WO2012146326A1

WO2012146326A1 - Method for operating a power line communication system, power line communication device, power line communication system

Info

Publication number: WO2012146326A1
Application number: PCT/EP2012/000473
Authority: WO
Inventors: Andreas Schwager
Original assignee: Sony Corporation; Sony Deutschland Gmbh
Priority date: 2011-04-26
Filing date: 2012-02-02
Publication date: 2012-11-01
Also published as: CN103460614B; CN103460614A; WO2012146326A8

Abstract

A power line communication device is provided comprising a detection unit, configured to detect an ingress in the very high frequency band; and a notching unit, configured to notch a frequency band during communication of the power line communication device with another power line communication device. A corresponding method for operating a power line communication device and a power line communication system are provided as well.

Description

Method for operating a power line communication system, power line communication device, power line communication system

Description

An embodiment of the present invention relates to a method for operating a PLC system. Further embodiments relate to a PLC modem device and a PLC system. BACKGROUND

Power line communication (PLC), also called mains communication, power line transmission (PLT), broadband power line (BPL), power band or power line networking (PLN), is a term describing a method for using power distribution wires for simultaneous distribution of data. A carrier can communicate voice and data by superimposing an analogue signal over standard 50 Hz or 60 Hz alternating current (AC). For indoor applications PLC equipment can use household electrical power wiring as a transmission medium.

Power line communication (PLC) might have interferences to fixed radio broadcasting or other external transmissions. Today, PLC modems or PLC devices have fixed notch filters for amateur radio bands. Filters for fixed notches can be implemented with a high suppression and very steep slopes.

Concepts of dynamic or smart notching enables PLC modems to detect an ingress of fixed radio broadcast stations in the short wave frequency range between 3MHz and 30 Mhz. The publication ETSI TS 105 578; Power line Telecommunications; "Coexistence between PLT modems and short wave radio broadcasting services"; ETSI 2008 describes an adaptive frequency notching technique, which on the one hand has a minimum impact on data throughput and QoS (Quality of Service) requirements and, on the other hand refuses interference between PLT (Power line telecommunications) and short wave radio broadcast. Communications and power line wires act as bidirectional antennas, wherein typically the transfer function or antenna gain is identical for signal radiation and for signal reception. Communications and power line wires that are suitable for receiving a broadcast signal and that transmit signals in the same frequency band can disturb a reception of the broadcast signal at a radio receiver.

There is a need to improve the prior art PLT communication systems in order to reduce influence on signals transmitted in other frequency ranges.

The object is solved by a method, a PLC modem device and a PLC system according to claims 1 , 12 and 13, respectively.

Details of the invention will become more apparent from the following description of embodiments in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic block diagram illustrating a wired communication system. Fig. 2 is a simplified flowchart of a method for operating a power line communication system in accordance with the further embodiment. shows an exemplary frequency diagram illustrating a notch for notching frequencies during power line communication.

DETAILED DESCRIPTION OF THE INVENTION In the following, embodiments of the invention are described. It is important to note that all described embodiments in the following may be combined in any way, i.e. there is no limitation that certain described embodiments may not be combined with others In Fig. 1 a schematic block diagram of a power line communication system 100 is depicted. The power line communication system 100 includes a first power line communication device 102 and a second power line communication device 104 which are connected via a power line communication channel 106. For communication purposes the first power line communication device 102 includes a first transmitter /receiver 1 12 which is controlled by a first controller 122. The second power line communication device 104 includes a transmitter /receiver 1 14, which is controlled by a second controller 124.

The first controller 122 includes a detection unit 132 and a notching unit 142. The second controller 124 includes a second detecting unit 134 and a second notching unit 144.

The first detection unit 132 as well as the second detection unit 134 is configured to detect a frequency of an ingress in the power line communication system 100 in a very high frequency band. The very high frequency band (VHF) is a frequency range between 30MHz and 300 MHz and is commonly used for TV broadcasting (e.g. in VHF Band I (47 MHz-68 MHz) and VHF Band III ( 174 MHz to 230 MHz)), radio broadcasting by frequency modulation (FM), (VHF Band II between 87,5 MHz and 108 MHz), air radio, marine radio or amateur radio.

The frequency of the ingress might be detected by measuring a noise signal received via the power line communication channel 106 or via an external antenna (not depicted). The wording "noise signal" used within this description also encompasses "mixed signals" that comprises a mix of noise, of ingress or disturbance signals of radio broadcast and of payload signals. The wording "noise signal" is used to emphasize that at least a disturbing signal (i.e. a broadcast station or some white noise) is present within the "noise signal" and disturbs or would disturb the reception of the payload signal.

In a PLC system signals are generally OFDM (orthogonal frequency division multiplex)-modulated, i.e. a plurality of sub-carriers is used for transmitting the payload signal. OFDM is a multi-carrier modulation scheme, which uses a large number of closely spaced orthogonal sub-carriers. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation (QAM)) at a low symbol rate, maintaining data rates similar to conventional single carrier modulation schemes in the same bandwidth. In practice, OFDM signals are generated using a fast Fourier transform (FFT) algorithm. The primary advantage of OFDM over a single carrier scheme is its ability to cope with severe channel conditions - for instance, attenuation of high frequency at a long copper wire, narrow band interference and frequency-selective fading due to multi path transmission, without complex equalization filters. The first notching unit 142 and the second notching unit 144 are adapted to notch the detected frequency for which the ingress has been detected by the first or second detection unit 132, 134. The term "frequency" might be understood in the context of this application also as "frequency range" or "frequency band". Notched frequencies or notched frequencies ranges or bands might also be referred to in the following as "notch".

The first notching unit 142 and the second notching unit 144 control the first and second transmitter/receiver 1 12, 1 14 so that sub-carriers are not used that might influence the frequency for which the ingress has been detected.

A corresponding flowchart of a method in accordance with an embodiment of the invention is depicted in Fig. 2, wherein in a first step S200 a frequency of an ingress in a very high frequency band is detected and in a step S202 a frequency range which includes the frequency of the ingress is notched during power line communication. An ingress shall be identified as a receivable radio broadcast service if the signal is at least 5.6 dB above a noise floor (relative threshold level) for protection of 4-QAM DRM transmissions (QAM: quadrature amplitude modulation, DRM: digital radio mondiale). This signal to noise ratio is required for an error free DRM+ reception using 4-QAM in a rural channel.

It might also be possible to identify a signal ingress if a receivable radio broadcast service is at least 1 3. 1 dB above the noise floor (relative threshold level) for protection of 1 6-QAM DRM transmissions .

A noise floor can be measured at adjacent frequencies lower and higher than the radio band . The adj acent frequency block to be monitored might be as wide as the radio band allocation itself. The adjacent frequency blocks should be completely monitored by the PLC modem devices without any gaps . The noise floor might be the median value of all measured values of the electrical energy in the adjacent frequency blocks on a power line communication channel 106 excluding all power line communication signals .

If the relative threshold level criterion is satisfied, the absolute threshold level of ingress of a broadcast signal identified as receivable should - 7 1 dBm, wherein the absolute threshold level is measured with a spectrum analyzer using an average detector and a resolution bandwidth of 120 kHz .

The absolute threshold value P_detect_on_mains of - 7 1 dBm might be derived as follows :

With a minimum electrical field strength E = 49.7 dB^V/ m (for an exemplary 4-QAM, portable Inhome receiving situation in the VHF band I between 47 MHz and 68 MHz) ) and an 80% reflection factor ReFa_80% = 1 2 1 dB(^V/ m) - dBm, the absolute threshold value P_detect_on_main_S results in

Pdetect_on_mains = E - ReFa_80% = 50dB^V/ m- 1 2 1 dB (μν/ m) - dBm = - 7 1 dBm ( 1 )

The reception factor describes the relationship between the electrical field strength of a radio broadcast station in the air and the received power to be measured at outlets . An 80% reception factor ReFa_80% covering 80% of the cases , with an 80% confidence level can be derived from a measured cumulative statistical probability as ReFa_80% = 121 dB( V/m) - dBm, as it is shown in A. Schwager: "Powerline Communications: Significant Technologies to become Ready for Integration" to be found at

http: / /duepublico.uni-duisburg- essen.de /serylets /DocumentSerylet?id=22425

When further considering that 120 kHz = 50.7 dB(Hz), 120 KHz/9 kHz = 13.3 = 1 1.2 dB it follows that the absolute threshold value is -71 dBm - l l dB + 95dBm = 13dB higher than the threshold in the high frequency (HF) band according to ETSI TS 102 578 , wherein an absolute threshold of -95 dBm is given, measured with a spectrum analyzer using an average detector and resolution bandwidth of 9 kHz. It is to be noted that in the HF band the absolute threshold value considers that HF broadcast transmissions fade with +5 dB above the average reception level (as specified in ITU-R Rec. P.842-2 (Computation of Reliability and Compatability of HF Radio systems). It is possible to measure the noise floor and the signal between the live and neutral conductors at a socket to which the power line communication device is connected.

A radio broadcast signal should be detected and the corresponding notch should be activated by the power line communication device in no more than 15 seconds after the receivable radio broadcast service is actually present. The notch shall remain active continuously for the whole time that the radio broadcast is present. After the radio broadcast services have been identified as no longer receivable the notch shall still remain active for at least 180 seconds. The frequency range of the very high frequency band might be chosen between 47 MHz to 68 MHz.

In Fig. 3 the shape of a notch is depicted. The corresponding values for the frequency spacings a, b and c and the distances from the lower level of the notch are depicted in table 1.

Table 1 : Definition of a notch in order to avoid adjacent carrier interference Frequency Distance from lower level of the notch: spacing A(x)

1^st step: 2 kHz 0 dB

a

2^nd step: 100 kHz ≤ 20 dB

b

3^rd step: 200 kHz ≤ 44 dB

c

The width of the notch might be scaled to integer multiples of 100 kHz plus a minimum width. The minimum width of a notch might be at least 96 kHz.

A center of a notch shall be aligned to the radio broadcast carriers which are arranged in the VHF band I as a 100 kHz raster. The 100 kHz raster helps PLC modems to identify a frequency location of the radio carrier. This avoids false detections at spurious emissions.

The lower level of the notch might be less than -99 dBm measured as differential mode signal at the power line communication device with a resolution bandwidth of 3 kHz and an average detector. This would result in a power spectral density (PSD) of - 134 dBm/Hz.

Claims

1 . Method for operating a power line communication system, comprising:

detecting a frequency of an ingress into the power line communication system in a very high frequency band; and

notching the frequency of the ingress during power line communication .

2. Method for operating a power line communication system according to claim 1 ,

wherein an ingress is detected when a signal strength is above an absolute threshold level of -71 dBm, wherein the absolute threshold level is measured with a spectrum analyzer using an average detector and resolution bandwidth of 120 kHz.

3. Method for operating a power line communication system according to any of claims 1 or 2,

wherein an ingress is detected when a signal is at a relative level of 5.6 dB above a noise floor.

4. Method for operating a power line communication system according to any of claims 1 or 2,

wherein an ingress is detected when a signal strength is at a relative level of 13. 1 dB above a noise floor.

5. Method for operating a power line communication system according to any of claims 1 to 4,

wherein a frequency range of the very high frequency band is from 47 MHz to 68 MHz.

6. Method for operating a power line communication system according to any of claims 1 to 5 ,

wherein a minimum width of a frequency range that is notched during communication is 96 kHz.

7. Method for operating a power line communication system according to any of claims 1 to 6, wherein the width of a frequency range that is notched during communication is scaled to integer multiples of 100 kHz plus a minimum width.

8. Method for operating a power line communication system according to any of claims 1 to 7, wherein a center of the frequency range that is notched is aligned to a radio broadcast carrier.

9. Method for operating a power line communication system according to any of claims 1 to 8, wherein a lower level of a transmit signal strength in the frequency range that is notched is less than -99dBm measured as differential mode signal at a power line communication device with a resolution bandwidth of 3 kHz and an average detector.

10. Power line communication device comprising:

a detection unit, configured to detect a frequency of an ingress in a very high frequency band; and

a notching unit, configured to notch the frequency detected by the detection unit during communication of the power line communication device with another power line communication device.

1 1. Power line communication system comprising:

at least a first power line communication modem device according to claim 10 and a second power line communication device according to claim 10, wherein the first and the second power line communication device are adapted to communicate with each other via a power line communication channel.