MXPA99001752A - Radio communications systems and methods for mobile assisted handover between a private network and a public mobile network - Google Patents

Abstract

Mobile assisted handover between a private radio communications network (14) connected to the public switch telephone network (64) and a public land mobile network also connected to the public switch telephone network are provided by a radio communications mobile terminal (30) supporting simultaneous communication connections between the two uncoordinated networks. The mobile terminal (30) monitors a base station (16) of the public land mobile network during idle frames of communication connections with the private radio communications network, thereby synchronizing the mobile terminal to both the base of the public land mobile network and the private radio communications network. Call interruption is prevented during handover by maintaining simultaneous communications with the private communications network and the public land mobile network through the use of two half-rate channels or dual-slot communications where both the public land mobile network and private radio communications network operate pursuant to compatible TDMA standards. Handover is initiated when the mobile terminal detects a signal quality which violates a predetermined switching criteria and passes the PSTN phone line number of the private radio communications network to the base station of the public land mobile network which in turn requests re-routing of the call from the PSTN switch.

Description

"RADIOCOMMUNICATION SYSTEMS AND METHODS FOR DELIVERY ASSISTED BY MOBILE NETWORK BETWEEN A PRIVATE NETWORK AND A MOBILE NETWORK PUBLISH " FIELD OF THE INVENTION This invention relates to communication systems and, more particularly, to private radiocommunication networks within the coverage area of a public land mobile network.

BACKGROUND OF THE INVENTION Public cellular networks (public land mobile networks) are commonly used to provide voice and data communications to a plurality of subscribers. For example, analog cellular radiotelephone systems, such as those designated AMPS, ETACS, NMT-450 and NMT-900 have been successfully deployed throughout the world. More recently, digital cellular radiotelephone systems such as those designated IS-54B in North America and pan-European GSM have been introduced.

These systems and others are described, for example, in the book entitled Cellular Radio Systems by Balston et al., Published by Artech House, Norwood, MA, 1993.

Additional analog radiotelephone systems generally employ a system referred to as a frequency division multiple access (FDMA) to create communication channels. As a practical matter well known to those skilled in the art, radiotelephone communication signals, being modulated waveforms are typically communicated through predetermined frequency bands in a spectrum of carrier frequencies. These discrete frequency bands serve as channels through which cellular radiotelephones communicate with a cell, through the base station or satellite serving the cell. In the United States, for example, federal authorities have assigned to cellular communications a block of the UHF frequency spectrum further subdivided into pairs of narrow frequency bands, a system designated EIA-553 or IS-19B. The pairing of channels results from the frequency duplex arrangement where the transmitter and receiver frequencies in each pair are off-center by 45 Mhz. Currently there are 832 30 Khz radio channels assigned to cellular mobile communications in the United States. The limitations on the number of available frequency bands present several challenges as the number of subscribers increases. The increase in the number of subscribers in a cellular radiotelephone system usually requires the most efficient use of the limited available frequency spectrum, in order to provide more total channels while maintaining the quality of the communications. This challenge is increased because the subscribers may not be evenly distributed among the cells in the system. More channels may be needed for specific cells in order to handle potentially higher local subscriber densities at any given time. For example, a cell in an urban area could conceivably contain hundreds or thousands of subscribers at any time, easily depleting the number of frequency bands available in the cell. Due to these reasons, conventional cellular systems employ frequency reuse to increase the capacity of the channel potential in each cell and increase the spectral efficiency. Frequency reuse involves assigning frequency bands to each cell, with cells using the same frequencies geographically separated to allow radiotelephones in different cells to simultaneously use the same frequency without interfering with one another. By doing so, many thousands of subscribers can be served by a system that only several hundred frequency bands.

The previous decades have shown a considerable rise in the deployment of mobile telephony. With a slow start of analog standards such as AMPS, NMT and TACS, mobile telephony has actually impacted consumer markets with advanced digital standards such as GSM and D-AMPS. In addition to the advance in the characteristics of the mobile phone such as size and battery life, much progress has been made on the side of the network as well. Newly dense cell reuse plans have been complemented with hierarchical cell structures, where the macrocells cover whole districts, the microcells cover smaller parts, such as streets, and the picocells cover very small areas, the size of a few rooms. It is important for the structure of the hierarchical cell, that each deployed base station (which varies from macro or pico-base stations) is part of the same Public Land Mobile Network (PLMN). When a mobile user moves from an area of a macrocell to a microcell, the call can be handled from a macrobase station to a microbase station without the user perceiving it. This is particularly the case for digital telephone systems that apply TDMA: they are delivered from one base station to another within a coordinated PLMN for the mobile telephone which usually involves only the change of a time interval. In order to make it easier for the network to re-route the call from one base station to another with the PLMN, the mobile phone carries out measurements that are made known to the base with which it is connected, using a control channel fast or slow associated (FACCH or SACCH). The mobile measures help the base station controller of the PLMN to find the best alternative base station in which the call can be continued. Recently, private radio telecommunication networks for residential and business areas are being developed which use the same air interface as the public cellular network, but are not integrated with the overlapping public cellular network. In this case, these private systems are neither micro or pico networks since there is no direct connection between these private systems and the public cellular network. For example, for residential use, private base stations may be used as described in U.S. Patent Number 5,428,668, which are only connected to the PSTN. In business or office networks a private branch exchange ("PBX") is applied, the base radio stations belonging to the same private network communicate with each other, but none of them communicates directly with the overlapping PLMN. Because private radio systems have only a limited scale, the result will be that the call is abandoned when the user of the mobile station moves out of the coverage range, unless the overriding public cellular network can service the call. Therefore, a delivery from the private mobile network to the public cellular network is highly desirable. However, because there is no coordination between the private radio system and the PLMN, there are problems to achieve a delivery to the PLMN of the private network.

COMPENDIUM OF THE INVENTION Therefore, an object of the present invention is to provide improved mobile radio terminals usable both with a public land mobile network and a private radio network within the coverage area of the public land mobile network. Another object of the present invention is to provide a method for the delivery assisted by the mobile network of a private radio network to a superimposed public land mobile network, without requiring interruption of the call. In the present invention, these and other objects are satisfied by providing a mobile terminal that communicates with both a private radio network and an overlapping public land mobile network. The mobile terminal can be synchronized with a base station of the public land mobile network while a call is being made between the mobile terminal and the private radio network. The mobile terminal in this way synchronizes the time of the transmissions between the otherwise uncoordinated base station of the public land mobile network and the private base station of the private radio network. The mobile terminal may further determine when the call in progress must be delivered to the overriding public land mobile network based on the indications of the deterioration of the communication signal with respect to a predetermined switching criterion. When a violation of the switching criterion is detected by the mobile terminal, it contacts the public land mobile network and transmits to the PLMN the PSTN number of the private radio network to initiate the re-routing of the call from the private radio network to the public land mobile network. In one embodiment of the present invention, the mobile terminal detects means operably connected to the radio transceiver means which detects the signal quality of the communications between the mobile terminal and the private radio network during radio communication between the mobile station and the radio station. private radio network. The mobile terminal also includes a comparison means operably connected to the detection means for comparing the quality of the detected signal to a predetermined switching criterion. A simultaneous communication establishment means includes synchronization means within the mobile terminal, synchronizes the mobile terminal to the public land mobile network by monitoring the public land mobile network during idle frames while the synchronized communications are being carried out between the mobile terminal and the mobile terminal. the private radio network. The information medium within the mobile terminal provides means for re-routing the first radiocommunication connection call from the private radiocommunication network to the public land mobile network when the quality of the detected signal from the private communication network violates the criteria of default switching. Delivery is achieved between the uncoordinated private radio communication network and the public land mobile network without call interruption by establishing a second simultaneous radio communication connection between the mobile terminal and the public land mobile network, when the quality of the detected signal violates a criterion Default switching The report medium discloses the line number of the private radio communication network to the public land mobile network and requests re-routing of the call that is being carried out between the mobile terminal and the private radio communication network. The two simultaneous radiocommunication connections are provided without the need for redundant transmitter and receiver circuits because the synchronization means of the mobile terminal synchronizes the terminal to both systems, thus allowing it to operate two half-channels, one for communications with each system. This synchronization can be achieved by the mobile terminal without any requirement for the private radio communication network and the public land mobile network that is otherwise to be coordinated. In accordance with another aspect of the present invention, methods are provided for the delivery assisted by a mobile network between a private radio network connected to a switch of the PSTN and a public land mobile network. The signal quality of the private radio network during a first radio communication with the mobile terminal is detected in the mobile terminal. If the quality of the detected signal violates a predetermined switching criterion, a second radio communication connection is established between the mobile terminal and the public land mobile network simultaneously with the first radio communication connection between the mobile terminal and the private radio network. The mobile terminal discloses the PSTN number of the private radio network to the public land mobile network through the second radio communication connection. In response to this report and request, the public land mobile network initiates the re-routing of the first radio communication connection from the PSTN switch to the public land mobile network from the original routed through the private radio communication network. The mobile terminal then accepts and continues the original call routed through the public land mobile network and terminates the simultaneous communications. Accordingly, the mobile terminal and the method for delivery from a private radio network to a superimposed public land mobile network of the present invention overcomes the specific problems of achieving a call delivery from a private radio network to a mobile network public terrestrial without interruption of the call. This object is achieved when both systems operate in accordance with compatible TDMA standards without the need for a redundant transmitter and receiver circuit within the mobile terminal. Synchronizing towards both the public land mobile network and the private radio network, the mobile terminal is capable of maintaining two communication connections by simply using two semi-channels or two intervals, one for each communication connection.

BRIEF DESCRIPTION OF LKOS DRAWINGS Figure 1 schematically illustrates a portion of a public land mobile network including private radio networks within the coverage area of the public mobile land network; Figure 2 is a schematic functional diagram of a mobile terminal in accordance with the present invention; Figure 3 illustrates schematically the operating environment of the present invention; Figure 4 is a flow chart illustrating the operations of delivering a call from a private radio network to a superimposed public land mobile network, in accordance with a method of the present invention; Figure 5A and Figure 5B schematically illustrate the routing of the call respectively before and after delivery, in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described more fully below with reference to the accompanying drawings, in which the preferred embodiments of the invention are shown. This invention, however, may be encompassed in many different forms and should not be construed as limited to the embodiments set forth herein; instead, these embodiments are provided so that this disclosure is complete and complete, and fully transmits the scope of the invention to those skilled in the art. Referring now to Figure 1, an operating environment of the present invention will be described. The present invention relates to mobile terminals and methods for using same within the structures of the hierarchical cell that may be found in advanced cell phone systems, for example, in order to increase capacity in densely populated areas. The structures of the hierarchical cell can be described in a variety of levels from the macrocell 10, 10 ', 10"in cells that cover the highest level with radios that can be within the order of a few kilometers and optionally can also include lower levels up to picocells, in the cells that cover the lowest level with radios that can be in the order of only a few tens of meters.The macrocells 10, 10 ', 10"define the cellular structure of the public land mobile network or the network wide-area cellular as is well known and as will be understood by a person skilled in the art. Uncoordinated radio networks such as private residential radio communications networks 12, 12 ', 12"may also be within the coverage area of the wide area cellular network and may be private base stations, such as those described in U.S. Patent No. 5,428,668, which is incorporated herein by reference as set forth in its entirety, is also illustrated in Figure 1, a private office radio communications network 14, 12, 12 ', 12"and the network 14 residential are private radio networks having connections to the public switched telephone network ("PSTN") through the PSTN switch or exchange 66 (not illustrated in Figure 1) or with an ISDN wire line network. Accordingly, the private office radio communications network 14 and the private residential radio communications networks 12, 12 ', 12"have an associated PSTN telephone number through which they communicate through the public switched telephone network (or ISDN). As illustrated in Figure 1, the macrocells 10, 10 ', 10"of the public land mobile network each include at least one base station 16, 16', 16." The base stations 16, 16 ' , 16"are connected through a connected infrastructure as is known to those skilled in the art. As illustrated in Figure 1, the connected infrastructure includes a base station controller 18 and the mobile services switching center 20. The specific details of the infrastructure of the public land mobile network will not be further discussed herein except to disclose that the connected infrastructure of the public land mobile network also includes a connection to the PSTN., providing the public land mobile network with access to switch 66 of the PSTN (not shown in Figure 1). When a user of the mobile terminal marches in a cellular area of the public land mobile network, the user's connection is delivered between the base stations 16, 16 ', 16"depending on the distance of the mobile-to-base and the Interference situation This ensures that the user of the mobile terminal maintains a high quality channel as the user moves from one cell to the other Because the base stations 16, 16 ', 16"are all interconnected, the methods for controlling the transmission of the base stations 16, 16 ', 16"and the re-routing of calls from one base station 16, 16', 16" to another in order to maintain a high quality channel ( delivery) is known in the current public land mobile networks. The private radio network 14 as illustrated in Figure 1 is a private radio network that connects to the PSTN through the private branch exchange ("PBX") 22. The private radio network 14 further includes the stations 24 of macrocell base. The macrocell 14 and the base stations 24 can not be controlled by the public land mobile network as they do not form a coordinated part of the PLMN. In addition, signals through the PSTN line to the PBX 22 can create problems when a call on the PSTN line is in progress. Referring now to Figure 2, a modality of a mobile radio terminal 30 according to the present invention is illustrated. The mobile terminal 30 includes a portable housing 32 or other accommodation means. A "chip" memory chip 34 or other storage means for storing the PSTN number of the private communications network 14 and for storing a switching criterion is also placed within the housing 32. It should be understood that the storage can, but does not need to be a common device for both the PSTN number and the switching criteria. For example, the PSTN number could be stored in a digital memory while the switching criterion could be stored as an analog reference voltage. The memory 34 is connected to the simultaneous communication establishment means 42 via the bus 35. The mobile terminal 30 also includes a transceiver 36 or other radio transceiver means that extends within the housing 32 for receiving and transmitting radiocommunication signals between the mobile terminal 30 and the private radio communication network 14, and between the mobile terminal 30 and the public land mobile network. The transceiver 36 may include an antenna (not shown) extending from the housing 32. The transceiver 36 is operably connected in the means of simultaneous communication establishment 42 via an electrical connection 46. The simultaneous communication establishment means 42 includes a sronization circuit 38 or other sronization means for sronizing the radio communications between the mobile terminal 30 and the private radio network 14 and the public land mobile network. Also positioned within the housing 32, there is a detector circuit 48 or other detection means for detecting a signal quality of the private radio communication network 14 during a first radio communication connection between the mobile terminal 30 and the private radio communication network 14. The detector circuit 48 is operably connected to the transceiver 36. This connection may alternatively be directly as illustrated by the dotted line 50 or via the bus 52 via the simultaneous communication establishment means 42. Also illustrated in Figure 2 placed within the housing 32, the comparator circuit 54 or other comparison means for comparing the quality of the detected signal of the detector 48., up to a predetermined switching criterion stored in the storage medium 34. The comparator 54 is operably connected to the detector 48 either directly as illustrated by the dashed lines 56 or through the bus 58 with the simultaneous communication establishment means 42.

- II The simultaneous communication establishment means 42 which is also located within the housing 32, provides a means of control for establishing a second radio communication connection between the mobile terminal 30 and the public land mobile network simultaneously with a first radio communication connection between the terminal 30 mobile and the private radio communication network 14, if the quality of the detected signal of the first connection decreases less than the switching criterion stored in the storage means 34. The report or sports circuit 57 or other report means disclose the telephone number of the line (PSTN or ISDN) of the private radio communications network 14, stored in the storage medium 34, to the public land mobile network when the quality of the detected signal decreases less than the stored switching criterion and to request a re-routing of the first radio communication connection from the private radio network 14 to the public land mobile network. The stored PSTN number and the request to redirect are transmitted to the public land mobile network through the second radio communication connection established by the simultaneous communication establishment means 42. The report circuit 57 is operably connected to the simultaneous means 42 to establish communications through the bus 59. The report circuit 57 is also operably connected to the transceiver 36 either directly as illustrated by dotted line 60 or through from bus 59 to simultaneous means of establishing communications. As will be appreciated by those skilled in the art, the above described aspects of the present invention in Figure 2 may be provided by hardware, software or a combination of the foregoing. Although the various components of the mobile terminal 30 are illustrated in Figure 2 as discrete elements, in practice they can be implemented by a macrocontroller which includes input and output ports and which operates the software code by customary integrated circuits or hybrids by means of discrete components or by a combination of the above. For example, the simultaneous communication establishment means 42, the report circuit 57, the storage circuit 34, the comparison means 46 and the synchronization means 38 could all be implemented as a single programmable device. Alternatively, the comparator 54 can be implemented as a discrete comparator device that compares an analog signal on the connection 56 with a reference switching level. Although two simultaneous communications can be implemented in a mobile terminal 30, in accordance with the present invention, in an analog cellular network environment with a duplicated transmitter and receiver circuit, the benefits of the present invention are particularly directed to land mobile networks. public radio networks and within the public land mobile networks operating in accordance with digital standards, specifically the time division multiple architecture ("TDMA") standards. Examples of these advanced digital standards include GSM and D-AMPS. The following discussion of the apparatus and methods of the present invention will be described with general reference to TDMA and particularly with the GSM standard for ease of understanding. A TDMA system can be implemented subvidiendo the bands of frequency employed in the systems of conventional FDMA in intervals of time in sequence. Although communication in the frequency bands typically occurs in a common TDMA frame that includes a plurality of time slots, communications in each frequency band may occur in accordance with the singular TDMA frame or unique time slots for that band. Examples of systems that employ TDMA are the analog / digital dual IS-54B standard used in the United States, where each of the original frequency bands of EIA-553 are subdivided into 3 time intervals, and the European GSM standard, which divides each of the frequency bands into 8 time intervals. In these TDMA systems, each user communicates with the base station using bursts of digital data transmitted during the time intervals assigned to the user. A channel of the TDMA system typically includes one or more time slots in one or more frequency bands. Because it would generally be inefficient to permanently allocate TDMA time slots to a mobile terminal, typical PLMNs allocate time slots on a basis as needed in order to more efficiently use the limited carrier frequency spectrum, available to the system. Therefore, a critical task in radiotelephone communications is to provide a mobile terminal with access to the system, i.e. allocating the time slots corresponding to a voice or data channel to a mobile terminal, when it is desired to communicate with another mobile terminal or with a landline telephone through the PSTN. This task is found both when the mobile terminal attempts to place a call and when the mobile terminal attempts to respond to a radiolocation of another mobile terminal or conventional telephone. Access to a PLMN can be provided in several ways. For example, a polling technique may be used whereby a central or base station polls the users in series, each providing the opportunity to request access in an orderly manner, without containment. However, serial polling tends to be impractical for PLMNs because typical PLMNs can have hundreds if not thousands of users. Those skilled in the art will appreciate that serial polling of so many users can be extremely inefficient, especially when it is taken into account that many of the users may not wish to give access or may not wish to give access at the specific time they are polled . Due to this reason, PLMNs typically use random access techniques whereby a mobile terminal desiring a voice channel or random data sends an access request to the base 16 or a centering station that the central or base station 16 recognizes establishing a communications channel with the requesting mobile terminal, if available. An example of a random access technique for a TDMA PLMN is that used in the GSM system. With the GSM system, a set of Common Control Channels (CCCHs) is shared by the mobile terminals in the system and includes one or more Random Access Channels (RACHs). Mobile terminals typically do not include an anchor link receiver with which the current state of the RACH is monitored to determine if other mobile terminals are currently requesting access. If the mobile terminal desires access, the mobile terminal typically transmits a random access channel signal which may include a random reference and synchronization sequence, which is often referred to as a "RACH-burst". An RACH burst typically contains several fields, including a plurality of protection bits, a sequence of synchronization bits and a sequence of information bits. Protection bits are used to prevent overlapping of communications that occur in adjacent time slots, as will be discussed below. The synchronization sequence is used by the receiving station 16 to synchronize with the RACH burst, in order to decode the information contained in the information sequence. The information sequence may also include a number of subfields, for example, a random reference number field that serves as a "tag" to identify a specific random access request of a specific mobile terminal. In the GSM system, an RACH is a dedicated TDMA time slot in a carrier frequency band used by the mobile terminals to request access to the communication system. The mobile terminals typically synchronize their RACH bursts to be within a TDMA time slot allocated for the RACH, for example, waiting for a predetermined period after a transition in the synchronization signal transmitted by the base station 16, and then transmitting the RACH burst. However, because mobile terminals conventionally use a common TDMA time slot to transmit the RACH burst, there is a possibility of collisions between access requests that are transmitted simultaneously or almost simultaneously through the neighboring mobile terminals. To deal with these shocks, base station 16 typically implements some form of discussion resolution protocol. For example, base station 16 may refuse to recognize simultaneous requests, requiring a mobile request terminal to reaffirm its request if it continues to desire access after it has ceased to establish a channel. The discussion resolution protocols may also use a variety of predetermined delays and similar techniques to reduce the possibility of the mobile terminal engaging in repeated crashes subsequent to a first crash. The discussion logic used in the GSM Euroepeo system is described in System for Mobile Communications published by M. Mouly and M.B. Pautet, 1992, on pages 368-72. In addition to colliding with other RACH bursts, a burst of RACH can overlap other time intervals of TDMA causing undue interference to the channels using those intervals. Before requesting a channel, a mobile terminal can only be synchronized more or less with the TDMA frame of the base station 16, for example, by aligning its internal time reference with the synchronization signal transmitted by the base station 16 in a manner of open circuit. In carrying out the present invention, it is only this synchronization that needs to be carried out by the mobile terminal 30 before establishing the call of the second simultaneous radio communication connection. Typically, however, finer synchronization occurs only after the base station 16 recognizes the request from the mobile terminal 30 for access and provides the mobile terminal 30 with signals allowing the propagation delay to be determined between the mobile terminal 30 and the base station 16. With this information, the mobile terminal 30 can adjust its TDMA bursts to prevent collision with bursts of other mobile terminals arriving at the base station 16 at the adjacent TDMA intervals. However, a mobile terminal requesting access before this synchronization usually suffers from a time-ambiguity with respect to the other TDMA bursts in the system, because the propagation delay varies with the position in the area of coverage. When a mobile terminal only synchronizes more or less, its internal synchronization can be significantly skewed with respect to the TDMA frame of the base station 16. Without compensating, this time bias may for example cause a burst of RACH transmitted by the mobile terminal to have a significant overlap with the voice or data communications transmitted by another mobile terminal in an adjacent time slot. This overlap can cause undesirable interference and decrease the quality of communications. TDMA PLMNs can compensate for this problem by incorporating a protection time or protection bits in each TDMA interval, which typically precedes the data bits carrying synchronization, voice, data or other information. The protection bits are inserted at each time interval during which the receiving unit ignores the input signals because they can be corrupted by overlapping the RACH bursts and other sources of interference. Because the ambiguity of maximum time in a PLMN tends to be relatively small with respect to a TDMA box, the number of protection bits needed to ensure the acceptable quality of the signal is typically small. For example, the GSM system incorporates approximately 68.25 bits of protection in each time slot for a burst of RACH to ensure that the RACH bursts from a mobile terminal that is so chosen as well as 35 kilometers from the base station 16 , does not cause undue interference in the other TDMA ranges. This can be contrasted with the 8.25 protection bits that are provided by GSM for a normal traffic burst (time slot). The finer synchronization required to the limited protection bits of a normal traffic burst depends on the time alignment information that is derived from the RACH reception, therefore, the RACH burst itself requires a longer protection time. . The synchronization can be achieved by the mobile terminal 30 by matching its synchronization of the transmission frame with that of the superimposed PLMN. The mobile terminal 30 applies the same frame synchronization to all its transmission, thus driving the - 21 frame synchronization reference of the private base station 24 in synchronization with the synchronization of the superimposed PLMN frame. Regardless of whether the private radio network is a 12, 12 ', 12"private residential radio communications network or a private multi-user office radio communications network 14, the smallest private radio network is contained within an overlapping PLMN common. Accordingly, in the case of network 14 of multiple users, any mobile terminal 30 may synchronize the entire network 14 of multiple users to the synchronization of the overlapping PLMN frame by setting the frame synchronization for its specific private base station 24 which it in turn interconnects with any other of the base stations 24 within the private network 14, via the PBX 22. The mobile terminal 30 is synchronized to the base station 16 of the PLMN during the empty frames. It then uses this synchronization reference for its transmissions to and receptions from the base station of the private radio network 12, 12 ', 12", not using time alignment (zero), because the distance of the mobile terminal 30 and the base station of the 12, 12 ', 12"private radio network is typically short, no time alignment is required. The base station of the private radio network 12, 12 ', 12"is synchronized to the transmission of the mobile terminal 30. When a second new radio connection is established with the PLMN base station 16, 16', 16" , the mobile terminal 30 may have to use a time alignment in its transmission to cover the (largest) distance from the mobile terminal 30 to the base station of the PLMN 16, 16 ', 16. "The transmission to the PLMN in the mobile terminal 30, it is then advanced with respect to the reception synchronization.This advance is not used in the transmission to the base station of the private radio network 12, 12 ', 12"to avoid misalignment of reception of the radio signals in the mobile terminal 30. Therefore, for the reception of the mobile terminal 30, the synchronization is based on the reception of the transmissions of the PLMN. The transmissions to the PLMN are based on the synchronization alignment ordered by the PLMN. Finally, no synchronization alignment is used for transmissions to the private radio communications network 12, 12 ', 12"For the semi-channels, the frames used for the PLMN transmission use synchronization alignment and the frames used for the transmissions. communications with the 12, 12 ', 12"private radio network, does not use synchronization alignment. For a double interval operation, the overlap of the two bursts from the mobile terminal 30 should be avoided. This can be achieved by avoiding the use of adjacent intervals or using the forward interval for the radio connection with the PLMN to be advanced (so that it can be advanced without overlapping the non-advanced radio connection interval). Referring now to Figure 3, an illustration is shown where the user of the mobile station 30 has moved to the edge of the coverage scale of the private radio communication network 14. The mobile terminal 30 has a first communication connection established with the wire line or the switch 66 of the PSTN which is partly a wire line connection but also includes a first radio communication connection with the private base station 24 of the 14 private communications network. During unoccupied frames of the communication via the mobile terminal 30 through the first radiocommunication connection, the mobile terminal 30 monitors the mobile base station 16 of the public land mobile network is more or less synchronized with the mobile base station 16 as described above. Accordingly, during the local call from the PSTN 64 via PBX 22 and the private base station 24 (the first radio communication connection), the mobile terminal 30 is synchronized to both the private network 14 and the public land mobile network. In addition, the private base station 24 is synchronized to the mobile terminal 30 which results in the synchronization of the private base station 24 and the mobile base station 16. As will be more fully described below in relation to the description of the operation of the present invention, once the mobile terminal 30 has moved sufficiently far from the private network 14 to cause a signal quality indicator to violate a predetermined switching level, the mobile terminal 30 establishes a second simultaneous radiocommunication connection between the mobile base station 16 of the public land mobile network and the mobile terminal 30. This second radiocommunication connection is provided without requiring double independent transceivers as will be described below because the mobile terminal 30 according to the present invention has synchronized the two TDMA networks operated otherwise independently. Referring now to Figure 4, a modality of mobile terminal operations and method for delivery of the present invention will be described. The mobile terminal 30 detects the quality of the signal from the private network 14 in the first radio communication connection from the private network 14 in the block 70. When the quality of the detected signal is determined as having violated an acceptable level based on the criterion of predetermined communication in block 72, the mobile terminal 30 initiates the delivery of the first communication connection from the private network 14 to the public land mobile network. The quality of the communication with the private network 14 can be determined by a variety of methods known to a person skilled in the art including derivation of an indication of the received signal strength ("RSSI") and / or the bit error regime ("BER"). The switching criterion can be a minimum RSSI or a maximum BER or a function of both. The switching criterion can also be based on the function of signal quality instead of absolute levels, for example, a derivation function that indicates a tendency to degrade the quality of the signal. In block 74, the mobile terminal 30 establishes a second radio communication channel with the public land mobile network simultaneously with the first radio communication connection with the private network 14. The second radio communication connection is initiated by the mobile terminal 30 initiating an establishment of the call in the public land mobile network as described above. The call is established in parallel with the local call that continues to be running through the first radio communication connection with the private network 14. Simultaneous calls can be achieved through the mobile terminal 30 without the need for a separate redundant circuit using two semi-channels in the mobile terminal 30 where one semi-channel is used for the first radio communication connection with the private network 14, and the other semi-channel -channel is used to communicate with the public land mobile network. Alternatively, the mobile terminal 30 may be a double-range mobile telephone where one interval constitutes the connection to the private network 14 and the other interval the connection to the public land mobile network. Any of these options can be used with the present invention due to the fact that the mobile terminal 30 is synchronized to the private base station 16 and the private network 14 through the first radio communication connection in operation with the private network 14. After the call is established, the mobile base station 16 assigns a dedicated control channel ("SDCCH") or traffic channel ("TCH") to the mobile terminal 30. In block 76, the mobile terminal 30 informs the PSTN or ISDN of the number of the private network 14 to the public land mobile network through the second radio communication connection. The line number is communicated to either the mobile terminal 30 during the establishment of the local call with the private network 14 or is transferred from the private base station 24 to the mobile terminal 30 through a fast associated communication control channel. or slow ("FACCH" or "SACCH"). To initiate the re-routing a message including the local number of the line of the private network 14 is then routed through the wire interconnection of the public land mobile network with the wire line interchange (PSTN) / switch 66 in block 78. In block 80, the wireline network redirects the first communication connection from the private network 14 to the public land mobile network. In block 82, the mobile terminal 30 receives and accepts the local call re-routed from the mobile base station 16 to the public land mobile network that sends signals to the mobile terminal 30 to switch to the cellular channel assigned for the call and continues the local call through the public land mobile network. In block 84, the mobile terminal 30 terminates the radiocommunication connection through the private network 14 and returns to the full rate (if a semi-rate had previously been used for simultaneous connections) or to the operation of a single interval ( if previously a double interval operation was used for simultaneous connections) or it remains in the semi-channel. This terminates the delivery procedure. Referring now to Figure 5A and Figure 5B, the routing of the local call (first communication connection) before and after delivery in accordance with the methods of the present invention has been illustrated. In Figure 5A the mobile terminal 30 is shown with its first radio communication connection through the private base station 24. As shown in Figure 5A, the exchange 66 of the PSTN is also operably connected to the mobile switching center 20 which is linked into the connected infrastructure of the public land mobile network including the base station controller 18 and the mobile base station 16. The routing of the local call after delivery according to the present invention is illustrated in Figure 5B. The mobile terminal 30 has a traffic communication channel established with the mobile base station 16 through which the local call of the first communication connection is now being transmitted. The re-routing of the call has been achieved as illustrated in Figure 5B, routing the local call from exchange 66 of the PSTN to the mobile switching center 20 instead of PBX 22 of the private network 14. In the drawings and in the specification, typical preferred embodiments of the invention have been disclosed and, even when specific terms are used, they are used in a generic and descriptive sense only and not for limitation purposes, the scope of the invention having been noted. invention in the following claims.

Claims (24)

CLAIMS:

1. A method for delivery assisted by a mobile network between the private radio network connected to a wireline switch and having a wireline number and a public land mobile network, of a first communication connection between a mobile terminal and the wire line switch including a first radio communication connection between the mobile terminal and the private radio network, the method comprising the steps of: detecting a signal quality of the first radio communication connection from the radio communication network private in the mobile terminal; establishing a second radio communication connection between the mobile terminal and the public land mobile network simultaneously with the first radio communication connection, if the quality of the detected signal has violated a predetermined communication criterion; reporting the wire line number of the private radio network to the public land mobile network through the second radio communication connection; and initiating the re-routing of the first communication connection from the wireline switch to the public land mobile network.

The method of claim 1, wherein the initiation step is followed by the step of accepting the first re-routed communication connection from the public land mobile network.

The method of claim 2, wherein the acceptance step is followed by the step of disconnecting the first radio communication connection between the mobile terminal and the private radio network.

The method of claim 1, wherein the public land mobile network and the private radio network are both TDMA systems and which includes at least one base station and wherein the establishment step includes the step of synchronizing the time of communications between a base station and the public land mobile network and the base station of the private radio network.

The method of claim 4, wherein the mobile terminal is a double-range mobile telephone and wherein the setting step includes the step of assigning a first interval to the first radio communication connection, and a second interval to the second radio communication connection.

6. The method of claim 4, wherein the setting step includes the step of assigning a first half-channel to the first radio communication connection and a second half-channel to the second radio communication connection.

The method of claim 4, wherein the synchronization step includes the step of monitoring a base station of the public land mobile network and synchronizing the mobile terminal with the supervised base station of the public land mobile network, while the first communication connection sends the mobile terminal through the private radio network.

The method of claim 7, wherein the step of monitoring is carried out by the mobile terminal during idle frames.

The method of claim 4, wherein the detecting step includes the step of determining an indication of the intensity of the received signal for the first radio communication connection between the mobile terminal and the private radio network.

The method of claim 9, wherein the detection step further includes the step of determining a bit error rate for the first radio communication connection between the mobile terminal and the private radio network.

11. The method of claim 4, wherein the step of reporting includes the step of obtaining the wire line number from the private radio network through the radio communication control channel between the mobile terminal and the private radio network.

12. A method for delivery assisted by a mobile network between a private radio network connected to a wire line switch and having a wire line number and a public land mobile network of a first communication connection between the terminal mobile and the wire line switch including a first radio communication connection between the mobile terminal and the private radio network, the method comprises the steps of: detecting a signal quality of the first radio communication connection from the private communications network in the mobile terminal. establishing a second radio communication connection between the mobile terminal and the public land mobile network simultaneously with the first radio communication connection if the quality of the detected signal has violated a predetermined communication criterion; and reporting the wire line number of the private radio network to the public land mobile network through the second radiocommunication connection.

The method of claim 12, wherein the step of reporting is followed by the steps of: accepting the first re-routed communication connection from the public land mobile network; and disconnecting the first radio communication connection between the mobile terminal and the private radio network.

The method of claim 13, wherein the public land mobile network and the private radio network are both TDMA systems and each includes at least one base station and wherein the establishment step includes the step of synchronizing the communication time between a base station of the public land mobile network and a base station of the private radio network.

The method of claim 14, wherein the synchronization step includes the step of monitoring a base station and the public land mobile network and synchronizing the mobile terminal with the supervised base station of the public land mobile network while the The first communication connection is routed to the mobile terminal through the private radio communication network.

16. A mobile radio terminal for use with a private radio network connected to a wire line switch and having a wire line number placed within the public land mobile network, comprising: a detection means for detecting a quality of the signal from the private radio network during a first radio communication connection between the mobile terminal and the private radio network; means for establishing simultaneous communication within the housing and responding to the detection means for establishing a second radio communication connection between the mobile terminal and the public land mobile network simultaneously with the first radio communication connection if the quality of the detected signal has violated a stored switching criterion; and, a wireline information means for reporting the number of the wireline stored to the public land mobile network through the second radiocommunication connection.

The mobile terminal of claim 16, wherein the public land mobile network and the private radio network are both TDMA systems and each includes at least one base station and wherein the means of establishing simultaneous communication includes a synchronization means for synchronizing the time of communications between a base station of the public land mobile network and a base station of the private radio network.

The mobile terminal of claim 17, wherein the synchronizing means includes a means for monitoring at least one base station of the public land mobile network during idle frames.

The mobile terminal of claim 17, wherein the means for establishing the simultaneous communication includes a means for assigning a first interval to the first radio communication connection and a second interval to the second radio communication connection.

The mobile terminal of claim 17, wherein the means for establishing the simultaneous communication includes a means for assigning a first half-channel to the first radiocommunication connection and a second half-channel to the second radiocommunication connection.

21. A mobile radio communication terminal for use with a TDMA private radio network connected to a wire line switch and having a wire line number placed within a public TDMA land mobile network comprising: a transceiver means radio to receive and transmit radio signals between the mobile terminal and the private radio network and between the mobile terminal and the public land mobile network; a detection means operably connected to the radio transceiver means for detecting a quality of the signal from the private radio network during a first radio connection between the mobile terminal and the private radio network; a comparison means within the housing and operably connected to the detection means for comparing the quality of the detected signal with a predetermined switching criterion; means for establishing simultaneous communication within the housing and electrically connected to the transceiver means and responding to the comparison means for establishing a second radio communication connection between the mobile terminal and the public land mobile network simultaneously with the first radio communication connection, if the quality of the detected signal has violated the stored switching criterion, the simultaneous communication establishment means includes a synchronization means operably connected to the radio transceiver means for synchronizing the radio communications between the mobile terminal and the private radio network, and the public land mobile network; and an information means for reporting the wireline number to the public land mobile network and requesting re-routing of the first radiocommunication connection from the private radiocommunication network to the public land mobile network through the second connection of radiocomunication.

22. The mobile terminal of claim 21, wherein the synchronization means includes a means for monitoring the public land mobile network during unoccupied frames and wherein the wire line switch is a PSTN switch and the wire line number is a PSTN number. The mobile terminal of claim 21, wherein the simultaneous communication establishment means includes a means for assigning a first interval to the first radiocommunication connection and a second interval to the second radiocommunication connection. The mobile terminal of claim 21, wherein the simultaneous communication establishment means includes a means for assigning a first half-channel to the first radio communication connection and a second half-channel to the second radio communication connection. SUMMARY OF THE INVENTION Delivery assisted by a mobile network between a private radio network (14) connected to the public switching telephone network (64) and a public land mobile network also connected to the telephone network of the public switch is provided by a terminal ( 30) mobile radiotelecommunications, supporting the simultaneous communication connections between the two uncoordinated networks. The mobile terminal (30) supervises a base station (16) of the public land mobile network during the idle frames of the communication connections with the private radio network, thereby synchronizing the mobile terminal with both the base of the network public land mobile as the private telecommunications network. The interruption of the call is prevented during delivery by maintaining simultaneous communications with the radiocommunication network and the public land mobile network through the use of two semi-channels or double-range communications, where both the public land mobile network As the private radio network they operate in accordance with the compatible standards of TDMA. The delivery is initiated when the mobile terminal detects a signal quality that violates a predetermined switching criterion and passes the PSTN telephone line number from the private radio network to the base station of the public land mobile network which it requests the re-routing of the call from the PSTN switch.