SEIFERT, Henryk (Seifertova 740, Trinec, 739 61, CZ)
| CLAIMS
1. A method of PLC communication comprises steps of data generation, modulation and signal amplification, signal transmitting, signal amplification on reception, signal demodulation, errors correction, data check up, data processing, confirmation of transmission and reception, characterized in that
- the data packets are generated in step of data generation having a constant length, comprising just data, redundant information for errors correction and a checksum for data check up,
- all received data regardless of signal amplitude and belonging to a concrete receiving modem are processed in steps of errors correction and data check up,
- the errors correction step is executed on the receiver in a time interval which is maximally equal to the time required for one bit of transferred data transmission with efficiency of minimally 5 % of corrected errors per one data packet,
- the data check up step is executed with a checksum realized on minimally 8 grade polynomial.
2. The method of PLC communication according to claim 1 , characterized in that the data packets are transmitted, after modulation step, to networks with the amplitude equal minimally to 0.7 multiple of the highest acceptable modulated signal amplitude.
3. The method of PLC communication according to claim 2, characterized in that
- the data packets are transmitted, after modulation step, to networks on a frequency and/or with a rate that is changing during operation depending on a rate of interference on the transmission trace,
- the operational digital filter characteristics at "slave" modem are aligned during modulation and demodulation steps without operation interruption by a control signal transmitted from the "master" modem.
4. The method of PLC communication according to any of the previous claims, characterized in that the signal is amplified with a constant gain in the reception step and then goes through demodulation step which is executed in the whole dynamic range of amplified signal amplitudes.
5. The method of PLC communication according to any of the previous claims, characterized in that the time interval is calculated during signal transmission step in which a reception confirmation on data packet reception from "slave" modem is awaited.
6. The method of PLC communication according to any of the previous claims, characterized in that the "slave" modem repeats all the received data packets addressed to another "slave" modem in such a way that alters transferred data addresses by the defined way and so altered sends them back to the networks with a maximum power.
7. An equipment for PLC communication comprises of successively connected modules, input signal processing module (ISPM), demodulator module (DM), errors correction module (ECM), data check up module (DCM), data processing module (DPM), transmission confirmation/repetition module (CRM), transmitter module (TM), modulator module (MM) and output amplifier module (OAM), characterized in that:
- minimally the errors correction module (ECM), check up module (DCM) and data processing module (DPM) are realized as logic blocks in at least one logic array,
- the errors correction module (ECM) and data check up module (DCM) are interconnected by a data bus of minimal length of 4 bits,
- the part of errors correction module (ECM) is a FIFO circular buffer of minimally one data packet volume,
- the data control module (DCM) comprises of a set of parallel configured elementary arithmetic units,
- the cumulative calculation power of the errors correction module (ECM) and data check up module (DCM) is minimally 10 8 operations per second.
8. The equipment for PLC communication according to claim 6, characterized in that the amplifier in input signal processing module (ISPM) is an amplifier with the constant gain.
9. The equipment for PLC communication according to claims 6 and 8, characterized in that it comprises the diagnostic module of transmission trace quality and states of the equipment itself (DMQ) interconnected with the modulator module (MM) demodulator module (DM), errors correction module (ECM) data check up module (DCM) and transmission confirmation/repetition module (CRM).
10. The equipment for PLC communication according to claims 6 to 9, characterized in that it comprises data packets repeater module (SRM) interconnecting data check up modules (DCM). |
METHOD AND APPARATUS FOR POWER LINE COMMUNICATION
Technical Field
The invention relates to a narrow-band way of the message transmission over power lines - so called PLC (Power Line Carrier) communication and equipment for its implementation.
Background Art
The PLC communication presents very interesting communication solution for industry and mainly for power engineering for it enables data networks construction without investment into building new data networks. Its utilization begun in the middle of the last century as one way communication (HDO system) and more intensive of PLC communication usage comes as late as in the middle of nineteen's in a form of both-way communication when further to the development of electronics parts expansion the transmission quality and signal evaluation systems were improved.
The scope of PLC communication is mostly determined by the quality of the transmission medium, i.e. power lines that are a very dynamic transmission environment with high rate of interference. Attenuation on the medium is very much dynamically changing and so the received signal magnitude with the network topology changes by the load connection and disconnection. Most of the modern electrical appliances have also a non-linear load characteristic which is concentrated in a single line. Further the appliances emit a broad spectrum of interference and even networks itself have no linear characteristic due to parallel capacity and longitudinal inductance and due to changing load current a broad frequency spectrum is generated with a very dynamic amplitude. From the signal distribution standpoint the power networks are very unsuitable transmission media and the transmission of undistorted data protection is a considerable technical problem in this environment.
Methods of PLC communication are divided into two basic types and the first one is a narrowband one with a limited rate and the other one is a broadband with the high volume of transported data usable in particular in the field of audio/video signal transmission. From the point of industrial utilization the narrowband PLC communication is an actual way that has a harmonized norm for operation conditions and in most of instances it is a master/slave type communication (master - supervisory modem starting and controlling communication, slave - subordinated modem receiving communication).
In practice it is more apparent need for robust PLC communication methods, in conjunction with increasing electromagnetic interference level, enabling a reliable communication even over strongly interfered traces. No such complex way is known from available resources and from known partial solutions (see e.g. patents from Echelon Corp. US 5,828,676 ..Method and apparatus for robust communication based upon angular modulation" and US 5,553,081 .Apparatus and Method for Detection a signal in Communications system", or ltran Communications Ltd. US 6,690,719 ,,Host to modem interface") of the PLC communication between master and slave provides a solution giving maximal reliability of the PLC communication according to actual state of technology that uses a BPSK modulation system (Binary phase shift keying), (ASK, FSK modulation) and a (redundant) checksum (CRC) as a standard for accuracy control. A system of synchronization header followed by proper message body is used for the proper transmitted data decoding. The communication system can work with an optional message body length and a carrier frequency switching over is implemented due to increasing of interference immunity and partly transmission trace attenuation. This asks for system restart every time, however. The solution according to the state of technology can be then characterized by sequence of following steps:
1) data generation - the data are generated on the ..master" in form of data packet with a variable length consisting of: synchronization information (preamble) standing on the beginning of packet serving for data synchronization on ..slave", i.e. defining the beginning of the following
block of transferred data, redundant information, serving for correction of errors on ,,slave" generated during transmission in the block of transferred data and checksum control which is a concrete value acquired after proper algorithms on transferred data and serving for data verification, the block of transferred data itself.
2) modulation and signal amplification - the data packet generated in step 1 is modulated in a modulator on the signal which is amplified for the required power level in an amplifier (see e.g. US 6,636,117 of Echelon Corp. Jnput/output buffer incorporating filter for power line Communications line").
3) signal transmission - the signal is transmitted into power networks and led to each ,,slave", in the vicinity of ..master", and possibly also to a repeater which the received signal, according to its directional table, advances further (see e.g. patents of Echelon Corp. US 5,485,040 ,,Powerline coupling network", US 7,103,016 ,,System and method for providing transaction control on a data network" and US 7,277,672 ,,System and method for selecting repeaters").
4) signal reception and amplification - the received signal on ,,slave" is from the point of its level optimized by a voltage controlled operational amplifier for further processing (see e.g. patent of ltran Communications Ltd. US 6,766153 ,,Dynamic automatic gain control circuit employing Kalman filtering").
5) signal demodulation- the signal on ,,slave" is gradually demodulated and data generated are transferred to the further processing.
6) information noise filtering - it is specified if the level of demodulated signal is higher than beforehand specified decision level (carrier detect), thus the information noise is excluded from further processing (see e.g. patents of Echelon Corp. US 5,553,081 ,,Aparatus and method for detecting a signal in Communications system" and US 95,260,974 ..Adaptive carrier detection").
7) data synchronization - according to information included in preamble the,,slave" gets know if the concrete data packet is scheduled to it, i.e. whether it should start to process the data comprised in the packet.
8) errors correction - the errors in data packet are corrected according to a redundant information.
9) data check-up - on base of CRC control checksum the verity of processed data is verified.
10) data processing - the verified data generally carry some command and the "slave" generates a confirmation before or after the command realization on data reception on "master" and also an preamble, control check-sum and redundant information is added to the confirmation.
12) confirmation transmission - confirmation is transmitted into power networks - see step 3 (see e.g. patent of Echelon Corp. US 7,103,016 ,,System and method for providing transaction control on a data network"),
13) confirmation reception - the confirmation is received on the ..master" (see step 4) and unless the ..master" does not obtain the confirmation or its reception was not successfully realized, the routine repeats from step 1 inclusive (see also patent of Echelon Corp. US 7,103,016 ..System and method for providing transaction control on a data network").
An important disadvantage of such PLC communication design based on well- known solutions is the fact that there are often problems to maintain connection on heavily interfered traces at all and the data transition is very slow caused mainly by manifold repetition of the same data resulting in: the method does not enable to process received signal in a full dynamic range, i.e. the signal with low and high amplitude changes cannot be processed, as a result of using synchronization sequence, so called preamble, transmitted ahead of valid data and redundant information lots of transmitted data packets are
lost not only due to occurrence of random erroneous preamble but mainly due to preamble devaluation by impulse interference and subsequently to no synchronization of transmitted data as the result. even if the preamble is in order and transmitted data are errorless often happen loosing of data packet for the signal amplitude is lower than the decision level (carrier detect). data are transferred by a constant rate on a constant frequency and when the transmission trace deterioration takes place the connection is lost. the systems are further designed so that they can work in a collision state, i.e. modems read on a standard defined frequency whether somebody is transmitting. In the instance when no transmitting is evaluated they can start transmitting themselves and the system asks for definition of signal decision level under which everything is considered as noise. at large-scale PLC systems with length over 200 to 500 meters external repeaters must be used. in case of using of variable length transmitted data packets it cannot be defined a time window up to the "master" beginning a data communication can await a confirmation from receiving modem and the "slave" does not indicate a reception on the side of "master" in further received data where the "master" makes confirmation on received data. high frequency signal transmission is executed in a standard frequency range of 9 kHz to 125 kHz and 140 kHz to 148.5 kHz and an auxiliary (collision) signal is transmitted on frequency 132.5 kHz, reporting to the other equipment in transmission trace that somebody is just transmitting and the others must be standing-by and it can be detected even by mistake during a strong interference. This means that the communication cannot be realized due to interference at all. General consequence of the above mentioned drawbacks is high operational unreliability of such designed PLC communication mainly in intensively interfered networks, putting of such outlined system in service is time-consuming and it must be often repeated at common dynamically variable transmission trace.
As no complex solutions of robust PLC communication are known in the state of technology as even no complex solutions of realization of such robust PLC
communication are known. Just the best possible solution according to the state of technology can be deduced from available resources based on known partial solutions of individual modules of such equipment described in numerous patents (see e.g. patents of Echelon Corp. US 5,828,676, US 6,636,117, US 5,553,081 , US 6,636,117, US 5,485,040, US 7,103,016, US 7,277,672 and ltran Communications Ltd. patents US 95,260,974 or US 6,690,719). All this known equipment is realized on the base of discrete elements generally as signal processors and microcontrollers with specialized communication circuits. The objective equipment then comprisesof following functional modules according to the state of art (see Fig.1):
1) input signal processing module ISPM- guarantee an input signal amplification with automatic gain control.
2) demodulator module DM - guarantee an input signal demodulation and its frequency processing after passing through frequency filters embedded in the module getting so a binary modulated signal from a modulated signal. The module comprisesof two parts - the demodulator itself and a circuit for signal level measurement and signal/noise evaluation.
3) synchronization module SM - defines the beginning of data transmission.
4) errors correction module ECM - guarantee a correction of errors generated during data packets transmission over power lines and cooperates on building of redundant information at transmitted data.
5) data check-up module DCM - guarantee a verity of received and in ECM module possibly modified data by way of checksums at transmitted data and cooperates at redundant information generation within transmitted data.
6) data processing module DPM - guarantee an analysis of received data and according to that type of data routes them further toward various I/O internal and external equipment.
7) transmission confirmation/repetition module CRM - guarantees a confirmation of data reception received from other modem and simultaneously watches a reception confirmation on transmission reception from another modem. As well as it does not get such confirmation in a given time period it generates a command to
the transmitter to repeat the transmission.
8) transmitter module TM - guarantees a transmitting of data received from an external input data module or from external record/display unit and simultaneously sends the information on the sent-out transmission to CRM module.
9) modulator module MM - guarantees a modulation of transmitted transmission consisting of two parts - numerical oscillator with differential coder and modulated signal filter since the modulated signal is a source of infinite spectrum of harmonic modulation signals with a gradually descending amplitude that must be eliminated by filtering.
10) output amplifier module OAM- guarantees transmitted signal amplification on the amplitude level desirable for the most quality of transmission over power lines. Substantial disadvantages of such design conception can be resumed in the following:
- the equipment can continually work just on a single constant, even if no matter how interfered, frequency and the data can be sent-out just with a single rate.
- low computation ability of the used discrete elements enables implementation just low- power self correction procedures able to correct just small part of errors generated during data packet transmission.
- low computation ability during data processing represents a limitation at routing toward various I/O equipment.
- low transmitter computation ability represents a limitation during data transmitting from external input data module or external record/display unit.
- the equipment lacks of diagnostic elements not just as to quality diagnostic and state of individual communication modems but also to transmission trace quality.
- input regulation amplifiers with automatic gain control (AGC) have generally slow response to step changes of signal level, i.e. they are not able to match optimally the signal with changing high and low amplitude for further procession and demodulator accordingly is not able to process the modulated data.
- the equipment does not comprise a repeater as its integral part which enables to "slave" the received but not to it belonging data to sent over toward other elements of given communication network.
An actual necessity of a new solution of the method and equipment for PLC
^ 9 000111
communication over massively interfered traces giving a more stable connection and faster data transmission is apparent from the above mentioned.
Disclosure of Invention
Drawbacks of PLC communication ways according to the state of the art essentially eliminates the solution according to the claim 1 and drawbacks of PLC communication equipment according to the state of the art essentially eliminates the solution according to the claim 7. Beneficial solution variations are the content of dependent claims.
The method of PLC communication according to presented invention comprises familiar steps of data generation, signal modulation and amplification, signal transmitting, signal amplification, signal demodulation, errors correction, data check-up, transmitting of confirmation and reception of confirmation and it differs from known methods so that data packets are generated as a constant length optional in the range from 8 B to 256 B comprising just the data and redundant information for errors correction and data check-up. They do not comprise any synchronization preamble, nor start and stop bits generally used in known methods of data transmission. Thus one of main reasons of data packets loss is eliminated as it exists at known solutions.
Further the errors correction step on receiver is performed periodically in a time interval that equals or is less than a time interval required for transmission of a single bit of transported data, i.e. one error correction cycle at least is executed during the time of one bit transmission. Thus the system immunity against impulse interference is considerably improved. The important fact is that the errors correction is executed with efficiency min. 5 % of corrected errors per one packet.
The remarkable benefit to the transmission quality improvement is a data packets check-up performed with checksum of min. 8 grade polynomial, i.e. minimal checksum length is 8 b and beneficial is also a fact that data selection is executed by processing of all received data packets no matter as how high is the amplitude
of modulated signal as to a competence to a concrete receiver - ,,slave". The received data are cyclically stored in a buffer memory the length of which is equals the transferred data packet length. Each time after one bit length data shift an error correction of a complete data chain by appropriate method is executed, e.g. by Reed-Solomon error corrector. Successively the robust checksum calculation is executed, e.g. CRC24, and its comparison with transported image generated in an output part of transmitting PLC modem. In case of positive results of both previous operations is the analyzed packet labeled as true one and proceeded to further procession, e.g. by a microcontroller. If the results are not equal the shift of bit length is executed in the buffer and the whole analysis process repeats.
The data packets after modulation step are favorably transmitted into power networks with the amplitude of minimally 0.7 multiple of the highest acceptable modulation signal amplitude defined by valid technical norms. Just more favorably they are transmitted into power networks at least on a single frequency with a single rate and the frequency and/or rate are changing depending on the rate of interference on the transmission trace in a given frequency spectrum. If the "master", for example, is not able to maintain a connection with the "slave" on a single frequency and rate it will change the frequency and/or rate in one or more steps downward to a lower frequency and/or rate until a stable connection is established. In case of longer persisting stable connection the frequency and/or rate can be gradually increased up to achieving of maximal frequency and/or rate for the stable connection in given conditions.
Operational digital filters characteristics during modulation and demodulation are aligned at the same time at "slave" by a control signal transmitted by the "master". The employed digital filters enable design of very selective band-pass filters being a part as output as input PLC modem circuitry. The goal is to achieve a narrowband signal transmission with a maximal power and an option of frequency realignment which can be realized immediately during full load operation so that an application firmware changes digital filters numerical parameters (particular mathematical equations coefficients which the signal "filtering" calculation is processing with). The filters so are retuned to a different frequency band and/or a
clock oscillator as a part of modulator module is numerically retuned to a required frequency. Possible transmission rate change can be aligned simply by series data shift change in the modem. This method of transmission eliminates a wideband noise on the noise in the band pass only. Big power concentrated into a narrow beam is less energy demanding then the wideband one and very low impedance in the band pass then effectively suppresses the noise.
It is further advantageous when the signal during a step of signal reception is amplified with a constant gain and then demodulated and the demodulation is executed in whole range of amplified signal amplitudes, i.e. in the extreme case the data are searched for even in the noise of power network. A signal of very low amplitude must be processed as well as maximal amplitude signal and mainly the signal with the least signal to noise ratio. This is achieved using a D-BPSK phase modulation which provides the least signal to noise ratio for received signal processing and as a differential method is used where a phase change of modulated signal is executed just at the modulation signal change, a carrier in the receiver need not be generated. The demodulation as well is not dependent on input signal amplitude which is remarkably changing during transmission due to transmission trace impedance variations (switching-on and off of the motor and such like)
In practice the PLC modem input circuits continuously measure a voltage on a connected trace no matter if there is a date packet or not. By the effect of an input band pass filter the measurement is executed e.g. just in the range of 60 kHz to 120 kHz by e.g. 12 bit AD converter with the minimal 50OkHz sampling rate. Such a processed signal already in a digital form is lead through a narrowband digital filter adjusted exactly on a high frequency carrier to the demodulation step. Here the phase change in the transmission channel initiates an event resulting in logic value change. This is passed to (e.g. 30 B) shift register (with an exactly data packet length) with a parallel output. The transmitted packet is encoded in the error correction circuit at the end phase of transmission and after modulation is sent out to a transmission trace.
From the standpoint of PLC communication transmission acceleration it is advantageous parallel with signal transmitting or immediately after that transmission to execute a time window calculation, i.e. the time interval in which the reception confirmation should be awaited on data packet reception from "slave". When the data transmission is adversely influenced by present strong interference an automatic transmission repetition starts after the time window elapses. The "slave" modem recognizes the reception on "master" side inside of following received data where the "master" confirms the reception of previous data. This method enables the data transmission with practically 100% success.
The function of signal repetition at "slave" modem in the presented invention is favorably modified and employed on coverage extension at the designed PLC communication method. It is achieved by the fact that the "slave" modem receiving though all data packets from transmission trace, repeats not only its unconfirmed transmissions, but repeats also all received data obtained from "master" or possibly adjacent "slave" that do not belong to it. The received data repetition is executed so that in the "slave" modem equipped with this function the addresses of received data packets are changed by beforehand defined procedure and such modified packets are sent out further into networks with maximum of power. The transmission trace behavior can be very dynamic, adverse conditions often turn in favorable ones and it can come to a situation when receiving "slave" suddenly gets a message from the "master" and successively the same one a bit delayed from a repeating mate which could lead to collision. That's why the receiving "slave" does not communicate with "master" directly (the massage of which it ignores) but only with the mate that has the message from the "master" modified and amplified.
The equipment for PLC communication comprisesof module of input signal processing ISPM, demodulator module DM, errors correction module ECM, data check up module DCM. data processing module DPM, transmission confirmation/repetition module CRM. transmitter module J_M, modulator module MM and output amplifier OAM. In contrary with known solutions (see Fig. 1) it does not comprise synchronization module SM which is logical for the transported data packets do not comprise synchronization preamble. At the same time the errors
correction modules ECM. data check up modules DCM and data processing modules DPM at least are realized as software generated (either during manufacture or before application) hardware logical modules at least in one gate array which is an electronic component disposing of big computing ability and big resistance against external interference. That's why the resulting modem function changes are made by reprogramming, e.g. by change of gate array modification itself or application software, so that even digital filters as a result of it are able to change their parameters. It enables to change as the modem transmission frequency as the data transmission/reception rate during operation with no problems. Further from the angle of manufacturing expenses and operational reliability it is favorable when at least modulator module MM, demodulator module DM, errors correction module ECM. data check up module DCM. data processing module DPM, transmission confirmation/repetition module CRM and transmission module TM are realized on base of one programmable logic array.
It is important that the interconnection between errors correction module ECM and data check up module DCM is realized by a data bus minimally 4 bits wide with a minimal data throughput of 10 6 b/s and a calculation capacity of each of those modules is minimally 10 8 operations per second. The data check up module DCM is made from a set of parallel elementary arithmetic units because due to requirement of very fast calculation, shorter than a bit length, a parallel method of calculation must be used. From the angle of required robustness and transmission data rate it is also important that FIFO buffer memory is a part of errors correction module ECM. The memory volume is minimally one data packet and it has an input serial bus and output parallel bus.
The input signal processing module ISPM beneficially has a constant gain amplifier which amplifies the input signal and more beneficially the PLC communication equipment has also module of transmission trace quality diagnostic DMQ and so the equipment states. Because the solution is focused on PLC data transmission over very much interfered medium such functional diagnostics is necessary for a proper layout and PLC network maintenance. It is understood that the transferred data comprise inside the information on states of
individual modems and also on measured signal level (amplitude) and interference intensity (noise amplitude) during the time of reception and data frame processing in the point of modem connection to the transmission trace. These diagnostic data serve to fast identification of possible breakdown or instability of connection reliability. As the transferred data include even a time information the problem on the trace can be very precisely analyzed and necessary measures to clear it can be made or to make a PLC network optimalization.
Sometimes the situation on the transmission trace is very adverse for high frequency signal transmission or the trace is very much impedance loaded. A real coverage of the effective signal is low (ca several hundred meters). Well known designs generally use individual signal repeaters for signal coverage extension that are situated in suitable positions of the transmission trace. To overcome such situation it is more convenient to equip some (or all) "slave" modems on trace with SRM signal repeaters modules.
Generally it can be noted that an application of the presented design provides a substantial PLC communication improvement thanks to new quality characteristics of data procession mainly in the reception part of the equipment - the modem. When the presented method and equipment is properly applied practically 100% transmission reliability can be achieved and the communication coverage is about one order higher than that with known solutions and however great area can be covered by means of original network of modems - repeaters. In practice is also remarkable that the invention makes possible a fast identification of transmission trace failure and is easily implementable in various equipments.
Brief Description of Drawings
The principle of the solution will be explained in greater details on examples of its design which is here given just for illustration and do not limit anyhow the range of protection defined in patent claims. Design examples are figured out on attached drawings as follow:
Fig.1 - block diagram of PLC modem according to an actual state of the art
Fig. 2 - block diagram of PLC modem according to the first variant of presented invention
Fig. 3 - block diagram of PLC modem according to the second variant of presented invention
Fig. 4 - block diagram of PLC modem according to the third variant of presented invention
Fig. 5 - block diagram of PLC modem according to the fourth variant of presented invention
Modes for Carrying Out the Invention
Example 1
The equipment for PLC communication according to Fig. 1 comprises of input signal processing module ISPM, demodulation module DM, errors correction module ECM, data check up module DCM 1 data processing module DPM, transmission confirmation/repetition module CRM. transmitter module TM 1 modulator module MM and output amplifier module OAM. ISPM, MM and DM modules are designed as logic units inside of ST Microelectronics ST7540 integrated circuit. ECM, DCM. DPM. TM and CRM modules are built up as software generated logic units in an XC3S200 FPGA logic array from Xilinx.
Method of PLC communication with the described equipment comprisesof following steps:
- data generation in form of data packets of 32 B constant length transferring data and a redundant information in form of 2 B for a checksum and 4 B for data required for errors correction on receiver side.
- a signal modulation using FSK modulation, frequency 110 kHz, 2 400 b/s rate.
- a signal amplification to 8V level.
- signal transmitting via galvanically isolated link (not represented) to a 230 V low voltage circuit.
- input signal processing by ST7540 from ST Microelectronics comprises its constant amplification that amplify an input signal amplitude so that it can still be
processed by demodulator at minimal magnitude of 1mV. The amplifier gain setup is 10. ST7540 circuit also demodulates the signal using FSK frequency demodulation.
- all data obtained by signal demodulation, regardless of belonging to the concrete equipment, are processed and:
- error correction step is executed by Reed-Solomon algorithm periodically in time interval of 0.2 ms and error correction step is executed by Reed-Solomon periodically in time period of 0.2 ms with a minimal efficiency of 7 % i.e. 2 to 16 corrected bits in a frame of two elementary Reed-Solomon algorithm symbols per one transferred data packet (2 B of corrected errors per one data packet),
- data checkup step is executed together with a checksum realized by 16 grade polynomial in form x 15 + x 13 + 1.
- the positive data checkup follows the data processing step where all data are processed without regard to the modulated signal amplitude. That step is realized by MicroBlaze embedded processor from Xilinx and in result the data gained are segmented to data to be stored in data memory, data determined to be processed in the input/output equipment, data commanding data transmission repetition and data commanding a dispatching confirmation on data reception.
Example 2
The PLC communication equipment according to example 1 and Fig. 3 differs so that repeater module SRM located inside of XC3S200 FPGA logic array is realized by MicroBlaze embedded processor from Xilinx internally connected with errors correction module ECM and data checkup module DCM. The repeater module SRM modifies the received packet which does not belong to the given equipment, however, so that it makes some changes in a packet address part by predefined way but the rest of data in the packet leaves unchanged. So modified packet is sent out to data checkup module DCM where a checksum from the modified data packet is carried out and is connected with the part transferring information for the following data check up. The redundant information from Reed-Solomon errors corrector is complemented in the errors correction ECM module and than after modulation and amplification to 8V is the data packet transferred to the network.
Example 3
The PLC communication equipment according to Fig. 4 comprisesof input signal processing module ISPM, demodulator module DM 1 errors correction module ECM, data check up module DCM, data processing module DPM, transmission confirmation/repetition module CRM. repeater module SRM, transmitter module TM. modulator module MM and output amplifier module OAM. MM. DM, ECM. DCM, CRM. SRM. TM and DPM modules are built as logic circuits software generated inside of Altera EP3C5 FPGA logic array.
PLC communication with presented equipment comprisesof the following steps: data generation in form of 38 B constant length data packets comprising transferred data and redundant information in form of 3 B for checksum and 4 B for data necessary for errors correction on receiver side. a signal modulation using DBPSK frequency modulation, frequency of 90 kHz, 105 kHz, and 120 kHz, rate of 10 kb/s and 2,5 kb/s. - a signal amplification to maximum level of 10V. a time window calculation is executed during the step of data transmission within which a reception confirmation on data packet from "slave" is waited for which is generated in confirmation/repetition module of transmission CRM. a signal transmission is realized via galvanically isolated link ( not represented) to a 230 V low voltage circuit. an input signal processing by a constant amplification in the receiver is realized by Texas Instruments TLC072 circuit which amplifies the input signal amplitude so that at minimal voltage of 0,5mV it can be sequentially demodulated. The amplifier's amplification factor is 20.
- the following is realized in demodulation and modulation steps:
- frequency channels and transmission rates change-over,
■ errors correction step executed by Reed-Solomon algorithm in the receiver periodically in time interval of 0,05 ms with minimum efficiency of 2 B of corrected errors per one data packet,
■ data checkup step is executed together with a checksum realized by 24 grade polynomial in form x 23 + x 20 + x 17 + x 14 + x 3 + x 2 +1
■ following the positive data check up succeeds the data procession step in which all
data irrespective of modulated signal amplitude magnitude realized by Niosll in embedded Altera processor. So acquired data consist of data intended for storing in memory, data intended for processing in input/output equipment, data commanding the data transmission repetition, data commanding sending out a confirmation on data reception and data commanding frequency and transmission rate change-over.
Example 4
The PLC communication equipment according to Fig. 3 and 5 differs so that it comprises transmission trace quality diagnostics DMQ and the state of that equipment for PLC communication module located in FPGA logic array type EP3C5 from Altera and which is connected with demodulation module DM, modulator module MM, errors correction module ECM. transmission confirmation/repetition modules CRM and Niosll in embedded Altera processor. The DMQ module complete the transferred data with the information on the state of equipment available to it for PLC communication and so on a measured signal amplitude, noise amplitude, number of corrected errors in received packet during reception time and data packet processing in the point of its connection to the transmission trace. It also adds an information on number of repeated and by "slave" unconfirmed data packets.
Industrial applicability
The solution can be utilized anywhere in industry e.g. during local measuring of various analog quantities (temperature, dampness, etc.) and their transmission over metallic line to distant nodes (control robots or operation control sites). The main focus of applications is in citizen media reading (electrical energy, water, gas, warm water, cold, etc.) and in data transmission in very large objects the system of which does not require transfer of big quantity of data ( the most noticeable examples are sensors in chemical plant).