HK1092964B - Radio network communication system and protocol using an automatic repeater - Google Patents

Description

Radio network communication system and protocol using automatic repeater

Technical Field

The invention relates to a network of devices communicating with each other by radio frequency.

Background

A network of devices may be created by arranging a set of devices that communicate with each other via Radio Frequency (RF) means to transfer data between the devices. Each device may effectively communicate with every other device in the network provided that it is within the maximum communication range of each device.

In many such networks, the devices may all be transceivers, i.e., each capable of both transmitting and receiving. To transfer data items, one device acts primarily as a transmitter, while the other device acts primarily as a receiver. In this context, a transceiver that acts primarily as a transmitter will be referred to as a transceiver/transmitter. Those transceivers that act primarily as receivers will be referred to as transceiver/receivers.

In contrast to "point-to-point" systems, in which communication takes place only between two devices at the same time, the present invention can be used in "point-to-multipoint" systems. In a point-to-multipoint communication system, communication occurs simultaneously between one device and two or more other devices in the network.

A reliable "point-to-multipoint" communication system allows for the creation of shared network variables. This is a variable known to all devices in the network. For example, if one device wants to change the value of a shared network variable, it must send a request and must ensure that all devices receive and process the updated variable at the same time. If simultaneous updates cannot be made or not all other devices in the network receive the updates, then the network does not have shared network variables.

Sharing network variables allows for the creation of networks without a central controller. All necessary data regarding the operation and control of the network are known to each device in the network at the same time. This data can be updated at any time by any device in the network and ensures that all other devices update their data accordingly. This allows for simple, more flexible and cost-effective control of devices within the network when compared to a network having a central controller.

The single communication activity between each device is referred to herein as a transaction. A transaction occurs between devices (transceivers/transmitters) that transmit data to one or more transceiver/receivers of the data. Transactions also include data sent from transceiver/receiver to transceiver/transmitter and to transceiver/receiver in the network to each other.

When transmitting to more than one transceiver/receiver at the same time (known as broadcast or multicast), it is important to know that all transceiver/receivers have successfully received the data. If even one transceiver/receiver does not successfully receive the data (e.g., due to bit errors that cause data corruption in one transceiver/receiver), all other transceiver/receivers must be notified that not all other transceiver/receivers have successfully received the data.

Such a network may use a transmission system with primary and secondary bits. This means that if there is a collision and both devices send primary and secondary bits simultaneously, each device will see the transmission of the primary bit when monitoring the communication medium. The device sending the secondary bits knows that a collision has occurred and can take any appropriate action. This may mean, for example, that all further transmissions are stopped.

In conventional point-to-point communication protocols, the usual procedure is for each device to send an acknowledgement statement some time after receiving the data. This has the drawback that the sending device must know exactly the number of receiving devices within the network and know how to contact each of them. Reliable transmission of the same data segment to multiple receiving devices requires multiple transmissions of the same data, and a corresponding wait for each transmission to be acknowledged. This repeated transmission of the same data to many recipients wastes the available bandwidth of the communication medium. This approach also requires the transmitter to acquire and store data about exactly which receiving device is to receive a given transmission. This approach allows for the creation of shared network variables at the cost of unnecessary complexity and inefficient use of the available bandwidth of the communication medium.

Alternatively, point-to-multipoint transmission may be used to send data to multiple recipients simultaneously without returning any acknowledgement. This results in unreliable data transmission and the transmitter is unable to determine whether all receiving devices have successfully received the data. Unreliable data transfer means that shared network variables cannot be created.

The situation is complicated when two or more devices are out of communication range of each other. As can be appreciated, each device has its maximum transmission range (determined by design factors including, but not limited to, transmit power, receiver sensitivity, antenna type, and signal processing algorithms). Communication and synchronous communication is further complicated when some devices are out of maximum range and therefore cannot communicate with each other.

It is an object of the present invention to provide a system and protocol for improving communication between devices in an RF multicast communication system, particularly between devices that are placed beyond the normal communication range of one or more other devices in the system.

Disclosure of Invention

According to a first aspect of the present invention there is provided a method for use in a radio communication system comprising a first transceiver, a second transceiver and a repeater, the first and second transceivers being spaced apart from each other by a distance greater than at least one of their respective maximum transmission ranges, and the repeater being disposed intermediate the first and second transceivers, the method comprising, upon receipt of data from either the first or second transceiver, the repeater transmitting a repeat flag to cause said transceiver to suspend further activity and subsequently transmitting data received from either the first or second transceiver.

According to a second aspect of the present invention there is provided a method for use in a network of devices for transmitting and receiving data in frames, the network of devices comprising a first transceiver, a repeater and at least one other transceiver, the first transceiver and the at least one other transceiver being spaced from each other by a distance greater than at least one of their respective maximum transmission ranges, and the repeater being interposed between the first transceiver and the at least one other transceiver, the method comprising the steps of: the first transceiver transmitting data for use in the at least one other transceiver in a first time slot of the frame; said repeater transmitting a repeat flag in a second time slot subsequent to said first time slot of said frame, causing said transceiver to suspend further activity; and the repeater repeats the data received in the first slot in a third slot after the second slot of the frame.

According to a third aspect of the present invention there is provided a radio communication system comprising a first transceiver, a second transceiver and a repeater, the first and second transceivers being spaced apart from each other by a distance greater than at least one of their respective maximum transmission ranges, and the repeater being disposed intermediate the first and second transceivers, wherein upon receiving data from either the first or second transceiver in a first time slot, the repeater transmits a repeat flag in a second time slot causing the transceiver to suspend further activity and then transmits data received in the first time slot in a third time slot.

According to a fourth aspect of the present invention there is provided a repeater for a radio communication system comprising at least two transceivers spaced apart from each other by a distance greater than at least one of their respective transmission ranges, the repeater being interposed, in use, between the at least two transceivers, wherein upon receipt of data in a first time slot, the repeater transmits a repeat flag in a second time slot causing the transceivers to suspend further activity and then transmits data received in the first time slot in a third time slot.

According to a fifth aspect of the present invention there is provided a transceiver for use in a radio communication system comprising at least one other transceiver and a repeater, the transceiver and the at least one other transceiver being spaced apart from each other by a distance greater than at least one of their respective transmission ranges, in use the repeater being interposed between the transceiver and the at least one other transceiver, wherein on receipt of a repeat flag from the repeater in a second time slot, the transceiver suspends further activity until it receives data from the repeater in a third time slot, the data being initially transmitted by the at least one other transceiver in a first time slot prior to the second time slot.

According to a sixth aspect of the present invention there is provided a method in a radio communication system comprising at least a first transceiver, a second transceiver and a repeater, the first transceiver and the second transceiver being spaced apart from each other by a distance greater than the maximum transmission range of the at least one transceiver, and the repeater being disposed intermediate the first and second transceivers such that upon receipt of data transmitted from the first transceiver, the repeater repeats the data transmitted from the first transceiver, wherein, on receipt of data transmitted from the second transceiver before the repeater completely receives or repeats the data transmitted from the first transceiver, the repeater transmits a data sequence instructing each transceiver to cease its respective transmission.

According to a seventh aspect of the present invention there is provided a radio communication system comprising at least a first transceiver, a second transceiver and a repeater, the first transceiver and the second transceiver being spaced apart from each other by a distance greater than the maximum transmission range of at least one of the transceivers, and the repeater being disposed intermediate the first and second transceivers such that, on receipt of data transmitted from the first transceiver, the repeater repeats the data transmitted from the first transceiver, wherein, on receipt of data transmitted from the second transceiver before the repeater completely receives or repeats the data transmitted from the first transceiver, the repeater transmits a data sequence instructing each of the transceivers to cease its respective transmission.

According to an eighth aspect of the present invention there is provided a repeater for use in a radio communication system comprising at least a first transceiver and a second transceiver, the first and second transceivers being spaced apart from each other by a distance greater than the maximum transmission range of at least one of the transceivers, in use the repeater being disposed intermediate the first and second transceivers such that, on receipt of data transmitted from the first transceiver, the repeater repeats the data transmitted from the first transceiver, wherein, on receipt of data transmitted from the second transceiver before the repeater has completely received or repeated the data transmitted from the first transceiver, the repeater transmits a data sequence instructing each transceiver to cease its respective transmission.

According to a ninth aspect of the present invention there is provided a transceiver for use in a radio communication system comprising at least one other transceiver and a repeater, in use, the transceiver and the at least one other transceiver being spaced apart from each other by a distance greater than the maximum transmission range of at least one of the transceivers, and the repeater being interposed between the transceiver and the at least one other transceiver such that, on receipt of data transmitted from the at least one other transceiver, the repeater repeats data transmitted from the at least one other transmitter, and on receipt of data transmitted from the transceiver prior to repeating data transmitted from the at least one other transceiver, the repeater transmits a data sequence instructing each transceiver to cease its transmission, wherein, on receipt of the data sequence from the repeater, the transceiver will stop transmitting.

Drawings

FIG. 1 illustrates a network architecture in accordance with a preferred embodiment of the present invention;

FIG. 2 illustrates a network protocol model for use in the context of the present invention;

fig. 3 illustrates a frame structure according to a preferred embodiment of the present invention;

fig. 4 shows one repeater and two transceivers deployed in a network according to the invention;

FIG. 5 shows a frame structure for use in the configuration of FIG. 4;

fig. 6 shows a preferred structure of a transceiver apparatus used in the present invention; and

fig. 7 shows a partial ISO 7 layer model in which certain functions of the transceiver device of fig. 6 are performed.

Detailed Description

A typical network architecture is shown in fig. 1, where a network 10 is formed by nodes 1, 2 and 3, the nodes 1, 2 and 3 being transceiver devices and being operable as transmitters and/or receivers in a given communication transaction. Network 10 may communicate with other networks 20 through gateway 11.

The protocol design of the present invention is based on the ISO 7 layer model and some terms are the same as used by ISO. The protocol used in the present invention is connectionless, meaning that once a single data transfer has occurred, it is undesirable to have other related data transfers before or after it.

The protocol model of the present invention is based on the ISO 7 layer model and is shown in fig. 2. For applications distributed over two nodes, each protocol layer has a virtual connection to a peer layer within the other node. As can be seen, each layer gets the data provided by the previous layer, processes it as a data unit and adds its own Protocol Control Information (PCI) field. At each layer, a Protocol Data Unit (PDU) is either data or a packet provided by the next higher layer. The name of a PDU is preceded by the layer to which it applies (e.g., an SPDU is a session PDU).

The physical layer relates to the mechanical and electrical network interfaces in ISO systems. In the system of the present invention, the physical layer refers to hardware and firmware elements used to transmit and receive bits over the communication medium.

In ISO systems, the link layer is used for data link control (e.g., framing, data transparency, error control). In the present invention, the link layer is used to divide bytes into bits, bit stuffing (if needed), framing, collision detection, prioritization, error detection, positive/negative acknowledgement generation, checking, forwarding and retransmission.

The network layer in the ISO system is used for network routing, addressing, call setup and clearing, whereas in the present invention, the network layer is used for network routing, addressing, transaction setup and clearing.

In ISO systems, the transport layer is used for end-to-end message transport, connection management, error control, segmentation and flow control. The transport layer is not used in the context of the present invention.

The session layer in the ISO system is used for dialog and synchronization control of application entities, but is not used in the context of the present invention.

The presentation layer is used in the ISO system for transport of syntax negotiations and data presentation transformations, whereas in the context of the present invention the presentation layer is used for optional encryption of application data.

The application layer in the ISO system is used for file transfer, access management, document and message exchange, job transfer and manipulation, whereas in the context of the present invention, the application layer supports sending and receiving application data.

Finally, the user application layer is used not only in ISO but also in the context of the present invention for any need to implement a specific function or behavior.

The present invention has features that mainly belong to the link layer.

In the protocol of the present invention, the usage can optionally consist of primary and secondary bits. If two devices transmit primary and secondary bits at the same time, then the receiver and transmitter (monitoring their own transmissions) will only detect the primary bits.

Media access is obtained by first monitoring the media by the transmitter and if no existing transmission is detected, the transmitter will attempt to request media access by sending a preamble. Such a preamble starts with at least one detectable bit. The requirement for media access defines the start of a transaction. The transaction contains all data transfers, data acknowledgements and forwarding. All nodes in the network must continuously monitor the medium and if they detect that a transaction has occurred, any attempt to require medium access will be delayed until the current transaction is complete.

The transaction is asynchronous: they may occur at any time, and the time difference from one transaction to the start of the next transaction is not necessarily an integer number of bit periods.

In this application, a transaction is defined specifically as a continuous period divided into several subslots containing different types of data. The transaction is preceded by a period of time set by a preamble followed by specific data to be transmitted from the transceiver/transmitter to the two or more transceiver/receivers. The time slots during which data is transmitted are variable in length and contain portions that serve as frame check sequences. A data transmission is followed by a time slot during which a positive acknowledgement can be sent by the transceiver/receiver, followed by a time slot during which a negative acknowledgement can be sent by the transceiver/receiver. Fig. 3 shows the structure of the frame.

As described above, transactions are asynchronous and may be initiated at any time. However, once started, the transaction has a time-based structure. Specific markers within the transaction are used to show the beginning and end of the variable length data portion. The time slots during which positive and negative acknowledgements are sent are fixed in time. By coding and redundancy of data encoded into these time slots, positive acknowledgements of one or more transceiver/receivers and negative acknowledgements of one or more transceiver/receivers can be transmitted. All devices involved in the transaction will see both of these acknowledgement slots.

A transceiver/receiver desiring a positive acknowledgement will transmit a special code during the positive acknowledgement time slot and receive (if no primary bit transmission is used) or transmit a secondary bit (if primary/secondary bits are used) during the negative acknowledgement time slot.

Similarly, a transceiver/receiver that wants a negative acknowledgement will send secondary bits (if primary/secondary bits are used) or receive (if primary bit transmission is not used) during a positive acknowledgement slot and send a special code during a negative acknowledgement slot.

The fact that the devices monitor the time slots in which they have not transmitted means that at the end of two acknowledgement time slots, each device detects a positive acknowledgement, a negative acknowledgement or both, and is therefore able to calculate the overall acknowledgement status of the network.

For example, a transceiver/receiver that sends a positive acknowledgement will be able to detect some other transceiver/receiver that sends a negative acknowledgement. In the case where a primary bit is used, the positively acknowledged transceiver/receiver will attempt to transmit a secondary bit during the negatively acknowledged time slot, but will detect the primary bit due to the other transceiver/receivers simultaneously transmitting the appropriate code during the negatively acknowledged time slot. Without the use of the dominant bit, the positively acknowledged transceiver/receiver will receive during the negatively acknowledged time slot and detect any bits due to the other transceiver/receiver transmitting the appropriate code during the negatively acknowledged time slot. The opposite applies to the transceiver/receiver which sends the negative acknowledgement.

At the end of the transaction, all devices do not know how many positive or negative acknowledgements there are, and all they need to know is some positive acknowledgements and some negative acknowledgements.

If there are any negative acknowledgements at all during the transaction, all transceivers/receivers are aware of this and will discard the received data. Similarly, the transceiver/transmitter also knows this and will attempt to rerun the transaction.

The positive acknowledgement is generated as follows. Once the data is received, the node generates a positive acknowledgement only when:

-the data slot has been checked for its embedded frame check sequence and found to be valid; and

any addressing information present within a data slot matches the addressing information used by the device.

Each device transceiver typically contains at least two different types of addresses, as follows:

-a unit address allowing the device to be uniquely addressed; and

-a multicast address allowing simultaneous addressing of those devices in the network for updating the shared network variable.

In addition, the apparatus may also optionally comprise:

network address, allowing the physical device to be grouped by the logical network in which it is located.

Other variations are possible, but these three address types are used as the basis for other more complex addressing schemes.

The procedure involved in generating a negative acknowledgement is as follows. The receiving device (transceiver/receiver) generates a negative acknowledgement only if the data slot is determined to be corrupted by performing a check on the received data using the embedded frame check sequence.

When the device determines that the data slot is corrupted, it further checks that any fields within the data slot are not useful.

Data transmitted by a transceiver/transmitter can only be accepted by a transceiver/receiver if the conditions for generating positive acknowledgements are met and if no other transceiver/receiver has generated a negative acknowledgement. This ensures that all transceiver/receivers receive a given message only once. For point-to-multipoint messages this may mean that the message is discarded by the transceiver/receiver even if the message appears to be valid and positively acknowledged.

The foregoing describes a general environment in which the present invention can be utilized. The above described sequence is only used when each device is within range of the other devices. It should be understood that each device has a maximum transmission range beyond which it cannot communicate with other devices. The maximum transmission range is determined by design factors including, but not limited to, transmit power, receiver sensitivity, antenna type, and signal processing algorithms. For shorter range (unlicensed) devices, the range is typically from tens to at most hundreds of meters. Difficulties may be encountered in performing the above-described process in situations where one or more devices are outside the maximum transmission range of another device (i.e., cannot communicate directly with that device). Especially in the case where the transceiver/transmitter transmits data and some or all of the other transceiver/receivers will not receive data from that particular transceiver/transmitter, it will not be possible to update the shared network variable.

According to one aspect of the invention, the protocol described above (subject of the co-pending patent application) is modified to allow forwarding of data between devices in order to extend the effective transmission range of devices used in the network. The modified protocol is used in conjunction with repeaters that are located approximately at the geometric center of the devices in the network and act as relays between devices distributed outside their normal transmission range.

Fig. 4 shows an example configuration of devices a and B in the network. Devices a and B are separated by a distance greater than each of their respective transmission ranges. Thus, if device a wants to send data as described above, device B will not be able to receive the data and will not be able to know how to proceed as described above. This would prevent efficient updating of the shared network variables. However, in accordance with the present invention, a forwarding device 40 is placed between devices A and B and acts as a repeater. Thus, if device a sends data, forwarding device 40 receives this transmission from device a and forwards the data so that device B can receive device a's data. When device B sends its acknowledgement, this will be received by the repeater. The repeater retransmits all acknowledgment status that can be received by both devices a and B. Both devices then know that the information is relayed by the repeater and is again accepted or rejected by all devices within range of the repeater. Devices a and B can then continue in the normal manner.

Of course, for example, device B need not be a transceiver/receiver but could be a transceiver/transmitter. In this case, however, device B will send information to the network because device a (e.g., transceiver/receiver) that is out of range of device B is unable to receive the transmitted data. Further, a forwarding device 40 disposed between device a and device B will receive data sent by device B and forward such data so that device a and any other devices within range of forwarding device 40 receive the forwarding. Similarly, the acknowledgement from device a will be received by the repeater, which in turn provides the full acknowledgement status back to device B.

It should be understood that the forwarding device 40 need not actually be placed directly between two devices but may be placed in any suitable location so that devices within the network are all reachable.

In some cases, it is possible that device a has sufficient range to reach device B, however device B, which has a shorter transmission range than device a, cannot communicate with device a. In this case, forwarding device 40 may be located closer to device B than to device a in order to allow transmissions from device B to reach forwarding device 40, then forwarded and sent to device a.

In fact, it is advantageous to construct all devices in the network in the same way. This means that each device, whether acting as a transceiver/transmitter, transceiver/receiver or repeater device, is constructed in the same manner and is capable of independently performing their intended functions. This provides significant savings in complexity and manufacturing costs, since only one device needs to be manufactured. The specific structure of the device will be described in more detail later with reference to fig. 6 and 7.

In use, if the device is set as a repeater, upon receiving the message in the first frame (see fig. 3), the repeater will immediately send a repeat flag in the new second time slot and then repeat the data received in the first time slot in the new third time slot. The network then functions normally as described above, with the transceiver/receiver devices that have received the forwarded information then continuing to acknowledge successful or unsuccessful receipt of those data, as discussed above, and the repeater will issue a final overall forwarding status to inform all devices in the network of the success or failure of the forwarded data.

The modified protocol frame is shown in fig. 5. The difference between the modified forward tagged transaction of fig. 5 and the non-forward tagged transaction of fig. 3 is clearly shown in comparison to the frame of fig. 3. In particular, there is a first time slot provided for data transmission in both transaction frames, whereas in the forwarding tag frame of fig. 5, a second time slot is provided for transmission of the forwarding tag flag. A third time slot is provided in which to retransmit the data transmitted in the first time slot. An acknowledgement slot is then provided, comprising a first sub-slot for transmitting a positive acknowledgement and a second sub-slot for transmitting a negative acknowledgement. In addition, in the forward tag frame of fig. 5, additional time slots are provided for transmitting forward state that provides confirmation to all devices that the transmission has been forwarded.

The above-described situation involving repeaters is even more complicated by the fact that there may be devices that will start transmitting at the same time. When all devices are within range of each other, collisions can be easily handled normally when using a system of primary and secondary bits. First, collisions are avoided by monitoring the transmission medium before transmission. This leaves a short period during which transmissions can begin simultaneously. If two devices start transmitting within this small period at the same time, there will inevitably be a difference in the data bits to be transmitted. When this difference occurs, the device transmitting the secondary bits will detect the primary bits due to the other transmitters and can therefore stop further transmissions.

The device that detects the collision reschedules its transmission at a later time. This delay may be based on a small random number, optionally scaled by the length of the message to be transmitted.

In the case of using a repeater device, there is a longer delay between the transmitting device and another device that receives the transmission via the repeater.

For example, referring again to fig. 4, if device a begins transmitting, there may be a delay between the time that repeater device 40 receives the transmission of device a and the time that it repeats the transmission to be received by device B. During this time, device B may begin transmitting its own data. This new transmission will cause a collision, which can be detected at the repeater, instead of at device a. This situation is addressed by another aspect of the present invention.

Specifically, the forwarding device 40 checks the data it receives. If it detects bit-stuffing corruption or data coding corruption during reception, this indicates that devices a and B are transmitting simultaneously. Upon detecting this, the repeater device 40 intentionally starts sending a long primary bit stream (e.g., 6 to 8 bits) that violates normal bit stuffing or data encoding rules. This will cause both devices a and B to detect the collision and stop transmitting according to normal collision detection and resolution rules.

As for normal collisions, each of devices a and B then schedules a retransmission, optionally scaled according to message length, after a random delay. The probability that this delay is exactly the same for each device is very small, however, in case each device starts transmitting again at the same moment, the delay period is recalculated, but this time each device multiplies its respective delay period by 2. For each subsequent fault, successive delay periods are doubled up to some predetermined multiple. At this point, the transmission will be abandoned and the operator may optionally be notified by any suitable means. However, in most cases, a random delay period will result in the transmission collision being eliminated and the network device will be able to continue transmitting in the normal manner.

Of course, it will be appreciated that any other suitable form of retransmission delay may be used.

As discussed above, it is advantageous to construct all devices in the network in virtually the same manner. This means that each device, whether it acts as a transceiver/transmitter, transceiver/receiver or repeater device, will be constructed in the same way and be able to perform their desired functions separately. This provides significant savings in complexity and manufacturing costs, as only one type of device needs to be manufactured.

A preferred implementation of the transceiver device 100 uses a radio receiver, a radio transmitter and a microprocessor. These first two items may optionally be combined into a transmitter/receiver as shown in fig. 6, which fig. 6 shows a device 100 comprising a microprocessor 110 and a transmitter/receiver 120. The transmitter/receiver 120 transmits and receives data through the antenna 130.

It will be appreciated that the use of a microprocessor is not mandatory. For example, the protocol may be implemented in an application specific integrated circuit, a programmable logic device, or a programmable gate array. The use of a microprocessor is convenient because it allows for an easily modifiable software implementation and reduces the overall component count. However, software implementations are only suitable for low to medium data rates.

The function of the transmitter/receiver 120 is to receive or transmit information. The choice of transmitter/receiver will be determined by a range of factors including (but not limited to):

a. a market management environment in which products are to be sold.

Each country has rules that determine factors including the allowed frequency, transmit power level and bandwidth. Transmitters/receivers suitable for use in certain countries may not be compliant in other countries.

For products with wide distribution requirements across countries, it may be necessary to select several different transceivers/receivers appropriate for each country.

b. Power consumption, along with any other considerations that determine the amount of power available.

For example, a transmitter/receiver with high power consumption may not be suitable for battery operation.

c. The time it takes for the transmitter/receiver to switch between receive and transmit modes.

In the communication protocol of the present invention, the time to switch between receiving and transmitting is important because the protocol contains a fixed set of time slices. A time slice may need to be received or sent depending on the total transactions performed.

The time to switch between receiving and transmitting constitutes overhead (dead time). The result of the long switching time is wasted bandwidth.

d. The type of interface.

There are many transmitter/receiver types available. The type of digital data input and output is provided to the simplest interface with the microprocessor.

e. The data rate.

The transmitter/receiver needs to support a data rate that is suitable for the overall product requirements. This data rate can be anywhere between very low and very high.

f. Physical size, and amount of available space.

g. And (4) cost.

h. The design effort.

At a minimum, the transmitter/receiver needs:

a. sending a data output for use by the microprocessor to place the communication state on the wireless medium;

b. receiving a data output for use by the transceiver in indicating to the microprocessor the status of the wireless medium; and

c. a control input used by the microprocessor to select a receive or transmit mode of operation of the transmitter/receiver.

The control input may vary between very simple and very complex. In the simplest case, it is used to select between receiving and transmitting. Some transmitters/receivers support a low power "sleep" mode. Others allow for complex setup and configuration of transmitter/receiver operating characteristics.

The type of control input is not critical to the protocol.

Some suitable transmitter/receivers include TR1000 to TR3100, Chipcon CC1000 and Nordic NRFs 401, NRF403 of the RFM ASH series.

Microprocessor 110 is operative to implement a communication protocol utilizing the transmitter/receiver as a means for placing communication states on and receiving communication states from the wireless medium.

The type and selection of the microprocessor is not critical as long as it can perform operations with precise timing. The degree of accuracy need only be sufficient to avoid generating bit errors in the communication protocol.

The protocol is preferably implemented in a bit-oriented manner, as this allows the point at which a time slice starts to be easily identified.

The microprocessor is responsible for performing at least some of the following functions:

a. data encoding and decoding schemes for transmission and reception, such as manchester encoding;

b. recovery of the transmit clock in the receiver-e.g. by synchronization to the preamble;

c. detecting a conflict;

d. creating each time slot and the appropriate transmission or reception during the time slice to exchange the relevant acknowledgement information;

e. implementing an error detection scheme that may be used by a receiving device to determine whether a received transmission is erroneous or not;

f. implementing an error correction scheme that can be used by a receiving device to correct a certain number of reception errors during transmission; and

g. the addition of a forwarder function available to change the structure of the transaction allows forwarding of information packets for the purpose of extending the range.

As previously mentioned, a common method for describing functionality used in communication protocols is the ISO 7 layer model. While a software architecture based on such a model is not mandatory, its use simplifies the overall design. With this model, the functions implemented in the bottom few layers are shown in fig. 7.

The microprocessor hardware provides the electrical interface (physical layer) while the microprocessor software performs all higher-level functions.

In particular, the software MAC-B part of the link layer is responsible for all time-critical functions of data transmission and reception, including at least some of the following:

a. initiating a new transmission (including the generation of any preamble);

b. transmitting data bits;

c. sending a frame marker;

d. starting to receive;

e. synchronization to the transmitted data stream and clock recovery;

f. receiving and decoding data bits;

g. receiving and decoding a frame marker;

h. detecting a conflict;

i. starting each time slice; and

j. transmission and reception of data bits within a time slice.

The software MAC-F part of the link layer is not so time critical. It is responsible for higher layer message-oriented processing, including at least some of the following:

a. constructing a packet from the received data bits;

b. checking a packet error;

c. determining when to acknowledge and the type of acknowledgement to be generated (using the time slice service of MAC-B);

(optional) scheduling forwarding operations for the transmission based on the packet structure;

e. initiating transmission of a new packet;

f. generating a packet error check sequence;

g. transmitting packets, each time a bit is transmitted;

h. the checking of acknowledgements and collisions, and determining whether and when a packet should be retransmitted.

Many different microprocessors are available. There are some special hardware functions available that eliminate some processor load for time critical functions, such as time interval generation, pulse generation, etc. While these hardware functions are not mandatory, their use greatly simplifies software design and coding.

Some microprocessors suitable for use in the present invention include the Texas instruments MSP430 series, the Atmel Atmega series, and the Hitachi H8/3644 series.

A useful feature of one aspect of the invention relates to the accurate detection of the end of a variable length time slice containing data transmitted by a transceiver/transmitter.

It is desirable for the communication medium to require some form of balanced transmission to avoid accumulation of dc offsets. This balance requires that the number of ON and OFF states ON the medium be equal when considering medium to long time periods.

There are many coding schemes that can be used to convert data bits to states on the media. These schemes vary according to the bandwidth they consume on the medium and the ease of recovery of the transmitted data within the receiver.

One of the most common schemes is manchester encoding. This encoding uses two states on the medium for each data bit and has a simple process for data recovery in the receiver. This scheme encodes bit 1 as a state pair (OFF, ON) and bit 0 as a state pair (ON, OFF).

Manchester encoding always has a state transition (OFF to ON, or ON to OFF) in the middle of each data bit, which greatly simplifies the process of data recovery and synchronization to the transmitter clock in the receiver.

In manchester encoding, the state pairs (OFF, OFF and ON, ON) are not allowed.

Manchester encoding may be utilized for illegal state pairs used to convey information about important points.

The exact choice of illegal state sequence is not very important as long as it is used all the time. Preferably, the DC balance of Manchester encoding should be maintained.

A suitable coding representing the end of the variable part of the transmission uses a simple illegal sequence: (ON, ON, OFF, OFF). This maintains dc balance and can be easily recognized by a manchester decoder.

This sequence can be used as an "introduction" if additional information needs to be conveyed. Thus, for example, other possible sequences may be:

(ON, ON, OFF, OFF, ON, OFF) as the first important point

(ON, ON, OFF, OFF, OFF, ON) as a second important point

When considering both methods and advantages, the preferred protocol implementation is bit-oriented, synchronous, and employs illegal coding to represent important points in the variable part.

This advantageously provides a high degree of time-based accuracy in finding the end of the variable part, is relatively easy to implement, and does not require escape sequences or bit stuffing. In addition, the higher time-based accuracy in finding the end of the variable part also creates a high accuracy in determining the start of the following fixed time slot.

It is easy to send a fixed time slice by simply counting the status or bits of the transmission. In the event that no information is transmitted during the receive slot period, the received slot requires a manchester decoder (without supporting illegal states) and a timer.

It will be understood that the above description has been made with reference to preferred embodiments and that many variations and modifications are possible within the scope of the invention.

Claims (43)

1. A method for use in a radio communication system including a first transceiver, a second transceiver, and a repeater, the first and second transceivers being spaced apart from each other by a distance greater than at least one of their respective maximum transmission ranges, and the repeater being disposed intermediate the first and second transceivers, the method comprising:

upon receiving data from either of the first or second transceivers, the repeater transmits a repeat flag, causing the transceiver to suspend further transmission activity and then transmit data received from either of the first or second transceivers.

2. A method according to claim 1, wherein said first and second transceivers transmit an acknowledgement indicating whether reception of said data transmitted by said repeater was successful or failed.

3. The method of claim 2, wherein upon receiving the acknowledgement from each of the first and second transceivers, the repeater will send an overall status for the forwarded transmission.

4. A method for use in a network of devices for transmitting and receiving data in frames, the network of devices including a first transceiver, a repeater and at least one other transceiver, the first transceiver and the at least one other transceiver being spaced apart from each other by a distance greater than at least one of their respective maximum transmission ranges, and the repeater being interposed between the first transceiver and the at least one other transceiver, the method comprising the steps of:

the first transceiver transmitting data for use in the at least one other transceiver in a first time slot of the frame;

said repeater transmitting a repeat flag in a second time slot subsequent to said first time slot of said frame, causing said transceiver to suspend further transmission activity; and

the repeater repeats the data received in the first time slot in a third time slot after the second time slot of the frame.

5. The method of claim 4, further comprising the steps of: each of the at least one other transceivers transmits an acknowledgement of whether data reception was successful or unsuccessful in a fourth time slot after the third time slot of the frame.

6. The method of claim 5, wherein the fourth time slot of the frame is divided into a first sub-slot for indicating a positive acknowledgement and a second sub-slot for indicating a negative acknowledgement.

7. The method of claim 6, wherein the first and third slot lengths of the frame are variable and the first and second sub-slot lengths are fixed.

8. The method of claim 6, wherein the positive acknowledgement comprises transmitting a particular coded value that contains sufficient redundancy to allow it to be recovered in the presence of a reception error, and the negative acknowledgement comprises transmitting a particular coded value that contains sufficient redundancy to allow it to be recovered in the presence of a reception error.

9. The method of claim 7, further comprising a fifth time slot for transmitting the overall status to the network.

10. A radio communication system comprising a first transceiver, a second transceiver and a repeater, the first transceiver, second transceiver and repeater each comprising a receiver, a transmitter and a microprocessor, the first and second transceivers being spaced apart from each other by a distance greater than at least one of their respective maximum transmission ranges, and the repeater being disposed intermediate the first and second transceivers, wherein upon receiving data from either of the first or second transceivers in a first time slot, the repeater transmits a repeat flag in a second time slot causing the transceivers to suspend further transmission activity and subsequently transmits data received in the first time slot in a third time slot.

11. A radio communications system according to claim 10 wherein the first and second transceivers transmit an acknowledgement in a fourth time slot indicating whether reception of the data transmitted in the third time slot was successful or unsuccessful.

12. A radio communications system according to claim 11 wherein the first and second transceivers transmit a positive acknowledgement in the first of the two sub-slots of the fourth time slot or a negative acknowledgement in the second of the two sub-slots of the fourth time slot.

13. A radio communication system according to claim 11 wherein in a fifth time slot the repeater transmits the overall status of the transmission for retransmission to all transceivers.

14. A repeater for a radio communication system comprising at least two transceivers spaced apart from each other by a distance greater than at least one of their respective transmission ranges, the repeater being disposed intermediate the at least two transceivers in use, the repeater comprising a receiver, a transmitter and a microprocessor, wherein upon receipt of data in a first time slot, the microprocessor causes the repeater to transmit a repeat flag in a second time slot, causing the transceiver to suspend further transmission activity and subsequently transmit data received in the first time slot in a third time slot.

15. The repeater of claim 14, wherein upon receiving acknowledgment data from the at least two transceivers in a fourth time slot, the microprocessor determines an overall acknowledgment status and causes the repeater to transmit the overall acknowledgment status in a fifth time slot.

16. A transceiver for use in a radio communication system comprising at least one other transceiver and a repeater, the transceiver and the at least one other transceiver being spaced apart from each other by a distance greater than at least one of their respective transmission ranges, in use, the repeater being interposed between the transceiver and the at least one other transceiver, the transceiver comprising a receiver, a transmitter and a microprocessor, wherein upon receiving a repeat flag from the repeater in a second time slot, the microprocessor causes the transceiver to suspend further transmission activity until the transceiver receives data from the repeater in a third time slot, the data being initially transmitted by the at least one other transceiver in a first time slot prior to the second time slot.

17. A transceiver according to claim 16 wherein the microprocessor determines whether the data transmitted by the repeater in the third time slot was successfully received and causes the transceiver to transmit an acknowledgement in the fourth time slot indicating whether the reception of the data transmitted in the third time slot was successful or failed.

18. A transceiver according to claim 17 wherein the microprocessor causes the transceiver to transmit a positive acknowledgement in the first of the two subslots of the fourth time slot or a negative acknowledgement in the second of the two subslots of the fourth time slot.

19. A method in a radio communication system comprising at least a first transceiver, a second transceiver and a repeater, the first transceiver and the second transceiver being spaced apart from each other by a distance greater than a maximum transmission range of at least one transceiver, and the repeater being disposed intermediate the first and second transceivers such that upon receiving data transmitted from the first transceiver, the repeater repeats the data transmitted from the first transceiver, wherein upon receiving the data transmitted from the second transceiver before the repeater completely receives or repeats the data transmitted from the first transceiver, the repeater transmits a data sequence instructing each transceiver to cease its respective transmission.

20. The method of claim 19, wherein the respective transmissions of the first and second transceivers begin with a continuous sequence of primary bits.

21. The method of claim 20, wherein the data sequence transmitted by the repeater begins with a primary bit sequence.

22. The method of claim 21, further comprising delaying each transceiver by a period before attempting to retransmit its original transmission upon receiving the data sequence from the repeater such that each transceiver ceases transmission.

23. A method according to claim 21, wherein the delay period is calculated by each transceiver by selecting a random number and scaling the random number according to the number of bits in its respective transmission.

24. The method of claim 23, wherein if subsequent transmission retries still collide, the subsequently calculated delay period is increased.

25. The method of claim 24, wherein the transceiver stops further transmission attempts after a predetermined number of failed retries.

26. The method of claim 25, wherein after stopping further transmission attempts, the network alerts the operator that further transmission attempts have stopped.

27. A radio communication system comprising at least a first transceiver, a second transceiver and a repeater, the first transceiver, the second transceiver and the repeater respectively comprise a receiver, a transmitter and a microprocessor, the first transceiver and the second transceiver are spaced apart from each other by a distance greater than a maximum transmission range of at least one transceiver, and the repeater is disposed intermediate the first and second transceivers such that upon receiving data transmitted from the first transceiver, the repeater repeats the data transmitted from the first transceiver, wherein upon receiving data transmitted from the second transceiver before the repeater completely receives or repeats the data transmitted from the first transceiver, the repeater transmits a data sequence instructing each transceiver to cease its respective transmission.

28. A radio communications system according to claim 27 wherein the respective transmissions of the first and second transceivers begin with a continuous sequence of primary bits.

29. A radio communications system according to claim 28 wherein the data sequence transmitted by the repeater begins with a sequence of primary bits.

30. A radio communications system according to claim 29 wherein each transceiver, upon receiving the data sequence from the repeater to cause each transceiver to cease transmission, delays by one period before attempting to retransmit its original transmission.

31. A radio communications system according to claim 30 wherein the delay period is calculated by each transceiver by selecting a random number and scaling the random number according to the number of bits in its respective transmission.

32. A radio communications system according to claim 31 wherein if subsequent transmission retries still collide, the subsequently calculated delay period is increased.

33. A radio communications system according to claim 32 wherein the transceiver ceases further transmission attempts after a predetermined number of failed retries.

34. A radio communications system according to claim 33 wherein upon cessation of further transmission attempts, the radio communications system alerts an operator to the fact that further transmission attempts have ceased.

35. A repeater for use in a radio communication system comprising at least a first transceiver and a second transceiver, the first transceiver and the second transceiver are spaced apart from each other by a distance greater than a maximum transmission range of at least one of the transceivers, in use, the transponder is disposed intermediate the first and second transceivers, the transponder comprising a receiver, a transmitter and a microprocessor, wherein the microprocessor causes the repeater to repeat the data transmitted from the first transceiver upon receiving the data transmitted from the first transceiver, wherein upon receiving data transmitted from the second transceiver before the repeater completely receives or repeats the data transmitted from the first transceiver, the microprocessor causes the transponder to transmit a data sequence instructing each transceiver to cease its respective transmission.

36. The repeater according to claim 35, wherein the data sequence transmitted by the repeater is a primary bit sequence.

37. A transceiver for use in a radio communication system comprising at least one other transceiver and a repeater, in use, the transceiver and the at least one other transceiver being spaced apart from each other by a distance greater than the maximum transmission range of at least one of the transceivers, and the repeater being interposed between the transceiver and the at least one other transceiver, the transceiver comprising a receiver, a transmitter and a microprocessor, wherein the microprocessor causes the transceiver to start transmitting data such that upon receiving data transmitted from the at least one other transceiver, the repeater repeats data transmitted from the at least one other transceiver and upon receiving data transmitted from the transceiver before repeating data transmitted from the at least one other transceiver, the repeater transmits a data sequence instructing each transceiver to cease its transmission, wherein the microprocessor causes the transceivers to cease transmission upon receipt of the data sequence from the repeater.

38. A transceiver according to claim 37 wherein transmissions from the transceiver begin with a continuous sequence of primary bits.

39. A transceiver according to claim 38 wherein, upon receipt of the data sequence from the transponder, the microprocessor delays for a period before attempting to retransmit its original transmission.

40. A transceiver according to claim 39 wherein the delay period is calculated by the microprocessor by selecting a random number and scaling the random number according to the number of bits in its transmission.

41. A transceiver according to claim 40 wherein if a subsequent retransmission still results in receiving the data sequence from the repeater, the microprocessor will increase the subsequent delay period before retransmitting its original transmission.

42. A transceiver according to claim 41 wherein after a predetermined number of failed retransmission attempts, the microprocessor causes the transceiver to stop further transmission attempts.

43. A transceiver according to claim 42 wherein, once further transmission attempts have ceased, the microprocessor alerts the operator to the fact that further transmission attempts have ceased.