WO2011161368A1

WO2011161368A1 - Transmission channel digital emulator

Info

Publication number: WO2011161368A1
Application number: PCT/FR2011/051418
Authority: WO
Inventors: Pascal Pagani; Mohamed Tlich
Original assignee: France Telecom
Priority date: 2010-06-23
Filing date: 2011-06-20
Publication date: 2011-12-29
Also published as: FR2961981A1

Abstract

The invention relates to a transmission channel emulator for testing a modem comprising just a single port fulfilling the functions of data input port, data output port and electrical supply port, said emulator comprising a digital filtering module (1) comprising at least two input/output ports (10, 16), characterized in that it comprises - at least one directional coupling module (3) comprising: - a first input-output port (31) able to be connected to an input-output port of a modem (5), - a second input-output port (32) connected to one of the input-output ports of the digital filtering module, - at least one connection module able to be interposed between the first input-output port of the at least one coupling module and the port of the modem.

Description

Digital transmission channel emulator

The present invention relates generally to the field of telecommunications. This domain includes the field of wireless communications (WiFi systems, mobile telephony, WiMax, etc.) and wireline communications (xDSL, coaxial cable communications, Power Line Bearer (PLC) systems).

First, a communication system can be analog or digital. In the second case, a received signal is digitized using an analog-to-digital converter (ADC), to be processed using a digital signal processor, and a digital signal to be transmitted is converted to the digital signal processor. using a digital-to-analog converter (DAC) before transmission.

A communication system transmits data on a medium, called a transmission channel. The transmission channel provides distortions to the transmitted signal due to signal attenuation and the presence of multiple propagation paths. In addition, the transmission channel adds different types of noise to the wanted signal. For example, background noise and narrow-band interference apply to both wireless and wired channels. In addition, the wired channels suffer the effects of impulsive noises generated by the equipment connected or located near the transmission medium. Examples of wired transmission media are the telephone copper pair for xDSL systems and the power distribution network for CPL power line systems.

In order to design communication systems adapted to the transmission medium and exploiting its characteristics optimally, channel models representative of the physical phenomena of transmission are generally established. Two types of models exist. Statistical empirical models reproduce the characteristic functions of the transmission channel in a random manner, by observing a certain number of statistics observed on a set of measurements. Deterministic models are based on a fine description of the transmission medium (for example, the topology of a wired network), and reproduce the effects of the channel in a given medium taking into account the small-scale physical interactions.

In addition to designing new systems, channel models allow you to test the performance of existing systems and validate products in a realistic configuration. To perform tests on real-time systems, it is necessary to implement channel models in hardware form, analog or digital, in a device called a channel emulator.

An example of an analog wired channel model is the cable simulator for the xDSL system, which includes analog components interconnected by relays to simulate different lengths of cable. Digital systems correspond to an implementation on a digital signal processor. The advantage of performing tests on a hardware channel emulator is that the test conditions are controlled and reproducible, which is not the case when testing on real channels, because the characteristics of the transmission channel can evolve significantly over time.

We are particularly interested in digital channel emulators. Partial digital channel emulator solutions exist and are limited to reproductions of mathematical models of filters representing the channels on programmable circuits. Articles [C. Briso- Rodriguez and JI Alonso-Montes, Multipath hardware and software mobile channel Simulator, IEEE Vehicular Technology Conference, vol. 4, pp. 3060-3063, May 2001] and [A. Dassatti, G. Masera, M. Nicola, et al., High performance channel model hardware emulator for 802. 11η, IEEE International Conference on Field-Programmable Technology, pp. 303-304, Dec. 2005 \ show examples of these hardware implementations of digital filters.

A digital channel emulator has been proposed in the OPERA project [IST Integrated Project No. 026920, OPERA, Deliverable of Task 7.2, Design and Implementation of the Channel Emulator, May 2008]. This solution includes:

- the analog-to-digital conversion (ADC) of an input signal and the digital-to-analog conversion (DAC) of an output signal,

the processing of the digitized and quantized signal in order to simulate the effect of the transmission channel, using a digital filter and the addition of a digital noise.

Figure 1 shows the structure of the proposed channel emulator in the OPERA project. This solution has several disadvantages:

1 / the emulator is composed of 2 independent transmission lines, one for transmission in one direction ("forward channel") and the other in a second direction ("backward channel"). At each end, the emulator communicates with the modem under test via two independent ports: an input port and an output port. The use of such an emulator is therefore not suitable for testing a commercial modem or an industrial prototype, because in practice, the modems have only one port used for the input and for the exit.

21 A CPL modem has only one port, consisting of a male AC outlet, that performs the functions of data input port, data output port, and power port. The emulator described above does not allow testing a CPL modem non-invasively, that is to say without disassembling and modifying the modem under test, because it does not provide the power function of the modems. 3 / As we have seen, to test a commercial modem using the emulator described above, it is necessary to dismount the modem under test, to connect the inputs and outputs of the modem to the outputs and corresponding entries of the emulator. Under these conditions, the modem under test no longer meets the electromagnetic compatibility standards according to which it was developed. In particular, the disassembled modem can emit unwanted electromagnetic radiation. On the other hand, this radiation promotes direct communication between the two modems under test by electromagnetic coupling, which compromises the efficiency of the filtering function performed by the emulator.

4 / the need to modify modems under test excludes any use of the emulator for usage compliance testing prior to product deployment to the general public. Indeed, such conformity tests require to respect the integrity of the products under test.

It is an object of the present invention to overcome the disadvantages of the prior art by providing a transmission channel emulator for testing a modem having only one port performing the functions of data input port, data output port and power supply port. The emulator comprises a digital filtering module comprising at least two input / output ports.

The emulator also comprises at least one directional coupling module comprising:

a first input / output port adapted to be connected to an input / output port of a modem,

a second input / output port connected to one of the input / output ports of the digital filtering module.

The at least one directional coupling module allows signal transmission only from an input of its first input-output port to an output of its second input-output port and from an input of its second input port - output to an output of its first input-output port. The emulator according to the invention makes it possible to communicate two commercial modems in real time without having to modify them. Thus, it addresses the need for an integrated transmission channel emulation solution, which allows simple connection of commercial modems or industrial prototypes, while realistically reproducing the effects of the transmission channel, and that of reproducible way.

According to a preferred characteristic, the emulator according to the invention further comprises at least one connection module able to be interposed between the first input-output port of the at least one coupling module and the input-output port. output of a modem.

The connection module is used to connect a CPL type modem.

According to a preferred characteristic, the connection module comprises a power supply port, at least one data input / output port and a connection port to the modem and allows the transmission of the signal only between its at least one port of data input-output and port connection to the modem, and allows power only between its power port and the modem connection port.

According to a preferred feature, the emulator further comprises at least one attenuation module interposed between the output of the second input-output port of the at least one directional coupling module and an input of one of the ports. input-output of the digital filtering module.

The attenuation module reduces the voltage range of the input signals to match the voltage range accepted by the digital filtering module.

The emulator according to the invention is used to connect at least two modems in order to test at least one of the modems.

Other features and advantages will appear on reading preferred embodiments described with reference to the figures in which: FIG. 1 represents a digital channel emulator according to the prior art,

FIG. 2 represents an embodiment of the digital channel emulator according to the invention,

FIG. 3 represents another embodiment of the digital channel emulator according to the invention.

According to one embodiment of the invention shown with reference to FIG. 2, a digital channel emulator according to the invention comprises a filtering module 1, or digital processing of the information. The function of this module is to simulate a transmission channel by performing a global filtering.

The digital processing module 1 has N input-output ports. To simplify the representation, N is equal to 2 in FIG.

From an input of an input-output port, the module 1 comprises a first processing chain. It comprises an analog-digital converter 1 1 which performs a digital conversion of a received analog signal.

The analog-digital converter 1 1 is connected to a filter circuit 12 which realizes the actual filtering of the digital signal according to a filtering function H (f).

The filter circuit 12 is connected to an adder 13 which also receives a noise N (f) from a circuit 14, so as to add the filtered signal and a noise. Noise addition is optional.

Signal filtering and optional noise addition models the transmission channel.

The output of the summator 13 is connected to a digital-to-analog converter 15 which converts the processed signal into analog.

The digital-to-analog converter is connected to the output of the input-output port 16 of the module 1. The module 1 comprises a second processing chain, identical to the previous one, between an input of the input-output port 16 and an output of the input-output port 10.

It is understood that there are thus two processing chains corresponding to the two communication directions existing between two modems.

The second processing chain comprises circuits 1 1 'to 15' respectively similar to the circuits 1 1 to 15.

The filter circuits, the summators and the noise generators can be realized by means of a programmable circuit (for example an FPGA).

The digital information processing module is typically implemented on an electronic signal processing board. The state of the art technological and complexity constraints do not necessarily allow to gather all the desired performance on an electronic card. For example, the analog-to-digital converters may have a limited voltage range for the input analog signals (for example between -1 V and +1 V).

If the signals generated by the modem under test have a higher voltage range (typically between -5 V and + 5V), an attenuation module 2 is interposed at the input of the analog-digital converter. The role of the attenuation module is to reduce the voltage range of the input signals to match the voltage range accepted by the analog-to-digital converter. The value of the appropriate attenuation can be automatically selected by the system. This value can also be transmitted to the digital information processing module, so as to be integrated in the filtering process.

As many attenuation modules can be provided as analog-to-digital converters.

The emulator comprises at least one directional coupling module 3. The directional coupling module comprises: a first input / output port 31 adapted to be connected to an input / output port of a modem to be tested,

a second input-output port 32 connected to the one 10, 16 of the input / output ports of the digital processing module.

The function of the directional coupling module 3 is to allow a signal transmission only from an input of its first input-output port 31 to an output of its second input-output port 32 and from an input of its second input-output port 32. input-output port 32 to an output of its first input-output port 31. The directional coupling module prohibits a data transmission between the input of its second input-output port and the output of this same second input-output port.

Thus, a direct loop between the two filtering channels corresponding to the two directions of communication is avoided. If such a direct loop existed, the injected signals would produce a succession of echoes that would disturb the proper functioning of the emulator.

The emulator may comprise a single directional coupling module 3, or several directional coupling modules, for example in number equal to that of the input-output ports of the digital processing module 1.

In practice, the directional coupling module can be realized by an analog directional coupler.

If an attenuation module 2 is used, it is connected in series between the directional coupling module 3 and the digital processing module 1.

To connect a modem CPL 5, a connection module 4 is interposed between the first input-output port 31 of the directional coupling module 3 and the input-output port of the modem.

The connection module performs three functions:

- supply the modem with energy (for example 230 V at 50 Hz),

isolating the PLC signal from the electrical network, in order to prevent the modems from communicating via the power supply network instead of passing through the emulator, - Transfer the CPL signal from the modem to the emulator and vice versa.

The connection module 4 is connected to a power supply 6 through a low-pass filtering circuit 41, which guarantees strong insulation by greatly attenuating the cut-off frequency band, and being resistant to the high powers of the sector.

An input-output port 42 of the connection module 4 is intended to be connected to the modem CPL. From this port 42, the connection module 4 comprises a high-pass filtering circuit 43 connected to a coupling circuit 44 (magnetic or inductive). Indeed, the transmitted signal must be free of the sector 50 Hz signal, the power of which would be destructive for the digital processing module. The coupling mechanism allows the transmission of the signal without metallic continuity. The coupling circuit 44 is connected to an input-output port 45 for connection to the previously described directional coupling module.

To use the emulator, two modems are connected either to the connection module 4 in the case of a PLC modem or to the directional coupling module 3 for other types of modems, such as the HPNA modem (according to the English: Home Phoneline Networking Alliance) operating on telephone pair, MoCA modem (according to English: Multimedia over Coax Alliance) running on coaxial cable, DSL modem operating on telephone pair.

The two connected modems are of the same type, that is to say two CPL modems, or of different types, that is to say a modem CPL and a modem of another type, HPNA for example.

All modules must each be shielded to prevent electromagnetic radiation, and avoid communication between the two modems by electromagnetic coupling. In particular, a shielded package can be used to isolate the connection module, the directional coupling module, or both. Referring to Figure 3, there is shown a second embodiment of digital channel emulator according to the invention, to which three modems can be connected.

This emulator comprises modules similar to those previously described: digital processing, directional coupling, attenuation and connection modules.

The digital processing module comprises three input-output ports and six filtering chains connected to the three input-output ports 10, 16 and 17. Each filtering chain is similar to that described with reference to FIG. an analog-digital converter 11, a filter circuit 12, an adder 13, a noise generator 14 and a digital-to-analog converter 15.

At least one directional coupling module 3 is connected to one of the input / output ports of the digital processing module. In FIG. 3, three directional coupling modules are respectively connected to the input / output ports of the digital processing module.

An optional attenuation module 2 may be interposed between each directional coupling module and an input of the input / output port of the processing module.

The modems 5 are connectable either directly to the directional coupling modules, or via a connection module 4 for the case of a PLC modem.

Of course, those skilled in the art may consider variants without departing from the scope of the invention. For example, CPL (Multiple Input, Multiple Output) MIMO modems can be tested. A MIMO PLC modem uses three wires.

In this case, to test two MIMO CPL modems, the digital information processing module is unchanged, but it has up to 6 I / O ports.

At least one directional coupling module is used as previously described. An attenuation module can be used. A connection module is used and is suitable for the MIMO CPL modem. It includes a power port, up to three data input / output ports, and a modem connection port consisting of a power outlet that includes phase, neutral, and ground connectors. It allows the transmission of the signal only between:

a first data input-output port and the phase and neutral connectors of the connection port to the modem,

a second data input-output port and the phase and ground connectors of the modem connection port,

a third data input / output port and the connectors of

neutral and earth modem port connection.

The connection module allows power only between its power port and the modem connection port.

The emulator according to the invention makes it possible not only to simulate a transmission channel of a useful signal, but also a transmission channel of the disturbances. For example, a 4-port I / O emulator has 2 CPL ports and 2 HPNA ports. The digital processing module can not only simulate the CPL-to-CPL and HPNA-to-HPNA channels, but also the various PLC-to-HPNA channels representing the coupling between power and telephone lines, to study the transmission of disturbances.

Claims

1. A transmission channel emulator for testing a modem having only one port fulfilling the functions of data input port, data output port and power supply port, said emulator comprising a digital filtering module comprising at least two input / output ports

characterized in that it comprises

at least one directional coupling module comprising:

a second input / output port connected to one of the input / output ports of the digital filtering module,

the at least one directional coupling module allowing signal transmission only from an input of its first input-output port to an output of its second input-output port and from an input of its second input port - output to an output of its first input-output port,

at least one connection module able to be interposed between the first input-output port of the at least one coupling module and the port of the modem,

the at least one connection module having a power port, at least one data input-output port and a modem connection port, and allowing signal transmission only between the at least one port of data input / output port and modem connection port, and power only between its power port and the modem connection port.

2. Emulator according to claim 1, characterized in that it further comprises a shield for isolating the at least one connection module and / or the at least one directional coupling module.

3. Emulator according to claim 1 or 2, characterized in that it further comprises at least one attenuation module interposed between the output of the second input-output port of the at least one directional coupling module and a input of one of the input / output ports of the digital filtering module.

4. Use of the emulator according to any one of claims 1 to 3 for connecting at least two modems for testing at least one of the modems.