MXPA01001005A - Improvements in downlink observed time difference measurements - Google Patents

Abstract

A mobile communication station in (MS1) a wireless communication network is used to measure the respective times of arrival of radio signals respectively transmitted by a plurality of radio transmitters (23, 28) in the network. The mobile communication station is provided with real time difference information indicative (RTDs) of differences between a time base (60) used by a radio transmitter (23) serving the mobile communication station and respective time bases used by the other radio transmitters. The mobile communication station determines, in response to the real time difference information and relative to the time base used by the radio transmittter serving the mobile communication station, a plurality of points in time at which the respective radio signals are expected to arrive at the mobile communication station. For each radio signal, the mobile communication station monitors for arrival of the radio signal during a period of time after the point in time at which the radio signal is expected to arrive.

Description

"IMPROVEMENTS IN TIME DIFFERENCE MEASURES OBSERVED IN DESCENDING LINK" This application is a continuation in part of the United States Patent Serial Number 09 / 131,150 (Touch of Attorney Number 34645-423) filed on August 7, 1998.

FIELD OF THE INVENTION The invention relates generally to locating the position of a mobile communication unit in a wireless communication network and, more particularly, to making time difference measurements observed in the downlink.

BACKGROUND OF THE INVENTION The ability to locate the position of a mobile communication unit operating in a wireless communication system (e.g., a cellular communication system) provides many well-known advantages. Exemplary uses of this position location capability include security applications, emergency response applications, and route guidance applications. Several known techniques for providing the location of position involve the measurement of certain characteristics of the communication signals, such as the arrival time (TOA), the round trip delay, or the arrival angle of a communication signal. Some of these techniques can be further divided into uplink or downlink approaches. In the uplink category, a base transceiver station (BTS) or other receiver performs measurements on the communication signals originating in a mobile communication unit (or mobile station). In downlink approaches, the mobile station carries out measurements on signals originating from base transceiver stations or other transmitters. An example of a downlink technique for locating the position of a mobile station is the observed time difference technique (OTD). This technique will now be described with respect to the Global System for Mobile Communications (GSM), which is exemplary of a cellular communication system where the techniques of time difference observed in the downlink are applicable. The OTD technique is implemented, for example, by causing the mobile station to measure the time difference between the arrival times of the signals of - - selected radio transmitted from different base transceiver stations. Assuming the geometry shown in Figure 1, and assuming further that two signals are transmitted simultaneously from the base transceiver stations, BTS1 and BTS2, and let TI and T2 represent the arrival times of the respective signals in the mobile station, then the observed time difference OTD is provided by the following equation: TI - T2 = (di - d2) / c, (Equation 1) where di and d2 are the respective distances from BTSl and BTS2 to the mobile station. The BTS1 and BTS2 locations are known, and the possible locations of the mobile station are described by the hyperbola 15 shown in Figure 1. By combining the measurements of at least three base transceiver stations, a position calculation can be obtained for the mobile station. Most conventional cellular communication systems (including GSM systems) are asynchronous, that is, each base transceiver station uses its own internal clock reference to generate the armature structure and time interval. Therefore, the reinforcement structures of the different base transceiver stations will tend to move in time one relative to the other, because the clocks t.afefet ~., x »* z r # £ .- & * are not perfectly stable. As a consequence, an OTD measure will not be really meaningful to locate the position of a mobile station unless the time differences between the base transceiver stations being used are known. This difference, which is often referred to as the real time difference or RTD, represents the real difference in absolute time between the transmission of the respective signals (eg, respective synchronization bursts in GSM) from the respective base transceiver stations, whose signals would be transmitted simultaneously if the reinforcement structures of the base transceiver stations were perfectly synchronized. Among several possible approaches to determine the real time difference RTD between the base transceiver stations, two conventional examples are: absolute time stamping of the respective base transceiver stations; and the use of stationary reference mobile stations placed at known positions. In the last example, the reference mobile station measures the downlink signals sent from several base transceiver stations. Because the respective distances between the various base transceiver stations and the stationary reference mobile station are known, the expected time difference in the arrival times of the respective signals from the base transceiver stations can be easily calculated. The real time difference RTD between the base transceiver stations is simply the difference between the expected time difference of arrival and the observed time difference of the arrival actually observed in the reference mobile station. The reference mobile station can carry out the downlink time of the arrival measures and report it to a mobile location node in the network so that the network can maintain an updated record of the RTDs. The techniques based on known OTD methods are very similar to the procedures conventionally used by the mobile stations to synchronize to a service base transceiver station and make measurements on a number of neighboring base transceiver stations as instructed by the service cell (as in operations of mobile stations not helped by hand). The mobile station needs to know which of the base transceiver stations will be monitored for OTD measurements. This information can typically be provided in conventional system information messages emitted in the cell, for example on a BCCH frequency (broadcast control channels) in a GSM cell. This system information typically includes a list of frequencies of neighboring cells to be measured. The mobile station scans the designated frequencies to detect a frequency correction burst which is an easily identifiable burst appearing approximately every 50 s in GSM. After successful detection of a frequency correction burst, the mobile station knows that in GSM the next frame will contain a sync burst SB. The sync burst SB contains the Identity Code of the Base Station (BSIC) and the information indicative of the armor number of the current armature where the sync burst SB is occurring. The mobile station measures the arrival time of the synchronization burst SB of the mobile station with respect to the time of the service cell proper of the mobile station. Since the mobile station now knows the frame structure of the neighboring base transceiver station in relation to its own service base transceiver station time, it is possible to repeat the time of the arrival measures to improve the accuracy. This procedure is repeated until all frequencies (ie, all BTSs) in the list have been measured. The observed time difference values recorded by the mobile station are then transferred to a location node of the mobile station in the cellular system, whose node carries out the determination of the position based on the time difference values observed, the actual time difference values and the geographic locations of the base transceiver stations. Because the mobile station does not know when the frequency correction burst (and hence the next SB sync burst) will appear, the brute force method described above, namely the supervision for the burst of Frequency correction, should be used. The time required to capture a sync burst will depend on the measurement mode. OTD measurements can be made, for example, when the call set-up is being carried out in GSM SDCCH (Dedicated Control Channel that is kept alone), or during empty armors when the mobile station is in a call mode, or during the interruption of conversation. For example, if the mobile station makes the measurements in the call mode, then the mobile station can only make measurements during empty armatures that conventionally occur in GSM systems every 120 ms. The probability that a specific synchronization burst appears within the empty armature is approximately 1 to 10, because the synchronization burst occurs conventionally every ten armor in GSM. Correspondingly, on average, 5 unoccupied armor will be needed, meaning 0.6 second per base transceiver station. Thus, if it is desired to measure at least 6 neighboring base transceiver stations, an average measurement time of 3 or 4 seconds will be required which can be prohibitively prolonged in many applications. The mobile station is guaranteed to have the sync burst SB measured if the mobile station seals and stores all signals (eg, all signals on the BCCH frequency of BTS in GSM) during 10 consecutive frames. However, providing the mobile station with memory and computing capacity to capture (and then process) all the signal information in 10 consecutive armatures is disadvantageously complicated. In addition, in areas such as urban areas characterized by high levels of interference, and in rural areas with large distances between base transceiver stations, the probability of detecting the SB burst may be unacceptably low, because the signals typically they will be characterized by low signal-to-noise ratios. Also due to the low signal-to-noise ratio, it will typically be very difficult to decode BSIC in the sync burst SB. The probability of taking the phantom escarpies instead of a sync burst SB is therefore disadvantageously increased in cases of the low signal-to-noise ratio. To locate a mobile station operating in a network using a Code Division Multiple Access (CDMA) air interface, a known OTD downlink approach, which has been proposed for normalization, uses some conventional cell search signals that they are provided in the CDMA network. This known downlink approach OTD will also be referred to below as the "proposed" approach or technique. Examples of conventional mobile communication systems employing a CDMA air interface include the so-called CDMA Broadband Systems (WCDMA) such as the ETSI Universal Mobile Telecommunication System (UMTS) and the IMT-2000 ITUs system. In these systems, the proposed OTD downlink placement technique is carried out by the mobile station during predetermined idle periods where the mobile station's base station transceiver ceases all transmissions in order to improve the capacity of the mobile station. mobile station to detect the signals transmitted by the neighboring base transceiver stations. Certain signals that are conventionally provided for cell search in the aforementioned CDMA systems, namely a first inquiry code (FSC) and a second inquiry code (SSC), are also used to carry out the downlink placement OTD . During the unoccupied period (s) of its service base transceiver station, a mobile station uses a matching filter which is matched to the first FSC inquiry code, just as it is done in conventional cell inquiry. The FSC is conventionally transmitted through all the base transceiver stations in the CDMA as mentioned above. The FSC is 256 long integrated circuits and is transmitted by each base transceiver station once in each time slot, that is, one tenth of the time (each time slot is 2,560 integrated circuits long). Each beam of the base transceiver station within the scale capable of being heard from the mobile station results in a peak at the output of the signal from the matching filter. In the conventional maximum detection process, the results of & .E. several time intervals are typically combined in a non-coherent manner to improve maximum detection. In conventional cell inquiry, the mobile station typically selects the most intense detected maximum. However, in the proposed OTD downlink placement technique, the arrival time (TOA) of each detected maximum is measured by the mobile station using conventional arrival time measurement techniques, so that the time differences observed ( OTDs) between the times of arrival of the respective maxima can be calculated. Each base transceiver station operating in the aforementioned CDMA networks also conventionally transmits a second associated inquiry code (SSC), which includes a set of 16 codes placed and transmitted in a certain order. The 16 codes are transmitted in sequence, one code per time interval, and each of the 16 codes is transmitted simultaneously with the FSC transmitted in that time interval. The aforementioned exemplary conventional CDMA systems have 16 timeslots per armature, so that the entire SSC pattern, including all 16 codes, is repeated once each armature. The SSC pattern, with its 16 codes placed in a certain order, specifies from a plurality of ? A - • > i. ' ^ ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡! ** fa, '• * *: < _ > .. .jm "possible code groups, a single code group associated with the base transceiver station Each code group includes a plurality of CDMA spread codes, and each base transceiver station uses one of the code codes dispersion from its associated code group For each base transceiver station within the scale capable of being heard, a mobile station carrying out the proposed OTD downlink placement technique correlates the maximum FSC temporal location of the transceiver station base with the 16 codes of its SSC pattern, just as it is done in the conventional cell inquiry.This correlation process typically uses the non-coherent combination.If the maximum correlates satisfactorily with the SSC pattern, then this result of the correlation indicates the group of code associated with the base transceiver station that produced the maximum FSC, the maximum FSC time (is deci r, the measured TOAs and / or OTDs) and the code group for each detected base transceiver station can then be made known to a mobile location node in the network, together with the power and quality measurements made during the process of Maximum FSC detection and during the FSC-SDC correlation process.

-JSaJfeHife jf ..j & tjt »» »The mobile location node already knows RTDs between base transceiver stations (conventionally obtained from, eg, absolute time stamping at base transceiver stations, or a mobile reference station) stationary), and in this way knows, within a scale of insecurity due to the unknown location of the mobile station, when the mobile station has received the maximum FSC of any given base transceiver station. Using this known RTD information, in combination with the aforementioned maximum time, the power and quality information received from the mobile station the mobile location node can identify the base transceiver station corresponding to each maximum FSC. For example, if the location of the mobile station is known within a 4.5 kilometer scale of insecurity, this scale corresponds to 64 integrated circuits. If the time frame of the framework of a candidate base transceiver station differs from another candidate base transceiver station in the same code group by more than the insecurity of 64 integrated circuits, then it can always be determined in the correct station of those base transceiver stations. Assuming that the time frame structure of each base transceiver station is random, the probability that any two base transceiver stations will have a time difference of the reinforcement structure between them, (ie, the real time difference RTD) of 64 integrated circuits or less is 64 / 40,960, due to that each armor includes 40,960 integrated circuits (16 time intervals x 2560 integrated circuits / time interval). In this way, the probability that a ridge produced by a base transceiver station can be distinguished from a ridge produced by another base transceiver station in the same code group is 99.8 percent. (1-64 / 40,960). The other 0.2 percent of situations can be handled through more advanced schemes, for example using power or energy measurements and selecting the base transceiver station that provides the best fit in a conventional location determination cost function. Once each maximum FSC has been matched to its corresponding base transceiver station, the TOA and / or OTD information can be used in combination with the known RTD information and the known geographic locations of the base transceiver stations, to determine the position graphic of the mobile station. The proposed downlink OTD placement technique has the following exemplary disadvantages. Because the time regulation of the neighboring base transceiver stations (which do not provide service) is completely unknown to the mobile station when the downlink process OTD begins, the mobile station must perform the correlation processing FSC-SSC during the whole of its unoccupied period (s) of the base transceiver station. In this way, the matched filter used to detect the maximum FSC must operate disadvantageously for the entire length of each unoccupied period. Also, because the codes in the SSC pattern are different in each time slot, the mobile station must correlate with several SSCs, and then economize the results for the non-coherent combination. This disadvantageously requires additional computing capacity and additional memory. Because the FSC-SSC correlation processing must sequentially track the maximum FSC detection, the acquisition time in the proposed OTD downlink approach may be disadvantageously prolonged. Likewise, urban areas characterized by high levels of interference, and rural areas with large distances between base transceiver stations, can make it difficult, and sometimes impossible, to detect FSC and SSC with sufficient probability.

Another problem ew that the codes associated with the different base transceiver stations have quite high cross-correlations, because the FSC codes are all identical and because the 16 codes of each SSC pattern represent a subset produced from a set of 17 unique codes. These high cross correlations do not expire with increased numbers of combined correlations, because the same codes repeat on each armature. This disadvantageously increases the probability that the mobile station can correlate a maximum FSC towards the wrong SSC pattern, especially if the FSC of an intense base transceiver station temporarily arrives near the FSC from a weaker base transceiver station. The PCT application Number WO 96 35306 (Telecom Sec.

Cellular Radio LTD) describes a method for determining the location of a mobile unit of a cellular radio system by determining the differences in the time regulation between the transmissions of the base stations as measured in the mobile unit, determining the differences in time regulation the differences in the distance of the mobile unit from each of the base stations, and deriving the location of the mobile unit from the differences in the distance determined in this way. Munday does not disclose using the time base difference information to define a measurement inquiry window, which simplifies the measurement of time intervals. Correspondingly, it is desirable in view of the foregoing to improve the ability of the mobile station to detect the downlink signals used in known approaches to the time difference observed in the downlink. The present invention seeks to overcome the aforementioned disadvantages of the known downlink observed time approaches by providing improved sensitivity for detecting the downlink communication signals used to make time difference measurements observed in the mobile stations.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates diagrammatically the manner in which the location of the mobile station can be determined using observed time difference measurements of the downlink. Figure 2 is a functional diagram of an exemplary wireless communications system that includes the observed time difference measurement capability - - of the downlink in accordance with the present invention. Figure 3 illustrates an example of the difference in the relative time regulation between the base transceiver stations as shown in Figure 2. Figure 4 illustrates an exemplary time interval structure of the reinforcements of Figure 3. Figure 5 illustrates an exemplary bit quarter structure of the time slot of Figure 4. Figure 6 illustrates the relevant portions of a mobile station having the observed time difference measurement capability of the downlink in accordance with a modality of the present invention. Figure 7 illustrates the manner in which an exemplary downlink monitoring window is determined in accordance with the invention. Figure 8 illustrates the relevant portions of a mobile station having downlink observed time difference measurement capabilities in accordance with the additional embodiments of the present invention.

DETAILED DESCRIPTION -.v¡áv «go« SiAiamacje- B. £ ~ Z -W. Figure 2 illustrates an example of a relevant portion of a wireless communication system including the observed time difference measurement capability of the downlink in accordance with the present invention. The invention is implemented in a GSM network in the example of Figure 2. As shown in Figure 2, a GSM mobile switching center MSC is coupled for communication with a plurality of GSM base station controllers BSCs, which at its they are then coupled to communicate with one or more GSM-based transceiver BTSs. The base transceiver stations are capable of radio communication with a plurality of mobile stations MSs through the air interface. Communication of MSC to MSs through BSCs and BTSs is well known in the art. Figure 2 also includes the mobile location center MLC coupled to communicate bidirectionally with a mobile switching center MSC using the conventional GSM signal protocol. In Figure 2, the MLC may receive a request to locate the position of a mobile station MSI. This request is typically received from a coupled location request 21 to communicate with MLC. The location request 21 may be a node within the network itself, or an external location request. In response to the - request to locate the position of the mobile station MSI, MLC interrogates the network to thereby determine service BTS 23 (ie the GSM service cell), and decides which BTSs should be selected for the observed time difference measurements of downlink. The MLC may then generate a placement request message for the mobile station MSI, indicating the frequencies and BSICs (BSICs are conventionally available in the networks such as the GSM network) of the base transceiver stations selected to be monitored, and the differences Real-time RTDs between service BTS and each of selected BTSs. The placement request message may be communicated from MLC to MSI through MSC, BSC 21, BTS 23, and the air interface between BTS 23 and MSI. Because MSI knows when synchronization bursts will arrive from its own service BTS, MSI can use the RTD information to calculate approximately when the synchronization bursts will arrive from the selected neighboring BTSs. This will be described in more detail below. The aforementioned information can also be sent to MSI as a dedicated message during for example, a call setup. In addition, the aforementioned information can also be sent to an MSI periodically in a broadcast control channel as a system information message. The RTDs can be calculated by MLC using OTD information received from a reference base station, as described above, or RTDs can be provided to MLC using other conventional techniques. Figures 3-5 illustrate the concept of the real-time differences between the base transceiver stations in the GSM networks such as the portion of the GSM network of the example of Figure 2. Figure 3 illustrates the real time difference between the time regulation of the reinforcement structure of a pair of base transceiver stations designated in Figure 3 as BTS2 and BTS1. In GSM, the TDMA reinforcements used by the base transceiver stations will be listed in a repeating cyclic pattern, each cycle (also called a hyper-burn) includes 2,715,648 reinforcements numbered as reinforcements 0 to reinforcement 2,715,647. In the example of Figure 3, time BTSl armor 0 overlaps with armor 828 of BTS2. Referring now to Figure 4, each TDMA frame in GSM is divided into eight time slots TS, numbered in time slot 0 to time slot 7. As shown in Figure 5, each GSM time slot is further divided. in 625 in a quarter bit of QB bit, so that during each time interval it is w ^^^^^^^^^ ¿^ ^ ¿^ ^ ^ ^ ^ ^ ^ ^? ^^ ¿? ^ ^ m ^^^^ ik ^^^ transmits a total of 625/4 = 156.25 bits . The real-time RTD difference between BTS2 and BT1 is therefore conventionally expressed as the triplet (FND, TND, QND), where FND is the difference (FN2 - FN1) between the numbers of the TDMA frame of BTS2 and BTSl, TND is the difference (TN2 - TN1) between the numbers of the time interval of BTS2 and BTSl, and QND is the difference (QN2 - QN1) between the numbers of the fourth bit of BTS2 and BTSl. For example, with reference to Figures 3 to 5, if the fourth bit portion of the time slot 0 of the armature is aligned with the fourth bit portion 37 of the time slot 6 of the 828 armature of BTS2, then the difference Real time RTD between BTS2 and BTSl is provided by the triplet (FN2 - FN1, TN2 - TN1, QN2 - QN1), where FN2, TN2 and QN2 are the number of the reinforcement, the number of the time interval and the number of the fourth bit of BTS2, and FN1, TN1 and QN1 are the same parameters of BTSl. In this way, the triplet is (828 - 0, 6 - 0, 37 - 0), or simply (828, 6, 37). When the mobile station MSI receives from MLC the real-time difference RTD between its own service base transceiver station, for example BTSl of Figure 3, and another base transceiver station in which it will make arrival measurements of downlink time, for example BTS2 of Figure 3, the station A mobile MSI can use the triplet RTD (FND, TND, QND) together with the time regulation of the structure of Known armor (FN1, TN1, QN1) of the service base transceiver station BTSl to determine the time regulation of the armor structure of BTS2 relative to that of BTS1 The following calculations can be made by the mobile station MSI for determine the number of the current reinforcement FN2 of BTS2 at any given point (FN1, TN1, QN1) in the time base of BTSl QN2 '= QN1 + QND (Equation 2) TN2 '= TN1 + TND + (QN2' div 625) (Equation 3) FN2 '= FN1 + FND + (TN2' div 8) (Equation 4) FN2 = FN2 'mod 2,715,648 (Equation 5) In the previous equations, "div" represents the integer division, and "mod" is the division of module n, where "x mod n" = "the remainder when x is divided by n". The sync burst SB in GSM contains 78 encoded information bits and a predetermined 64 bit training sequence, as is well known in the art. The 78 bits of encoded information contain BSIC and the so-called reduced armature number, conventionally expressed in three parts, TI, T2 and T3 '. The conventional relationship between the number of the 'iáfcÁ. ITagí &dS-armor (FN) of the sync burst SB and the parameters TI, T2 and T3 'is as follows: TI = FN div (26 x 51) (Equation 6) T2 = FN mod 26 (Equation 7) T3 = FN mod 51 (Equation 8) T3 '= (T3. 1) dsiv 10 (Equation 9) In this way, once the current reinforcement number FN2 of BTS2 has been calculated as shown above with respect to Equations 2-5, then parameter T3 can be determined by plugging FN2 into equation 8 above. In conventional GSM networks, the synchronization burst SB occurs in time slot 0 of the reinforcements 1, 11, 21, 31 and 41 of a 51-ar reinforcement sequence of the TDMA armatures transmitted on the BCCH carrier (channels of broadcast control) of BTS. In this way, T3 previously mentioned indicates where the current reinforcement FN2 is placed within the repetition sequence of 51 reinforcements. Because as mentioned above, the sync burst SB occurs in time slot 0 of the reinforcements 1, 11, 21, 31 and 41 of this repeat sequence of 51 reinforcements, the next T3 (we will call it T3n) satisfying the relation, (T3-1) mod 10 = 0, will designate the armor of BTS2 where the next sync burst SB will occur. He *****,. corresponding armor number (we will call it FN2n) is then determined by: FN2n = (FN2 + DT3) mod 2,715,648 (Equation 10) where DT3 = (T3n - T3) mod 51. Now, the parameters TI, T2 and T3 'are you can determine by plugging FN2n into equations 6 and 7 and plugging T3n into equation 9. In accordance with the GSM standard, the parameters TI, T2 and T3 ', together with BSIC, can be expressed using 25 bits. The bits BSIC can be determined from the received BSIC information in MSI, and the bits representing TI, T2 and T3 'can be determined from the equations 6, 7 and 9. The mobile station MSI can then apply to the 25 bits, previously mentioned, a well-known coding algorithm described in the GSM standard (ETSI GSM Specification 05.03), in order to generate from those 25 bits the 78 bits encoded in the synchronization burst. In this way, the mobile station MSI now knows, with respect to the time relationship of the armor structure of its own service BTSl, the number of the armature FN2n of BTS2, where the synchronization burst will occur. As mentioned above, the synchronization burst always occurs in the time interval 0, so that the mobile station MSI now knows exactly when the synchronization burst is detected. ? &? 3 & will transmit through BTS2. In addition, the mobile station MSI now also knows all the 78 coded bits together with all 64 training bits of the synchronization burst. With the knowledge of 142 bits instead of just 64 bits, the mobile station can achieve better accuracy by making the measurements of the arrival time in the conventional situation where only 64 bits are known. Furthermore, with 142 known bits, it is possible for the mobile station MSI to achieve, in a much noisier environment, the same accuracy that could be achieved using 64 bits with a less noisy environment. Because the position of the mobile station MSI relative to a given neighbor BTS is not known (eg, BTS 28 of Figure 2), the BTS sync burst SB will not reach the mobile station MSI precisely at the time when it was calculated by the mobile station. Figure 7 illustrates an example of how an inquiry window can be defined to encompass the time at which the synchronization burst can be expected to arrive at the mobile station MSI. Let FN represent the armor number of the next SB (SB2) that is expected to arrive from neighboring BTS2 (which does not service). The manner in which this armor number is calculated can be found in Equation 10. MSI knows when the corresponding SB (SBl) with the same armor number .-. afc.-i - ,. * & a. - will arrive, or will have arrived from BTSl of service. Let this moment of time be represented by TO, in relation to the time base of the mobile station. MSI remains within circle 71. The radius r of this circle may e.g., be determined by the radius of the cell or derived from the advanced value of time regulation. Consider the two extreme cases. An extreme case is when MSI is at 74. Then SB2 arrives during the time TO + RTD + dl2 / c since SB2 marches dl2 in addition to what SBl does. The other extreme case is when MSI is at 75. Then SB2 arrives at TO + RTD + (dl2 - 2r) / c. In this way, when the mobile station is between 75 and 74, SB2 arrives in the window [TO + RTD + (dl2 - 2r) / c - k, TO + RTD + dl2 / c + k], where k is responsible for the inaccuracies in the RTD and dl2 values provided. Since RTD is known, MSI can predict with some uncertainty when SB2 will arrive from BTS2 (which does not serve). The ability to calculate an inquiry window allows the synchronization burst to be detected with greater reliability compared to when the arrival time is completely unknown, the complexity of the mobile station is reduced compared to the mobile stations in the prior art. For example, the data from the entire inquiry window can be received in real time and stored for further processing, which is not realistically feasible if the inquiry window is required to be 10 long TDMA reinforcements, as is necessary to guarantee the capture of the synchronization burst using conventional techniques. In addition, the inquiry window allows the total measurement time to be reduced. The use of the RTD knowledge to calculate the starting time and the inquiry window for the sync burst SB, can significantly reduce the measurement time to make the measurements of the downlink OTD. Without receiving the RTD information, the mobile station is conventionally required to interrogate continuously until the frequency correction burst is detected so that the mobile station knows that the synchronization burst will occur in the next frame. With the RTD information corresponding to all the transceiver stations that are to be measured, the mobile station can project the different measurements and limit the supervision time to the periods of the window of inquiry, which is not possible using the techniques of exploration of the prior art. Figure 6 illustrates an example implementation of a relevant portion of the mobile station MSI of Figure 2 to make time difference measurements . -, dMat-S «-. - observed the downlink in accordance with the present invention. The mobile station includes a synchronization burst determiner 61 which receives as an input (for example from MLC of Figure 2 through MSC, BSC 21 and BTS 23) the frequency, the BSIC and RTD relative to the transceiver station of service base of each base transceiver station that is selected for OTD measurements. The synchronization burst determiner also receives information about the distances between its service base transceiver station and all neighboring base transceiver stations along with the cell radio information for all neighboring base transceiver stations. This information can be updated periodically by MLC (as MSI roams), and is stored in a memory as shown at 63 in Figure 6, or the information can be included in the placement request message that is provided to the determiner of the synchronization burst using MLC. The synchronization burst determiner 61 determines for each selected BTS the approximate expected arrival time of the synchronization burst with respect to the time base 60 of the service cell frame structure (service base transceiver station)., and sends this information at 64 to a 65 arrival time monitor. Likewise at 64, the synchronization burst determiner sends the arrival monitor time on the 78 encrypted bits and the 64 training bits of the # burst of synchronization of each selected BTS. The synchronization burst detergent also calculates the inquiry windows for each selected base transceiver station, and sends this information from the inquiry window at 62 to the arrival time monitor. The arrival time monitor performs arrival time measurements on the signals received from BTSs at 68. The arrival time monitor can use the calculated arrival time information, the window information and the sequence information of 142 bit to make the arrival time measurements for each selected base transceiver station. With this information, the arrival time monitor can efficiently program the different measurements and, as necessary, can capture and store the signals received during the different windows of inquiry and then process those signals for a subsequent time. The processing of the signals received for the determination of the arrival time can be carried out in any desired conventional manner, in the ways described in detail in the North American Patent. v. v.r ^ .eiít ^. copending Serial No. 08 / 978,960 filed on November 26, 1997, which is incorporated herein by reference. After having made the desired arrival time measurements, the arrival time monitor can send in 66 either the arrival time information or the time difference information observed to the MLC (through BTS 23, BSC 21 and MSC). MLC then uses this information in a conventional manner to determine the location of the mobile station MSI, whose location is then provided in an appropriate message to the application application 21 in Figure 2. Alternatively, if MSI knows the geographic locations of BTSs measurements, then MSI can calculate its own position. Even though the OTD measurements in the GSM synchronization burst are described in detail above, it should be evident that the techniques of the invention are applied to several types of bursts as well. In CDMA systems such as those mentioned above, providing the RTD information to the mobile station results in significant improvements in relation to the known OTD downlink techniques. The mobile station can use the RTD information to calculate an inquiry window generally in the manner described in what j-aB ^ sao -... above with respect to Figure 7. Because the mobile station now knows the time relationship differences between its service base transceiver station and the respective neighboring base transceiver stations, the geometry of Figure 7 can be used as above for determine the inquiry windows for the respective neighboring base transceiver stations. Then, for a given base transceiver station, the maximum FSC detection and the associated SSC correlations need to be carried out only during the inquiry window where the FSC and SSC signals are expected to reach the mobile station. In addition, because the RTD information identifies not only when the mobile station must monitor for the arrival of signals from a given base transceiver station but also identifies the base transceiver station and its code group, the SSC pattern associated with the station The base transceiver can be determined at first through the mobile station. In this way, for the base transceiver station of interest, the maximum FSC detection and the FSC-SSC correlation can be carried out simultaneously, thus advantageously reducing the acquisition time significantly compared to the previously known known techniques. where the FSC-SSC correlation should follow the maximum FSC detection. The reduction in the acquisition time allows a corresponding reduction in the length of the inactive periods during which it acquires the arrival time information. This reduction in idle or idle periods improves the downlink capacity of the network. As an additional result the a priori knowledge of the mobile station of the SSC pattern, there is no need to correlate maximum FSC with several SSC patterns, as in the known techniques. This reduces the memory and computing requirements in the mobile station. Because the maximum FSC detection and FSC-SSC correlation are carried out simultaneously, the results of these two operations can be combined for each time interval, which provides improved signal strength and therefore improved hearing ability. . Because an inquiry window is established for each supervised base transceiver station, the probability of selecting signals from the wrong base transceiver station is significantly reduced. In addition, because the correlations are carried out only in the vicinity of the true maximum, the plurality of selecting a false maximum is also reduced.

Another advantage of providing the RTD information to the mobile station is that, with the RTD information and the corresponding inquiry window, the mobile station can be correlated with signals other than FSC and SSC. For example, a mobile station may be correlated with a broadcast channel of the base transceiver station (e.g., a broadcast channel identified from a neighboring list of neighboring base transceiver stations) instead of, or in addition to, FSD / SSC. Together with the RTD information, the network can identify for the mobile station the respective code groups of the base transceiver stations, and also the respective long (spread) codes of the broadcast channels. From the identification information of the code group and the identification information of the long code, the mobile station can, using conventional techniques, generate all the long code (eg, 40,960 integrated circuits) of the broadcast channel of a given base transceiver station . A broadcast channel, for example the CCPCH Common Control Physical Channel of the WCDMA communication systems mentioned above, typically has a power level of the same order as the sum of the power of the FSC signal plus the power of the SSC signal. Likewise, this broadcast channel is transmitted continuously, instead of ten percent of time as with FSC / SSC. jc-nfa -2? ^ - Correspondingly, the broadcast channel signal contains much more energy than the FSC / SSC signals. This ntvßi ele (sft * 5? Eri »mft * I * ITV» «ÍT syßsseirßien» or & © seAej »< * s -íAfcAv * improved and allows faster acquisition Because the broadcast channel signal is transmitted continuously, allows much higher utilization of idle periods than can be achieved using FSC / SSC For example, at any given time interval, the broadcast channel provides ten times more symbols to be correlated than FSC / SSC. This allows the use of shorter and / or less frequent idle periods, thus improving the downlink capacity of the network, because the broadcast channel represents only a "code", the amount of memory required for the The non-coherent combination is half of that required when FSC and SSC are correlated (two codes), and because the base transceiver stations in the same proximity will have unique broadcast channels, and s negligible the probability of selecting the wrong base transceiver station. Singular channels provide cross-correlation properties that are much better (smaller cross-correlation) than with FSC / SSC, so the probability of selecting a false maximum when using FSC / SSC is much lower. Figure 8 illustrates diagrammatically the relevant portions of an example mobile station that can perform downlink measurements OTD in the CDMA systems as mentioned above. These CDMA systems can generally have the same architecture as shown in Figure 2, but with the air interface implemented according to the CDMA or WCDMA techniques. The mobile station of Figure 8 includes an input 81 for receiving from the network (eg, MLC of Figure 2) the RTD information indicative of the real time differences between the service base transceiver station and the neighboring base transceiver stations respective in which the mobile station is going to carry out the downlink OTD measurements. The input 81 also receives from the network the identification information of the code group for each base transceiver station. In a mode where the broadcast channels are to be measured, the input 81 receives, in addition to the identification information of the code group, the identification information of the long code for the broadcast channel of each base transistor station. A window determiner 83 receives the RTD information from the network, calculates the windows of o-j-to .. "-" _ ^. r * * * j.jm £ ^. * # Mf¡üt »? to inquiry generally in the manner described above with respect to Figure 7, and sends the information of the window to a supervisor 85 CDMA of arrival time (TOA ). The supervisor 85 carries out the required operations (e.g., maximum detection and correlation) to produce the arrival time measurement for each desired base transceiver station. In a mode using FSC / SSC monitoring, a code generator 87 receives input from the input 81 of the code group identification information for each base transceiver station, generates the SSC patterns therefrom, and in 84 provides these patterns SSC to the monitor 85. In another embodiment where the broadcast channels are to be measured, the code generator 87 also receives from the input 81 the identification information of the long code for the broadcast channel of each base transceiver station, generates the long codes in response to the identification information of the code group and the long code identification information and at 84 provides the long codes to the monitor 85. The monitor 85 monitors the CDMA air interface at 89 in accordance with the windows of inquiry, and makes the desired arrival time measures. The monitor 85 can send to the network at 86 either the TOA information or the OTD information. The network (e.g., MLC of Figure 2) - 3í You can use this information in a conventional manner to determine the location of the mobile station. Alternatively, if the mobile station knows the geographic locations of the measured base transceiver stations, then the mobile station can calculate its own position. The window determiner 83 may receive the input information about the distances between the service base transceiver station and all neighboring base transceiver stations, along with the cell radius information for all neighboring base transceiver stations, order to help the window determiner to determine the windows of inquiry. The distance information may be periodically updated by MLC (as the mobile station roams), and stored in a memory as shown at 82 in Figure 8, or the information may be included in a placement request message sent to the mobile station using MLC. The window determiner uses the RTD information to determine for each supervised base transceiver station the approximate expected time of arrival of the monitored signal relative to the time base 80 of the service base transceiver station, and combines this time information of expected arrival with distance information to produce an appropriate inquiry window. It will be apparent to the workers in the art of the portions of the exemplary mobile station of Figure 6 and Figure 8 that they can be easily implemented by appropriately modifying the hardware, software or both, in a data processing portion of a conventional mobile station. . In view of the foregoing description, it should be evident that the observed time difference techniques of the downlink of the present invention improves the sensitivity of the observed time difference measurements of the downlink by providing the mobile station with better known bits of the SB synchronization burst, improve the accuracy of arrival time and observed time difference measurements, reduce the risk of measurement errors, reduce the time required to make the necessary measurements and require less memory and data processing capacity in the station mobile. -.i & "-

Claims (46)

1. CLAIMS: 1. A method of using a mobile communication station (MSI) in a wireless communication network to measure the respective arrival times of the radio signals transmitted respectively by a plurality of radio transmitters (23, 28) in the network, comprising : providing in the mobile communication station the information of the real time difference (RTD) indicative of the differences between a time base (80) used by a radio transmitter that will service the mobile communication station and time bases respective used by the other radio transmitters; the mobile communication station uses the real-time difference information to calculate the measurement of the inquiry windows for each radio transmitter; the mobile communication station determines (83), in response to the information of the real time difference and in relation to the time base used by the radio transmitter serving the mobile communication station, a plurality of points ( 74, 75) at which time it is expected that the respective radio signals reach the mobile communication station; . -, 'Aft - ¿gk.-' -. > . for each radio signal, the mobile communication station monitors (85) the arrival of the radio signal during the period of the inquiry window; and during the period of the inquiry window, the mobile communication station simultaneously performs a first investigation of the maximum detection of the code and a second correlation of the associated inquiry code signal for at least one radio transmitter that gives service to the mobile communication station.
2. 2. A method for using a mobile communication station (MSI) in a wireless communication network to measure the respective arrival times of the radio signals transmitted respectively by a plurality of radio transmitters (23, 28) in the network, comprising: providing information indicative of when the radio signals are expected to arrive at the mobile communication station; the mobile communication station monitors (85) the arrival of the radio signals during a window of inquiry period in response to the information; and during the window of inquiry period, the mobile communication station simultaneously correlates a radio signal with a true crest for at least one radio transmitter serving the mobile communication station.
3. 3. The method of claim 2, wherein the step of providing includes providing information indicative of the respective time periods during which the respective radio signals are expected to reach the mobile communication station, and the step of supervision includes supervision of the mobile communication station for the arrival of each radio signal during the corresponding period of time. The method of claim 2, wherein the step of further providing includes: providing the real time difference information indicative of the differences between a time base (80) used by a radio transmitter serving the station of mobile communication and respective time bases used by the radio transmitters being measured; and in response to the information of the real time difference (RTD), determine (83), in relation to the time base used by the service radio transmitter, a plurality of points (74, 75) at which time it is expected that the respective radio signals reach the mobile communication station. - £? - & The method of claim 4, wherein the step of further providing includes using the points in time to determine the respective periods of time during which the respective radio signals are expected to arrive at the mobile communication station, and the Monitoring step includes supervision of the mobile communication station for the arrival of each radio station during the corresponding time period. 6. The method of claim 5, wherein the step of using includes the mobile communication station using the points in time to determine the respective time periods. The method of claim 5, wherein the step of use includes taking into account the respective distances (82) that are to be traversed by the radio signals in order to reach the mobile communication station. The method of claim 7, wherein the step of giving an account includes calculating, for each radio signal, a maximum possible travel distance and a minimum possible travel distance. The method of claim 8, wherein the step of reporting includes, for each radio signal, establishing a starting point (74) of the associated time period based on the point in time at which the arrival is expected and the minimum possible travel distance, and establishing a termination point (75) of the associated time period based on the point in time at which the arrival is expected and the maximum possible travel distance. The method of claim 4, wherein the determining step includes that the mobile communication station determines the points in time. The method of claim 4, wherein the radio signals are transmitted in time division multiple access channels, and the step of providing the real time difference information includes expressing a real time difference using at least one of a difference of the armature number, a difference of number of time interval (TS) and a difference of the number of a quarter of a bit (QB). The method of claim 2, wherein the communication network is a cellular communication network. The method of claim 12, wherein the communication network is a GSM network. A method for locating the position of a mobile communication station (MSI) in a wireless communication network, comprising: measuring in the mobile communication station, the respective times of arrival of the radio signals transmitted respectively by a plurality of , * £ ".- radio transmitters (23, 28) in the network, including providing information indicative of when the radio signals are expected to reach the mobile communication station, and supervision of the mobile communication station ( 85) for the arrival of the radio signals during a period of inquiry window in response to information, during the window of inquiry period, the mobile communication station simultaneously performs a correlation of the signal together with a true crest for at least one radio transmitter serving the mobile communication station, and using the measured arrival times to locate the position of the mobile communication station 15. A method for determining the arrival time of a mobile communication signal. radio in a radio communication station (MSI) operating in a wireless communication network, comprising: obtaining from the network information of common wireless communication (63) from which an information content of the radio signal can be determined but whose information does not reveal the content of the radio signal information; determining (61) the content of the radio signal information in response to the information; and using the content of the radio signal information to measure the arrival time of the radio signal. 16. The method of claim 15, wherein the information includes information indicative of the regulation of transmission time of the radio signal. The method of claim 16, wherein the transmission time regulation information is the real time difference information (RTD) indicative of a difference between a known time base (60) to the communication station of radio and a time base used by a radio transmitter (23) from which the radio signal is to be transmitted. The method of claim 15, wherein the information includes information indicative of a radio transmitter from which the radio signal will be transmitted. The method of claim 18, wherein the communication network is a GSM network, and wherein the information indicative of the radio transmitter includes a base station identity code (BSIC) that identifies a base station in the GSM network. 20. An apparatus for use for locating the position of a mobile communication station (MSI) in a wireless communication network, comprising: a determiner (61) for determining when each plurality of the radio signals is expected to arrive at the mobile communication station; and a radio signal monitor (65) for measuring the respective arrival times of the radio signals, the monitor is provided in the mobile communication station and has an input coupled with the determiner to receive the same indicative information as when the radio signals are expected to reach the mobile communication station, and the monitor responds to the information to monitor the arrival of the radio signals during a window of inquiry period. The apparatus of claim 20, wherein the determiner is provided in the mobile communication station. 22. The apparatus of claim 20, wherein the determiner determines the respective time periods during which it is expected that the respective radio signals will reach the mobile communication station. The apparatus of claim 20, wherein the determiner includes an input to receive the real time difference information (RTD) indicative of the differences between a tender base (60) used by a radio transmitter (23) that it serves the mobile communication station and the respective time bases used by the radio transmitters that transmit the radio signals, the determiner responds to the real time difference information to determine, with respect to the time base used by the service radio transmitter, a plurality of points (74, 75) in time at which it is expected that the respective radio signals reach the mobile communication station. 24. The apparatus of claim 23, wherein the determiner is operable to use the points in time to determine the respective time periods during which it is expected that the respective radio signals will reach the mobile communication station. 25. The apparatus of claim 24, wherein the determiner is capable of operating during the determination of the time periods to account for the respective distances (63) that are to be traversed by the radio signals in order to reach the mobile communication station, the determiner is capable of operating to calculate the maximum possible travel distances and the minimum possible travel distances and, for each radio signal, to establish a start or initiation point (74) of the time period associated based on the point in time at which the arrival and the minimum possible travel distance is expected and to establish the termination point (75) of the associated time period based on the point in time at which the arrival is expected and the distance of possible maximum travel. 26. The apparatus of claim 20, wherein the communication network is a cellular communication network. 27. The apparatus of claim 26, wherein the communication network is a GSM network. 28. An apparatus for measuring the arrival time of a radio signal to it comprising: an input (81) for receiving the information from which an information content of the radio signal can be determined but whose information per se does not reveals the content of the radio signal information; a determinator (83) coupled with the input and responding to the real time difference information (RTD) to determine the content of the radio signal information, and to calculate the measurement of the windows of inquiry; and a radio signal monitor (85) for measuring the arrival time of the radio signal, the monitor is coupled with the determiner to use the information content of the radio signal to measure the arrival time of the radio signal. radio, and to monitor the arrival of the radio signal during the window of inquiry period. 29. The apparatus of the. claim 28, wherein the information includes the information indicative of the regulation of transmission time of the radio signal. 30. The apparatus of claim 29, wherein the transmission time regulation information is the real time difference information (RTD) indicative of a difference between a time base (80) known to the apparatus and a time base. used by a radio transmitter (23) from which the radio signal will be transmitted. 31. The apparatus of claim 28, wherein the information includes information indicative of a radio transmitter from which the radio signal is to be transmitted. The apparatus of claim 31, wherein the communication network is a GSM network, and wherein the information indicative of the radio transmitter includes a base station identity code (BSIC) that identifies a base station in the GSM network. 33. The apparatus of claim 28, wherein the apparatus is a mobile radio communication station (MSI). 34. The method of claim 2, wherein the radio signals are Code Division Multiple Access (CDMA) signals. 35. The method of claim 14, wherein the radio signals are Multiple Access signals of Division of Code (CDMA). 36. The apparatus of claim 20, wherein the radio signals are Code Division Multiple Access (CDMA) signals. 37. The method of claim 34, wherein the monitoring step includes, for each radio signal, the correlation of the radio signal with a first code that is periodically transmitted by the associated radio transmitter and, simultaneously with the step of correlation, correlating the radio signal with a code pattern that includes a plurality of second codes that are codes in the code pattern that is transmitted simultaneously with one of the periodic transmissions of the first code. 38. The method of claim 37, which includes providing, for each radio transmitter, the information indicative of a code group to which the radio transmitter belongs, and which further includes the mobile communication station that determines the code pattern in response to the information in the code group. 39. The method of claim 37, which includes detecting the first and second transmitted codes by combining the results of the correlation steps. 40. The method of claim 34, which includes providing information indicative of dispersing the codes respectively used by the radio transmitters, and the mobile communication station determining the scatter code information of the scatter codes used by the transmitters of the radio transmitters. respective radios, the monitoring step includes using the scatter codes to monitor the radio signals of the broadcast channels associated with the respective radio transmitters. 41. The apparatus of claim 36, including a code generator (87) coupled to the radio signal monitor to provide the same in the codes to be used to monitor the radio signals. 42. The apparatus of claim 41, wherein the codes include scatter codes associated respectively with the radio signals. 43. The apparatus of claim 41, wherein the codes include codes carried by the radio signals. 44. The apparatus of claim 43, wherein the codes include associated code patterns. (-iigi &faith - * "" - ^. respectively with the radio transmitters used to produce the respective radio signals. 45. The apparatus of claim 41, wherein the code generator includes an input to receive the code identification information in response to which the codes are provided. 46. The apparatus of claim 41, wherein the code generator is provided in the mobile communication station.