Patent Publication Number: US-2022225137-A1

Title: Wireless communication characteristic evaluation method and wireless communication characteristic evaluation device

Description:
TECHNICAL FIELD 
     The present invention relates to a wireless communication characteristics evaluation method and a wireless communication characteristics evaluation device that evaluate wireless communication characteristics in an environment in which partial channel interference exists, in a wireless communication system where a plurality of wireless communication terminals perform wireless communication. 
     BACKGROUND ART 
     Since wireless LAN terminals that can be inexpensively used for a wireless LAN or the like have increased, a lot of wireless terminals are mixed in the same wireless communication area. These wireless LAN terminals can use a plurality of frequency bands, and they transmit wireless signals according to the rules specified for autonomous decentralized access control, which is specified in Non-Patent Literature 1. In the same area, however, wireless communication is sometimes performed while the wireless LAN terminals are interfering with one another. 
     In the environment in which a lot of wireless LAN terminals are mixed, there may be a case where wireless LAN terminals with different bandwidths are mixed or a case where wireless LAN terminals that interfere with one another because channels partially overlap are mixed. Such a situation is shown in  FIG. 8 . 
     In  FIG. 8 , the horizontal axis indicates frequency and the vertical axis indicates power. When a desired wireless signal arrives at a receiving terminal through a channel 1 with a bandwidth of 20 MHz with power P 1  [mW], an interference signal simultaneously arrives at a channel 2 deviated from the channel 1 by 5 MHz with P 2  [mW]. In this case, it is possible to separate the desired wireless signal every 5 MHz into four blocks and compare received power of the desired wireless signal and received power of the interference signal within a range of the channel 1 to evaluate influence of interference. 
       FIG. 9  shows a calculation image for the four channel blocks. 
     In  FIG. 9 , after execution of SINR calculation for each of channel blocks c 1  to c 4 , an effective number of bits is determined with a map function of each PBIR. After that, a real SINR eff  is determined, and a PER (Packet Error Rate) is determined. 
       FIG. 10  shows an interference calculation flow of computer simulation in a conventional example (Non-Patent Literature 2). 
     In  FIG. 10 , when interference calculation is started, interference power information such as a band for evaluating a desired signal, received power of the desired signal and power of an interference signal is acquired (S 1 ). Next, variables used for the calculation are initialized (S 2 ). In the present example, an index n of a calculation target channel block and an effective number of bits I of a calculation target channel are set to “0”. 
     Next, it is confirmed whether the index n of the channel block is smaller than the number of channel blocks N ch  (S 3 ). If the index n is smaller, an SINR n  is calculated from total interference power in the channel block n (S 4 ). Here, SINR is an abbreviation of Signal to Interference Noise Ratio. From the calculated SINR n , an effective number of bits i n =Φ (SINR n ) of the channel block n is determined using a map function Φ of an RBIR (Received Bit Information Rate) (S 5 ). 
     Next, the effective number of bits I of the whole band is calculated. Here, a value obtained by dividing the effective number of bits in by the number of channel blocks: i n /N ch  is added to the effective number of bits I of the calculation target channel (S 6 ). Next, 1 is added to the index n of the channel block to obtain an index of the next channel block (S 7 ). Next, the flow returns to S 3 , where calculation for the next channel block is executed if n is smaller than the number of channel blocks N ch . Otherwise, a real SINR eff  of the whole channel band=Φ −1 (I) is determined from the effective number of bits I of the calculation target channel blocks, using the map function of the RBIR (S 8 ). Here, the real SINR eff  is an SINR value used when a PER (Packet Error Rate) is determined for the whole calculation target channel. Next, the PER of the desired signal is determined from data and the like prepared in advance, using the real SINR eff  (S 9 ). 
     CITATION LIST 
     Non-Patent Literature 
     Non-Patent Literature 1: “IEEE P802.11-2016,” December 2016 
     Non-Patent Literature 2: “11ax Evaluation Methodology,” doc.: IEEE802.11-14/0571r12, January 2016 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     In an environment in which a lot of wireless terminals are mixed, there may be a case where interference occurs only in a partial frequency band in a channel used for transmission/reception as shown in  FIG. 8 . In the case of reproducing influence of the interference by computer simulation, it is necessary to calculate an apparent packet error rate by performing theoretical calculation described in Non-Patent Literature 2 for each block and adding up results thereof. Further, though, in the conventional calculation procedure, it is required to perform the calculation for each interference event (a timing when a PER of a desired signal has to be determined because there is a possibility that some interference has occurred against the desired signal), the calculation requires a lot of time and furthermore, it is thought to be insufficient to perform estimation only by the theoretical calculation in an actual environment. 
     An object of the present invention is to provide a wireless communication characteristics evaluation method and a wireless communication characteristics evaluation device capable of calculating influence of interference according to a real environment using data measured in the real environment and shortening calculation time in comparison with theoretical calculation. 
     Means for Solving the Problem 
     A first invention is a wireless communication characteristics evaluation method for evaluating wireless communication characteristics of a wireless communication system where a plurality of wireless communication terminals perform communication by transmitting or exchanging signals, the wireless communication characteristics evaluation method including: a step 1 of acquiring power and a band of an interference signal; a step 2 of calculating an interference band rate showing a rate of the band of the interference signal that overlaps with a band of a desired signal; a step 3 of calculating an interference power rate from interference power and the interference band rate and furthermore, calculating steady noise power from the interference power and the interference power rate; a step 4 of determining a real SINR from received power of the desired signal and the steady noise power; and a step 5 of determining wireless communication characteristics of the desired signal from the real SINR. 
     In the wireless communication characteristics evaluation method of the first invention, the step 3 acquires a modulation/demodulation scheme and a retransmission rate from packet capture data in a state in which there is interference at the interference band rate, calculates real interference power from an SINR corresponding to the retransmission rate in the case of performing transmission in the modulation/demodulation scheme, and calculates a ratio of the real interference power relative to actual interference power as the interference power rate. 
     In the wireless communication characteristics evaluation method of the first invention, the step 3 acquires a modulation/demodulation scheme from a throughput value in a state in which there is interference at the interference band rate, acquires an SINR at which transmission can be performed by the modulation/demodulation scheme from a datasheet, calculates real interference power from the SINR, and calculates a ratio of the real interference power relative to actual interference power as the interference power rate. 
     In the wireless communication characteristics evaluation method of the first invention, the step 3 acquires a corresponding SINR from a throughput value in a state in which there is interference at the interference band rate, from a datasheet, calculates real interference power from the SINR, and calculates a ratio of the real interference power relative to actual interference power as the interference power rate. 
     A second invention is a wireless communication characteristics evaluation method for evaluating wireless communication characteristics of a wireless communication system where a plurality of wireless communication terminals perform communication by transmitting or exchanging signals, the wireless communication characteristics evaluation method including: a step 11 of acquiring power and a band of an interference signal and calculating an interference band rate showing a rate of the band of the interference signal that overlaps with a band of a desired signal; a step 12 of determining steady noise power using interference power and a mapping function corresponding to the interference band rate; a step 13 of determining a real SINR from received power of the desired signal and the steady noise power; and a step 14 of determining wireless communication characteristics of the desired signal from the real SINR. 
     A third invention is a wireless communication characteristics evaluation device evaluating wireless communication characteristics of a wireless communication system where a plurality of wireless communication terminals perform communication by transmitting or exchanging signals, the wireless communication characteristics evaluation device including: an interference band rate calculation unit that acquires power and a band of an interference signal and calculates an interference band rate showing a rate of the band of the interference signal that overlaps with a band of a desired signal; a steady noise power calculation unit that calculates an interference power rate from interference power and the interference band rate and furthermore, calculates steady noise power from the interference power and the interference power rate; a real SINR calculation unit that determines a real SINR from received power of the desired signal and the steady noise power; and a wireless communication characteristics determination unit that determines wireless communication characteristics of the desired signal from the real SINR. 
     A fourth invention is a wireless communication characteristics evaluation device evaluating wireless communication characteristics of a wireless communication system where a plurality of wireless communication terminals perform communication by transmitting or exchanging signals, the wireless communication characteristics evaluation device including: an interference band rate calculation unit that acquires power and a band of an interference signal and calculates an interference band rate showing a rate of the band of the interference signal that overlaps with a band of a desired signal; a steady noise power mapping unit that determines steady noise power using interference power and a mapping function corresponding to the interference band rate; a real SINR calculation unit that determines a real SINR from received power of the desired signal and the steady noise power; and a wireless communication characteristics determination unit that determines wireless communication characteristics of the desired signal from the real SINR. 
     Effects of the Invention 
     In the present invention, communication quality deterioration due to partial channel interference is calculated by replacing the communication quality deterioration with noise of the whole channel, based on data obtained by experiments and measurement. The present invention is: (1) a method for calculating an amount of deterioration in a case where data obtained by experiments and measurements is replaced with noise of the whole channel; and (2) a method for utilizing the amount of deterioration obtained by the calculation, in computer simulation. 
     In the present invention, since an amount of interference is computed based on data measured in a real environment, evaluation of wireless communication characteristics that is more appropriate for a current environment becomes possible in comparison with the case of performing computing only with theoretical calculation. Further, since computer simulation of a wireless communication system is performed using numerical values calculated from data, it is possible to reduce an amount of calculation in comparison with the case of performing theoretical calculation each time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a relationship between a desired signal and an interference signal, and a relationship between an interference band rate and a mapping function. 
         FIG. 2  is a diagram showing a configuration example of a wireless communication characteristics evaluation device of the present invention. 
         FIG. 3  is a diagram showing an interference calculation flow of a wireless communication characteristics evaluation method of the present invention. 
         FIG. 4  is a diagram showing a first procedure for calculating an interference power rate R from measurement data. 
         FIG. 5  is a diagram showing a second procedure for calculating the interference power rate R from measurement data. 
         FIG. 6  is a diagram showing a third procedure for calculating the interference power rate R from measurement data. 
         FIG. 7  is a diagram showing a relationship between theoretical calculation of throughput and an SINR in the case of IEEE802.11ac (20 MHz, 1 ss). 
         FIG. 8  is a diagram showing a relationship between a desired signal and an interference signal in a conventional example. 
         FIG. 9  is a diagram showing a calculation image of computer simulation in the conventional example. 
         FIG. 10  is a diagram showing an interference calculation flow of the computer simulation in the conventional example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a relationship between a desired signal and an interference signal, and a relationship between an interference band rate and a mapping function.  FIG. 2  shows a configuration example of a wireless communication characteristics evaluation device of the present invention.  FIGS. 1 and 2  correspond to  FIGS. 8 and 9  shown as a conventional method. 
     In  FIGS. 1 and 2 , an interference band rate calculation unit  1  inputs interference power information such as power and a band of an interference signal to calculate an interference band rate L showing a rate of the band of the interference signal that overlaps with a band of a desired signal. Note that, if the interference band rate L is 1 when the interference signal completely overlaps with the whole channel band occupied by the desired signal, and 0 when the interference signal does not overlap at all, then L=3/4 is satisfied in examples of  FIGS. 1 and 8  because bands that the interference signal overlaps with are c 2  to c 4  among bands c 1  to c 4  of the desired signal. 
     A steady noise power mapping unit  2  specifies interference power P 2  [dBm] and a mapping function corresponding to the interference band rate L. Since L=3/4 is satisfied in the example of  FIG. 1 , a mapping function M 1 (P 2 ) is used to convert the interference power P 2  [dBm] to steady noise power Ns [dBm]. A real SINR calculation unit  3  determines a real SINR eff  from this steady noise power Ns [dBm] and received power P 1  [dBm] of the desired signal and furthermore, a PER determination unit  4  determines PER from the real SINR eff . Note that it is assumed that the mapping function is created using measurement data in order to enhance calculation accuracy even in a simplified calculation method, which is the present invention. 
       FIG. 3  shows an interference calculation flow of the wireless communication characteristics evaluation method of the present invention. 
     In  FIG. 3 , when interference calculation is started, interference power information such as power and a band of an interference signal is acquired first (S 11 ). Next, an interference band rate L, which is a rate of the band of the interference signal that overlaps with the channel band occupied by a desired signal, is calculated (S 12 ). 
     Next, an interference power rate R is calculated from the interference band rate L and actual interference power Nr (P 2  in the example of  FIG. 1 ) based on data prepared in advance (details are shown in  FIGS. 4 to 6 ), and furthermore, steady noise power Ns (=R·Nr) is calculated from the interference power rate R and the actual interference power Nr (S 13 ). Note that, in the example of  FIG. 2 , the interference power Nr is changed to the steady noise power Ns using a mapping function corresponding to the interference band rate L instead of using the interference power rate R. Next, a real SINR eff  is determined from received power of the desired signal and the steady noise power Ns calculated at S 13  (S 14 ). Next, a PER of a packet that the desired signal carries is determined from the real SINR eff  (S 15 ), and the interference calculation is ended. 
     Note that, since this interference calculation flow can significantly reduce the number of calculations through the whole computer simulation and furthermore, does not have to repeatedly perform calculation for each channel block, it is possible to simplify the calculation itself and reduce calculation costs. Therefore, the interference calculation flow is advantageous when calculation is executed each time an interference event occurs or when fixed values are used for prerequisites of computer simulation. 
     Three procedures for calculating the interference power rate R for calculating the steady noise power Ns from measurement data will be described below. 
       FIG. 4  shows a first procedure for calculating the interference power rate R from measurement data. 
     In  FIG. 4 , measurement data is acquired first (S 20 ). Note that measurement data required for the present procedure is an RSSI, a modulation/demodulation scheme (hereinafter referred to as an MCS), a retransmission rate for each MCS, and a noise factor or an NF (Noise Floor) determined from the noise factor. 
     Next, an SINR a  in a state in which there is no interference is calculated (S 21 ). As a method for the calculation, for example, the following two methods are conceivable. (a) The SINR a  in the state in which there is no interference is calculated from an RSSI in the state in which there is no interference and a noise factor of a receiving terminal. (b) A used MCS and a retransmission rate thereof are examined from packet capture data acquired in the state in which there is no interference; a PER in the MCS is checked; and a corresponding SINR is determined as the SINR a  in the state in which there is no interference. Note that, in order to determine an SINR from a corresponding PER, map functions of the SINR and the PER and data shown in Non-Patent Literature 2 are used. Otherwise, an average value among SINRs examined by a plurality of MCSs or an expected value weighted by a frequency rate is calculated. 
     Next, an SINR b  in a state in which there is interference at the interference band rate L is calculated (S 22 ). As a method for the calculation, for example, the following method is conceivable. A used MCS and a retransmission rate thereof are acquired from packet capture data acquired in the state in which there is interference, and an SINR corresponding to a retransmission rate (PER) in a case where transmission is performed in the MCS is determined as the SINR b  in the state in which there is interference. Note that, in order to determine an SINR from a corresponding PER, map functions of the SINR and the PER and data shown in Non-Patent Literature 2 are used. Otherwise, an average value among SINRs examined by a plurality of MCSs or an expected value weighted by a frequency rate is calculated. 
     Next, increased real interference power N is calculated from the two SINRs, the SINR a  and the SINR b  (S 23 ). For example, if the SINR a  without interference and the SINR b  with interference are assumed as follows: 
       SINR a : RSSI/NF 
       SINR b : RSSI/(NF+ N ) 
     then, the real interference power N is as follows: 
         N =(SINR a /SINR b −1)·NF
 
     Next, a ratio between the real interference power N and the actual interference power Nr (N/Nr) is calculated and set as the interference power rate R (S 24 ). Otherwise, a mapping function may be created from a plurality of pieces of data. At S 13  in  FIG. 3 , the steady noise power Ns=R·Nr is calculated from the interference power Nr and the interference power rate R. 
       FIG. 5  shows a second procedure for calculating the interference power rate R from measurement data. 
     In  FIG. 5 , measurement data is acquired first (S 30 ). Note that measurement data required for the present procedure is an RSSI, a throughput, and PER-to-MCS data. 
     Next, an SINR a  in the state in which there is no interference is calculated (S 31 ). A method for the calculation is the same as S 21  shown in  FIG. 3 . 
     Next, a corresponding MCS is determined from throughput values in the state in which there is interference at the interference band rate L (S 32 ). Here, throughput values when transmission is performed by MCSs are kept as data, and a value that is the closest to a measured value, or the closest value among values higher/lower than the measured value is selected. 
     Next, an SINR at which transmission can be performed by the MCS is referred to on the datasheet and the like, and the SINR is determined as an SINR b  in the state in which there is interference at the interference band rate L (S 33 ). Here, for example, such an SINR that the PER is below a predetermined value may be specified, or one value among SINRs at which it is thought that the transmission can be performed by the MCS, such as an intermediate value between such an SINR that the PER is below a predetermined value (sinr f ) and such an SINR that the PER is below the predetermined value in an MCS higher than the above MCS by one (sinr u ), can be determined. 
     Next, increased real interference power N is calculated from the two SINRs, the SINR a  and the SINR b  (S 34 ). This process is the same as that of S 23  shown in  FIG. 4 . 
     Next, a ratio between the real interference power N and the actual interference power Nr (N/Nr) is calculated and set as the interference power rate R (S 35 ). Otherwise, a mapping function may be created from a plurality of pieces of data. This process is the same as that of S 24  shown in  FIG. 4 . 
       FIG. 6  shows a third procedure for calculating the interference power rate R from measurement data. 
     In  FIG. 6 , measurement data is acquired first (S 40 ). Note that measurement data required for the present procedure is an RSSI, a throughput, and PER-to-MCS data. 
     Next, an SINR a  in the state in which there is no interference is calculated (S 41 ). A method for the calculation is the same as S 21  shown in  FIG. 3 . 
     Next, an SINR for a throughput value in the state in which there is interference at the interference band rate L is referred to on the datasheet and the like, and the SINR is determined as an SINR b  in the state in which there is interference at the interference band rate L (S 42 ). From SINR-to-throughput data or the like obtained by theoretical calculation, computer simulation, or pre-measurement, throughputs and SINRs are mapped and made into a datasheet, and the SINR b  in the state in which there is interference is selected from the datasheet.  FIG. 7  shows a graph example of the SINR-to-throughput data.  FIG. 7  shows a relationship between theoretical calculation of throughput and an SINR in the case of IEEE802.11ac (20 MHz, 1 ss) as a graph. For each SINR, an MCS having the largest throughput can be mapped one to one as shown by thick lines. 
     Next, increased real interference power N is calculated from the two SINRs, the SINR a  and the SINR b  (S 43 ). This process is the same as that of S 23  shown in  FIG. 4 . 
     Next, a ratio between the real interference power N and the actual interference power Nr (N/Nr) is calculated and set as the interference power rate R (S 44 ). Otherwise, a mapping function may be created from a plurality of pieces of data. This process is the same as that of S 24  shown in  FIG. 4 . 
     REFERENCE SIGNS LIST 
       1  Interference band rate calculation unit 
       2  Steady noise power mapping unit 
       3  Real SINR calculation unit 
       4  PER determination unit