Time-multiplex transmission system.

p0001The invention relates to a time-division multiplex transmission system according to the preamble of claim 1. Such a system is known from DE-OS 34 23 640..

p0002The so-called GSM system, a digital cellular mobile telephone system (described in: Conference Proceedings, Digital Cellular Radio Conference, Copenhagen, October 1988), to be installed in Europe from 1991, a distinction is made between the initial access of a mobile station to a base station with short signals (access bursts) and the time-ordered communication in time slots, which, apart from a very short period of protection, shall be fully utilized for signal transmission (normal bursts). The initial access is performed when a mobile station after it has synchronized to the time frame of a fixed station, tries to connect to this base station. The purpose made use of radio signal (access burst) is so short that the time slot even a guard time of 0.25 ms is left, so that the access of distances can be done up to about 37 km distance. This maximum distance twice the signal propagation time is equal to the guard time.

p0003The base station measures the signal propagation time and sends to the mobile station a message to bring forward the time frame by the value of the signal propagation time, so that the time slots can be accessed during subsequent time-ordered communication.

p0004For operation from a distance the GSM system is not designed, because the effort to rise and the utilization rate would decrease due to long periods of protection.

p0005It is an object of the present invention to provide a time-division multiplex transmission system in which much larger signal transit times can be admitted without having to therefore extend the protection period.

p0006This object is accomplished by the means mentioned in the claim. 1 In the dependent claims further developments of the transmission system are claimed.

p0007The transmission system according to the invention has the advantage that it can be implemented very cost-effective if the fixed part of the system (base stations, switching equipment, etc.) is largely the same example with the known from the GSM system or another TDMA system, and also the mobile stations are largely, but extended with the usual in the GSM system identical to means for determining the distance. This extension can be achieved for example by coupling with a commercial navigation device. The new transmission system is therefore particularly suitable as an aircraft telephone system, since aircraft are anyway equipped with navigation systems that can be shared according to the invention.

p0008The invention is explained below with reference to an exemplary embodiment.

p0009The single figure shows the relative timing of the time slots in the mobile and fixed station.

p0010The new time-division multiplex transmission system comprises at least a base station and a mobile station that communicate with each other in time multiplex. In this case, each base station specifies a time frame having multiple time slots, which are separated by guard times S. The guard times prevent induced different Signallaufzzeiten temporal overlap of shipments of different mobile stations communicating in adjacent time slots to the base station, at the site of the base station. Within this time frame, each base station periodically transmits a unique identifier that allows for their identification, or clear or encrypted data on their geographical location.

p0011The mobile station receives the signal of at least one base station, is synchronized to the received time frame and determines the exact geographical location of the base station. For this, the mobile station has a memory, in which the locations and identities of all members of the transmission system base stations are stored, or an evaluation for the transmitted by the beacon clear or encrypted information.

p0012Further, the mobile station has means for determining its own respective geographical location and to calculate the distance to the base station. For this purpose has the mobile station, for example, a GPS (Global Positioning System) receiver or other suitable navigation means. Since the signal propagation time is proportional to the distance, the mobile station determines the distance from the time offset by which it must bring forward the start of its mission to ensure that their mission arrives in the correct temporal position relative to the time frame of the base station in this.

p0013This is illustrated schematically by the single figure, which shows a portion of the time frame of the base station under a) and d). There are there shaded time slots and not hatched the protection times S shown.

p0014Due to the signal propagation time of the time frame of the mobile station by a certain amount with respect to the time frame of the base station is moved. This is shown in b). The amount of displacement is generally variable in time, according to the movement of the mobile station and changing propagation conditions of radio signals.

p0015Under c) it is shown that the mobile station due to start at an earlier time than their time frame shown in b) by sending, so that the signals transmitted to the time frame of the base station arrive sufficiently in sync with this.

p0016In another embodiment of the time-division multiplex transmission system, the fixed stations additionally have means for the precise determination of the temporal position of the signal transmitted from the mobile station with respect to the time frame of the base station, and send, as described in DE-OS 34 23 640, a control signal for fine adjustment of the transmission timing the mobile station, which then shifts its transmission timing accordingly.