U.S. Philips Corporation

Christopher K Davis

Richard F Mitchell

Diana M Ball

Paul J Stein

A multiple-access communications system for an unlimited user population wherein a system controller continuously transmits Aloha signals on a slot-by-slot basis giving an updated number of time slots available whereby a calling party can select any one of the designated time slots at random. The calling party checks the time slot immediately preceding its selected time slot to ascertain if the current Aloha number is zero (or an equivalent thereof). If it is zero then the calling party reverts to listening for a time slot containing an Aloha number greater than zero. Alternatively if it is not zero the calling party apparatus sends a signal to the system controller in its selected time slot. Multipurpose signalling in each time slot can be carried out by the system controller thereby reducing the overhead on the system and speeding-up the setting-up of calls which may be off-air or non off-air.

Multiple-access communications system

In order to make optimum use of the available transmission channels in an information transmission system, such as a trunked mobile ratio transmission system, where a number of uncoordinated users may wish to signal to a central control point in addition to using the channels for another purpose, the central control point monitors the channels and, when a channel is or becomes free, sends a command signal on that channel. When a user who is waiting to signal receives the command signal he chooses one of a predetermined number of immediately following time slots in an effectively random manner and sends his request in that slot in digital message form. The central control point sends an acknowledgement in the next time slot if and only if it receives the request in an error-free manner. If a user does not receive such an acknowledgement in response to the transmission of such a request he tries again when he receives the next command. The channel is used for other purposes, if necessary, at times other than those occupied by a command signal plus the subsequent predetermined number of time slots. If requests from more than one user should clash in the same time slot they will not be received by the control point in an error-free manner, this being determined by means of error check bits provided in the request message.

Information transmission system

In order to form a first-come first-served queue in an information transmission system employing a common transmission channel when several transmitters of the system try to gain access to the channel when it is already occupied, without employing a further transmission channel to a point at which an account is kept of the order in which the various transmitters request access, each transmitter which tries to gain access in these circumstances is caused to delay after the channel subsequently free before it actually accesses the channel, this delay being inversely proportional to the time the corresponding transmitter has waited. Thus the transmitter which has waited the longest gains the channel first and causes the other waiting transmitters to continue to wait.

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Crawley, United Kingdom

Christopher K Davis