JP2015130626A - Radio communication device and communication parameter determination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize a communication parameter according to radio link quality, when a communication cycle is longer than a variation cycle of the radio link quality.SOLUTION: In a communication terminal 10, a link quality measurement section 14 measures radio link quality between the communication terminal 10 and a base station being a communication partner of the communication terminal 10. The link quality measurement section 14 measures the radio link quality which fluctuates at a variation cycle smaller than the communication cycle of the communication terminal 10 using the communication cycle of the communication terminal 10, and obtains a plurality of samples of the radio link quality. The link quality measurement section 14 stores the most recent M pieces of samples, among the samples obtained orderly according to the communication cycle. A communication parameter determination section 15 references the link quality measurement section 14, and determines an optimal value in a predetermined communication parameter on the basis of the most recent N pieces of samples (N<M, however) among the M pieces of samples stored in the link quality measurement section 14.

Description

  The present invention relates to a wireless communication apparatus and a communication parameter determination method.

  In the radio communication system, the radio link quality between the communication terminal and the base station changes every moment, so that the optimum value of the communication parameter also changes according to the change in the radio link quality. For example, in a wireless communication environment in which BER (Bit Error Rate), which is one of the radio link qualities, changes, the optimum value of the packet size, which is one of the communication parameters, changes. That is, if the packet size is large when the BER is large, the PER (Packet Error Rate) increases and the throughput decreases. For this reason, a small packet size is suitable when the BER is large. On the other hand, if the packet size is small when the BER is small, the overhead of the header portion in the packet becomes relatively large, resulting in a decrease in throughput. For this reason, a large packet size is suitable when the BER is small. That is, in order to prevent a decrease in throughput, it is preferable to reduce the packet size as the BER increases. Therefore, conventionally, there is a packet communication device that determines the packet size of a transmission packet based on the BER calculated from the received packet.

JP-A-11-205216

  Recently, with the cost reduction of communication devices, devices connected to the network are related to M2M communication (Machine to Machine Communication) that realizes services by exchanging data autonomously without user's judgment. Technology development is underway. M2M communication in 3GPP (3rd Generation Partnership Project), which is a mobile communication standardization project, is called MTC (Machine Type Communication), and in MTC, data is exchanged between a base station and a communication terminal. Hereinafter, a communication terminal used for MTC may be referred to as an “MTC terminal”.

  Examples of the MTC terminal include a smart meter having a wireless communication function, a vending machine having a wireless communication function, a measuring instrument having a wireless communication function, and the like. A smart meter having a wireless communication function transmits, for example, power usage data measured every month to the base station. A vending machine equipped with a wireless communication function transmits, for example, sales information, inventory information in the vending machine, etc. to the base station every day. A measuring instrument equipped with a wireless communication function measures the temperature in the office every minute and transmits temperature data to the base station, for example.

  As described above, since there are many applications for the MTC terminal that only need to communicate with the base station at fixed time intervals of a relatively long time, in general, the communication cycle of the MTC terminal is the communication cycle of the conventional packet communication apparatus. Bigger than. For this reason, when the conventional packet communication apparatus is applied to MTC, the difference between the reception timing of the reception packet that is a BER calculation target for determining the packet size of the transmission packet and the transmission timing of the transmission packet is It becomes larger than before. In general, the communication cycle of the MTC terminal is larger than the fluctuation cycle of the radio link quality between the MTC terminal and the base station.

  Therefore, when the conventional packet communication apparatus is applied to MTC, there is a high possibility that the difference between the BER used for determining the packet size of the transmission packet and the actual BER at the transmission timing of the transmission packet becomes large. For this reason, when the conventional packet communication apparatus is applied to MTC, there is a high possibility that the packet size of the transmission packet does not become the optimum packet size according to the actual BER, and thus the throughput is lowered. As described above, in the conventional packet communication apparatus, when the communication cycle is longer than the fluctuation cycle of the radio link quality, it is not possible to determine the optimum packet size according to the radio link quality.

  The disclosed technology has been made in view of the above, and an object thereof is to set communication parameters to optimum values according to the radio link quality when the communication cycle is longer than the fluctuation cycle of the radio link quality.

  In the disclosed aspect, the wireless communication device includes a measurement unit and a determination unit. The measurement unit measures a radio link quality that fluctuates with a fluctuation period smaller than a predetermined communication period, and acquires a plurality of samples of the radio link quality by measuring the predetermined communication period. The determination unit uses a plurality of nearest samples among the plurality of samples acquired by the measurement unit, and each of a plurality of different candidate values in a predetermined communication parameter corresponds to each of the plurality of candidate values. The average throughput is calculated. Then, the determining unit sets any one candidate value among the plurality of candidate values as the determined value of the communication parameter based on the plurality of average throughputs.

  According to the aspect of an indication, when a communication period is longer than the fluctuation | variation period of radio link quality, a communication parameter can be made into the optimal value according to radio link quality.

FIG. 1 is a functional block diagram illustrating an example of the configuration of the communication terminal according to the first embodiment. FIG. 2 is a flowchart for explaining the operation of the communication terminal according to the first embodiment. FIG. 3 is a diagram illustrating an example of a sample number determination table according to the first embodiment. FIG. 4 is a diagram illustrating an example of the relationship between the standard deviation of the RSSI distribution and the required number of samples according to the first embodiment. FIG. 5 is a graph illustrating an example of the relationship between the payload length and the average throughput according to the first embodiment. FIG. 6 is a diagram illustrating an example of actual measurement of the RSSI and the number of used samples according to the first embodiment. FIG. 7 is a diagram illustrating an actual measurement example of throughput according to the first embodiment. FIG. 8 is a diagram illustrating an actual measurement example of throughput according to the first embodiment. FIG. 9 is a diagram illustrating an actual measurement example of throughput according to the first embodiment. FIG. 10 is a diagram illustrating an example of the relationship between the modulation scheme and the average throughput according to the second embodiment. FIG. 11 is a diagram illustrating an example of a relationship between transmission power and average throughput in the third embodiment. FIG. 12 is a diagram illustrating a hardware configuration example of the communication terminal.

  Embodiments of a wireless communication apparatus and a communication parameter determination method disclosed in the present application will be described below in detail with reference to the drawings. Note that the wireless communication device and the communication parameter determination method disclosed in the present application are not limited by this embodiment. Hereinafter, a communication terminal will be described as an example of a wireless communication device. The communication terminal described below is, for example, an MTC terminal.

[Example 1]
<Configuration example of communication terminal>
FIG. 1 is a functional block diagram illustrating an example of the configuration of the communication terminal according to the first embodiment. A communication terminal 10 shown in FIG. 1 includes an antenna 11, a radio reception unit 12, a reception processing unit 13, a link quality measurement unit 14, a communication parameter determination unit 15, a communication parameter control unit 16, and a transmission processing unit 17. And a wireless transmission unit 18. The communication cycle of the communication terminal 10 is determined in advance, and this communication cycle is longer than the fluctuation cycle of the radio link quality. For example, the communication terminal 10 communicates with the base station at a predetermined communication period of 1 minute or more.

  The wireless reception unit 12 performs a down-conversion process, an analog-digital conversion process, and the like on the reception signal received via the antenna 11 to obtain a baseband reception signal and outputs the baseband reception signal to the reception processing unit 13. Further, when the link quality measurement unit 14 measures RSSI (Received Signal Strength Indicator) or SINR (Signal-to-Interference and Noise power Ratio) as the radio link quality, the radio reception unit 12 The obtained baseband received signal is input to the link quality measurement unit 14.

  The reception processing unit 13 performs predetermined reception processing such as demodulation processing and decoding processing on the baseband reception signal input from the wireless reception unit 12 to obtain a reception packet. Further, when the link quality measurement unit 14 measures BER or PER as the radio link quality, the reception processing unit 13 counts the number of error bits in each received packet during the decoding process, and sends it to the link quality measurement unit 14. Output.

  The link quality measurement unit 14 measures the radio link quality between the communication terminal 10 and the base station with which the communication terminal 10 communicates. The link quality measurement unit 14 measures the radio link quality in accordance with the communication cycle of the communication terminal 10. As described above, since the predetermined communication cycle of the communication terminal 10 is larger than the fluctuation cycle of the radio link quality, the link quality measurement unit 14 sets the radio link quality that fluctuates with a fluctuation cycle smaller than the predetermined communication cycle at the predetermined communication cycle. taking measurement. The link quality measurement unit 14 acquires a plurality of samples of the radio link quality by measurement at a predetermined communication cycle. That is, the link quality measurement unit 14 measures the radio link quality that fluctuates with a fluctuation period smaller than the predetermined communication period at the predetermined communication period, and acquires a plurality of samples of the radio link quality. For example, the link quality measurement unit 14 measures RSSI, SINR, BER, or PER as the radio link quality. Moreover, the link quality measurement part 14 memorize | stores the some recent M sample among the samples acquired sequentially according to the communication period. For example, M = 30.

  The communication parameter determination unit 15 refers to the link quality measurement unit 14 and, based on the most recent N samples (where N <M) among the M samples stored in the link quality measurement unit 14, An optimum value for a predetermined communication parameter is determined. The predetermined communication parameter in the present embodiment is a packet size. Each packet formed by the transmission processing unit 17 is generally composed of a header and a payload excluding the header. While the header length is fixed, the payload length is variable. Therefore, controlling the payload length is equivalent to controlling the packet size. Therefore, the communication parameter determination unit 15 according to the present embodiment determines the optimum value of the payload length (that is, the optimum value of the packet size) based on the latest N samples. Details of the N determination method and the optimum value determination method will be described later. The communication parameter determination unit 15 outputs the determined optimum value of the payload length to the communication parameter control unit 16.

  Here, in a predetermined communication cycle, the reception timing of the received signal that is the measurement target of the radio link quality used to determine the optimal value of the communication parameter is based on the transmission timing of the transmission packet that is the determination target of the optimal value of the communication parameter. The timing is one cycle or more before (one cycle or more in the past). Therefore, “the most recent samples” refers to a plurality of samples respectively obtained at a plurality of reception timings retroactive from a reception timing one cycle before the specific transmission timing on the basis of a specific transmission timing. Become.

  The communication parameter control unit 16 controls the payload length of the transmission packet formed by the transmission processing unit 17 to the optimum value determined by the communication parameter determination unit 15. When the predetermined communication parameter for which the optimum value is determined is the packet size, the communication parameter control unit 16 does not control the wireless transmission unit 18.

  The transmission processing unit 17 performs predetermined transmission processing such as encoding processing, modulation processing, and packet formation processing on the input transmission data to form a transmission packet, and the formed transmission packet is transmitted to the wireless transmission unit 18. Output to. When forming a transmission packet, the transmission processing unit 17 changes the payload length of each packet according to the control from the communication parameter control 16.

  The wireless transmission unit 18 performs digital-analog conversion processing, up-conversion processing, and the like on the transmission packet input from the transmission processing unit 17 and transmits the transmission packet after the up-conversion to the base station via the antenna 11.

<Operation of communication terminal>
FIG. 2 is a flowchart for explaining the operation of the communication terminal according to the first embodiment. The flowchart shown in FIG. 2 is repeatedly executed at a communication cycle (for example, every one minute) of the communication terminal 10. Hereinafter, the case where RSSI is used as the radio link quality, the case where SINR is used, the case where BER is used, or the case where PER is used will be described separately.

<When RSSI is used as the radio link quality>
First, the link quality measurement unit 14 measures RSSI as the radio link quality between the communication terminal 10 and the base station, acquires an RSSI sample, and stores the acquired sample (step S31).

  Next, the communication parameter determination unit 15 refers to the link quality measurement unit 14 and determines whether the number of RSSI samples stored in the link quality measurement unit 14 is M or more (step S32). Even when the fading characteristic of the received signal at the communication terminal 10 follows the Rayleigh distribution, the required number of samples is sufficient, so here, for example, M = 30 is preferable.

  When the number of samples is M or more (step S32: Yes), the communication parameter determination unit 15 calculates the latest M sample values, that is, the average μ and variation of the most recent M RSSI values (step S34). ). The communication parameter determination unit 15 obtains a standard deviation σ of the most recent M RSSI values as a value indicating variation in RSSI values.

  Next, the communication parameter determination unit 15 may call the number of the most recent samples used for calculating the average throughput based on the average μ of the RSSI value and the standard deviation σ (hereinafter referred to as “number of used samples”). ) N is determined (step S35). However, N <M. FIG. 3 is a diagram illustrating an example of a sample number determination table according to the first embodiment. The communication parameter determining unit 15 refers to the table in FIG. 3 based on the average μ and the standard deviation σ of the RSSI values and determines the number N of used samples. For example, when the average μ of the RSSI value is in the range of −88 dBm or more and less than −86 dBm, and the standard deviation σ of the RSSI value is in the range of 2 dB or more and less than 3 dB, the communication parameter determination unit 15 determines the number of used samples. N is determined to be “13”.

  Note that the table shown in FIG. 3 is derived from FIG. 4 in advance. FIG. 4 is a diagram illustrating an example of the relationship between the standard deviation of the RSSI distribution and the required number of samples according to the first embodiment. This relationship is obtained by simulation. As shown in FIG. 4, the required number of samples for determining the optimum value of the payload length increases as the average μ of the RSSI value increases (that is, as the radio link quality becomes better), and the RSSI value The standard deviation σ increases as the standard deviation σ increases.

  Returning to FIG. 2, the communication parameter determination unit 15 then calculates, for each of a plurality of candidate values of payload length, a plurality of throughputs respectively corresponding to the plurality of candidate values (step S36).

  First, the communication parameter determination unit 15 acquires the latest N RSSI values from the link quality measurement unit 14 according to the number N of used samples determined in step S35.

  Next, the communication parameter determination unit 15 converts the RSSI sequence composed of N RSSI values into a BER sequence composed of N BER values. For example, the RSSI sequence (dBm) acquired when N = 5, the noise floor level of the communication terminal 10 is −95 dBm, and the modulation method of the received signal is BPSK (Binary Phase Shift Keying) is (−90 −89 −85). -88 -89). In this case, this RSSI column (-90 -89 -85 -88 -89) is converted into a BER column (0.01878 0.00731 0.00001 0.00231 0.00731).

  Here, the conversion from the RSSI sequence to the BER sequence can be performed based on the reception sensitivity of the communication terminal 10 and the modulation method of the received signal. That is, the reception sensitivity of the communication terminal 10 is represented by the noise floor level n of the communication terminal 10, and the signal level s is calculated by subtracting the noise floor level n from RSSI. Further, SNR (Signal-Noise Ratio) = s / n can be obtained by dividing the signal level s by the noise floor level n. The relationship between BER and SNR (= s / n) is determined according to the modulation method of the received signal. For example, when the modulation method is BPSK, “BER = erfc (sqrt (s / n)) / 2”, and when the modulation method is QPSK (Quadrature Phase Shift Keying), “BER = erfc (sqrt (s / 2n)”. ) / 2 ". Therefore, each BER value in the BER sequence can be obtained based on each RSSI value in the RSSI sequence, the reception sensitivity of the communication terminal 10, and the modulation method of the received signal. The reception sensitivity of the communication terminal 10 and the received signal modulation method are known to the communication parameter determination unit 15.

  Next, the communication parameter determination unit 15 converts a BER sequence including N BER values into a PER sequence including N PER values for each of a plurality of candidate values of payload length. Here, if the sum of the header length and the payload length is k bits, PER can be expressed by an expression “PER = 1− (1−BER) ^ k”. Therefore, conversion from the BER sequence to the PER sequence can be performed based on the header length and the payload length. The k bits are known to the communication parameter determination unit 15.

For example, if five candidate values of payload length (bits) are 60, 80, 100, 150, and 200 and the header length is 50 bits, the BER sequence (0.01878 0.00731 0.00001 0.00231 0.00731) has the following five PERs: Converted to a column.
PER sequence with payload length = 60 bits: (0.8758 0.5537 0.0012 0.2245 0.2434)
PER string with payload length = 80 bits: (0.9150 0.6146 0.0014 0.2595 0.6146)
PER string with payload length = 100 bits: (0.9418 0.6672 0.0017 0.2930 0.6672)
PER sequence with payload length = 150 bits: (0.9775 0.7694 0.0022 0.3701 0.7694)
PER string with payload length = 200 bits: (0.9913 0.8402 0.0028 0.4389 0.8402)

Here, the throughput can be expressed by the following equation.
Throughput = (1-PER) × (payload length) / (header length + payload length)
Therefore, according to this equation, the communication parameter determination unit 15 converts the PER sequence made up of N PER values into a throughput sequence made up of N throughput values for each of a plurality of candidate values of payload length. Next, the communication parameter determination unit 15 calculates an average of N throughput values, that is, an average throughput, for each of a plurality of payload length candidate values. For example, the following five average throughputs are calculated from the above five PER columns. FIG. 5 shows these relationships. FIG. 5 is a graph illustrating an example of the relationship between the payload length and the average throughput according to the first embodiment.
Average throughput with payload length = 60 bits: 0.304
Average throughput with payload length = 80 bits: 0.319
Average throughput with payload length = 100 bits: 0.323
Average throughput with payload length = 150 bits: 0.317
Average throughput with payload length = 200 bits: 0.301

  Next, the communication parameter determination unit 15 determines an optimum value for the payload length from among a plurality of candidate values for the payload length (step S37). In other words, the communication parameter determination unit 15 sets any one of the plurality of candidate values for the payload length as the determined value for the payload length. In the present embodiment, the communication parameter determination unit 15 determines a candidate value having the maximum average throughput as an optimum value among a plurality of candidate values of payload length. For example, in the above example, the average throughput is maximized when the payload length = 100 bits among the five candidate values 60, 80, 100, 150, and 200 of the payload length (bits). Therefore, the optimum value of the payload length is 100 bits. Therefore, the communication parameter determination unit 15 determines the payload length of the transmission packet formed by the transmission processing unit 17 to be 100 bits.

  When the number of samples is less than M (step S32: No), the communication parameter determination unit 15 determines the optimum value of the payload length from the most recent sample of RSSI (step S33). For example, the communication parameter determination unit 15 determines a larger payload length as the optimum value as the value of the latest one sample of RSSI increases. The correspondence relationship between the RSSI value and the payload length is determined in advance.

<When SINR is used as the radio link quality>
Only differences from the case of using RSSI as the radio link quality will be described. In step S31 of FIG. 2, the link quality measurement unit 14 measures SINR as the radio link quality between the communication terminal 10 and the base station, acquires the SINR sample, and stores the acquired sample. The subsequent processing is obtained by replacing “RSSI” with “SINR” in the above-described series of processing when RSSI is used as the radio link quality.

<When using BER as radio link quality>
Only differences from the case of using RSSI as the radio link quality will be described.

  In step S31 of FIG. 2, the link quality measurement unit 14 measures the BER as the radio link quality between the communication terminal 10 and the base station, acquires the BER sample, and stores the acquired sample. For example, the reception signal input to the reception processing unit 13 is error correction encoded using a block code such as a BCH (Bose Chaudhuri Hocquenghem) code, and the reception processing unit 13 receives error bits in each received packet during decoding processing. The number is counted and output to the link quality measurement unit 14. The link quality measurement unit 14 measures the BER based on the number of error bits input from the reception processing unit 13.

  The processing in the next step S32 is the same as when RSSI is used as the radio link quality.

  When the number of samples is M or more (step S32: Yes), the communication parameter determination unit 15 calculates the latest M sample values, that is, the average μ and variation of the most recent M BER values (step S34). ). The communication parameter determination unit 15 obtains the standard deviation σ of the most recent M BER values as a value indicating the variation in the BER values.

  Next, the communication parameter determination unit 15 determines the number of used samples N based on the average BER of the BER values and the standard deviation σ (step S35). However, N <M. The number of used samples is determined using a table similar to the sample number determination table shown in FIG. That is, in the table used for determining the number of used samples, the number of used samples increases as the average μ of the BER value decreases (that is, as the radio link quality improves), and the standard deviation σ of the BER value increases. The larger the is, the more it becomes.

  Next, the communication parameter determination unit 15 calculates a plurality of throughputs corresponding to the plurality of candidate values for each of the plurality of candidate values for the payload length as follows (step S36).

  First, the communication parameter determination unit 15 acquires the latest N BER values from the link quality measurement unit 14 according to the number N of used samples determined in step S35.

  Next, as in the case of using RSSI as the radio link quality, the communication parameter determination unit 15 forms a BER sequence composed of N BER values for each of a plurality of candidate values of payload length, from N PER values. Convert to PER string.

  The subsequent processing is the same as the processing when RSSI is used as the radio link quality. However, when the number of samples is less than M (step S32: No), the communication parameter determination unit 15 determines the optimum value of the payload length from the one sample nearest to the BER (step S33). For example, the communication parameter determination unit 15 determines a smaller payload length as the optimum value as the value of the one sample nearest to the BER is larger. The correspondence relationship between the BER value and the payload length is determined in advance.

<When PER is used as the radio link quality>
Only differences from the case of using BER as the radio link quality will be described.

  In step S31 of FIG. 2, the link quality measurement unit 14 measures the PER as the radio link quality between the communication terminal 10 and the base station, acquires the PER sample, and stores the acquired sample. Here, the measurement of PER is performed as follows. That is, first, the link quality measurement unit 14 measures the BER based on the number of error bits input from the reception processing unit 13 as described above. If the sum of the header length and payload length of the received packet is k bits, PER can be expressed by the expression “PER = 1− (1−BER) ^ k”. Therefore, the link quality measurement unit 14 obtains PER from BER according to this equation. The k bits are known to the link quality measurement unit 14.

  The subsequent processing is obtained by replacing “BER” with “PER” in the description of a series of processing when BER is used as the radio link quality. However, conversion from the BER sequence to the PER sequence is not necessary.

<Measurement example of the number of samples used>
FIG. 6 is a diagram illustrating an example of actual measurement of the RSSI and the number of used samples according to the first embodiment. The upper diagram of FIG. 6 shows RSSI measured every minute in the actual office environment, and the lower diagram of FIG. 6 shows the number of used samples N measured every minute in the actual office environment.

  As shown in the upper diagram of FIG. 6, in time zone A including daytime and evening time, the movement of people in the office is intense, so the fluctuation of RSSI is large, and thus the fluctuation of RSSI is also large. In particular, the variation around 17:00 is remarkable. On the contrary, in the time zone B including the time zone of midnight or early morning, since the movement of people in the office is small, the fluctuation of the RSSI is small, and hence the variation of the RSSI is also small. On the other hand, in the lower diagram of FIG. 6, the number of used samples in the time zone A is generally larger than the number of used samples in the time zone B. Thus, the number N of samples used increases as the variation in RSSI increases and the variation in RSSI increases.

<Measurement example of throughput>
7, 8, and 9 are diagrams illustrating examples of actual measurement of throughput in the first embodiment. 7 shows the average throughput measured in time zone A of FIG. 6, and FIG. 8 shows the average throughput measured in time zone B of FIG. FIG. 9 shows average throughput measured in all time zones A and B shown in FIG. 7, 8 and 9, the bars 41, 51, 61 determine the packet size using N samples determined according to the RSSI variation as in steps S 34 to S 37 described above. Is the first throughput. The bars 42, 52, and 62 are the second throughputs when the packet size is always determined using only the latest one sample as in step S33 above. Bars 43, 53, and 63 are the third throughput when the packet size is fixed regardless of RSSI. When FIG. 7 is compared with FIG. 8, the improvement in the first throughput with respect to the second and third throughputs is larger in the time zone A in which the RSSI variation is large than in the time zone B in which the RSSI variation is small. I understand that. Further, it can be seen from FIG. 9 that the first throughput is the highest in all time zones.

  In the above, Example 1 was demonstrated.

[Example 2]
The present embodiment is different from the first embodiment in that the predetermined communication parameter whose optimum value is determined by the communication parameter determination unit 15 is the data rate. Since the configuration of the communication terminal 10 in the present embodiment is the same as that of the first embodiment (FIG. 1), description thereof is omitted. Since the basic operation of the communication terminal 10 in the present embodiment is the same as that of the first embodiment, the operation of the communication terminal 10 in the present embodiment will be described below with reference to FIG. In the following, differences from the first embodiment will be described. In the following description, only the case where RSSI is used as the radio link quality will be described. However, in this embodiment, SINR, BER, or PER can also be used as the radio link quality as in the first embodiment.

<Operation of communication terminal>
Steps S31, S32, S34, and S35 are the same as those in the first embodiment.

  In step S36, the communication parameter determination unit 15 calculates, for each of a plurality of candidate values of the data rate, a plurality of throughputs respectively corresponding to the plurality of candidate values (step S36).

  First, the communication parameter determination unit 15 acquires the latest N RSSI values from the link quality measurement unit 14 according to the number N of used samples determined in step S35. For example, the RSSI sequence (dBm) acquired when N = 5, the noise floor level of the communication terminal 10 is −95 dBm, and the modulation method of the received signal is BPSK is (−90 −89 −85 −88 −89). Suppose there was.

Next, the communication parameter determination unit 15 converts the RSSI sequence composed of N RSSI values into the BER sequence composed of N BER values for each of a plurality of candidate values of the data rate in the same manner as in the first embodiment. . Since the data rate can be changed by changing the modulation method used for the modulation processing in the transmission processing unit 17, a plurality of candidates for the modulation method can be regarded as a plurality of candidate values for the data rate. Therefore, for example, if the modulation scheme candidates are three candidates of BPSK + double DSSS (Direct Sequence Spread Spectrum), BPSK, and QPSK, the RSSI sequence (-90 -89 -85 -88 -89) has the following three BER sequences: Is converted to In these three modulation schemes, the data rate is higher for QPSK than for BPSK, and higher for BPSK than for BPSK + 2 × DSSS.
BER sequence with modulation scheme = BPSK + 2 × DSSS:
(0.00164 0.00028 0.00000 0.00003 0.00028)
BER sequence with modulation scheme = BPSK:
(0.01878 0.00731 0.00001 0.00231 0.00731)
BER sequence with modulation scheme = QPSK:
(0.07072 0.04212 0.00135 0.02259 0.04212)

Next, the communication parameter determination unit 15 converts a BER sequence including N BER values into a PER sequence including N PER values for each of a plurality of modulation scheme candidates. Conversion from the BER sequence to the PER sequence is performed in the same manner as in the first embodiment. Thereafter, the communication parameter determination unit 15 converts the PER sequence composed of N PER values into a throughput sequence composed of N throughput values. Next, the communication parameter determination unit 15 calculates an average of N throughput values, that is, an average throughput, for each of a plurality of modulation scheme candidate values. However, the conversion from the PER sequence to the throughput sequence reflects the difference in transmission time due to the difference in data rate. For example, if the transmission time t in BPSK is “1”, the transmission time t in BPSK + double DSSS is “2”, and the transmission time t in QPSK is “0.5”. By multiplying each throughput value by the reciprocal of the transmission time, the difference in transmission time due to the difference in data rate can be reflected in the throughput column. That is, the conversion from the PER sequence to the throughput sequence is performed according to the following equation.
Throughput = (1-PER) × (payload length) / (t × (header length + payload length))
Therefore, for example, the following three average throughputs are calculated from the above three BER sequences. FIG. 10 shows these relationships. FIG. 10 is a diagram illustrating an example of the relationship between the modulation scheme and the average throughput according to the second embodiment. Here, the header length is 50 bits and the payload length is 60 bits.
Modulation method = BPSK + 2x average DSSS throughput: 0.26
Modulation method = Average throughput with BPSK: 0.31
Modulation method = Average throughput with QPSK: 0.21

  Next, the communication parameter determination unit 15 determines an optimum value of the data rate by determining an optimum modulation method from among a plurality of modulation method candidates (step S37). That is, the communication parameter determination unit 15 sets any one of the plurality of candidate values for the data rate as the determined value for the data rate. In this embodiment, the communication parameter determination unit 15 determines a modulation scheme that maximizes the average throughput among a plurality of modulation scheme candidates as an optimal modulation scheme. That is, in the present embodiment, the communication parameter determination unit 15 determines the data rate at which the average throughput is maximum among the plurality of candidate data rate values as the optimum value. For example, in the above example, of the three modulation scheme candidates, the average throughput is maximized when the modulation scheme = BPSK. Therefore, the optimum modulation method is BPSK. Therefore, the communication parameter determination unit 15 determines the modulation scheme used for the modulation processing in the transmission processing unit 17 to be BPSK.

  When the number of samples is less than M (step S32: No), the communication parameter determination unit 15 determines the optimum value of the data rate from the most recent sample of RSSI (step S33). For example, the communication parameter determination unit 15 determines a modulation scheme having a higher data rate as the optimum modulation scheme as the value of the one sample nearest to RSSI increases. The correspondence relationship between the RSSI value and the modulation method is determined in advance.

  The above is the optimum value determination process in the communication parameter determination unit 15.

  Then, the communication parameter determination unit 15 notifies the communication parameter control unit 16 of the determined modulation scheme.

  The communication parameter control unit 16 controls the modulation method used for the modulation process in the transmission processing unit 17 to the modulation method determined by the communication parameter determination unit 15. When the predetermined communication parameter for which the optimum value is determined is the data rate, the communication parameter control unit 16 does not control the wireless transmission unit 18.

  The transmission processing unit 17 changes the modulation method according to the control from the communication parameter control 16 during the modulation process.

  The example 2 has been described above.

[Example 3]
This embodiment is different from the first embodiment in that the predetermined communication parameter whose optimum value is determined by the communication parameter determination unit 15 is transmission power. Since the configuration of the communication terminal 10 in the present embodiment is the same as that of the first embodiment (FIG. 1), description thereof is omitted. Since the basic operation of the communication terminal 10 in the present embodiment is the same as that of the first embodiment, the operation of the communication terminal 10 in the present embodiment will be described below with reference to FIG. In the following, differences from the first embodiment will be described. In the following description, only the case where RSSI is used as the radio link quality will be described. However, in this embodiment, SINR, BER, or PER can also be used as the radio link quality as in the first embodiment.

<Operation of communication terminal>
Steps S31, S32, S34, and S35 are the same as those in the first embodiment.

  In step S36, the communication parameter determination unit 15 calculates, for each of a plurality of candidate values of transmission power, a plurality of throughputs respectively corresponding to the plurality of candidate values (step S36).

  First, the communication parameter determination unit 15 acquires the latest N RSSI values from the link quality measurement unit 14 according to the number N of used samples determined in step S35.

  Next, the communication parameter determination unit 15 converts an RSSI sequence composed of N RSSI values into a BER sequence composed of N BER values for each of a plurality of candidate values of transmission power.

  Here, the conversion from the RSSI sequence to the BER sequence includes the reception sensitivity of the communication terminal 10, the modulation method of the received signal, the transmission power of the communication terminal 10, and the transmission power of the base station that is the communication partner of the communication terminal 10. Can be determined based on That is, the reception sensitivity of the communication terminal 10 is represented by the noise floor level n of the communication terminal 10, and the signal level s is calculated by subtracting the noise floor level n from RSSI. If the transmission power of the base station is P1 and the transmission power of the communication terminal 10 is P2, the SNR at the base station of the signal transmitted from the communication terminal 10 at transmission power = P2 is “SNR = (P2 / P1) × (s / n) ". The relationship between BER and SNR is determined according to the modulation method of the received signal. For example, when the modulation method is BPSK, “BER = erfc (sqrt (SNR)) / 2”, and when the modulation method is QPSK, “BER = erfc (sqrt (SNR / 2)) / 2”. Therefore, each BER value of the BER sequence is based on each RSSI value of the RSSI sequence, the reception sensitivity of the communication terminal 10, the modulation method of the received signal, the transmission power of the communication terminal 10, and the transmission power of the base station. Can be sought. The reception sensitivity of the communication terminal 10, the received signal modulation scheme, the transmission power of the communication terminal 10, and the transmission power of the base station are known to the communication parameter determination unit 15.

For example, the RSSI sequence (dBm) acquired when N = 5, the noise floor level of the communication terminal 10 is −95 dBm, and the modulation method of the received signal is BPSK is (−90 −89 −85 −88 −89). Suppose there was. Here, a plurality of transmission power candidate values (dBm) are determined based on the transmission power T (dBm) of the base station with which the communication terminal 10 is communicating. The communication parameter determination unit 15 knows in advance the transmission power T (dBm) of the base station. When the transmission power T is constant, or when the received signal at the communication terminal 10 includes information indicating the transmission power T, the communication parameter determination unit 15 can know the transmission power T in advance. . For example, if a plurality of candidate values (dBm) of transmission power are three candidates of T-3, T, and T + 3, the RSSI sequence (-90 -89 -85 -88 -89) is converted into the following three BER sequences: The
BER sequence with transmit power = T-3:
(0.07072 0.04212 0.00135 0.02259 0.04212)
BER sequence with transmit power = T:
(0.01878 0.00731 0.00001 0.00231 0.00731)
BER sequence with transmit power = T + 3:
(0.00164 0.00028 0.00000 0.00003 0.00028)

Next, the communication parameter determination unit 15 converts a BER sequence composed of N BER values into a PER sequence composed of N PER values for each of a plurality of candidate values of transmission power in the same manner as in the first embodiment. Thereafter, the communication parameter determination unit 15 converts the PER sequence composed of N PER values into a throughput sequence composed of N throughput values. Next, the communication parameter determination unit 15 calculates an average of N throughput values, that is, an average throughput, for each of a plurality of transmission power candidate values. For example, the following three average throughputs are calculated from the above three BER columns. FIG. 11 shows these relationships. FIG. 11 is a diagram illustrating an example of a relationship between transmission power and average throughput in the third embodiment. Here, the header length is 50 bits and the payload length is 60 bits.
Average throughput with transmit power = T-3: 0.11
Average throughput with transmit power = T: 0.30
Average throughput with transmit power = T + 3: 0.52

  Next, the communication parameter determination unit 15 determines an optimum value of transmission power from among a plurality of candidate values of transmission power (step S37). That is, the communication parameter determination unit 15 sets any one optimal candidate value of the plurality of transmission power candidate values as the transmission power determination value.

  Here, in order to maximize the throughput, the transmission power should always be maximized. However, in order to suppress the interference given to the communication of other communication terminals or to reduce the power consumption of the communication terminal 10, it is preferable that the transmission power is as small as possible. Therefore, in this embodiment, the optimum value of the transmission power is defined as “the minimum transmission power among the transmission powers capable of obtaining a throughput equal to or higher than a predetermined threshold”. For example, the predetermined threshold value for throughput is 0.3. Thus, for example, in the above example, of the three transmission power candidate values T-3, T, and T + 3, T and T + 3 correspond to transmission power that provides a throughput equal to or higher than a predetermined threshold. Of the candidate values T and T + 3, the minimum transmission power is T. Therefore, the optimum value of transmission power is T. Therefore, the communication parameter determination unit 15 determines the transmission power as T.

  When the number of samples is less than M (step S32: No), the communication parameter determination unit 15 determines the optimum value of transmission power from the latest one sample of RSSI (step S33). For example, the communication parameter determination unit 15 determines a smaller transmission power as the optimum value as the value of the latest one sample of RSSI increases. The correspondence relationship between the RSSI value and the transmission power value is determined in advance.

  The above is the optimum value determination process in the communication parameter determination unit 15.

  Then, the communication parameter determination unit 15 outputs the determined optimum transmission power value to the communication parameter control unit 16.

  The wireless transmission unit 18 has an amplifier (not shown), and amplifies the power of the transmission packet by the amplifier and transmits it. Therefore, the communication parameter control unit 16 instructs the wireless transmission unit 18 on the optimum value of the transmission power. The radio transmission unit 18 changes the amplification factor of the amplifier in accordance with the instruction, and amplifies the transmission power of each transmission packet so as to become the optimum value instructed from the communication parameter control unit 16. When the predetermined communication parameter for which the optimum value is determined is the transmission power, the communication parameter control unit 16 does not control the transmission processing unit 17.

  The example 3 has been described above.

  As described above, the communication terminal 10 according to the first to third embodiments includes the link quality identification unit 14 and the communication parameter determination unit 15. The link quality measurement unit 14 measures the radio link quality that fluctuates with a fluctuation period smaller than a predetermined communication period at a predetermined communication period, and acquires a plurality of M samples of the radio link quality. The communication parameter determination unit 15 uses a plurality of nearest N samples among a plurality of M samples acquired by the link quality measurement unit 14 for each of a plurality of different candidate values in a predetermined communication parameter. A plurality of average throughputs corresponding to a plurality of candidate values are calculated. Then, the communication parameter determination unit 15 sets any one candidate value among the plurality of candidate values as the communication parameter determination value based on the plurality of average throughputs.

  In this way, the communication terminal 10 determines the communication parameter based on the radio link quality of the most recent N samples. For this reason, the communication parameter can be determined based on the statistical property of the radio link quality reproduced using the ergodic property of the radio link quality. Therefore, when the communication period is longer than the fluctuation period of the radio link quality, the communication parameter can be set to an optimum value according to the radio link quality. Also, throughput can be improved by optimizing the communication parameters. Furthermore, since the amount of transmission data per unit time increases due to the improvement in throughput, data transmission can be completed in a shorter time. Therefore, the power consumption of the communication terminal 10 can be suppressed.

  In addition, the communication parameter determination unit 15 determines the most recent number of samples N used for calculation of the plurality of throughputs, that is, the number N of used samples, of the variation in the values of the plurality of M samples acquired by the link quality measurement unit 14. Determine based on size.

  When the fluctuation of the radio link quality is large, the calculated average throughput error becomes large. Therefore, it is preferable to increase the number of used samples N to reduce the average throughput error. On the other hand, when the variation in the radio link quality is small, the calculated average throughput error is small in the first place, so that the number N of used samples is sufficient. Therefore, by determining the number of used samples N based on the magnitude of variation indicating the magnitude of the fluctuation in radio link quality, the number of used samples N can be determined as the minimum number that can keep the average throughput error to a minimum. it can. In addition, if the number N of samples used is too large, the average throughput is excessively calculated based on the past radio link quality, so the communication parameter cannot be optimized when the statistical properties of the radio link quality change. Increases nature. Therefore, by determining the number of used samples N to be the minimum number that can keep the average throughput error to a minimum, the communication parameter can always be set to the optimum value.

  The radio link quality is, for example, RSSI, SINR, BER, or PER. By doing so, it is possible to grasp the statistical properties of the radio link quality by observing changes in the radio link quality.

  The predetermined communication parameter is, for example, a packet size, a data rate, or transmission power. By doing so, it is possible to select a communication parameter to be determined as an optimum value among the packet size, data rate, and transmission power in accordance with a communication parameter that is variable for each communication system.

[Other examples]
[1] In the above embodiment, a communication terminal is cited as an example of a wireless communication apparatus to which the disclosed technology is applied. However, the disclosed technology can also be applied to wireless communication devices other than communication terminals. For example, the disclosed technique can also be applied to a base station.

  [2] The communication terminal 10 of the above embodiment can be realized by the following hardware configuration. FIG. 12 is a diagram illustrating a hardware configuration example of the communication terminal. As illustrated in FIG. 12, the communication terminal 10 includes a bus 10a, a processor 10b, a memory 10c, and a wireless communication module 10d as hardware components. Examples of the processor 10b include a central processing unit (CPU), a digital signal processor (DSP), and a field programmable gate array (FPGA). Further, the communication terminal 10 may have an LSI (Large Scale Integrated circuit) including a processor 10b and peripheral circuits. Examples of the memory 10c include RAM such as SDRAM, ROM, flash memory, and the like. The antenna 11, the wireless reception unit 12, and the wireless transmission unit 18 are realized by the wireless communication module 10d. The reception processing unit 13, the link quality measurement unit 14, the communication parameter determination unit 15, the communication parameter control unit 16, and the transmission processing unit 17 are realized by the processor 10b.

DESCRIPTION OF SYMBOLS 10 Communication terminal 11 Antenna 12 Wireless receiving part 13 Reception processing part 14 Link quality measurement part 15 Communication parameter determination part 16 Communication parameter control part 17 Transmission processing part 18 Wireless transmission part

Claims (5)

A measurement unit that measures a radio link quality that fluctuates with a fluctuation period smaller than a predetermined communication period, and acquires a plurality of samples of the radio link quality by the predetermined communication period;
Using a plurality of nearest samples among the plurality of samples acquired by the measurement unit, for each of a plurality of different candidate values in a predetermined communication parameter, a plurality of average throughputs respectively corresponding to the plurality of candidate values. A determination unit that calculates, based on the plurality of average throughputs, any one of the plurality of candidate values as a determination value of the communication parameter;
A wireless communication apparatus comprising: The determining unit determines the number of the plurality of latest samples used for the calculation of the plurality of throughputs based on the magnitude of variation in the values of the plurality of samples acquired by the measuring unit;
The wireless communication apparatus according to claim 1. The radio link quality is received signal strength, SINR, bit error rate, or packet error rate.
The wireless communication apparatus according to claim 1. The predetermined communication parameter is a packet size, a data rate, or transmission power.
The wireless communication apparatus according to claim 1. A plurality of samples of the radio link quality are obtained by measuring a radio link quality that fluctuates with a fluctuation cycle smaller than a predetermined communication cycle,
For each of a plurality of different candidate values in a predetermined communication parameter, a plurality of average throughputs respectively corresponding to the plurality of candidate values are calculated using a plurality of the most recent samples of the acquired plurality of samples, Based on a plurality of average throughputs, any one of the plurality of candidate values is set as the determined value of the communication parameter.
Communication parameter determination method.

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