MXPA97004862A - Registration of position for movi phones - Google Patents

Abstract

A method for determining the position of a mobile radiotelephone in a satellite communication system is disclosed. First, a mobile radiotelephone scans a plurality of paging channels and measures the strength of the signal of the paging channels. The mobile radiotelephone then selects the paging channels with the strongest signal strength and decodes the information broadcast on the selected channel. The information contained in the paging channel may include frequencies or time slots of paging channels in surrounding zone beams. The mobile station then measures the signal strength of paging channels in beams of surrounding areas and quantizes the measurements to determine an approximate position of the mobile radiotelephone.

Description

POSITION REGISTER FOR MOBILE TELEPHONES Field of the Invention The present invention relates to an improved satellite communications system for handling portable telephones and, particularly, to the interaction between the satellite system and mobile telephones that are in the standby mode. Background of the Invention When mobile telephones are in the standby or standby mode, they must listen to a signal radiated by the communication system in order to recognize if, and when, the mobile telephone is being called. An attractive communication system from the point of view of the user would be a satellite / cellular telephone, in a double way, that could listen and connect the calls with a basic cellular ground system, when the mobile phone is in a certain zone interval, or to a satellite system when the basic cellular ground system is not in this interval. The main advantage of such a double system is that the number of subscribers outside the cellular coverage at any time can be only a small fraction of the total number of subscribers, thus, the number of subscribers that need to have access to the satellite system is reduced. This allows a satellite system of limited capacity to take a much larger number of subscribers than its capacity would otherwise allow, perhaps 100 times the equivalent ratio in cellular systems. In addition, the number of subscribers actively listening to a call channel, that is, those in idle mode, always exceeds the number actually involved in the conversation by a factor of 20 to 200. As a result, the number of potential subscribers in The dual-mode satellite / cellular system can be from 2,000 to 20,000 times the calling capacity of the satellite system. It is clear that in such a dual-mode communication system, the network should preferably know whether a particular mobile telephone must be called by means of the basic cellular system on land or by means of the satellite system. However, to call each subscriber for both systems there is a very severe call channel load, in view of a potential 100-fold increase in subscribers, as mentioned above. Therefore, it would be desirable to restrict subscriber calls / paging via the satellite system to only those mobile phones that are known or suspected to currently listen to the satellite call channel. In a cellular communication system or a satellite communication system, it is necessary to restrict the paging / calling areas to those areas in which the called mobile telephone is thought to be located. Both cellular and satellite systems are more or less global and the paging ability to call each mobile phone over the entire globe is difficult to supply. This problem is solved by means of the registry. Registration means that a mobile phone informs the network which call channel is currently listening. The network then knows in which, from a limited number of paging areas the mobile phone, will most likely be and calls to that mobile phone can then be broadcast to the paging area. This process may involve transmitting the calls to a mobile telephone by means of several transmitters of the base station in different places in the same paging area. This increases the paging load for the transmission, but reduces the network load for handling records, since a mobile phone does not need to transmit more than one registration message each time it finds a stronger transmitter to listen to it. In this example, the mobile phone only needs to be re-registered or re-registered when it detects that the transmission changes to the surveillance belonging to a different paging area of the previous one. The above description of the paging areas and the re-registration criteria is well known in the art. For example, is used in the Pan European GSM cellular system. To achieve an economically useful capacity, to serve a large number of subscribers, satellite communication systems need to allow the reuse of the spectrum available many times on the globe. This is achieved by the use of multi-zone beam antennas that divide the illumination of the chosen service area among many smaller regions. Ideally, the available spectrum can be reused in each of the smaller regions by the use of the invention described in US Patent Application No. 08 / 179,953, entitled "A Cellular / Satellite Communications System with Enhanced Reuse of Frequency ", presented on January 11, 1994, which is incorporated here as a reference. The most promising satellite systems for such applications can be considered as those in a near-Earth orbit, which is stationary. The disadvantage of satellites in stationary orbits is that huge antennas are necessary to create beams of zone of the same size, from a distance of 40,000 km, and the extra delay in the signals that cross the distance create a problem for two-way conversations. However, the disadvantage of satellites in orbits close to Earth is that the satellites move and thus the areas that illuminate the zone beams change as the satellites surround the Earth. Even if steps are taken to govern the zone beams to more or less the same regions, the satellite will eventually pass over the horizon and will have to be replaced by an ascending satellite. When this happens, the whole population of mobile phones that listen in inactive mode to a paging channel of the satellite that is close to passing over the horizon should be prevented from attempting re-registration simultaneously to the fact that they are now listening to a new paging channel for the new satellite. As mentioned before, the number of mobile phones in idle mode is much greater than the capacity of the satellite system to handle traffic. Therefore, the problem of volume registration is difficult to manage. Compendium of the Invention To solve the problems of re-registration, mentioned above, it is convenient to define paging areas in absolute coordinates related to the Earth, instead of coordinates related to beams of satellite zones and coverage of area beams. Therefore, the system must be able to determine what to use to paginate a given mobile phone if the approximate absolute position of the mobile phone is also known. A typical diameter of a zone beam can be 100 to 100 km, so it is enough for a mobile phone to determine and record its approximate position.

According to one embodiment of the present invention, a simple method is provided for a mobile telephone to determine its absolute position within an accuracy sufficient to inform the network of which paging area is located therein. In accordance with one embodiment of the present invention, a method for determining the position of a radiotelephone in a satellite communication system is disclosed. First, a mobile radiotelephone scans a plurality of paging channels and measures the signal strength of the paging channels. This mobile radiotelephone then selects the paging channel with the strongest signal strength and decodes the information broadcast on the selected channel. The information contained in the paging channel may include frequencies or time slots of paging channels in the surrounding zone beams. The mobile station then measures the strength of the signal from the paging channels in the surrounding area beams and quantizes the measurements to determine the approximate position of the mobile radiotelephone. In accordance with another embodiment of the present invention, a method for re-registering a mobile radiotelephone in a satellite communication system is described. First, a mobile radiotelephone measures the signal strength of a plurality of paging channels, and using the information broadcast in the instant beams centers calculates the absolute position of the mobile radiotelephone with the use of measured signal strength and information. widespread. The mobile station then determines whether the absolute position of the mobile station has changed by a predetermined amount and re-registers it with the system when the absolute position has changed by the predetermined amount. BRIEF DESCRIPTION OF THE DRAWINGS These and other features and advantages of the present invention will be readily apparent to one of ordinary skill in the art from the following description, used in conjunction with the drawings, in which: Figure 1 illustrates a communications system of satellite according to one embodiment of the present invention; Figure 2 is a flow chart of a method for determining the position of the mobile radiotelephone according to an embodiment of the present invention; Figure 3 is a flow chart of a method for re-registering a mobile radiotelephone in a satellite communication system, according to another embodiment of the present invention; Figure 4 is a flow chart illustrating another embodiment of the present invention; Figure 5 is a flow chart illustrating another embodiment of the present invention; Figure 6 is a diagram of the arrangement of the interstitial beams in the network, according to an embodiment of the present invention. Detailed Description of the Preferred Modes Figure 1 illustrates a plurality of mobile radiotelephones 120, in communication via satellite 110 with a hole-type station 100. This hole station is connected, for example, by means of a local exchange, to the telephone network connected to the public PSTN, to allow placing calls between portable telephones and any telephone subscriber in the world, as well as between telephones Satellite 110 receives signals from mobile radiotelephones at a relatively low microwave frequency, such as 1,600 MHz. At this frequency, transmitters on battery-operated telephones can be efficient and their antennas can also be small and omnipresent. directional The satellite transfers the received signal from 1,600 MHz to a higher frequency for transmission to the hole-type station. The reason for using a higher frequency is mainly due to the fact that the necessary bandwidth in the satellite link to the hole is at least n times the bandwidth assigned to 1,600 MHz for each beam, where n is the number of beams, example, if 6 MHz of bandwidth is reused in every 37 beams of 1, 600 MHz, then at least 37 x 6 = 222 MHz of bandwidth will be needed in the satellite to cube link. Since a simple method of handling a coherent beam signal transport requires at least twice this minimum bandwidth, and the reverse direction requires the same amount, one GHz bandwidth? it may be necessary, which suggests that a carrier frequency of about 20 GHz is appropriate for satellite links to forward and reverse holes. At this frequency, even relatively small hole station dishes will have very narrow bandwidths, so the exclusive use of this bandwidth by any system is not necessary and the entire bandwidth can be reassigned to other satellite stations and ground without interference, as long as the straight line from the ground station to a first satellite does not intersect with a second satellite. This is prevented by assigning unique "stations" to satellites in geo-stationary orbit or in the case of low-moving orbiting satellites, the probability of intersection is low and they can be managed having an alternative hole location that is activated when such an event occurs. it happens In accordance with one embodiment of the present invention, which is illustrated in Figure 2, the mobile telephone tracks a number of frequency channels or time slots in which the paging spreads are likely to be encountered in step 200. The mobile telephone then determines the paging channel with the highest signal strength in step 202. The mobile telephone decodes the paging channel broadcasts in the selected channel in step 204 and the mobile telephone obtains the information in the frequencies or slots of time of the paging channels in the surrounding area beams, as well as the information in the current absolute coordinates of the center of the beam of the decoded paging channel. The mobile telephone then attempts to measure the strength of the signal from the paging channels in neighboring beams in step 206. The measurements can be quantified approximately in step 208 to indicate, for example, whether the mobile telephone is capable of decoding in all the neighboring paging channels, and if so, by what percentage of time or with what bit error rate. This is facilitated when a much higher degree of coding is used in the paging channels to help decode messages correctly in the mobile unit, poorly arranged. The reason for preferring paging channels for the measurement of signal strength is that those channels are known to be permanently active. It is also possible to make measurements of the strength of the signal in channels that carry telephone traffic, but these are probably to use the so-called Discontinuous Transmission (DTX), whose purpose is to save the energy of the satellite transmitter when a conversation direction of the Duplex phone is temporarily silent. Thus, the traffic channels that are actually in use may not temporarily contain signals, while the paging channels are those that permanently contain signals. It may also be possible to determine the strength of the signal using traffic channels if it can be determined whether or not they contain a valid signal, such as by the ability to decode the signal correctly. This works as long as the signal strength is high, but not when the strength of the signal is low. Paging channels can consist of dedicated frequencies (such as in an FDMA system) or dedicated time slots (such as in a TDMA system), or broad-spectrum transmissions that use dedicated codes (such as a CDMA system) or in fact any case hybrid of them. Regardless of the method of access employed, the term "paging channel" attempts to encompass any single combination of frequency, time slots, or codes used to disseminate paging information., as opposed to traffic. US patent application No. 08 / 179,953, entitled "A Cellular / Satellite Communications System with Enhanced Frequency Reuse", filed on January 11, 1994, which was assigned and incorporated herein by reference, describes how such channels can advantageously be radiated in slightly different directions, so that each point on the Earth is close to the center of beams of a channel. The object is to provide the system with a number of channels to choose from the ones closest to it centrally directed to any particular mobile phone, thus avoiding the loss of the edge of the beam that occurs for certain mobile locations if the beam signaling is not so staggered . To illustrate this, let us consider a greatly simplified case of a conventional system and a system according to the patent application of E. U. A., cited above, in which three communication channels are available. For this illustration, the FDPMA can be assumed so that the three channels are, in fact, in three different frequencies, which will be denoted by the colors black, red and green. In a conventional system that does not employ the method of the invention of the aforementioned US patent application, a number of antenna beams, for example 37, can be supplied, as determined by the fixed physical characteristics of a system of satellite antenna and is used to illuminate the Earth in the named area coverage regions. According to conventional wisdom, the gain at the worst point, which is placed halfway between three zones, is maximized by selecting the width of the beam so that the gain is approximately 4dB down at the midpoint with relationship to the gain of the center of the beam of the crest, This is in agreement with the conventional theory that is believed to be the optimal compromise between, on the one hand, reducing the peak gain by diffusing the beam, in order to reduce the edge loss and, on the other hand, narrowing the beam to increase the peak gain, but then suffering a greater beam edge loss at the same distance displaced from the center, as before. Having achieved this commitment, the conventional system will then have to decide whether all three frequency channels can be used in each of the 37 touch beams, with the consequence that a mobile unit at the midpoint between three beams will receive the same signals. Overlap in each frequency from the three beams, ie two, equal force interferes in the upper part of each desired signal, or if in order to avoid this interference problem the frequencies must be distributed between the beams in a reuse pattern of frequencies of 3 cells. In the latter case, a mobile unit at the midpoint between the three beams will receive all three frequencies with equal force from the three different surrounding beams, but one frequency only from each beam, with somewhat reduced interference from the side lobes of the beams with additional distance. A mobile unit at the midpoint between two cells will receive equal signal strength at two frequencies and somewhat reduced signal strength from two equal signals on the third frequency. A mobile unit in the center of a cell, of course, receives mainly the frequency of that cell with the somewhat reduced signal strength in the other two frequencies of the six surrounding cells. Thus, it is possible for a mobile station to obtain an approximate idea of its position based on the relative strength of the signal at the three frequencies. We can also suppose for the purposes of this illustration that the three frequencies in question are all of paging channels and that we have other sets of three to distribute in the same reuse patterns of three cells to pass the telephone traffic. A mobile unit needs only to know its position with sufficient accuracy to determine which beam or group of beams it must broadcast in a cell. The system information through the satellite of this is the purpose of the registration procedure. In this illustrative conventional system, a mobile unit can quantify its position to: 1. Receive mainly the red beam (RED) No. k (k = 1 to 12) 2. Receive mainly the black beam (BLACK) k (k 3. Receive mainly the green beam (GREEN) k, (k = 1 to 12) 4. Receive the beams red (RED) (i) and black (BLACK) (j) more or less equally 5. Receive the beams red (RED) (i) and green (GREEN) (j) more or less equally 6. Receive the beams green (GREEN) (i) and black (BLACK) (j) more or less equally 7. Receive the beams red (RED) (i), black (BLACK) (j) ) And green (GREEN) (k) more or less equally The above categories define six times as many sub-regions as existing beams, so it may be approximately that a mobile unit can quantify its position at 1/6 of the area of a zone beam. The mobile unit may use, as a criterion for which of the above categories it belongs, whether the dissemination of paging information in a beam is decodable without errors or not. Paging messages and broadcast information are continuously transmitted in the paging channel and protected with error correction and error detection encoding. The error correction coding is preferably an intricate code, while the error detection is preferably a Cyclic Redundancy Check (CRC) code. If the CRC of a decoded message checks in > 50% of messages, the mobile unit can quantify the "receipt of a beam". If the CRC checks in < 50% of the messages, the mobile unit can quantify the "no beam reception". Thus, if the "RECEPTION" is decided only for the green beam and the "NO RECEPTION" is the decision quantified for the other colors, the mobile unit belongs to category three. Reading the information in the green beam at its instantaneous center coordinates, the mobile unit takes these coordinates as its quantized (approximate) position. However, if the "RECEPTION" is the quantized decision for all three color beams, the mobile unit is in category 7 and by reading the coordinates of the center of the beam from the broadcast information, the mobile unit can calculate its position as a half between the three beams. Clearly, finer degrees of quantification can be used, such as receiving a color with 95% of the correct CRC, another with 45% of the correct CRC and the third with 15% of the correct CRC. In addition, the correct decoding is not the only indication of the position, but also the strength of the signal. The relative strength of the signal can, for example, be quantified as follows: 1. Make RED No. dominant (means the others> 5dB down) 2. make BLACK k dominant (means the others> 6dB towards below) 3. GREEN beam k dominant (means the others> 6dB down) 4. RED and BLACK beams equal (means that <6dB delta, but make GREEN> 6dB down) 5. GREEN and BLACK beams equal (means <6dB delta, but make RED> 6dB down) 6. make V ^ RDE and RED equal (meaning <6dB delta, but make BLACK> 6dB down) 7. All beams equal (means that all are within 6dB). Similarly, in the case of signal strength, it is not necessary to quantify too much. Having determined how many beams can be correctly decoded at all, their relative signal strengths can be used in a measured average of their center coordinates of the beam, using the beam configuration information stored or disseminated if desired, in order to obtain a finer estimate of the position of the mobile unit. As a further degree of sophistication, the estimated values can be subjected to the Kalman filtration which estimates both the mobile position and the velocity, with practical limits on speed. Especially in the case where the satellite beams move through the Earth, due to an uncompensated satellite movement, the estimation of the position in a period of tens of minutes based on the estimates are in several of the different previous categories, averaged by the Kalman filtration process. Once a position estimate is available, the mobile unit can determine if it has moved by a sufficient amount, since the last record of the verified activation of the re-registration. Nevertheless, the reregistration is activated by a change of the absolute position of the mobile unit and not by the movement of the beams on the Earth, due to the movement of the uncompensated satellite. The above description of a conventional FDMA, the 3-cell frequency re-use system, can also be extended to the case where the three channels in question are three different time slots in a TDMA system. In this case, the paging channel bursts cycles periodically between three neighboring beams, and the mobile unit can, by receiving a total cycle, determine the changes in amplitude if it is mainly in a beam (channels amplitude of depth in 2 of the three slots and strong signal in one), or in the middle between three beams (little or no amplitude modulation), etc. The description is now extended to the configuration of the beam of the invention, mentioned in the above associated description. In this system of the invention, a beam direction is not necessarily restricted to those directions associated with particular physical structures of the antenna, and can be taken in a continuous form of the directions by the use of electronic beam interpolation. For example, a mobile unit placed halfway between three beams will not have to suffer a loss of 4dB of any signal used in communications, but by virtue of the satellite transmitting 1/3 of the energy attempted for the mobile unit, consistently In all three cells, you can receive a virtual or interstitial beam centered on that mobile unit. To optimize the minimum gain at all points, such interstitial beams can be directed, a different optimum form of the bandwidths is applied so that the conventional gain, and considerably extreme minimum gains, which can be achieved generally with the same aperture of antenna. Figure 6 illustrates the formation of red and green interstitial beams between a set of black beams, which may be while corresponding to conventional beams. The large circles represent the transverse diameters of conventional beams. In the conventional approach, beams are used for straight communication outside their edges. The smaller circles show how much diameter of the beam needs to be used for communications in the approach of the invention. The solid shaded areas of the black beams stand out, indicating that the mobile units that use the black beams do so at approximately 1 / root (3) of the diameter of the black beam before a better option to switch to the red or green interstitial beam. In practice, much more three communication channels are supplied and produce staggered interstitial beams for each element that each beam needs to be used only at the root (N) of the conventional beam radius, where N is the number r \ e channels . Suppose that a set of FDMA of 256 frequencies are each associated with a set of virtual beams, the beam centers can in principle be arranged in a grid of 16 x 16 points within areas equivalent to conventional coverage areas. of the area beam. The mobile station can, by measuring the signal strength on all 256 frequencies, construct a 16 x 16 2D projection of measurements of which its most probable position will be evident. The correct mathematical method of determining the most probable position is to adjust a known configuration curve, equal to the beam pattern to the measurements, finding the optimal North-South and East-West displacement of the curve that best fits the measurements of x 16. In a TDMA system of 256 time slots at a single carrier frequency, the beam centers can be programmed to move systematically through the 16 x 16 grid from one time slot to another and then repeat. It is easier in the case of TDMA for the mobile unit to collect measurements of 16 x 16, as they need to reside on the same frequency for a TDMA framework to collect the signal strength measurements in all time slots, which are then processed by the two-dimensional curve fitting procedure, mentioned above, to determine a position estimate of the mobile unit. These estimates can then be averaged by the Kalman filter technique mentioned above. A supplementary device that the mobile telephone can use to determine if the paging channels are received weakly, even under the co-channel interference, from the traffic channels or paging channels in the current beam using the same frequency, is the subtraction demodulation process disclosed in commonly assigned US Patent No. 5,151,919, which is incorporated herein by reference. The technique described therein involves decoding the strongest of a number of overlap signals and subtracting the decoded signal from the received signal and then decoding the next stronger signal. As a result, weak signals from paging channels can be decoded with better accuracy, decoding and subtracting stronger interference signals.

In addition, the mobile phone can also make measurements of the signal strength in the traffic channels that it can decode. Different channels can be simply different TDMA time slots on the same frequency and not necessarily different frequencies. In some satellite communications systems, satellite energy can be redirected, based on one time slot to another, to mobile phones and respective conversations, so that the zone beam can be considered to oscillate around a limited region of a known way in the system. Therefore, by reporting when, ie in what time slot, the mobile phone obtains the greater or lesser signal strength, stronger traces can be supplied according to its present location. A mobile unit that has just been switched can have a moved position, since it is the last one registered in the satellite system. To ensure that the mobile unit can be reached, it must be determined if this mobile unit has moved and if so, it is re-registered with a new position. As a result, the mobile unit tracks the satellite signals to find the paging or active traffic channels in which it can make signal measurements. This is shown in step 300 of the flow chart illustrated in Figure 3. The mobile unit then measures the signal strength of the paging channels detected in step 301. If the mobile unit does not have a current record with the satellite , this mobile unit is in any case to your record and so you do not need to determine if your position has changed before accessing the satellite. In this case, the mobile unit can proceed to step 304, in which the mobile unit tries to access the satellite. The satellite responds by granting access to the mobile unit in step 305, which may, if desired, involve the temporary allocation of a traffic channel to the satellite for a longer interchange. It is preferable, therefore, if the mobile unit has determined and transported its position estimate to the satellite already in step 304 of access request, but alternatives are also described here; for example, the satellite system can determine in which of all its virtual beams the mobile unit receives the strongest of the random access signals and estimates the mobile position in the same way as the mobile unit estimates its position from the measurements of the satellite signal. Thus, the satellite can without aid, if necessary, estimate which traffic channel and combinations of beams are better adapted to the mobile unit. One reason for a longer exchange may be that the satellite system wishes to perform authentication of the mobile station, so that a pirated mobile unit will not be able to alter the registration information stored in a genuine mobile unit.

When, however, the mobile unit is not sure that it needs to re-register, because the previous record seems to be still in progress, the system does not want to generate an unnecessary re-registration charge. Therefore, the mobile unit must determine its own position before attempting to transmit to the satellite in step 302. This step requires that the information in the central positions of the current beam broadcast in the paging channels to be read by the mobile station and used in the position estimation together with the signal measurements. The mobile station then proceeds to step 303, where the new position estimate is compared with the position estimate associated with the last record. If the mobile unit has moved more than the threshold amount, for example, by more than one beam radius of -ldB, then this mobile unit proceeds to step 304 for the re-registration. On the other hand, if the mobile unit has not moved for more than the threshold amount, it proceeds to step 308 where it enters a power stop mode to save it and start the stopwatch. When the stopwatch generates an alarm, which is arranged to coincide almost exactly with the instants in the selected paging channel, when the mobile unit can be paged (i.e., its time slot of the idle mode), the mobile unit re-tracks the paging channels, making signal measurements, which he uses to update his position estimate, and then repeats the cycle. If the mobile unit has determined that it needs to re-register in step 303 and proceeds to step 304, this mobile unit can properly transport any position estimates or measurements that it has to make to the satellite already in the access request, if there is space in the data format for both this and the ID of the mobile unit, of at least 34 bits. The mobile unit may, optionally, if there is space in the format, send a position estimate, if available, or signal measurements if not. It may be possible that the measurements exist without the mobile unit being able to estimate the position, because it is unable to read any information in the paging channel with respect to the positions of the center of the beam. This could, for example, be temporarily unavailable due to system malfunction, such as a link failure between the satellite track system and the paging transmitter. If it is possible to provide the satellite position or the signal information already in step 304 or during a prolonged exchange in step 306, or subsequent communications, the satellite system has the option of combining these with its own measurements of the mobile signal, to obtain a refined position. This refined position can, optionally, be returned to the mobile unit in step 307, while acknowledging the re-registration. The mobile station, in that case, will remember the refined position for comparison with future estimates in step 303. The satellite system also stores the mobile position in its memory against the ID of the mobile unit, and can also transport that position in encoded form to the cellular Home Location Registry of the mobile unit station. In the context of a dual-mode satellite / cellular communication system, a more frequent and annoying re-registration problem may arise. Considering when a mobile telephone listens to a paging channel or call in a satellite system, rather than a cellular call channel in a basic cellular system on the ground, for example in the loss of cellular signal. The loss of cellular signals can very often occur in cell phones mounted on cars traveling on a highway. On busy roads, between two major cities, for example, a gap in cellular coverage may exist in a particular location, and each mobile unit with a satellite / cellular telephone may attempt to re-register with the satellite system, as in the area not covered by the cellular system. This is not normally a problem for cellular systems, because when there is no coverage, the phone of the mobile unit does not try to re-register. Also, the size of cells in cellular systems is perhaps 100 times smaller in area than satellite cells, so the load of systematic re-registration, described above, can be easily handled. However, such re-registration in mass can cause problems for the satellite system. Therefore, another object of the present invention is to prevent improper satellite re-registration, caused by the regular passage of vehicles through a hole in the cellular coverage. According to one embodiment of the present invention, as illustrated in Figure 4, mobile phones that are fixed to the cellular communication system, monitor a preferred call channel in step 400, but also have a list of call channels. neighbors that can be used as alternatives in the case of signal loss. A paging area comprises a number of base stations that simultaneously transmit a call message for a mobile unit. It will be convenient to transmit a call message in a group of surrounding base stations, to prevent the mobile unit from continuously re-registering as it wanders along the boundary between two base stations. The network will simply know that the mobile unit is listening to one of the two base stations, or others, and will transmit a page to all base stations. Such a group of stations transmits a "paging area ID" so that a mobile unit can detect when it changes to listen to a base station in a group with a different paging area ID; only in this case will the re-registration be required. Normally, a base station broadcasts a list of call channel frequencies of the surrounding stations, which can be received by the mobile unit in step 402. If the mobile unit detects, in step 404, the signal quality of the the monitored base station currently falls below a predetermined threshold, the mobile unit scans the list of alternative call channel frequencies, in step 406, and switches to one of the alternative channels, in step 408, if it has a quality of signal above the threshold. In certain systems, for example in TDMA systems, the mobile unit may have time saved between monitoring the current base station in certain time slots in which it can effectively and continuously scan the alternative list without expecting the signal quality of the the current station is degraded. If the mobile unit switches to the monitoring of a different base station, the mobile station does not need the re-registration unless the paging group ID is no longer the same. The new base station, however, will broadcast another list of call channel frequencies of the surrounding base stations, which the mobile unit now scans. Finally, the mobile unit can change to a station not in the original paging group, thus needing a re-registration procedure. In the prior art, each mobile unit obtains the same list of surrounding base stations from its currently monitored base station, and the paging areas are thus defined by the system to be the same for each mobile unit. In the patent application of E. u. A., No. 07 / 882,607, a method for supplying each mobile unit with the customary paging area is described. The technique is to download a list of alternative call channels in the re-registration, specifically for that mobile unit. The network remembers this and knows that a particular mobile station will be paged on all these channels. Thus, the paging area for a mobile unit can be recentrated around the actual position of each mobile unit in the re-registration, delaying the time when the re-registration can again become necessary. On the other hand, if no alternative call channel meets the criteria of signal quality in step 408, the mobile unit may, before moving too far from the current base station, report that it is entering a "black hole". performing a deregistration with the cellular system in step 410. The cellular system then informs the satellite system of the last known position of the mobile unit, within the cellular system in step 412, which is a sufficiently accurate position for the satellite system is capable of determining 1 paging beam appropriate for the mobile station. The mobile telephone then changes from cellular mode to satellite mode in step 414. The mobile telephone then determines the strongest satellite call channel in step 416 and then monitors the selected paging channel in step 418. The mobile telephone then it estimates its absolute position of the signal strength measurements without requiring registration with the satellite system, thus avoiding the recording load on the satellite. Alternatively, the cellular system may include information in an appropriate satellite paging channel in the list of alternative channels that it downloads. The estimates of the mobile unit in absolute position from the satellite signal in the deregistration of the cellular system so, if subsequently in its journey it detects that its position has changed by more than the threshold, in step 306, without having to find again a cellular signal, can, at that moment, perform a re-registration directly with the satellite system. There is sufficient security that this does not represent an unnecessary re-registration, since it must be out of cellular contact for at least several hours and several hundred kilometers.

An alternative in step 412 is that the cellular system informs the satellite system of the last known position of the mobile unit within the cellular system, it can be understood by remembering that a call for the mobile satellite / cellular unit, in a double way, does not it is necessary to be guided to the satellite system, in the first instance, but to the "Home Location Recorder" of the mobile unit telephone, which resides in the mobile switching center belonging to the cellular operator with which the telephone has a subscription . In alternative step 413, either the satellite system or the cellular system may inform the Home Location Recorder or the Visiting Location Recorder of the last known position of the mobile telephone. According to the previous description of how a mobile telephone is reached when it is fixed to the satellite system instead of the cellular system, the current location of the mobile unit and the route information should be housed in the HLR in terms of a VLR ID. The VLR or Visitor Location Recorder is provided in third-party cellular switching centers to retain information in non-native mobile units that are temporarily registered in their areas. The entire PSTN, however, can not know where each mobile unit is currently registered, only where the native switch of the mobile unit, that is, the route to an HLR of the mobile unit. The route to the VLR in which a mobile unit is currently registered is thus first retrieved by a call from the PSTN from the HLR. Figure 7 illustrates an example of the flow of call information in such a system. When a call is placed to a mobile unit, the PSTN contacts the HLR of the mobile unit to determine the last position (the ID of the VLR or a virtual ID of the VLR). When the call is routed to the cellular system, this call goes to the VLR using the ID of the VLR stored in the HLR. The VLR then requests authentication and hidden information from the HLR. The VLR then sends the call and authenticity of the mobile unit. However, when the call is routed to the satellite system, the virtual ID of the VLR is sent to the satellite ground station, which requests the security information from the HLR. After the satellite ground system has received the security information, the mobile unit is paged in the satellite beam that covers the absolute location associated with the VLR ID. Therefore, it is sufficient that the cellular system, in the deregistration of a mobile unit, hosts an appropriate virtual ID of the VLR, associated with the absolute position known by the satellite system. However, this requires that the cellular switching systems be reprogrammed to accommodate an implicit virtual ID of the VLR in the HLR, when the mobile unit cancels records of that cellular region. The implicit ID of the VLR has to be provided by the satellite system that uses this invention and is the ID of the VLR, associated with the absolute paging area of the satellite, where the VLR is located. There are other alternatives, all of which are considered within the spirit and scope of the invention. For example, the VLR from which the mobile unit has just canceled the registration may merely inform the HLR that it no longer has records. The HLR is responsible for offering dual satellite / cellular subscriptions, then it is required to determine the virtual ID of the satellite VLR to replace the last visited ID of the VLR with the implicit one. This can, in turn, involve the HLR contact to the satellite system to receive this information. Alternatively, only the gate ID of the nearest satellite is lodged in the HLR implicitly. The satellite gate, when a call is re-directed to it, will determine the last known absolute position of the mobile unit from its memory, or using the last known VLR ID supplied by the HLR. The goal of such alternatives is to eliminate the need to reprogram all cellular systems to accommodate dual-mode satellite / cell phones, and limit any reprogramming requirement only to systems that offer subscriptions in a double way, or even limit such programming to elements of the satellite system. Yet another alternative considered within the spirit and scope of the present invention is that the VLR in a mobile unit, which cancels the records, does not inform the HLR of the change. Only when the next PSTN attempts to call the mobile unit, the HLR will receive notification from the VLR that the mobile unit no longer has records. The HLR will then make implicit contact with a satellite service center and report the last VLR ID with which the mobile unit was registered. The satellite system can have a stored map relative to the VLR IDs to its own absolute paging areas, and will guide the call to the paging area in which the mobile unit will most likely be located. When the mobile unit initiates a call, the problem will be solved since the satellite system will now be positively informed of the position of the mobile unit and can be properly registered in the satellite system and the appropriate virtual ID of the VLR housed in the HLR where appropriate. If the call is guided to an unwanted site on the satellite gate, this gate can inform the HLR of an alternative route. This may depend on how the operators of the system wish to handle the guide and bill different branches of the connection.

Since the cellular system is presumed to have the proper recording capacity, even for mobile phones that regularly emerge from a systematic "black hole", the re-registration emission from satellite to cellular is not an emission of capacity, so the Emission consumes much more energy to maintain mobile phones. It is not convenient when using battery power to listen to the satellite system and also simultaneously listen to the cellular system. According to another embodiment of the present invention, deregistration of the mobile unit in the satellite system is avoided, instead re-registering the mobile unit in the cellular system when this mobile unit detects that it is possible to register with the mobile unit. the cellular system. A method to detect when it is possible to register with the cellular system is described below. In this case, the cellular system can notify the satellite system by a signal of cancellation of registration by land lines, for example, that the mobile telephone no longer needs to be paged by the satellite system. This, of course, is not necessary when all calls to the mobile unit from the PSTN will in any case be first referred to the HLR to obtain the current location information. It is then sufficient to rewrite the virtual ID of the VLR or ID of the gateway VLR of the satellite system with the address of the physical cell VLR with which the mobile unit has just been re-registered. In the GSM system, a subscriber with a company that provides a particular service has a corresponding data record in one of the exchangers or switches of cellular phones of the company. The record is called the home location register or HLR and contains an entry for the last known position of the mobile telephone in the communications system. For example, if a mobile phone calls another GSM country and connects to it, it will determine which call channel has the strongest signal strength and then send a registration request to the foreign system. The request will indicate the HLR of the local country and the foreign system will make contact with the HLR by international circuits in order to obtain data that authenticate the identity of the mobile phone. In successful authentication, the mobile unit is registered in the foreign system in a visitor location register (VLR) and the location of the mobile station will be sent to be stored in the HLR: Next, the telephone system will relate any call from any caller in the world first to the HLR automatically, to get the current location of the VLR and then to the VLR. The method described above is one embodiment of the present invention; however, in some cases, the old exchanges can not understand the re-guidance instructions and the voice signals must be guided through the HLR, known as the "trombone movement". According to the present invention, when a mobile phone, in a double way, sends a cancellation message to the cellular system, this cellular system makes contact with the HLR to change the data of the current location from the VLR to the satellite system. . In addition, the absolute location is housed in the HLR, so that the satellite system can obtain it or optionally so that the HLR can go forward to the location to the satellite system. The reverse process takes place when the mobile phone re-registers from the satellite system to the cell phone. To avoid the need to change the software of all the VLRs to execute the satellite-related location and registration functions, as an alternative, the VLR performs its normal functions. The HLR in which the telephone is registered as having satellite capacity then has the task of determining the equivalent coordinates of the satellite system, looking in a table for the information belonging to the VLR from which a registration or cancellation of registration is received. one of its mobile units. The HLR can then, if necessary, inform the satellite system of the approximate position of the mobile unit.

Still, power consumption for portable mobile phones is a problem when cellular and satellite modes operate at the same time. This can arise when a mobile phone is fixed to the satellite in the absence of cellular signals, and there must be a method to detect when a cellular call channel is again able to receive. Normally, it does not take much battery power to listen to a cellular call channel, since a special feature has or will have to be made in future cellular systems, to reduce the waiting power of mobile phones. Sleep mode groups represent a used primary candidate technique, in which a mobile unit is assigned to the subgroup of mobile units, according to, for example, the last digit of the telephone number or the sum of the digits of its telephone number and calls to the group are transmitted only in certain time slots that the module can anticipate and activate for reception. Thus, the mobile station can spend at least 90% of the time energized. However, the mobile unit can only enter idle mode when it is set to a call channel and has its idle mode group identified. In accordance with the present invention, the satellite call channel also performs idle mode groups, which allow the mobile telephone to activate its satellite call channel mode for only a fraction of the time. In principle, the mobile unit can activate for a second fraction of time, that is, one millisecond every 20 milliseconds, in order to explore one of the 1,000 cellular channels. The channel contains significant energy then it will be identified in 20 seconds, which may be an adequate response time for the transfer from satellite mode back to cellular mode. However, both consume power and the response time can be improved by having the satellite call channels broadcast a list of cellular call channels that exit within the area currently illuminated by the call channel beam. As illustrated in Figure 5, each satellite paging channel broadcasts a list of cellular call channel frequencies in step 500. A mobile telephone then receives the list of call channel frequencies in step 502 and attempts to measure the signal strengths of the cellular call channels in step 504. The mobile units in the cellular black holes that are listening to the satellite call channel temporarily, may then limit the list of possible call channel frequencies from 1,000 to perhaps 21, on the basis that call channels can reuse the same frequencies in a 21-cell reuse pattern. As a result, it is only necessary to inform the mobile unit that you have selected frequencies in a given area. In the case that mobile units can operate in more than one cellular standard, the call channel standard as well as the frequency can be indicated, for example in channel 137 of AMPS or channel 104 of GSM. Using the sleep mode, mobile phones only need to activate their cellular receivers for perhaps 21 to 63 milliseconds of every 20 seconds, to check the presence of any call channel they can receive. The active time will, in fact, be determined by the speed at which the cellular synthesizer can change the frequency and is probably minimized by activating the cellular receiver once every 20 seconds and exploring all potential call channels as fast as the cellular synthesizer can change the frequency and then go back to the resting state. The mobile telephone then determines whether the strength of the signal of one of the call channels is above a predetermined threshold in step 506. The mobile telephone has registers with the cellular communication system in step 508 if one of the channels of Cellular call has a signal strength above the predetermined threshold. The patent application of E. U. A., No. 08 / 305,652 describes a method for directing a call to a mobile telephone in a satellite or cellular communications network on the ground, comprising the steps of first transmitting a call at a normal power level in the cell or groups of cells that more likely form a paging area, and when there is no recognition of the first call, transmit a second call to a higher power in the paging area and, optionally, simultaneously, call a normal power in an area Extended paging The technique described in the patent application of E.U.A., No. 08 / 305,652 is complementary and may be used in combination with the present invention to provide an improved probability of successfully alerting a mobile phone of an impaired call. The aforementioned description does not disclose transmitting a message with omitted registration from the mobile telephone to the cellular network, upon detecting the eminent deterioration of quality of all cellular signals that can be received. Rather, the aforementioned description, exposes continuing to direct calls to the mobile telephone first by means of base stations in the last known paging area. The implicit form of a period of time is invoked to receive a recognition from the mobile phone of this first call. At the expiration of the time period, a second call is transmitted at a higher power or in a larger paging area. The disclosed method can be incorporated in the present invention, since the preferred method of calling a mobile telephone is by means of a cellular network. The disclosed procedure can then be applied a second time, since the preferred method of calling the mobile telephone is by means of a satellite network. In other words, the transmission of a call in a "most probable beam", as indicated by an indication sent to the satellite system from the cellular network, and the non-recognition within a period of time, transmit a second call in the make a higher power more likely or transmit a second call in a number of beams that make up a larger satellite paging area, or both. In addition, the combined procedure can be used by depleting all cell call modes first and then continuing the process through a number of satellite call modes until either mobile unit answers or all attempts are exhausted, at which point it is You can send a "not temporarily available or disconnected" message to the calling party. This calling party can then be directed to a reserved voice area or a short message service, similar to the alphanumeric paging service. All combinations of the descriptions incorporated in the present invention are considered within the scope and spirit of this invention. It will be appreciated by one of ordinary skill in the art that the present invention can be incorporated into other specific forms without departing from the spirit or its essential character. The modalities currently disclosed, therefore, are considered, in all aspects, as illustrative and not restrictive. The scope of the invention is indicated by the appended claims, rather than by the foregoing description and all changes within the meaning and range of their equivalents are intended to be encompassed by this invention.

Claims (22)

1. CLAIMS 1. A method for directing a call to a mobile telephone in a cellular-satellite communications network, in a double way, this method comprises the steps of: receiving, at a satellite communications station, an indication on a cellular network, from the last known location of the mobile phone; determining a satellite antenna beam most likely to be received by the mobile telephone, using said indication; and transmit a warning signal to the mobile phone, using the antenna beam.
2. 2. A method for directing a call, according to claim 1, further comprising the step of: transmitting from the mobile telephone a response in recognition of a correctly received alert signal.
3. 3. A method for directing a call, according to claim 2, wherein said response is transmitted on a satellite access channel, if the alert is received by means of a satellite, and is transmitted on a cellular access channel if the alert is received from a cellular network.
4. 4. A method for directing a call, according to claim 3, further comprising the steps of: receiving the acknowledgment at a satellite ground station; and send a signal from the satellite ground station to the cellular network, that the mobile telephone can be reached by means of the satellite network.
5. 5. A method to direct a call to. a mobile phone, in a cellular-satellite communication network, in a double way, this method comprises the steps of: transmitting an alert signal to the mobile phone, from a land base cellular station, if the mobile phone is registered as active in this cellular network; and transmitting an indication from the cellular network to the ground station of satellite communications of the last known position of the mobile telephone, if this mobile telephone can not currently be reached within the cellular network.
6. 6. A method for directing a call, according to claim 5, further comprising the step of: determining the satellite antenna beam most likely to be received by the mobile telephone, using said indication.
7. A method for directing a call, according to claim 5, further comprising the step of: governing a satellite antenna beam in the direction most likely to be received by the mobile telephone, using said indication.
8. 8. A method for directing a call, according to claim 6, further comprising the step of: transmitting an alert signal in the determined antenna beam to the mobile telephone, by means of the satellite.
9. 9. A method for directing a call to a mobile telephone in a cellular-satellite communication network, in a double way, this method comprises the steps of: transmitting an alert signal to the mobile telephone, using base stations of the cellular network if this mobile phone is currently registered as active in the cellular network; receive the alert signal on the mobile phone; transmit a response to the cellular network, as a recognition; by not receiving recognition by the cellular network, within a defined period of time, transmitting an indication from the cellular network to the satellite ground station, of the last known location of the mobile telephone.
10. A method for directing a call, according to claim 9, further comprising the step of: upon receiving the indication at the satellite ground station, using this indication to determine the satellite antenna beam most likely to be received by the mobile telephone and transmitting an alert signal to the mobile telephone by means of the satellite, using this antenna beam.
11. A method for directing a call, according to claim 10, further comprising the steps of: receiving the alert signal on the mobile telephone; transmit a response from the mobile phone through the satellite, recognizing this warning signal.
12. 12. A method for directing a call, according to claim 11, further comprising the steps of: receiving the acknowledgment transmitted via the satellite to the satellite ground station; assign a traffic channel to communicate with the mobile phone and complete the two-way connection between the mobile phone and the calling party.
13. 13. A method for directing a call, according to claim 12, further comprising the step of: transmitting a signal from the ground station of the satellite to the cellular network, which the mobile telephone can reach, by means of the satellite ground station.
14. A method for directing a call, according to claim 9, wherein the alert signal transmitted from the cellular network comprises a first call at normal power levels and a second call at a higher power level.
15. 15. A method for directing a call, according to claim 9, wherein the alert signal transmitted from the cellular network comprises a first call at normal power levels and a second call at a higher power level, in a paging area most likely, and simultaneously at a normal power level in a wider paging area.
16. 16. A method for directing a call, according to claim 9, wherein the alert signal transmitted from the cellular network comprises a first call, transmitted in the last known paging area, and a second call, transmitted in a wider paging area.
17. 17. A method for directing a call, according to claim 9, wherein the alert signal transmitted using the satellite antenna beam comprises a first call at normal power levels, and a second call at a level of greater power.
18. 18. A method for directing a call, according to claim 11, further comprising the steps of: not receiving on the ground station of the satellite the recognition from the mobile telephone, transmitting one more call using the satellite, in a Extended paging area of the satellite.
19. 19. A method for directing a call, according to claim 18, wherein the extended paging area of the satellite comprises several beams.
20. 20. A method for directing a call, according to claim 18, wherein the extended paging area of the satellite comprises a beam of greater bandwidth.
21. A method for directing a call, according to claim 18, further comprising the step of: transmitting the additional call in the first paging area of the satellite to an increased power level.
22. 22. A method for directing a call, according to claim 18, further comprising the step of: transmitting the additional call in the first paging area of the satellite, using a more powerful error correction code.