JP2012173070A - Mobile terminal position estimating device, mobile terminal position estimating method, and calculating method of radio wave environmental index - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that in a position estimation of mobile terminal utilizing RSSI (Received Signal Strength Indicator: reception electric field intensity), a tolerance of the position estimation does not become constant by fading and NLOS (Non Line Of Sight: out of prospect) that is influence of radio wave environment.SOLUTION: The mobile terminal receives a signal transmitted from an access point by making the band variable to calculate the RSSI and calculates a radio wave environmental index therefrom. This index calculation is used for weighing each access point at the position estimation by performing the index calculation for every access point.

Description

  The present invention relates to estimation of a mobile terminal position in a wireless communication system such as a wireless LAN, and in particular, a mobile terminal position estimation apparatus that estimates a mobile terminal position using received electric field strength from a received signal received from an access point, The present invention relates to a terminal location estimation method and a radio wave environment index calculation method.

  Conventionally, a radio device mounted on a mobile terminal not equipped with GPS measures and collects a received signal strength indicator (RSSI: Received Signal Strength Indicator) of a signal transmitted from a wireless LAN access point (hereinafter referred to as AP). A system that estimates the position of a mobile terminal from collected RSSI data is known.

  For example, by utilizing the property that RSSI patterns by a plurality of APs differ depending on locations, a database is constructed by collecting RSSI patterns for each location to be measured in advance. There is a method of outputting the location where the RSSI pattern in the database is the closest as an estimation result. In another example, using the fact that the relationship between the distance from the AP and the RSSI value can be approximated by a distance attenuation (path loss) curve of the electric field strength, the distance is estimated from the obtained RSSI combination, and the estimation is performed. For example, a method of estimating the position of the mobile terminal using the principle of triangulation from the distance and the AP position information given in advance is adopted.

JP 2009-47556 A

IEICE Transactions B VolJ89-B No-5 pp. 742-750

  In an actual radio channel, there are multiple reflections of signals (multipath) and movement of the mobile terminal itself and surrounding people / objects. As a result, fading occurs, and the RSSI value varies greatly. Therefore, the position estimation method using RSSI as described above is greatly affected. Therefore, it is common to take measures against fading. For example, in Non-Patent Document 1, the variation due to RSSI fading is regarded as an exponential distribution, and the maximum likelihood estimation method is used to improve the position estimation performance of the mobile terminal. However, fading characteristics vary greatly from place to place. For this reason, even if the above fading countermeasures are taken, variation in measurement error depending on the location occurs. Even if RSSI can be calculated without fading due to fading countermeasures, if there is an obstacle between the mobile terminal and the AP, an error in position estimation becomes large. This is because in an out-of-sight state where there is an obstacle between the mobile terminal and the AP (referred to as NLOS: Non Line of Light), the absorption of radio waves passing through the obstacle, diffraction at the end, or other objects This is due to the fact that the linear distance between the mobile terminal and the AP cannot be calculated because it receives attenuation other than distance attenuation, such as being reflected and detoured. On the other hand, for example, Patent Document 1 discloses a system for estimating a position from a radio wave arrival time and received signal strength as a terminal position estimation system under an environment affected by a shielding object or the like. Note that a state where there is a line of sight with respect to NLOS is called LOS (LOS: Line of Light).

  As described above, the position estimation of a mobile terminal using RSSI has a problem that the position estimation error is not constant due to the influence of fading and NLOS, that is, the radio wave environment.

  Each calculated from a received signal related to a wireless communication system received from a plurality of access points around a mobile terminal of the wireless communication system, such as a beacon packet periodically transmitted from an AP to notify communication parameters and synchronization information The RSSI of the access point is determined by the band variable RSSI calculated by varying the bandwidth of the received signal and the evaluation standard of the radio wave environment index calculated using the RSSI, and the RSSI of the access point taking the determination result into consideration The positioning calculation of the mobile terminal is performed and the position of the mobile terminal is estimated.

  Further, the variable bandwidth of the received signal is set to be narrower than the original bandwidth of the received signal from the access point, and the RSSI is evaluated by the slope of a CDF (Cumulative Distribution Function) as a radio wave environment index, or This is done using the RSSI variance.

  ADVANTAGE OF THE INVENTION According to this invention, the mobile terminal position apparatus and mobile terminal position estimation method which determine the radio wave environment with a communication destination, predict the position estimation of a mobile terminal according to a determination result, and can estimate a mobile terminal position with sufficient accuracy Can be provided.

It is a figure which shows the mobile terminal position estimation system of one Embodiment of this invention. It is a figure which shows the basic procedure of the mobile terminal position estimation of one Embodiment of this invention. It is a figure which shows the position estimation calculation procedure (least square method) of the mobile terminal of this invention. It is a figure which shows the position estimation calculation procedure (maximum likelihood estimation method) of the mobile terminal of this invention. It is a figure which shows the position estimation RSSI calculation procedure of the mobile terminal of one Embodiment of this invention. It is a figure which shows the radio wave environment calculation of one Embodiment of this invention, and its determination procedure (the 1). It is a figure which shows the LOS / NLOS determination example of the radio wave environment parameter | index calculation of this invention, and its determination procedure (the 1). It is a figure which shows the radio wave environment parameter | index calculation of one Embodiment of this invention, and its determination procedure (the 2). It is a figure which shows the dispersion | distribution value of the electromagnetic wave environment parameter | index calculation of one Embodiment of this invention, and its determination procedure (the 2). It is a figure which shows the radio wave environment parameter | index calculation of one Embodiment of this invention, and its determination procedure (the 3). It is a figure which shows the band variable RSSI calculation example of the radio wave environment parameter | index calculation and its determination procedure (the 3) of this invention.

Example 1
FIG. 1 is a diagram showing a mobile terminal position estimation system according to an embodiment of the present invention. The mobile terminal location estimation system includes a plurality of mobile terminals 2 (only one mobile terminal is shown) and a plurality of access points AP3-i (i = 1 to N) and a mobile terminal location estimation device 4 in the wireless network 1. Constitute.

  The mobile terminal position estimation device 4 is configured inside the mobile terminal 2. The mobile terminal 2 receives signals from a plurality of APs, for example, beacon packets, by the receiver 10, and the received signal is sent to the mobile terminal position estimation device 4. The mobile terminal location estimation apparatus 4 samples the received time domain signal of each access point at a predetermined period of the received signal determined by the bandwidth of the received signal, and the path of the RSSI calculator 1 (11) and the RSSI calculator 2 (14 ) To the route to.

Note that this configuration is not necessarily required to implement the present invention. For example, the mobile terminal location estimation device 4 may be connected to the mobile terminal 2 via a network and may be on another server that can send the data of the receiver 10. Furthermore, the calculation units do not necessarily have to exist on the same terminal / server, as long as the respective parts are connected to each other and can exchange predetermined data. Further, in the following description, RSSI is calculated using a signal sent from the AP to the mobile terminal 2, and position estimation is performed using the RSSI. However, due to radio wave reciprocity, a signal transmitted from the mobile terminal 2 is You may perform the same calculation with respect to the signal received by each AP.
The description will be made on the flow of a received signal from one AP, but it is performed on received signals from all APs.

  In the path of the RSSI calculation unit 1 (11), the RSSI calculation unit 1 (11) that calculates RSSI from the amplitude of each sampling point of the reception signal predetermined cycle, the calculated RSSI and the radio wave environment index calculation / determination unit 15 described below It is comprised by the positioning calculation part 12 which measures the position of the mobile terminal 2 based on a determination result.

  On the other hand, in the path of the RSSI calculation unit 2 (14), the bandwidth variable unit 13 for changing the bandwidth of the signal of the predetermined period of the received signal, and the RSSI for calculating the bandwidth variable RSSI of the received signal with the variable bandwidth. A radio wave environment for calculating and determining a radio wave environment index from the calculated RSSI and generating a flag indicating whether or not the RSSI calculated by the RSSI calculator 1 (11) is applied to the positioning of the mobile terminal 2 The index calculation / determination unit 15 is configured. Furthermore, it is configured by a DB (database) 16 that holds information used for RSSI calculation and temporarily holds the calculated RSSI.

The processing contents of the bandwidth variable unit 13, the radio wave environment index calculation / determination unit 15, and the positioning calculation unit 12 will be described.
1) The bandwidth variable unit 13 varies the bandwidth of the received signal from the signal sequence of the received signal from the receiver 10 by decimation of time, by band designation, or by using a filter.

  The bandwidth variable by time thinning makes the bandwidth variable by thinning out the signal of the signal sequence of the sampling points of the reception signal from the receiver 10 in a predetermined cycle. For example, it is possible to generate a signal whose band is reduced to ½ of the original band by thinning the original signal sequence once every two times, and further, when the same thinning is performed, the band is reduced to ¼.

  In the band variable by the band designation, the signal sequence of the sampling points of the reception signal from the receiver in a predetermined cycle is converted into the frequency domain by FFT conversion, the band is designated in the obtained frequency domain, and the bandwidth is made variable.

In the variable bandwidth using the filter, a digital filter having a predetermined bandwidth characteristic is configured to change the bandwidth of the received signal. Here, the filter is not necessarily a digital filter, and may be an analog filter, for example.
2) The radio wave environment index calculation / determination unit 15 calculates a cumulative probability density function (CDF) or a variance value as the radio wave environment index, and calculates the RSSI LOS and NLOS from each AP used for position estimation. Make a decision.

  In the determination of LOS and NLOS, even if the AP is located at the same distance from the position of the position terminal position estimation device 4, in the case of NLOS, the radio wave is greatly attenuated by the environment and the RSSI is reduced. Become. Therefore, it is important to determine whether the AP is in the LOS state or the NLOS state, and calculate the position based on the RSSI of the AP for LOS determination.

  The radio wave environment index calculation / determination unit 15 performs LOS or NLOS determination evaluation based on the calculated slope of the RSSI CDF. The following properties are generally known for determining the signal bandwidth and its LOS and NLOS. If the RSSI measurement bandwidth is sufficiently larger than the coherent bandwidth, the fading fluctuation of the RSSI value becomes small due to the averaging effect of a plurality of paths. Conversely, if the RSSI measurement bandwidth is sufficiently small, the RSSI value fading fluctuation appears to be large. Further, fading fluctuation is small in the LOS environment, and fading fluctuation is large in the NLOS environment. Therefore, in the determination of LOS or NLOS based on the slope of RSSI, when the RSSI measurement bandwidth is wide, even if there is not much difference in fading fluctuation between LOS and NLOS, by reducing the RSSI measurement bandwidth, A difference is seen, and LOS and NLOS are easily discriminated.

In addition, the radio wave environment index calculation / determination unit 15 performs LOS or NLOS determination evaluation based on the magnitude (concentration) of the calculated RSSI variance. In the LOS environment, the variance value of RSSI is large.
3) The positioning calculation unit 12 calculates the mobile terminal position. As a method for estimating the position of the mobile terminal based on the RSSI of the received signal, a least square method or a maximum likelihood estimation method is known. The procedure for estimating the position of the mobile terminal 2 from the multiple packets and the RSSI of the multiple packets for each AP will be described with reference to FIGS.

  FIG. 2 is a diagram showing a basic procedure of mobile terminal position estimation according to an embodiment of the present invention.

S1: Initial setting of reception signal information, variable bandwidth information, radio wave environment index, and radio wave environment index calculation parameters.

  The received signal information includes a predetermined period Ta determined by the bandwidth of the received signal, two predetermined minimum numbers M1, and a predetermined minimum number M2. M1 is the minimum number of samples required to calculate RSSI from the received signal of one packet on the communication protocol of the received signal (RSSI calculated minimum number of samples), and M2 is necessary for use in position estimation of the mobile terminal 2 This is the minimum number of RSSIs (positioning calculation minimum RSSI number).

Bandwidth variable information is a method for varying the bandwidth of a received signal. The radio wave environment index is a designated radio wave environment index. The parameters (two predetermined minimum numbers) are a predetermined number required for the radio wave environment index evaluation, and are the variable variable RSSI calculation minimum sample number and the radio wave environment index calculation minimum packet number.
S2: The signal for each AP from the receiver 10 is sampled at a predetermined period Ta. The processes in S3 to S8 below are performed for all N APs.
S3, S4, S5: This is a procedure for calculating RSSI used for positioning calculation for each packet of a predetermined number M2.

Sampling is performed from one packet of the communication protocol sequentially received at a cycle of Ta, and the sampling value is held until the number reaches a predetermined number M1 necessary for calculating the RSSI in the corresponding packet, and becomes M1. In that case, the RSSI is calculated therefrom and held. Similarly, RSSI is calculated and held for M2 packets received sequentially. When the flag instruction by the processing of S6 to S8 is “The RSSI of the corresponding AP is applicable to position positioning”, the M2 RSSIs of the corresponding AP are sent to the positioning calculation unit 12.
S6, S7, S8: This is a procedure for determining whether the RSSI of the corresponding AP calculated in S3, S4, S5 based on the designated radio wave environment index is applicable to the positioning calculation.

  A signal obtained by changing the bandwidth of the received signal from one packet (which is narrower than the bandwidth of the received signal) is sampled, and a predetermined number (band variable RSSI calculation) necessary for calculating the band variable RSSI specified by the number is sampled. The sampling value is held until the minimum number of samples) is reached. When the predetermined number is reached, the band variable RSSI is calculated from the sampling value to be held and held.

Similarly to the next packet, a predetermined number of radio wave environment index evaluations (minimum number of radio wave environment index calculation packets) are performed. The specified radio wave environment index is calculated from the band variable RSSI having the minimum number of packets of the radio wave environment index to be held, it is determined whether or not a predetermined standard is satisfied, and the following flags are generated according to the determination result.
A. Satisfy a predetermined value: M2 RSSIs of the corresponding AP are applied to mobile terminal location positioning.
A. The predetermined value is not satisfied: M2 RSSIs of the corresponding AP are not applied to the mobile terminal location measurement.
S9: The position of the mobile terminal is calculated from M2 RSSIs for each AP determined to be applicable to position measurement. (Positioning method Fig. 3 and Fig. 4)
Next, a least square method and a maximum likelihood estimation method will be described as a method for estimating the position of the mobile terminal 2 from a plurality of (N) APs based on RSSI calculated from a plurality of M2 packets for each AP. “I” and “k” below correspond to the number (N) of APs described later and the number M2 of packets for calculating a plurality of RSSIs for each AP, and i = 1 to N and k = 1 to M2.

  In general, since radio waves are attenuated by the distance r, the received power p when the transmission power is constant is expressed as (Equation 1) if the transmission power is constant.

ここで、α、βは環境により決まるパラメータである。（式１）を基に移動端末の位置推定の手順を図３、図４で説明する。

Here, α and β are parameters determined by the environment. The procedure for estimating the position of the mobile terminal based on (Equation 1) will be described with reference to FIGS.

FIG. 3 is a diagram showing a position estimation calculation procedure (least square method) of the mobile terminal according to the present invention.
S11: The RSSI value by the k-th signal of the i-th AP at the position xi is calculated by (Expression 2).

The RSSI value (p _{i, k} ) by the k th signal received from the i th AP at the position x _{i of the} mobile terminal at the position x = (x, y) is expressed by using (Expression 2) It becomes.

ここで、ｎは雑音である。
Ｓ１２：移動端末の推定位置を（式３）、（式４）、（式５）で算出する。
１）ＡＰのｋ番目の信号による移動端末の推定位置を（式３）で算出する。

Here, n is noise.
S12: The estimated position of the mobile terminal is calculated by (Expression 3), (Expression 4), and (Expression 5).
1) The estimated position of the mobile terminal based on the k-th signal of the AP is calculated by (Equation 3).

  At this time, the received power from all APs obtained by the mobile terminal

なるベクトルとすれば、移動端末のｋ番目の信号からの推定位置

The estimated position from the k-th signal of the mobile terminal

は（式３）となる。

Becomes (Equation 3).

ここで、

here,

であり、

And

である。

It is.

2) The position of the mobile terminal including all APs is calculated by (Equation 4).

  The position of the mobile terminal estimated from the number of signals (k = 1 to M2) for calculating RSSI with all APs taken into consideration is (Equation 4).

３）ＡＰ毎に重みの重要度を加味した移動端末の位置を（式５）で算出する。

3) Calculate the position of the mobile terminal taking into account the importance of the weight for each AP using (Equation 5).

  When importance is added to RSSI for each AP, the estimated position of the mobile terminal is (Expression 5).

ここで、ＷはＡＰ毎の重要度に対応した重み行列で、０≦ｗ_ｉ≦１であり、ｗ_ｉが「１」に近い程、該当のＡＰのデータが重視され、「０」の場合は全く反映されない。

Here, W is a weight matrix corresponding to the importance for each AP, and 0 ≦ w _i ≦ 1, and the closer the w _i is to “1”, the more important the data of the corresponding AP is. Is not reflected at all.

  FIG. 4 is a diagram showing a position estimation calculation procedure (maximum likelihood estimation method) of the mobile terminal according to the present invention.

The least square method is equivalent to a method in which an AWGN (Additive White Gaussian Noise) whose communication path is affected only by white noise is assumed. However, in general, the wireless communication path is affected by fading. When a signal undergoes Rayleigh fading, its signal power is exponentially distributed. Then, the position estimation of a mobile terminal is demonstrated about the case where it receives to the influence of Rayleigh fading.
S15: The probability density (formula 6) and likelihood (formula 7) at the distance r between the mobile terminal and the AP are calculated.

  The conditional probability density distribution at the distance r of the received power is the average power

を用いて（式６）となる。

(Equation 6).

また、尤度はＰ＝（Ｐ_１，Ｐ_２，・・・Ｐ_ｋ）但し、Ｐ_ｋ＝（Ｐ_ｉ，ｋ，Ｐ_２，ｋ，・・・Ｐ_ｉ，ｋ・・・Ｐ_ｎ，ｋ））を用いて（式７）と表される。

The likelihood is P = (P ₁ , P ₂ ,... P _k ), where P _k = (P _{i, k} , P _{2, k} ,... P _{i, k} ... P _{n, k} )) Is used to express (Equation 7).

Ｓ１６：移動端末の位置を（式８）で算出する。

S16: The position of the mobile terminal is calculated by (Equation 8).

  The position of the position of the mobile terminal is calculated using the likelihood. Estimated position

は尤度が最大になる地点であり、対数尤度を用いて（式８）で算出できる。

Is the point where the likelihood is maximum, and can be calculated by (Equation 8) using the log likelihood.

ここで、尤度は（式９）である。

Here, the likelihood is (Equation 9).

Ｓ１７：対数尤度を（式１０）算出する。

S17: The log likelihood is calculated (Equation 10).

  The log likelihood is (Equation 10).

Ｓ１８：ＡＰ毎に重要度を加味した重み行列を導入した対数尤度を（式１１）で算出する。

S18: Logarithmic likelihood into which a weight matrix that takes importance into consideration for each AP is introduced is calculated by (Expression 11).

A log likelihood is calculated by introducing a weight matrix taking into account the weight for each AP.
Weight line _W in consideration of the weight for each _{AP (W = (w 1,} w 2, ·· w i ··· w N)) When to, weighted log likelihood is represented by (Equation 11).

Ｓ１９：移動端末の位置を対数尤度（式１０）あるいは（式１１）を用いて（式８）で算出する。

S19: The position of the mobile terminal is calculated by (Equation 8) using the log likelihood (Equation 10) or (Equation 11).

  The position of the mobile terminal is calculated using the log likelihood and the weighted log likelihood. The position of the mobile terminal is estimated using (Expression 10) instead of (Expression 9). Furthermore, when weighting is performed according to the importance for each AP, the position of the mobile terminal can be estimated according to the radio wave environment using (Expression 11) instead of (Expression 9). In the first line of (Equation 11)

は、２行目以降で用いられる演算を実行するための演算子である。また、重み行列の要素ｗ_ｉは、０≦ｗ_ｉ≦１であり、最小二乗法と同様にｗ_ｉが「１」に近い程、該当のＡＰのデータが重視され、「０」の場合は全く反映されない。

Is an operator for executing operations used in the second and subsequent lines. Also, the weight matrix element w _i is 0 ≦ w _i ≦ 1, and as w _i is closer to “1” as in the least square method, the data of the corresponding AP is more important. Not reflected at all.

  FIG. 5 is a diagram showing a location estimation RSSI calculation procedure of the mobile terminal according to the embodiment of the present invention.

S21: As reception signal information, initial setting of reception signal acquisition predetermined period Ta, RSSI calculation minimum sample number M1, and positioning calculation minimum RSSI number M2 is performed.

The reception signal acquisition predetermined period Ta is a predetermined period determined by the bandwidth of the reception signal. M1 is the number of received signal samples of a predetermined period Ta necessary for RSSI calculation for one packet. M2 is the minimum number of packets necessary for performing RSSI calculated from one packet for a plurality of packets necessary for positioning calculation.
S22: The procedure of S23 to S26 is performed for all APs for each AP.
S23: This is a procedure for calculating the RSSI of the corresponding AP used for positioning calculation.

M1 pieces of received signal sampling corresponding to positions are acquired from one packet of the corresponding AP at intervals of the received signal acquisition period Ta determined by the band, and when the number of samples reaches M1, the RSSI at this AP is calculated and held.
S24, S25, S26: This is a procedure performed for a predetermined number of packets M2 for sequentially receiving the processing of S23.

The processing of S23 is sequentially performed, and the acquired M2 RSSIs are calculated and held from the next packet.
S27: Each of the APs whose radio wave environment index determination result satisfies a predetermined standard, M2 RSSIs are sent to the positioning calculation unit.

  FIG. 6 is a diagram showing radio wave environment index calculation and determination procedure (part 1) according to an embodiment of the present invention. The LOS / NLOS determination from the slope of the RSSI CDF as a radio wave environment index will be described.

  S31: Initial setting of variable bandwidth information, radio wave environment index, radio wave environment index parameter (threshold), and a predetermined number of parameters.

  The bandwidth is varied by thinning the received signal, and the signal acquisition interval is Tb. The radio wave environment index is CDF, and the threshold value of the CDF slope is L. Also, the predetermined number of parameters are the band variable RSSI calculation sample number M1a and the radio wave environment index (CDF) calculation minimum packet number M2a.

M1a is the number of received signal samples with a predetermined period Tb necessary for calculating RSSI from a received signal whose band is variable for one packet, and M2a is the RSSI of one packet calculated from the number of samples M1a. CDF) is the minimum number of packets required for evaluation.
S32: The following processing is performed for all APs for each AP.
S33, S34, S35, S36: This is a procedure for calculating the variable bandwidth RSSI from the number of M1a samples of the signal sequence obtained by changing the bandwidth of the packet of the received signal from the corresponding AP.

The received signal at the time Tj (j = 1) of the corresponding AP is sampled, and the sample value at that time is held. j = j + 1 is set, and the received signal at time Tj = Tj + Tb is sampled sequentially. In the bandwidth variable processing, for example, the band of the signal sequence that is sequentially sampled with the signal acquisition period Tb of 2 × Ta is ½ of the band of the original received signal (specifically, the bandwidth signal is If you thin out once every two times, the bandwidth will be halved). The RSSI in the corresponding packet is calculated from the M1a sample values and held.
S37, S38: A procedure in which the processing of S33 to S36 is performed for a predetermined number of packets M2a to evaluate the radio wave environment index CDF.

The bandwidth variable RSSI is calculated for each of the M2a packets (S33 to S36), and evaluation is performed based on whether or not the slope of the CDF calculated from the M2a bandwidth variable RSSI of the corresponding AP to be held exceeds the threshold L. Then, LOS / NLOS determination is performed (LOS / NLOS determination: FIG. 7).
S39: This is a procedure for generating a flag based on the LOS and NLOS determination results.

The following flags are generated according to the evaluation result.
LOS determination: [applicable AP is applied to positioning calculation] flag NLOS determination: “applicable AP is not applied to positioning calculation” flag Note that if the slope shown in FIG. Is an NLOS determination, but the weight w _i may be calculated according to the size as described later.

  FIG. 7 is a diagram showing an example of LOS / NLOS determination in the radio wave environment index calculation and determination procedure (part 1) of the present invention.

  The LOS index and its determination example are shown based on the cumulative probability density distribution function CDF (Cumulative Distribution Function) of RSSI.

  The characteristic gradient g is calculated from the intercept of the CDF characteristic inclination calculation expressed by two-dimensional coordinates (values of predetermined rising points and convergence range points). g is expressed as (Equation 12).

ここで、Ｃ１、Ｃ２は得られたＲＳＳＩのＣＤＦとし、ｆ^−１（ｃ）は図面化したＣＤＦ特性を近似した関数の逆関数である。
ア.ＬＯＳ判定
この場合、傾きｇが所定の閾値より大きいのでＬＯＳと判定する。
イ.ＮＬＯＳ判定
この場合、傾きｇが所定の閾値より小さいのでＮＬＯＳと判定する。

Here, C1 and C2 are the CDFs of the obtained RSSI, and f ⁻¹ (c) is an inverse function of a function approximating the CDF characteristics shown in the drawing.
A. LOS determination In this case, since the slope g is larger than a predetermined threshold, it is determined as LOS.
In this case, since the slope g is smaller than a predetermined threshold value, it is determined as NLOS.

  FIG. 8 is a diagram showing radio wave environment index calculation and determination procedure (part 2) according to an embodiment of the present invention. This is a procedure in which the evaluation based on the slope of the radio wave environment index CDF described in FIG. 6 is changed to the evaluation based on the magnitude of the dispersion value. Some explanations are duplicated.

  S41: Initial setting of variable bandwidth information, radio wave environment index, radio wave environment index parameter (threshold), and a predetermined number of parameters.

  The bandwidth is varied by signal decimation, and the signal acquisition cycle is Tb. The radio wave environment index is a variance value, and the variance value threshold is B. Further, the predetermined number of parameters are the band variable RSSI calculation sample number M1b and the radio wave environment index (dispersion) calculation minimum packet number M2b.

M1b is the number of received signal samples of a predetermined period Tb necessary for calculating RSSI from a received signal whose bandwidth is variable for one packet, and M2b is the RSSI of one packet calculated from the number of samples M1b. This is the minimum number of packets required for evaluating the index variance.
S42: The following processing is performed for all APs for each AP.
S43, S44, S45, S46: This is a procedure for calculating the band variable RSSI from the number of M1b samples from the signal sequence variable in band from the received signal of one packet from each AP.

The received signal at the time Tj (j = 1) of the corresponding AP is sampled, and the sample value is held. j = j + 1 is set, and the received signal at time Tj = Tj + Tb is sampled sequentially. The bandwidth variable processing is the same as in the example of FIG.
S47, S48: This is a procedure for performing the processing of S44 to S46 for a predetermined number of packets M2b to evaluate the radio wave environment index dispersion.

The bandwidth variable RSSI is calculated for each of the M2b packets (S43 to S46), and evaluation is performed based on whether or not the dispersion value of the M2b bandwidth variable RSSI of the corresponding AP held exceeds the threshold value B. Here, as in the case of CDF, a weight w _i corresponding to the magnitude of the value may be given. (Dispersion judgment: Fig. 9)
S49: The following flags are generated based on the dispersion value determination result.
Satisfies predetermined value: “applicable AP applies to positioning calculation” flag Does not satisfy predetermined value: “corresponding AP does not apply to positioning calculation” flag Note that the variance value is smaller than B (satisfies predetermined value) Is a LOS determination, and when it is large (a predetermined value is not satisfied), it is an NLOS determination.

  FIG. 9 is a diagram showing a variance value of radio wave environment index calculation and determination procedure (part 2) according to an embodiment of the present invention. The determination of the RSSI variance value as a radio wave environment index will be described.

If RSSI at each time from one APi is P _{i, k} (k = 1 to M2b), the variance is expressed by (Equation 13).

図１０は本発明の一実施形態の電波環境指標算出とその判定手順（その３）を示す図である。
Ｓ５１：帯域幅可変情報、電波環境指標パラメータ、所定数パラメータＭ１ｃ、Ｍ２ｃの初期設定を行う。

FIG. 10 is a diagram showing radio wave environment index calculation and determination procedure (part 3) according to an embodiment of the present invention.
S51: Initial setting of variable bandwidth information, radio wave environment index parameter, and predetermined number of parameters M1c and M2c is performed.

  The variable bandwidth designates a frequency region obtained by converting the received signal by FFT. Also, the received signal acquisition period of the FFT calculation is a predetermined period Ta determined by the received signal bandwidth. The predetermined number parameters are the variable band RSSI calculation sample number M1c and the radio wave environment index calculation minimum packet number M2c.

M1c is the number of received signal samples with a predetermined period Ta determined by the bandwidth of the received signal for one packet, and performs FFT (Fast Fourier Transform) with the number of samples acquired at the period of Ta. Here, if the signal processing is to be converted into the frequency domain, the FFT is not necessarily required. For example, DFT (Digital Fourier Transform) may be used. M2c is the minimum number of packets required for the RSSI calculated from the number of samples M1c to evaluate the radio wave environment index (CDF or dispersion).
S52: The processes of S53 to S55 are performed for all target APs.
S53, S54: This is a procedure for calculating the RSSI of the region designated as the frequency region obtained by FFT conversion from the received signal of one packet from each AP.

M1c reception signals are acquired at intervals of a predetermined period Ta of the reception signal, FFT is performed, and signal conversion on the frequency axis is performed. The RSSI in that band is calculated using the amplitude of the specified band on the frequency axis. When a plurality of areas are specified discontinuously, the RSSI is calculated and held.
S55, S56: This is an evaluation procedure based on the radio wave environment index (CDF or dispersion) by performing the processing of S53 to S54 for a predetermined number of packets M2c.

Based on the radio wave environment index (CDF or dispersion value) based on the M2c RSSI of the corresponding AP to be held, the following flags are generated based on the determination result.
Satisfies predetermined value: Applicable AP applies to mobile terminal position positioning "Flag does not satisfy predetermined value: Applicable AP does not apply to mobile terminal position positioning" flag

  In addition, instead of performing FFT conversion on the RSSI signal sequence of the reception signal acquisition predetermined period used for positioning calculation, a method of designating a band using frequency response data obtained at the time of channel estimation or the like is also conceivable. In addition, when the modulation method is OFDM (Orthogonal Frequency Division Multiplexing), a method of designating a band using data on the frequency axis created at the time of OFDM demodulation can be considered.

  FIG. 11 is a diagram showing a band variable RSSI calculation example of the radio wave environment index calculation and determination procedure (part 3) according to the present invention.

  A. The band variable unit 13 performs FFT conversion on the received signal shown in FIG. It becomes a signal of the bandwidth shown by. In the bandwidth variable unit 13, for example, C.I. Are specified, and the RSSI calculator 2 (14) calculates the RSSI of the RRSI in that region. As a result, RSSI # 1, RSSI # 2, RSSI # 3, and RSSI # 4 are obtained. Using these, the variable band RSSI at this AP is obtained.

  This time, the method used to determine whether or not the corresponding AP is used for positioning calculation depending on whether the slope g or the variance value satisfies a predetermined threshold has been described. It is also conceivable to evaluate the other environmental elements of the communication channel and estimate the position of the mobile terminal using the parameters for determining the weight applied to the positioning calculation for each AP described in FIGS.

  From the above, the RSSI CDF of the received signal with variable bandwidth, or the LOS and NLOS judgment evaluation by dispersion, fading, the influence of the obstacle between the mobile terminal and the AP (absorption by the obstacle, diffraction at the end), or By reducing the effects of radio waves that have been attenuated other than distance attenuation, such as being reflected by other objects (such as variations in radio wave environment indicators, noise, etc.) Position estimation can be realized with high accuracy.

DESCRIPTION OF SYMBOLS 1 Wireless network 2 Mobile terminal 3-1, 3-2, 3-i AP (access point)
4 Mobile terminal location estimation device 10 Receiver 11 RSSI calculation unit 1
12 Position Calculation Unit 13 Bandwidth Variable Unit 14 RSSI Calculation Unit 2
15 Radio wave environment index calculation / determination unit 16 DB (database)

Claims (10)

Signal receiving means for receiving a signal related to the wireless communication system from a plurality of access points in the vicinity of a mobile terminal of the wireless communication system;
A received electric field strength calculating means for calculating a received electric field strength of each access point from a signal received from each of the access points;
Bandwidth varying means for varying the bandwidth of the signal received from each access point;
Bandwidth variable electric field strength calculating means for calculating the electric field strength of the received signal obtained by the bandwidth variable means;
Radio wave environment index calculation / determination means for calculating / determining the radio wave environment index by calculating the radio wave environment index of each access point from the bandwidth variable electric field strength calculation means;
A position estimation calculation unit that estimates the position of the mobile terminal from the received electric field strength of each access point according to the determination result of the radio wave environment index of each calculated access point;
A mobile terminal position estimation apparatus comprising: a mobile terminal position estimation apparatus comprising: Receiving a signal related to the wireless communication system from a plurality of access points in the vicinity of a mobile terminal of the wireless communication system;
Calculate the received electric field strength to calculate the received electric field strength of each access point from the signal received from each access point,
Varying the bandwidth of the signal received from each access point;
Calculate the electric field strength of the received signal obtained by varying the bandwidth,
Calculate and evaluate the radio wave environment index by calculating the radio wave environment index of each access point from the bandwidth variable electric field strength calculation result,
According to the determination result of the radio wave environment index of each access point calculated, the position of the mobile terminal is estimated from the received electric field strength of each access point,
A mobile terminal position estimation method, wherein the mobile terminal position is estimated. In the mobile terminal position estimation method according to claim 2,
3. The mobile terminal position estimation method according to claim 2, wherein the bandwidth of the signal received from each access point is changed to a bandwidth narrower than a normal bandwidth of the signal. In the mobile terminal position estimation method according to claim 2,
3. The mobile terminal position estimation method according to claim 2, wherein the calculated radio wave environment index is a slope or a variance value of a cumulative probability density distribution of received electric field strength with a variable bandwidth. In the mobile terminal position estimation method according to claim 2,
The mobile terminal position estimation method according to claim 2, wherein the bandwidth is made variable by changing a sampling interval of the received signal. In the mobile terminal position estimation method according to claim 2,
3. The mobile terminal position estimation method according to claim 2, wherein the bandwidth is made variable by dividing a frequency response of the received signal into a plurality of bands. In the mobile terminal position estimation method according to claim 2,
The received electric field strength of each access point used for position estimation of the mobile terminal according to the radio wave environment index is selected depending on whether the radio wave environment index satisfies the condition, and the position of the mobile terminal is estimated. The mobile terminal position estimation method according to claim 2. In the mobile terminal position estimation method according to claim 2,
When estimating the position of the mobile terminal according to the radio wave environment index, the position of the mobile terminal is estimated by using a weight corresponding to the value of the radio wave environment index of each access point. The mobile terminal position estimation method according to claim 2. In the mobile terminal position estimation method according to claim 4,
The received electric field strength for each access point used for position estimation of the mobile terminal has a slope of a cumulative probability density distribution of the received electric field strength with variable bandwidth or a received electric field with variable bandwidth. 5. The mobile terminal position estimation method according to claim 4, wherein the intensity variance value is equal to or less than a predetermined value. Receiving a signal related to the wireless communication system from an access point of the wireless communication system;
Calculate the received electric field strength from the received signal for each access point to calculate the received electric field strength,
Receiving a variable bandwidth of the received signal for each access point;
Calculate the electric field strength of the received signal obtained by varying the bandwidth,
A radio wave environment index calculation method comprising: calculating a radio wave environment index from the bandwidth variable electric field strength calculation result, and evaluating and determining the radio wave environment index.

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