Patent Publication Number: US-7898473-B2

Title: Method for positioning, a positioning system, and an electronic device

Description:
This is a Divisional Application of U.S. patent application Ser. No. 10/953,737, filed on 29 Sep. 2004 and issued as U.S. Pat. No. 7,576,692 on 18 Aug. 2009, which is a Continuation In Part application of U.S. patent application Ser. No. 10/081,294, filed on Feb. 21, 2002 and issued as U.S. Pat. No. 7,277,054 on 2 Oct. 2007, which claims priority from Finnish patent application 20010365 filed on Feb. 23, 2001. 
    
    
     FIELD 
     The presently disclosed embodiments relates to a method for positioning of a wireless communication device. The disclosed embodiments further relate to a positioning system to be used in the positioning of a wireless communication device. The disclosed embodiments relate also to an electronic device to be used in a positioning system, which electronic device comprises at least positioning means and mobile communication means. The disclosed embodiments also relate to a wireless communication device, and a method for delivering assistance data for positioning of a wireless communication device. 
     BACKGROUND 
     In positioning systems based on satellite positioning, a positioning receiver attempts to receive signals of at least four satellites in order to detect the position of the positioning receiver and the time data. An example of such a satellite positioning system is the GPS system (Global Positioning System) comprising a plurality of satellites orbiting the globe according to predefined orbits. These satellites transmit positioning data, on based of which the position of a satellite can be defined at each moment of time, in case the exact time data used in the satellite positioning system is known in the positioning receiver. In the GPS system, the satellites transmit a spread spectrum signal which is modulated with a code that is individual for each satellite. Thus, the positioning receiver can distinguish signals transmitted by different satellites from each other by using a reference code corresponding to the satellite code generated locally in the positioning receiver. 
     A drawback with such positioning systems based on satellite positioning is often the fact that a signal transmitted by a satellite is strongly attenuated when arriving to the positioning receiver, wherein it is very difficult to distinguish the signal from the background noise. The signal can be attenuated inter alia due to climatic conditions and obstacles, such as buildings and surrounding grounds in the routing of the signal. Also, the signal can wander to the positioning receiver through a plurality of different routes which causes so-called multipath propagation and aggravates the synchronizing of the positioning receiver to a wished signal because the transmitted signal arrives to the receiver through different routings, for example straight from the satellite (line-of-sight) and, in addition to this; reflected. Due to this multipath propagation the same signal is received as a plurality of signals with different phases. It is particularly difficult to perform positioning inside a building, because a building itself strongly attenuates the signal transmitted by satellites and, on the other hand, multipath propagation can be even stronger since possibly reflected signals coming for example through a window are not necessarily as attenuated as signals coming straight through the roof. In this case, the receiver can make erroneous interpretations about the time of flight and the positioning of the satellite during the moment of transmission, inter alia due to said increase in the signal time-of-flight caused by multipath propagation 
     Each operating satellite of the GPS system transmits a so-called L1 signal in the carrier frequency of 1575.42 MHz. This frequency is also indicated with 154f 0 , where f 0 =10.23 MHz. Furthermore, the satellites transmit another ranging signal at a carrier frequency of 1227.6 MHz called L2, i.e. 120f 0 . In the satellite, these signals are modulated with at least one pseudo random sequence. This pseudo random sequence is different for each satellite. As a result of the modulation, a code-modulated wideband signal is produced. The modulation technique used makes it possible to distinguish in the receiver the signals transmitted by different satellites, even though the carrier frequencies used in the transmission are substantially the same. This modulation technique is called code division multiple access (CDMA). In each satellite, for modulating the L1 signal, the pseudo sequence used is e.g. a so-called C/A code (Coarse/Acquisition code), which is a code from the family of the Gold codes. Each GPS satellite transmits a signal by using an individual C/A code. The codes are formed as a modulo-2 sum of two 1023-bit binary sequences. The first binary sequence G 1  is formed with a polynome X 10 +X 3 +1, and the second binary sequence G 2  is formed by delaying the polynome X 10 +X 9 +X 8 +X 6 +X 3 +X 2 +1 in such a way that the delay is different for each satellite. This arrangement makes it possible to produce different C/A codes by an identical code generator. The C/A codes are thus binary codes of which chipping rate in the GPS system is 1.023 MHz. The C/A code comprises 1023 chips, wherein the iteration time (epoch) of the code is 1 ms. The carrier wave of the L1 signal is further modulated by navigation information at a bit rate of 50 bit/s. The navigation information comprises information about the “health”, orbit, time data of the satellite, etc. 
     During their operation, the satellites monitor the condition of their equipment. The satellites may use for example so-called watchdog operations to detect and report possible faults in the equipment. The errors and malfunctions can be instantaneous or longer lasting. On the basis of the health data, some of the faults can possibly be compensated for, or the information transmitted by a malfunctioning satellite can be totally disregarded. Furthermore, in a situation in which the signal of more than four satellites can be received, the information received from different satellites can be weighted differently on the basis of the health data. Thus, it is possible to minimize the effect of errors on measurements, possibly caused by satellites which seem unreliable. 
     To detect the signals of the satellites and to identify the satellites, the receiver must perform acquisition, whereby the receiver searches for the signal of each satellite at the time and attempts to be synchronized and locked to this signal so that the data transmitted with the signal can be received and demodulated. 
     The positioning receiver must perform the acquisition e.g. when the receiver is turned on and also in a situation in which the receiver has not been capable of receiving the signal of any satellite for a long time. Such a situation can easily occur e.g. in portable devices, because the device is moving and the antenna of the device is not always in an optimal position in relation to the satellites, which impairs the strength of the signal coming in the receiver. 
     The positioning arrangement has two primary functions: 
     1. to calculate the pseudorange between the receiver and the different GPS satellites, and 
     2. to determine the position of the receiver by utilizing the calculated pseudoranges and the position data of the satellites. The current position data of the satellites can be calculated on the basis of the Ephemeris and time correaction data received from the satellites. 
     Distances to the satellites are called pseudoranges, because the time is not accurately known in the receiver. Thus, the determinations of position and time are repeated until a sufficient accuracy is achieved with respect to time and position. Because the time is not known with absolute precision, the position and the time must be determined e.g. by linearizing a set of equations for each new iteration. 
     A pseudorange can be calculated by measuring the pseudo transmission time delays between signals of different satellites. 
     Almost all known GPS receivers utilize correlation methods for acquisition to the code as well as for tracking. In a positioning receiver, reference codes ref(k), i.e. the pseudo random sequences for different satellites are stored or generated locally. A received signal is subjected to conversion to an intermediate frequency (down conversion), whereafter the receiver multiplies the received signal with the stored pseudo random sequence. The signal obtained as a result of the multiplication is integrated or low-pass filtered, wherein the result obtained is data about whether the received signal contained a signal transmitted by a satellite. The multiplication is iterated in the receiver so that the phase of the pseudo random sequence stored in the receiver is shifted each time. The correct phase is inferred from the correlation result for example so that when the correlation result is at its peak, the correct phase has been detected. Thus, the receiver is correctly synchronized with the received signal. After the code acquisition has been completed, the next steps are frequency tuning and phase locking. 
     The above-mentioned acquisition and frequency control process must be performed for each signal of a satellite received in the receiver. Some receivers may include several receiving channels, wherein an attempt is made on each receiving channel to be synchronized with the signal of one satellite at a time and to detect the information transmitted by this satellite. 
     The positioning receiver receives information transmitted by satellites and performs positioning on the basis of the received information. For the positioning, the receiver must receive a signal transmitted by at least four different satellites to find out the x, y, z coordinates and the time data. The received navigation information is stored in a memory, wherein this stored information can be used to find out e.g. the positioning data of satellites. 
       FIG. 1  shows, in a principle chart, positioning, by means of a signal transmitted from four satellites SV 1 , SV 2 , SV 3 , SV 4  in a wireless communication device MS comprising a positioning receiver. In the GPS system, the satellites transmit positioning data as well as time data, on the basis of which the positioning receiver can perform calculations to determine the current position of the satellite. These positioning data and time data are transmitted in frames which are further divided into subframes. In the GPS system, each frame comprises 1500 bits, which are divided into five subframes of 300 bits each. Since the transmission of one bit takes 20 ms, the transmission of each subframe thus takes 6 s, and the whole frame is transmitted in 30 seconds. The subframes are numbered from 1 to 5. In each subframe  1 , e.g. time data is transmitted, indicating the moment of transmission of the subframe as well as information about the deviation of the satellite clock with respect to the time in the GPS system. 
     The subframes  2  and  3  are used for the transmission of positioning data. The subframe  4  contains other system information, such as universal time, coordinated (UTC). The subframe  5  is intended for the transmission of almanac data of all the satellites. The entity of these subframes and frames is called a GPS navigation message which comprises 25 frames, i.e. 125 subframes. The length of the navigation message is thus 12 min 30 s. 
     In the GPS system, time is measured in seconds from the beginning of a week. In the GPS system, the starting time of a week is the midnight between a Saturday and a Sunday. Each subframe to be transmitted contains information on the moment of the GPS week when the subframe in question was transmitted. Thus, the time data indicates the time of transmission of a certain bit, i.e. in the GPS system, the time of transmission of the last bit in the subframe in question. In the satellites, time is measured with high-precision atomic chronometers. In spite of this, the operation of each satellite is controlled in a control centre for the GPS system (not shown), and e.g. a time comparison is performed to detect chronometric errors in the satellites and to transmit this information to the satellite. 
     In the precision of positioning it is of great importance how precisely the actual GPS time is known by the receiver. In practice, the precise GPS time can be determined after positioning calculation, in which the chronometric error of the receiver is determined relative to the GPS time. However, in the very first positioning calculation an estimation of the GPS time can be used, because the actual GPS time is not necessarily known in the receiver. The estimated GPS time at a moment of time k can be derived on the basis of measurement of three time elements according to the following formula:
 
 T   GPS   j ( k )= T   TOW ( k )+ T   ms   j ( k )+ T   chip   j ( k )+0.078  (1)
 
in which
 
T TOW   j =the time data (time of week) in seconds contained in the last received subframe,
 
T ms   j (k)=the time in seconds corresponding to the number of C/A epochs received after the beginning of the last received subframe,
 
T chip   j (k)=the time in seconds corresponding to the number (from 0 to 1022) and code phase of whole chips received after the change of the last epoch, and
 
j=the receiving channel index.
 
     In Formula 1, the average time of flight (ToF) of the signal from the satellite to the receiver is 78 ms. As a reference it is possible to use any such receiving channel in which the signal-to-noise ratio (SNR) is sufficient. 
     The time data (ToW) is transmitted in the navigation message at intervals of six seconds and it indicates the time passed from the last change of the GPS week. Thus, the value range of the time data is the remainder of one week. In a corresponding manner T ms   j (k) equals the remainder of six seconds and T chip   j (k) equals the remainder of 1 ms. The first three terms of the Formula (1) can also be used in the measurement of the time of arrival (ToA) of the signal. 
     In poor receiving conditions in which the navigation data cannot be indicated inter alia due to a high bit error rate (BER), it is not possible, due to the missing time data ToW, to determine the GPS time directly by means of the Formula 1. However, the code phase can normally still be measured. 
     The first three terms in the Formula 1 determine the time of transmission {circumflex over (T)} ToT   k  of the received signal. 
     SUMMARY 
     The presently disclosed embodiments provide a positioning method and a positioning receiver in which the location of a known reference point is used as the default location of the positioning receiver. The location of the known reference point can be detected in a database, or the like. The database can be arranged in a data network, such as the Internet network and/or a mobile communication network. Moreover, the positioning data of one or a plurality of reference points can be stored into an electronic device comprising a positioning receiver. The disclosed embodiments are based on the idea that the position of a such reference point of which position is known is used as the default position of the electronic device, and the position of the reference point is stored in the database, wherein this positioning data is retrieved from the database to the electronic device. In case the positioning data are not stored in the electronic device, they are retrieved at the time when the positioning is wished to be performed. 
     According to a first aspect of the disclosed embodiments there is provided a method for positioning of a wireless communication device, the method comprising:
         storing position data relating to one or a plurality of reference areas to at least one database,   examining which of said reference areas is located in the vicinity of the wireless communication device, and   retrieving at least position data about said reference area located in the vicinity of the wireless communication device,   wherein in order to perform the positioning, the method further comprises selecting said reference area located in the vicinity of the wireless communication device as the default position of the wireless communication device.       

     According to a second aspect of the disclosed embodiments there is provided a positioning system to be used in the positioning of a wireless communication device, the positioning system comprising:
         at least one database for storing one or a plurality of reference areas,   means for detecting which of said reference areas is located in the vicinity of the wireless communication device,   means for retrieving the position data of the reference area located in the vicinity of said wireless communication device,   wherein for performing the positioning, the positioning system comprises a selecting element for selecting said reference area in the vicinity of the wireless communication device as the default position of the wireless communication device.       

     According to a third aspect of the disclosed embodiments there is provided an electronic device to be used in a positioning system, which electronic device comprises at least:
         positioning means, and   mobile communication mean,   means for detecting which of the reference areas stored in the database of the positioning system is located in the vicinity of the electronic device,   means for retrieving the position data of the reference area located in the vicinity of the electronic device, and   means for selecting the reference area located in the vicinity of said electronic device as the default position of the electronic device in the positioning.       

     According to a fourth aspect of the disclosed embodiments there is provided a wireless communication device to be used in a positioning system, which wireless communication device comprises at least:
         positioning means, and   mobile communication means,   means for detecting which of the reference areas stored in the database of the positioning system is located in the vicinity of the wireless communication device,   means for retrieving the position data of the reference area located in the vicinity of the wireless communication device, and   means for selecting the reference area located in the vicinity of said wireless communication device as the default position of the wireless communication device in the positioning.       

     According to a fifth aspect of the disclosed embodiments there is provided a computer program product for positioning of a wireless communication device, the computer program product comprising machine executable steps for:
         storing position data relating to one or a plurality of reference areas to at least one database,   examining which of said reference areas is located in the vicinity of the wireless communication device, and   retrieving at least position data about said reference area located in the vicinity of the wireless communication device,   wherein in order to perform the positioning, the computer program product further comprises machine executable steps for selecting said reference area located in the vicinity of the wireless communication device as the default position of the wireless communication device.       

     According to a sixth aspect of the disclosed embodiments there is provided a method for delivering assistance data for positioning of a wireless communication device, the method comprising:
         storing position data relating to one or a plurality of reference areas to at least one database,   examining which of said reference areas is located in the vicinity of the wireless communication device, and   transmitting to the wireless communication device at least position data about said reference area located in the vicinity of the wireless communication device,   invoicing a user of the wireless communication device of the transmitted assistance data.       

     According to a seventh aspect of the disclosed embodiments there is provided a module to be used in an electronic device which module comprises at least:
         means for detecting which of the reference areas stored in the database of the positioning system is located in the vicinity of the electronic device,   means for retrieving the position data of the reference area located in the vicinity of the electronic device, and   means for selecting the reference area located in the vicinity of said electronic device as the default position of the electronic device for positioning of the electronic device.       

     Advantages can be achieved by the disclosed embodiments when compared to the positioning methods and receivers of prior art. Since the method of the disclosed embodiments uses, as the default position of the electronic device, the position of a reference point, for example a base station of a mobile communication network that is situated relatively close to the electronic device, and auxiliary data is transmitted to the electronic device, the real position of the electronic device can be detected relatively fast. Additional advantages are provided in the method by the fact that the electronic device may store the auxiliary data and location data of the reference points it has received, wherein it is not always necessary for the electronic device to detect this information by using the mobile communication network, which reduces network traffic. In addition, this kind of retrieval of auxiliary data from a mobile communication network is usually subject to charge, wherein the costs of the positioning system paid by the user can be cut down by the arrangement of the disclosed embodiments. Yet another advantage to be mentioned is that the decrease in network traffic can reduce also the power consumption of the electronic device, which is beneficial particularly in portable electronic devices. The use of the method according to the disclosed embodiments may allow in some situations positioning also indoors, which is not necessarily possible with prior art solutions. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In the following, the disclosed embodiments will be described in more detail with reference to the appended drawings, in which 
         FIG. 1  shows in a reduced manner a system in which the method according to a first embodiment of the disclosed embodiments can be applied, 
         FIG. 2  shows an electronic device according to a first embodiment of the disclosed embodiments in a reduced block chart, and 
         FIG. 3  shows in a reduced manner a system in which the method according to a second embodiment of the disclosed embodiments can be applied, 
         FIGS. 4   a  and  4   b  depict examples of radiation patterns of an omnidirectional antenna and a directional antenna respectively 
         FIG. 5   a  depicts a first example embodiment of the disclosed embodiments as a simplified flow diagram, 
         FIG. 5   b  depicts a second example embodiment of the disclosed embodiments as a simplified flow diagram. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, the operation of the method according to an example embodiment will be described with reference to the system shown in  FIG. 1 . An electronic device performing positioning is in  FIG. 2  exemplified by a wireless communication device MS comprising, in addition to the mobile communication means MT, also a positioning receiver PR. Thus, the mobile communication means MT can be used for transmitting information between the wireless communication device MS and the base stations BS, BS′, BS″ of the mobile communication network MN. 
     The base station BS, BS′, BS″ has an antenna  16  which can be an omnidirectional antenna or a directional antenna. When an omnidirectional antenna is used at the base station the base station constitutes one cell. Respectively, when a directional antenna is used at the base station the base station constitutes more than one cell, one for each sector of the directional antenna. The radiation pattern of the antenna  16  at least partly defines the coverage area of the cell. In  FIGS. 4   a  and  4   b  examples of the radiation patterns of an omnidirectional antenna and a directional antenna are depicted, respectively. When the wireless communication device MS moves from one cell to another cell a handover is performed to change the serving cell for the wireless communication device MS. Thus, it may happen that the base station BS, BS′, BS″ remains the same although the serving cell changes. 
     In a positioning receiver PR according to  FIG. 2 , a signal to be received via a first antenna  1  is converted for example to an intermediate frequency in the converter block  2 . The signal converted to the intermediate frequency comprises two components known as such: I and Q components, with a phase difference of approximately 90° therebetween. These analog signal components converted to the intermediate frequency are digitized. During the digitizing of the signal components, for example at least one sample is taken of each chip, i.e. at least 1,023,000 samples per second are thus taken in the GPS system. Furthermore, the I and Q components of the digitized signal are multiplied by a signal formed by a first numerically controlled oscillator (NCO)  5 . The purpose of the signal of this first numerically controlled oscillator  5  is to correct the frequency deviation caused by the Doppler shift and a frequency error of the local oscillator (not shown) of the receiver. The signals formed in the converter block  2  are preferably led to a digital signal processor  3 . Reference codes ref(k) corresponding to the codes used in code modulation of the satellites to be received at a time are generated in block  16 . Using e.g. this reference code ref(k), the positioning receiver PR attempts to find the code phase and frequency deviation of the signal of the satellite received on each receiving channel, to be used in the operations after the synchronization. 
     A control block  7  is used for controlling inter alia a code phase detector  9  which is used for adjusting the frequency of the numerically controlled oscillator  5 , if necessary. The synchronization will not be described in more detail in this specification, since it is prior art known per se. If necessary, after the receiving channel has been synchronized to the signal of a satellite SV 1 , SV 2 , SV 3 , SV 4 , the demodulation and storage of the navigation information transmitted in the signal can be initiated, if possible. The digital signal processor  3  stores navigation information for example in a memory  4 . In the method according to the disclosed embodiments, it is not necessary to modulate and store this navigation information, but the positioning receiver PR has to define the chip and epoch of the signals received from the satellites. 
     The wireless communication device MS also comprises mobile communication means MT for performing the functions of the wireless communication device, such as a second antenna  10 , a radio part  11 , audio means, such as a codec  14   a , a speaker  14   b  and a microphone  14   c , a display  12 , and a keypad  13 . However, it is obvious that a part of the functional blocks of the wireless communication device MS can be common to both the positioning receiver PR and the mobile communication means MT. For example the display  12  and the keypad  13  can be used in some applications also in connection with the positioning receiver PR, for example to show the result of the performed positioning. The control block  7  can also be common both for the control of the positioning receiver PR and the mobile communication means MT, or one or a plurality of individual control blocks can be arranged for both units. 
     In the mobile communication network MN every cell has an individual identifier CGI (Cell Global Identity). For example in the GSM system the cell global identity CGI usually comprises the following four parts:
         mobile country code MCC,   mobile network code MNC,   location area code LAC, and   cell identity Cl.       

     When the base station BS, BS′, BS″ has an omnidirectional antenna the coverage area of the base station constitutes one cell. However, base stations BS, BS′, BS″ in which directional antennas are used each sector of the directional antenna can define one cell. Thus, the base station BS, BS′, BS″ may in fact constitute more than one cell and each cell can be identified by the individual identifier CGI of the cell. 
     Thus, every cell can be identified on the basis of the cell global identity CGI of this cell. The cell global identity CGI also identifies the base station BS, BS′, BS″. However, it may happen that the cell global identity CGI is not totally available or is partly unreadable for some reasons. For example the cell identity CI is not available for the wireless communication device MS. In such a situation the wireless communication device MS cannot identify the cell but it may use the mobile country code MCC, the mobile network code MNC and/or the location area code LAC to get some estimate of the position of the wireless communication device. 
     The serving cell, that is the cell of the base station BS, BS′, BS″ through which the wireless communication device MS communicates with the mobile communication network MN at a time, transmits to the mobile communication device the cell global identity CGI of the serving cell. The cell global identity can be transmitted, for example, via a control channel of the mobile communication network MN. Thus, inter alfa in connection with a cell handover the wireless communication device MN can detect the cell change on the basis of the change in the cell global identity CGI (block  500  in  FIG. 5   a ) if the cell identity CI is available. In the method according to the disclosed embodiments the location area code LAC and also the mobile country code MCC and the mobile network code MNC of the cell global identity CGI are utilized in the following manner. In the wireless communication device MS the information transmitted by the base station BS, BS′, BS″ is received  501 , from which information inter alia on the cell global identity CGI or parts of it is found out. According to this identity it is detected  502  whether any information related to the position of this particular base station BS, BS′, BS″ is stored in the memory means  4 ,  8  of the wireless communication device. If no positioning data in accordance with the cell global identity or the location area code LAC is found in the memory means  4 ,  8 , the necessary positioning data is searched  504  from the database DB. In this embodiment the positioning data is stored in the mobile communication network MN, for example in each base station BS, BS′, BS″, in the mobile switching center MSC, or in the GPRS packet network. The wireless communication device MS transmits  503  to the mobile communication network MN a request to transmit the positioning data of the base station in question to the wireless communication device MS. It is not necessary to transmit the cell global identity of the base station in the interrogation message because the mobile communication network knows through which base station the connection to the wireless communication device is arranged at a time. As a response, the base station transmits  505  the positioning data of the base station and, if necessary, other auxiliary data in accordance with the satellite positioning system as well, such as the orbit parameters and the almanac data of the satellites. The transmitted information is received in the wireless communication device MS, wherein at least the positioning data of the base station is stored  506  in the memory means  4 ,  8 . In addition, the received parts of the cell global identity CGI of the base station are stored, which can then be used as an index to the positioning data stored into the memory means  4 ,  8 . 
     If the wireless communication device MS does not receive all the fields of the cell global identity CGI or if the base station BS does not for some reason send all of them, the wireless communication device MS checks which parts of the global cell identity GCI the wireless communication device MS has received. If the received parts contain the location area code LAC, the mobile country code MCC and the mobile network code MNC, the wireless communication device MS uses these data to determine the reference position to be used in the positioning process. 
     The location area code LAC determines the area in which the cell and the respective base station BS is located. More than one cell and base station BS can contain the same location area code LAC wherein the position information, which the location area code LAC gives may not be so accurate than what is available if the cell identity CI were known, but the position information can still be accurate enough to help the positioning receiver PR perform more accurate positioning. Even a coarse reference position can be helpful for starting signal acquisition in a satellite positioning receiver, if the receiver would not have otherwise any information about the current position in the globe. Therefore, the position information achievable by using the location area code LAC may speed up the operation of the positioning receiver PR in finding more accurate position information of the wireless communication device MS. 
     The position relating to the location area code LAC can be determined by a table, for example, which is defined by the operator of the mobile communication network. The same location area code may mean different positions in different mobile communication networks. Therefore, the mobile country code MCC and the mobile network code MNC are used to find out the correct interpretation of the location area code LAC. The interpretation table or other data for determining the position data on the basis of the location area code LAC may be loadable via a base station BS or it may have been stored into the wireless communication device MS. 
     When the wireless communication device MS has determined the position data on the basis of the location area code LAC, the position of the reference point can be used by the positioning receiver PR to perform more accurate positioning  508 . 
     An uncertainty measure can also be estimated, which relates to the size of location area. The location area includes all the cells (base stations) having the same location area code LAC. Because more than one cell can have the same location area code LAC, the uncertainty measure can be greater when using only the location area code LAC compared to situations in which also the cell identity CI is available. 
     The wireless communication device MS can have previously received and stored identity information of the same or another cell. The wireless communication device MS can then use  507  the previously stored mobile country code MCC, the mobile network code MNC and the location area code LAC if the cell global identity CGI is not available from the current base station. In many cases it can be assumed that the location of the wireless communication device has not changed too much since the previous time when wireless communication device MS was able to receive at least the mobile country code MCC, the mobile network code MNC and the location area code LAC. Therefore, the previously received location area code LAC may give accurate enough estimation of the position for the reference point to assist the positioning receiver PR perform the positioning. 
     In some situations it will be sufficient that only the location area code LAC is received from the serving cell. The reason for that is that the mobile country code MCC remains the same in the same country and also the mobile network code MNC usually remains the same when the wireless communication device MS is operating inside the network coverage area. However, it may happen that if the wireless communication device MS is not in its “home” country it may happen that the serving cell varies between cells of different operators. This affects that the mobile network code MNC also varies when the cell of another operator becomes the serving cell. 
     After the position of the serving cell is known in the wireless communication device MS, it is possible to utilize this positioning data of the respective base station in the positioning by setting it as the default position of the positioning receiver. According to this positioning data the wireless communication device is informed of the approximate position of the wireless communication device on the globe. On the basis of the time data transmitted by the base station it is possible to estimate in the wireless communication device which satellites are above the horizon, that is, visible as seen from the wireless communication device. Next, the wireless communication device can attempt to search for the signals of these visible satellites. Positioning can thus be performed in a manner known as such by first using this default position and by precisioning the positioning on the basis of the signals received from the satellites SV 1  to SV 4 . Later in this specification there will be described an example on how said position of a known reference point can be utilized in the positioning. 
     As a wireless communication device MS moves from the coverage area of a cell to the coverage area of another cell (e.g. in  FIG. 1  from the coverage area of a first base station BS to the range of a second base station BS&#39;), the afore-mentioned detection of the cell data stored in the storage means  4 ,  8  is performed in connection with the handover to detect whether any information on this second base station is stored in the wireless communication device MS, or whether the information should be retrieved from the database DB. Next, preferably the position of this second base station BS′, if available, is used as the default position of the wireless communication device MS in the positioning of the wireless communication device MS. If the cell identity CI of the second serving base station BS&#39; is not available then the location area code LAC of the second serving base station BS&#39; is used to determine the default position of the wireless communication device MS. As it was previously mentioned, it may happen that the location area code LAC does not change although the change in serving base station changes. 
     On the other hand, if there is a change in the location area code LAC because the wireless communication device MS moved from the coverage area of one base station BS to the coverage area of a second base station BS′, it is possible to use at this stage for example some other positioning data calculated on the basis of these two base stations, for example the midpoint between centers of areas defined by these two location area codes, as the default position of the wireless communication device MS. In this case, it is very probable that in connection with a handover the wireless communication device MS is positioned closer to this midpoint than to either of the base stations BS, BS&#39;. In this manner it is possible in some situations to faster achieve the wished positioning precision in the positioning receiver MS. 
     In some mobile communication systems, such as systems based on the CDMA, the wireless communication device MS can simultaneously communicate with more than one base station. Thus, as the default position of the wireless communication device MS can be used for example the positioning data calculated according to the position of those base stations that communicate simultaneously with the wireless communication device MS, if available. For example, if three base stations are used in the communication, e.g. the geometric midpoint, which can be used as the default position, is calculated on the basis of the positioning data of these three base stations. It is obvious that the motion data of the wireless communication device MS can also be used in the definition of the default position, that is, in accordance with the previously performed positionings the direction of movement of the wireless communication device MS is estimated and, on the basis of this, attempt is made to select the base station positioned close to the direction of movement of the wireless communication device MS, e.g. the wireless communication device is moving towards one of these base stations. 
     It is also possible to use other positioning data than the position of the base station as the default position of the wireless communication device MS. For example, if the base station comprises more than one cell, a reference point (e.g. a center point) of the cell can be evaluated for example on the basis of the positioning information stored in the database DB of the cell in question. It is also possible that the reference point is evaluated on the basis of the radiation pattern of the sector of the antenna which forms the cell in question. 
     In the above-described method according to an example embodiment it was presumed that the database used in the positioning data of the base stations is located in the mobile communication network, wherein the positioning data can be retrieved from the mobile communication network. The positioning data can also be transmitted enciphered. In this case an enciphering code required in the deciphering is retrieved to the wireless communication device MS from the mobile communication network, for example as point-to-point messages. This kind of messaging is usually subject to a charge to the user of the wireless communication device, wherein the user has to pay for the positioning data of the location area codes LAC that he/she has retrieved. However, by using the method according to an embodiment it is possible to decrease the need to retrieve auxiliary data, because the auxiliary data is stored in the memory means  4 ,  8  of the positioning receiver at the stage when new or changed data is received. 
     In the following, a method according to another example embodiment is described, in which auxiliary data is not retrieved from the mobile communication network, but from a database DB provided elsewhere, e.g. in the Internet network I.  FIG. 3  illustrates, in a reduced chart, a system in which this method according to a second example embodiment can be applied and  FIG. 5   b  depicts the second example embodiment of the disclosed embodiments as a simplified flow diagram. The database DB is located in such an information network or information system, which can communicate with a mobile communication device. The database DB is arranged for example in a database server S that is connected to communicate with the Internet network I. Identification data and position information relating to location area codes LAC are stored in the database DB. Through the database server S possibly other auxiliary data of the satellite positioning system can also be downloaded to the wireless communication device MS. 
     The communication connection set up from the wireless communication device MS can be for example a connection according to a so-called WAP protocol, by means of which the wireless communication device MS can be used for example for browsing information on the Internet network, inter alia www pages of companies and other sites where data is stored. In this case, from the memory means  4 ,  8  of the wireless communication device MS the cell position data is retrieved  511 , in accordance with which it is possible to communicate with said database server S that maintains the database DB for the positioning data of the cells. In addition to this position data the cell global identifier CGI of the cell or part of it is detected, a message is formed  512 , for example as a message or messages according to said WAP protocol, and transmitted  513  to the mobile communication network, where the messages are converted for example to messages according to the Internet Protocol and transmitted further to the Internet network in a manner known as such. The identifier of the wireless communication device MS that has transmitted the message is also added to the messages, wherein the response messages can be transmitted back to the communication device that has transmitted the interrogation message. Another example that can be mentioned in this context is the use of short messages (SM) in transmission of positioning data and possible auxiliary data. 
     Setting up a communication connection with the database server S can in some situations also be performed for example with a wireless local area network WLAN. Thus, the wireless communication device MS creates a communication connection with a wireless local area network, which is situated in the vicinity of a wireless communication device MS and through which for example the Internet network I can be contacted. 
     In the Internet network the messages are transmitted to the target address, in this case to the database server S in which said database DB is located, by using the message transmission mechanisms of the Internet network, in a manner known as such. The database server interprets the arrived message and detects  514 , on the basis of the cell global identity CGI of the cell that has been transmitted in the message, the information about this cell from the database DB. Next, the database server creates a response message comprising said positioning data, if positioning data related to said cell are stored in the database DB. Subsequently, the response message is transmitted  515  from the database server S to the Internet network I, where the message is routed to the mobile communication network MN. The mobile communication network transfers the response message to the base station which is communicating with the wireless communication device at the time. The base station sends the response message to the wireless communication device MS. Next, in the wireless communication device MS the received positioning data is stored  516  into the memory means  4 ,  8 , and the positioning is performed  517 , if necessary. 
     In this method according to a second example embodiment the default position of the wireless communication device MS is also defined according to the positioning data of one or a plurality of cells/base stations or location area codes LAC. When the wireless communication device MS moves to the range of a cell, an interrogation message can be transmitted from the wireless communication device requesting the positioning data of said cell to be transmitted to the wireless communication device, in case the positioning data are not yet stored in the wireless communication device MS. This interrogation message is transferred to the database server S, where it is detected whether the information related to said base station is found in the database DB. If the data are found in the database DB, the data are transmitted to the wireless communication device MS. The positioning can thereafter be performed in the positioning receiver PR by using this positioning data of the cell as the default position or using the position information relating to the location area code LAC if the position of the cell is not available. In the same context, positioning data of several cells and/or base stations BS, BS′, BS″ can be transmitted, and for example the database server S finds out which cells/base stations are positioned in the vicinity of said cell/base station, e.g. the base station(s) of the adjacent cells. In this case the database server transmits to the wireless communication device MS also positioning data of these cells/base stations positioned close to said cell/base station. However, if the cell identity CI is not available, the transmission of positioning data of these different cells/base stations may be restricted to situations in which the location area codes of different base stations differ from each other. This arrangement provides the advantage that when the wireless communication device MS is moving from the range of one cell/base station to the range of a second cell/base station the wireless communication device MS already has the positioning data of this second cell/base station. 
     Even if an existing mobile communication network MN can also be utilized in the transfer of the positioning data of the cells/base stations BS, BS′, BS″ in this embodiment, the positioning data are retrieved from outside the mobile communication network MN. The transfer service of such positioning data of the cells/base stations BS, BS′, BS″ can be arranged to be independent of operators. Thus, service providers can themselves price the service and, on the other hand, limit the use of the service if necessary. A service provider can be for example an Internet service provider, that gives preferably to registered users the possibility to retrieve information from the database DB. 
     In practice, the database DB can be decentralized, wherein a plurality of database servers S of an embodiment can be located in different geographical locations. Thus, when a user arrives close to such a database server S, a communication connection can be set up between the database server S and the wireless communication device MS, for example by using a local communication method, such as a so-called Bluetooth or WLAN connection. Through this connection it is possible to transfer for example the positioning data of one or a plurality of reference points of the neighboring area to the wireless communication device MS. 
     In addition to the positioning data of the cell/base station the default position of the wireless communication device MS can also in some embodiments be the WLAN access point, the positioning data of which is known and the signals transmitted by which have the necessary information for the identification of the access point. The positioning data of other short-range access points or the like, such as the Bluetooth system, can be applied in connection with the method of the disclosed embodiments if the location of these access points is known and the access points can be identified in the wireless communication devices. 
     In some cases (for example Monaco) the country code expresses a sufficiently small geographical area in view of the positioning according to the disclosed embodiments. The mobile network code MNC can also in some cases indicate the default position of the wireless communication device MS at a sufficient precision. 
     As was previously mentioned the directional pattern of the base station antenna is not necessarily omnidirectional, but it can be directed to some direction. Antenna structures are also known in which the direction of the directional pattern can be changed to a wished direction, for example towards a wireless communication device in order to improve the signal-to-noise ratio in this direction. The directional pattern can also be composed of a plurality of segments directed to different directions. In these kind of situations the default position used is not necessarily the position defined by the location area code LAC, but a point within the location area determined according to the directional pattern of the antenna of the base station, such as the center of the directional pattern. This can is some systems be calculated for example in such a manner that the parameters of the directional pattern are transmitted from the mobile communication network to the wireless communication device, or the calculation is performed in the mobile communication network from which the location obtained as a result of the calculation is transmitted to the wireless communication device. 
     In the system according to a second example embodiment of the disclosed embodiments the information of the database DB can be updated  509 ,  518  for example as follows. When a wireless communication device MS has successfully determined its position and is positioned inside the location area of a cell of a base station BS, or BS′, or BS″ (Note: MS is communicating actively only with one BS, but it has knowledge about the neighbouring stations) and connected to this base station, the wireless communication device transmits the information on its location, the location area code LAC, the mobile country code MCC and the mobile network code MNC of the cell global identity CGI of the cell and advantageously also the information on timing advance TA, for example via the mobile communication network MN, to said database server S in which the database DB is located. Thus, the database server S updates information of said cell in the database DB according to the positioning data transmitted from the wireless communication device MS. However, this data is not necessarily the precise position of the base station, because it is, nevertheless, not probable that the wireless communication device MS would be positioned exactly at the base station and because more than one base station may have the same location area code LAC. However, these positioning data located in the coverage area of the cell of the base station can be used as reference points, because these reference points are, nevertheless, relatively close to the base station. In this case, a group of positioning data is stored into the database with the location area code LAC, the mobile country code MCC and the mobile network code MNC of the cell global identity CGI of said cell, which data can be transmitted to the wireless communication device MS that has requested for the positioning data. When a plurality of wireless communication devices having a positioning receiver perform positioning within the location area and transmit the information on their position to the database server it is thus possible, on the basis of a set of data, to calculate e.g. a mean value, a geometric center or the like, which is sent as the reference point to the wireless communication device MS. In this case the position data of the BS&#39;s can also be created by using the system. Moreover, this arrangement does not require that the operator of the mobile communication network would be involved in the system maintenance, that is, the system is operator independent. 
     Said advance timing data can be used in the database server S in order to estimate how close to said base station BS, BS′, BS″ the wireless communication device MS is located. The smaller the advance timing the closer to the base station the wireless communication device is normally located. 
     Wireless communication devices can transmit said positioning data and other information to the database server S for example at regular intervals, or when a predetermined criterion is fulfilled, for example when the location area code LAC is changed. Additionally, a local database containing information on the position of the databases can be created in the wireless communication device MS. Thus, the wireless communication device can transmit the positioning data of the base stations that it has stored to a second wireless communication device and/or to a database server, for example as short messages, wherein these data can be used also in the positioning functions of this second wireless communication device and, on the other hand, the database DB of the database server is updated. The transmission of data to the second wireless communication device can be initiated e.g. by the user of the wireless communication device. 
     When describing above some embodiments of the disclosed embodiments it was noted that the wireless communication device makes a request on the positioning data of the cell while the wireless communication device is located within the range of a certain cell. The disclosed embodiments can also be applied in such a manner that the wireless communication device performs an information request for example when the positioning receiver PR and/or the mobile communication means MT are switched on. In this case, the information that relates for example to the position of cells/base stations BS, BS′, BS″ in a certain geographical area can be transmitted to the wireless communication device MS, and the information can be used without a delay at the stage when the wireless communication device MS is moving within the range of the mobile communication network. Thus, it is not necessary to waste time for the transfer of base station data, but the information already exists stored in the memory means  8  of the wireless communication device. This, in its part, cuts down the power consumption of the wireless communication device MS and also decreases the load to the mobile communication network MN, because the need for data transfer is diminished. It is obvious that this alternative also allows to detect which base station data is already stored in the wireless communication device MS, whereby it is not necessary to transfer these data again, unless there has been changes in the data. 
     By using the above-described method, the positioning can be performed also in poor signaling conditions. Also, no precise time data is required if the position of the reference point is known. Moreover, the transmission of auxiliary data is not dependent on the positioning services provided by the operator. 
     In the following, an example is given on how said positioning data defined on the basis of the location area code LAC can be used in the positioning of a wireless communication device. In the definition of time of transmission ToT according to the formula (1), only the number and code phase T chip   j (k) of the chips received after the epoch change can be defined in a situation in which the strength of the signal to be received is weak. By means of this parameter it is possible to measure only the differences on the chip level (&lt;1 ms) in the signals of different satellites SV 1 , SV 2 , SV 3 , SV 4 , because the same code is repeated at intervals of one epoch (=1 ms). Because the distance between each satellite and receiver can differ significantly, there may be large differences, even differences over 10 ms, in the times of flight of signals received from different satellites. Thus, the definition of the differences on the chip level is not sufficient. One millisecond in time represents a distance of approximately 300 km when the signal propagates substantially at the speed of light. Correspondingly, one chip (approximately 1 μs=1 ms/1023) equals approximately 300 meters. 
     In such a situation the differences of milliseconds have to be defined in different receiving channels on the basis of the distances between the satellites SV 1 , SV 2 , SV 3 , SV 4  and the wireless communication device MS. However, generally the estimated location of the wireless communication device MS is not necessarily known. Instead, in the systems according to  FIGS. 1 and 3  it is possible to estimate the location of the wireless communication device MS by using a selected reference point, such as the location of the base station BS. Thus, the positioning data of the base station BS, BS′, BS″, the orbit parameters of the satellites SV 1 , SV 2 , SV 3 , SV 4 , and the time data stored into the memory means  4 ,  8  can be used in the wireless communication device MS. In the GSM mobile communication system the distance between the wireless communication device and the base station with which the wireless communication device is communicating at the time is generally about 30 kilometers at the most. In this case it can be assumed that the wireless communication device MS is located within a radius of 30 kilometers from the location of the base station BS. Thus, the time of flight of the signal transmitted by the satellite from the satellite to the base station and the time of flight from the satellite to the wireless communication device differ approximately 100 at the most. The distance between the wireless communication device MS and the base station BS in view of the times of flight does not change to a significant degree either within the base station BS range, wherein it can be assumed that there is a difference of less than one millisecond in the reception times of the same signal in the wireless communication device MS and in the base station BS. Thus, the distance can be calculated at an accuracy of one millisecond as follows: 
                         N   ^     ms   j     ⁡     (   k   )       =     ⌈                  x   _     SV   j     ⁡     (   k   )       -         x   ^     _     u            c     ⌉             (   2   )               
in which ┌.┐ indicates rounding up to the nearest integer, and the line above the variable indicates that it is a vector. In this case, the same result is obtained both in view of the base station BS and in view of the wireless communication device MS. It has been possible to transmit from the base station BS a sort of estimate of the GPS time {circumflex over (T)} GPS  to the wireless communication device MS. If this GPS time data is very precise, it is also possible to calculate the position of the satellites very accurately, wherein errors in positioning can mainly be caused by the distance between the wireless communication device MS and the base station BS, which is not necessarily known. Even if no time data were transmitted from the base station to the wireless communication device, the wireless communication device contains some kind of an estimation of the GPS time {circumflex over (T)} GPS , e.g. the time of the reference clock  15 , which, at this stage, can be several seconds, even minutes fast or slow.
 
     After the distance {circumflex over (N)} ms   j (k) in time has been calculated in milliseconds for all receiving channels according to formula 2, it is possible to estimate the times of transmission of the signals according to the following formula.
 
 {circumflex over (T)}   ToT   j ( k )= T   GPS   j ( k )− {circumflex over (N)}   ms   j ( k )+ T   chip   j ( k )  (3)
 
     Any measured value of the time of transmission of the satellite signal can be selected as the reference time. The time of the satellite at the time of reception, i.e. the GPS time, {circumflex over (T)} GPS (k), can thereafter be estimated by supplementing the time of transmission ToT attained on the basis of the measurement selected as reference time with the estimated transfer delay, i.e. the time of flight of the signal from the satellite to the receiver. The estimated transfer delay is usually 78 ms.
 
 {circumflex over (T)}   GPS ( k )= {circumflex over (T)}   ToT   j ( k )+0.078  (4)
 
     After the GPS time has been preliminarily defined, it is possible to define the measured pseudoranges by subtracting the calculated times of transmission of the signal from the estimated GPS time and multiplying the result with the speed of light in the following manner:
 
ρ m   k =( {circumflex over (T)}   GPS   −{circumflex over (T)}   ToT   j ( k )) c   (5)
 
     in which c indicates the speed of light in a vacuum, the superscript k indicates from which satellite signal the measured value comes from (e.g. 1 to 4) and the subindex m indicates that the pseudorange is a measured pseudorange, not an estimated one. 
     The estimated pseudoranges are calculated in relation to the location  {circumflex over (x)}   u  of the wireless communication device MS and to the locations  x   SV   j ({circumflex over (T)} GPS ) of the satellites at an estimated time of transmission ToT. The selected default location of the wireless communication device is the location defined on the basis of the location area code LAC of the base station BS which is communicating with the wireless communication device at the time. The locations of the satellites are calculated as a function of time by means of equations known as such. Here, for the sake of simplicity, the estimated pseudoranges are expressed by means of the following formula:
 
ρ p   k   =f ( {circumflex over (T)}   GPS   ,  {circumflex over (x)}     u   (6)
 
     to indicate that the estimated pseudoranges are based solely on the estimated GPS time and to the estimated location of the wireless communication device. In formula (6), the term f represents a (strongly) non-linear function, the subindex p indicates that this is estimation, and  {circumflex over (x)}   u  is the estimated location of the wireless communication device, in which the line above the variable indicates that it is a vector. 
     The location  {circumflex over (x)}   u  of the wireless communication device and the difference between the estimated GPS time and the real GPS time can be calculated iteratively for example by the least mean squares method. This method is known as such. In the least mean squares method the following set of equations is solved:
 
ρ m   k   =∥  x     SV   j ( k )−  {circumflex over (x)}   u   ∥+ct   u   ,j= 1  . . . M   (7)
 
     The aim is to find such location data  {circumflex over (x)}   u  and time error Δt u , which best suit to a number M of measurements. The solution of this set of equations is straightforward as such: 
                     [           Δ   ⁢           ⁢         x   ^     _     u                 Δ   ⁢           ⁢     t   u             ]     =         (       H   T     ⁢   H     )       -   1       ⁢     H   T     ⁢   Δ   ⁢           ⁢     ρ   _               (   8   )               
in which
 
Δ  ρ =  ρ   m   j −  ρ   p   j   ,j= 1  . . . M   (9)
 
Δ  {circumflex over (x)}   u  is the correction vector of the location,
 
Δt u  is the correction of the time error,
 
and
 
H=the linearized Jacob&#39;s matrix of the pseudoranges estimated in point  {circumflex over (x)}   u .
 
     The solution given by the least mean squares method is optimal with respect to the sum of squared errors (SSE). This sum of squared errors can be estimated by means of a formula: 
     
       
         
           
             
               
                 
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     By rearranging the terms and using slightly different expressions for the terms, it is possible to write the formula (7) in the following manner:
 
ρ m   j ( T   GPS )=∥  x   SV   j ( {circumflex over (T)}   GPS )−   {circumflex over (x)}     u   ∥+ct   u   ,j= 1  . . . M   (11)
 
     The parentheses indicate that the term in question is based on the parameter presented in the parentheses. When such a presentation mode is used, it can clearly be seen that the measured pseudoranges are functions of the real GPS time and the rest of them are functions of the estimated GPS time. Thus, the time difference between the estimated GPS time and the actual GPS time can be calculated according to the measurements, and in this case it is also possible to synchronize the receiver to the actual GPS time. The time error of the receiver can here be expressed as the time difference according to the following formula:
 
Δ t   u   ≅ΔT=T   GPS − GPS   −{circumflex over (T)}   GPS   (12)
 
     in which Δt u  represents the estimated time (or calculated) clock error and ΔT is the actual clock error between the estimated time, {circumflex over (T)} GPS , and the real GPS time. 
     It is now possible to use this time difference in a wireless communication device MS to correct the estimated GPS time, whereafter it is possible to better calculate the satellite locations in order to perform positioning particularly in a situation where the calculated time difference is significant. 
     The calculation of distance as described above in formula 2 can in some situations cause rounding errors. For example, if the distance in milliseconds prior to rounding down is close to the next integer and the wireless communication device MS is close to a base station BS, an error closing to one millisecond can occur. This can mean an error of up to 300 km when calculating the distance between the wireless communication device and the satellite, which distorts the positioning to a significant degree. In some cases, this error can be detected from the height data calculated for the position of the wireless communication device, which height data indicates that the wireless communication device is located at an altitude of tens of kilometers or deep below the ground. In this case, the error is easy to verify. However, this is not always the case. The method according to an example embodiment utilizes the information that the wireless communication device MS is close to the base station BS, the position of which is known at a sufficient precision. In this manner, it is possible to set the limits within which the positioning data calculated for the wireless communication device MS should be. This limit is in the direction of the earth&#39;s surface e.g. a base-station-centered circle having a radius of approximately 30-50 km. Correspondingly, appropriate limit values can be defined in the elevation. If the calculation gives to the wireless communication device MS a positioning data that is outside said limit, it can be assumed that the rounding has caused an error. Subsequently, it is determined at which satellite/satellites the error has occurred. This can be performed by examining the remainders of the values calculated with the formula 2. 
     By using this method it is possible to fast detect the possible errors caused by rounding and to perform the necessary corrective actions. Another method for detection of rounding errors is to examine the error values calculated with formula 9 and if a value differs clearly from the other values (is significantly larger), the rounding has probably caused the error in the calculation of the distance of the satellite corresponding to said value. 
     The disclosed embodiments can be implemented at least partly as a software, for example as machine executable steps in a program code of the control block  7  and/or the digital signal processor  3 . Some parts of the software can also be implemented in the mobile communication network MN and/or the server S. 
     The user of the wireless communication device may be invoiced of the assistance data (e.g. the location area code LAC) transmitted to the wireless communication device for the positioning. 
     It is obvious that the disclosed embodiments is not limited solely to the above-presented embodiments, but it can be modified within the scope of the appended claims.