Patent Description:
In the state of the art, time division multiple access communication networks as well as the respective methods are known that generally relate to channel access methods for wireless transmission. The general purpose of a time division multiple access is to enable several nodes to transmit data on the same frequency channel wherein the corresponding frequency channel is divided into frames that in turn are divided into time slots which might be occupied by the several nodes.

A problem encountered by these networks and methods corresponds to detecting a collision of several transmissions occurring simultaneously, in particular within the same time slot, and to avoid such collisions in a most efficient manner. Actually, an occurring collision is detected in the application layer of the respective telecommunication standard according to the Open System Interconnection Model (OSI Model). This, however, provokes time outs and/or confirmations to be processed which result in longer transmission times while reducing the available data rate massively.

In the time division multiple access communication networks and their respective methods according to the state of the art, a present data transmission has to be interrupted in order to be enabled to detect another occurring transmission. The data transmission in the time slot affected has to be transmitted again. Thus, the corresponding bandwidth of the wireless transmission channel is reduced.

<CIT> describes a communication system using its own communication protocol in order to provide a collision detection of simultaneous data transmission. According to the communication protocol, a coded portion indicating the start of data transmission and an associated end of data marker indicating the end of data transmission for each frame are used. A receiver receiving two different data streams is enabled to detect a collision of simultaneous data transmission when two coded portions indicating the start of data transmission are received subsequently.

The paper "CSMA/CN" by Souvik Sen et al discloses a communication network in which a receiving node detects colliding transmissions and issues a collision notification to be received by a transmitter. The transmitter receiving the collision notification aborts its transmission that is continued if no transmission occurs.

It is an object of the present invention to improve the time division multiple access communication networks with regard to collision detection such that the data rate can be substantially maintained.

The invention provides a time division multiple access communication network with collision detection, wherein the network comprises at least two transmitting nodes and at least one receiving node that has a correlation receiver for signaling, wherein at least one of the transmitting nodes provides a respective predefined signal pattern for signaling, wherein the receiving node is configured to detect one or more incoming transmissions based on correlation of the predefined signal pattern received, wherein the receiving node is configured to indicate more than one colliding transmissions to all other nodes of the network. At least one of the transmission nodes is configured to stop transmission due to reception of a collision information. The receiving node is configured to indicate at least one valid transmission to all other nodes of the network, wherein the receiving node is configured to send a first signal pattern indicating the at least one valid transmission, which informs the other transmission nodes and blocks at least one respective time slot ensuring that no collision will occur in the appropriate time slot. The at least one transmission node, which stopped transmission, is configured to reinitiate transmission after a certain time after stopping transmission. The respective transmission nodes involved in the collision are configured to use different back off values or times ensuring that the collision is avoided in the future.

Further, the invention provides a method for performing collision detection in a time division multiple access communication network comprising at least two transmitting nodes and at least one receiving node, with the following steps:.

The invention is based on the finding that the at least one receiving node can be used to provide information to all participants of the network, in particular the several transmission nodes, with regard to the current status of the signaling. Therefore, the receiving node distributes the information according to which a valid transmission of one of the transmission nodes is currently performed. Furthermore, the predefined signal pattern is taken into account in order to detect a valid transmission and/or colliding transmission within a certain time slot.

Particularly, the at least two transmitting nodes each provide a respective predefined signal pattern for signaling wherein the receiving node is configured to detect one or more incoming transmissions based on correlation of the predefined signal patterns received.

The different (individual) signal patterns are taken into account in order to determine the number of streams occurring within the same time slot, namely simultaneously. Provided that two or more streams (transmissions) are detected within the same time slot, a collision indication is outputted and distributed among the participants of the network.

In fact, the receiving node correlates with all predefined signal patterns of the transmission nodes of the system such that colliding transmissions can be detected by the receiving node appropriately.

In order to break up the collision detected, at least one of the transmission nodes involved in the collision stops its transmission appropriately. For instance, all transmission nodes involved stop their respective transmissions.

The transmissions occurring a collision may relate to requests of the respective transmission nodes to send data packages wherein these requests occur simultaneously, in particular in the same time slot.

Particularly, the at least one transmission node is configured to reinitiate transmission after a certain time after stopping transmission. This ensures that the data to be sent will be send afterwards such that no data gets lost. In fact, the data transmission is only postponed to a time that ensures no colliding transmissions.

The collision detected can be broken up appropriately when at least one of the transmission nodes involved in the collision stops its transmission. For instance, all transmission nodes involved stop the corresponding transmissions. The reinitiating ensures that the data to be sent will be send afterwards such that no data gets lost. In fact, the transmission is only postponed to a time that ensures no colliding transmissions.

This first signal pattern is sent out as soon as a request, a data stream or anything else from a transmission node with regard to a transmission is detected such that the other transmission nodes of the network are informed about the (upcoming) transmission. The first signal pattern shall inform the other transmission nodes and, preferably, block respective time slot(s).

According to an aspect, the receiving node, in particular the correlation receiver, comprises a threshold metric that is configured to determine at least one of the number of simultaneous transmissions and a collision of transmissions. The threshold metric receives the signals received by the receiving node and processes them appropriately. Thus, the number of simultaneous signals, in particular the ones from different transmission nodes, can be separated in order to determine the number of simultaneous transmissions. Two simultaneous transmissions already relate to a collision as two colliding transmission occur within the same time slot.

Moreover, the receiving node may be configured to send a second signal pattern indicating colliding transmissions of at least two transmission nodes. As already described, the receiving node correlates with all predefined signal patterns of the several transmission nodes such that the receiving node can detect the occurrence of a collision. By informing the transmission nodes of the network with regard to a collision detected, the transmission nodes may change their status in order to dissolve the collision occurred.

This collision information may accompany with a new requesting phase for the respective transmission nodes for establishing a transmission.

According to another aspect, the certain time is of random length based on multiple reservation times. The random length relates to a back off value based on a pseudo-random process.

The different back off times may correspond to different time slots.

A first back off time for the first transmission node ensures that only this first transmission node transmits the appropriate signal in the time slot intended again. The other transmission nodes are informed by the receiving node appropriately, in particular via the first signal pattern sent. Accordingly, the other transmission nodes receive the information that the appropriate time slot is used by the first transmission node.

This information is sent out as long as the transmission is ongoing such that the appropriate time slot becomes available once the transmission of the first transmission node has finished.

Accordingly, a new requesting phase being robust is ensured as the transmission nodes involved in the collision transmit their (new) requests at different times due to the certain times (of random length based on multiple reservation times). The first of the several transmission nodes involved in the collision will establish a connection with the receiving node such that the receiving node informs the other transmission nodes about the (valid) transmission ensuring that no collision will occur in the appropriate time slot.

For instance, the network is configured to execute a frequency hopping method. With regard to the method, a frequency hopping method is executed. Accordingly, the collision may be break up by using different carrier frequencies provided that this is possible within the transmission channel. The frequency hopping may also be based on a pseudo-random process.

Another aspect provides that at least one of the receiving node and the transmission node is configured to indicate a collision to a user of the network. Thus, the user of the network gets informed about a collision detected. Moreover, the user may also be informed that the collision has broken up appropriately.

Another embodiment provides that the correlation receiver is configured to process data communication. Thus, the data transmission is also done by the respective receiver. Hence, the receiver is not only intended for establishing the respective transmissions, but also for processing the appropriate data.

According to an embodiment, the network is a mobile ad-hoc network and/or a multi hop network. The mobile ad-hoc network, also called MANET, has no fixed wireless infrastructure as it is a continuously self-configuring network of mobile devices that are connected with each other wirelessly. The connections are direct connections between the participants or through multiple hop relays. Multi hop networks, comprising (additional) relays, improve the transmission range, throughput and coverage. In such networks, the connections are changed frequently which generally increases the risk of collisions.

According to an aspect, the receiving node transmits a second signal pattern indicating colliding transmissions of at least two transmission nodes. As already described, the receiving node correlates with all predefined signal patterns of the several transmission nodes such that the receiving node can inform the transmission nodes of the network with regard to a collision detected. This collision information may accompany with a new requesting phase for the respective transmission nodes for establishing a transmission.

The invention will now be described with reference to a preferred embodiment which is shown in the enclosed drawings. In the drawings,.

The invention made is disclosed in the embodiment referring to <FIG>.

In <FIG>, a time division multiple access communication network <NUM> is shown that comprises a receiving node <NUM> and three transmission nodes <NUM>, <NUM>, <NUM> wherein the range <NUM> of the first and second transmission nodes <NUM>, <NUM> as well as the range <NUM> of the third transmission node <NUM> are also indicated.

As shown in <FIG>, the third transmission node <NUM> is a hidden node for the first and second transmission nodes <NUM>, <NUM> due to the ranges <NUM>, <NUM>.

The receiving node <NUM> receives the transmission signals of all transmission nodes <NUM>, <NUM>, <NUM> wherein the signals received are processed by an internal correlation receiver <NUM> that comprises a threshold metric <NUM> as shown in <FIG> illustrating the receiving node <NUM> in more detail.

The correlation receiver <NUM> receives the different signals (streams S1 to Sn) and processes the appropriate data in order to detect different transmission, in particular different transmission occurring simultaneously (#Streams < <NUM>).

For this purpose, the threshold metric <NUM> is used that correlates the different (predefined) signal patterns for signaling of the transmission nodes <NUM>, <NUM>, <NUM>, namely the different streams S1 to Sn. As the receiving node <NUM> correlates with the signal patterns for signaling of all transmission nodes <NUM>, <NUM>, <NUM>, the receiving node <NUM> is enabled to dissolve an occurring collision of more than one transmission signals.

In other words, the correlation receiver <NUM>, in particular the threshold metric <NUM>, takes the different signal patterns of the transmission nodes <NUM>, <NUM>, <NUM> into account in order to determine the number of transmission signals (streams) occurring simultaneously, in particular within a certain time slot.

In <FIG>, a schematic overview is shown that represents a method for performing collision detection and/or a time slot reservation indication in a time division multiple access communication network <NUM> as shown in <FIG>. In the shown embodiment, a collision between the second and the third nodes <NUM>, <NUM> occurs as will be described hereinafter.

In a first time slot <NUM> of the transmission shown, the receiving node <NUM> sends out a signal pattern indicating the status of the currently transmissions. This signal pattern is indicated by "N". The appropriate signal (pattern) informs the other transmission nodes <NUM>, <NUM> appropriately. The signal pattern indicated by "N" is always sent once the receiving node <NUM> detects an incoming signal, for instance a request.

At the beginning of the second time slot <NUM>, a synchronization pattern S is used to detect a collision of at least two colliding transmissions. This can be done as the receiving node <NUM> correlates with all possible signal patterns such that a collision of two different transmission nodes <NUM>, <NUM> can be determined appropriately.

In the second time slot <NUM>, a collision is detected in a certain time slot. Accordingly, the receiving node <NUM> emits a collision pattern which is labeled by "K" as shown in <FIG> and <FIG>. The collision pattern K corresponds to a second signal pattern sent out by the receiving node <NUM>.

The respective collision pattern K is received by the transmission nodes <NUM>, <NUM>, <NUM> of the network <NUM> and processed appropriately.

The transmission nodes <NUM>, <NUM> transmitting signals in this time slot stop their transmissions due to reception of the collision information, namely the collision pattern K.

Further, the collision pattern K indicates to the transmission nodes <NUM>, <NUM>, <NUM> that a new request phase has to be initiated after a certain time after stopping the respective transmission.

This will be done based on a pseudo-random process wherein new back off values for the time slots are generated, in particular for following time slots, for instance subsequent time slots.

This pseudo-random process causes the different transmission nodes <NUM>, <NUM>, <NUM> to initiate their request at different times due to the different back off values ensuring that only one of the different transmission nodes <NUM>, <NUM>, <NUM> tries to establish a connection with the receiving node <NUM> at a certain time slot as shown for the third time slot <NUM>. In general, the certain time is of random length based on multiple reservation times.

Thus, the third time slot <NUM> is used by the third node <NUM>, for instance, for the new attempt to establish a connection with the receiving node <NUM>.

Therefore, the receiving node <NUM> sends out a first signal pattern indicating the at least one valid transmission with the third node <NUM> in the respective time slot(s) such that all transmission nodes <NUM>, <NUM>, <NUM> are informed about the occurring transmission.

As indicated in the fourth time slot <NUM> and the fifth time slot <NUM>, the first node <NUM> and the fourth node <NUM> would try to establish a connection later due to the different back off values. However, these connections will not be established due to the connection already established with the third node <NUM> before in the third time slot <NUM> until this transmission has been finished.

Accordingly, the collision occurring in the second time slot <NUM> has been dissolved appropriately.

Furthermore, hidden nodes such as the fourth node <NUM> can be handled by the network <NUM> appropriately.

In addition, the network <NUM> may be configured to execute a frequency hopping method simultaneously such that the carrier frequency is altered. This may also be based on a pseudo-random process.

Once, a collision has been detected and the respective collision pattern K, namely the second signal pattern, is sent out by the receiving node <NUM> (and received by the transmission nodes <NUM>, <NUM>, <NUM>), at least one of the receiving node <NUM> and the transmission nodes <NUM>, <NUM>, <NUM> may inform the user of the system <NUM> with regard to the occurrence of a collision.

The correlation receiver <NUM> used for determining the number of simultaneous transmission and/or collisions may also be configured to process data streams of the respective transmission nodes <NUM>, <NUM>, <NUM> once a data transmission has been established such that the appropriate data can be processed by the receiving node <NUM>.

In general, the network <NUM> may be a mobile ad-hoc network and/or a multi hop network which usually comprise participants frequently changing their transmission properties.

Claim 1:
A time division multiple access communication network (<NUM>) with collision detection, wherein the network (<NUM>) comprises at least two transmitting nodes (<NUM>, <NUM>, <NUM>) and at least one receiving node (<NUM>) that has a correlation receiver (<NUM>) for signaling, wherein at least one of the transmitting nodes (<NUM>, <NUM>, <NUM>) provides a respective predefined signal pattern for signaling, wherein the receiving node (<NUM>) is configured to detect one or more incoming transmissions based on correlation of the predefined signal pattern received, wherein the receiving node (<NUM>) is configured to indicate more than one colliding transmissions to all other nodes (<NUM>, <NUM>, <NUM>) of the network (<NUM>), and wherein at least one of the transmission nodes (<NUM>, <NUM>, <NUM>) is configured to stop transmission due to reception of a collision information, characterized in that the receiving node (<NUM>) is configured to indicate at least one valid transmission to all other nodes (<NUM>, <NUM>, <NUM>) of the network (<NUM>), wherein the receiving node (<NUM>) is configured to send a first signal pattern indicating the at least one valid transmission, which informs the other transmission nodes (<NUM>, <NUM>, <NUM>) and blocks at least one respective time slot ensuring that no collision will occur in the appropriate time slot, characterized in that the at least one transmission node (<NUM>, <NUM>, <NUM>), which stopped transmission, is configured to reinitiate transmission after a certain time after stopping transmission, and wherein the respective transmission nodes (<NUM>, <NUM>, <NUM>) involved in the collision are configured to use different back off values or times ensuring that the collision is avoided in the future.