WO2001011799A1 - Repeteur de paquets de donnees - Google Patents

Repeteur de paquets de donnees Download PDF

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Publication number
WO2001011799A1
WO2001011799A1 PCT/GB2000/002667 GB0002667W WO0111799A1 WO 2001011799 A1 WO2001011799 A1 WO 2001011799A1 GB 0002667 W GB0002667 W GB 0002667W WO 0111799 A1 WO0111799 A1 WO 0111799A1
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WO
WIPO (PCT)
Prior art keywords
repeater
packet
base station
subscriber
station
Prior art date
Application number
PCT/GB2000/002667
Other languages
English (en)
Inventor
Robin Paul Rickard
Original Assignee
Nortel Networks Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nortel Networks Limited filed Critical Nortel Networks Limited
Priority to EP00946091A priority Critical patent/EP1208656A1/fr
Priority to AU59978/00A priority patent/AU5997800A/en
Publication of WO2001011799A1 publication Critical patent/WO2001011799A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/54—Systems for transmission via power distribution lines
    • H04B3/58—Repeater circuits

Definitions

  • This invention relates to the use of a repeater in a packet-based communications system.
  • Communications signals are attenuated by the medium over which they are carried.
  • repeaters In both wireline and wireless communications systems, it is common to use repeaters to extend the reach of a transmitted signal. In most wireline systems this can be achieved by inserting a repeater in the transmission line, the repeater receiving a weak signal, amplifying it, and retransmitting it.
  • the reach of power line communications systems can be extended by siting repeater units along distribution cables leading from the electricity substation.
  • US Pat. No. 5,726,980 describes a way in which repeaters can be provided on a power line. A received signal is repeated into a different frequency band. This avoids the need for RF blocking devices since the original and repeated signals are separated in frequency. However, repeating the signal into another frequency band has a disadvantage that part of the available spectral band has to be allocated for repeater use.
  • the present invention seeks to provide an alternative way of using a repeater in a communications system.
  • a first aspect of the invention provides a power line communications system comprising:
  • a base station coupled to the line, for serving the plurality of subscriber stations
  • the system being a packet-based system
  • the repeater is arranged to receive a packet in a first time period and to retransmit it in a subsequent time period.
  • Another aspect of the invention provides a repeater for use in the system.
  • the use of a repeater which repeats in a different time period rather than a different frequency band offers particular advantages in a power line communications system where there are considerable constraints on the available spectrum.
  • An advantage of using this type of repeater is that the full spectral band that is allowed for powerline communications can be used at once, rather than having to reserve part of the band for use by a frequency- translating repeater. By using the full spectral band, data throughput can be increased.
  • a further aspect of the invention provides a communications system comprising:
  • the system operating in a polled manner whereby the base station sends a polling packet in a downstream direction to a subscriber station and receives, in reply, a reply packet in an upstream direction
  • the repeater is arranged to receive a packet in a first time period and to retransmit it in a subsequent time period in both the downstream direction and the upstream direction, and the base station is arranged to allow for the time taken to reach a subscriber station via the repeater before polling another subscriber station.
  • the polling mechanism is adapted to allow for the additional time needed to reach a subscriber via a repeater.
  • a further aspect of the invention provides a repeater for use in a communications system which comprises a plurality of subscriber stations and a base station for serving the plurality of subscriber stations, the repeater being for use in serving subscriber stations that cannot be directly reached by the base station,
  • the repeater being arranged to receive a packet in a first time period, to inspect the received packet and, if the inspection indicates that the packet should be repeated, to retransmit the packet in a subsequent time period.
  • a similar problem is encountered when operating a polled packet data system on other cabled systems, where time division duplexing and multiplexing is employed within a certain band on cables primarily used for another purpose, where it is also not practical to insert isolation into the cable at the location of the repeater.
  • a wireless packet data system employing omnidirectional antennas which do not afford isolation between receive and transmit sections also requires this solution, if efficient use is to be made of the bandwidth available.
  • the system may be used to extend reach in low power systems, or for in-fill of fades or obstructions to line-of-sight paths.
  • FIGURE 1 shows a power line communications system
  • FIGURE 2 shows the communications network in more detail
  • FIGURE 3 shows equipment for use at a subscriber premises
  • FIGURE 4 shows operation of the direct polling method
  • FIGURE 5 shows operation of the polling method via a repeater
  • FIGURE 6 shows timing detail of the polling method via a repeater
  • FIGURE 7 shows a packet structure
  • FIGURE 8 shows a repeater
  • FIGURE 9 shows functional blocks of a repeater
  • FIGURE 10 shows a base station; and, FIGURE 11 shows a flow chart for a polling method by the base station.
  • FIG. 1 shows an electricity distribution network which is adapted to carry telecommunications signals.
  • Mains electricity enters the network from an 11 kV or 6.6kV transmission line 105 and is transformed by substation 100 into a 400V supply which is delivered over distribution cable 120 to customer premises S1 to S6.
  • a substation 100 typically has between 4 and 8 distribution cables of the kind shown as 120, 121 leading from it, each distribution cable serving a number of premises.
  • a distribution cable can extend for several hundreds of metres.
  • Distribution cable 120 comprises blue, red and yellow phase lines and a neutral line.
  • Subscriber communications stations CPE are typically located at houses or businesses.
  • a full system will usually include more than the six premises shown here and will typically include a more elaborate tree-and-branch distribution network.
  • Subscriber premises may receive a single phase electricity supply (230V) or a three-phase electricity supply (400V).
  • 230V single phase electricity supply
  • 400V three-phase electricity supply
  • domestic subscriber premises usually receive a single phase supply and neighbouring subscriber premises are usually coupled to different phase lines.
  • subscriber S1 is shown coupled to the red phase line
  • subscriber S2 is coupled to the yellow phase line. This helps to distribute the load of the network evenly across the three phases.
  • a base station BS couples data communications signals onto distribution cable 120.
  • the base station can be coupled to one or more distribution cables 120 at a point near to substation 100, as shown in figure 1 , or it may be coupled to the bus bars at substation 100, the bus bars acting as a star point for serving all of the distribution cables.
  • the communications signals propagate over the electricity distribution cable to transceiver stations at subscriber premises S1 to S6, with a coupling unit CU 151 coupling the communications signals to/from the power line.
  • Subscriber premises couple to a phase line of distribution cable 120 by a branch line 150. In the upstream direction, communications signals are transmitted from the subscriber transceiver stations CPE over cable 120 towards the base station.
  • Communications signals can be transmitted between a phase line and neutral or earth, or in a differential manner.
  • a repeater 160 is shown connected to cable 120. The purpose of the repeater is to extend the reach of the base station BS to those subscriber stations that cannot be directly reached by BS. The positioning of the repeater is a matter of choice, determined by measurements made on the particular network. Such measurements determine those parts of the network which will receive an inadequate service and which need a repeater.
  • a repeater may serve one phase line or a number of phase lines.
  • a dedicated repeater can be coupled to the distribution line 120 at a convenient point, such as a lamp post, or a subscriber station CPE can be used as a repeater.
  • Figure 2 shows a top level diagram of an example power line communications (PL) system configuration.
  • PL power line communications
  • the end-user computer connects to the customer premises equipment (CPE), within the customer premises.
  • CPE customer premises equipment
  • the CPE is connected to the power line base station using a power line protocol across the low-voltage LV power line.
  • Communications traffic from multiple base stations accesses the core network through the main station via concentration in a hub, FDDI ring or Ethernet daisy chain.
  • a manager station allows remote management of the base stations and CPEs.
  • Intranet and Internet access is available directly or indirectly via the core network, via gateways where appropriate.
  • the CPE is a freestanding unit, powered from the customer premises mains supply.
  • the CPE provides two data connections:
  • the coupling unit provides the link between the CPE and the external power line. Preferably this is at the street side of the electricity meter.
  • the CPE need not be located close to the customer's computer.
  • the Ethernet link is preferably via unshielded twisted-pair (UTP) cable.
  • UTP unshielded twisted-pair
  • a number of data terminals can connect to the CPE in the form of a local area network, as shown in figure 3.
  • the CPE is intended to be left powered up continuously, i.e. it does not need to be turned on and off at the same time as the computer.
  • Frequency shift keying is preferred as a modulation scheme.
  • MSK minimum shift keying
  • QAM spectrally-efficient modulation schemes
  • CNR carrier-to-noise ratio
  • the PL system delivers around 1 Mbps peak bit rate, shared between all CPEs connected to a given Base station.
  • This peak shared bit rate may be reduced, such as to 250kbps or 500kbps, or raised depending on available bandwidth and modulation schemes that are used. Reduced bit rates will also be supported to provide service to end-users at the extremes of the system range and end-users with adverse link transmission characteristics.
  • bit rate and frequency band for the CPE can be set via control signals from a network management unit.
  • the range over which a PL link can be reliably maintained is dependent on the loss characteristics of the electricity distribution cable and the noise levels experienced at the receiver. For reliable operation, it is expected that a carrier to (background) noise ratio (CNR) of greater than 10 dB is required.
  • CNR carrier to (background) noise ratio
  • the use of multiple frequency bands and multiple data rates allows individual CPEs to be configured to best match the transmission characteristics to the customer premises. Where appropriate, such parameters will be capable of being configured across the network from the management system.
  • the base station and repeater units support the same frequency bands and data rates as the CPEs connected to it. When communicating with any CPE, the Base station and repeater automatically switch to the frequency and data rate used by that CPE.
  • the communications network comprises a primary station (base station) and a number of secondary stations (subscriber stations) communicating over a power line system.
  • the primary station controls access to the network by the secondary stations through the use of polling.
  • the primary station allocates physical station addresses to each secondary station.
  • As the Power line protocol emulates an Ethernet LAN service each station is also uniquely identified by the use of an Ethernet address which would be fixed at manufacture.
  • Each secondary station on the network is registered with the primary station through the management interface, using its unique Ethernet address, before service can be provided to it.
  • the primary station is responsible for determining if registered secondary stations are operating in an active, degraded or inactive state. Changes in the operational state of a secondary station do not affect the normal operation of other stations.
  • the primary station continuously polls all active secondary stations in sequence using either information or polling frames, selecting the appropriate modem frequency and data rate as required. Secondary stations can only transfer information when they have been polled.
  • the primary station waits for a response to its poll or moves on to the next active secondary station if a response is not received within the expected time.
  • a repeater is inserted between a base station and an outstation in this polled packet data system and it performs a store and forward function.
  • the repeater has both its receive and transmit stages connected to the power line with little or no isolation between the two. If communication is required between a base station and an outstation, and if the two are beyond communications range by a direct path, then a packet is first sent by the base station and received by the repeater unit. The packet is demodulated and stored, and then retransmitted in the next timeslot. The polling sequence is under control of the base station, which ensures that only the repeater is transmitting in its allocated timeslot. The repeated packet is then received by the outstation. The reverse procedure is employed in the return path, also under the control of the base station.
  • base station BS polls subscriber S1.
  • S1 is located close to BS and can be reached directly.
  • BS transmits a polling packet POLL 201 and receives, in reply, a reply packet REPLY 202 in the next time period.
  • base station BS polls subscriber S4.
  • S4 cannot be reached directly by the BS and requires the help of repeater 160.
  • BS transmits a polling packet POLL 210. This is received by repeater 160, amplified and retransmitted as POLL' 211.
  • S4 receives the polling packet and replies with a reply packet REPLY 212 which is again received, amplified and retransmitted by the repeater as REPLY' 213.
  • the base station is aware that S4 cannot be reached directly and waits a suitable time before polling another subscriber station.
  • FIG. 6 shows timing of the signalling sequence of fig. 5.
  • the activities of the three elements: base station BS, repeater and subscriber station are shown on respective lines.
  • BS transmits a polling packet 301 to the repeater. This is received 302 by the repeater.
  • the repeater waits until BS has finished transmitting before retransmitting the polling packet as POLL' 303. This is received 304 by the subscriber station.
  • the subscriber station then transmits a reply packet 305 which is received 306 by the repeater.
  • the repeater waits until the subscriber station has finished transmitting before retransmitting the reply packet 307 which is received 308 by BS.
  • BS waits a suitable time for the reply 308 from the repeater.
  • the polling packet POLL and the reply packet REPLY are of equal length. In this case, BS waits for a reply for a period of at least three times the length of a packet before polling another station.
  • the polling packet and reply packet may be of different lengths, and doing so can improve throughput. Where a station is polled and has nothing to send in return both the polling and reply packets will be short. Where data is primarily being delivered to a station e.g. downloading a web page to a terminal at the subscriber, the polling packet will contain a long payload and the reply packet will be short. Where a subscriber is sending data, this will result in a short polling packet and a long reply packet.
  • the base station upon polling a station that it knows is being served by a repeater, waits until either: (a) it receives a reply, or (b) a time-out period has expired, the time-out period being based on the expected packet length.
  • Figure 7 shows an example format for a polling packet.
  • This comprises a synchronising field 320, an address field 321 , repeater information field 322 and a payload portion 323.
  • the repeater information field can be used in a number of ways.
  • the repeater field can simply indicate whether or not the packet requires repeating.
  • a repeater upon receiving the packet can use this field to determine whether or not it needs to repeat the packet. For greater control over how a packet is handled during transmission, it is preferable to assign a unique address to a repeater or to a group of repeaters.
  • a repeater upon receiving a packet, examines the address and compares it with its own address to determine whether or not it needs to repeat the packet.
  • Each repeater or group of repeaters on a particular phase line (red, yellow, blue), distribution line (120, 121 fig. 1) or combination of these can be assigned a unique address. It may even be desirable to allocate a unique address to each repeater.
  • BS wishes to reach a subscriber S4 on red phase, then BS sends a polling packet that identifies a repeater on red phase. This prevents repeaters on other phase lines from attempting to repeat the packet, since mutual coupling between phase lines will often cause repeaters on blue and yellow phase lines to receive the packet as well as those repeaters on the red phase line.
  • a base station has knowledge of the repeater or group of repeaters that will be needed to serve a given station and inserts the appropriate address into the packet.
  • Figure 8 shows a repeater unit. This can be based on a subscriber station CPE. Indeed, one alternative to providing dedicated repeater units on a distribution line is to designate certain home units as repeaters.
  • the repeater includes a transformer 400, a receive chain comprising an amplifier 410 and a demodulator/decoding block 420 and a transmit chain comprising a coding/modulator block 440 and an amplifier 430.
  • the modulator/coding block converts raw digital data signal into a coded form before modulating it to RF in a suitable form for transmission over the power line.
  • the modulation may be Frequency Shift Keying (FSK), Quadrature Amplitude Modulation, Orthogonal Frequency Division Multiplexing (OFDM) or some other appropriate modulation scheme.
  • FSK Frequency Shift Keying
  • OFDM Orthogonal Frequency Division Multiplexing
  • Demodulator/decoding block 440 performs a complementary operation.
  • Processor 450 processes the digital data stream supplied by the demod/decode block 420.
  • a repeater can examine an address field in a received packet to determine whether the packet needs to be repeated. Figure 9 shows how this can be achieved.
  • a header extraction block 460 extracts the repeater address field from a received packet.
  • the packet is stored in a buffer 470 and also supplied to a control function 465 which compares the address in the received packet with a stored address from address store 467. If the stored address matches the address in the received packet, a control signal causes a gate 480 to release the packet from buffer 470 to the output, for retransmission.
  • the functions shown in figure 9 can be performed by processor 450 under the control of software, by hardware or by a combination of these.
  • the address store 467 can be implemented as a code stored in a non-volatile memory, by a code set by a DIL switch or some other appropriate manner.
  • Figure 10 shows an example of equipment provided at base station BS.
  • Communications signals at RF are received from power line coupling units at the power line drivers 500. These signals are fed to RF modems 510 which convert the signals between RF and base band.
  • Backhaul card 530 converts the data into a format for transmission over the backhaul network.
  • the digital interface card 520 manages the polling protocol on the distribution cables.
  • This card comprises a processor under software control, with a memory that stores a table of details for each subscriber station in the system. This table includes the following details for each subscriber station:
  • Figure 11 shows a flow chart of a method that the base station processor can perform in polling the subscriber stations.
  • the address of the next station is retrieved, together with the connection details for that station.
  • it is determined whether the station is reachable directly by inspecting the retrieved connection data. If the CPE is reachable directly, it is polled at step 610 and two tests are performed.
  • step 615 it is determined whether a reply has been received. If no response has been received, the processor waits a 'normal' time out period at step 620. This is the normal period expected for sending a polling packet and receiving a reply packet without the use of a repeater.
  • the CPE is polled via a suitable repeater, the repeater being determined by the stored details.
  • the same two tests are performed at steps 635 and 640 but there is a difference in that the time out period is extended to cover the time that it would normally take to send a polling packet and receive a reply via a repeater.

Abstract

La présente invention concerne un système de communication se basant sur les paquets, tel qu'un système de communication à ligne de puissance, qui utilise un répéteur pour atteindre des postes d'abonnés ne pouvant être directement atteints par un poste de base. Ledit répéteur est conçu pour recevoir un paquet dans un premier intervalle de temps et pour le retransmettre dans un intervalle de temps suivant, évitant ainsi la nécessité de réserver une partie de la bande de fréquence pour une utilisation par un répéteur à translation de fréquence. Ledit système peut être un système interrogé et le poste de base accorde le temps mis pour atteindre un poste d'abonné par le répéteur avant d'interroger un autre poste d'abonné.
PCT/GB2000/002667 1999-08-09 2000-07-10 Repeteur de paquets de donnees WO2001011799A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP00946091A EP1208656A1 (fr) 1999-08-09 2000-07-10 Repeteur de paquets de donnees
AU59978/00A AU5997800A (en) 1999-08-09 2000-07-10 Data packet repeater

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US37071799A 1999-08-09 1999-08-09
US09/370,717 1999-08-09

Publications (1)

Publication Number Publication Date
WO2001011799A1 true WO2001011799A1 (fr) 2001-02-15

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PCT/GB2000/002667 WO2001011799A1 (fr) 1999-08-09 2000-07-10 Repeteur de paquets de donnees

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EP (1) EP1208656A1 (fr)
AU (1) AU5997800A (fr)
WO (1) WO2001011799A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003030396A2 (fr) * 2001-09-27 2003-04-10 Siemens Aktiengesellschaft Procede pour faire fonctionner un systeme de transmission, et systeme de transmission dans un reseau d'alimentation electrique
WO2005116668A1 (fr) * 2004-05-25 2005-12-08 Enel Distribuzione S.P.A. Procede et appareil de detection d'une tension de phase inconnue par rapport a une tension de phase de reference

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4250489A (en) * 1978-10-31 1981-02-10 Westinghouse Electric Corp. Distribution network communication system having branch connected repeaters
US5617329A (en) * 1993-06-25 1997-04-01 Remote Metering Systems Ltd. Mains phase determination
EP0852419A2 (fr) * 1996-12-04 1998-07-08 Powercom Control Systems Ltd. Système pour gérer une alimentation en énergie électrique

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4250489A (en) * 1978-10-31 1981-02-10 Westinghouse Electric Corp. Distribution network communication system having branch connected repeaters
US5617329A (en) * 1993-06-25 1997-04-01 Remote Metering Systems Ltd. Mains phase determination
EP0852419A2 (fr) * 1996-12-04 1998-07-08 Powercom Control Systems Ltd. Système pour gérer une alimentation en énergie électrique

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003030396A2 (fr) * 2001-09-27 2003-04-10 Siemens Aktiengesellschaft Procede pour faire fonctionner un systeme de transmission, et systeme de transmission dans un reseau d'alimentation electrique
WO2003030396A3 (fr) * 2001-09-27 2003-08-07 Siemens Ag Procede pour faire fonctionner un systeme de transmission, et systeme de transmission dans un reseau d'alimentation electrique
WO2005116668A1 (fr) * 2004-05-25 2005-12-08 Enel Distribuzione S.P.A. Procede et appareil de detection d'une tension de phase inconnue par rapport a une tension de phase de reference
US8013592B2 (en) 2004-05-25 2011-09-06 Enel Distribuzione S.P.A. Method and apparatus for detecting the phase wiring of an arbitrary unknown phase voltage relative to a reference phase voltage
US8791688B2 (en) 2004-05-25 2014-07-29 Enel Distribuzione S.P.A. Method and apparatus for detecting the phase wiring of any arbitrary unknown phase voltage relative to a reference phase voltage

Also Published As

Publication number Publication date
EP1208656A1 (fr) 2002-05-29
AU5997800A (en) 2001-03-05

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