阅读说明：本技术 用于电网控制的无线通信网络中的包检测 (Packet detection in wireless communication networks for grid control ) 是由 庞智博 M·卢维索托 D·宗 于 2018-02-13 设计创作，主要内容包括：提供了用于在用于电网控制的无线通信网络中包检测的机制。无线通信网络采用包的基于时间的调度。一种方法由无线通信网络中的包接收器执行。该方法包括接收来自包发射器的包。该包包括前导码。前导码由单个OFDM符号构成并由样本序列表示。前导码的至少部分(基于争用)在包检测窗口内被接收。该方法包括执行包检测以便仅在包检测窗口内所接收的那些样本上查找包的起始。(Mechanisms are provided for packet detection in a wireless communication network for grid control. Wireless communication networks employ time-based scheduling of packets. A method is performed by a packet receiver in a wireless communication network. The method includes receiving a packet from a packet transmitter. The packet includes a preamble. The preamble is composed of a single OFDM symbol and is represented by a sequence of samples. At least a portion of the preamble is received (on a contention basis) within a packet detection window. The method includes performing packet detection to look for the start of a packet only on those samples received within a packet detection window.)

1. A method for packet detection in a wireless communication network (100) for grid control, the wireless communication network (100) employing time-based scheduling of packets (600), the method being performed by a packet receiver (200a) in the wireless communication network (100), the method comprising:

receiving (S102) a packet (600) from a packet transmitter (200b, 200c, …, 200N),

wherein the packet (600) comprises a preamble (610), wherein the preamble (610) is comprised of a single orthogonal frequency division multiplexing, OFDM, symbol and is represented by a sequence of samples, and wherein at least a portion of the preamble (610) is received within a packet detection window (630); and the number of the first and second groups,

performing (S104) packet detection to find the start (640') of the packet (600) only on those samples received within the packet detection window (630).

2. The method of claim 1, wherein performing packet detection comprises determining a similarity metric value between a representation of those samples received within the packet detection window (630) and a default normalized test sequence.

3. The method of claim 1, wherein the samples received within the packet detection window (630) define a test sequence, and wherein performing packet detection further comprises:

the test sequence is multiplied by a one-sample delayed copy of the test sequence (S104a), resulting in a multiplied test sequence.

4. The method of claim 3, wherein performing packet detection further comprises:

the multiplied test sequences are normalized with respect to their total power (S104b), resulting in a normalized test sequence.

5. The method of claim 4, wherein performing packet detection further comprises:

the normalized test sequence is associated with a default normalized test sequence (S104c), resulting in an associated test sequence.

6. The method of claim 2 or 5, wherein the default standardized test sequence is a default preamble (610) sequence.

7. The method of claims 2 and 5, wherein a representation of those samples received within the packet detection window (630) is defined by the normalized test sequence.

8. The method of any of claims 5 to 7, wherein performing packet detection further comprises:

identifying (S104d) samples in the test sequence for which the associated test sequence has its maximum value,

wherein the samples are determined to define the start (640') of the packet (600).

9. The method of claim 8, wherein performing packet detection further comprises:

comparing (S104e) the maximum value with a packet detection threshold, and

wherein the sample is determined to define the start (640') of the packet (600) only if the maximum value exceeds the packet detection threshold.

10. The method of claim 1, wherein the packet detection window (630) is opened according to the time-based schedule.

11. The method of claim 1, wherein the packet detection window (630) has a time length of between 100ns and 200ns, preferably between 125ns and 175ns, most preferably 150 ns.

12. The method of claim 1, wherein the packet receiver (200a) is part of a gateway, a circuit breaker, a circuit protector, a transformer, or a switchgear.

13. The method of claim 1, wherein the packet transmitter (200b, 200c, …, 200N) is part of a gateway, a circuit breaker, a circuit protector, a transformer, or a switchgear.

14. A packet receiver (200a) for packet detection in a wireless communication network (100) for grid control, the wireless communication network (100) employing time-based scheduling of packets (600), the packet receiver (200a) comprising processing circuitry (210) configured to cause the packet receiver (200a) to:

receiving a packet (600) from a packet transmitter (200b, 200c, …, 200N),

wherein the packet (600) comprises a preamble (610), wherein the preamble (610) is comprised of a single orthogonal frequency division multiplexing, OFDM, symbol and is represented by a sequence of samples, and wherein at least a portion of the preamble (610) is received within a packet detection window (630); and;

performing packet detection to find the start (640') of the packet (600) only on those samples received within the packet detection window (630).

15. A computer program (820) for packet detection in a wireless communication network (100) for grid control, the wireless communication network (100) employing time-based scheduling of packets (600), the computer program comprising computer code which, when run on processing circuitry (210) of a packet receiver (200a), causes the packet receiver (200a) to:

receiving a packet (600) from a packet transmitter (200b, 200c, …, 200N),

wherein the packet (600) comprises a preamble (610), wherein the preamble (610) is comprised of a single orthogonal frequency division multiplexing, OFDM, symbol and is represented by a sequence of samples, and wherein at least a portion of the preamble (610) is received within a packet detection window (630); and

performing packet detection to find the start (640') of the packet (600) only on those samples received within the packet detection window (630).

16. A computer program product (810) comprising a computer program (820) according to claim 15, and a computer readable storage medium (830), the computer program being stored on the computer readable storage medium.

Technical Field

Embodiments presented herein relate to a method, a packet receiver, a computer program and a computer program product for packet detection in a wireless communication network for grid control.

Background

Wireless networks for grid control (e.g. in substation automation) require low latency and high reliability. Currently available industrial wireless standards, such as wireless HART (HART is an abbreviation for "addressable remote sensor data highway") or wireless network-factory automation (WIA-FA) for industrial automation, do not provide very high performance in these respects, as they rely on a non-optimized Physical (PHY) communication layer. For example, WIA-FA is based on the IEEE802.11 g/n PHY layer, with a minimum transmission time of about 30 μ s for 100-bit packets, whereas many IEC 61850 compliant grid applications that are currently based on wired Local Area Networks (LANs) require a time slot of a few μ s or even less.

One reason for the long transmission time in IEEE802.11 is that a long preamble sequence is used at the PHY layer. However, the long preamble in IEEE802.11 is used for many purposes, including robust packet detection and timing synchronization, which is critical to ensure reliable message delivery. In this regard, packet detection generally refers to the process of approximately identifying the beginning of a packet, while timing synchronization generally refers to the process of finding the exact sample at the beginning of the useful portion (e.g., payload) of a packet.

Existing schemes for packet detection and timing synchronization (e.g. as disclosed in US 7480234B1 and US 7280621B 1) rely on the presence of long repetitive sequences in the packet preamble so that the packet receiver can first associate the preamble of a known transmission with the received samples in order to detect the packet and then associate the repeated portions to achieve accurate sample level synchronization. However, when the packet size is short (e.g., as is the case in grid control applications), using a long preamble is not efficient, and thus this fundamentally limits the achievable delay.

Therefore, there is still a need for improved packet detection in wireless communication networks suitable for grid control.

Disclosure of Invention

It is an object of embodiments herein to provide an efficient packet detection which is free from, or at least reduced or alleviated from, the above-mentioned problems.

According to a first aspect, a method for packet detection in a wireless communication network for grid control is presented. The wireless communication network employs time-based scheduling of packets. The method is performed by a packet receiver in the wireless communication network. The method includes receiving a packet from a packet transmitter. The packet (packet) includes a preamble. The preamble is composed of a single orthogonal frequency division multiplexing, OFDM, symbol and is represented by a sequence of samples. At least a portion of the preamble is received within a packet detection window. The method includes performing packet detection to look for the start of the packet only on those samples received within the packet detection window.

According to a second aspect, a packet receiver for packet detection in a wireless communication network for grid control is presented. The wireless communication network employs time-based scheduling of packets. The packet receiver includes processing circuitry. The processing circuit is configured to cause the packet receiver to receive a packet from a packet transmitter. The preamble is composed of a single OFDM symbol and is represented by a sequence of samples. At least a portion of the preamble is received within a packet detection window. The processing circuitry is configured to cause the packet receiver to perform packet detection to look for the start of the packet only on those samples received within the packet detection window.

According to a third aspect, a computer program for packet detection in a wireless communication network for grid control is presented, the computer program comprising computer code which, when run on a packet receiver, causes the packet receiver to perform the method according to the first aspect described above.

According to a fourth aspect, a computer program product is proposed, comprising a computer program according to the third aspect, and a computer readable storage medium having the computer program stored thereon. The computer readable storage medium may be a non-transitory computer readable storage medium.

Advantageously, this provides for efficient packet detection.

Advantageously, the proposed packet detection is free from the above-mentioned problems.

Advantageously, the proposed method allows an efficient packet structure, thereby enabling low-latency wireless communication.

In fact, reducing the preamble duration from 5 OFDM symbols (as in IEEE802.11 g) to only one OFDM symbol allows reducing the transmission time of 100-bit packets by nearly 5 times, thereby achieving transmission delays similar to wired communication networks.

Advantageously, the proposed method allows to perform robust packet detection and timing synchronization also when the preamble is short.

Advantageously, the use of a packet detection window allows disabling of the packet detection when not needed, thereby saving energy.

It should be noted that any feature of the first, second, third and fourth aspects may be applied to any other aspect where appropriate. Similarly, any advantages of the first aspect may equally apply to the second, third and/or fourth aspect, respectively, and vice versa. Other objects, features and advantages of the appended embodiments will become apparent from the following detailed disclosure, from the appended dependent claims and from the drawings.

In general, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, device, component, means, module, step, etc" are to be interpreted openly as referring to at least one instance of said element, device, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

Drawings

The inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

fig. 1 is a schematic diagram illustrating a wireless communication network according to an embodiment;

fig. 2 schematically illustrates a packet receiver according to the prior art;

FIG. 3 schematically illustrates a packet structure according to the prior art;

FIG. 4 is a flow diagram of a method according to some embodiments;

fig. 5 is a schematic diagram showing functional modules of a packet receiver according to an embodiment;

FIG. 6 schematically illustrates packet detection within a packet detection window according to an embodiment;

fig. 7 is a schematic diagram showing functional units of a packet receiver according to an embodiment; and

FIG. 8 illustrates one example of a computer program product comprising a computer-readable storage medium according to an embodiment.

Detailed Description

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like reference numerals refer to like elements throughout the specification. Any steps or features illustrated by dashed lines should be considered optional.

Fig. 1 schematically illustrates a wireless communication network 100 to which embodiments disclosed herein are applied. The network entities, denoted as nodes 200a, 200b, …, 200N, are equipped with Radio Frequency (RF) front ends that allow the network entities to communicate over the wireless network 110. Each node may represent a component of the substation automation system that is configured to exchange control messages (e.g., gateways, circuit breakers, circuit protectors, transformers, switchgear, etc.).

Each node 200a to 200N may selectively act as a packet transmitter or a packet receiver. Without loss of generality, it will be assumed in the following that node 200a will act as a packet receiver, and that any of nodes 200b to 200N will act as a packet transmitter.

Fig. 2 schematically shows typical modules of a packet receiver 200 a. The packet receiver 200a of fig. 2 includes an automatic gain control module, a packet detection module, a timing synchronization module, a frequency synchronization module, a channel equalization module, and a demodulation and decoding module. The functions of these modules are known in the art, and thus a description thereof is omitted for the sake of brevity. In the currently existing packet receiver 200a, these modules are implemented based on utilizing long repeated sequences in the preamble of the received packet.

As an illustrative example, fig. 3 schematically shows a packet structure of a packet 300 used in ieee802.11g. In IEEE802.11g, the legacy short training field (L-STF) portion of the PHY layer preamble is preceded by a short training sequence a₁，a₂，...，a₇For packet detection, followed by a short training sequence a₈，a₉，a₁₀And a long training sequence L of a legacy long training field (L-LTF) portion₁，l₂For coarse timing synchronization and fine timing synchronization, respectively.

To achieve low latency for short packets exchanged in wireless networks for grid control applications, the size of the PHY layer preamble should be kept small, possibly limited to only a single Orthogonal Frequency Division Multiplexing (OFDM) symbol. However, to ensure a good level of reliability, the packet receiver 200a must still be able to perform its usual functions, including packet detection and timing synchronization, using only this single OFDM symbol.

Accordingly, embodiments disclosed herein relate to mechanisms for packet detection in a wireless communication network 100 for grid control. To obtain such a mechanism, a packet receiver 200a, a method performed by the packet receiver 200a, a computer program product comprising code, e.g. in the form of a computer program, is provided, which when run on the packet receiver 200a causes the packet receiver 200a to perform the method.

To achieve low latency, the packet structure is optimized and a short preamble is used. In addition, to ensure reliable communication, the packet start prediction mechanism also uses knowledge of packet scheduling, which allows simple and reliable packet detection and timing synchronization even with short preambles.

Fig. 4 is a flow chart illustrating an embodiment of a method for packet detection in a wireless communication network 100 for grid control. The wireless communication network 100 employs time-based scheduling of packets. The method is performed by the packet receiver 200 a. The method is advantageously provided as a computer program 820.

Assume that the node serving as the packet receiver 200a receives the packet 600 from one of the other nodes serving as the packet transmitters 200b to 200N. Thus, the packet receiver 200a is configured to perform step S102:

s102: packet receiver 200a receives packets 600 from packet transmitters 200 b-200N.

The packet 600 includes a preamble 610. The preamble 610 is composed of a single OFDM symbol and is represented by a sample sequence. In some aspects, a single OFDM symbol has a duration corresponding to the first five L-STF short sequences in fig. 3.

At least a portion of the preamble 610 is received within the packet detection window 630. Indeed, in a wireless communication network for controlling applications, channel access is regulated by a time slot scheduling strategy (e.g. Time Division Multiple Access (TDMA)) to ensure certainty and avoid collisions, unlike conventional communication networks. In this way, each node in the wireless communication network 100 (acting as a packet receiver 200a) knows that it can receive packets only during predetermined time slots. The packet receiver 200a utilizes this fact to receive only packets within the packet detection window 630.

Then, the packet receiver 200a performs packet detection. Specifically, the packet receiver 200a is configured to perform step S104:

s104: the packet receiver 200a performs packet detection to find the start 640' of the packet 600. The packet detection is performed only on those samples received within the packet detection window 630.

Advantageously, this enables simultaneous packet detection and timing synchronization. As described above, packet detection generally refers to the process of approximately identifying the beginning of a (received) packet 600, and timing synchronization generally refers to the process of finding the exact sample at the beginning of a useful portion (e.g., payload) of the packet 600.

Embodiments will now be disclosed relating to additional details of packet detection in the wireless communication network 100 for grid control performed by the packet receiver 200 a.

Referring to fig. 5 in parallel, fig. 5 shows the functional blocks of a packet receiver 200a for packet detection and timing synchronization according to one embodiment.

The packet receiver 200a in fig. 5 includes a packet start prediction module 510. The packet start prediction module 510 is configured to selectively enable and disable detection of packets 610, and thus selectively when to open and close the packet detection window 630. Other aspects of the packet start prediction module 510 will be disclosed below.

There are different ways to perform packet detection in step S104. Various embodiments related thereto will now be described in turn.

In some aspects, the packet detection in step S104 is based on comparing those samples received within the packet detection window 630 to a default sequence. In particular, according to an embodiment, performing packet detection involves the determination of a similarity measure value between a representation (representation) of those samples received within the packet detection window 630 and a default standardized test sequence. In the example of fig. 5, the similarity metric value is determined by the differential detection module 520.

There are different ways to derive a representation of a sample from the sample itself.

The packet receiver 200a in fig. 5 includes a delay and multiply module 530. The delay and multiply module 530 is configured to create a one-sample delayed copy of the received sequence by a Hadamard product and multiply the one-sample delayed copy with the original received sequence.

In particular, according to one embodiment, the samples received within the packet detection window 630 define a test sequence. Then, the packet receiver 200a is configured to perform (optional) step S104a as part of performing packet detection in step S104:

step S104 a: the packet receiver 200a multiplies the test sequence by its one-sample delayed copy to obtain a multiplied test sequence.

In this way, the impact of frequency offset on detection performance is minimized.

The packet receiver 200a in fig. 5 includes a normalization module 540. The normalization module 540 is configured to normalize the multiplied test sequences with respect to their average power. Thus, according to one embodiment, the packet receiver 200a is configured to perform (optional) step S104b as part of performing packet detection in step S104:

step S104 b: packet receiver 200a normalizes the multiplied test sequences with respect to their total power, resulting in a normalized test sequence.

In this way, the detection process is independent of the received power.

The packet receiver 200a in fig. 5 includes an association module 550. The correlation module 550 is configured to compare the normalized test sequence to a default sequence. According to one embodiment, the packet receiver 200a is thus configured to perform (optional) step S104c as part of performing packet detection in step S104:

step S104 c: packet receiver 200a correlates the normalized test sequence with the default normalized test sequence, resulting in a correlated test sequence.

Thus, the representation of those samples received within the packet detection window 630 is defined by the normalized test sequence.

The default standardized test sequence may have different examples. According to one embodiment, the default normalized test sequence is the default preamble sequence (also multiplied by its one-sample delayed copy and normalized).

The packet receiver 200a in fig. 5 includes a maximum lookup module 560. The maximum lookup module 560 is configured to lookup the maximum of the associated test sequence. In particular, according to one embodiment, the packet receiver 200a is configured to perform (optional) step S104d as part of performing packet detection in step S104:

step S104 d: packet receiver 200a identifies the sample in the test sequence (for which the associated test sequence has the largest value). The sample is then determined to define the start 640' of the package 600.

This enables accurate sampling of where the packet 600 starts to be located.

In some aspects, the start 640' of the packet 600 is successfully identified only when the maximum value of the associated test sequence exceeds a particular packet detection threshold Δ. Thus, according to one embodiment, the packet receiver 200a is configured to perform (optional) step S104e as part of performing packet detection in step S104:

step S104 e: the packet receiver 200a compares the maximum value with the packet detection threshold Δ. Then, only when the maximum value exceeds the packet detection threshold Δ, the sample is determined to define the start 640' of the packet 600. In some aspects, the value of Δ depends on an expected signal-to-noise ratio (SNR) at the packet receiver 200a and/or the length of the preamble 610. The SNR may be determined based on, for example, transmission bandwidth, transmission power, and link distance. The optimal packet detection threshold Δ may be obtained by theoretical analysis or simulation for each SNR and preamble length.

Other aspects of the packet detection window 630 and the packet start prediction module 510 will now be disclosed.

In some aspects, as shown in fig. 6, the packet detection window 630 is centered around the expected start time 640 of the received packet 600. Packet 600 includes a preamble 610 and a data portion 620. As described above, packet detection is enabled only during this window as described above. According to one embodiment, the packet detection window 630 is opened according to a time-based schedule. As shown in fig. 6, a packet detection window 630 of two or more samples is considered, rather than a single sample, because the actual arrival time of the packet 600 may be slightly delayed or advanced relative to the expected time due to synchronization mismatch between the packet receiver 200a and the packet transmitters 200 b-200N.

The duration of the packet detection window 630 is sized to ensure that the maximum deviation between the expected arrival time (defined by the start time 640) and the actual arrival time (defined by the start 640) of the packet 600 is within the packet detection window 630.

May be based on the nominal distance d between the packet transmitters 200b-200N and the packet receiver 200a₀To arrive at the expected arrival time of packet 600. The actual arrival time depends on the packet transmitters 200b-200N andthe actual distance d between packet receivers 200 a. From d_maxDefined, d and d₀The maximum absolute difference between is strictly related to the maximum transmission and reception range of the wireless communication network 100.

The duration of the packet detection window (in seconds) should be set to:

where c is the speed of light, and c is 2.99792 m/s.

According to one embodiment, the packet detection window 630 has a time length of between 100ns and 200ns, preferably between 125ns and 175ns, and most preferably 150 ns.

The duration W of the packet detection window 630 in samples is typically dependent on the sampling interval T at the packet receiver 200a_sAnd may be determined as:

as a non-limiting illustrative example, the maximum distance deviation is d_max20m, sample interval T_sThe length of the packet detection window corresponding to W-3 samples is T-133.4 ns.

Using the packet detection window 630 to enable/disable packet detection allows for a simpler decoding process and lower energy consumption, since the packet receiver 200a does not need to continuously correlate all received samples, but only those within the packet detection window 630.

In addition, the use of the packet inspection window 630 improves the reliability of the packet inspection process. In more detail, since the preamble 610 is short, the association determined in step S104c is generally weaker relative to typical associations computed over longer sequences (e.g., using IEEE802.11 preambles). As a result, so-called "false alarms" occur in which a sequence of noisy samples is erroneously identified as the beginning of a packet. The use of the packet detection window 630 allows this problem to be substantially alleviated, since detection is only performed on the sample window where the packet 600 is expected to arrive.

Fig. 7 schematically illustrates, in a number of functional units, components of a packet receiver 200a according to an embodiment. The processing circuit 210 is provided using any combination of one or more suitable Central Processing Units (CPUs), multi-processors, microcontrollers, Digital Signal Processors (DSPs), etc., capable of executing software instructions stored in a computer program product 810 (e.g., in the form of storage medium 230 in fig. 8). The processing circuit 210 may further be provided as at least one Application Specific Integrated Circuit (ASIC) or Field Programmable Gate Array (FPGA).

In particular, the processing circuit 210 is configured to cause the packet receiver 200a to perform a set of operations or steps S102 to S104e as disclosed above. For example, the storage medium 230 may store the set of operations, and the processing circuit 210 may be configured to retrieve the set of operations from the storage medium 230 to cause the packet receiver 200a to perform the set of operations. The set of operations may be provided as a set of executable instructions.

Thus, the processing circuitry 210 is thereby arranged for performing the method as disclosed herein. The storage medium 230 may also include persistent storage, which may be any one or combination of magnetic memory, optical memory, solid state memory, or even remotely mounted memory, for example. The packet receiver 200a may further comprise a communication interface 220 at least configured for communication with at least one packet transmitter 200a to 200N. As such, communication interface 220 may include one or more transmitters and receivers, including analog and digital components. Processing circuit 210 controls the general operation of packet receiver 200a, for example, by sending data and control signals to communication interface 220 and storage medium 230, receiving data and reports from communication interface 220, and retrieving data and instructions from storage medium 230. Other components of packet receiver 200a and related functions have been omitted so as not to obscure the concepts presented herein.

Fig. 8 illustrates one example of a computer program product 810 comprising a computer-readable storage medium 830. On the computer-readable storage medium 830, a computer program 820 may be stored, which computer program 820 may cause the processing circuit 210 and entities and devices operatively coupled to the processing circuit, such as the communication interface 220 and the storage medium 230, to perform a method according to embodiments disclosed herein. Accordingly, the computer program 820 and/or the computer program product 810 may provide means for performing any of the steps as disclosed herein.

In the example of fig. 8, the computer program product 810 is illustrated as an optical disc, such as a CD (compact disc) or DVD (digital versatile disc) or blu-ray disc. The computer program product 810 may also be embodied as a memory such as a Random Access Memory (RAM), a Read Only Memory (ROM), an Erasable Programmable Read Only Memory (EPROM) or an Electrically Erasable Programmable Read Only Memory (EEPROM), and more particularly as a non-volatile storage medium of the device in an external memory such as a USB (universal serial bus) memory, or a flash memory such as a compact flash memory. Thus, although the computer program 820 is here schematically shown as a track on the depicted optical disc, the computer program 820 may also be stored in any way suitable for the computer program product 810.

The inventive concept has been described above generally with reference to some embodiments. However, it is readily appreciated by a person skilled in the art that other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.