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An Intelligent Mobile Locator hi-GPS 1000 and the Precision Assessment

WU Xinhua, Daisuke Maruo, Naokazu Monma, Kenji Terada, Mitsutaka Katou
PASCO Corporation
153-0043 Higashiyama, Meguro-ku,
Tokyo, 153-0043, Japan
shinka_go@pasco.co.jp, Daisuke_Maruo@pasco.co.jp,
Naokazu_Monma@pasco.co.jp, kenji_terada@pasco.co.jp, mitsutaka_katou@pasco.co.jp


1. Introduction
In recent years, there is an increasing demand for mobile position information services. In other hand, the telecom infrastructure has been substantially upgraded with the spreading of data communication and building up of packet communication networks.

We have developed a new multi-functional terminal called “HI-GPS1000” to meet the needs of LBS (Location Based Service).

HI-GPS1000 is not only consisting 8 channels L1/CA code tracking GPS receiver, but also connecting some external sensors by the interface of serial port or USB. It’s a compact and lightweight terminal with multi functions of GPS positioning and communication.

The system of HI-GPS1000 is an intelligent mobile locator and micro-server with loaded Linux OS. It can be used in LBS, such as vehicles monitoring and operation management, mobile communication terminal, car navigation and so on.

HI-GPS1000 is able to transmit the GPS positioning information, digital map, application program, e-mail, information of operating state, the data of CF (Compact Flash) card and PDA (Personal Data Assistant), and the information of external sensor etc. via the network of packet communications or wireless LAN such as the DoPa (NTT DoCoMo Packet), Air H” (DDI pocket) and PHS (P-in Comp@ct).

In addition, HI-GPS1000 incorporates a diversity of functions including protocol conversion, external port control and GPS time synchronized data logging. With these functions, HI-GPS1000 is available for various applications.

2. Key Features of System
HI-GPS1000 is an intelligent terminal unit for mobile position information. As a mobile locator loaded with multi-functional GPS sensor, Linux OS and 2 CF-card slots for memory and communication, the system of HI-GPS1000 has following features (Table 1).

Table 1. Key features of HI-GPS1000 system
MAIN PART   GPS
Linux   Armadilo Linux   GPS Module   Lassen SQ Trimble 
Distribution   Debian Gun / Linux2.2   GPS Positioning Precision   7m (CEP90%) Single
Kernel  2.4.X     1m (CEP50%) Differencial
CPU   ARM7TDMI + MMU 75MHZ   GPS Sensitivity   under -130dbm
RAM   SDRAM 32 Mbyte   DGPS Correction   RTCM SC104 format
FLASH   4 Mbyte   GPS Interface Protocol   Trimble TSIP
LAN   10 BaseT   GPS Driver   NMEA interface
CF Slot (2 slots)     Update Rate   Minimum 1 Hz
1) True IDE   Compact Flash   Development Environment
    IBM micro drive (1 G class)   Sample PG   THTTPD WEB server 
2) Simple CF   PHS Card, Wireless LAN Card     FTP server
    Modem Card, USB Card     Logging / Switch program
External I/F   RS232C- D-SUB 9pin     API for setup
    GPIO-1 D-SUB 15pin for external SW box   Operating System  
    ADC- D-SUB 9pin for external PC box 4Ch   Linux    Bin Utility, gcc g++, Libstd++ (Remote debug using LAN)
Size   120 x 125 x 70 mm   Windows    Possible with Cygwin
Weight   700 g     Library for cross development
Temperature   0 to 70 °C   Library for ARM   Libc6-arm-cross
Power   4 Watts, 8 to 32 VDC     Libc6-Dev-arm-cross
    Keep up with special vehicles   Flash Write in Tool   Support Win32 & Linux version

3. Functions and Benefits
HI-GPS1000 has four functions for saving the information on mobile as digital data:

  1. The function of measurement
    1. Location and time from GPS positioning
    2. Operating states of the front panel switches
    3. Information of multi-sensors
  2. The function of saving the data by communication
    1. To CF memory card
    2. To the server
  3. The function of intelligent trigger based on measured data by communication
    1. Data transmission
    2. Application change
  4. The function of communication in carrier-free using service network of
    1. Portable phone
    2. PHS
    3. Wireless LAN
There are some benefits of HI-GPS1000 such as:
  1. Providing an convertible environment for development with loaded OS of Linux.
    1. It could be a different terminal corresponding to the use just by writing user's application in the CF memory.
    2. A terminal program can be replaced by using communication.
  2. Providing reliable location information per second.
    1. Differential GPS positioning with correction received by communication.
    2. Single GPS positioning as a mobile locator for the general user.
  3. Providing the environment for packet telecommunication in carrier-free (by portable phone, PHS, wireless LAN etc.).
    1. It is possible to choose the way of communication for matching user’s conditions and operation cost.
    2. It can cope with the various packet telecommunication using the networks of portable phone, PHS and wireless LAN.
  4. Providing the interfaces for function expansion by using USB, PDA and so on.
    1. It has the expansion function to connect with other external sensors for sharing information by USB card (CF type) and USB hub.
    2. It is possible to make digital map or text information and text information visible by linking with PDA.
4. Test Examples and Results
The experiments aimed at the performance assessment and precision estimation of HI-GPS1000 by single and differential GPS positioning in stationary and moving state respectively.

(1) Continuous stationary positioning
The testes were carried out at the baselines field for GPS calibration of GSI (Geographical Survey Institute, Japan). More than 2 times of this static observation testing had been done since last year.

In every time, several HI-GPS1000s were used simultaneously and set up at the top of the pillars one by one for single and differential GPS positioning throughout 24 hours (Figure 1). The reference station for differential GPS was set up in Tokyo and the distance between the testing field and the reference station was about 52Km.


Figure 1. 24 hours continuous stationary positioning in Tsukuba, Japan

Table 2 gives the typical results of the experimental test done in November 2003 [ (1) in Table. 2 ] and July 2004 [ (2) in Table. 2 ] respectively.

In general, well precision has been obtained from these tests under the good conditions for GPS observation such as the open sky visibility and ignorable multi-path.

As the result, the standard deviations of differential GPS are much smaller than that of single GPS. The positioning precision of differential GPS is about 2 times as higher as the single positioning.

Moreover, the results of tests of (2) are better than (1) since some improvements of HI-GPS1000 with the most suitable configuration and reduction of noises in communication and the electric circuit.

Table 2. The results of the stationary positioning in 24 hours continually
    Single GPS Positioning   Differential GPS Positioning
(1)  (2)  (1)   (2)
Positioning Rating (%)  99.58  99.75  93.50   98.40
S.D. in NS (m)   +/- 2.00   +/- 1.40    +/- 0.76    +/- 0.60
S.D. in EW (m)   +/- 1.89    +/- 1.06    +/- 0.57    +/- 0.48 
dD (Obs. Mean – known ) (m)  3.12  1.63  1.18   0.89
Circular Error Probability (m)  2.96  1.57  1.14   0.83

(2) Continuous positioning in movement
We have carried out many actual positioning tests in movement with the HI-GPS1000 set up on a car. By running the car in urban area, in residential area, on highway and so on, a lot of actual measured data of single GPS continuous positioning have been obtained.

In order to presume the probability of location errors by single GPS in movement, we made a rough estimation based on the logged positioning data with following steps.

Firstly, determine the lanes with width of 5m, 10m and 15m from the center line of road by using the digital map with the scale of 1 to 2500. Then extract and total up the numbers of positioning within each lane.

Table 3 shows the results of estimation as mentioned above. According to this table, more than 50% of the mobile locating keeps the error within 5m, and, the probability of the location error with 10m is 80%.

As an example, Figure 2 plots the mobile track by single GPS positioning on running in Dennenntyoufu city, Tokyo.

As a mobile locator, HI-GPS1000 can satisfy the needs of management and observation of moving vehicles.

Table 3. The probability estimation of location error by single GPS positioning in movement
DATE  District  Milegae D   Number ofPositioning N   < 5 m   5 to 10 m    10 to 15 m   > 15 m
(D)  (N)  (D)  (N)  (D)  (N)  (D)   (N)
2004/04/02  (A)  100.379  5,387  3,427  63.6%  1,521  28.2%  289  5.4%  150   2.8%
2004/04/03  (B)  117.345  9,240  6,238  67.5%  1,693  18.3%  376  4.1%  933   10.1%
2004/04/07  (C)  129.528  12,857  6,545  50.9%  5,051  39.3%  1,056  8.2%  205   1.6%
2004/04/08  (D)  64.783  15,353  6,783  44.2%  2,985  19.4%  1,836  12.0%  3,749   24.4%
Total  412.035  42,837  22,993  53.7%  11,250  26.3%  3,557  8.3%  5,037   11.8%




Figure 2. The mobile track by single GPS positioning in Dennenntyoufu city, Tokyo

5. Conclusion
This paper introduced a new GPS terminal unit, HI-GPS1000, developed by PASCO Corporation, and used for location based services.

As an intelligent mobile locator with Linux OS loaded, HI-GPS1000 is filling the role of micro-server and suitable for secondary developments. Also, it can provide positional information per second with a precision of about 1 to 3m when it uses the differential correction and 5 to 7m if no correction information is used.

HI-GPS1000 has its unique added value and many advantages with its excellent customizing and programmable function that can change the terminal configurations and exchange information with the server by a remote controlling method.

With the communication functions, HI-GPS1000 can make use of wireless LAN, a data communications network such as the DoPa, Air H” and GSM. Moreover, HI-GPS can solve the problems as following:
  1. The precision of log in moving
  2. Terminal customizing and secondary developing
  3. Terminal extending
  4. Running cost for communication
  5. The security of system
  6. Communication in overseas
This suggests that HI-GPS1000 can be used for vehicle monitoring, fleet operating, logistical management, and the prediction for traffic congestion and so on.

We expect that the HI-GPS1000 will be effectively utilized as a practical mobile locator and a micro-server in various applications.

Acknowledgements
The authors wish to acknowledge to the Geographical Survey Institute for allowing to use the baselines for GPS calibration.

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