Patent Publication Number: US-8990046-B2

Title: Method and portable terminal for estimating step length of pedestrian

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
     The present application is related to and claims priority to application entitled “Method and Portable Terminal for Estimating Step Length of Pedestrian” filed in the Korean Industrial Property Office on Jul. 9, 2010, and assigned Serial No. 10-2010-0066296, the contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a portable terminal, and more particularly to a method and portable terminal for estimating the step length of a pedestrian. 
     BACKGROUND OF THE INVENTION 
     In recent years, personal navigation systems capable of pedestrian-centric route guidance have been widely equipped in portable terminals, such as cellular phones, smart phones, PDAs and MP3 players. The personal navigation system refers to a system that detects the location of a pedestrian to be guided by the system and guides a route for the pedestrian by using the detected location of the pedestrian. 
     A personal navigation system for pedestrian navigation may be implemented by equipping a portable terminal with a GPS receiver, an accelerometer, a gyroscope, and such. This personal navigation system estimates the step length of a pedestrian and produces a navigation solution by using the estimated step length to thereby provide a navigation service. Thus, in order to provide an accurate navigation service, the step length of a pedestrian should be accurately measured. 
     In the prior art, the step length of a pedestrian is estimated without considering in which body part the pedestrian carries a portable terminal during his/her movement. In the process of estimating the step length in this manner, a considerable error may occur depending on the position of the portable terminal carried by the pedestrian in different body parts which, in the worst case scenario, may result in a large deterioration in step length estimation performance. 
     SUMMARY OF THE INVENTION 
     To address the above-discussed deficiencies of the prior art, it is a primary object to provide a method and apparatus for estimating a step length, which can provide a more accurate route for a pedestrian by determining the carrying position of the portable terminal in the pedestrian&#39;s body by using an accelerometer and a gyroscope and applying a different step length estimation algorithm depending on the determined carrying position of the portable terminal. 
     In accordance with an aspect of the present invention, there is provided a portable terminal including an accelerometer, a gyroscope, and a controller. The accelerometer detects acceleration due to a movement of the portable terminal as a pedestrian carrying the portable terminal walks. The gyroscope detects angular velocity due to the movement of the portable terminal as the pedestrian walks. And the controller determines a magnitude of a swinging motion of the portable terminal by using at least one of the detected acceleration and angular velocity, determines that the portable terminal makes the swinging motion when the magnitude of the swinging motion is equal to or greater than a predetermined value, determines a carrying position of the portable terminal in the pedestrian&#39;s body by using at least one of the detected acceleration and angular velocity, and estimates a step length of the pedestrian according to the determined carrying position of the portable terminal. 
     In accordance with another aspect of the present invention, there is provided a step length estimation method. As a pedestrian carrying a portable terminal walks, acceleration due to a movement of the portable terminal is detected by using an accelerometer embedded in the portable terminal. As the pedestrian carrying the portable terminal walks, angular velocity due to the movement of the portable terminal is detected by using a gyroscope embedded in the portable terminal. A magnitude of a swinging motion of the portable terminal is determined by using at least one of the detected acceleration and angular velocity. When the magnitude of the swinging motion is equal to or greater than a predetermined value, the portable terminal is determined to be making the swinging motion. A carrying position of the portable terminal is determined by using at least one of the detected acceleration and angular velocity. And the step length of the pedestrian is estimated according to the determined carrying position of the portable terminal. 
     According to yet another aspect of the present invention, a portable terminal is provided. The portable terminal includes an accelerometer, a gyroscope, and a controller. The accelerometer detects acceleration due to a movement of the portable terminal. The gyroscope detects direction information for the movement of the portable terminal. And the controller determines a magnitude of a swinging motion of the portable terminal by using the detected acceleration and direction information, and applies a corresponding pedestrian step length estimation algorithm according to the magnitude of the swinging motion. 
     Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIGS. 1A and 1B  are graphs illustrating a relation between a walking frequency and a step length and a relation between an acceleration variance and a step length; 
         FIG. 2  is a block diagram of a portable terminal in accordance with an embodiment of the present invention; 
         FIGS. 3A-3B  and  4 A- 4 B are views of four possible carrying positions of a portable terminal under consideration in the present invention; 
         FIG. 5  illustrates a step length estimation process in accordance with an embodiment of the present invention; and 
         FIG. 6  illustrates a process of determining the carrying position in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 through 6 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged portable terminal. In the following description, the same elements will be designated by the same reference numerals although they are shown in different drawings. Furthermore, various specific definitions found in the following description, such as specific values of packet identifications, contents of displayed information, and such, are provided only to help general understanding of the present invention, and it is apparent to those skilled in the art that the present invention can be implemented without such definitions. Furthermore, in the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention. 
       FIGS. 1A and 1B  illustrate a relationship between a walking frequency and a step length and a relationship between an acceleration variance and a step length. 
     As shown in  FIGS. 1A and 1B , walking frequency and acceleration variance serve as parameters used to calculate step length estimates that properly reflect the characteristics of a change in step length according to a step pattern.  FIG. 1A  is a graph illustrating a relationship between a step length and a walking frequency, and  FIG. 1B  is a graph illustrating a relationship between a step length and an acceleration variance. From the graphs of  FIGS. 1A and 1B , it can be noted that the step length has a linear relation with each of the walking frequency and the acceleration variance. Accordingly, a step length can be represented by a linear combination of these two parameters, that is, a walking frequency and an acceleration variance, as given in the following equation:
 
step length= a   1 ·WF+ a   2 ·AV+ b   [Eqn. 1]
 
     In Equation 1, a 1  is a weight of a walking frequency, a 2  is a weight of an acceleration variance respectively, b is a constant term, WF is a walking frequency, and AV is an acceleration variance. 
     Therefore, since a walking frequency and the variance value of an accelerometer output at the moment when a pedestrian takes each step can be calculated, the total walking distance can be calculated by summating step lengths of respective steps after the pedestrian takes several steps, as given in the following equation: 
     
       
         
           
             
               
                 
                   
                     walking 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     distance 
                   
                   = 
                   
                     
                       ∑ 
                       
                         i 
                         = 
                         1 
                       
                       n 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           
                             a 
                             1 
                           
                           · 
                           
                             WF 
                             i 
                           
                         
                         + 
                         
                           
                             a 
                             2 
                           
                           · 
                           
                             AV 
                             i 
                           
                         
                         + 
                         b 
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 2, n is the number of detected steps, and coefficients a 1 , a 2 , and b are weights of respective parameters in a linear combination of a walking frequency and an acceleration variance, which are calculated by a linear regression. The step length estimation parameter coefficients are obtained by modeling a relation between the step length and the walking frequency and a relation between the step length and the acceleration variance. 
     Reference will now be made to a process and apparatus for estimating a step length as given in Equation 1, that is, a process setting parameter coefficients a 1 , a 2 , and b. 
       FIG. 2  illustrates a portable terminal according to an embodiment of the present invention. 
     Referring to  FIG. 2 , the portable terminal according to this embodiment includes an accelerometer  21 , a gyroscope  22 , and a controller  26 . As shown in  FIG. 2 , the portable terminal may further include a display unit  23 , a memory unit  24 , and a communication unit  25 . 
     More specially, the accelerometer  21  is a sensor that measures the acceleration of a portable terminal, such as a cellular phone, a smart phone, a PDA, or an MP3 player. In the portable terminal according to the present invention, the accelerometer  21  may be a MEMS (Micro Electro Mechanical System) type accelerometer, such as a subminiature accelerometer that can be embedded in the portable terminal. The accelerometer  21  may be designed such that it can detect the acceleration of the portable terminal on three axes. According to an embodiment of the present invention, the accelerometer  21  may be implemented using a 3-axis accelerometer or three 1-axis accelerometers. 
     The accelerometer  21  is mounted in the portable terminal in such a manner that the three axes are oriented in a lateral direction (right or left direction), a forward direction, and a downward direction (e.g. x, y, and z axes on a Cartesian coordinate system). Of course, it is preferred that each axis of the accelerometer  21  is correctly oriented. However, because the acceleration components due to walking are more important than directions in the present invention, the accelerometer  21  can maintain its characteristics even when each axis slightly deviates from each direction within a range that does not affect the acceleration signal detection. Also, even when the accelerometer  21  is much distorted in attitude (e.g. orientation), an attitude angle can be estimated by an accelerometer average. Thus, the accelerometer  21  can always measure acceleration components in the lateral, forward, and downward directions. The accelerometer  21  detects linear movements in the lateral, forward, and downward directions, and outputs an acceleration signal corresponding to each detection result. 
     The gyroscope  22  is a sensor that measures a rotation direction with respect to a reference direction. That is, when a reference direction is set to 0 degree direction, the gyroscope  22  measures how many degrees a current direction is rotated from the reference direction. The gyroscope  22  is also a subminiature sensor, such as a MEMS type gyroscope, which can be embedded in the portable terminal. The gyroscope  22  is so designed that it can detect the angular velocity of the portable terminal on three axes. 
     The moving path of an object can be expressed using both the accelerometer  21  and the gyroscope  22 . The position of a starting point is determined first, and then a current direction is measured using the gyroscope  22 . Next, an acceleration value is measured using the accelerometer  21 , and a distance is calculated by integrating the measured acceleration value twice. In this way, it is possible to determine a current position by using the distance and direction from the starting point. Alternatively, it is also possible to determine a current position by estimating a moving direction by means of a geo-magnetometer and estimating a moving distance through a step length estimation algorithm based on walking detection derived from the accelerometer  21 . 
     The display unit  23  displays general driving states of the portable terminal, and may display the carrying position of the portable terminal, which is determined according to the present invention. The display unit  23  may include a liquid crystal display (LCD), an organic light emitting diode (OLED), and such. 
     The memory unit  24  may store common programs and applications for driving the portable terminal. Furthermore, the memory unit  24  may store a step length estimation algorithm and such according to an embodiment of the present invention. 
     The communication unit  25  is responsible for transmission and reception of voice data, text data, image data, and control data. To this end, the communication unit  24  includes an RF transmitter for up-converting and amplifying the frequency of a transmitted signal, an RF receiver for low-noise amplifying and down-converting a received signal, an antenna for transmitting and receiving a signal, and so forth. Using the communication unit  25 , the carrying position of the portable terminal or an estimated step length may be stored in the memory unit embedded in the portable terminal or in an external memory unit. 
     The controller  26  controls the accelerometer  21 , the gyroscope  22 , the display unit  23 , the memory unit  24 , and the communication unit  25  in order to drive the portable terminal. According to an embodiment of the present invention, the controller  26  determines the magnitude of the swinging motion of the portable terminal by using acceleration detected by the accelerometer  21  or angular velocity detected by the gyroscope  22 . Subsequently, the controller  26  compares the magnitude of the swinging motion with a predetermined value to thereby determine whether the portable terminal makes a swinging motion, and based on the result of this determination, determines in which body part a pedestrian carries the portable terminal. 
       FIGS. 3A-3B  and  4 A- 4 B illustrate four carrying positions of a portable terminal under consideration in the present invention. 
     As shown in  FIGS. 3A-3B  and  4 A- 4 B, carrying positions of a portable terminal under consideration in the present invention are broadly grouped in two categories according to whether or not the portable terminal swings. The first category is when a portable terminal swings as shown in  FIGS. 3A and 3B , and the second category is when the swinging motion of a portable terminal is slight, that is, a portable terminal does not swing as shown in  FIGS. 4A and 4B . 
     In  FIGS. 3A and 3B , the category corresponding to when a portable terminal swings is in turn divided into a situation in which a portable terminal held in a pedestrian&#39;s hand swings ( FIG. 3A ) and a situation in which a portable terminal carried in a pedestrian&#39;s pocket swings ( FIG. 3B ). Also, in  FIGS. 4A and 4B , the category in which a portable terminal does not swing is in turn divided into a situation in which a portable terminal is carried on a pedestrian&#39;s waist ( FIG. 4A ) and a situation in which a portable terminal is held in a pedestrian&#39;s hand without a swinging motion ( FIG. 4B ). 
     A normal way for a pedestrian to carry a portable terminal is largely divided into the above four types of situations, and any carrying position may be included in one of the four situations, based on the magnitude of a swinging motion and such. For example, when a portable terminal is carried in a pedestrian&#39;s handbag, the carrying position of the portable terminal may be included in the category in which the portable terminal held in the pedestrian&#39;s hand swings or the category in which the portable terminal is carried on the pedestrian&#39;s waist, according to whether or not the handbag makes a swinging motion. 
     Of the above four types of situations, the former two situations ( FIGS. 3A and 3B ), that is, the situation in which a portable terminal held in a pedestrian&#39;s hand swings ( FIG. 3A ) and the situation in which a portable terminal carried in a pedestrian&#39;s pocket swings ( FIG. 3B ), correspond to the category in which a swinging motion is applied to the portable terminal as the pedestrian walks. In contrast, the latter two situations ( FIGS. 4A and 4B ), that is, the situation a portable terminal is carried on a pedestrian&#39;s waist ( FIG. 4A ) and the situation in which a portable terminal is held in a pedestrian&#39;s hand without a swinging motion ( FIG. 4B ), correspond to the category in which although the pedestrian walks, a very weak swinging motion or no swinging motion is applied to the portable terminal. 
     Whether or not a portable terminal swings is identified by the magnitude of a swinging motion. Using acceleration and angular velocity detected by the accelerometer  21  and the gyroscope  22 , the magnitude of a swinging motion is derived from the magnitude of acceleration, a pitch variation, or a combination thereof. The magnitude of acceleration and the pitch variation are calculated by the following equations:
 
magnitude of acceleration ( A )=√{square root over ( A   x   2   +A   y   2   +A   z   2 )}  [Eqn. 3]
 
pitch variation (Δpitch)=pitch max −pitch min   [Eqn. 4]
 
     If the magnitude of acceleration or the pitch variation is equal to or greater than a predetermined value of a corresponding threshold, then a portable terminal is determined to make a swinging motion. Otherwise, the portable terminal is determined not to make a swinging motion. Also, when the magnitude of acceleration and the pitch variation are used at the same time, their weights are set according to values preset for the magnitude of acceleration and the pitch variation respectively. If a sum of the set weights is equal to or greater than a predetermined value, then a portable terminal is determined to make a swinging motion. Otherwise, the portable terminal is determined not to make a swinging motion. 
     When as a result of the above determination procedure, a portable terminal is determined to make a swinging motion, whether the portable terminal is held in a pedestrian&#39;s swinging hand or is carried in the pedestrian&#39;s pocket is determined using the magnitude of horizontal acceleration, the pitch variation, or a combination thereof. The magnitude of horizontal acceleration is expressed as the resultant magnitude of acceleration in the north direction and acceleration in the east direction with respect to a horizontal plane parallel to the ground, and is calculated by the following equation:
 
magnitude of horizontal acceleration ( F )=√{square root over ( F   n   2   +F   e   2 )}  [Eqn. 5]
 
     If the magnitude of horizontal acceleration or the pitch variation is equal to or greater than a predetermined value of a corresponding threshold, then a portable terminal is determined to be held in a pedestrian&#39;s swinging hand. Otherwise, the portable terminal is determined to be carried in the pedestrian&#39;s pocket. Also, when the magnitude of horizontal acceleration and the pitch variation are used at the same time, their weights are set according to values preset for the magnitude of horizontal acceleration and the pitch variation, respectively. If a sum of the set weights is equal to or greater than a predetermined value, then a portable terminal is determined to be held in a pedestrian&#39;s swinging hand. Otherwise, the portable terminal is determined to be carried in the pedestrian&#39;s pocket. 
     When as a result of the above procedure of determining whether a portable terminal swings, the portable terminal is determined not to make a swinging motion, whether the portable terminal is held in a pedestrian&#39;s non-swinging hand (fixed hand) or is carried on the pedestrian&#39;s waist is determined using the magnitude of angular velocity, the variance of the magnitude of yaw rate, the variance of yaw, or a combination thereof. The magnitude of angular velocity, the variance of the magnitude of yaw rate, and the variance of yaw are calculated by the following equations: 
     
       
         
           
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       magnitude 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       of 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       angular 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         rate 
                         ⁡ 
                         
                           ( 
                           W 
                           ) 
                         
                       
                     
                     = 
                     
                       
                         
                           W 
                           x 
                           2 
                         
                         + 
                         
                           W 
                           y 
                           2 
                         
                         + 
                         
                           W 
                           z 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ] 
                 
               
             
             
               
                 
                   
                     variance 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     of 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     magnitude 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     of 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     yaw 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     rate 
                   
                   = 
                   
                     
                       1 
                       
                         N 
                         - 
                         1 
                       
                     
                     ⁢ 
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           1 
                         
                         N 
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             
                               W 
                               
                                 z 
                                 ⁢ 
                                 _ 
                                 ⁢ 
                                 i 
                               
                             
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                               _ 
                             
                           
                           ) 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ] 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       variance 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       of 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       yaw 
                     
                     = 
                     
                       
                         1 
                         
                           N 
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         
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                             i 
                             = 
                             1 
                           
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                           2 
                         
                       
                     
                   
                 
               
               
                 
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                     Eqn 
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                     ⁢ 
                     8 
                   
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     If the magnitude of angular velocity, the variance of the magnitude of yaw rate, or the variance of yaw is equal to or greater than a predetermined value of a corresponding threshold, then a portable terminal is determined to be carried on a pedestrian&#39;s waist. Otherwise, the portable terminal is determined to be held in the pedestrian&#39;s fixed hand. Also, when the magnitude of angular velocity, the variance of the magnitude of yaw rate, or the variance of yaw are used concurrently, their weights are set according to values preset for the magnitude of angular velocity, the variance of the magnitude of yaw rate, or the variance of yaw, respectively. If a sum of the set weights is equal to or greater than a predetermined value, then a portable terminal is determined to be carried on a pedestrian&#39;s waist. Otherwise, the portable terminal is determined to be held in the pedestrian&#39;s fixed hand. 
     The reason why a portable terminal is determined to be held in a pedestrian&#39;s fixed hand when the magnitude of angular velocity, the variance of the magnitude of yaw rate, or the variance of yaw is less than a predetermined value is that because an arm joint connecting a pedestrian&#39;s body and hand acts as a damper for the pedestrian&#39;s movement, the angular velocity of the portable terminal is smaller when held in the pedestrian&#39;s fixed hand than when carried on the pedestrian&#39;s waist. 
     After the carrying position of a portable terminal is identified, a step length is estimated by using Equation 1. A step length estimation algorithm for a pedestrian is applied in such a manner that the parameters (a 1 , a 2 , b) in Equation 1 are set to different values according to the above four types of carrying positions. For example, the values of the parameters according to the above four types of carrying positions are shown in Table 1. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 a 1   
                 a 2   
                 b 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 hand (swinging) 
                 0.45 
                 0.23 
                 0.23 
               
               
                   
                 trousers pocket 
                 0.51 
                 0.65 
                 0.19 
               
               
                   
                 waist 
                 0.73 
                 0.91 
                 0.22 
               
               
                   
                 hand (fixed) 
                 0.68 
                 0.79 
                 0.29 
               
               
                   
                   
               
            
           
         
       
     
     Using a 1 , a 2 , and b obtained from Table 1, a walking frequency (about 2 Hz), and an acceleration variance, the step length of a pedestrian can be estimated by using Equation 1. 
       FIG. 5  illustrates a step length estimation process according to an embodiment of the present invention. 
     As shown in  FIG. 5 , the step length estimation process according to this embodiment includes an acceleration detection operation (block S 51 ), an angular velocity detection operation (block S 52 ), determining the magnitude of a swinging motion (block S 53 ), determining whether there is a swinging motion (block S 54 ), determining the carrying position of a portable terminal (block S 55 ), and using a step length estimation algorithm (block S 56 ). 
     In the acceleration detection operation (block S 51 ), as a pedestrian carries a portable terminal, acceleration due to a movement of the portable terminal is detected using an accelerometer embedded in the portable terminal. Here, the accelerometer may be a MEMS type accelerometer that is small enough to be embedded in the portable terminal. 
     In the angular velocity detection operation (block S 52 ), as the pedestrian carrying the portable terminal walks, angular velocity due to the movement of the portable terminal is detected using a gyroscope embedded in the portable terminal. Here, the gyroscope measures angular velocity in three axis directions and may also be a MEMS type gyroscope that is small enough to be embedded in the portable terminal. 
     When determining the magnitude of a swinging motion (block S 53 ), the magnitude of the swinging motion of the portable terminal is determined using at least one of the detected acceleration and angular velocity. The magnitude of the swinging motion is derived from the magnitude of acceleration, a pitch variation, or a combination thereof. In particular, according to an embodiment of the present invention, the magnitude of the swinging motion may be derived from a combination of the magnitude of acceleration and the pitch variation. In this situation, weights of the magnitude of acceleration and the pitch variation are set respectively, and the magnitude of the swinging motion is determined by a sum of the set weights. 
     When determining whether there is a swinging motion (block S 54 ), whether or not the portable terminal makes a swinging motion is determined by comparing the determined magnitude of the swinging motion with a predetermined value (α 1  or α 2 ). That is, if the magnitude of the swinging motion is equal to or greater than a predetermined value (α 1  or α 2 ), then the portable terminal is determined to make a swinging motion. Otherwise, the portable terminal is determined not to make a swinging motion. 
     When determining the carrying position of a portable terminal (block S 55 ), the position of the pedestrian&#39;s body part in which the pedestrian carries the portable terminal is determined using at least one of the detected acceleration and angular velocity. 
     According to an embodiment of the present invention, when the portable terminal is determined in block S 54  to make a swinging motion, the step length estimation method further includes determining the magnitude of horizontal acceleration according to the swinging motion of the portable terminal and comparing the magnitude of horizontal acceleration with a predetermined value (β1). If the magnitude of horizontal acceleration is equal to or greater than the predetermined value (β1), then the portable terminal is determined to make a swinging motion while being held in the pedestrian&#39;s hand. In contrast, if the magnitude of horizontal acceleration is less than the predetermined value (β1), then the portable terminal is determined to make a swinging motion while being carried in the pedestrian&#39;s pocket. 
     According to an embodiment of the present invention, when the portable terminal is determined in block S 54  to make a swinging motion, the step length estimation method further includes determining the pitch variation according to the swinging motion of the portable terminal and comparing the pitch variation with a predetermined value (β2). If the pitch variation is equal to or greater than the predetermined value (β2), then the portable terminal is determined to make a swinging motion while being held in the pedestrian&#39;s hand. In contrast, if the pitch variation is less than the predetermined value (β2), then the portable terminal is determined to make a swinging motion while being carried in the pedestrian&#39;s pocket. 
     According to another embodiment of the present invention, when the portable terminal is determined in block S 54  to make a swinging motion, the step length estimation method further includes determining the magnitude of horizontal acceleration and the pitch variation according to the swinging motion of the portable terminal, setting weights of the magnitude of horizontal acceleration and the pitch variation, respectively, and comparing a sum of the weights with a predetermined value. If the sum of the weights is equal to or greater than the predetermined value, then the portable terminal is determined to make a swinging motion while being held in the pedestrian&#39;s hand. In contrast, if the sum of the weights is less than the predetermined value, then the portable terminal is determined to make a swinging motion while being carried in the pedestrian&#39;s pocket. 
     According to an embodiment of the present invention, when the portable terminal is determined in block S 54  not to make a swinging motion, the step length estimation process further includes determining the magnitude of the angular velocity of the portable terminal and comparing the magnitude of the angular velocity of the portable terminal with a predetermined value (γ1). If the magnitude of the angular velocity of the portable terminal is equal to or greater than the predetermined value (γ1), then the portable terminal is determined to be carried on the pedestrian&#39;s waist. In contrast, if the magnitude of the angular velocity of the portable terminal is less than the predetermined value (γ1), then the portable terminal is determined to be held in the pedestrian&#39;s hand without a swinging motion. 
     According to an embodiment of the present invention, when the portable terminal is determined in block S 54  not to make a swinging motion, the step length estimation process further includes determining the variance of the magnitude of the yaw rate of the portable terminal and comparing the variance of the magnitude of the yaw rate of the portable terminal with a predetermined value (γ2). If the variance of the magnitude of the yaw rate of the portable terminal is equal to or greater than the predetermined value (γ2), then the portable terminal is determined to be carried on the pedestrian&#39;s waist. In contrast, if the variance of the magnitude of the yaw rate of the portable terminal is less than the predetermined value (γ2), then the portable terminal is determined to be held in the pedestrian&#39;s hand without a swinging motion. 
     According to another embodiment of the present invention, when the portable terminal is determined in block S 54  not to make a swinging motion, the step length estimation process further includes determining the variance of the yaw of the portable terminal and comparing the variance of the yaw of the portable terminal with a predetermined value (γ3). If the variance of the yaw of the portable terminal is equal to or greater than the predetermined value (γ3), then the portable terminal is determined to be carried on the pedestrian&#39;s waist. In contrast, if the variance of the yaw of the portable terminal is less than the predetermined value (γ3), then the portable terminal is determined to be held in the pedestrian&#39;s hand without a swinging motion. 
     According to yet another embodiment of the present invention, when the portable terminal is determined in block S 54  not to make a swinging motion, the step length estimation process further includes determining the magnitude of the angular velocity, the variance of the magnitude of the yaw rate, and the variance of the yaw of the portable terminal, setting weights of the magnitude of the angular velocity, the variance of the magnitude of the yaw rate, and the variance of the yaw of the portable terminal, respectively, and comparing a sum of the weights with a predetermined value. If the sum of the weights is equal to or greater than the predetermined value, then the portable terminal is determined to be carried on the pedestrian&#39;s waist. In contrast, if the sum of the weights is less than the predetermined value, then the portable terminal is determined to be held in the pedestrian&#39;s hand without a swinging motion. 
     When using a step length estimation algorithm (S 56 ), the step length of the pedestrian is estimated differently depending on the carrying position of the portable terminal. That is, the step length of the pedestrian is estimated by applying optimal parameters (a 1 , a 2 , and b in Equations (1) and (2)) for each of the four carrying positions of the portable terminal. The optimal parameters may be experimentally obtained in advance, or may also be obtained through learning of the portable terminal. 
       FIG. 6  illustrates process for determining the carrying position according to an embodiment of the present invention. 
     One example of a process for estimating the step length of a pedestrian will be given through  FIG. 6 . When a signal for step length estimation is input, first of all, it is necessary to determine whether a portable terminal swings. Acceleration detected by an accelerometer of the portable terminal may be used to determine whether the portable terminal swings. The magnitude of acceleration is derived from acceleration components in three axis directions, and then the derived magnitude of acceleration is compared with a predetermined value α1. If the magnitude of acceleration is equal to or greater than α1, then the portable terminal is determined to make a swinging motion. Alternatively, it is also possible to obtain the pitch variation and then compare the obtained pitch variation with another predetermined value α2. Similarly, if the pitch variation is equal to or greater than α2, then the portable terminal is determined to make a swinging motion. 
     After the portable terminal is determined to make a swinging motion, whether the portable terminal makes a swinging motion while being held in the pedestrian&#39;s hand or carried in the pedestrian&#39;s pocket is determined. The magnitude of horizontal acceleration, the pitch variation, or a combination thereof may be used for this determination. When the magnitude of horizontal acceleration is equal to or greater than a predetermined value β1, the portable terminal is determined to make a swinging motion while being held in the pedestrian&#39;s hand. Furthermore, when the pitch variation is equal to or greater than a predetermined value β2, the portable terminal is also determined to make a swinging motion while being held in the pedestrian&#39;s hand. 
     After the portable terminal is determined not to make a swinging motion, whether the portable terminal is carried on the pedestrian&#39;s waist or held in the pedestrian&#39;s non-swinging hand (for example, when the pedestrian talks over the portable terminal held in his/her hand) is determined. The magnitude of angular velocity, the variance of the magnitude of yaw rate, the variance of yaw, or a combination thereof may be used for this determination. When the magnitude of angular velocity is equal to or greater than a predetermined value γ1, the portable terminal is determined to be carried on the pedestrian&#39;s waist. Furthermore, when the variance of the magnitude of yaw rate is equal to or greater than a predetermined value γ2, the portable terminal is also determined to be carried on the pedestrian&#39;s waist. Furthermore, when the variance of yaw is equal to or greater than a predetermined value γ3, the portable terminal is determined to be carried on the pedestrian&#39;s waist. 
     In the method and portable terminal for estimating the step length of a pedestrian according to the present invention, a series of tests were conducted to verify the step length estimation algorithm, and the test results will be described hereinafter. 
     The test conditions were as follows: a pedestrian walked 50 m in a straight line, and this 50 m walk test was conducted with a portable terminal carried on the pedestrian&#39;s waist, held in the pedestrian&#39;s hand (fixed), carried in the pedestrian&#39;s pocket, and held in the pedestrian&#39;s hand (swinging) respectively. The pedestrian walked 50 m and then the result of recognizing the corresponding carrying position of the portable terminal was checked while the carrying position of the portable terminal was changed from the pedestrian&#39;s waist to the pedestrian&#39;s hand (swinging), the pedestrian&#39;s hand (fixed), and the pedestrian&#39;s pocket in that order. The same test was also conducted for three different pedestrians. 
     The result of recognizing the carrying position corresponding to the pedestrian&#39;s hand (fixed) is relatively better than the result of recognizing the carrying position corresponding to the pedestrian&#39;s waist. This is because since there are probably many occasions when a pedestrian holds a portable terminal in his/her hand (fixed) in an actual situation, the step length estimation algorithm has been established with the aim of minimizing an error rate for a pedestrian&#39;s hand (fixed). 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                 trousers 
                 hand 
               
               
                   
                 waist 
                 hand (fixed) 
                 pocket 
                 (swinging) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 error rate 
                 3.5048 
                 0.3854 
                 1.5562 
                 0.2973 
               
               
                   
                 (%) 
               
               
                   
                   
               
            
           
         
       
     
     Table 2 given above shows results obtained by applying the above algorithm for recognizing the carrying position of a portable terminal. Error rates for the four carrying positions substantially range from approximately 1 to 3%. The walking distance of a pedestrian can be more accurately estimated using the algorithm for recognizing the carrying position of a portable terminal to apply the step length estimation parameters (a 1 , a 2 , and b in Equations 1 and 2) suitable to each carrying position. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 hand 
                 trousers 
                   
               
               
                   
                 (fixed) 
                 pocket 
                 hand (swinging) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 error rate (%) 
                 5.92/27.11 
                 3.60/14.03 
                 6.49/14.35 
               
               
                   
                   
               
            
           
         
       
     
     Table 3 given above shows error rates in % for the worst case scenario of the prior art step length estimation and the worst scenario of the inventive step length estimation when the step length estimation algorithm is applied to each carrying position. Through the results of Table 3, it can be noted that the inventive step length estimation process has a significantly improved effect of estimating a step length. 
     As described above, the inventive portable terminal for estimating a step length can advantageously guide a more accurate route for a pedestrian by determining the carrying position of the portable terminal in the pedestrian&#39;s body by using an accelerometer and a gyroscope and applying a different step length estimation algorithm depending on the determined carrying position of the portable terminal. 
     Although the present disclosure has been described with embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.