a vast number of time slots. Users transmit in rapid succession, one after the other, each using their own time slot. One of the drawbacks of TDMA is that it requires a central station for slot assignment and time synchronization. STDMA proposes a method for assigning slots without the involvement of a central station. Time synchronization is usually taken care of using [[Coordinated Universal Time]] (UTC). Slot assignment is handled by each transmitter broadcasting its next slot reservation as part of the message during its current slot.

STDMA is in use by the [[Automatic Identification System]] (AIS), a standard marine short-range coastal tracking system, and is the base of the [[International Civil Aviation Organization]] [[VHF Data Link#ICAO VDL Mode 4|VHF Data Link Mode 4]].

While the method was patented,<ref name=patent/> a [[United States Patent and Trademark Office|US patent]] ex-parte [[reexamination]] certificate was issued in 2010 canceling all claims.<ref>[https://patents.google.com/patent/US5506587A#legalEvents USPTO ex-parte reexamination certificate 7428, issued on March 30, 2010.]</ref>

==References==
{{reflist}}

== External links ==
* [http://www.gpc.se/ GP&C Systems International AB] Holding company of STDMA patent rights in Europe

{{Channel access methods}}

[[Category:Maritime communication]]