HK1092609B - System and method for data communication over power lines - Google Patents

Description

System and method for data communication over power lines

Technical Field

The present invention relates to a system and a method for broadband data communication over a power line distribution network comprising regional and/or in-house distribution lines between low voltage substations and house connection units.

Background and related evaluation

Prior art systems for data communication on power distribution lines, such as between a low voltage substation and a house connection unit and/or on distribution lines indoors, typically employ at least one master station and slave modems that must register with the master station. The same network architecture is also used for broadband data communication over the indoor power distribution lines.

Such systems are based on Time Division Multiple Access (TDMA) and/or employ Orthogonal Frequency Division Multiplexing (OFDM) techniques. Although OFDM techniques allow higher data rates than time division multiple access techniques, they suffer from a major drawback in that they have poor stop band attenuation performance.

A disadvantage of the master-slave approach is that the transmit power level of the master station must be high enough to allow reaching the furthest slave modem and that the communication bandwidth must be shared between several slave modems.

The main drawbacks of the prior art systems for data communication over power distribution lines are as follows:

the transmit power level required to reach the furthest slave modem is higher, causing corresponding electromagnetic radiation;

the random access scheme required to control the slave modem to send the permission rights is complex;

the master represents a single point of failure; and

if multiple power line master-slave systems are employed simultaneously, time synchronization between different master stations is required to avoid interference between simultaneous power line communications.

These drawbacks are the main obstacles to widespread deployment of power line communications.

Summary of The Invention

It is an object of the present invention to provide a system and method for data communication over a power line that allows high data communication rates to be achieved.

It is another object of the present invention to provide a system and method for data communication over a power line that allows several power line modem to power line modem data transmissions to occur simultaneously over a power distribution network in an asynchronous manner.

It is a further object of this invention to provide a system and method for data communication over a power line that allows the power line modem to employ different transmit power levels.

It is a further object of the present invention to provide a system and method for data communication over a power line that does not require any synchronization between different power line communications conducted in parallel.

These objects are achieved by a system and a method having the features of the respective independent claims, different embodiments of which are given by the dependent claims.

These objects are achieved in particular by a data communication method and a data communication system for communicating data from a plurality of transmitters to a plurality of receivers connected through a single power network having a determined data transmission channel bandwidth; the method comprises the following steps: simultaneously communicating data asynchronously over a plurality of peer-to-peer transmission channels established between the transmitter and the receiver; and the data communication system comprises a plurality of communication devices for transmitting and/or receiving data over a power grid having a determined data transmission channel bandwidth; the plurality of communication devices each include a transceiver system designed to communicate data in an asynchronous manner over a plurality of peer-to-peer transmission channels established therebetween.

According to a preferred embodiment of the data communication method of the present invention, the power line channel bandwidth is divided into n sub-channels of the same bandwidth or different bandwidths, n being an integer greater than 2. According to a preferred embodiment of the invention, the n subchannels are separated, for example, with a digital filter having a high stop-band attenuation.

The power line modem of the present invention preferably comprises means for detecting communication activity, for example in a pre-selected subset of said n sub-channels, in order to identify a free sub-channel for transmitting data to be transmitted over said physical channel. The data is modulated using, for example, a discrete cosine modulated filter bank or discrete wavelet modulation. The receiver performs symbol synchronization and time domain equalization of the sub-channel impulse responses and inverse function processing of the data used by the transmitter to recover the data using, for example, a discrete cosine modulated filter bank or a discrete wavelet filter bank.

The invention thus allows a plurality of power line modem to power line modem data communications to be conducted in parallel and the transmit power can be determined separately for each sub-channel communication, thereby optimally reducing interference between the sub-channels. According to the invention, synchronization need not be achieved between parallel data communications, since they are performed on separate sub-channels. There is no longer any single point of failure because no master station and/or no complex access mechanism is required.

Brief description of the drawings

The invention may be better understood by consideration of the following detailed description of embodiments of the invention in conjunction with the accompanying drawings, in which:

FIG. 1 is a conceptual block diagram of a transceiver system in accordance with a preferred embodiment of the present invention;

fig. 2 illustrates the division of a power line channel bandwidth into sub-channels, in accordance with a preferred embodiment of the present invention;

FIG. 3a shows three concurrent asynchronous data transmissions performed in parallel using different sub-channels of the power line channel bandwidth, in accordance with a preferred embodiment of the present invention;

FIG. 3b schematically shows the three data transmissions shown in FIG. 3a being performed in parallel over a power distribution network;

FIG. 4 is a block diagram of the transmitter shown in FIG. 1;

FIG. 5 is a block diagram of the receiver shown in FIG. 1;

FIG. 6a shows the frequency response of a 1MHz bandwidth discrete cosine modulated filter bank in accordance with an embodiment of the present invention;

FIG. 6b shows the frequency response of a 4MHz analog bandpass filter employed in a receiver according to another embodiment of the invention; and

fig. 7 shows 24 subcarriers used in the normalized frequency range of 0.70 to 0.125 of fig. 6a, according to a preferred embodiment of the present invention.

Detailed description of the invention

Fig. 1 is a block diagram of a transceiver system 10 implemented in a power line modem in accordance with a preferred embodiment of the present invention. The transceiver system preferably comprises a transmitter 11 based on, for example, a discrete cosine modulated filter bank or a wavelet packet modulated filter bank and a receiver 13 also based on, for example, a discrete cosine modulated filter bank or a wavelet packet modulated filter bank. The data communication activity detector 12 is connected to the receiver 13. The transmitter 11 and the receiver 13 are connected to a hybrid circuit 14, via which hybrid circuit 14 the transceiver system 10 is connected to a power distribution network 16.

According to a preferred embodiment of the invention, the transceiver system implemented in the power line modem of the invention comprises a transmitter 11 and a receiver 13, so that it is able to both transmit and receive data, possibly simultaneously and on different sub-channels. However, a person skilled in the art realizes that within the framework of the present invention it is possible to build a communication device, such as a modem, which is only capable of sending data or receiving data. The transceiver system implemented in such a device then comprises the transmitter 11 without the receiver 13 or the receiver 13 without the transmitter 11, respectively.

Fig. 2 shows how the bandwidth of a power line communication network is divided into n sub-channels of different bandwidths according to an embodiment of the invention. The bandwidth of these sub-channels is, for example, 4MHz, 2MHz, 1MHz or 0.5 MHz.

According to a preferred embodiment of the invention, the receiver 13 of the power modem that is to transmit selects different pre-selected sub-channels one by the activity detector 12 and monitors the presence of data communication activity on the sub-channel by measuring the signal energy on the sub-channel. The activity detector 12 identifies in this way the free sub-channels available for transmission and passes this information to the transmitter 11. If more than one sub-channel is available, the transceiver system preferably selects the best sub-channel based on one or more predefined criteria, such as the bandwidth, frequency range, attenuation characteristics, noise, etc. of the sub-channel.

The selected free power line sub-channel is then used for transmitting data over the power distribution network, e.g. sub-channel 302 is used for data transmission between power line modem B and power line modem S, as shown in fig. 3 a. Thereby establishing a peer-to-peer data transmission channel between the two modems. Fig. 3a and 3b also show how three communications take place simultaneously over three parallel peer-to-peer transmission channels, each communication using a different sub-channel of the power line channel bandwidth. These parallel communications are completely independent of each other and can therefore be performed in an asynchronous manner. The transceiver system of each power line modem A, B, C, R, S and T is preferably implemented according to fig. 1.

The data communication method of the invention thus allows to generate a mesh data communication network based on a power distribution network, wherein each communication device can establish peer-to-peer communication with any other device of the network. The transmission power of each peer-to-peer communication is preferably adjusted to accommodate the transmission line characteristics between the two devices. However, to avoid interference from the network environment, the transmission power must be kept within certain ranges. Since the inventive network has a mesh architecture, one or more communication devices can be used as repeaters or relays between two communication devices, for example, which are located far apart from each other. One or more of the communication devices of the inventive network may also act as a relay device or gateway to other networks, such as the internet.

As shown in fig. 4, which shows a block diagram of a transmitter in more detail, data 15 to be transmitted is first interleaved in an interleaver 401, then converted from serial to parallel in a converter 402, and then encoded with a constellation encoder 403.

The parallel output of the constellation encoder 403 is fed to a discrete cosine modulated filter bank or wavelet packet modulated filter bank 404. The filter bank 404 has a bandwidth of, for example, 1MHz, and the cosine modulated filter bank or wavelet packet modulated filter bank preferably has, for example, 24 or 64 carriers, each with a high stopband attenuation.

The serial output of the filter bank 404 is digitally up-shifted in frequency to the frequency of the selected free sub-channel by a modulator 405 comprising a frequency generator 407. The output of modulator 405 is provided to a digital to analog converter 406 for transmission over the selected power distribution network subchannel.

As shown in fig. 5. The received signal is preferably bandpass filtered using a bandpass filter 501 and then amplified using a low noise amplifier 502 and up-shifted to a selected Intermediate Frequency (IF) using a modulator 503. The signal is then again amplified by automatic gain control 505, band-pass filtered by band-pass filter 506, and then fed to analog-to-digital converter 507 for digitization and possibly oversampling.

According to a preferred embodiment of the present invention, a matched filtering technique is employed at the synchronization unit 508 to achieve coarse synchronization with the transmitter of the transmitting modem using training symbols known to the receiver 13. These training symbols are preferably transmitted by the transmitter at least once for each newly established peer-to-peer data transmission. The start position of the transmitted training symbol is detected by the synchronization unit 508, and the synchronization unit 508 then starts the synchronization process. These training symbols are also used to determine the coefficients of the time-domain recursive equalizer 509. Fine synchronization and compensation for frequency offset between the transmitter sample clock and the receiver sample clock are performed based on the pilot symbols.

To recover the transmitted data, the output of the time domain equalizer 509 is fed to a filter bank 510, which filter bank 510 is constituted by, for example, a discrete cosine modulated filter bank or a wavelet packet modulated filter bank. The parallel outputs of the filter bank 510 are fed to a constellation decoder 511. The parallel output of the constellation decoder 511 is then fed to a parallel-to-serial converter 512, and the output of the parallel-to-serial converter 512 is then fed to a de-interleaver 513. The output of the deinterleaver 513 is an estimate 17 of the transmitted data.

Fig. 6a shows an example of the frequency response of a discrete cosine modulated filter bank 510 of 1MHz bandwidth. The horizontal axis shows the normalized frequency [. times.2 π rad/s ], while the vertical axis shows the amplitude in dB. It can be seen that the energy of the modulated data signal is confined to a very narrow frequency range, outside which it is strongly attenuated. Due to this unique property, such signals using different frequency ranges can be transmitted on one transmission line without significant crosstalk between each other. Different data transmissions can thus be started asynchronously in parallel on adjacent sub-channels without the risk of mutual interference.

At the receiver side, a bandpass filter with a frequency response similar to that shown in fig. 6b is used to filter the received signal in order to retrieve the transmitted information. In fig. 6b, the horizontal axis shows frequency in MHz, and the vertical axis shows amplitude in dB. By centering the frequency response of the filter on the desired subchannel, only the signal transmitted on that subchannel may be received.

According to a preferred embodiment of the present invention, the transceiver system 10 comprises a transmitter 11, the transmitter 11 modulating the data to be transmitted with a discrete cosine modulated filter bank or a wavelet packet modulated filter bank 404. The transceiver system 10 is thus a multi-carrier transceiver system and the transmitted data is modulated on a plurality (e.g., 24) of sub-carriers (fig. 7) within the available frequency bandwidth in the selected sub-channel. In fig. 7, the horizontal axis shows normalized frequency, and the vertical axis shows amplitude in dB. Transceiver system 10 is preferably configured such that the transmit power level and the number of encoded data bits or data rate that are different for each subcarrier may be selected based on predetermined or measured transmission characteristics in a particular subchannel band. The transmission characteristics may depend on, for example, signal-to-noise ratio, available bandwidth, attenuation, etc. Transceiver system 10 therefore preferably includes means and/or memory areas, not shown, for determining and/or storing characteristics specific to these subcarriers.

Claims (20)

1. A method for data communication from a plurality of transmitters (11) to a plurality of receivers (13) connected through a single power network having a determined data transmission channel bandwidth; the channel bandwidth is divided into a plurality of sub-channels, the method comprising the steps of: simultaneously transmitting data in an asynchronous manner over a plurality of peer-to-peer transmission channels established between the plurality of transmitters (11) and the plurality of receivers (13), each of the plurality of peer-to-peer transmission channels employing a different one of the plurality of sub-channels, wherein a free sub-channel is determined from the plurality of sub-channels for channel data communication, and if more than one free sub-channel is available, a best sub-channel is determined from the plurality of sub-channels based on a predetermined criterion.

2. The method of claim 1, wherein: the channel bandwidth is divided into a plurality of sub-channels using a band-pass filter with high band-stop attenuation.

3. The method of one of claims 1 or 2, wherein: comprising the following steps performed by the transmitter:

detecting data transmission activity on a plurality of the sub-channels; and

a subchannel without any data transmission activity is selected for transmitting data.

4. The method of any one of claims 1 to 2, wherein: the data transmission channel bandwidth is comprised in a frequency band of 1.6MHz to 40 MHz.

5. The method of any one of claims 1 to 2, wherein: comprising the step of modulating the data with a discrete cosine modulated filter bank (404).

6. The method of any one of claims 1 to 2, wherein: comprising the step of modulating said data with a wavelet packet filter bank.

7. The method of any one of claims 1 to 2, wherein: comprising the step of synchronizing each of said receivers with a corresponding transmitter.

8. The method of claim 7, wherein: the synchronization step is performed using a training sequence known to the receiver and transmitted by the corresponding transmitter.

9. The method of any one of claims 1 to 2 and 8, wherein: data transmission on each of the peer-to-peer transmission channels is performed at a different transmission power.

10. The method of claim 9, wherein: the transmission power accommodates signal attenuation along the peer-to-peer transmission channel.

11. The method of any one of claims 1 to 2, 8 and 10, wherein: comprising the step of encrypting said data using a public-private key encryption method.

12. A system for data communication comprising a plurality of communication devices for transmitting and/or receiving data over a power grid having a determined data transmission channel bandwidth; the channel bandwidth is divided into a plurality of sub-channels, the plurality of communication devices each comprising a transceiver system (10) designed to communicate data in an asynchronous manner over a plurality of peer-to-peer transmission channels established between the plurality of communication devices, each of the peer-to-peer transmission channels being established over an idle sub-channel determined from the plurality of sub-channels, and if more than one idle sub-channel is available, determining a best sub-channel from the plurality of sub-channels based on a predetermined criterion, wherein each of the peer-to-peer transmission channels is established using a different sub-channel of the data transmission channel.

13. The system of claim 12, wherein: the transceiver system (10) comprises a transmitter (11) and/or a receiver (13).

14. The system of claim 13, wherein: the transmitter (11) and/or receiver (13) comprises a filter bank (404, 510) for modulating and/or demodulating data to be transmitted and/or received over the sub-channels with a plurality of sub-carriers.

15. The system of claim 14, wherein: the transceiver system (10) is configured to transmit at different data rates and/or transmit power levels for each of the plurality of sub-carriers according to transmission characteristics in the respective sub-carrier frequency range.

16. The system of one of claims 14 or 15, wherein: the filter bank (404, 510) is a discrete cosine modulated filter bank.

17. The system of one of claims 14 or 15, wherein: the filter bank (404, 510) is a wavelet packet filter bank.

18. The system according to any one of claims 14 and 15, wherein: the transceiver system (10) comprises an activity detector (12) for detecting data transmission activity on a plurality of the sub-channels.

19. The system of any one of claims 13, 14 and 15, wherein: the receiver (13) comprises a synchronization device (507) for synchronizing the receiver (13) with a corresponding transmitter (11).

20. The system of claim 19, wherein: the receivers are synchronized by means of a training sequence known to the receivers and sent by the corresponding transmitters.