DE102015201296A1 - Device for load emulation for ad hoc networks - Google Patents

Abstract

The invention relates to a device (1) for load emulation for ad hoc networks. The device (1) has at least one first connection (IO ₁ ) for connection to a first transceiver (TRX ₁ ) of an ad hoc network and at least one second connection (IO ₂ ) for connection to a second transceiver (TRX ₂ ) of the ad hoc network, wherein between the first terminal (IO ₁ ) and the second terminal (IO ₂ ) at least a first signal branch (S ₁ ) and a second signal branch (S ₂ ) are arranged, wherein the first signal branch ( S ₁ ) comprises an attenuator (ATT) with which the signal can be attenuated in real time switchable so that an input signal of the second transceiver (TRX ₂ ) from the first transceiver (TRX ₁ ) can no longer be detected, and wherein the second signal branch (S ₂ ) has a series circuit of at least two circulators (Z ₁ , Z ₂ ), so that an input signal of the first transceiver (TRX ₁ ) can reach the second transceiver (TRX ₂ ) almost unhindered during a Eingangssigna l of the second transceiver (TRX ₂ ) almost can not get to the first transceiver (TRX ₁ ).

Description

The invention relates to a device for load emulation for ad hoc networks.

Background of the invention

Many areas of technology use ad-hoc networks. For example, printers, media devices, smart phones, smart TVs, personal computers, etc. are often connected via wireless ad hoc networks. But also in other areas these Ad-Hoc networks can be found. For example, hands-free devices, wireless headphones, navigation devices, etc. are also connected via Bluetooth. Also in the industrial sector are increasingly such ad hoc networks.

Recently, the application is also expanding towards vehicle-to-vehicle and vehicle-to-infrastructure communication.

However, in many areas of these ad-hoc networks, it is necessary to test the behavior of individual devices under network load.

The example of a radio-based communication between vehicles will be explained below.

The radio-based communication between vehicles is based, for example, on the WLAN adapted for this application Standard IEEE 802.11p that adds to the general IEEE 802.11 standards which describes the protocols for wireless communication in WLAN networks in general.

In the vehicle-to-vehicle communication, in general, the radio modules in the vehicles build a so-called vehicular ad-hoc network (VANET) in a radio channel with each other. New participants can enter this network dynamically and at any time, and participants can leave the network dynamically and at any time. Each of these wireless modules can act as a participant of an ad hoc network.

Within an ad-hoc network, messages are typically sent by the participating subscribers in a broadcast procedure and forwarded messages are received. That the communication generally takes place unconfirmed. In this respect, there is no mutual establishment of a radio connection between individual subscribers of the ad hoc network, but each subscriber of the ad hoc network sends messages to the radio channel and typically also receives no confirmation of the reception or processing by another subscriber of the ad hoc network. Hoc network.

In communication networks, the accessibility of competing subscribers to the communication channel is to be controlled to ensure operability. This is done in network protocols in the so-called data link layer (Layer 2 in the OSI Model - Data Link Layer - DLL) and there in the sub-layer Media Access Control Layer (Layer 2a in the OSI Model - Media Access Control - MAC).

In many networks, in particular the already cited VANET, it is not possible to use access control to a central control point, since the network does not provide a permanently available unit due to the mobility of the nodes involved. In such ad-hoc networks, therefore, the access control will usually be implemented individually in each node.

A MAC method for this, also called the access control method in the IEEE 802.11p standard is the so-called "Carrier Sense Multiple Access" (CSMA) method. This method is based on the fact that each network subscriber listened to the radio channel before sending a data packet and sends its packet only if the radio channel is not occupied for a defined minimum period of time. As long as the radio channel is busy, the subscriber does not send, resulting in high utilization of the radio channel by other participants to the fact that the own message can be sent only with great delay or even not.

For functional tests of the radio modules, it is necessary to deliberately set the radio channel under load in order to be able to observe and analyze the behavior of individual subscribers and to be able to make statements about the probability of message delivery in specific load situations. Such tests should generally be carried out according to an end-to-end procedure, that is to say avoiding interferences with the implementation of the mechanisms in the radio modules, since such an intervention is not readily available to the end user. All radio modules involved in the communication should therefore be used unmodified for a functional test.

A desired starting situation - in this case the corresponding load on the radio channel - must therefore be able to be provided with the help of other devices, the other devices not changing the basically specified behavior of the participating network participants.

For tests and simulations on wireless connections in the laboratory, the radio link is typically not built up over the air, but the corresponding high-frequency signals are passed through suitable conductors, for example by coaxial cable. In this case, typically all radio modules participating in the test or in a simulation are connected to one another via a wired distribution network.

In order to avoid uncontrollable radio contact of the individual radio modules with one another and also to avoid interference from devices not involved in the functional test, in general each of the radio modules is provided in a high-frequency-tight shielded box which provides a connection for the high-frequency coaxial cable as an interface to the outside, stored.

The starting point for a load test setup is that two or more (the IEEE standard 802.11p implementing) radio modules are connected to each other in this way with conductor connections.

Now, if all wireless modules are stimulated to send messages to the radio channel with an intensity that would cause each module to completely block the channel, then the channel access control mechanism implemented in the radio modules should ensure that all radio modules are equally likely to access the radio channel and the wireless modules so the radio channel to the same extent use the same parts.

The provision of a variety of radio modules for load generation as well as the provision of a wired distribution network is costly and time consuming, since a variety of devices each have to be interconnected. In addition, a variety of radio modules must be procured for different ad-hoc networks.

Based on this situation, it is an object of the invention to provide a device which makes it possible to test a large number of ad-hoc networks with low cost and time.

The object is achieved by a device for load emulation for ad hoc networks, the device having at least one first connection for connection to a first transceiver of an ad hoc network and at least one second connection for connection to a second transceiver of the Ad Hoc network, wherein between the first terminal and the second terminal at least a first signal branch and a second signal branch are arranged, wherein the first signal branch comprises an attenuator with which the signal can be attenuated in real time switchable so that an input signal of second transceiver of the first transceiver can no longer be detected, and wherein the second signal branch comprises a series connection of at least two circulators, so that an input signal of the first transceiver can pass almost unhindered to the second transceiver, while an input signal of the second transceiver almost can not get to the first transceiver.

Further advantageous embodiments are in particular subject of the dependent claims.

The invention will be explained in more detail with reference to the figures. In these shows:

1 the general construction of a circulator for use in embodiments of the invention,

2 a construction with exemplary two circulators, which passes a signal from a first transceiver to a second transceiver, but blocks a signal from the second transceiver to the first transceiver, according to embodiments of the invention,

3 another structure in which a plurality of transceivers are connected to each other,

4 an example sketched construction of a device according to the invention, and

5 an exemplary sketched construction of a test ensemble according to an embodiment of the invention with further optional devices.

With the invention, among other things, a device is provided which can be used to influence the utilization of a radio channel from the outside, without having to change the channel access mechanism implemented in the transceivers to avoid load.

The number of messages that a single transceiver transmits is affected by the load that other transceivers generate, and thus the radio channel is considered busy.

In order to increase the number of messages, it is ensured by means of the invention that the radio channel is considered to be free by a specific transceiver TRX ₁ more frequently than is actually permissible.

The radio channel is considered free if the transceiver while listening to the channel does not receive messages from other subscribers of the ad hoc network, i. other transceivers, notes.

In order to increase the load by a transceiver TRX ₁ , by means of the invention, the reception of messages from one or more other transceivers TRX ₂ , TRX ₃ , TRX ₄ , ... targeted obstructed, but at the same time the transmission of their own News not hindered.

To accomplish this, the "radio channel" (wire-guided) is split into two (logical) signal branches.

A particularly simple way, for example, split a high-frequency transmission provide so-called circulators Z ₁ , Z ₂ ready.

Circulators Z ₁ , Z ₂ , as in 1 shown, allow to transmit a high-frequency signal from port 1 to the gate 2. However, a transmission from port 1 to port 3 is heavily damped. Furthermore, the circulators Z ₁ , Z ₂ allow signal from port 2 to be transmitted to a high frequency port 3. However, a transfer from goal 2 to goal 1 is strongly damped. Furthermore, the circulators Z ₁ , Z ₂ allow a high-frequency signal from port 3 to be transmitted to the port 1. However, a transfer from goal 3 to goal 2 is strongly damped. Circulators Z ₁ , Z ₂ can be made active or passive.

If the application is relatively narrow-band, which is usually the case with ad-hoc networks, inexpensive passive circulators Z ₁ , Z ₂ suitable for the frequency range of the transceivers can be used.

For example, as a communication in the WLAN 802.11p standard in a narrow frequency band between 5,850 and 5,925 MHz, this also passive circulators are suitable.

With such circulators Z ₁ , Z ₂ , a signal branch can be split easily.

In 2 For example, a cascading of circulators Z ₁ , Z _{2 is} shown. In this case, a high-frequency signal from the terminal IO ₁ coming from the first circulator Z ₁ from port _{1 to} port 2 and then pass the second circulator Z ₂ of port 1 to port ₂ , while a signal coming from port IO ₂ , at port 2 of Circulator Z _{2 is} received and passed from there to port 3 of the circulator Z ₂ . At the output of the gate 3, however, a load resistor R _{L is} provided, which derives the signal low reflection. As a rule, the load resistance R _{L is} adapted to the characteristic impedance.

However, a small part of the signal will also arrive at port 1 of the circulator Z ₂ . If this part of the signal is significant, then it can be further attenuated in the same way with the first circulator Z ₁ . This means that by cascading two or more circulators, the damping of connection IO ₂ to connection IO ₁ can be set specifically.

For example, it may be that a damping of port 2 to port 1 of a single circulator Z ₁ , Z _{2 is} only 50 dB. Since the output power of an 802.11p-capable transceiver is usually 0 dBm, the receive threshold is specified with a maximum of -85 dBm, but in practice is well below -90 dBm, but above -100 dBm, cascading of two circulators Z ₁ , Z _{2 provide} the desired "one-way street effect". By completing the third gate with a load resistance R _L of, for example, 50 ohm resistance, the messages sent from terminal IO ₁ are now passed to terminal IO ₂ , but all messages sent by terminal IO _{2 are} attenuated by at least 100 dB with respect to terminal IO ₁ . At a transmission power of 0 dBm by a transceiver at port IO ₂ , the messages thus fall below the sensitivity threshold of another transceiver to port IO ₁ and are therefore no longer perceived by this transceiver as a channel load. Thus, the carrier sensing of the transceiver at the port IO ₁ no longer responds and a higher message volume from the transceiver to port IO ₁ on the radio channel is now possible.

Without further ado, this basic idea can be extended to other test scenarios. For example, in 3 a test scenario shown in the terminal IO _1, for example, only a transceiver TRX ₁ is to be provided, while to port IO ₂ for one or more transceiver, for example, two transceivers TRX ₂ and TRX ₃ , is to be provided. In the case of multiple transceivers TRX ₂ and TRX ₃ , these can be interconnected, for example, by one (or more) RF power dividers.

Such a structure now ensures ensure that it is the transceiver TRX ₁ allows to terminal IO ₁ to set with a corresponding message generating the channel at full load, while the transceiver TRX ₂ and TRX ₃ to port IO ₂ due to the access control method Carrier Sensing can not send messages to the channel.

Now it is not necessarily desired to always generate the full channel capacity with the transceiver TRX ₁ .

In order to be able to selectively influence the channel access by the transceiver TRX ₁ at the terminal IO ₁ , it would be desirable in the load control mechanism one way to enable the access control for the transceiver TRX ₁ at port IO ₁ for a selectable period of time. This means that it would be desirable to be able to switch the one-way street effect on and off.

For this purpose, the invention proposes, for example, to supplement the practically unidirectional signal path S ₁ from terminal IO ₁ to terminal IO ₂ by a second, bidirectional signal path S ₂ between terminal IO ₁ and terminal IO ₂ which can be selectively switched on.

This can be provided, for example, via high-frequency switches and / or power dividers.

Alternatively, for example, a (digitally controllable) attenuator ATT can be inserted on a parallel path S ₂ . The parallel path S ₂ is provided via power dividers PD ₁ and PD ₂ .

The attenuator ATT should provide approximately the required attenuation in the relevant frequency range.

For example, in the above numerical example, an attenuation of approximately 95 dB by the attenuator ATT should be sufficient, since the power dividers PD1, PD2 also provide an attenuation of approximately 3 dB (50:50 power divider),

Advantageously, the attenuator ATT can now be controllable in at least two stages corresponding to minimal to no attenuation (first stage) and maximum attenuation (second stage).

With minimal to no attenuation, it is ensured that a signal transmitted by transceiver TRX ₂ at connection IO _{2 is} detected by a transceiver TRX ₁ at connection IO ₁ above the sensitivity threshold of transceiver TRX ₁ , so that the carrier Sensing the transceiver TRX ₁ is active.

Other possible controllable stages of an attenuator ATT can be used for other measurements.

For the control of the attenuator ATT a real-time capable interface is usually necessary. The attenuator ATT, should therefore not be controlled with interfaces that have their own access control mechanisms, but via an interface that allows the access of the controlling user in real time, so reliable within a defined period of time. Such a possibility represents, for example, the control via a parallel port, in which a pulse on selected lines causes the immediate switching of the attenuator ATT.

In an embodiment of the invention, which is exemplified in 4 in one embodiment, a device is disclosed 1 provided for load emulation for ad-hoc networks. The device 1 has at least a first terminal IO ₁ for connection to a conventional first transceiver TRX _{1 of} an ad hoc network. Furthermore, the device has at least one second connection IO ₂ for connection to a second transceiver TRX _{2 of} the ad hoc network. Between the first terminal IO ₁ and the second terminal IO ₂ at least a first signal branch S ₁ and a second signal branch S ₂ are arranged. Of course, other signal branches can be shown. The first signal branch S ₁ has an attenuator ATT, with which the signal can be attenuated in real time switchable so that an input signal of the second transceiver TRX ₂ from the first transceiver TRX ₁ can no longer be detected. The second signal branch S ₂ has a series connection of at least two circulators Z ₁ , Z ₂ , so that an input signal of the first transceiver TRX ₁ can pass almost unhindered to the second transceiver TRX ₂ while an input signal of the second transceiver TRX ₂ almost can not get to the first transceiver TRX ₁ , for example, it is attenuated by about 100 dB.

In one embodiment of the invention, the attenuator ATT is digitally controllable.

According to a further embodiment, the attenuator ATT has an attenuation of 95 dB and more. As a result, the output power of an 802.11p-capable transceiver, which is usually 0 dBm, at a reception threshold of less than -90 dBm, but over -100 dBm is reliably suppressed.

In a particularly advantageous embodiment, a parallel interface is used to control the attenuation ATT in real time. It goes without saying, however, that other real-time interfaces, such as IEEE-488 can be found without further use.

The signal branches can be switchable or can be realized via power dividers PD ₁ , PD ₂ . In addition, mixed forms are feasible. If one or more switches or equivalent multiplexers are used, preferably real-time capable switches or multiplexers are also used here. These are preferably also controllable via the same interface as the attenuator ATT.

For example, the first signal branch S ₁ and the second signal branch S _{2 may} be connected to the first terminal IO ₁ by means of a first power divider PD ₁ . For example, alternatively or additionally, the first signal branch S ₁ and the second signal branch S _{2 may also} be connected to the second terminal IO ₂ by means of a second power divider PD ₂ . If power dividers are used, their insertion loss can be subtracted from the attenuator ATT. For example, in the case of a 50:50 power divider, an insertion loss of 3dB can be deducted from the necessary total attenuation in each case in order to determine the maximum necessary attenuation of the attenuator ATT.

Particularly advantageous, the device 1 for load emulation device in Ad-Hoc network selected from the group comprising Bluetooth, ZigBee, W-Lan, in particular according to Standards IEEE 802.11p , be used.

According to a in 5 variant shown, the invention may also find application in a test ensemble. In this, in addition to a first transceiver TRX _{1 is} also a device 1 for load emulation for ad-hoc networks.

Hereby, the load with respect to another transceiver TRX ₂ or, as far as a plurality of transceivers TRX _{2,3,4, ... are} provided to be emulated via a distribution network VN.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Standard IEEE 802.11p [0006]
• IEEE 802.11 standards [0006]
• IEEE 802.11p standard [0011]
• IEEE standard 802.11p [0016]
• WLAN 802.11p standard [0037]
• IEEE-488 [0058]
• Standards IEEE 802.11p [0061]

Claims (8)

Contraption ( 1 ) for load emulation for ad hoc networks, comprising • at least one first connection (IO ₁ ) for connection to a first transceiver (TRX ₁ ) of an ad hoc network, • at least one second connection (IO ₂ ) for connection to one Second transceiver (TRX ₂ ) of the ad hoc network, Where between the first terminal (IO ₁ ) and the second terminal (IO ₂ ) at least a first signal branch (S ₁ ) and a second signal branch (S ₂ ) are arranged , Wherein the first signal branch (S ₁ ) has an attenuator (ATT) with which the signal can be attenuated in real time switchable so that an input signal of the second transceiver (TRX ₂ ) from the first transceiver (TRX ₁ ) not More can be recognized, and • Wherein the second signal branch (S ₂ ) has a series connection of at least two circulators (Z ₁ , Z ₂ ), so that an input signal of the first transceiver (TRX ₁ ) almost unhindered to the second transceiver (TRX ₂ ) can arrive while an input signal of the second transceiver (TRX ₂ ) almost can not get to the first transceiver (TRX ₁ ). Apparatus according to claim 1, characterized in that the attenuator (ATT) is digitally controllable.  Device according to claim 1 or 2, characterized in that the attenuator (ATT) has an attenuation of 95 dB and more. Device according to one of the preceding claims, characterized in that a parallel interface is used for controlling the damping (ATT) in real time. Device according to one of the preceding claims, characterized in that the first signal branch (S ₁ ) and the second signal branch (S ₂ ) by means of a first power divider (PD ₁ ) to the first terminal (IO ₁ ) are connected. Device according to one of the preceding claims, characterized in that the first signal branch (S ₁ ) and the second signal branch (S ₂ ) by means of a second power divider (PD ₂ ) to the second terminal (IO ₂ ) are connected. Device according to one of the preceding claims, characterized in that the ad hoc network is selected from the group comprising Bluetooth, ZigBee, W-Lan, in particular according to the IEEE 802.11p standard. Test ensemble comprising a first transceiver (TRX ₁ ) and a device according to one of the preceding claims.

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