Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-12-02
2003-01-14
Urban, Edward F. (Department: 2685)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C455S402000, C340S870070, C340S315000, C340S315000, C375S137000, C379S344000
Reexamination Certificate
active
06507573
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for data transmission in two-way communication via low-voltage systems that are linked to a higher order telecommunication network, and to an arrangement for implementing said method.
2. Background of the Prior Art
Utility companies have highly ramified power supply networks through which they are connected with their customers. This benefit has for a long time been utilized beyond mere energy supply, for example, for tone frequency remote control where data was transmitted in one-way communication systems though with the disadvantage that there was no feedback.
More recently, however, proposals were made to enable the use of the low-voltage systems of utility companies for two-way communication independent of other carriers. While one-way communication just allows the collection of data such as meter readings for electricity, gas, water, etc. or registration of measured values such as temperature, pressure, or alarms, two-way communication can be used to query switching states and to control complex technical facilities. In addition to regular data transmission, the low-voltage system that utility companies have and to which each household is connected can be used for plain ordinary telephone service. According to a known proposal of this kind, the power suppliers who use their low-voltage system for telecommunication have to provide, on the one hand, facilities that act as data filters to make sure that the data is received by its addressees only. On the other hand, devices are required at the network stations that transpose the data to a copper, cellular, or fiber network that connects the stations. It has been assumed as yet that about 100 to 200 households can be connected to one network station. In compliance with the European Celenec EN 50065-1 standard, a theoretically usable data rate of up to 70 kbps would be available for data communication in duplex mode on a dedicated frequency band up to 95 kHz.
A two-way communication system for data transmission between a central station and side stations and between substations and end user facilities is known from DE 195 04 587. Node controllers linked to the low-voltage network function as substations, and a large-area telecommunication network such as a cellular data network or a circuit-switched network, in particular, an optical fiber network, is used for data transmission between the central station and the substations. The node controllers associated with the distributed network transformers are equipped with standard modems that provide an interface between the low-voltage and the large-area telecommunication network whereas a modem with repeater function is provided as an intermediate station on the transmission path between the node controller and the end user facility; data transmission within the local low-voltage network is based on the spread spectrum method.
Data transmission in low-frequency networks uses the frequency range up to 148.5 kHz that is permitted in Europe. However, one setback is that transmission quality is restricted in this frequency range due to numerous interference signals and a high noise level, another setback is that the narrow-band transmission frequency band is limited with regard to the number of subscribers and the bit rate per subscriber.
It is therefore the problem of this invention to provide such a method and such an arrangement for using low-voltage systems that differs from conventional systems in that it combines a high data transfer rate with improved transmission quality, transmission security in ISDN quality, and real-time processing.
SUMMARY OF THE INVENTION
This problem is solved according to the invention by a data transmission method for two-way communication using a low-voltage system linked to a higher-order telecommunications network in that data transmission within the low-voltage system takes place at a high-frequency range of up to 30 MHz using band spreading of data signals and a transmitting level below the specified interference or noise voltage limit of line and radio disturbance characteristics, in that said band-spread data is given a direction coding to specify a logical direction within the low-voltage system using different sequences of a family of pseudo-random numbers to enable multiple-user operation, and in that a correlator placed at an attenuation-dependent distance identifies and regenerates the binary sequences of data with their user-specific spreading and direction-specific coding are identified by correlation using specified sequences at attenuation-dependent distances within the low-voltage system, then said data sequences are regenerated and assigned new direction codes for forwarding.
Alternatively, the process of sequence generation and additional directional coding can be carried out by controlled selection of sequences from various sequence families. Another sequence family is used as direction ID in each network area for band spreading of each user signal.
The limits for radio and line frequency interference are much lower at a higher frequency range, e. g. 10 MHz, than in the frequency range up to 148.5 kHz. But narrow-band interference caused by harmonic waves from other frequency ranges occurs at this range, too, and even the standard radio transmitters interfere with data transmission at this frequency range. On the other hand, the specified maximum output levels, which are very low, must not be exceeded. Furthermore, a signal output at a low level may drop below the noise level due to transmission loss that increases with growing distance and frequency, so that non-spread signal can no longer be received.
Due to its low output level and the high attenuation at this frequency range, the signal to be transmitted would drop below the noise level at a transmission loss of 50 to 70 dB/100 m but in buried cables it can be received below noise level and successfully regenerated at a distance of 100 m. A direction coding using code, time, or frequency multiplexing converts the physical separation which is impossible with data transfer in low-frequency systems into a logical separation, thus enabling duplex operation. Code multiplexing also ensures a multiple-user structure. As direct sequence band spreading is used where, instead of a single information symbol, a sequence of pseudo-random numbers is transmitted in the same time, the bandwidth required for transmission increases by a factor that corresponds to the sequence of pseudo-random numbers. In this way, narrow-band sources of interference and frequency-selective attenuation properties lose their influence on the transmission system.
The proposed method of data transmission at a high frequency range facilitates low-cost bidirectional data transmission in real time via the low-voltage systems of utility companies if buried cables are used. Transmission channels in ISDN quality with a data rate of 64 kbps can be provided, and the overall transmission capacity of the low-voltage line between connected users and the interface between low-voltage system and higher order telecommunication network is a minimum of 2 Mbps for each the forward and back channel with a bit error rate of 10
−6
over 100 m.
In a further development of the invention, a family of pseudo-random sequences such as Gold sequences is used for user-specific band spreading. To prevent mutual interference of users or their terminals, different families of pseudo-random sequences are used in the various network areas.
In an advantageous embodiment, the logical direction of the data stream is preset using code multiplexing, i. e. multiplying the data stream by Walsh sequences the length of which is shorter than that of the band spreading sequences. Alternatively, additional multiplication by Walsh sequences can be left out when specially selected pseudo-random sequences that undercut each other are used in different network areas. The benefit would be reduced signal processing requirements in real-time signal processing but increased
Brandt Frank
Hensen Christian
Lukanek Frank
Schoenfeldt Kay
Schulz Wolfgang
Brandt Frank
Craver Charles
Urban Edward F.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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