GB2478004A - Activation or deactivation of decoding at a relay node in response to signal quality - Google Patents

Abstract

A relay device obtains a first data and a second data intended for a destination device, in a non-decoded form. The relay device needs to perform the data relay as a combination of the first and second data. As the first and/or second data may have been subject to a signal distortion on at least one path , up to the relay device, the relay device needs to determine in what form it is appropriate to transmit the combination of the first data and the second data. The relay device performs decoding by parts of the first and second data and, each time one part is decoded, checks whether residual errors remain in the decoded data part. If an error is detected, the relay device transmits to the destination device a combination of the first and second data in the non-decoded form. Else if no error remains once the decoding is complete, the relay device transmits to the destination device a combination of the first and said second data in a decoded form. Therefore the decoding of the first and second data at the destination device is made more reliable and power savings made at the relay node.

Description

Transmitting data from a relay device to a destination device

1. FIELD OF THE INVENTION

The present invention relates to a method and a device for transmitting data from a relay node to a destination node, a computer program product which causes a computer or processor to carry out the steps of the transmitting method, and an information storage means storing the computer program product.

The invention falls within the technical field of communication networks and is particularly applicable in the implementation of wireless mesh communication networks.

2. TECHNOLOGICAL BACKGROUND

Recently network coding has been investigated as a method to improve network performance in a mesh network, comprising several source nodes, a destination node and multiple relay nodes. Relaying (also referred to as "retransmitting") data to by a relay node in wireless communication networks, and in communication networks more generally, is a problematic widely addressed in the state of the art.

Assuming the destination node, receiving data from the source nodes and a relay node, cannot decode the received data perfectly, a belief propagation scheme has been proposed. It consists, for the relay node, in employing logarithm likelihood values to build the relayed data. One should for instance refer to the conference paper, S. Yang and R. Koetter, "Network Coding over a Noisy Relay: a Belief Propagation Approach", IEEE International Symposium on Information Theory 2007.

In the context of wireless communications, an additional problem shall be taken into account. Indeed, wireless communication links are more subject to interferences than wired communication links. For instance, communications around 60 GHz are easily disturbed by moving objects because of its strong directivity. These objects create a so called shadowing phenomenon.

The shadowing phenomenon implies a quality degradation of the decoded data at the destination node. The belief propagation scheme at the relay node is also applicable for 60 GHz communication; however, there are still some room to improve the quality of decoded data at the destination node, because the belief propagation does not guarantee improving it in any case. For example, if the data from the source node to the destination node is strongly affected by shadowing and the data from the source node to the relay node is affected by shadowing but errors can be corrected at the relay node, transmitting the data made by logarithm likelihood may incur rather worse results at the destination node.

3. OBJECTIVES OF THE INVENTION In at least one embodiment, it is desirable to overcome these various drawbacks of the state of the art.

In particular, it is desirable to improve error rate of a destination node it is desirable to reduce the power consumption at the relay node, while improving error rate at the destination node.

it is desirable to provide an interface to manage a brief propagation strategy so that the path diversity can be achieved.

4. SUMMARY OF THE INVENTION

According to a first aspect, in at least one embodiment, the invention relates to a method for transmitting data from a relay device to a destination device, the relay device obtaining in a non-decoded form a first data and a second data intended for the destination device. The relay device performs: -a first determining step of determining if said first and second data have been subject to a signal distortion on at least one path up to said relay device; -a transmitting step of transmitting to said destination device, on the basis of the result of the first determining step, either: o a combination of said first and said second data in the non-decoded form; or o a combination of said first and said second data in a decoded form.

Thus, the invention relies on the principle that if the first and second data have been subject to unrecoverable errors remain (or are estimated to remain), the relayed data is based on a combination of soft values (first and second data in their non-decoded form). Else, if all errors have been recovered in the decoding process, the relayed data is based on a combination of hard values (first and second data in their decoded form). Therefore, a bit error rate (denoted as BER) obtained at the destination device can be improved when the relayed data is deterministically reconstructed from non-decoded or decoded data at the relay device.

Advantageously, the determining step comprises: -a decoding step of decoding at least one part of said first data; and -a checking step of checking the result of said decoding step, and in case the result of said decoding step shows residual errors, the method further comprises: -a cancelling step of cancelling a decoding of at least one part of data among said first data and said second data.

Therefore, while BER at the destination device is improved, the relay device can decrease the power consumption due to an interruption of the decoding process.

Advantageously, only a header part of the first data is decoded in said decoding step.

Therefore, as usually the header of a data frame is transmitted with a modulation and channel coding scheme more robust than the payload of the data frame, a non-recoverable error in the header lets suspect non-recoverable errors would remain the payload.

Advantageously, the first determining step comprises: -a second determining step of determining a signal-to-noise ratio corresponding to a reception at least one data among the first and second data by the relay device, and wherein, in case the result of said second determining step shows one signal-to-noise greater than a predefined threshold, the method further comprises: -a second cancelling step of cancelling a decoding of at least one part of data among said first data and said second data.

Therefore, while BER at the destination node is improved, the relay node can decrease the power consumption due to the decoder. Indeed, a bad signal-to-noise ratio indication lets suspect non-recoverable errors would in data packet.

Preferably, said combination of said first and said second data in the non-decoded form consists in applying a likelihood function to the first and second data.

According to a second aspect, in at least one embodiment, the invention relates to a relay device for transmitting data to a destination device, the relay device obtaining in a non-decoded form a first data and a second data intended for the destination device. The relay device comprises: -first determining means for determining if said first and second data have been subject to a signal distortion on at least one path up to said relay device; -transmitting means for transmitting to said destination device, on the basis of the result of the first determining step, either: o a combination of said first and said second data in the non-decoded form; or o a combination of said first and said second data in a decoded form.

According to a third aspect, in at least one embodiment, the invention relates to a computer program product comprising instructions for implementing the abovementioned method (in any one of its various embodiments), when said program is run on a computer.

According to a fourth aspect, the present invention also proposes an information storage means, storing a computer program comprising a set of instructions that can be run by a computer to implement the abovernentioned method (in any one of its various embodiments), when the stored information is read by the computer. In an embodiment, this storage means is totally removable.

Since the particular features and benefits of this device, of this computer program product and of this information storage means, are similar to those of the corresponding transmitting method, they are not repeated here.

5. LIST OF FIGURES Other features and benefits of the invention will become more apparent from the following illustrative and non-limiting description, illustrated by the appended drawings, in which: -Figure 1 schematically illustrates a communication network comprising communication devices, according to one embodiment of the present invention; -Figure 2 schematically illustrates a configuration of a wireless communication device; -Figure 3 schematically illustrates a format of a data packet, as exchanged by communication devices in the network of Figure 1; -Figure 4 schematically illustrates a flow diagram and data exchanges i n a relay node of the network of Figure 1, according to a first embodiment; -Figure 5 schematically illustrates a flow diagram and data exchanges in a relay node of the network of Figure 1, according to a second embodiment; -Figure 6 schematically illustrates a flow diagram and data exchanges in a relay node of the network of Figure 1, according to a third embodiment.

6. DETAILED DESCRIPTION

The method and the device according to the invention are more fully described hereinafter in the context of an implementation of a 60 GHz transmission system. However, the application of the present invention is by no means limited to this implementation scenario. Indeed, the present invention applies generally to wireless communication systems.

Figure 1 schematically illustrates a communication network.

The wireless communications network 100 comprises communication devices: a first source node A 110, a second source node B 120, a relay node R 200 and a destination node D 130.

The source node A 110 is connected to the relay node R 200 by a first wireless link 151. The source node B 120 is connected to the relay node R 200 by a second wireless link 152. The source node A 110 is connected to the destination node D 130 by a third wireless link 153. The relay node 200 is connected to the destination node D 130 by a fourth wireless link 154. The source node B 120 is connected to the destination node D 130 by a fifth wireless link 155.

The source node A 110 transmits a packet "a" to the relay node R 200 and to the destination node D 130. Also the source node B 120 transmits a packet "b" to the relay node R 200 and the destination node D 130. The relay node R transmits a packet combining packets a and b by using an exclusive or (XOR) function. The combination is denoted as (a b). The destination node D decodes a, b; and, (a b) is used as a parity check.

Figure 2 schematically illustrates a configuration of a wireless communication device, as used as a relay node in the network 100.

A communication device 200, as used in at least one embodiment of the present invention and adapted to perform wireless communications, comprises: -a radio frequency module (denoted as RF) 210; -a base band processor (denoted as BBP) 220; and -a medium access controller (denoted as MAC) 230; and -a network manager 240 enabling communications with other wireless communication devices of a network.

The RF module 210 is in charge of converting baseband signals supplied by BBP 220 to a radio frequency to transmit those with an antenna and down converting a radio frequency signals received at the antenna to the baseband signals to deliver it to BBP.

BBP 220 comprises at least the following sub-modules: -an analogue signal converter (denoted as ADC) 221; -a received signal strength indicator (denoted as RSSI) 222; -a digital to analogue converter (denoted as DAC) 223; -a demodulator (denoted as DEMOD) 224; -a modulator (denoted as MOD) 225; -a PHY Frame Memory (denoted as PFM) 226; -a Logarithm Likelihood Operator (denoted as RSSI) 222; -a decoder (denoted as DEC) 228; -an encoder (denoted as ENC) 229.

BBP 220 is responsible for encoding the digital signals supplied by MAC 230 by ENC 229 with an error correction code, modulating the encoded signals by the modulator 225, converting the modulated signals to analogue signals by DAC 223 and outputting the analogue signals to RF 210. BBP 220 is also responsible for converting analogue signals to digital signals by ADC 221, decoding the digital signals by DEC 228 and outputting the decoded signals to MAC 230. The modulation and demodulation scheme applied by BBP 220 is of Bi-Phase Shift Keying (BPSK) type or of Quadrature Phase Shift Keying (QPSK) type, for instance. BBP 220 uses received signal strength indication provided by RSSI 222 to detect if signals are received at RF 210. While demodulated data is sent to DEC 228 from DEMOD 224, those demodulated data are stored in PFM 226. The distinct data are stored in different areas in PFM 226, to be retrieved to compute logarithm likelihood of those data by LXOR 227, performing the operation with a and b shown in equation (1).

L(ab)=tog (1) MAC 230 comprises at least the following sub-modules: -a CRC Error Detector (denoted as CED) 231; -a MAC Frame Memory (denoted as MFM) 232; -a Logarithm Likelihood Controller (denoted as LCTRL) 233.

MAC 230 manages the accesses to the wireless medium. MAC 230 also acts as a synchronization control unit, which controls synchronization relatively to a superframe, scheduling the transmissions via the network. It means that MAC 230 schedules the beginning and the end of an emission of data. MAC 230 checks residual error in the received (and decoded) MAC frame data by checking cyclic redundancy code (CRC) by CED 231. At the same time, MAC stores the received signal in MFM 232. On the basis of the presence of residual errors, LCTRL 233 decides which data are used for retransmission: data in PFM 226 or data in MFM 232.

The network manager 240 at least comprises (not shown): -a Random Access Memory (RAM), whose capacity can be extended by an additional Random Access Memory connected to an expansion port; -a Read-Only Memory (ROM); and -a micro-controller or Control Process Unit (CPU).

CPU, RAM, ROM and MAC 230 exchange data and control information via a communication bus (not shown).

CPU is capable of executing instructions loaded from ROM into RAM.

After the relay node has been powered on, CPU is capable of executing, from RAM, instructions pertaining to a computer program, once these instructions have been loaded from ROM or from an external. A computer program of this kind causes CPU to execute some or all of the steps of the algorithms described hereinafter in relation to Figures 4, 5 and 6.

RSSI 222, PFM 226, LXOR 227, LCTRL 233, MFM 232 are means specific to the relay node R 200. The source node A 110, the source node B 120 and the destination node D 130 can be built with the same basis as the node configuration of Figure 2, except the aforementioned means specific to the relay node R 200.

Figure 3 schematically illustrates a format of a data packet, as exchanged by communication devices in the network 100 over the wireless links 151, 152, 153,lS4and 155.

The data packet 300 is divided into three parts (in the order of transmission): -a PHY header 310; -a MAC header 320; -a MAC payload 330.

The PHY header 310 is a portion of the data packet (also referred to as frame) 300 that is generated (at a source node A 110 or B 120) and treated (at the destination node D 130) by the baseband processor 220.

The MAC header 320 is a portion of the data packet 300 that is generated (at the source node A 110 or B 120) and treated (at the destination node D 130) by MAC 230.

The PHY header 310 comprises: -a preamble 311, which is used for detecting the transmission of the data packet 300 at the destination node D 130; the preamble 311 furthermore enables the destination node D 130 to estimate the parameters necessary for being synchronized with the source nodes A 110 and B 120, and for adjusting reception parameters, such as Automatic Gain Control (denoted AGC) or coarse and fine frequency estimations.

-a PHY rate field 312, which indicates a physical layer speed that is used for transmitting the data packet 300; -a length field 513, which indicates the length of the data packet 300; -a padding field 314, which may or not be present, depending on the length of the PHY header.

The MAC header 320 comprises a MAC Header Data field 321 which comprises: -a frame control field 322, which indicates a data packet type; the packet type may for instance be: beacon, a request to send (denoted RTS), a clear to send (denoted CTS), an acknowledge (denoted ACK). Each packet type defined according to the transmission protocol applicable in the network has a predefined identifier, which is then indicated in the

control field 322;

-a source address field 323, which indicates the identifier (ID) of the source device of the data packet 300; and -a destination address field 324, which indicates the identifier (ID) of the destination device.

The MAC header 320 further comprises: -a header check sequence field 325, which indicates the cyclic redundancy

check for the MAC Header Data field 321;

-a padding field 326, which may or not be present, depending on the length of the preceding data in the MAC header 320.

The MAC payload 330 comprises: -a data field 331, which may or not be present, depending on the packet type indicated in the frame control field 322; when present, the data field 331 contains application data (video data, audio data, file transfer data...); -a FCS field 331, which indicates the cydic redundancy check for MAC Payload Data 331; -a padding field 333, which may or not be present, depending on the length of the preceding data in the MAC Payload 330.

Figure 4 schematically illustrates a flow diagram and data exchanges in the relay node R 200, according to a first embodiment.

Any step of the algorithm shown in Figure 4 may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC ("Personal Computer"), a DSP ("Digital Signal Processor") or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA ("Field-Programmable Gate Array") or an ASIC ("Application-Specific Integrated Circuit").

Figure 4 illustrates data exchanges between BBP 220 and MAC 230 in the relay node R 200. It is assumed that RF 210 receives distinct packets a and b, and a combination (for instance in the form of exclusive or (XOR) operation) of a and b (or the like) shall be transmitted to the destination node D 130.

In this first embodiment, the appropriate data packet combination is selected according to the result of the decoding by DEC 228 of the demodulated data packets.

In a step S401, ADC 221 receives the data packets from RF 210, a-and b-, representing the encoded and modulated data with the effects of the communication channel, and passes those to DEMOD 224. DEMOD 224 demodulates a-and b-producing un-decoded a1' and b", which are then delivered to DEC 228 in S402 and to PFM 226 in S403.

The data packets a1' and b1' are stored in PFM 226 in S404. After DEC 228 has decoded a1' and b1', the decoded data packets a and b are delivered to CED 231 in S405. CED 231 checks if any error remains in the decoded data packets a and b by HCS or I and FCS and stores the decoded data packets a and b into MFM 232 in S406. The result of the CRC check is then delivered to LCTRL 233 in S408. In S409, LCTRL 233 determines if either a or b (or a and b) has an error; if there is no error remaining (all errors have been recovered), the algorithm proceeds to S410, otherwise it proceeds to S420.

In S410 LCTRL 233 selects to use decoded data for retransmission. In S41 1 LCTRL 233 requests MFM 232 to retrieve the stored data packets a and b, then MFM 232 uploads them in S412 and delivers them in S413. LCTRL 233 performs XOR operation of a and b (decoded data packets) in S413 and send the combined data packet to ENC 229 in S415. Then, ENC 229 encodes a b, which is sent to MOD 225 in S416. After, MOD 225 modulates the encoded data packet a b, which is then sent to ADC 221 in S418 and ADO 221 converts the digital data into analogue signals. And the process ends.

LCTRL 233 selects un-decoded data for retransmission in S420. LCTRL 233 requests PFM 226 to retrieve the stored data packets a" and b' through LXOR 227 in S421 and in S422 PFM 226 uploads the stored data packets aA and b1' in S423 and delivers those to LXOR 227 in S424. LXOR 227 performs a combination (based on the already mentioned logarithm likelihood) of a1' and bA in S425 and send the combined data packet to MOD 225 in S426. After, MOD 225 modulates the encoded data packet representative of a b in S427 and ADC 221 converts the digital data into analogue signals. And the process ends.

Figure 5 schematically illustrates a flow diagram and data exchanges in the relay node R 200, according to a second embodiment.

Any step of the algorithm shown in Figure 5 may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC ("Personal Computer"), a DSP ("Digital Signal Processor") or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA ("Field-Programmable Gate Array") or an ASlO ("Application-Specific Integrated Circuit").

Figure 5 illustrates data exchanges between BBP 220 and MAO 230 in the relay node R 200. It is assumed that RF 210 receives distinct packets a and b, and a combination (for instance in the form of an XOR operation) of a and b (or the like) shall be transmitted to the destination node D 130.

In this second embodiment, the appropriate data packet combination is selected according to the result of the decoding by DEC 228 of the respective header of the demodulated data packets, and also according to the result of the decoding by DEC 228 of the respective payload of the demodulated data packets.

While ADC 221 receives the data packets from RF 210, a and b-, representing the encoded and modulated data with the effects of the communication channel (distortion). Each data packets respectively comprise one header part, respectively ah-and bh-. The header parts ah-and bh-are delivered to DEMOD 224 in S501. Then, DEMOD 224 demodulates ah and producing un-decoded data packets ahA and bh1', which are then delivered to DEC 228 in S502 and to PFM 226 in S503. ahA and bh1' are also stored into PFM 226 in S504. Then, DEC 228 decodes ah1' and bh1', and decoded ah and bh are delivered to CED 231 in S505. CED 231 checks if any error remains in the decoded ah and bh by HCS and stores the decoded data packet header parts ah and bh into MFM 232 in S506. The result of the CRC check is delivered to LCTRL 233 in S508. In S509, LCTRL 233 determines if either ah or bh (or ah and bh) has an error; if there is no error remaining (all errors have been recovered) in any one of the decoded headers ah and bh, LCTRL 233 requests DEC 228 to stop its operation in S510 (cancellation of the decoding of the remaining parts, i.e. their payload parts and the other header part if remaining).

After ADC 221 has processed ah-and ADO 221 continues with the processing of the payload part of the data packets received from RF 210, and br-, and delivers them to DEMOD 224 in S521. Then, DEMOD 224 demodulates a-and br-, producing un-decoded data packets a1' and bRA, which are then delivered to DEC 228 in S522 and to PFM 226 in S523. a1' and b1' are also stored in PFM 226 in S524. Then, DEC 228 decodes a1' and bRA, and decoded a and b are delivered to CED 231 in S525. CED 231 checks if any error remains in the decoded a and b by FCS and stores the decoded data packet header parts a and b into MFM 232 in S526. The result of the CRC check to LCTRL 233 is delivered in S528. In S529, LCTRL 233 determines if either ah or bh (or a and b) has an error; if there is no error remaining (all errors have been recovered) in any one of the decoded payloads a and b, LCTRL 233 requests DEC 228 to stop its operation in S530 (cancellation of the decoding of the remaining parts, i.e. the other payload part if rerna in i ng).

If LCTRL 233 detects no error in the received packets so far, S410 is performed; otherwise S420 is performed.

Figure 6 schematically illustrates a flow diagram and data exchanges in the relay node R 200, according to a third embodiment.

Any step of the algorithm shown in Figure 6 may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC ("Personal Computer"), a DSP ("Digital Signal Processor") or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA ("Field-Programmable Gate Array") or an ASIC ("Application-Specific Integrated Circuit").

Figure 6 illustrates data exchanges between BBP 220 and MAC 230 in the relay node R 200. . It is assumed that RF 210 receives distinct packets a and b, and a combination (for instance in the form of an XOR operation) of a and b (or the like) shall be transmitted to the destination node D 130. This embodiment may be combined with the first embodiment or the second embodiment already described.

While RSSI 222 receives no packet from RF 210, n, representing noise due to the communication channel, it is delivered to LCTRL 233 in S601.

LCTRL 233 measures the noise power in S602. While RSSI 222 receives the packets from RF 210, ail-and representing the encoded and modulated data with the effects of communication channel (distortion), ah-and bh are delivered to LCTRL 233 in S611. LCTRL 233 measures the signal power in S612. LCTRL 233 decides if the signal to noise ratio (SNR), obtained from the noise power and the signal power, is above a predefined threshold or not in S612. If SNR is below the threshold, LCTRL 233 requests DEC 228 to stop its operation in S622 (cancellation of the decoding of the remaining parts). If this request is performed, S420 is performed whenever the retransmission data are ready, otherwise S410 is performed.

Claims (9)

1. CLAIMS1. A method for transmitting data from a relay device to a destination device, the relay device obtaining in a non-decoded form a first data and a second data intended for the destination device, wherein the relay device performs: -a first determining step of determining if said first and second data have been subject to a signal distortion on at least one path up to said relay device; -a transmitting step of transmitting to said destination device, on the basis of the result of the first determining step, either: o a combination of said first and said second data in the non-decoded form; or o a combination of said first and said second data in a decoded form.
2. 2. The method for transmitting data according to Claim 1, wherein the determining step comprises: -a decoding step of decoding at least one part of said first data; and -a checking step of checking the result of said decoding step, and wherein, in case the result of said decoding step shows residual errors, the method further comprises: -a first cancelling step of cancelling a decoding of at least one part of data among said first data and said second data.
3. 3. The method for transmitting data according to Claim 2, wherein only a header part of the first data is decoded in said decoding step.
4. 4. The method for transmitting data according to any one of Claims 1 to 3, wherein the first determining step comprises: -a second determining step of determining a signal-to-noise ratio corresponding to a reception at least one data among the first and second data by the relay device; and wherein, in case the result of said second determining step shows one signal-to-noise greater than a predefined threshold, the method further comprises: -a second cancefling step of cancefling a decoding of at least one part of data among said first data and said second data.
5. 5. The method for transmitting data according to any one of Claims 1 to 4, wherein said combination of said first and said second data consists in applying a likelihood function to the first and second data.
6. 6. Computer program product, characterized in that it comprises program code instructions for implementing the method according to at least one of Claims 1 to 5, when said program is run on a computer.
7. 7. Computer-readable storage means, storing a computer program comprising a set of instructions that can be run by a computer to implement the transmission method according to at least one of Claims 1 to 5.
8. 8. A relay device for transmitting data to a destination device, the relay device obtaining in a non-decoded form a first data and a second data intended for the destination device, wherein the relay device comprises: -first determining means for determining if said first and second data have been subject to a signal distortion on at least one path up to said relay device; -transmitting means for transmitting to said destination device, on the basis of the result of the first determining step, either: o a combination of said first and said second data in the non-decoded form; or o a combination of said first and said second data in a decoded form.
9. 9. A method, program or device for configuring wireless nodes substantially as hereinbefore described with reference to the accompanying drawings.