Method, apparatus and computer readable storage medium for establishing precise location of a terminal in wireless communication with base stations

A method, applied in an apparatus and computer readable storage medium, for establishing location of a target terminal in an obstructed environment comprises determining, based on indoor environmental information and data observed by a plurality of base stations in communication with the terminal, establishes lines of signals from the terminal scattered by local obstructions, and based on positional information as to the obstructions which cause the scattering, estimating a more precise positional information of the terminal.

FIELD

The subject matter herein generally relates to wireless communications, and more particularly, to a method, apparatus, and computer readable storage medium for indoor locating.

BACKGROUND

Indoor locating is used in wireless communication systems for a variety of applications. The common method is to locate the target mobile terminal by analyzing data of a plurality of base stations in respect of signals emitted by the target terminal. The data comprises: arrival time, arrival angle, arrival time difference, and received signal strength.

However, although establishing location based on the data observed has good performance, the estimated location of the target mobile terminal has some errors with the actual location because the overall layout of the indoor environment of the target terminal is not considered. Providing users with an accurate, real-time, and robust location estimation is problematic.

DETAILED DESCRIPTION

References to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one”.

In general, the word “module” as used hereinafter, refers to logic embodied in computing or firmware, or to a collection of software instructions, written in a programming language, such as, Java, C, or assembly. One or more software instructions in the modules may be embedded in firmware, such as in an erasable programmable read only memory (EPROM). The modules described herein may be implemented as either software and/or computing modules and may be stored in any type of non-transitory computer-readable medium or other storage device. Some non-limiting examples of non-transitory computer-readable media include CDs, DVDs, BLU-RAY, flash memory, and hard disk drives. The term “comprising”, when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series, and the like.

FIG.1is a flow chart of a method for establishing an indoor location, the method comprising the following main steps:

At step S101, obtaining indoor environmental information. In one embodiment, the indoor environmental information can be created in advance. In one embodiment, the indoor environmental information comprises positional information of a plurality of base stations and a distribution of scatterers, the plurality of scatterers comprising walls, furniture, and metal devices, etc.

At step S102, receiving a set of data from a base station of the plurality of base stations for a mobile terminal to be positioned. The data set comprises Time Difference of Arrival (TDOA), Angle of Arrival (AOA), and Angle of Departure (AOD).

During indoor transmission of wireless signals, reflections occur due to the presence of scatterers. If multiple reflections from many different scatterers occur during transmission, the signal strength is severely degraded. Therefore, multiple reflections of signals should be ignored and only single reflections need to be considered, i.e., the signals which are only reflected once after emission from the transmitter to the receiver. In following examples, the symbols with subscripts screpresent symbols used in a single reflection in a non-line-of-sight indoor environment.

At step S103, determining a line, based on the indoor environmental information and the set of observation data, that pass through a scatterer corresponding to the base station, a two-dimensional (2D) planar projection point of the base station, and a 2D planar projection point of the mobile terminal.

Referring toFIG.2, a schematic diagram of the line in a 2D plane is shown, where the scatterer corresponding to the base station is located on the line.

At step S104, obtaining positional information of the scatterer with a constraint that the scatterer must be located on the line.

Specifically, the positional information of the k-th base station BSkis denoted as xB,k=[xB,k,yB,k]T, the positional information of the mobile terminal is denoted as xM=[xM,yM]T, and the line is denoted as an equation of askx+bsky+csk=0. The coordinates of the 2D planar projection point of the base station are denoted as xSB,k(xB,k)=[xSB,k,ySB,k]Tand the coordinates of the 2D planar projection point of the mobile terminal are denoted as xSM,k(xM)=[xSM,k,ySM,k]T, and the following expressions obtained:

According toFIG.2, the projection distance between the k-th scatterer (the scatterer corresponding to the base station) and the BSkis denoted as dSB,k, and the projection distance between the k-th scatterer and the mobile terminal is denoted as dSM,k, then

By the interpolation on xB,kand xMusing dSB,kand dSM,k, the position of the k-th scatterer can be obtained by:

At step S105, estimating positional information of the mobile terminal based on the positional information of the base station, the data set, and the positional information of the scatterer corresponding to the base station.

In one embodiment, the positional information of the mobile terminal is estimated using a constrained Iterative Weighted Least-squares (CIWL) method.

The positional information of the scatterer corresponding to the base station can be expressed as a relation between the positional information of the base station and the positional information of the mobile terminal, with the constraint that the scatterer corresponding to the base station must be located on the line. In a conventional single reflection model, the positional information of the scatterer corresponding to the base station and the positional information of the mobile terminal need to be estimated together when using an Iterative Weighted Least-squares (IWL) method. In the embodiment, since the indoor environmental information is known, the positional information of the scatterer corresponding to the base station can be substituted by the positional information of the base station and the positional information of the mobile terminal. That is, the positional information of the scatterer can be considered as a known parameter, and only the position information of the mobile terminal need to be estimated. This is referred to as the CIWL method.

Since the data set which is observed is subject to errors caused by noise, a model using by the CIWL can be expressed by the equation: zsc=hsc(xM)+nsc, where hsc(xM)∈is a mapping function between the data set and the positional information of the mobile terminal, nscis a noise vector and be can be a Gaussian distribution with mean zero and covariance matrix KSc.

According to the model, a cost function can be defined with a maximum likelihood criteria as: Jsc(xM)=(zsc−hsc(xM))TKsc−1(zsc−hsc(xM)). However, since Jsc(xM) is a nonlinear and nonconvex function for xM, the estimation cannot be obtained directly.

In the embodiment, an iterative approach is used. Let {circumflex over (x)}M,ibe the estimated positional information in the i-th iteration. Expanding Jsc({circumflex over (x)}M,i+1) by a first-order Taylor series with respect to xM, then hsc({circumflex over (x)}M,i+1) can be linearized as the equation: hsc({circumflex over (x)}M,i+1)≅hsc({circumflex over (x)}M,i)+Hsc,i({circumflex over (x)}M,i+1−{circumflex over (x)}M,i), where Hsc,i∈is the Jacobian matrix for the i-th iteration.

From the above equation, the positional information of the mobile terminal xMcan be estimated by using the IWL method. The specific estimation equation is: {circumflex over (x)}M,i+1={circumflex over (x)}M,i+(Hsc,iTKsc−1Hsc,i)−1Hsc,iTKsc−1(zsc−hsc({circumflex over (x)}M,i)).

In one embodiment, the geometric localization (GL) method is used to estimate the positional information of the mobile terminal based on the positional information of the scatterer, the positional information of the base station, and the data set observed in the base station, and the estimated positional information obtained from the GL method can be used as an initial value of the CIWL method. The GL method is a commonly used positioning method and is not described here.

Since the CIWL method is an iterative algorithm, determining when to stop the method is important. In one embodiment, the determination can be applied by using a ratio of a log likelihood function (LLF) calculated in the current iteration and that in the previous iteration. If a difference of one and the ratio is below a threshold γ, a determination to stop the CIWL can be made. In one embodiment, the LLF is defined based on a standard deviation of path length differences, azimuth and elevation AoD, and azimuth and elevation AoA.

FIG.3is a block diagram of a apparatus300for establishing an indoor location. In one embodiment, the apparatus300is a server. The apparatus300comprises a processor302, a memory304, and a communication unit306. The processor302comprises a microcontroller, a microprocessor, a complex instruction set computing microprocessor, a compact instruction set computing microprocessor, an ultra-parallel instruction set computing microprocessor, and a digital signal processor or other circuitry having processing capability. The processor302is configured to execute or process instructions, data, and computer programs stored in the memory304. The memory304comprises read-only memory, random access memory, magnetic memory medium devices, optical memory medium devices, flash memory devices, electrical, optical or other computer readable memory medium, comprising physical/tangible and non-transitory devices. The memory304is coupled to the processor302to store one or more computer programs that control the operation of the apparatus300, and are executed by the processor302. In one embodiment, the method ofFIG.2is applied in the apparatus300and is executed by the processor302and stored in the memory304.

In summary, the indoor positioning method and apparatus make use of known indoor environmental information to reduce the need for an element of estimation in establishing positional information of the scatterer during the positioning process and so improve the efficiency of establishing location of a target terminal.