Method and communication station for transmitting data

The invention relates to a method for error-monitored transmission of data via parallel interfaces of a multi-hop communication system with the preamble features of claims 1 and 2, as well as to corresponding communication systems.

In multi-hop communication systems, also referred to as multi-hop communication systems, data is transmitted from a transmitting station to a final receiving station either directly over or a plurality of intermediate intermediate or Transmit relay stations. In addition to the transmission of data via a single intermediate relay station, the data can also be transmitted via a plurality of series-connected relay stations, which is also referred to as multi-hop. In addition, especially in single frequency network (SFN) communication systems, one and the same signal, and thus one and the same data from multiple relay stations, can be simultaneously receive little delayed and together, that is at the same time or correspondingly slightly delayed and transmitted on the same frequency directly to the receiving station or to another relay station. Predeldering or equalization techniques can be used in relay stations to increase performance. In order to ensure error-free data transmission, error detection and error correction methods known per se from such or other communication systems are used, for example an automatic request for the repeated transmission of an original or modified data packet (ARQ: Automatic Repeat Request). Also known is the application of a so-called cyclic redundancy check (CRC: Cyclic Redundancy Check). These procedures are applied to each of the transmissions, that is, to each transmission from the transmitting station to an adjacent relay station, to each transmission from one relay station to another relay station and to every transmission from a relay station to the receiving station. Although this procedure ensures that the data reach the receiving station as error-free as possible via as many paths as possible, the high associated computational and time expenditure is disadvantageous. In addition, high energy consumption is associated with this approach because, on the one hand, the unpacking, decoding and testing of received data in the relay stations and the request for retransmission or retransmission and retransmission consumes energy and ultimately the repeated transmission of resent packets also consumes energy ,

From WO 01/15374 A1 a method for transmitting an alarm message is known in which, when first transmission means are out of range of destination receiver means, the message is repeatedly transmitted from one or more transceivers located within reach, until the receipt of the message is confirmed by the destination receiver means by an acknowledgment signal.

US 4 882 765 discloses a method in which a repeater station autonomously retransmits a message to the receiving station due to a certain number of retransmissions already made by the transmitting station or due to an unreceived acknowledgment from the receiving station.

Finally, WO 00/74306 A2 discloses a system with a number of nodes, in which each node forwards a message received from another node to a subsequent one. All nodes use a uniform reference frequency.

The object of the invention is to improve a method for error-monitored transmission of data via parallel interfaces of a multi-hop communication system, in particular with a view to improving the processing complexity of the overall system, and to propose a communication system for carrying out such a method.

This object is achieved by methods for error-monitored transmission of data via parallel interfaces of a multi-hop communication system having the features of claims 1 and 2, as well as by communication systems having the features of claims 10 and 11.

Advantageous embodiments are the subject of dependent claims.

Because confirmations or Requests for retransmissions generated only by the receiving station, that is, usually the last station in the transmission chain, must also only monitor this station received data to a sufficient reception quality. When a sufficient reception quality is detected, only this station also sends such confirmation or Request in the direction of the originally transmitting the data station. The intermediate relay stations serve in the simplest case only to forward received data or for forwarding received acknowledgments or requests. Accordingly, in this simple case, verification for forwarding received data to the relay stations is eliminated, allowing for faster forwarding and lower power consumption.

A relay station, which checks the forwarding of received data to an inadequate reception quality and does not forward or forward the data depending on it; Although the data connection maintains or shuts down with respect to this reception quality, it does require energy and time to check the received data, but energy is also ultimately saved by an inhibited forwarding and an inhibited request for a renewed data transmission. The fact that in such a communication system, the originally transmitted data is transmitted over a plurality of parallel data paths, there is a sufficiently high probability that in the case of data loss on a transmission path and the subsequent deactivation of this data path, the original data on at least one or more more the parallel transmission paths to the intended destination station or get to the receiving station. Thus, a communication system is advantageous or a procedure in which the transmission of the data is made only via relay stations, the data sufficiently well or received with sufficient freedom from errors.

While it is advantageous when a relay station independently decides whether data received for forwarding is of sufficient quality to be forwarded, a methodology that takes account of information from relay stations of parallel transmission paths is particularly advantageous for the decision making process. Tells a relay station on a parallel path that they have a transmission with very good or high-quality data forwarded for forwarding, a parallel relay station informed about it does not have to carry out an additional transmission of possibly even badly received data. This is especially true when the parallel data paths intersect each other or from each relay station, the forwarded data from other relay stations can be received in their environment.

Advantageously, a plurality of per se known error correction methods or error detection methods can be used in the relay stations, this method being used only to detect the quality of the received data to be forwarded, but not to request again in the case of poor reception quality.

Particularly advantageous is the use of such methods in a communication system in which the various transmitting and receiving stations and relay stations communicate on a single frequency. These conditions can be found, in particular, in decentrally organized, that is, self-organizing, communication networks typical of so-called ad-hoc communication systems.

Advantageously, the data received in parallel and superimposed via different parallel paths are superimposed on the receiver side in the receiving station and processed together in order to be able to achieve a further quality improvement by statistical averaging and the like.

In particular, for the conditionally dependent forwarding of data in relay stations, a higher summation data rate results on the receiver side, ie an increased reproduction quality due to the fact that the data received on the receiver side has a better quality in the aggregate as a whole.

A communication station for performing such a method may be a transmitting station, a received station or a relay station, but may also combine two or all three of the functionalities. Such a communication station expediently has, in addition to a reception transmitting device, also an analysis device which may be part of the station-specific control device and is designed to analyze received data with regard to their reception quality.

An embodiment and variants thereof are explained below with reference to the drawing. Show it:<dl id="dl0001"><dt>Fig. 1</dt><dd>schematically a communication system with a plurality of communicating via parallel data connections stations and</dd><dt>Fig. 2</dt><dd>schematically the various possibilities for the treatment of data received for forwarding in relay stations.</dd></dl>

As can be seen from FIG. 1, an exemplary communication system MHSFN has a plurality of stations communicating with one another. As a communication system, a multi-hop (MH) communication system is exemplified, which is designed as a single frequency network (SFN). However, transmission to other communication systems, in particular ad-hoc communication systems, is possible.

Shown is a situation in which a sending station SS sends data D to a receiving station RS. The distance between the transmitting station SS and the receiving station RS is assumed to be so large that a direct transmission via a direct communication link between the two is not possible. The transmitting station SS transmits its data D via a plurality of communication interfaces V11, V12, V13 to various intermediate stations, which are referred to below as relay stations HS1, HS2, HS3 for ease of distinctness. The relay stations HS1, HS2, HS3 detect, for example, at the header of received data packets, that it is to be forwarded received data D and forward this receiving data D towards the destination station, that is, the receiving station RS via further communication interfaces V21, V23 continue. The communication interfaces V11, V12, V13, V21, V23 are preferably radio interfaces, which with the same or operate on a single frequency. In the event that the receiving station RS is already in the transmission range of the relay stations HS1, HS3, the received data D to be forwarded are transmitted directly to the receiving station RS. Otherwise, the transmission takes place via further intermediate relay stations.

From the received station RS a check is made after receiving the data D, whether they have been received sufficiently error-free. For checking conventional, known per se error detection and error correction methods, eg ARQ and / or CRC. After such an analysis, the receiving station RS sends an acknowledgment ACK about a sufficient reception quality and / or a request for retransmission or modified transmission of the original data D in the direction of the original transmitting station SS. The confirmation ACK or In turn, the request is transmitted via a direct connection or a plurality of mutually parallel connections V21, V11, V23, V13, V22, V12 with the interposition of the relay stations HS1, HS2, HS3. Depending on the receipt of an acknowledgment ACK or a request, the transmitting station SS subsequently transmits new data D or new data packets or causes a repeated and optionally modified transmission of the original data.

Advantageously, according to a preferred embodiment data received in the relay stations HS1, HS2, HS3 for forwarding D are not simply forwarded unchecked but before forwarding with respect to the reception quality or the data quality checked. If one of the relay stations HS2 determines that the data quality of the data D received for forwarding is insufficient or this data D has been received in error, it does not establish a connection V22 for forwarding the received data D. As a result, the corresponding data path V12, V22, which was originally set up by the transmitting station SS via the second relay station HS2 to the received station RS, interrupts. In particular, the second relay station HS2 also does not cause re-transmission of the original or modified original data D.

In the intermediate relay stations HS1-HS3, in addition to a receiving device R and a transmitting device S as well as more generally for the operation of required control devices and memory, facilities and functions for the verification of data received for forwarding are provided. In particular, an analysis device A is provided for this purpose, which may be part of the central control device of the relay stations HS1-HS3.

Further devices and / or functions are advantageously used to carry out predistortion or equalization processes, by means of which, for example, a constructive superimposition of the signals at the receiving station RS and optionally further intermediate relay stations can be achieved. For example, known per se methods such as a phase or equal gain, maximum ratio or a selection or Selection distortion can be used. Also possible are combinations or extensions as well as other predistortion techniques.

According to a further embodiment, a communication of different relay stations HS2, HS3 is possible with each other. Communication takes place via a corresponding interface VH, which can preferably be designed as a radio interface, but in principle also as a line-bound interface. In addition, information relating to the forwarding of received data D or are transmitted via their reception quality. This makes it possible that a third relay station HS3 can transmit this fact to a second relay station HS after receiving data D with a very good reception quality, which has received the same data D in parallel as a parallel station, but with a poorer reception quality. In such a case, the relay station HS with the poorer reception quality can suppress the forwarding for forwarding received data D since the same data D with better forwarding quality is transmitted via a parallel data path SS-HS3-RS.

In general, before forwarding in the relay stations HS1-HS3, data processing of data received for forwarding can be undertaken. The type of processing and forwarding or Retransmission can be subject to different characteristics. For example, signal-to-noise ratios (SNR: Signal to Noise Relation) can be evaluated at the inputs of the intermediate relay stations HS1-HS3. It is also possible to determine the number of corrected bits in a Viterbi decoder or to take into account the result of a cyclic redundancy check CRC. In particular, methods for equalizing and amplifying a signal received for transmission without further additional demodulation are preferred as processing techniques. In relay stations HS1-HS3, in which a check is made of data received for forwarding, the received data D are expediently demodulated and decoded in order to be able to carry out the actual analysis. Both an embodiment in which the analyzed data D or Data packets are then re-encoded and modulated for forwarding, but also an embodiment in which the data originally received for forwarding D are held in a buffer to be passed unchanged from the cache can, if a doubled set of data after a Demodulation, decoding and analysis were found to be sufficient for forwarding. Advantageously, methods for retransmitting a faulty or insufficiently received data packet can be deactivated if the data D receiving station is not the destination station but only a relay station.

In the context of forwarding or forwarding, it is also possible to perform a predistortion in addition to the re-encoding and modulating data D or data packets. In particular, the forwarding of a received signal or received data D after an equalization, amplification and possible predistortion can be carried out.

In principle, an application is centralized as well as decentralized or self-organized networks possible. The exchange of the abovementioned characteristics between individual stations, in particular between relay stations on mutually parallel data paths, can be used particularly advantageously, as stated above. However, only parameters which were used in the own station can also be used for the analysis, for example by means of fault recognition and error correction methods known per se. The application of an error correction method can in this case be limited to the error-detecting part in the case of a relaying relay station, a corrective part being used only in the event of a retransmission which is not required for that purpose, provided transmission of the data over a sufficient number of parallel data connections is ensured. The same applies to error detection methods, which are preferably used in the case of a relay station limited to the detection of the error, wherein a corresponding error detection message is suppressed.

In the case of communication between neighboring stations, in particular relay stations HS2, HS3, on the one hand only a direct transmission of an analysis result to neighboring stations can be made, but it is also possible to negotiate or Negotiation of the analysis or Evaluation results between such neighboring stations, which decide to conclude such a negotiation over which of the negotiating stations HS3 a forwarding of the data is to be made.

FIG. 2 serves to illustrate different variants of the illustrated embodiment. One focus is on the organization of the evaluation process. For simplification, it can be assumed, for example, that only a single parameter which is the result of a cyclic redundancy check is used. Furthermore, it is assumed in the simple example that the at the intermediate stations or Relay stations HS1-HS3 for forwarding received signals can be completely demodulated and decoded. The starting point is an error correction method in a 2-hop SFN communication system in which the error correction ARQ end-to-end connection is performed. Error corrections, as known per se for the individual connections, can be omitted according to the concept described above. The originally transmitting station SS thus receives no confirmations for data or Data packets which were received correctly by the intermediate relay stations HS1-HS3. It is accordingly no separate protection of the first jumps or Hops performed. Only the receiving station RS confirms correctly received packets, whereupon packets with a missing acknowledgment are repeatedly transmitted from the transmitting station SS in the absence of the acknowledgment.

For the intermediate relay stations HS, there are various possibilities, the received data D or To handle data packets. According to a particularly simple embodiment a) an unconditional forwarding takes place in the relay station HS. It may happen that an incorrectly received data packet or a signal with a poor signal-to-noise ratio is forwarded to the receiving station RS. The evaluation of parameters or the like is omitted in this case.

Therefore, the conditionally linked or conditional forwarding b) of receiving data D. These conditions can be independently evaluated in each of the different parallel relay stations HS or with the help of information from all or several mutually communicating relay stations HS2, HS3. Accordingly, there are two other variants. In the simpler case c), only one station-internal analysis of data D received for forwarding is undertaken. If the analyzed data have sufficient data quality, the forwarding is initiated in the direction of the receiving station RS. If the data quality is insufficient, forwarding in the direction of the received station RS is prevented. Advantageously, the acknowledgment of confirmations or requests for retransmissions can also be omitted.

According to the other embodiment d), the communication described with reference to the second and third relay stations HS2, HS3 takes place, in which at least one of the relay stations HS2 accesses information from at least one other of the relay stations HS3 in order to make a decision regarding possibly not optimally received data D to meet their forwarding.

Surprisingly, even the unconditional forwarding a) of data D is advantageous even independently of an analysis and thus independent of a sufficient or insufficient reception quality in the relay station HS. It is assumed that all data paths SS-HS1-RS, SS-HS2-RS, SS-HS3-RS have an approximately equal average packet error rate PER₀ The probability that exactly n relay stations of a total of K mutually parallel relay stations correctly receive a transmitted data packet can be formulated as follows: <maths id="math0001" num=""><math display="block"><mrow><mi mathvariant="normal">p</mi><mrow><mo>(</mo><mi mathvariant="normal">n</mi><mo>)</mo></mrow><mo>=</mo><mrow><mo>(</mo><mtable><mtr><mtd><mi mathvariant="normal">K</mi></mtd></mtr><mtr><mtd><mi mathvariant="normal">n</mi></mtd></mtr></mtable><mo>)</mo></mrow><mo>⋅</mo><msup><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msub><mrow><mi mathvariant="normal">BY</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>)</mo></mrow><mrow><mi mathvariant="normal">n</mi></mrow></msup><mo>⋅</mo><msup><mrow><msub><mrow><mi mathvariant="normal">BY</mi></mrow><mrow><mn>0</mn></mrow></msub></mrow><mrow><mi mathvariant="normal">K</mi><mo>-</mo><mi mathvariant="normal">n</mi></mrow></msup><mo>⋅</mo></mrow></math><img file="EP1523835B1_D0001.tif" /></maths>

The average number of relay stations that have correctly received the packet or data and forward accordingly can be calculated as follows: <maths id="math0002" num=""><math display="block"><mrow><mi mathvariant="normal">e</mi><mrow><mo>(</mo><mi mathvariant="normal">n</mi><mo>)</mo></mrow><mo>=</mo><mrow><munderover><mo>Σ</mo><mrow><mi>n</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>K</mi></mrow></munderover><mrow><mi mathvariant="normal">n</mi><mo>⋅</mo><mi mathvariant="normal">p</mi><mrow><mo>(</mo><mi mathvariant="normal">n</mi><mo>)</mo></mrow></mrow></mrow><mo>≈</mo><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msub><mrow><mi mathvariant="normal">BY</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>)</mo></mrow><mo>⋅</mo><mi mathvariant="normal">K</mi><mn>,</mn></mrow></math><img file="EP1523835B1_D0002.tif" /></maths>

While in the unconditional forwarding all K intermediate stations transmit together in the SFN communication system, in the case of a conditional forwarding, that is to say in the case of analyzing a reception quality of receiving data D in relay stations HS1-HS3 according to the more preferred embodiments, only data D will have a smaller number of data paths SS-HS1-RS; SS-HS3-RS arrive at the receiving station RS. Thus, in the case of a condition-dependent forwarding, the received power at the receiving station RS may be comparatively lower than in the case of an unconditional forwarding of the data C by all the relay stations. However, in the case of the partially suppressed forwarding, the data D received at the receiving station RS has a higher data quality or higher data quality. a lower signal-to-noise ratio, so that an overall improvement in data quality is recorded.