Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-09-24
2001-01-23
Bost, Dwayne D. (Department: 2744)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S554100, C455S464000, C455S450000, C370S477000
Reexamination Certificate
active
06178330
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a point-to-multipoint radio transmission system, made up of a central station and a plurality of subscriber stations, the transmission channels between the central station and the subscriber stations being assignable as needed.
BACKGROUND INFORMATION
Radio transmission systems, whether terrestrial radio relay systems or satellite transmission systems, make it possible to install new radio links, or to add to existing ones, very quickly. In such radio transmission systems, on one hand, the frequency spectrum available should be utilized as optimally as possible, and on the other hand, the radio transmission should be as resistant as possible to interfering influences (fading caused by weather, frequency-selective fading, interference by reflections, interference by neighboring radio cells, interference by other radio communication services, amplitude and phase distortions).
The demand for optimal frequency-spectrum utilization can be realized with point-to-multipoint radio transmission systems (radio relay, satellite radio). A point-to-multipoint radio relay system is explained in
Mikrowellen-Magazin
(Microwave Magazine), Vol. 10, No. 6, 1984, pp. 629, 630. According to that, utilization of the frequency band of the radio frequency channel available can be improved by usage of the necessary frequency band only as needed. The communication between the central station and the individual subscriber stations can be effected either through multiple access in frequency-division multiplexing (FDMA), in time-division multiplexing (TDMA), in code-division multiplexing(CDMA), in space-division multiplexing (SDMA), or in mixed forms of these access methods, it being possible to assign the frequency channels, the time slots, the spread codes and the spatial antenna lobes depending on the need of the subscribers.
In a point-to-multipoint radio relay system according to the German Patent Application No. 44 26 183, the transmission capacity is adapted flexibly to the need of the subscribers by adjusting the band width of the individual transmission channels to the data-transmission rate required in each case by the individual subscribers. Provision is also made for variable adjustment of the modulation type and the modulation depth (e.g. N-PSK, where N=2 . . . 16, or M-QAM, where M=4 . . . 256) to the individual transmission channels.
Channel coding represents a first aid for improving the resistance to interference. A further increase in interference resistance can be achieved by spectrum spreading and/or frequency hopping, as well as by orthogonal multi-carrier transmission according to a fixed, predefined scheme.
European Patent Application No. 0 719 062 describes a point-to-multipoint radio transmission system in which provision is made for a variable band-width allocation (band width on demand) between a central station and the individual subscribers. In this conventional transmission system, the signal transmission is based on a combination of code-division multiplexing (CDMA) and time-division multiplexing (TDMA). This European Patent Application discloses nothing about the operation of transmission and receiving devices of the subscribers and of the central station in response to a change in the band-width allocation.
Another conventional point-to-multipoint signal-transmission system is described in PCT International Patent Publication No. WO 95/34149, which includes no measures which permit a flexible adaption of transmission capacities to connected subscribers without interruption and interference.
At this point, the object of the present invention is to specify a point-to-multipoint radio transmission system of the type named at the outset, which both allows a flexible allocation and adaptation of transmission capacities to the connected subscriber stations, free of interruption and interference, on one hand, and, on the other hand, makes the radio transmission as resistant as possible to interfering influences (fading caused by weather, frequency-selective fading, interference by reflections, interference by neighboring radio cells, interference by other radio communication services, amplitude and phase distortions).
SUMMARY OF THE INVENTION
The stipulated objective is fulfilled in that provision is made for a control device, which, only in case of need for a higher resistance to interference in a transmission channel in the associated multiple-carrier modems with which both the central station and each subscriber station are equipped, given a transmission of the digital data in a single carrier, initially so adjusts one or a plurality of transmission parameters that the radio frequency channel is made as resistant as possible to interference, accompanied by the best possible utilization of the band width. In this context, each multi-carrier modem has at least two transmission channels and at least two receiving channels, the signal transmission in the modem being effected initially via only one transmission channel and one receiving channel, respectively. In the event of a change in the transmission channels, the control unit adjusts the new transmission parameters in the at least one transmission channel and receiving channel, respectively, not in operation, while the signal transmission is continued in the other transmission or receiving channels, and after acquisition of the radio frequency channel with the new transmission parameters has been concluded, a switchover is made to the transmission channel or receiving channel not previously in operation. On the other hand, only in case of need, if the interference resistance is not sufficient when transmitting with a single carrier, the objective according to the present invention is achieved by the fact that an existing control device triggers the transition from a single-carrier transmission to a multi-carrier transmission in such a way that, in the existing multi-carrier modems of the central station and of the subscriber stations, the data stream to be transmitted, if it does not already consist of a plurality of individual data streams (e.g. N×2 Mbit/s or M×1.5 Mbit/s), is demultiplexed into individual data streams, and these are transmitted in individual carriers, the transmission parameters of the individual carriers being optimized by the control device in response to the necessary resistance to interference. The quantity of carriers for a multi-carrier transmission is limited by the number implemented in the modems of the central station and of the subscriber station, and can be adapted accordingly, if necessary.
The transition from a one-carrier transmission to a multi-carrier transmission can be effected according to the present invention, without interruption or disturbance of the transmission, in that the multi-carrier modems of the central station and of the subscriber stations have more than two transmission channels and receiving channels, where, to change the transmission channels, triggered by the control device, both in the case of one-carrier transmission and in the case of multi-carrier transmission, at least one transmission channel or receiving channel is always available for the adjustment of new transmission parameters for one of the remaining transmission and receiving channels, while the signal transmission in the remaining transmission or receiving channels is continued. In this case, only after acquisition of the radio frequency channel having the new transmission parameters has been concluded is a switchover made to the at least one transmission or receiving channel previously not in operation.
Using the measures indicated above, given a point-to-multipoint radio transmission system, the available radio frequency channel can be adapted very flexibly to the necessary transmission channels of the individual subscribers, without the radio links having to be interrupted or being disturbed. All the transmission parameters of all transmission and receiving channels can be controlled by one control device in the case of a
Alberty Thomas
Auer Erich
Bost Dwayne D.
Gary Erika A.
Kenyon & Kenyon
Robert & Bosch GmbH
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