WO2011070537A2

WO2011070537A2 - Wireless packet data transmission system with signal validity detector

Info

Publication number: WO2011070537A2
Application number: PCT/IB2010/055728
Authority: WO
Inventors: Vintu Jose Alappat; Martin Kubisch; Anoop Kumar Krishna
Original assignee: Eads Singapore Pte. Ltd
Priority date: 2009-12-11
Filing date: 2010-12-10
Publication date: 2011-06-16
Also published as: WO2011070537A3; SG181635A1

Abstract

The application provides a receiver device (40) of a data packet communication network (13). The receiver device (40) comprises a receiver unit, a decoder unit (40) and, a data validity module. The receiver unit receives data packets. The decoder unit (40) decodes the received data packets. The data validity module comprises a data validity unit (37) and a data validity controller unit (39). The data validity unit (37) generates data validity information of the received data packet. The data validity controller unit (39) is connected with the decoder unit (40) and causes the decoder unit (40) to abort the decoding of the data packet if the data validity information indicates that the data packet is invalid.

Description

WIRELESS PACKET DATA TRANSMISSION SYSTEM WITH SIGNAL VALIDITY DETECTOR

The present application relates to digital transmission of data. In particular, the application relates to a decoding method and to a decoding device.

The Manchester protocol provides an encoding and decoding protocol for digital signals. This is often utilized in com- munication systems where a minimum transition density is re^¬ quired, or where a direct current (DC) balanced signal is re^¬ quired. In accordance to the Manchester protocol, the digital signals are encoded using an encoder and are decoded using a decoder .

The Manchester encoded signal comprises a self-clocking code with a minimum of one and a maximum of two-level transitions per bit. The code assigns a data of zero, which is logic low, to a low-to-high transition, and assigns a data of one, which is logic high, to a high-to-low transition. For data of two identical consequent bits, the code ignores an extra level transition .

US 7,133,482 B2 shows a hardware structure of a data packet decoder for the Manchester protocol. The use of central bit transitions and time measurements between transitions is used for improving the Manchester decoding. This method depends on the incoming Manchester encoded data for decoding. Any erroneous packets could be discarded at the higher layers.

US 6,628,212 Bl shows a Manchester decoder that uses oversam- pling techniques. These techniques can be time consuming as the techniques depend on the incoming Manchester encoded data for decoding and erroneous packets could be discarded at the higher communication layers only.

It is an objective of this application to provide an improved communication system. The communication system can support digital signal. In particular, the application provides a data packet based communication for wireless systems that can use infrared signals. The wireless systems can be used in in^¬ door applications.

One of the main thoughts of the application is that reducing or eliminating processing time of "lost" data packets during packet-based communication can improve data throughput and efficiency. It is believed that the packets are often consid- ered "lost" due to non-detection of the packets.

To detect the "lost" packets, the application provides a sig^¬ nal validity controller for a signal decoder or receiver. The signal validity controller receives the same data signal as the signal decoder and it performs statistical operations on the data signal. The operations generate validity information about the signal in relation to data packets that are con^¬ tained in the signal. The validity information can be used for processing the data packets at a very low communication layer, thereby reducing time wasted on processing unwanted data .

The application provides a receiver device of a data packet communication network. The receiver device comprises a re- ceiver unit, a decoder unit, and a data validity module.

The receiver unit is used for receiving one or more data packets that are encoded at a transmitter side and that are then transmitted over a wireless medium to the receiver unit. The data packets can be encoded with the Manchester coding scheme. The encoding often allows efficiency transmission of the data packets over the wireless medium.

The decoder unit is used for decoding the received data pack^¬ ets to its form.

Referring to the data validity module, it comprises a data validity unit and a data validity controller unit.

The data validity unit also receives the transmitted data packets and it is used for generating data validity informa^¬ tion of the received data packets. Several techniques can be used to determine that the received data packets are valid.

The data validity controller unit is connected with the de^¬ coder unit and which causes the decoder unit to abort the de^¬ coding of the data packet if the data validity information indicates that the data packet is invalid. The data packet can be corrupted or damaged during its transmission over a transfer medium.

This aborting of data packet has obvious advantages of saving processing time. System resources are saved from processing invalid data packets. The decoder unit can be adapted for de^¬ coding Manchester data packet or other decoding scheme.

The application provides a data validity module for a re- ceiver device that receives data packets. The data validity module includes a data validity unit and a data validity con^¬ troller unit. The data validity unit is used for generating data validity information of one or more data packets. The data validity controller unit, which comprises an output con^¬ nection for a receiver decoder unit that decodes the data packet. The data validity controller unit outputs a predeter^¬ mined value indicating the data validity information of the data packet.

The data validity controller unit includes an output connec^¬ tion for a receiver decoder unit that decodes the data packet, wherein the data validity controller unit outputs a predetermined value indicating the data validity information.

The application provides a method of operating a receiver device of a data packet communication network. The method comprises a step of receiving least one or more encoded data packets. The received encoded data packets are then decoded according to a predetermined coding scheme. Af^¬ ter this, validity information of the data packets is gener^¬ ated using one of several possible techniques. The decoding of one or more data packets is aborted if the validity infor^¬ mation indicates that the data packets are invalid.

The aborting allows system resources to be saved from or not used for processing invalid data packets. One invalid data packet can also caused associated data packets to be aborted when the associated data packets cannot be decoded or proc^¬ essed due to the invalid data packet.

The received data packets can be encoded with a Manchester coding scheme or other coding scheme.

The method can include a step of receiving a next data packet directly after the aborting or stopping the decoding of data packet. In this case, there is no or reduced lost of system time due to invalid data packets.

The aborted data packet is not often transmitted to next layer. The next layer is then saved or is prevented from processing invalid data packets.

The decoding can comprise one or more possible steps. The possible steps include receiving a preamble and a start of frame limiter (SFD) of the data packet or getting length value from a Physical Layer Convergence Procedure (PLCP) header of the data packet. The step can also include checking Cyclic Redundancy Check (CRC) value of the data packet or sending the packet data from a Physical layer to a Media Ac- cess Control (MAC) layer.

The application provides a method of operating a data valid^¬ ity module of a data packet receiver device. The method com^¬ prises a step of generating validity information of a (en- coded) data packet and outputting a predetermined value indi^¬ cating the data validity information.

In short, the application has the advantage of improving ef^¬ ficiency of a communication system in terms of both through- put and use of energy. The system prevents erroneous data packets from going into upper communication layers for further processing. This thereby saves or conserves system re^¬ sources for processing next incoming data packets. Further processing of the erroneous data packets can consume system resources such that the system is prevented from re^¬ ceiving the next incoming data packets. A retransmission of these non-processed or non-detected data packets may be trig- gered. This would consume transmission bandwidth. Hence, the application increases usable bandwidth by reducing overhead in packet transmissions. This is especially of significance in cases of already congested systems.

In a generic sense, the application can be applied to any type of packet data transmission scheme beside the Manchester coding scheme.

In the following description, details are provided to de^¬ scribe the embodiments of the application. It shall be appar ent to one skilled in the art, however, that the embodiments may be practised without such details. Fig. 1 illustrates a local area network (LAN) that uses the Manchester encoder/decoder encoding, Fig. 2 illustrates an improved LAN that includes the LAN of Fig. 1 and a signal validity device,

Fig. 3 illustrates steps of a receiver state machine at a receiver side of the LAN of Fig. 1, and

Fig. 4 illustrates steps of an improved receiver state ma^¬ chine at a receiver side of the improved LAN of Fig. 2. Figs. 1 to 4 have similar parts. The similar parts have same names or same part numbers. The description of the similar parts is hereby incorporated by reference, where appropriate, thereby reducing repetition of text without limiting the dis^¬ closure .

Fig. 1 shows a first local area network (LAN) 10 that uses the Manchester coding scheme. The LAN 10 has a transmitter side 12 and a receiver side 13. A wireless medium 15 separate the transmitter side 12 from the receiver side 13.

The transmitter side 12 includes an upper layer wireless lo- cal area network (WLAN) module 17 that is communicatively connected to a Manchester encoder module 18 whilst the Man^¬ chester encoder module 18 is connected to a transmitter 19. The Manchester encoder module 18 comprises a Physical Layer Convergence Procedure (PLCP) preamble and Start of Frame De- limiter (SFD) device 22, PLCP header and Cyclic Redundancy Check (CRC) computation device 23 and a Manchester encoder device 24.

The receiver side 13 includes a receiver 26 that is connected to a Manchester decoder module 27. The Manchester decoder module 27 is communicatively connected to an upper layer WLAN module 28. The Manchester encoder module 27 comprises a Man^¬ chester decoder device 30 that communicatively connected to a send device 31.

Functionally, the transmitter side 12 is used for sending digital data signals via the wireless medium 15 to the re^¬ ceiver side 13. Referring the transmitter side 12, the upper layer WLAN module 17 sends digital data packets to the Manchester encoder module 18 to encode for transmitting via the transmitter 19. The PLCP preamble and SFD device 22 generates a packet pream^¬ ble segment and a packet start of frame delimiter segment for the data packets. The PLCP header and CRC computation device 23 generates a packet header segment and a packet CRC infor^¬ mation segment for the digital data packets. The Manchester encoder device 24 encodes the preamble, the SFD segment, the header segment, the CRC information segment, and the digital data using the Manchester coding scheme.

Referring the receiver side 13, the Manchester encoder module 27 receives the encoded data packets via the receiver 26. The Manchester decoder device 30 decodes the encoded packets in accordance to the Manchester coding scheme and it sends the decoded packets the send device 31. The send device 31 re^¬ moves the header segment, checks the packets using the CRC information segment, and sends the checked packets to the up^¬ per layer WLAN module 28.

The data packets are transmitted over the wireless medium 15 in single information bits that are formatted using the Man- Chester encoding scheme. The Manchester encoding scheme provides a modulation scheme that is suitable for low-cost ra^¬ dio-frequency transmission of digital data. The modulation scheme provides a simple method for encoding a digital serial of data of arbitrary bit pattern that is without any long string of continuous zeros or ones. The encoded data also em^¬ beds an encoding clock rate.

These two characteristics allow the decoder device 30 to have low-cost data-recovery circuits for decoding the encoded data that is transmitted with variable signal strengths and with imprecise, low-cost, data-rate clocks. The clock rate can be extracted from the encoded data by using a digital phase locked loop (DPLL) . The Manchester decoder device 30 uses a special signature for detecting of a start of a data packet. An end of the data packet does not carry a specific signature. Instead, no change of signal is used for detecting the end of the data packet .

In a noisy environment, noise can exert a certain threshold such that it is difficult to differentiate between noise and valid data. The wireless medium 15 can have more noise that a wired medium, as the wireless medium 15 can receive signals from other networks or signal sources. In this respect, transmission via a wireless standard, such as the WLAN 802.11 standard, is often less reliable as compared to the wired transmission .

The noise may be present at the end of data packet in a man^¬ ner that prevents the decoder device 30 from detecting the end of data packet. The noise signal thus causes the data packet to be decoded incorrectly. This would cause the de^¬ coder device 30 been left incorrectly in an active state in which it still tries to decode the data packet. Some waiting time is then required, for example x ns (nanoseconds) , in or- der for the decoder device 30 to come to the IDLE state that is a normal state such that the receiver is able to receive the next incoming data packet. During this waiting time, the decoder device 30 is unable to decode any incoming data pack^¬ ets and these incoming data packets are then dropped or ig- nored. This may trigger a retransmission of the dropped data packet .

Considering the accumulative effects of noise signal and these often-unnoticed effects, the system efficiency can de- crease by a great margin.

Fig. 2 shows an improved LAN 35 that includes the LAN of Fig. 1 and a signal validity device 37. The signal validity device 37 includes a signal validity de^¬ tector 38 and a signal validity controller 39. The signal va^¬ lidity detector 38 is also called a data validity detector circuit or a data validity detector module. The signal valid^¬ ity detector 38 is incorporated in the receiver 26 whilst the signal validity controller 39 is incorporated in the Manches^¬ ter encoder module of Fig. 1 to form an improved Manchester encoder module 40.

To support the digital transmission, the transmitter 19 incorporates an Analog Front End (AFE) and an Analog to Digital Converter (ADC) whilst the receiver 26 also incorporates an AFE and a Digital to Analog Converter (DAC) .

Functionally, the Manchester decoder device 30 starts gener^¬ ating a clock signal as soon as it finds incoming data packet signals and it starts to pump or send l's and 0's into a re^¬ ceiver state machine. The clock starts at a first edge of the incoming data packet signals.

The signal validity detector 38 acts to validate the incoming data packet signals and it sends validity control signals to the signal validity controller 39. The validity control sig- nals are also called validity signals or data valid signals.

The validity can use statistical operations on the signal in order to generate information about the start and the end of each data packet, which is contained in the received signal. The statistical operations can include correlation analysis, such as auto-correlation functions. Other techniques, which are used for cognitive radio spectrum sensing, can be applied accordingly. Alternatively, the validation can use techniques such as energy detection method, cyclostationary feature detection methods, or other advanced methods, to distinguish between noise and modulated signals. The signal validity controller 39 controls the Manchester de^¬ coder device 30 and the send device 31 using the received va^¬ lidity control signals. The control can stop the Manchester decoder device 30 quickly if necessary, thus saving the precious processing time. This would in turn reduce occurrence of retransmission due to "lost" or to non-detected data sig^¬ nals .

This is unlike other LANs where the Manchester decoder de^¬ vices cannot be stopped. A waiting period is then required for the entire LAN to come to the IDLE State. Once the data and the clock signals enters into a state machine or a Physi^¬ cal layer, it takes up precious clock cycles, which is in the order of magnitude of microseconds for it to come to the IDLE State. The Physical Layer, here, provides hardware for trans- mitting signals of a network.

A data packet format of WLAN system can designate the first 128 bits as preamble and the next 8 bits as Start of Frame Delimiter (SFD) . This would take about 134 clock cycles for the WLAN system to receive the SFD after it starts receiving the l's and 0's from Manchester decoder 30. This translates into 134 clock cycles for the WLAN system to come back to the IDLE State before it can start receiving the next data packet signal. By utilizing the validity signal, the WLAN system can come to the IDLE state before the WLAN system goes through 134 clock cycles. This would thus reduce stabilization time and errors that occur due to this. Indirectly, this trans^¬ lates into improved efficiency. In short, by utilizing the validity signal that is provided by the signal validity detector 38, the LAN 35 can stopped further processing of the packet signal and the LAN 35 can be set to the IDLE State earlier for receiving further packets. This way of stopping the entire LAN would not be possible for other systems, which depend only on received encoded data.

Fig. 3 shows a flow chart 43 of steps or states of a receiver state machine or Physical layer state machine at a receiver side of the LAN of Fig. 1.

The receiver state machine processes received data signal through four check steps before a Media Access Control Proto- col Data Unit (MPDU) is passed on to a Media Access Control (MAC) layer. These steps do not perform error-coding correc^¬ tion. In other words, an error of even a single bit can lead to a discarding of the data. The flow chart 43 includes an Idle state 46, a Preamble & SFD state 47, a Length state 48, a CRC check state 49, a PLCP

Protocol Data Unit (PPDU) length state 52, and an end of re^¬ ception state 54. Referring to the flow chart 43, the Preamble & SFD state 47 follows the Idle state 46. The Length state 48 follows the Preamble & SFD state 47. The CRC check state 49 follows the Length state 48. The PPDU length state 52 or the Idle state 46 follows the CRC check state 49. The end of reception state 54 follows the PPDU length state 52.

Preamble & SFD state 47 In this state 47, the state machine looks for a preamble, which has a "10101010" word pattern. Once it finds this pat^¬ tern, it searches for a SFD pattern, which has a "10101011" word pattern. This state 47 takes about 128 clock cycles of processing time before it decides whether it needs to discard the data or not.

Length state 48

The state 48 stores up the next 16 bits after the SFD, which has a length value of the PPDU as the information. This state 48 takes 16 clock cycles of processing to determine the length value of the received data.

CRC check state 49

In this state 49, the length is used to generate a CRC data using a CRC generator in the receiver circuit. This generated CRC data is then compared with a CRC data that is within the incoming data packet to make sure that the received data packet is correct. This state 49 takes 16 clock cycles of processing time to get the length from the received data.

PPDU length state 52

This state 52 mainly pumps or transmits the data from the Physical layer into the MAC layer. The clock cycles taken for this depend on the length of the sent data. However, the PPDU data goes into the MAC and a predetermined error correction of the PPDU data is done. This means, that even few bits are missing, the missing bits can be recovered. The MAC layer provides addressing and channel access control mechanisms for several terminals or network nodes to communi^¬ cate within a multipoint network. Put simply, the MAC layer also acts as an interface between a Logical Link Control (LLC) layer and physical layer of the network.

The state machines would go through all the states before coming to the Idle state 46 to process any received new in^¬ coming data, even if the received data is erroneous in na^¬ ture .

Fig. 4 shows a flow chart 60 of steps or states of an im- proved receiver state machine at the receiver side of the im^¬ proved LAN of Fig. 2.

The improved receiver state machine uses the validity signal that is described above to reduce largely redundancy. Analyz- ing each block or state of the state machine in detail would shows that a number of clock cycles can be gained by effi^¬ ciently utilizing the data validity signal.

The flow chart 60 includes the Idle state 46 of Figure 3, an improved Preamble & SFD state 64, an improved Length state 65, an improved CRC check state 67, an improved PPDU length state 68, and the end of reception state 54 of Figure 3.

Referring to Fig. 4, the Idle state 46 can follow the im- proved Preamble & SFD state 64, the improved Length state 65, the CRC check state 67, the improved PPDU length state 68, and the end of reception state 54. The improved Preamble & SFD state 64 follows the Idle state 46. The improved Length state 65 follows the improved Preamble & SFD state 64. The CRC check state 67 follows the improved Length state 65. The improved PPDU length state 68 follows the CRC check state 67. The end of reception state 54 follows the improved PPDU length state 68. To illustrate the flow chart 60, several cases are described below. The cases assume a packet structure that has a Pream^¬ ble segment of 120 bits and a SFD segment of 8 bits followed a Data Length segment of 16 bits, a CRC value segment of 16 bits and a MAC Protocol Data Unit (MPDU) .

Case 1 :

This case illustrates a working of the improved Preamble & SFD state 64.

When the decoder 30 receives a preamble, the decoder 30 would start to recover the clock signal together with the data packet signal. In this case, say a few bits of the preamble of 10 bits arrives at the receiver 26 and after this, nothing else arrives. Watching and using the validity signal, the state machine can quickly stop this process and not wait for the entire process to complete. The state machine would then move to the IDLE state, where the state machine can start looking for the next data packet signal. For an extreme case, this manner can save 128 clock cycles. This is unlike other state machine that would wait for the completion of 128 clock cycles to detect the SFD pattern. If it then does not detect the SFD pattern, it would discard the data packet signal and later move to the IDLE state.

Case 2 :

This case illustrates a working of the improved Length state 65.

The improved Length state 65 calculates a CRC value of the length value of the received data packet. For any invalid or erroneous data that is coming into the state machine, the calculated CRC value of the length of received data packet would not be equal to the received CRC value that is within the received data packet. By utilizing the data validity sig^¬ nal, the state machine can predict in advance whether the length value is wrong or not, thus saving the precious clock cycles. The number of clock cycles saved would depend on which bit of the length value the error occurred. This is unlike other state machine where invalid data is discarded only after the 16 clock cycles.

Case 3 :

This case illustrates a working of the CRC check state 67.

The CRC value has 16 bits length. This state utilizes the data validity signal to make sure that the data is valid or not and thus saving few clock cycles. Again, the number of clock cycles saved would depend on which bit of the CRC value the error is detected or which data bit is invalid. This is different from other state machine where the state machine waits for 16 clock cycles to make sure that CRC is correct or not .

Case 4 :

This case illustrates a working of the improved PPDU length state 68.

In this case, a data packet of 30 bytes length is sent to the receiver end. Due to unforeseen or unknown reasons only 20 bytes of the data arrives at the receiver side. Unlike other state machine that waits for the other 10 bytes to come - the probability of other bytes coming to the receiver is very rare - the improved PPDU length state 68, by utilizing the data validity signal, determines that the data arrived is in- valid. By this way, several clock cycles are saved, which contribute to efficiency improvement of the entire system.

In summary, by utilizing the data signal and the data valid- ity signal, the receiving state machine can efficiently stop unnecessarily different steps or states and it can spend more time in the IDLE state and be ready for receiving new valid data packets. This also prevents retransmissions and colli^¬ sions from happening and thus improving overall efficiency of the system.

Put simply, the embodiment uses the history of the signal for generating information on the validity of each received data packet. This is unlike other methods that only uses past in- formation at a much higher communication layer that involves much more computing power. The embodiment circumvents the lost of data packets. In a generic sense, the embodiment can be applied to other types of packet data transmission. Although the above description contains much specificity, these should not be construed as limiting the scope of the embodiments but merely providing illustration of the foresee^¬ able embodiments. Especially the above stated advantages of the embodiments should not be construed as limiting the scope of the embodiments but merely to explain possible achieve^¬ ments if the described embodiments are put into practise. Thus, the scope of the embodiments should be determined by the claims and their equivalents, rather than by the examples given . Reference

10 local area network

12 transmitter side

13 receiver side

15 wireless medium

17 upper layer WLAN module

18 Manchester encoder module

19 transmitter

22 PLCP preamble and SFD device

23 PLCP header and CRC computation device

24 Manchester encoder device

26 receiver

27 Manchester decoder module

28 upper layer WLAN module

30 Manchester decoder device

31 send device

35 LAN

37 signal validity device

38 signal validity detector

39 signal validity controller

40 Manchester encoder module

43 flow chart

46 Idle state

47 Preamble & SFD state

48 Length state

49 CRC check state

52 PPDU length state

54 an end of reception state

60 flow chart

64 improved Preamble & SFD state

65 improved Length state

67 improved CRC check state improved PPDU length state

Claims

1. A receiver device (40) of a data packet communication network (13), comprising

a receiver unit (26) for receiving at least one data packets,

a decoder unit (30) for decoding the at least one received data packets and

a data validity module (37) comprising

- a data validity unit (38) for generating data validity information of the at least one re^¬ ceived data packet and

a data validity controller unit (39) which is connected with the decoder unit (30) and which causes the decoder unit (30) to abort the de^¬ coding of the at least one received data packet if the data validity information indi^¬ cates that the data packet is invalid. 2. A receiver device (40) of claim 1 wherein

the decoder unit (30) is adapted for decoding Manchester data packet.

3. A data validity module (37) for a data packet receiver device, the data validity module comprising

a data validity unit (38) for generating data va^¬ lidity information of at least one data packet and

a data validity controller unit (39) which com^¬ prises an output connection for a receiver decoder unit (30) that decodes the data packet, wherein the data va^¬ lidity controller unit (39) outputs a predetermined value indicating the data validity information.

1. A method of operating a receiver device (40) of a data packet communication network (13), the method comprising receiving at least one data packet,

decoding the at least one data packet,

generating validity information of the at least one data packet, and

causes the decoding of the at least one data packet to be abort if the validity information indicates that the at least one data packet is invalid.

3. A method of claim 4, wherein

the at least one received data packet is encoded with a Manchester coding scheme.

A method of claim 4 or 5 further comprising

receiving a next data packet.

A method of one of claims 4 to 6, wherein

the aborted data packet is not transmitted to next layer .

8. A method of one of claims 4 to 7, wherein

the decoding comprises receiving a preamble and a start of frame limiter (SFD) of the data packet.

9. A method of one of claims 4 to 7, wherein

the decoding comprises getting length value from a

Physical Layer Convergence Procedure (PLCP) header of the data packet.

10. A method of one of claims 4 to 9, wherein

the decoding comprises checking Cyclic Redundancy Check (CRC) value of the data packet.

11. A method of one of claims 4 to 10, wherein

the decoding comprises sending the packet data from a Physical layer to a Media Access Control (MAC) layer.

12. A method of operating a data validity module (37) of a data packet receiver device (40), the method comprising generating validity information of a (encoded) data packet and

outputting a predetermined value indicating the data validity information.