JP5964317B2 - Carrier Sense Multiple Access (CSMA) protocol for power line communications (PLC) - Google Patents

Description

  Embodiments are generally directed to power line communications (PLC), and more specifically to routing protocols for PLCs.

  Power line communication (PLC) includes a system for communicating data over the same medium (i.e., wire or conductor) that is also used to send power to residences, buildings, and other sites. Once installed, a PLC system may enable a variety of applications, for example, automatic meter reading and load control (ie utility-type applications), automotive applications (eg, electric vehicle charging, to name a few examples) ), Home automation (eg, control of equipment, lighting, etc.), and / or computer networking (eg, Internet access), etc.

Currently, various PLC standardization efforts with unique features are being made around the world. In general, the PLC system may be implemented differently depending on local regulations, local power grid characteristics, and the like. Examples of competing PLC standards include IEEE 1901, HomePlug AV, PRIME (Powerline
Intelligent Metering Evolution), and ITU-TG Include specifications such as hn (eg, G.9960 and G.9961).

  Systems and methods for implementing a carrier sense multiple access (CSMA) protocol in power line communication (PLC) are described. In an exemplary embodiment, the method may include performing a virtual carrier detection operation and calculating a contention window in response to the virtual carrier detection operation indicating that the communication channel is idle. The method may also include performing a physical carrier detection operation following the virtual carrier detection operation, where the physical carrier detection operation is based at least in part on the contention window. Thereafter, in response to the physical carrier sense operation indicating that the communication channel is idle, the method may include transmitting data on the channel.

  In some cases, for example, calculating the contention window may include setting the length of the contention window, and the physical carrier detection operation is performed at a randomly selected time within the contention window. Can be done. The method may also include repeating the virtual carrier detection operation until it indicates that the communication channel is idle.

  Additionally or alternatively, the method repeats the virtual carrier detection operation until it indicates that the communication channel is idle in response to the physical carrier detection operation indicating that the communication channel is not idle. And increasing the length of the contention window to create a modified contention window. For example, increasing the contention window length may include increasing the contention window length by an amount corresponding to multiple prior attempts to transmit data. The method may also include performing a second physical carrier detection operation following the repeated virtual carrier detection operation, wherein the second physical carrier detection operation is at least partially in the modified contention window. Based. For example, the second physical carrier detection operation may be performed at a randomly selected time within the modified contention window. The method may further include transmitting data on the communication channel in response to the second physical carrier sensing operation indicating that the communication channel is idle.

  In another exemplary embodiment, the method includes: (a) a physical carrier detection operation based at least in part on the original time window in response to the virtual carrier detection operation indicating that the access channel is free. (B) in response to the physical carrier sense operation indicating that the access channel is free, initiating data transmission on the access channel; (c) data transmission being unicast transmission; In response to being and the confirmation message not being received by the PLC device, incrementing the back-off counter and increasing the original time window; and (d) the back-off counter is In response to having a value less than the maximum number, It may include repeating at least (a) and (b) using a large time window.

  In some implementations, increasing the original time window may include increasing the length of the original time window. Also, the physical carrier detect operation can be performed at a randomly selected time within the original time window, and the repeated physical carrier detect operation is performed at a randomly selected time within the incremented time window. Can be done.

  The method may also include monitoring the output of the virtual carrier detect operation until it indicates that the access channel is free. Additionally or alternatively, the method may increase the backoff counter, maintain the original time window in response to the physical carrier sense operation indicating that the access channel is busy, And performing a second physical carrier detection operation subsequent to the second virtual carrier detection operation, wherein the second physical carrier detection operation is based at least in part on the original time window. For example, the second physical carrier detection operation may be performed at a randomly selected time within the original time window. The method may also include transmitting data on the access channel in response to the second physical carrier sense operation indicating that the access channel is free.

  In yet another exemplary embodiment, the method may include transmitting data at a selected time within the contention window in response to a determination that the channel is available by a carrier sense operation. . The method may also include determining that the data transmission is a unicast transmission, determining that no confirmation message has been received, and increasing the contention window. The method further includes retransmitting the data at a selected time within the increased contention window.

  The method may also include retransmitting the data in response to another determination that the channel is available due to repeated carrier sensing operations. In various implementations, the carrier detection operation may be a virtual carrier detection operation, a physical carrier detection operation, or a combination of physical and virtual carrier detection operations.

  In some embodiments, one or more methods described herein may be performed by one or more PLC devices (eg, a PLC modem, etc.). In other embodiments, a tangible electronic storage medium may have program instructions stored thereon that, when executed by a processor in one or more PLC devices, one or more Causing a PLC device to perform one or more of the operations disclosed herein. Examples of such processors include, but are not limited to, digital signal processors (DSPs), application specific integrated circuits (ASICs), system on chip (SoC) circuits, field programmable gate arrays (FPGAs), microprocessors, A microcontroller is included. In yet other embodiments, the PLC device may include at least one processor and a memory coupled to the at least one processor, the memory performing one or more operations disclosed herein for the PLC device. It is configured to store program instructions that can be executed by the at least one processor for execution.

1 is a diagram of a PLC system according to some embodiments. FIG.

FIG. 2 is a block diagram of a PLC device or modem according to some embodiments.

FIG. 2 is a block diagram of a PLC gateway according to some embodiments.

FIG. 3 is a block diagram of a PLC data concentrator according to some embodiments.

It is a flowchart of the CSMA method of a prior art.

Some embodiments according to the flow chart of the CSMA approach.

1 is a block diagram of an integrated circuit according to some embodiments. FIG.

Example for carrying out the invention

  FIG. 1 illustrates a power line communication (PLC) system in accordance with some exemplary embodiments. The medium voltage (MV) power line 103 from the substation 101 typically carries a voltage in the range of tens of kilovolts. The transformer 104 steps down the MV power to low voltage (LV) power on the LV line 105 that carries a voltage in the range of 100-240 VAC. The transformer 104 is designed to operate at a very low frequency, typically in the range of 50-60 Hz. The transformer 104 typically prevents high frequencies, such as signals exceeding 100 KHz, from passing between the LV line 105 and the MV line 103. The LV line 105 typically supplies power to the customer via meters 106a-n attached outside the residences 102a-n. (Although referred to as “residential,” the premises 102a-n may include any type of building, facility, or location where power is received and / or consumed.) For example, a breaker panel, such as panel 107 Provides an interface between meter 106n and electrical wire 108 in residence 102n. Electrical wire 108 delivers power to outlet 110, switch 111, and other electrical devices in residence 102n.

  The power line topology illustrated in FIG. 1 can be used to deliver high speed communications to residences 102a-n. In some implementations, power line communication modems or gateways 112a-n may be coupled to LV power line 105 at meters 106a-n. PLC modem / gateways 112a-n may be used to send and receive data signals via MV / LV lines 103/105. Such data signals are used to support metrology and power delivery applications (eg, smart grid applications), communication systems, high-speed Internet, telephony, video conferencing, and video delivery, to name a few examples. obtain. By transmitting telecommunications and / or data signals over the power transmission network, there is no need to install new wiring for each subscriber 102a-n. Thus, considerable cost savings are possible by using existing power distribution systems to carry data signals.

  An exemplary method for transmitting data over a power line may use a carrier signal having a frequency that is different from the frequency of the power signal. The carrier signal may be modulated with data using, for example, an orthogonal frequency division multiplexing (OFDM) scheme.

  The PLC modems or gateways 112a-n in the residences 102a-n use MV / LV power grids to carry data signals to and from the PLC data concentrator or router 114 without the need for additional wiring. Use. Concentrator 114 may be coupled to either MV line 103 or LV line 105. The modems or gateways 112a-n may support applications such as, for example, high-speed broadband Internet links, narrowband control applications, low bandwidth data collection applications. In a home environment, for example, modems or gateways 112a-n may further enable home and building automation in air conditioning, lighting, and security. The PLC modem or gateway 112a-n may also allow AC or DC charging of electric vehicles or other equipment. An example of an AC or DC charger is shown as PLC device 113. Outside the premises, a power line communication network may provide street lighting control and remote power meter data collection.

  One or more PLC data concentrators or routers 114 may be coupled to the control center 130 (eg, a utility company) via the network 120. The network 120 may include, for example, an IP-based network, the Internet, a cellular network, a WiFi network, a WiMax network, or the like. Accordingly, the control center 130 may be configured to collect power consumption and other types of related information from the gateway 112 and / or device 113 via the concentrator 114. In addition or alternatively, the control center 130 is configured to implement smart grid policies and other regulations or commercial rules by communicating such rules to each gateway 112 and / or device 113 via the concentrator 114. obtain.

  FIG. 2 is a block diagram of PLC device 113 according to some embodiments. As illustrated, the AC interface 201 allows the PLC device 113 to switch off the connection between the electrical wires 108a and 108b using a switch circuit or the like in an electrical manner within the site 112n. It can be coupled to wires 108a and 108b. However, in other embodiments, the AC interface 201 may be connected to a single wire 108 (ie, without dividing the wire 108 into wires 108a and 108b) without providing such a switching function. Good. In operation, the AC interface 201 may allow the PLC engine 202 to receive and transmit PLC signals via wires 108a-b. In some cases, the PLC device 113 may be a PLC modem. Additionally or alternatively, the PLC device 113 may be a smart grid device (eg, AC or DC charger, meter, etc.), equipment, or other electrical element (eg, street) located within or outside the site 112n. Part of a control module for lighting etc.).

  The PLC engine 202 may be configured to transmit and / or receive PLC signals on the wires 108a and / or 108b via the AC interface 201 using a specific frequency band. In some embodiments, PLC engine 202 may be configured to transmit an OFDM signal, although other types of modulation schemes may be used. Accordingly, PLC engine 202 may include or be configured to communicate with a metering or monitoring circuit (not shown), which may be configured via wires 108, 108a, and / or 108b or Configured to measure power consumption characteristics of a device or apparatus. The PLC engine 202 receives such power consumption information, encodes it as one or more PLC signals, and transmits it to a higher level via wires 108, 108a, and / or 108b for further processing. To PLC devices (eg, PLC gateway 112n, data aggregator 114, etc.). Conversely, the PLC engine 202 may, for example, provide instructions and / or instructions from such higher level PLC devices encoded in the PLC signal to allow selection of a particular frequency band in which the PLC engine 202 operates. Or other information may be received.

  FIG. 3 is a block diagram of the PLC gateway 112 according to some embodiments. As shown in this example, the gateway engine 301 is coupled to a meter interface 302, a local communication interface 304, and a frequency band usage database 304. Meter interface 302 is coupled to meter 106 and local communication interface 304 is coupled to one or more of various PLC devices, such as PLC device 113, for example. The local communication interface 304 may provide various communication protocols that may allow the gateway 112 to communicate with a variety of different devices and equipment, such as, for example, ZIGBEE, BLUETOOTH, WI-FI, WI-MAX, ETHERNET. In operation, gateway engine 301 collects communications from PLC device 113 and / or other devices and meter 106 and serves as an interface between these various devices and PLC data concentrator 114. Can be configured. The gateway engine 301 may also be configured to allocate frequency bands to specific devices and / or to provide information that allows such devices to self-assign their own operating frequencies.

  In some embodiments, PLC gateway 112 may be located in or near site 102n and may serve as a gateway for all PLC communications to and / or from site 102n. However, in other embodiments, the PLC gateway 112 may not be present, and the PLC device 113 (and meter 106n and / or other equipment) may communicate directly with the PLC data concentrator 114. If a PLC gateway 112 is present, this may include, for example, a database 304 with a record of the frequency bands currently used by the various PLC devices 113 in the premises 102n. An example of such a record may include, for example, device identification information (eg, serial number, device ID, etc.), application profile, device class, and / or currently allocated frequency band. Accordingly, the gateway engine 301 may use the database 304 in assigning, allocating, or otherwise managing frequency bands allocated to its various PLC devices.

  FIG. 4 is a block diagram of a PLC data concentrator or router 114 according to some embodiments. Gateway interface 401 may be coupled to data concentrator engine 402 and configured to communicate with one or more PLC gateways 112a-n. Network interface 403 may also be coupled to data concentrator engine 402 and configured to communicate with network 120. In operation, data concentrator engine 402 may be used to collect information and data from multiple gateways 112a-n prior to transfer to control center. In the absence of PLC gateways 112a-n, gateway interface 401 is a meter and / or device interface (not shown) configured to communicate directly with meters 116a-n, PLC device 113, and / or other equipment. It may be replaced. Also, in the absence of PLC gateways 112a-n, the frequency usage database 404 may be configured to store records similar to those described above with respect to the database 304.

  In general, before transmitting a signal over power lines or wires 103, 105, and / or 108, the PLC device will attempt to detect whether a given communication or access channel (eg, frequency band) is currently in use. You can try. Channel access may be achieved, for example, by using a carrier sense multiple access (CSMA / CA) mechanism with collision avoidance with random backoff time. The random backoff mechanism may spread in time when the PLC device attempts transmission, thereby reducing the likelihood of collision. In other words, whenever a device attempts to send a data frame, it may wait for a random period. If the channel is found to be idle or free, the device may transmit its data following its random backoff. If the channel is found to be busy, following its random backoff, the device may wait for another random period before attempting to access the channel again.

  In various embodiments, different CSMA approaches can be used. For example, physical carrier sensing (PCS) may be provided by the physical layer (PHY) upon detection of the preamble. In contrast, a virtual carrier detection (VCS) mechanism may be provided by the medium access control (MAC) layer by tracking the expected duration of channel occupancy. The virtual carrier detection can be set by the length of the received packet (or at the time of collision), for example. In these cases, the VCS tracks or estimates the expected duration of the medium's “busy” state (ie, when a given PLC device transmits data on the power line or wires 103, 105, and / or 108). To do.

  FIG. 5 shows a flowchart of a prior art CSMA method that may be applied to a non-beacon personal area network (PAN) as described, for example, in the IEEE 802.15.4 standard. Using this method, the random backoff mechanism spreads over the time the station attempts to transmit (thus reducing the possibility of collisions). This CSMA algorithm is typically used prior to the transmission of data or MAC command frames, and this algorithm uses a time period called a “backoff period” where one backoff period is equal to a unit Backoff Period symbol. Implemented using units.

As illustrated in block 501, each device may maintain two variables, NB and BE, for each transmission attempt. Specifically, NB is the number of times the CSMA algorithm is required for backoff while attempting the current transmission, which can be initialized to “0” before each new transmission attempt. On the other hand, BE is a backoff index, which relates to how many backoff periods a device can wait before trying to evaluate a channel, and can be initialized to a value of minimum BE. The method may initialize NB and BE and then proceed to block 502. At block 502, the method may create a delay for a random number for the entire backoff period (e.g., in the range of 0-2 ^BE -1), after which a block 503 requests that a PCS operation be performed. The backoff time may be obtained by Backoff = Random (2 ^BE −1) × SlotTime, where SlotTime is equal to the duration of the contention window slot (eg, the number of symbols).

  If, at block 504, the channel is evaluated as busy, the method ensures that the BE does not exceed the maximum BE (for high priority packets, the maximum BE may be equal to the minimum BE). On the other hand, both NB and BE may be incremented by 1 in block 506. In block 507, if the value of NB is less than or equal to the maximum CSMA backoff, the method may return to block 502. If the value of NB is greater than the maximum CSMA backoff, the method may end with a channel access failure status or indication, for example. Moving again to block 504, if the channel is evaluated as idle, the method may immediately begin transmitting a frame at block 505.

  However, as those skilled in the art will appreciate with respect to this method shown in FIG. 5, PCS is detected prematurely. Each PCS interval is calculated independently of the VCS detection result. If one node is sending large packets, competing nodes can easily fail due to unnecessary PCS attempts. Additionally or alternatively, the contention window is prematurely increased. Every time the PCS is busy, BE is increased. Thus, if a node fails in the first time of PCS, that node is more likely to fail in subsequent PCS than other nodes due to its increased window, resulting in an unfair problem.

  To address these and other issues, the embodiments described herein provide an approach for using one or more VCS operations to save one or more unwanted PCS operations. To do. Also, in some embodiments, the contention window may be increased when an ACK message or package is lost, so that collision events are distinguished from busy medium detection. In various embodiments, the techniques described herein can be applied in PLC mesh networks with random media access, although other types of networks can be used. These embodiments can also be used with various PLC standards, such as, for example, the G3-PLC standard or the like.

  Turning now to FIG. 6, a flowchart of the CSMA method is shown according to some embodiments. In various embodiments, the method of FIG. 6 may be performed by, for example, PLC device 103, PLC gateway 112, and / or PLC data concentrator 114. At block 601, the method may include setting one or more backoff parameters (eg, NB counter and / or BE) to their initial values. At block 602, the method may perform the VCS operation until, for example, the VCS operation determines that the communication channel is idle or free. Thereafter, at blocks 602 and 603, the method may create a delay and request that a PCS operation be performed as in blocks 501 and 502 of FIG. However, in this case, in contrast to the method of FIG. 5, PCS is attempted when VCS (Virtual Carrier Detection) is not busy. That is, VCS is considered before PCS. When the VCS goes from busy to idle, all nodes (ie PLC devices) can be aligned simultaneously for fair competition for the channel. In this way, both VCS and PCS can be used, and VCS saves unnecessary PCS so that CSMA does not fail due to large packet transmissions, for example.

  At block 605, the method may determine whether the channel is idle or free based on the PCS operation. If idle, the method may send data over the channel at block 606. At block 607, the method may determine whether the data transmission is a broadcast transmission or a unicast transmission (the latter is involved in receiving a confirmation message in response to a successful transmission, while the former is is not). If the data transmission is a unicast transmission, the method may determine at block 608 whether a confirmation has been received. If the data transmission is a broadcast transmission or if a confirmation is received for a unicast transmission, the method may end with a success indication. Otherwise, at block 609, both NB and BE can be incremented.

  Returning to block 605, if the channel is busy, only NB may be incremented (but the contention window size is not increased). Thereafter, if the maximum number of backoffs is reached at block 611, the method may end with a failure indication. Otherwise, the method may return to block 602. Thus, the BE can be increased if no acknowledgment (ACK) message or packet is received (in the case of unicast transmission). When the PCS returns to idle, a data frame may be sent out. Otherwise, the method can wait for the VCS to finish and BE remains the same value. When data is sent without receiving an ACK message, BE is incremented. However, after a busy indication from PCS operation, the node or device may not increase its contention window so that all nodes may have fair CSMA contention. That is, only after the ACK has been lost, suggesting possible packet collisions and crowded media, the node may increase the contention window to compete with other devices for channel usage.

  Note that there are two most likely reasons when an ACK is lost. First, the channel condition may be bad, in which case the sender can try again without increasing the contention window size. Second, packet collisions may have occurred (due to the channel being busy), in which case competing senders increase their time or contention window dimensions before attempting transmission. obtain. In some implementations, the sender and receiver interact with each other with respect to lost ACKs (past) using extra bits in NACK (if NACK can be sent) or some additional exchange of information. Can do. The receiver may use this information to help the sender distinguish bad channel conditions from packet collisions so that the sender can respond differently when the ACK is lost. Additionally or alternatively, if the receiver finds that the received packet has a low quality indicator (LQI), it may use an extra bit in the ACK packet to alert the sender about the bad channel. it can.

  FIG. 7 is a block diagram of an integrated circuit according to some embodiments. In some cases, one or more of the devices and / or apparatuses shown in FIGS. 2-4 may be implemented as shown in FIG. In some embodiments, the integrated circuit 702 is a digital signal processor (DSP), application specific integrated circuit (ASIC), system on chip (SoC) circuit, field programmable gate array (FPGA), microprocessor, microcontroller, etc. It can be. Integrated circuit 702 is coupled to one or more peripherals 704 and external memory 703. In some cases, the external memory 703 can be used to store and / or maintain the databases 304 and / or 404 shown in FIGS. Further, the integrated circuit 702 may include a driver for sending signals to the external memory 703 and another driver for sending signals to the peripheral device 704. A power supply 701 is also provided that provides a power supply voltage to the integrated circuit 702 and one or more power supply voltages to the memory 703 and / or peripheral device 704. In some embodiments, multiple instances of integrated circuit 702 may be included (and multiple external memories 703 may be included as well).

  Peripheral device 704 may include any desired circuit elements depending on the type of PLC system. For example, in certain embodiments, peripheral device 704 may implement local communication interface 303, including various types of devices for wireless communication, such as WI-FI, ZIGBEE, BLUETOOTH, cellular, global positioning systems, and the like. obtain. Peripheral device 704 may also include additional storage, including RAM storage, solid state storage, or disk storage. In some cases, peripheral device 704 may include a user interface device, such as a display screen including a touch display screen or multi-touch display screen, a keyboard or other input device, a microphone, a speaker, and the like.

  The external memory 703 can include any type of memory. For example, the external memory 703 may be SRAM, non-volatile RAM (NVRAM, for example, “flash” memory, etc.), and / or synchronous DRAM (SDRAM), double data rate (DDR, DDR2, DDR3, etc.), SDRAM, DRAM And may include dynamic RAM (DRAM). The external memory 703 may include one or more memory modules to which a memory device is attached, such as a single inline memory module (SIMM), a dual inline memory module (DIMM), and the like.

  It will be appreciated that the various operations described with respect to FIG. 6 may be performed simultaneously and / or sequentially. It will also be appreciated that each operation can be performed in any order and can be performed once or repeatedly. In various embodiments, the modules shown in FIGS. 2-4 may represent a set of software routines, logical functions, and / or data structures that are configured to perform specific operations. Although these modules are shown as separate logical blocks, in other embodiments, at least some of the operations performed by these modules may be combined into fewer blocks. Conversely, any given one of the modules shown in FIGS. 2-4 may be implemented such that its operation is divided into two or more logical blocks. Also, although these various modules are shown in a particular configuration, they may be rearranged in other suitable ways in other embodiments.

  Many of the operations described herein may be implemented in hardware, software, and / or firmware, and / or any combination thereof. When implemented in software, the code segment performs the necessary tasks or operations. The program or code segment may be stored in a processor readable, computer readable, or machine readable medium. A processor readable, computer readable, or machine readable medium may include any device or medium that can store or transfer information. Examples of such processor readable media include electronic circuits, semiconductor memory devices, flash memory, ROM, erasable ROM (EROM), floppy disks, compact disks, optical disks, hard disks, fiber optic media, and the like.

  The software code segment is, for example, a hard drive, flash memory, solid state memory, optical disc, CD, DVD, computer program product, or other that provides tangible computer readable or machine readable storage for a processor or middleware container service It can be stored on any volatile or non-volatile storage device, such as any memory device. In other embodiments, the memory may be a virtualization of several physical storage devices, which are the same type or different types. The code segment may be downloaded or transferred from the storage to the processor or container via another computer network such as an internal bus, the Internet or an intranet, or via another wired or wireless network.

  Those skilled in the art will appreciate that variations can be made to the exemplary embodiments described and that other embodiments can be implemented within the scope of the claims of the present invention.

Claims (2)

A power line communication (PLC) device,
A processor comprising a digital signal processor (DSP), application specific integrated circuit (ASIC), system on chip (SoC) circuit, field programmable gate array (FPGA), microprocessor, or microcontroller;
A memory coupled to the processor;
Including
The memory is connected to the PLC device.
(A) performing a physical carrier detect operation based at least in part on the original time window in response to a virtual carrier detect operation indicating that the access channel is free;
(B) in response to the physical carrier detect operation indicating that the access channel is free, initiating data transmission on the access channel;
(C) In response to the data transmission being a unicast transmission and a confirmation message not being received by the PLC device, incrementing a back-off counter and increasing the original time window; Increasing the original time window increases the length of the original time window, incrementing the back-off counter, and increasing the original time window;
(D) repeating at least (a) and (b) with the increased time window in response to the backoff counter having a value less than the maximum number of allowed backoff operations; ,
(E) In response to the physical carrier detect operation indicating that the access channel is busy, the backoff counter is incremented, the original time window is maintained, and following a second virtual carrier detect operation Performing a second physical carrier detect operation, wherein the second physical carrier detect operation increases the backoff counter based at least in part on the original time window, and Maintaining a time window and performing the second physical carrier detection operation following the second virtual carrier detection operation;
(F) transmitting data on the access channel in response to the second physical carrier detection operation indicating that the access channel is free;
A device configured to store program instructions that may be executed by the processor. The device of claim 1 , comprising:
The device, wherein the second physical carrier detection operation is performed at a randomly selected time within the original time window.

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