WO2017203522A1

WO2017203522A1 - Method and system for tdma-fh network synchronization

Info

Publication number: WO2017203522A1
Application number: PCT/IL2017/050571
Authority: WO
Inventors: Zvi KOMAROV; Boaz DAGAN; Alex Yakov HONIG
Original assignee: Maxtech Communication Networks Ltd.
Priority date: 2016-05-23
Filing date: 2017-05-23
Publication date: 2017-11-30

Abstract

A system and a method for a real time synchronization among communication devices in a TDMA-FH network without relying on a mobile wireless communication device global positioning system (GPS) or an external clock. Particularly, a wireless frequency hopping (FH) communication system comprising a plurality of wireless communication devices communicating with one another via time division multiple access (TDMA), said plurality of wireless communication devices comprising: a first wireless communication device, said device is configured to transmit one or more synchronization packets comprising: a first synchronization message comprising at least one TDMA synchronization value; a second synchronization message comprising at least one FH synchronization value; and an identification message comprising at least one identification value (IVs) of other wireless communication devices in a range of communication from said first wireless communication device; a second wireless communication device wherein said device defines a timing wireless communication device configured to receive said first synchronization message, said second synchronization messages and said identification message; said first synchronization message, said second synchronization messages and said identification message are processed and synchronized between of said plurality of said of wireless communication devices.

Description

METHOD AND SYSTEM FOR TDMA-FH NETWORK SYNCHRONIZATION

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims priority to co-pending U.S. patent application Ser. No. 2014/0105205 for DYNAMICALLY SELF-ORGANIZING AD-HOC TDMA COMMUNICATIONS SYNCHRONIZATION METHOD, filed Apr. 1, 2012, which is incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates to the field of communication and, more particularly, to wireless Time Division Multiple Access network Frequency Hopping communication and synchronization and related methods.

BACKGROUND OF THE INVENTION

With advances in processing capabilities and programming technologies, software defined mobile wireless communication devices (e.g., radios) continue to increase in popularity. Rather than relying upon hardware and circuitry-components to perform tasks such as frequency, modulation, bandwidth, security functions, and waveform requirements, these functions are performed by software modules or components in a software radio. That is, with a software radio analog signals are converted into the digital domain where the above-noted functions may be performed using digital signal processing.

Because most of the functions of the radio are controlled by software, software radios may typically be implemented with relatively standard processor and hardware components. This may not only reduce device hardware costs, but is also provides greater flexibility in upgrading the device since new communication waveform modules can be uploaded to the device relatively easily and without the need to interchange new hardware components.

Frequency hopping networks are widely used in wireless communication. For example, frequency hopping (FH) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both the transmitter and receiver.

A frequency hopping network offers three main advantages over a fixed-frequency network. First, signals in a frequency hopping network are typically highly resistant to narrowband interference, for example. Signals in a frequency hopping network may also be difficult to intercept. For example, an FH signal typically appears as an increase in background noise to a narrowband receiver. Signals in a frequency hopping network may also share a frequency band with many types of conventional transmissions with reduced interference.

One approach to address the timing in a Time Division Multiple Access Frequency Hopping (TDMA-FH) network includes using fixed frequency rules, where each communication device is informed of timing information using a single frequency, for example. More particularly, a static time server, a beacon, or a rendezvous channel may be used. For example, a given communication device may be pre-designated as the static time server. However, a failure or stoppage of the communication device designated as the static time server would cause a failure of the entire network.

Additional communication devices may be designated as a static time server so the network does not have a single point of failure. However, coordinating or selecting the additional static time servers may be relatively complex. For example, conflicts may arise when two or more static time servers are selected. Conflicts may also arise as static time servers move in and out of communication range with other communication devices and each other.

In a wireless mobile ad hoc network (MANET), formed by a group of mobile nodes not having any fixed infrastructure, it is important that all mobile nodes synchronize to the same clock. In a frequency hopping ad hoc network, the phase of the hopping sequence is typically derived from the local time reference (clock reading) of each node. Therefore, network-wide time synchronization is needed in order to get the nodes to simultaneously switch to the same frequency channel, i.e., hop synchronously. Due to the characteristics of ad hoc networks there is no centralized control, e.g., no unambiguous entity, to define a common time reference. Thus, a distributed decision has to be made between the nodes as to whose local time reference is chosen as the common time reference for other nodes to synchronize to. For that purpose, there has to be a predefined procedure for frequency hopping nodes to exchange synchronization information out-of-phase, e.g., through a control channel. Thus, in frequency hopping (FH), synchronization is required so hopping can take place at the same time.

Several methods for frequency hopping (FH) synchronization are known.

Article "A Novel Parallel State Search based Synchronization Scheme for Frequency Hopping System" by Xiujuan Dou et al. discloses a new synchronization-word scheme using a parallel state search based on energy detection and correlation code detection. It discusses the existing synchronization methods that can be classified into four basic types: independent synchronization channel (ISC), reference clock (RC), synchronization-word (SW), and self- synchronization (SS). In SW, a synchronization-word, i.e. synchronization sequence is transmitted prior to the message transmission to synchronize the receiver and the sender. The method has the advantage of rapid synchronization, but the synchronization-word is not so secure since it can easily be interfered. In order to enhance the concealment of the synchronization-word and to improve anti-reconnaissance and anti-jamming capability, SW is generally combined with TOD, where synchronization frequencies change with the higher bits of TOD.

Synchronization is also required for the identification of slot boundaries in TDMA. Time synchronization in all networks either wired or wireless is important. It allows for successful communication between nodes on the network. It is, however, particularly vital for wireless networks. Synchronization in wireless nodes allows for a TDMA algorithm to be utilized over a multi-hop wireless network. Wireless time synchronization is used for many different purposes including location, proximity, energy efficiency, and mobility to name a few. In sensor networks when the nodes are deployed, their exact location is not known so time synchronization is used to determine their location. Also time stamped messages will be transmitted among the nodes in order to determine their relative proximity to one another. Lastly, having common timing between nodes will allow for the determination of the speed of a moving node. The need for synchronization is apparent. Besides its many uses like determining location, proximity, or speed, it is also needed because hardware clocks are not perfect. There are variations in oscillators, which the clocks may drift and durations of time intervals of events will not be observed the same between nodes. The concept of time and time synchronization is needed, especially in wireless networks. TDMA requires careful time synchronization since users share the bandwidth in the frequency domain. Without such clock synchronization, TDMA networking is impossible due to transmission contention.

That is, in a TDMA-FH network full synchronization cannot be acquired until both elements of TDMA timing and FH schedule are synchronized. Henceforth, the TDMA-FH devices cannot communicate successfully if at least one of the TDMA or FH mechanisms is out-of-sync.

U.S. Pat. No. 2014/0105205, Uzi Hanuni et al. discloses a method and system for TDMA synchronization including providing an ad-hoc TDMA mobile communication network, the communication network includes a plurality of mobile units, transmitting an information packet from a mobile unit of the plurality of mobile units to each remaining one of the plurality of mobile units. The method and system further including comparing at each remaining one of the plurality of mobile units the corresponding preamble detection time t_rxiwith a predetermined time parameter t_corr, and adjusting the corresponding preamble detection time t_{rx i}of each remaining one of the plurality of mobile units accordingly. In addition, a method for logical timeslot synchronization and its enhancement using directed synchronization procedure with a refresh procedure are disclosed if a transmitting mobile unit exits the communication network and reconnects thereto.

U.S. Pat. No. 8804603, Nelson H. Powell et al. discloses a wireless communication system that may include wireless communication devices communicating with one another via time division multiple access (TDMA). The wireless communication devices may include a time master device that may transmit a first synchronization message, a first maintenance message, and a timing head relay designation message. The wireless communication devices also include a timing head relay device corresponding to the timing head relay designation and may receive the first synchronization message, first maintenance message and timing head relay designation message. The timing head relay device may also transmit a second synchronization message and a second maintenance message. The wireless communication devices may also include a time forwarding device that may receive the second synchronization message and the second maintenance message, transmit a third synchronization message when a downstream wireless communication device is outside a range of the timing head relay device, and transmit a third maintenance message. U.S. Pat. No. 7,710,944 to Yoon et al. discloses a method of time of day synchronization between network nodes. More particularly, a network that includes a plurality of nodes is arranged in islands. Head nodes from each island are in communication with each other. Network time is synchronized with a node that has local global positioning system (GPS) time. Network nodes transition to common GPS time after an island or group head node determines that the transition in network time does not disturb the communication links. However, as known to those skilled in the art, many prior art systems pertain to a time-of-day (TOD) synchronization scheme or protocol. Prior to any exchange of information between any set within a mobile wireless communication device group, each mobile wireless communication device determines the status of its global positioning system (GPS) or external clock. The vast majority of communicating entities contain a clock source, which ticks at a frequency governed by a given application. For two such entities, the process of synchronization involves aligning the phase and the period of their clocks. Once this is achieved, the two devices effectively share the same sense of time, and can thus more effectively coordinate future tasks between each other. Environmental fluctuations, or imperfections in the clock construction, will cause one of the clocks to tick faster than the other. Even if this difference in clock frequency is small, it will eventually cause the two clocks to fall out of phase, widening the synchronization error, and thus requiring re- synchronization. The acceptable error is governed by an application, from seconds (e.g. a wrist watch) to nano-seconds (e.g. time-of-flight localization).

In addition to the basic functionality discussed above, more complex functionality cannot be achieved in TDMA-FH systems without relying on mobile wireless communication device global positioning system (GPS) or external clock. In such conventional systems, the master clock must be reset or otherwise synchronized with the start of a new data frame to ensure proper clocking of received data bits and adequate tolerance allowed for jitter, etc. Furthermore, because master transmit and receive clocks typically will drift with respect to one another, the position of the first bit in the TDMA frame will occasionally move relative to the receive master clock. The absence of the master clock may cause local various clock drifts which subsequently may lead to system failure.

Therefore, there is a long felt and unmet need for a system and method that overcomes the problems associated with the prior art. The present system and method provide real time synchronization among communication devices in a TDMA-FH network without relying on a mobile wireless communication device global positioning system (GPS) or an external clock.

SUMMARY

The present invention provides a system and a method for a real time synchronization among communication devices in a TDMA-FH network without relying on a mobile wireless communication device global positioning system (GPS) or an external clock, namely a wireless frequency hopping (FH) communication system comprising a plurality of wireless communication devices communicating with one another via time division multiple access (TDMA), said plurality of wireless communication devices comprising: a first wireless communication device, said device is configured to transmit one or more synchronization packets comprising: a first synchronization message comprising at least one TDMA synchronization value; a second synchronization message comprising at least one frequency hop synchronization value; and an identification message comprising at least one identification value (IVs) of other wireless communication devices in a range of communication from said first wireless communication device; a second wireless communication device wherein said device defines a timing wireless communication device configured to receive said first synchronization message, said second synchronization messages and said identification message; said first synchronization message, said second synchronization messages and said identification message are processed and synchronized between of said plurality of said of wireless communication devices.

It is another object of the current invention to disclose a method of wireless frequency hopping (FH) communication in a wireless communication system comprising a plurality of wireless communication devices communicating with one another via time division multiple access (TDMA), the method comprising: transmitting from a first wireless communication device from among the plurality of wireless communication devices one or more synchronization packets comprising: a first synchronization message comprising at least one TDMA synchronization value; a second synchronization message comprising at least one FH synchronization value; and an identification message comprising at least one identification value (IVs) of other wireless communication devices in a range of communication from said first wireless communication device; receiving at a second wireless communication device defining from among the plurality of wireless communication devices, said first synchronization message, said second synchronization messages and said identification message; processing and synchronizing said first synchronization message, said second synchronization messages and said identification message between of said plurality of said of wireless communication devices.

BRIEF DESCRIPTION OF THE FIGURES

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part thereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured.

FIG. 1 schematically presents, in topological form, a system environment according to the present invention;

FIG. 2 is a flow diagram illustrating and a method for real time synchronization among communication devices in a TDMA-FH network.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured. Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

Referring initially to Figs. 1 and 2, a wireless communication system 10 includes mobile wireless communication devices 20 communicating with one another via time division multiple access (TDMA) and via frequency hopping (FH). As will be appreciated by those skilled in the art, the wireless communication system 10 may be in a form of a TDMA with frequency hopping mobile ad hoc network (MANET), for example. In some embodiments, one or more of the wireless communication devices 20 may not be mobile.

Each of the mobile wireless communication devices 20 may be classified as a particular type of mobile wireless communication device based upon its functionality within the network, as will be described in further detail below.

Reference is made to Fig. 1, presenting, in topological form, a schematic and generalized presentation of the present invention environment where said system 10 comprising: mobile wireless communication device 20b' has moved into the wireless communication range 30a' of mobile wireless communication device 20a'.

For example, mobile wireless communication device 20a' transmits a synchronization packet 40 independently of the units' awareness. As mobile wireless communication device 20b' moves into the communication range 30a' of mobile wireless communication device 20a', subsequently upon receiving said synchronization packet 40 becomes aware of mobile wireless communication device 20a' being in communication range 30a'. The mobile wireless communication device 20b' is operable to determine when said second mobile wireless communication device 20a' transmits the first synchronization message comprising the TDMA synchronization value in an adaptive synchronization event. After the synchronization packet 40 is received and processed by mobile wireless communication device 20b', the wireless communication devices 20a' 20b' become TDMA-FH synchronized. The wireless communication devices may generally be fixed or mobile. The wireless communication devices may also be referred to as subscriber units, mobiles, mobile stations, mobile units, users, terminals, subscriber stations, user equipment (UE), user terminals, wireless communication devices, relay nodes, or by other terminology used in the art.

Reference is now made to Fig. 2, presenting a flow diagram illustrating a method for real time synchronization among communication devices in a TDMA-FH network 20. Said method comprises, for a number of repetitions, steps of providing a wireless communication system 10 comprising a plurality of wireless communication devices communicating with one another via time division multiple access frequency hopping (TDMA-FH) communication, the method comprising: transmitting 202 from a first wireless communication device from among the plurality of wireless communication devices one or more synchronization packet comprising: a first synchronization message comprising at least one TDMA synchronization value; a second synchronization message comprising at least one FH synchronization value; and an identification message comprising at least one identification value (IVs) of other wireless communication devices in a range of communication from said first wireless communication device; receiving 204 at a second wireless communication device defining from among the plurality of wireless communication devices, said first synchronization message, said second synchronization messages and said identification message; processing and synchronizing 206 said first synchronization message, said second synchronization messages and said identification message between of said plurality of said of wireless communication devices.

Claims

CLAIMS What claimed is:

1. A wireless frequency hopping (FH) communication system comprising a plurality of

wireless communication devices communicating with one another via time division multiple access (TDMA), said plurality of wireless communication devices comprising:

a. a first wireless communication device wherein said device is configured to

transmit one or more synchronization packets comprising:

i. a first synchronization message comprising at least one TDMA

synchronization value;

ii. a second synchronization message comprising at least one FH

synchronization value; and

iii. an identification message comprising at least one identification value (IVs) of other wireless communication devices in a range of

communication from said first wireless communication device;

b. a second wireless communication device wherein said device among the plurality of wireless communication devices configured to receive said first synchronization message, said second synchronization messages and said identification message.

wherein said first synchronization message, said second synchronization messages and said identification message are processed and synchronized between of said plurality of said of wireless communication devices.

2. The wireless communication system of claim 1 , wherein said plurality of wireless

communication devices also communicate with one another via frequency hopping.

3. The wireless communication system of claim 1, wherein said first wireless communication device is configured to transmit said first synchronization message and the identification message in one or more TDMA time-frame.

4. The wireless communication system of claim 1 , wherein said first wireless communication device is configured to transmit said second synchronization message and the identification message in one or more TDMA time-frame.

5. The wireless communication system of claim 1, wherein said second wireless communication device is configured to determine when said first wireless communication device transmits the first synchronization message comprising at least one TDMA synchronization value in an adaptive synchronization event.

6. The wireless communication system of claim 1 , wherein said second wireless communication device is configured to determine when said first wireless communication device transmits the second synchronization message comprising at least one FH synchronization value in an adaptive synchronization event.

7. The wireless communication system of claim 1, wherein said second wireless communication device is configured to determine when said first wireless communication device transmits the third synchronization message comprising at least one identification value (IVs) of other wireless communication devices in a range of communication from said wireless

communication device.

8. A method of wireless frequency hopping (FH) communication in a wireless communication system comprising a plurality of wireless communication devices communicating with one another via time division multiple access (TDMA), the method comprising steps of:

a. transmitting from a first wireless communication device from among the plurality of wireless communication devices one or more synchronization packets comprising:

i. a first synchronization message comprising at least one TDMA

synchronization value;

ii. a second synchronization message comprising at least one FH

synchronization value; and

communication from said first wireless communication device;

b. receiving at a second wireless communication device from among the plurality of wireless communication devices, said first synchronization message, said second synchronization messages and said identification message. c. processing and synchronizing said first synchronization message, said second synchronization messages and said identification message between of said plurality of said of wireless communication devices.

9. The method of claim 8, wherein said plurality of wireless communication devices also

communicate with one another via frequency hopping.

10. The method of claim 8, wherein said first wireless communication device is configured to transmit said first synchronization message and the identification message in one or more TDMA time-frame.

11. The method of claim 8, wherein said first wireless communication device is configured to transmit said second synchronization message and the identification message in one or more TDMA time-frame.

12. The method of claim 8, wherein said second wireless communication device is configured to determine when said first wireless communication device transmits the first synchronization message comprising at least one TDMA synchronization value in an adaptive

synchronization event.

13. The wireless communication system of claim 8, wherein said second wireless communication device is configured to determine when said first wireless communication device transmits the second synchronization message comprising at least one FH synchronization value in an adaptive synchronization event.

14. The method of claim 8, wherein said second wireless communication device is configured to determine when said first wireless communication device transmits the second

synchronization message comprising at least one identification value (IVs) of other wireless communication devices in a range of communication from said wireless communication device.