WO2015064257A1

WO2015064257A1 - Reception device and reception method

Info

Publication number: WO2015064257A1
Application number: PCT/JP2014/075635
Authority: WO
Inventors: 信成田中
Original assignee: 株式会社村田製作所
Priority date: 2013-10-30
Filing date: 2014-09-26
Publication date: 2015-05-07

Abstract

A reception signal, which includes a preamble field and a plurality of spectrum-spread-modulated data parts, is inputted to an input port. A demodulation unit demodulates the reception signal inputted thereto from the input port. The demodulation unit searches the reception signal, which has been inputted thereto from the input port, for the preamble field. When having detected the preamble field, the demodulation unit sequentially demodulates the plurality of data parts. When the demodulation of a data part is found impossible, the demodulation unit ceases the demodulation of the data parts following the data part for which the demodulation is found impossible, and the demodulation unit then reverts to the search for the preamble field. In this way, even when an erroneous detection of the preamble field occurs, the wasted processing time can be shortened.

Description

Receiving apparatus and receiving method

The present invention relates to a receiving apparatus and a receiving method for receiving a spread spectrum modulated signal.

-A packet signal transmitted and received by wireless communication usually includes a preamble field consisting of repetition of a known sequence at the head. The receiving apparatus detects a packet by detecting a preamble field from the received signal. The packet includes a data part following the preamble field. When the preamble field is detected, the data portion is then demodulated.

JP 2010-45597 A

When a noise that is not the original preamble field in the received signal is erroneously detected as the preamble field, the part following the erroneously detected part is recognized as the data part. After detection of the preamble field, demodulation processing is performed on a portion recognized as a data portion. However, since this portion is not an original data portion, normal demodulation processing is not performed and a demodulation error occurs. For this reason, the time spent for demodulating a portion that is not the original data portion is wasted.

An object of the present invention is to provide a receiving apparatus and a receiving method that can reduce useless processing time even when a preamble field is erroneously detected.

According to one aspect of the invention,
An input port to which a received signal including a preamble field and a plurality of data portions subjected to spread spectrum modulation is input;
A demodulator that demodulates the received signal input from the input port;
The demodulator
Search the preamble field from the received signal input from the input port;
When the preamble field is detected, a plurality of the data portions are demodulated in order,
If the data part cannot be demodulated, a receiving apparatus is provided that stops demodulating the data part after the data part that could not be demodulated and returns to the preamble field search.

If the data part cannot be demodulated, the demodulation of the subsequent data part is stopped and the process returns to the preamble field search, so that the useless processing time for attempting to demodulate the data part can be shortened.

The preamble field may include a plurality of flags composed of mutually orthogonal flag patterns, and the flag pattern may be orthogonal to the plurality of spreading codes used when attempting to demodulate the data portion.

The number of the data parts included in the received signal is known, and after the demodulator detects the preamble field, when the demodulation of all the data parts is completed, it returns to the search for the preamble field. Good. This makes it possible to search for the next packet immediately after demodulating all data parts.

According to another aspect of the invention,
Searching the preamble field for a received signal having a preamble field and a plurality of spread spectrum modulated data portions following the preamble field;
In the step of searching for the preamble field, when the preamble field is detected, the step of trying to demodulate the next data portion;
When the demodulation of the data part is impossible, the method returns to the step of searching the preamble field, and when the demodulation of the data part is possible, the receiving method includes the step of trying to demodulate the data part. Provided.

The step of searching for the preamble field may return to the step of searching for the preamble field when demodulation of a predetermined number of the data parts is completed after the preamble field is detected. This makes it possible to search for the next packet immediately after demodulating all data parts.

FIG. 1 is a block diagram of a receiving apparatus according to an embodiment. FIG. 2A is a diagram illustrating an example of a frame format of one packet of a received signal converted into a digital signal by an AD converter, and FIG. 2B is a diagram illustrating a preamble field search procedure. FIG. 3A is a diagram showing input / output data of the spread spectrum modulation processing section, and FIG. 3B is a diagram showing a bit string of the spread spectrum modulation signal. FIG. 4 is a diagram for explaining the demodulation processing of the spread spectrum modulation signal. FIG. 5 is a flowchart of a reception process executed by the demodulation unit of the reception apparatus according to the embodiment. FIG. 6 is a schematic diagram of a data transmission / reception system according to an embodiment. FIG. 7 is an example of a timing chart of transmission data transmitted from a plurality of transmission apparatuses.

FIG. 1 shows a block diagram of a receiving apparatus 10 according to the embodiment. The receiving apparatus 10 according to the embodiment includes an RF processing unit 11, an AD converter 12, a demodulation unit 13, and a receiving antenna 14. The RF processing unit 11 includes a down converter, a band pass filter, a log amplifier, and the like. The received signal is converted to a baseband analog signal by the RF processing unit 11, converted to a digital signal by the AD converter 12, and input to the input port 15 of the demodulation unit 13.

FIG. 2A shows an example of the frame format of one packet included in the received signal converted into a digital signal by the AD converter 12 (FIG. 1). The packet includes a preamble field 20 and a data field 21 following the preamble field 20. The preamble field 20 includes flags F1 and F2. The flags F1 and F2 have, for example, a predetermined 1024-bit fixed code (code). The field length of each of the flags F1 and F2 is not limited to 1024 bits. Further, as the preamble field 20, another format that can detect and synchronize a packet may be adopted.

The data field 21 includes a plurality of data parts D1 to D4. FIG. 2A shows an example in which the data field 21 includes four data parts D1 to D4, but the number of data parts included in one data field 21 is not limited to four. The number of data parts included in one data field 21 is known, and the number of data parts is preset in the demodulator 13 of the receiving device 10. The field length of the data parts D1 to D4 is, for example, 1024 bits. By making the field lengths of the flags F1 and F2 equal to the field lengths of the data portions D1 to D4, the demodulation process can be easily performed. The data parts D1 to D4 are configured by spread spectrum modulated signals using spreading codes SC1 to SC4, respectively. The codes of the flags F1 and F2 and the spread codes SC1 to SC4 are orthogonal to each other.

The search procedure for the preamble field 20 (FIG. 2A) will be described with reference to FIG. 2B. A flag search process is performed on the bit string of the received signal for each field length of the flags F1 and F2, that is, for each 2048 bit length. In one flag search process, a correlation operation between a bit string of a 2048-bit received signal and a flag pattern is performed. In the received signal bit string, a 2048-bit section to be subjected to correlation calculation is referred to as a flag search section 23. If a flag pattern identical to the flag F1 or F2 exists in the flag search section 23, a correlation peak appears at a position on the time axis where this flag pattern exists. When a peak exceeding the determination threshold appears, it is determined that the flag F1 or F2 is included in the position where the peak appears (position on the time axis) in the flag search section 23 of the received signal.

FIG. 2B shows the relationship between the received signal and the flag search section 23 in time series. At time t1, a part of the flag F1 is included in the flag search section 23. The flag search process is performed at time t1, but no correlation peak exceeding the threshold value appears, and no flag is detected. Further, flag search processing is performed at time t2 when the received signal is shifted by 1024 bits. At this time, the flag F1 is detected in the flag search section 23.

Furthermore, the flag F2 is detected in the flag search section 23 at time t3 when the received signal is shifted by 1024 bits. If the position where the flag F1 is detected at the time t2 and the position where the flag F2 is detected at the time t3 are the same, it can be said that the preamble field 20 (FIG. 2A) has been detected. Increasing the field length of the preamble field 20 can also reduce the false detection probability.

A method of performing spread spectrum modulation on data to be transmitted will be described with reference to FIGS. 3A and 3B. However, the spread spectrum method is not limited to the following method. Spread spectrum modulation is performed by a transmission device that transmits a radio signal received by the reception device 10 (FIG. 1).

FIG. 3A shows input / output data of the spread spectrum modulation processing unit 30. The data 31 to be transmitted and the spread code SC are input to the spread spectrum modulation processing unit 30. The data 31 to be transmitted has, for example, 10-bit information. That is, the data 31 to be transmitted takes values from 0 to 1023. The spread code SC is composed of 1024 bits. The spread spectrum modulation processing unit 30 performs spread spectrum modulation on the data 31 to be transmitted using the spread code SC. The spread spectrum modulation processing unit 30 outputs a spread spectrum modulation signal 32 subjected to spread spectrum modulation.

FIG. 3B shows an example of a bit string of the spread spectrum modulation signal 32. When the value of the data 31 to be transmitted is “0”, the spread spectrum modulation signal 32 has the same bit string as the spread code SC. That is, the values of the 0th bit to the 1023th bit of the spread code SC are equal to the values of the 0th bit to the 1023th bit of the spread spectrum modulation signal 32, respectively.

When the value of the data 31 to be transmitted is “n”, the spread spectrum modulation processing unit 30 generates the spread spectrum modulation signal 32 by cyclically shifting the spread code SC by n bits. That is, the values from the 0th bit to the (1023-n) th bit of the spread code SC coincide with the values from the nth bit to the 1023th bit of the spread spectrum modulation signal 32, respectively. The values from the (n + 1) th bit to the 1023rd bit match the values from the 0th bit to the (n−1) th bit of the spread spectrum modulation signal 32, respectively.

With reference to FIG. 4, the demodulation process of the spread spectrum modulation signal 32 will be described. FIG. 4 illustrates an example in which the data to be transmitted is “n”. Correlation between the spread spectrum modulation signal 32 and the spread code SC is performed.

An example of the correlation calculation result is shown in a graph 35, and another example is shown in a graph 36. The horizontal axes of the

graphs

35 and 36 represent the number of bits for shifting the spread code SC when the spread spectrum modulation signal 32 is generated, and the vertical axis represents the correlation value. On the other hand, in the graph 35, a peak appears at the position of the number of shift bits n during modulation. When the height of this peak, that is, the correlation value exceeds the determination threshold Th, the spread spectrum modulation signal 32 is demodulated to the value “n”, and the demodulation process ends normally. As shown in the other graph 36, when a peak exceeding the determination threshold Th does not appear, it is determined that demodulation is impossible.

FIG. 5 shows a flowchart of the reception process executed by the demodulator 13 (FIG. 1) of the receiving apparatus 10 according to the embodiment. In step ST1, the preamble field 20 (FIG. 2A) of the received signal is searched. The method described with reference to FIG. 2B is applied to search for the preamble field 20.

In step ST2, it is determined whether the preamble field 20 is detected. If the preamble field 20 is not detected, the process returns to step ST1, and the search for the preamble field 20 is continued. When the preamble field 20 is detected, the data parts D1 to D4 are demodulated in order in steps ST3 to ST6. Immediately after the preamble field 20 is detected, the first data portion D1 (FIG. 2A) is demodulated in step ST3. The demodulation method of the spread spectrum modulation signal 32 described with reference to FIG. 4 is applied to the demodulation of the data parts D1 to D4.

In step ST4, it is determined whether or not the demodulation is normally completed. As shown in the graph 35 of FIG. 4, if a peak exceeding the determination threshold Th appears, it is determined that the demodulation is normally completed. As shown in the graph 36, when a peak exceeding the determination threshold Th does not appear, it is determined that demodulation is impossible. If the demodulation is normally completed, it is determined in step ST5 whether or not the demodulation of all the data parts D1 to D4 is completed. If the demodulation is impossible, the demodulation of the data part is stopped, the process returns to step ST1, and the search process for the preamble field 20 is resumed.

If it is determined in step ST5 that the demodulation of all the data parts D1 to D4 has been completed, the process returns to step ST1 and the search process for the preamble field 20 is resumed. If there is a data part that has not been demodulated, in step ST6, the demodulation target is moved to the next data part, and then the process returns to step ST3 to resume demodulation of the data part. For example, when the demodulation of the data part D1 is completed, the demodulation of the next data part D2 is executed.

In the embodiment, if demodulation of a data part is impossible in step ST3, the search for the preamble field 20 is resumed in step ST4 without performing demodulation of the subsequent data part. For this reason, useless demodulation processing of the data portion can be avoided.

FIG. 6 shows a schematic diagram of a data transmission / reception system according to the embodiment. The data transmission / reception system according to the embodiment includes at least one receiving device 10 and a plurality of, for example, six transmitting devices 41 to 46. The number of transmission devices 41 to 46 is not limited to six. Each of the plurality of transmission devices 41 to 46 transmits a signal having the frame format shown in FIG. 2A, for example. The frequencies of the carrier waves used in the plurality of transmission apparatuses 41 to 46 are the same, and the flag patterns of the flags F1 and F2 are also the same.

As described with reference to FIG. 2A, the codes of the spread codes SC1 to SC4 and the flags F1 and F2 for generating the data parts D1 to D4 of the packets transmitted from the transmission devices 41 to 46 are mutually Orthogonal. For example, Gold series codes are used as the codes of the flags F1 and F2 and the spreading codes SC1 to SC4. Further, the codes of the flags F1 and F2 and the spread codes SC1 to SC4 are the same among the plurality of transmission apparatuses 41 to 46. When unidirectional communication is adopted as the communication method, the plurality of transmission devices 41 to 46 transmit data independently of each other in terms of time.

The receiving apparatus 10 demodulates the data parts D1 to D4 of the data field 21 after detecting the preamble field 20. In the data field 21, an identification number for identifying the transmission devices 41 to 46 is included. From this identification number, it is possible to recognize from which of the transmission devices 41 to 46 the demodulated packet is transmitted.

FIG. 7 shows an example of a timing chart of transmission data transmitted from the transmission devices 41 to 46. In the example shown in FIG. 7, first, the preamble field 20 of the packet PK1 transmitted from the transmission device 41 is detected (steps ST1 and ST2 in FIG. 5), and the demodulation of the data parts D1 to D4 ends normally (FIG. 7). 5 steps ST3 to ST5).

Since the plurality of transmission apparatuses 41 to 46 transmit data independently in time, the flags F1 of the packets PK1 and PK2 transmitted from two

different transmission apparatuses

41 and 42 are shown in FIG. 2B. In some cases, they are detected simultaneously in the flag search section 23. In this case, two peaks appear in the correlation calculation result. When two peaks appear, it is determined that the flag F1 exists at the position where the peak with a high degree of correlation appears (position on the time axis). Note that scheduling of packet transmission times may be performed so that packets transmitted from different transmission apparatuses 41 to 46 do not overlap on the time axis.

In the example shown in FIG. 7, the data part D1 of the packet PK1 and the flag F1 of the packet PK3 transmitted from the transmission device 43 almost overlap on the time axis. When demodulating the data part D1 of the packet PK1, the spread code SC1 for the data part D1 is used. Since the spreading code SC1 and the flag F1 are orthogonal to each other, the flag F1 of the packet PK3 is recognized as simple noise when demodulating the data part D1 of the packet PK1. Similarly, even if the data part D1 of the packet PK1 and the data parts D2 to D4 other than the data part D1 of other packets overlap on the time axis, signals other than the packet PK1 are recognized as noise. Therefore, the data part D1 of the packet PK1 can be demodulated. Similarly, the data parts D2 to D4 of the packet PK1 can be demodulated.

When the demodulation of the data part D4 is completed, it is determined that “demodulation is completed” in step ST5 of FIG. 5, and the process returns to step ST1 to resume the search for the preamble field. FIG. 7 shows an example in which noise 25 is erroneously detected as a preamble field. When the preamble field is detected, demodulation of the data part D1 is attempted (step ST3 in FIG. 5).

However, since the data part D1 following the noise 25 is not a regular signal subjected to spread spectrum modulation, the data part D1 cannot be demodulated. Since it is determined in step ST4 in FIG. 5 that the demodulation is not normally completed, the process returns to step ST1 and the search for the preamble field 20 is resumed.

In the example shown in FIG. 7, the preamble field 20 of the packet PK4 transmitted from the transmission device 44 is detected. Thereafter, the demodulation of the data parts D1 to D4 of the packet PK4 is normally completed. After the demodulation process of the packet PK4 is completed, the reception process of the packet PK5 transmitted from the transmission device 43 is executed.

Next, reception processing according to a comparative example will be described. In the comparative example, after the preamble field 20 is detected, the decoding process for all the data parts D1 to D4 is performed. After the decoding process of the data parts D1 to D4 is completed, the search for the preamble field 20 is resumed. According to this comparative example, when the noise 25 shown in FIG. 7 is erroneously detected as the preamble field 20, all of the data parts D1 to D4 following the noise 25 are demodulated.

Preamble field 20 cannot be detected during the period when demodulation is attempted. For this reason, it is impossible to detect the preamble field 20 of the packet PK4 that has arrived at the receiving apparatus during the period when the demodulation of the data parts D1 to D4 following the noise 25 is attempted. After attempting to demodulate the data parts D1 to D4 following the noise 25, the preamble field 20 of the packet PK5 is detected. In the method according to the comparative example, the information of the packet PK4 cannot be received.

In the embodiment, after attempting to demodulate the data part D1 following the noise 25, the preamble field 20 is searched without attempting to demodulate the data parts D2 to D4. For this reason, the preamble field 20 of the packet PK4 can be detected. Thus, in the transmission / reception system according to the embodiment, signals from the plurality of transmission devices 41 to 46 can be received efficiently.

In particular, when a weak wireless device that does not require a license is used, erroneous detection of the preamble field 20 is likely to occur because the radio wave output is weak. Furthermore, in order to ensure a sufficient communicable distance, the bandwidth must be limited. When the band is limited, the modulation speed is reduced, and the communication time of the data parts D1 to D4 (FIG. 2A) is increased. As a result, when erroneous detection of the preamble field 20 occurs, useless time for demodulating the data parts D1 to D4 becomes long. Thus, the above embodiment is particularly effective when a weak wireless device is used. The demodulation method according to the above embodiment can be easily executed by software radio using a microcomputer, a field programmable gate array (FPGA), or the like.

Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

DESCRIPTION OF SYMBOLS 10 Receiver 11 RF processor 12 AD converter 13 Demodulator 14 Receiving antenna 15 Input port 20 Preamble field 21 Data field 23 Flag search section 25 Noise 30 Spread spectrum modulation processor 31 Data to be transmitted 32 Spread spectrum modulated

signals

35 and 36 Graphs 41 to 46 Transmitters D1 to D4 Data part F1, F2 Flags PK1 to PK5 Packet SC, SC1 to SC4 Spread code Th Determination threshold

Claims

An input port to which a received signal including a preamble field and a plurality of data portions subjected to spread spectrum modulation is input;
A demodulator that demodulates the received signal input from the input port;
The demodulator
Search the preamble field from the received signal input from the input port;
When the preamble field is detected, a plurality of the data portions are demodulated in order,
A receiving apparatus that, when demodulation of the data part is impossible, stops demodulation of the data part after the data part that was not demodulated and returns to the search for the preamble field.
The receiving apparatus according to claim 1, wherein the demodulating unit attempts to demodulate the data unit using a plurality of spreading codes orthogonal to each other.
3. The reception according to claim 2, wherein the preamble field includes a plurality of flags composed of mutually orthogonal flag patterns, and the flag patterns are orthogonal to the plurality of spreading codes used when attempting to demodulate the data part. apparatus.
The number of the data parts included in the received signal is known;
The demodulator
The receiving apparatus according to any one of claims 1 to 3, wherein after the preamble field is detected, the demodulation of all the data parts is completed, and the search returns to the preamble field search.
Searching the preamble field for a received signal having a preamble field and a plurality of spread spectrum modulated data portions following the preamble field;
In the step of searching for the preamble field, when the preamble field is detected, the step of trying to demodulate the next data portion;
A step of returning to the step of searching for the preamble field when the demodulation of the data part is impossible, and a step of attempting to demodulate the data part when the demodulation of the data part is possible.
6. The receiving method according to claim 5, wherein in the step of trying to demodulate the data part, the data part is demodulated using a plurality of mutually orthogonal spreading codes.
The preamble field includes a plurality of flags composed of mutually orthogonal flag patterns, and the flag patterns are orthogonal to the plurality of spreading codes used when attempting to demodulate the data part. Receiving method.
8. The step of searching for the preamble field returns to the step of searching for the preamble field when demodulation of a predetermined number of the data parts is completed after the preamble field is detected in the step of searching for the preamble field. The receiving method according to any one of the above.