WO2013178237A1 - Communication node and method for self-organizing synchronization of a communication network - Google Patents

Communication node and method for self-organizing synchronization of a communication network Download PDF

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Publication number
WO2013178237A1
WO2013178237A1 PCT/EP2012/002320 EP2012002320W WO2013178237A1 WO 2013178237 A1 WO2013178237 A1 WO 2013178237A1 EP 2012002320 W EP2012002320 W EP 2012002320W WO 2013178237 A1 WO2013178237 A1 WO 2013178237A1
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WIPO (PCT)
Prior art keywords
oscillator
synchronization
communication
period
phase
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PCT/EP2012/002320
Other languages
French (fr)
Inventor
Marc TIMME
Christoph Kirst
Johannes KLINGLMAYR
Christian Bettstetter
Original Assignee
Max-Planck-Gesellschaft zur Förderung der Wissenschaften e. V.
Alpen-Adria-Universität Klagenfurt
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Priority to PCT/EP2012/002320 priority Critical patent/WO2013178237A1/en
Publication of WO2013178237A1 publication Critical patent/WO2013178237A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0676—Mutual
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/001—Synchronization between nodes
    • H04W56/002—Mutual synchronization

Definitions

  • the invention relates to a communication node for a communication network. Further, the invention relates to a communication network comprising several communication nodes. Moreover, the invention is directed to a method for synchronization of a communication node in a communication network.
  • communication networks comprising a plurality of intercon nected communication nodes (e.g. mobile phones, sensors, etc.), it is often necessary to ensure a synchronization of all communication nodes of the network in order to enable da ta communication between the communication nodes via the dat links between the communication nodes.
  • intercon nected communication nodes e.g. mobile phones, sensors, etc.
  • This synchronization can be achieved by a central control unit which generates a central clock signal which will be forwarded to the individual communication nodes.
  • This objective is achieved by a communication node and a method for synchronization according to the invention.
  • the invention provides a self-organized synchronization method which achieves a guaranteed synchronization for any pos sible network topologies of the communication network.
  • the communication node comprises an oscillator generating periodic synchronization pulses for synchronizing the communication nodes of the communication network, wherein the oscillator generates the syn chronization pulses by using a specific period and phase. Further, it should be noted that the synchronization pulses are generated with a specific probability in each period.
  • the communication node comprises a transmitter for transmitting the synchronization pulses to other communication nodes of the communication net work.
  • the communication node comprises a receiver for receiving synchronization pulses from other communication nodes of the communication network.
  • the invention is not restricted to a wireless communication between the individual communication nodes of the communication network. It is rather possible that the communication nodes are interconnected by wire connections.
  • the communication node comprises a synchronization unit for synchronizing the phase of the synchronization pulses generated by the oscillator and transmitted to other communication nodes with the phase of the synchronization pulses received from other communication nodes by adjusting the phase of the synchronization pulses generated by the oscillator upon receipt of a synchronization pulse from another communication node.
  • the synchronization unit adjusts the phase of the internal oscillator of the communication node upon receipt of a synchronization pulse from another communication node. In conventional synchronization methods, this phase adjustment made by the synchronization unit does not result in a guaranteed synchronization of the entire communication network for any possible network topologies of the communication network.
  • the synchronization unit adjusts the phase of the synchronization pulses generated by the os- cillator in such a way that a guaranteed network-wide syn- chronization of the oscillators is achieved for all communication nodes of the communication network for any possible network topologies of the communication network.
  • phase adjustment is made in such a way that a guaranteed network-wide synchronization is achieved for any possible initial states of the phases of the individual communication nodes of the communication network.
  • phase adjustment is made in such a way that a guaranteed network-wide synchronization is achieved for any possible transmission times of the synchronization pulses between the communication nodes provided that the transmission times do not exceed one eighth of the period of the oscillator.
  • the guaranteed synchronization is also achieved for transmission times which satisfy the following criteria:
  • the phase adjustment of the oscillator is made upon receipt of a synchronization pulse from another communication node, wherein the synchronization unit determines the relative position of the received synchronization pulse within the period of the oscillator and adjusts the phase of the oscillator by maintaining, advancing or retarding the phase of the oscillator depending on the position of the received synchronization pulse within the period of the oscillator.
  • the synchroni- zation unit selects one of three different synchronization actions (maintaining, advancing or retarding the phase) for synchronizing the oscillator with the oscillators of the oth er communication nodes.
  • the synchronization unit preferably divides the period of the oscillator into a refractory interval, an inhibitory interval and an excitatory interval, wherein these intervals are non-overlapping and cover the en tire period of the oscillator.
  • the synchronization unit preferably determines whether a synchronization pulse is received within the refractory interval, the inhibitory interval or within the excitatory interval of the oscillator. If a synchronization pulse from another communication node is received within the refractory interval, no phase adjustment is made. However, i a synchronization pulse from another communication node is received within the inhibitory interval of the oscillator, the phase of the oscillator is retarded, i.e. the phase of the oscillator is set to a new specific phase value, lower than the value before However, if a synchronization pulse from another communication node is received within the excitatory interval of the oscillator, the phase of the oscillator is advanced, i.e. the phase is set to a new specific phase value, higher than the value before.
  • the synchronization unit For retarding the phase of the oscillator, the synchronization unit preferably determines the adjusted phase of the o cillator according to a first adjustment function hi depend ing on the phase ⁇ of the oscillator at the time of receipt of a synchronization pulse from another communication node. If the period of the oscillator is normalized to a range be tween zero and one, the phase of the oscillator varies be- tween zero and one. In such a case, the first adjustment function hi preferably satisfies the following criteria:
  • the synchronization unit For advancing the phase of the oscillator, the synchronization unit preferably determines the adjusted phase of the oscillator according to a second adjustment function h2 depending on the phase ⁇ of the oscillator at the time of receipt of a synchronization pulse from another communication node. If the period of the oscillator is normalized to a range between zero and one, the phase of the oscillator varies between zero and one. In such a case, the second adjustment function h2 preferably satisfies the following criteria:
  • >) 1, if the synchronization pulse is received at the end of the excitatory interval of the period of the interval.
  • h2 ( ⁇ ) > 0.75, if the synchronization pulse is received at the beginning of the excitatory interval of the period of the oscillator .
  • the transmission times of the synchronization pulses between the communication nodes of the communication network statistically vary between a minimum transmission time ⁇ ⁇ ⁇ ⁇ and a maximum transmission time TMAX, wherein the minimum transmission time ⁇ ⁇ ⁇ ⁇ is ⁇ ⁇ ⁇ 0 and the maximum transmission time TMAX is preferably ⁇ 0.125 of the period of the synchronization signal generated by the oscillator .
  • the afore-mentioned adjustment functions hi and h2 preferably satisfy the following criteria:
  • the afore-mentioned refractory interval is preferably between The inhibitory interval pref ⁇ erably consists of two parts between
  • the synchronization pulses are generated and transmitted with a specific probability in each period, wherein the probability is preferably less than 1.
  • the probability is preferably less than 1.
  • the afore-mentioned probability is preferably in the range between 0.3 and 0.8, which ensures a fast synchronization of the entire communication network.
  • the communication network is preferably connected, i.e. each of the communication nodes of the communication network is connected with each other communication node either directly or indirectly by so-called multi-hop-connections.
  • each of the communication nodes of the communication network is connected with each other communication node either directly or indirectly by so-called multi-hop-connections.
  • it is not necessary that the communication network is constantly connected without any interruptions. It is rather possible that there are interruptions in which no communication between the communication nodes is possible.
  • the communication network is preferably undirected, i.e. it allows a bidirectional communication via the communication links between the communication nodes.
  • the transmission times of the synchronization pulses between the communication nodes of the communication network are not greater than one eight of the period of the synchronization pulses. This allows a guaranteed self-synchronization of the entire network.
  • both the first and second adjustment functions hi and h2 are mathematically smooth and satisfy the following criteria: dhl/d ⁇
  • the communication node according to the invention can be a cell phone, while the communication network according to the invention is a cellular telephone network.
  • the self-organization of the entire cellular telephone network allows a data communication within the cellular telephone network using data slots .
  • Another example of a communication node of the invention is sensor for measuring a measured variable, wherein the communication nodes transmit the measured variable to an evaluation unit.
  • the synchronization of the individual sensors ensures a synchronized measurement of the measured variables by the individual sensors.
  • the communication nodes can be arranged in moveable units, for example in vehicles, planes, drones, nano-robots or space crafts, which execute individual movements, wherein the synchronization of the communication nodes ensures that the motions of the moveable units are coordinated.
  • the invention is not restricted to the afore-mentioned communication node as a single component.
  • the invention rather claims protection for an entire communication network comprising a plurality of these communication nodes, wherein the communication nodes are intercon nected with each other according to a specific network topol ogy.
  • the network topology of the communication network can be, fo example, star-shaped, ring-shaped, tree-shaped or linear.
  • Figure 1 schematically shows a communication network comprising a plurality of communication nodes interconnected by communication links .
  • Figure 2 shows a schematic diagram of a communication node according to the invention.
  • Figure 3A shows adjustment functions for adjusting the phase of the individual communication node for synchronization of the communication network.
  • Figure 3B shows alternative examples for these adjustment functions.
  • Figures 4A and 4B illustrate the synchronization method of the invention in the form of a flow chart.
  • FIG. 5A illustrates the phase of the oscillator
  • a synchronisation pulse is received in refractory interval.
  • Figure 5B shows the phase of the oscillator if a syn- chronization pulse is received in the in- hibitory interval.
  • Figure 5C shows the phase of the oscillator if a synchronization pulse is received in the excitatory interval.
  • Figure 1 schematically shows a communication network 1 comprising a plurality of individual communication nodes 2 interconnected by communication links 3 so that each of the communication nodes 2 is connected to each of the other communication nodes 2 either directly or indirectly by so-called multi-hop-connections.
  • the communication network 1 is a connected and directed network with a specific topology, wherein the network topology of the communication network 1 can be arbitrary.
  • the invention assures a self-organized synchronization of the communication nodes 2 of the communication network 1 without any central control unit providing a central clock signal.
  • Figure 2 shows a schematic diagram of one of the communication nodes 2 which is in connection with the communication network 1.
  • the communication node 2 comprises an oscillator 4 which generates periodic synchronization pulses for synchronizing the communication nodes 2 of the communication network 1.
  • all communication nodes 2 of the communication network 1 comprise such an oscillator 4 generating a synchronization pulse, wherein the period of all the oscillators 4 is identical while the phase of the oscillators 4 of the individual communication nodes 2 of the communication network 1 can be different in an initial state before synchronization .
  • the communication node 2 comprises a transmitter 5 for transmitting the synchronization pulses generated by the oscillator 4 to the other communication nodes 2 of the communication network via the communication links 3.
  • the communication node 2 comprises a receiver 6 for receiving synchronization pulses from other communication nodes 2 of the communication network 1 via the communication links 3.
  • the communication node 2 comprises a synchronization unit 7 for synchronizing the phase of the oscillator 4 with the phase of the other communication nodes 2 of the communication network 1.
  • the synchronization unit 7 determines a minimum transmission time ⁇ ⁇ and a maximum transmission time TMAX of the synchronization pulses between the individual communication nodes 2 of the communication network 1. It should be noted that the transmission time of the synchronization pulses between the individual communication nodes 2 of the communication network 1 depends on the distance between the transmitting communication node and the receiving communication node and also on the properties of the communication link 3 between these communication nodes and on the internal processing time. Therefore, the transmission time of the synchronization pulses statistically varies between the minimum transmission time T M IN and the maximum transmission time TMAX. The values of the minimum transmission time ⁇ ⁇ and the maxi- mum transmission time TMA can be predetermined and stored in the synchronization unit 7.
  • a second step S2 adjustment functions hi ( ⁇ ) und h2 ( ⁇ ) are determined for making the phase adjustment of the phase of the oscillator 4 by the synchronization unit 7. Examples of these adjustment functions hi and h2 are shown in Figures 3A and 3B. However, it should be noted that the invention is not restricted to the adjustment functions hi, h2 shown in Figure 3A and 3B. However, the adjustment functions hi, h2 must satisfy the following criteria:
  • the adjustment functions hi, h2 must be mathematically smooth .
  • the excitatory interval is defined as follows :
  • synchronization pulses are generated by the oscillator 4 with a specific period, phase and probability in each period, wherein the synchronization pulses are transmitted to other communication nodes 2 of the communication network 1 via the communication links 3.
  • the receiver 6 also checks whether any synchronization pulses are received from other communication nodes 2 of the communication network 1 (step S10).
  • the synchronization unit 7 checks whether the synchronization pulse is received within the inhibitory interval (Sll).
  • the synchronization phase retards the phase ⁇ of the oscillator 4 as follows (step S12) :
  • the synchronization unit 7 checks whether the syn- chronization pulse is received within the excitatory interval (step S13) . If so, the synchronization unit 7 advances the phase of the oscillator 4 as follows (step S14):
  • the synchronization pulse has been received in the refractory interval so that the synchronization unit does not adjust the phase of the oscillator 4 (step S15) .
  • the afore-mentioned synchronization method ensures a synchronization of all the communication nodes 2 of the communication network 1 for any possible network topologies.
  • Figure 5A shows the phase adjustment if the synchronization pulse is received in the refractory interval of the oscillator 4. The drawing clearly shows that no phase adjustment is made in such a case.
  • Figure 5B shows the phase adjustment if the synchronization pulse is received within the inhibitory interval of the oscillator 4. In such a case, the phase of the oscillator 4 is retarded.
  • Figure 5C shows the phase adjustment if a synchronization pulse is received within the excitatory interval of the oscillator 4. In such a case, the phase of the oscillator 4 is advanced.

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Abstract

The invention relates to a communication node (2) for a communication network (1) comprising a plurality of interconnected communication nodes (2), said communication node (2) comprising: an oscillator (4) generating periodic synchronization pulses for synchronizing the communication nodes (2); a transmitter (5) for transmitting the synchronization pulses; a receiver (6) for receiving synchronization pulses from other communication nodes (2); a synchronization unit (7) for synchronizing the phase oscillator (4), wherein the synchronization unit (7) adjusts the phase of the oscillator (4) in such a way that a guaranteed network-wide synchronization of the oscillators is achieved for all communication nodes (2) of the communication network (1) for any possible network topologies, initial states and transmission times of the communication network (1). Further, the invention relates to a corresponding method.

Description

Description
Communication node and method for self-organizing synchronization of a communication network
Field of the invention
The invention relates to a communication node for a communication network. Further, the invention relates to a communication network comprising several communication nodes. Moreover, the invention is directed to a method for synchronization of a communication node in a communication network.
Background of the invention
In communication networks comprising a plurality of intercon nected communication nodes (e.g. mobile phones, sensors, etc.), it is often necessary to ensure a synchronization of all communication nodes of the network in order to enable da ta communication between the communication nodes via the dat links between the communication nodes.
This synchronization can be achieved by a central control unit which generates a central clock signal which will be forwarded to the individual communication nodes.
However, if there is no such central control unit, synchroni zation is to be achieved in a distributed self-organized way Typically, knowledge on whether or not self-organized syn¬ chronization can be achieved in a realistic setting, so far relies on numerical simulations of hand-picked examples of network topologies. Therefore, it cannot be guaranteed that the conventional synchronization methods actually work with arbitrary network topologies. However, it is desirable to provide a synchronization method which achieves a guaranteed self-organized synchronization for communication networks re gardless of the network topology of the communication network.
Summary of the invention
This objective is achieved by a communication node and a method for synchronization according to the invention.
The invention provides a self-organized synchronization method which achieves a guaranteed synchronization for any pos sible network topologies of the communication network.
Firstly, the communication node according to the invention comprises an oscillator generating periodic synchronization pulses for synchronizing the communication nodes of the communication network, wherein the oscillator generates the syn chronization pulses by using a specific period and phase. Further, it should be noted that the synchronization pulses are generated with a specific probability in each period.
Further, the communication node according to the invention comprises a transmitter for transmitting the synchronization pulses to other communication nodes of the communication net work.
Moreover, the communication node according to the invention comprises a receiver for receiving synchronization pulses from other communication nodes of the communication network. In this connection, it should be noted that the invention is not restricted to a wireless communication between the individual communication nodes of the communication network. It is rather possible that the communication nodes are interconnected by wire connections.
It should further be noted that there are specific transmission times between the transmission of one of the synchronization pulses by one of the communication nodes and the following receipt of said synchronization pulse by another one of the communication nodes of the communication network. Thi is important since the transmission times of the synchroniza tion pulses affect the synchronization of the individual com munication nodes, which will be described in detail later.
Further, the communication node according to the invention comprises a synchronization unit for synchronizing the phase of the synchronization pulses generated by the oscillator and transmitted to other communication nodes with the phase of the synchronization pulses received from other communication nodes by adjusting the phase of the synchronization pulses generated by the oscillator upon receipt of a synchronization pulse from another communication node. In other words, the synchronization unit adjusts the phase of the internal oscillator of the communication node upon receipt of a synchronization pulse from another communication node. In conventional synchronization methods, this phase adjustment made by the synchronization unit does not result in a guaranteed synchronization of the entire communication network for any possible network topologies of the communication network.
According to the invention, the synchronization unit adjusts the phase of the synchronization pulses generated by the os- cillator in such a way that a guaranteed network-wide syn- chronization of the oscillators is achieved for all communication nodes of the communication network for any possible network topologies of the communication network.
Further, the phase adjustment is made in such a way that a guaranteed network-wide synchronization is achieved for any possible initial states of the phases of the individual communication nodes of the communication network.
Finally, the phase adjustment is made in such a way that a guaranteed network-wide synchronization is achieved for any possible transmission times of the synchronization pulses between the communication nodes provided that the transmission times do not exceed one eighth of the period of the oscillator. However, the guaranteed synchronization is also achieved for transmission times which satisfy the following criteria:
TWIN mod T > 0
TMAX mod T < 0.125 · T with
T Period of the oscillator,
TMAX Maximum transmission time of the oscillator,
τΜΙΝ Maximum transmission time of the oscillator.
In a preferred embodiment of the invention, the phase adjustment of the oscillator is made upon receipt of a synchronization pulse from another communication node, wherein the synchronization unit determines the relative position of the received synchronization pulse within the period of the oscillator and adjusts the phase of the oscillator by maintaining, advancing or retarding the phase of the oscillator depending on the position of the received synchronization pulse within the period of the oscillator. In other words, the synchroni- zation unit selects one of three different synchronization actions (maintaining, advancing or retarding the phase) for synchronizing the oscillator with the oscillators of the oth er communication nodes.
In this embodiment, the synchronization unit preferably divides the period of the oscillator into a refractory interval, an inhibitory interval and an excitatory interval, wherein these intervals are non-overlapping and cover the en tire period of the oscillator.
Further, the synchronization unit preferably determines whether a synchronization pulse is received within the refractory interval, the inhibitory interval or within the excitatory interval of the oscillator. If a synchronization pulse from another communication node is received within the refractory interval, no phase adjustment is made. However, i a synchronization pulse from another communication node is received within the inhibitory interval of the oscillator, the phase of the oscillator is retarded, i.e. the phase of the oscillator is set to a new specific phase value, lower than the value before However, if a synchronization pulse from another communication node is received within the excitatory interval of the oscillator, the phase of the oscillator is advanced, i.e. the phase is set to a new specific phase value, higher than the value before.
For retarding the phase of the oscillator, the synchronization unit preferably determines the adjusted phase of the o cillator according to a first adjustment function hi depend ing on the phase ψ of the oscillator at the time of receipt of a synchronization pulse from another communication node. If the period of the oscillator is normalized to a range be tween zero and one, the phase of the oscillator varies be- tween zero and one. In such a case, the first adjustment function hi preferably satisfies the following criteria:
hl(<J>)=(j), if the synchronization pulse is received at the beginning of the inhibitory interval of the period of the oscillator .
hi ( φ ) <0.25, if the synchronization pulse is received at the end of the inhibitory interval of the period of the oscillator .
For advancing the phase of the oscillator, the synchronization unit preferably determines the adjusted phase of the oscillator according to a second adjustment function h2 depending on the phase φ of the oscillator at the time of receipt of a synchronization pulse from another communication node. If the period of the oscillator is normalized to a range between zero and one, the phase of the oscillator varies between zero and one. In such a case, the second adjustment function h2 preferably satisfies the following criteria:
h2((|>)= 1, if the synchronization pulse is received at the end of the excitatory interval of the period of the interval. h2 ( φ ) >=0.75, if the synchronization pulse is received at the beginning of the excitatory interval of the period of the oscillator .
In a realistic environment, the transmission times of the synchronization pulses between the communication nodes of the communication network statistically vary between a minimum transmission time τΜιΝ and a maximum transmission time TMAX, wherein the minimum transmission time τΜιΝ is τΜΙΝ≥0 and the maximum transmission time TMAX is preferably τΜΑχ<0.125 of the period of the synchronization signal generated by the oscillator . Further, the afore-mentioned adjustment functions hi and h2 preferably satisfy the following criteria:
hi ( φ ) <0.25-TMAX-TMIN, if the synchronization pulse is re¬ ceived at the end of the inhibitory interval of the period of the oscillator.
h2 ( φ ) >0.75+TMAX_TMIN/ if the synchronization pulse is re¬ ceived at the beginning of the excitatory interval of the period of the oscillator. Moreover, the afore-mentioned refractory interval is preferably between
Figure imgf000009_0001
The inhibitory interval pref¬ erably consists of two parts between
Figure imgf000009_0002
and between φ=ξ with h2 {ξ) =1 and φ=1. The excitatory interval preferably consists of two parts wherein the first part of the excitatory interval is between
Figure imgf000009_0003
and φ=ξ, while the second part of the excitatory interval is between φ=0 and
It has already been mentioned that the synchronization pulses are generated and transmitted with a specific probability in each period, wherein the probability is preferably less than 1. In other words, there are at least from time to time periods of the oscillator in which no synchronization pulse is generated and transmitted to other communication nodes of the communication network. The afore-mentioned probability is preferably in the range between 0.3 and 0.8, which ensures a fast synchronization of the entire communication network.
It should further be noted that the communication network is preferably connected, i.e. each of the communication nodes of the communication network is connected with each other communication node either directly or indirectly by so-called multi-hop-connections. However, it should be noted that it is not necessary that the communication network is constantly connected without any interruptions. It is rather possible that there are interruptions in which no communication between the communication nodes is possible.
Moreover, it has to be mentioned that the communication network is preferably undirected, i.e. it allows a bidirectional communication via the communication links between the communication nodes.
However, it should be noted that this is not necessary, the guaranteed synchronization still holds if the network is directed and it is possible to finde one entity in the network that can send pulses to any other entity in the network either directly or indirectly, via multi-hop-connections.
Further, it should be noted that the transmission times of the synchronization pulses between the communication nodes of the communication network are not greater than one eight of the period of the synchronization pulses. This allows a guaranteed self-synchronization of the entire network.
Moreover, it should be noted that preferably both the first and second adjustment functions hi and h2 are mathematically smooth and satisfy the following criteria: dhl/d<|) > 0 dh2/d<|> > 0.
Is has already been mentioned that the communication node according to the invention can be a cell phone, while the communication network according to the invention is a cellular telephone network. In such a case, the self-organization of the entire cellular telephone network allows a data communication within the cellular telephone network using data slots .
Another example of a communication node of the invention is sensor for measuring a measured variable, wherein the communication nodes transmit the measured variable to an evaluation unit. In such a case, the synchronization of the individual sensors ensures a synchronized measurement of the measured variables by the individual sensors.
Further, the communication nodes can be arranged in moveable units, for example in vehicles, planes, drones, nano-robots or space crafts, which execute individual movements, wherein the synchronization of the communication nodes ensures that the motions of the moveable units are coordinated.
It has to be mentioned that the invention is not restricted to the afore-mentioned communication node as a single component. The invention rather claims protection for an entire communication network comprising a plurality of these communication nodes, wherein the communication nodes are intercon nected with each other according to a specific network topol ogy.
The network topology of the communication network can be, fo example, star-shaped, ring-shaped, tree-shaped or linear.
Further, the invention also claims protection for a method for synchronization of a communication node in a communication network, wherein the method has already been described above . The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.
Brief description of the drawings:
Figure 1 schematically shows a communication network comprising a plurality of communication nodes interconnected by communication links .
Figure 2 shows a schematic diagram of a communication node according to the invention.
Figure 3A shows adjustment functions for adjusting the phase of the individual communication node for synchronization of the communication network.
Figure 3B shows alternative examples for these adjustment functions.
Figures 4A and 4B illustrate the synchronization method of the invention in the form of a flow chart.
Figure 5A illustrates the phase of the oscillator
a synchronisation pulse is received in refractory interval.
Figure 5B shows the phase of the oscillator if a syn- chronization pulse is received in the in- hibitory interval. Figure 5C shows the phase of the oscillator if a synchronization pulse is received in the excitatory interval.
Detailed description of the drawings
Figure 1 schematically shows a communication network 1 comprising a plurality of individual communication nodes 2 interconnected by communication links 3 so that each of the communication nodes 2 is connected to each of the other communication nodes 2 either directly or indirectly by so-called multi-hop-connections. In other words, the communication network 1 is a connected and directed network with a specific topology, wherein the network topology of the communication network 1 can be arbitrary.
The invention assures a self-organized synchronization of the communication nodes 2 of the communication network 1 without any central control unit providing a central clock signal.
Figure 2 shows a schematic diagram of one of the communication nodes 2 which is in connection with the communication network 1.
Firstly, the communication node 2 comprises an oscillator 4 which generates periodic synchronization pulses for synchronizing the communication nodes 2 of the communication network 1. It should be noted that all communication nodes 2 of the communication network 1 comprise such an oscillator 4 generating a synchronization pulse, wherein the period of all the oscillators 4 is identical while the phase of the oscillators 4 of the individual communication nodes 2 of the communication network 1 can be different in an initial state before synchronization . Further, the communication node 2 comprises a transmitter 5 for transmitting the synchronization pulses generated by the oscillator 4 to the other communication nodes 2 of the communication network via the communication links 3.
Moreover, the communication node 2 comprises a receiver 6 for receiving synchronization pulses from other communication nodes 2 of the communication network 1 via the communication links 3.
Finally, the communication node 2 comprises a synchronization unit 7 for synchronizing the phase of the oscillator 4 with the phase of the other communication nodes 2 of the communication network 1.
In the following, the synchronization method according to the invention is described referring to the flow chart shown in Figures 4A and 4B.
In a first step SI, the synchronization unit 7 determines a minimum transmission time τΜΙΝ and a maximum transmission time TMAX of the synchronization pulses between the individual communication nodes 2 of the communication network 1. It should be noted that the transmission time of the synchronization pulses between the individual communication nodes 2 of the communication network 1 depends on the distance between the transmitting communication node and the receiving communication node and also on the properties of the communication link 3 between these communication nodes and on the internal processing time. Therefore, the transmission time of the synchronization pulses statistically varies between the minimum transmission time TMIN and the maximum transmission time TMAX. The values of the minimum transmission time τΜΙΝ and the maxi- mum transmission time TMA can be predetermined and stored in the synchronization unit 7.
In a second step S2, adjustment functions hi ( φ ) und h2 ( φ ) are determined for making the phase adjustment of the phase of the oscillator 4 by the synchronization unit 7. Examples of these adjustment functions hi and h2 are shown in Figures 3A and 3B. However, it should be noted that the invention is not restricted to the adjustment functions hi, h2 shown in Figure 3A and 3B. However, the adjustment functions hi, h2 must satisfy the following criteria:
The adjustment functions hi, h2 must be mathematically smooth .
dhl/d(|> > 0
- dh2/d(|> > 0
hi ( 0.5+τΜιΝ) <0.25-TMAX
- h2 ( 0.5+TMIN ) >0.75+TMAX—TMIN
h2 ( φ ) >φ for φ€ [0, τΜΙΝ ]
1ι2(ξ)=1
- hi ( φ ) >0 for φ€ [ξ, 1] .
In another step S3, the afore-mentioned boundary ξ between the excitatory interval and the inhibitory interval is deter¬ mined as follows: ξ=φ for h2 ( φ ) =1.
In a next step S4, the so-called refractory interval is de¬ fined as follows:
Τ ΙΝ≤Φ<ΤΜΙ +ΤΜΑΧ In a next step S5, the so-called inhibitory interval is defined as follows:
ΤΜΙΝ+ΤΜΑΧ ≤φ<0.5+τΜΙΝ ξ<φ<1
In another step S6, the excitatory interval is defined as follows :
Figure imgf000016_0001
In the following steps S7-S9, synchronization pulses are generated by the oscillator 4 with a specific period, phase and probability in each period, wherein the synchronization pulses are transmitted to other communication nodes 2 of the communication network 1 via the communication links 3. In an endless loop, the receiver 6 also checks whether any synchronization pulses are received from other communication nodes 2 of the communication network 1 (step S10).
If a synchronization pulse is received by the receiver 6, the synchronization unit 7 checks whether the synchronization pulse is received within the inhibitory interval (Sll).
If so, the synchronization phase retards the phase φ of the oscillator 4 as follows (step S12) :
Figure imgf000016_0002
Otherwise, the synchronization unit 7 checks whether the syn- chronization pulse is received within the excitatory interval (step S13) . If so, the synchronization unit 7 advances the phase of the oscillator 4 as follows (step S14):
†NEw=h2 ((|>OLD)
Otherwise, the synchronization pulse has been received in the refractory interval so that the synchronization unit does not adjust the phase of the oscillator 4 (step S15) .
The afore-mentioned synchronization method ensures a synchronization of all the communication nodes 2 of the communication network 1 for any possible network topologies.
Figure 5A shows the phase adjustment if the synchronization pulse is received in the refractory interval of the oscillator 4. The drawing clearly shows that no phase adjustment is made in such a case.
Figure 5B shows the phase adjustment if the synchronization pulse is received within the inhibitory interval of the oscillator 4. In such a case, the phase of the oscillator 4 is retarded.
Finally, Figure 5C shows the phase adjustment if a synchronization pulse is received within the excitatory interval of the oscillator 4. In such a case, the phase of the oscillator 4 is advanced.
A variety of modifications and alternatives of the invention is possible without departing the scope of protection as defined in the claims. Further, it should be noted that the application also claims protection for the subject-matter and the features of the dependent claims without the features of the preceding claims .
List of reference numerals
1 Communication network
2 Communication node
3 Communication link
4 Oscillator
5 Transmitter
6 Receiver
7 Synchronization unit
TMIN Minimum transmission
ΈΜΑΧ Maximum transmission ■ hi Adjustment function h2 Adjustment function

Claims

Claims
1. Communication node (2) for a communication network (1) comprising a plurality of interconnected communication nodes (2), said communication node (2) comprising:
a) an oscillator (4) generating periodic synchronization pulses for synchronizing the communication nodes (2) of the communication network (1), wherein the oscillator (4) generates the synchronization pulses with a specific period and phase and with a specific probability in each period,
b) a transmitter (5) for transmitting the synchronization pulses to other communication nodes (2) of the communication network (1),
c) a receiver (6) for receiving synchronization pulses
from other communication nodes (2) of the communication network ( 1 ) ,
d) wherein there are specific transmission times between the transmission of one of the synchronization pulses by one of the communication nodes (2) and the following receipt of said synchronization pulse by another one of the communications nodes (2) of the communication network ( 1 ) ,
e) a synchronization unit (7) for synchronizing the phase of the synchronization pulses generated by the oscilla¬ tor (4) and transmitted to other communication nodes (2) with the phase of the synchronization pulses re¬ ceived from other communication nodes (2) by adjusting the phase of the synchronization pulses generated by the oscillator (4) upon receipt of a synchronization pulse from another communication node (2),
characterized in that f) the synchronization unit (7) adjusts the phase of the synchronization pulses generated by the oscillator (4) in such a way that a guaranteed network-wide synchronization of the oscillators is achieved for all communication nodes (2) of the communication network (1) fl) for any possible network topologies of the communication network (1), and
f2) for any possible transmission times of the synchronization pulses between the communication nodes (2) of the communication network (1) provided that the transmission times do not exceed one eighth of the period of the oscillator, and f3) for any possible initial states of the phases of the communication nodes (2) of the communication network ( 1 ) .
2. Communication node (2) according to claim 1, wherein upon receipt of a synchronization pulse from another communication node (2), the synchronization unit (7)
a) determines the relative position of the received synchronization pulse within the period of the oscillator (4), and
b) adjusts the phase of the oscillator (4) by maintaining, advancing or retarding the phase of the oscillator (4) depending on the position of the received synchronization pulse within the period of the oscillator (4).
3. Communication node (2) according to claim 2, wherein a) the synchronization unit (7) divides the period of the oscillator (4) into the following non-overlapping intervals :
al) a refractory interval,
a2) an inhibitory interval, and
a3) an excitatory interval, and b) the synchronization unit (7) determines whether a synchronization pulse is received
bl) in the refractory interval,
b2) in the inhibitory interval or
b3) in the excitatory interval, and
c) upon receipt of a synchronization pulse, the synchronization unit (7)
cl) maintains the phase of the oscillator (4) unchanged if the synchronization pulse is received in the refractory period of the oscillator (4), c2) retards the phase of the oscillator (4) if the synchronization pulse is received in the inhibitory interval of the oscillator (4), c3) advances the phase of the oscillator (4) if synchronization pulse is received in the excitatory interval of the oscillator (4) .
4. Communication node (2) according to claim 3, wherein for retarding the phase of the oscillator (4), the synchroniza- tion unit (7) determines the adjusted phase of the oscillator (4) according to a first adjustment function hi depending on the phase φ of the oscillator (4) at the time of receipt of the synchronization pulse, with:
a) [0,1] is the period of the oscillator (4),
b) φ£[0,1] is the phase of the oscillator (4),
c) hi (φ) is the first adjustment function,
d) hl((|>)=(|), if the synchronization pulse is received at the beginning of the inhibitory interval of the period of the oscillator (4), and
e) hl(<(>)<0.25, if the synchronization pulse is received at the end of the inhibitory interval of the period of the oscillator (4) .
5. Communication node (2) according to claim 3 or 4, wherein for advancing the phase of the oscillator (4), the synchronization unit (7) determines the adjusted phase of the oscillator (4) according to a second adjustment function h2 depending on the phase φ of the oscillator (4) at the time of receipt of the synchronization pulse, with
a) [0,1] is the period of the oscillator (4),
b) φ e [0, 1] is the phase of the oscillator (4),
c) h2 (φ) is the second adjustment function,
d) h2((j))=l, if the synchronization pulse is received at the end of the excitatory interval of the period of the oscillator ( 4 ) ,
e) h2 (φ) >0.75, if the synchronization pulse is received at the beginning of the excitatory interval of the period of the oscillator (4) .
6. Communication node (2) according to claims 4 and 5,
wherein
a) the transmission times of the synchronization pulses between the communication nodes (2) of the communication network (1) statistically vary between a minimum transmission time τΜιΝ and a maximum transmission time fMAX and
b) the minimum transmission time TMIN is τΜΙΝ>0, and
c) the maximum transmission time TMAX is XMAX<0.125 of the period of the synchronization signal generated by the oscillator ( 4 ) .
7. Communication node (2) according to any of claims 4 to 6, wherein
a) the transmission times of the synchronization pulses statistically vary between a minimum transmission time xMIN and a maximum transmission time TMAX, and b) hi ( φ ) =0.25-τΜΑΧ-τΜΙ Ν , if the synchronization pulse is received at the end of the inhibitory interval of the pe riod of the oscillator (4), and
c) h2 ( φ )
Figure imgf000024_0001
if the synchronization pulse is received at the beginning of the excitatory interval of the period of oscillator (4) .
Communication node (2) according to any of claims 4 to wherein
the transmission times of the synchronization pulses statistically vary between a minimum transmission time τΜΐ and a maximum transmission time
Figure imgf000024_0002
the refractory interval of the period of the oscillato (4) is between
Figure imgf000024_0003
the inhibitory interval of the period of the oscillato (4) is between
Figure imgf000024_0004
and φ=1, with _ι2(ξ)=1,
the excitatory interval of the period of the oscillato and φ=ξ and between φ=0 and
Figure imgf000024_0005
9. Communication node (2) according to any of the preceding claims, wherein
a) in each period of the oscillator (4), one of the synchronization pulses is transmitted with the specific probability of less than 1, and/or
b) the probability is in the range between 0.3 and 0.8, and/or
c) the communication network (1) is connected and the topology of the communication network (1) is undirected, and/or
d) the communication network (1) has at least one communi cation node (2) with direct or indirect communication paths to all other communication nodes (2) of the communication network (1), and/or
e) the transmission times of the synchronization pulses between the communication nodes (2) of the communication network (1) are not greater than one eighth of the period of the synchronization pulses, and/or
f) the communication network (1) gets disconnected from time to time.
10. Communication nodes (2) according to any of claims 4 to 9, wherein
a) the first adjustment function hi is mathematically
smooth, and
b) the second adjustment function h2 is mathematically
smooth, and
c) the first adjustment function hi satisfies dhl/d<|»0, and
d) the second adjustment function h2 satisfies dh2/d(|)>0.
11. Communication node (2) according to any of the preceding claims, wherein the communication node (2) is a cell phone and the communication network (1) is a cellular telephone network .
12. Communication network (1) comprising a plurality of the communication nodes (2) according to any of the preceding claims, wherein the communication nodes (2) are interconnected with each other according to a specific network topology.
13. Communication network (1) according to claim 11, wherein the network topology of the communication network (1) is
a) star-shaped, b) ring-shaped,
c) tree-shaped or
d) linear
14. Communication network (1) according to claim 12 or 13, wherein
a) the communication nodes (2) include a sensor for measuring a measured variable,
b) the communication nodes (2) transmit the measured variable to an evaluation unit,
c) the synchronization of the communication nodes (2) ensures a synchronized measurement of the measured vari^ ables by the individual communication nodes (2) .
15. Communication network (1) according to claim 14 or 15, wherein
a) the communication nodes (2) are arranged in moveable units, particularly vehicles, planes, drones, nano- robots or spacecrafts,
b) the communication nodes (2) execute a movement,
c) wherein the synchronization of the communication nodes
(2) ensures that the motions of the communications are coordinated .
16. Method for synchronization of a communication node (2) in a communication network (1) comprising a plurality of interconnected communication nodes (2), said method comprising the following steps:
a) generating periodic synchronization pulses for synchronizing the communication nodes (2) of the communication network (1), wherein the synchronization pulses are generated in the communication node (2) by an oscillator (4) with a specific period and phase and with a specific probability in each period, b) transmitting the synchronization pulses to other communication nodes (2) of the communication network (1), c) receiving synchronization pulses from other communication nodes (2) of the communication network (1), d) wherein there are specific transmission times between the transmission of one of the synchronization pulses by one of the communication nodes (2) and the following receipt of said synchronization pulse by another one of the communications nodes (2) of the communication network ( 1 ) ,
e) synchronizing the phase of the synchronization pulses transmitted to other communication nodes (2) with the phase of the synchronization pulses received from other communication nodes (2) by adjusting the phase of the oscillators generated by the oscillator (4) upon receipt of a synchronization pulse from another communication node (2 ) ,
characterized in that
f) the phase of the synchronization pulses generated by the oscillator (4) is adjusted in such a way that a guaranteed network-wide synchronization of the synchronization signals is achieved for all communication nodes (2) of the communication network (1)
fl) for any possible network topologies of the communication network, and
f2) for any possible transmission times of the synchronization pulses between the communication nodes (2) of the communication network (1) provided that the transmission times do not exceed one eighth of the period of the oscillator, and f3) for any possible initial states of the phases of the communication nodes (2) .
17. Method according to claim 16, wherein the following steps are carried out upon receipt of a synchronization pulse from another communication node (2):
a) determining the relative position of the received synchronization pulse within the period of the oscillator (4), and
b) adjustment of the phase of the oscillator (4) by maintaining, advancing or retarding the phase of the oscillator (4) depending on the position of the received synchronization pulse within the period of the oscillator (4) .
18. Method according to claim 17, further comprising the following steps:
a) Dividing the period of the oscillator (4) into the following non-overlapping intervals:
al) a refractory interval,
a2) an inhibitory interval, and
a3) an excitatory interval, and
b) Determining whether a synchronization pulse is received bl) in the refractory interval,
b2 ) in the inhibitory interval or
b3) in the excitatory interval, and
c) upon receipt of a synchronization pulse,
cl) maintaining the phase of the oscillator (4) unchanged if the synchronization pulse is received in the refractory period of the oscillator (4), c2) retarding the phase of the oscillator (4) if the synchronization pulse is received in the inhibitory interval of the oscillator (4), c3) advancing the phase of the oscillator (4) if synchronization pulse is received in the excitatory interval of the oscillator (4).
19. Method according to claim 18, wherein for retarding the phase of the oscillator (4), the adjusted phase of the oscillator (4) is determined according to a first adjustment function hi depending on the phase φ of the oscillator (4) at the time of receipt of the synchronization pulse, with
a) [0,1] is the period of the oscillator (4)
b) φε[0,1] is the phase of the oscillator (4)
c) hi (φ) is the first adjustment function
d) 1ι1(φ)=φ, if the synchronization pulse is received at the beginning of the inhibitory interval of the period of the oscillator (4),
e) hl^)<0.25, if the synchronization pulse is received at the end of the inhibitory interval of the period of the oscillator ( 4 ) .
20. Method according to claim 18 or 19, wherein for advancing the phase of the oscillator (4), the adjusted phase of the oscillator (4) is determined according to a second ad¬ justment function h2 depending on the phase φ of the oscilla- tor (4) at the time of receipt of the synchronization pulse, with
a) [0,1] is the period of the oscillator (4)
b) φ e[0,l] is the phase of the oscillator (4)
c) h2 (φ) is the second adjustment function
d) 1ι2(φ)=1, if the synchronization pulse is received at the end of the excitatory interval of the period of the oscillator ( 4 ) ,
e) η2(φ)>0.75, if the synchronization pulse is received at the beginning of the excitatory interval of the period of the oscillator (4) .
21. Method according to claims 19 and 20, wherein a) the transmission times of the synchronization pulses between the communication nodes (2) of the communication network statistically vary between a minimum transmission time TMIN and a maximum transmission time XMAX, and/or
b) the minimum transmission time τΜιΝ is τΜιΝ>0,
c) the maximum transmission time TMAX is TMAX<0.125 of the period of the synchronization pulses.
22. Method according to any of claims 19 to 21, wherein a) the transmission times of the synchronization pulses statistically vary between a minimum transmission time TMIN and a maximum transmission time XMAX, and/or
b) hi (φ)
Figure imgf000030_0001
if the synchronization pulse is re¬ ceived at the beginning of the inhibitory interval of the period of the oscillator (4), and/or
c) h2 (φ)
Figure imgf000030_0002
if the synchronization pulse is received at the beginning of the excitatory interval of the period of oscillator (4).
23. Method according to any of claims 19 to 22, wherein a) the transmission times of the synchronization pulses statistically vary between a minimum transmission time τΜιΝ and a maximum transmission time TMAX,
b) the refractory interval of the period of the oscillator
(4) is between
Figure imgf000030_0003
c) the inhibitory interval of the period of the oscillator
(4) is between
Figure imgf000030_0004
and φ=1, with h2 (ξ) =1,
d) the excitatory interval of the period of the oscillator
(4) is between
Figure imgf000030_0005
and between φ=0 and with h2 (ξ) =1.
24. Method according to any of claims 16 to 23, wherein a) in each period of the oscillator (4), one of the synchronization pulses is transmitted with the specific probability of less than 1, and/or
b) the probability is in the range between 0.3 and 0.8, and/or
c) the communication network (1) is connected and the topology of the communication network (1) is undirected, and/or
d) the communication network (1) has at least one communication node (2) with direct or indirect communication paths to all other communication nodes (2) of the communication network (1), and/or
e) the transmission times of the synchronization pulses between the communication nodes (2) of the communication network (1) are not greater than one eighth of the period of the synchronization pulses, and/or
f) the communication network (1) gets disconnected from time to time.
25. Method according to any of claims 16 to 24, wherein a) the first adjustment function hi is mathematically
smooth, and
b) the second adjustment function h2 is mathematically
smooth, and
c) the first adjustment function hi satisfies dhl/d<|>>0, and
d) the second adjustment function h2 satisfies dh2/d<|)>0.
26. Method according to any of the preceding claims, wherein the communication node (2) is a cell phone and the communication network (1) is a cellular telephone network.
PCT/EP2012/002320 2012-05-31 2012-05-31 Communication node and method for self-organizing synchronization of a communication network WO2013178237A1 (en)

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