MXPA98010317A - Method and apparatus for carrying out an unlocked transfer in a multi access communication system - Google Patents

Abstract

A method and an apparatus allowing transferring is presented while the mobile station (2) is in the state of access to the system. This is achieved by providing channel allocation messages, which will be sent over the radiolocation channel of a plurality of base stations (26), which increases the probability that one of the messages is communicated. In addition, this ensures that the mobile station (2) will be able to effect the transfer to a different base station (26) and will have a traffic channel assigned to it in the new base station (26) without delay. There is further provided a method and apparatus that allows the mobile station (2) to be assigned directly to a soft transfer state by assigning the traffic channel.

Description

METHOD AND APPARATUS FOR CARRYING OUT AN UNEMPLOYED TRANSFER IN A MULTIPLE ACCESS COMMUNICATION SYSTEM FIELD OF THE INVENTION The present invention relates to communication systems. More particularly, the present invention relates to a novel and improved method and apparatus for effecting free or idle transfer in a multiple access communication system. In addition, the present invention relates to ur. improved method for assigning a traffic channel in a multiple access communication system. The invention also relates to a method for reducing the number of required transfers that occur while a mobile station is formed waiting for a traffic channel in a multiple access communications system ANTECEDENTS OF THE. INVENTION Normally, communications systems prohibit transfers while the mobile station is in a state of access to the system. The state of access to the system is the state in which the communications are initiated either by the mobile station, by means of transmissions on an access channel or by a base station by means of transmissions on a transmission channel.

P1782 / 98MX radiolocation. In the exemplary mode, messages are sent in accordance with a multiple code communication format by code division (CDMA), which is disclosed in detail in U.S. Patent No. 4,901,307 entitled "Spread Spectrum Multiple Access Communication System üsing Satellite or Terrestrial Repeaters "and in the Patent of United States of America No. 5,103,459, entitled "System • and Method for Generating Waveforms in a CDMA Cellular Telephone System ", both assigned to the assignee of the present invention and incorporated herein by reference.The use of radiolocation and access channels for the initiation of a call is well known in The technique is detailed in the provisional standard TIA / EIA IS-95-A, entitled "Mobile Station-Base Station Compatibility Standard for Dual Mode Windeband Spread Spectrum Cellular System." One of the characteristics of CDMA systems is that each cell is reused or reuses the same frequency The combination in diversity is a method by which a receiver that receives signals that convey the same information, combine these signals which are propagated through different trajectories to provide an improved estimate of the signals The design of a receiver to take advantage of the P1782 / 98MX diversity signals that convey the same information but travel through different propagation paths or that are transmitted by different transmitters are described in detail in U.S. Patent No. 5,109,390, entitled "Diversity Receiver in. to CDMA Cellular Telephone System ", assigned to the assignee of the present invention and incorporated herein by reference. Soft transfer is a method by which a mobile station that moves or moves from one cell to another receives information from the base stations serving or serving the two or more cells in the boundary area, as long as the mobile station is located near the limit. The signals sent by the base stations are combined in the receiver of the mobile station by the aforementioned diversity combining method. A method and system for providing soft handoff in a CDMA communication system, wherein a plurality of base stations are in communication with a mobile station in the limits or near the cell boundaries, is disclosed in the Patent of United States of America No. 5,101,501, entitled "Method and System for Providing a Soft Handoff in a CDMA Cellular Telephone System" and in United States Patent No. 5,267,261, entitled "Mobile Station Assisted P1782 / 98MX Soft Handoff in a CDMA Cellular Communication System ", both assigned to the assignee of the present invention and incorporated herein by reference. The hard transfer, in contrast to the soft transfer, is where the mobile station that passes from one cell to another is released or released by the cell from which it is leaving before being captured or picked up by the cell it is entering. The use of the same frequency in each cell and the use of soft transfer results in a high capacity of the CDMA system. The reuse or reuse of the same frequency in the neighboring cell causes very rapid changes in the ratio of uplink signal to noise, near the limits of the cell. This is because the cell that will be received by the mobile station may vanish and the neighboring cell may increase in intensity (anti-fading). In general, when the mobile station is receiving two cells, the energy of the traffic channel received per dispersion or propagation chip, with respect to the total spectral noise density for the signal transmitted by the cell 1 is provided by the following equation (1 ): P1782 / 98MX And the energy of the traffic channel received by propagation or dispersion chip with respect to the total spectral noise density for the signal transmitted by the cell 2 is provided by the following equation (2): where in equations (1) and (2) Iro ,, c. is the total thermal noise, EF is the fraction of the channel power of the traffic transmitted by cell 1 and cell 2, respectively, and Jorl,? or2 is the fraction of the power of the traffic channel received at the station mobile from cell 1 and cell 2, respectively. Consider that Ioc will be small with respect to íorl and íor2- When cell 1 fades with respect to P1782 / 98MX cell 2, íorl becomes small with respect to? Or2 (the Ior2 ratio becomes large). In this way, 1 is done IOG2 E 1 becomes small. If the mobile station is not found I, in soft transfer, then this change is the ratio of signal to noise can cause problems. However, if the mobile station is in soft transfer with the neighboring cell, then the change in the signal-to-noise ratio is not a problem, because the mobile station is effecting the combination of upward traffic channels in diversity. of the two cells. While the first path provided by -1 becomes small, the second path or provided by -2 becomes large. In this way, the fading in one cell increases the signal-to-noise ratio of the other cell. Radiolocation is a method for sending information to a mobile station indicating the start of the mobile finished service or for receiving an indication of new supplementary information. A method for initiating a call initiated at the base station is described in detail in U.S. Patent No. 5,392,287, entitled "APPARATUS AND METHOD FOR REDUCING POWER CONSUMPTION IN A MOBILE COMMUNICATIONS P1782 / 98MX RECEIVER "and in copending application of the United States of America No. 08 / 206,701, filed March 7, 1994, which is a continuation of the United States of America Patent with Serial No. 5,392,287, both assigned to the assignee of the present invention and incorporated herein by reference The present invention is equally applicable to calls initiated at the mobile station, the method of which is described in detail in the co-pending United States of America Patent Application No. of Series 08 / 219,867, filed on January 18, 1996, assigned to the assignee of the present invention and incorporated herein by reference. In a radiolocation system with intervals or slots, a mobile station monitors the radiolocation channel for a short period of time. default time interval and then does not return to monitor the radiolocation channel until the next predetermined time interval In the IS-95-A, This method of periodically monitoring the radiolocation channel is called interval or slot mode and the mobile station can monitor the radiolocation channel for 80 ms. every 1.28 seconds. The period between monitoring intervals can be made as long as the user wishes. Before each predesignated time slot or slot in which a mobile station can be radiolocated, the P1782 / 98MX mobile station wakes up (ie activates) and synchronizes or updates its synchronization with the base station. The mobile station then monitors location messages or other messages in the slot or interval. After a certain interval, the mobile station can be inactivated and not monitor the radiolocation channel until exactly before the next assigned slot. Prior to the time when a mobile station is actively communicating traffic information with the mobile communication system and after the time when the mobile station has obtained synchronization in time with the communication system, the mobile station is in a state referred to as the free or unoccupied state. In the idle state, the mobile station can receive messages, receive an incoming call, initiate a call, initiate registration or initiate the transmission of a message. When the mobile station is in the idle state, the IS-95-A allows the mobile station to perform a free or unoccupied transfer at any other time than the interval at which the mobile station is required to monitor its allocated slot. However, when the mobile station originates a call or receives a radiolocation message, the mobile station enters the state of access to the system for P1782 / 98MX send a source message or a reply message to the radiolocation. While in the state of access to the system, a mobile station IS-95-A does not work in slot or interval mode. This is an operation called non-slotted or non-slotted operation. Specifically, the mobile station continues to monitor the radiolocation channel until it is directed by the base station to a different state or an error condition occurs that allows the mobile station to leave the access state to the system. The exemplary modality will be described in the context of the source operation and the origin message, but the concepts are applied directly to the finished call process in the mobile and to the response message to the radiolocation. After the mobile station sends the originating message and receives the acknowledgment or acknowledgment, the mobile station waits for a channel assignment message, indicating in which channel the traffic communications from the base station to the mobile station will be conducted. . Upon receiving the channel assignment message, the mobile station is tuned to the assigned traffic channel, receives the information in the upstream traffic channel and begins to transmit in the downstream traffic channel. The ascending traffic channel is the channel P1782 / 98MX on which the information from the base station is sent to the mobile station and the downstream traffic channel is the traffic channel in which the information from the mobile station is sent to the base station. The interval between the time or moment at which the mobile station sends the originating message and the time or moment at which the mobile station receives the channel allocation message, depends on the implementation of the individual infrastructure of the vendor or provider. This can vary from less than half a second to several seconds. Until the moment in which the mobile station receives the channel assignment message, the mobile station is in the state of access to the system. The radiolocation channel normally does not support soft transfer. In this way, the fading issues previously described occur. These are normally balanced or counteracted by making the radiated power of the radiolocation channel greater than that of the traffic channel. Because a radiolocation channel can handle the origin and termination of the call of many traffic channels, the loss of capacity due to its superior power is minimal. In order to support smooth transfer in the radiolocation channel, the system would essentially have to send the same information over the channel of P1782 / 98MX radiolocation in all cells, dramatically reducing the total capacity of the radiolocation channel. While in the free or idle state, the mobile station is allowed to make transfers. Normally, the mobile station makes a transfer every time that the level of the signal received from one cell is sufficiently above another cell. This free or unoccupied transfer is normally carried out before the mobile station begins to monitor the interval or slot. However, there may be cases in which the mobile station is unable to select the correct cell before the interval or slot begins and the mobile station must continue to monitor the existing cell. While in the state of access to the system, the mobile station is not allowed to make unoccupied transfers. However, when the mobile station is in the state of access to the system, there may be cases in which the change in the signal to noise ratio, - £ -1, is so fast that the error rate in the message becomes so high that the mobile station can not correctly receive the signaling messages sent on the radiolocation channel. As a result, the mobile station may not receive the assignment message P1782 / 98MX channel. This means that the origin of the call was not successful. The IS-95-A allows that. the mobile station leaves the state of access to the system and returns to the idle state of the mobile station, if it has not received any radiolocation channel message for one second, this means that the mobile station does not receive the channel assignment message and that the origin of the call was unsuccessful. A similar problem exists when the mobile station is first assigned to the traffic channel. The IS-95-A allows only a single base station to be assigned to the mobile station. If another cell is strong or becomes stronger, the mobile station may not satisfactorily receive the upstream traffic channel. As a result, the call may be lost. The problem is that the mobile station is assigned to a traffic channel with only one active set member and is not in smooth transfer. According to IS-95-A, with the. In order for the mobile station to enter the soft transfer, the following steps must occur. First, the mobile station detects that the pilot of another base station is above a predetermined threshold value of energy. Second, the mobile station sends a pilot intensity measurement message. Third, the infrastructure P1782 / 98MX installs or establishes the transfer, and the infrastructure sends the transfer address message to the mobile station. Depending on the circumstances and the implementation, this may require a few hundred milliseconds to considerably more than a second. Thus, although soft transfer is generally supported on IS-95-A systems. However, soft transfer is not supported when the mobile station is in the state of access to the system. Thus, there is a need for a system that allows smooth transfer while the mobile station is in the state of access to the system to provide an increase in reliability in the process of accessing the system and other benefits.

SUMMARY OF THE INVENTION The present invention describes several modifications that can improve the operation in the road and alignment channels. The first particularity of the present invention is that it allows transfers while the mobile station is in the state of access to the system. This allows the mobile station to receive a base station whose signal-to-noise ratio is high, so that the error rate in the message is low. This avoids having to lose P1782 / 98MX call establishments, due to the inability to receive the radiolocation channel. By allowing the transfer, the base station needs to send the channel assignment message on the radiolocation channel through a plurality of base stations. A second particularity of the present invention is that it allows the infrastructure to know which base stations should send the channel assignment message to the mobile station. Furthermore, this ensures that the mobile station will be able to transfer to a different base station and have a traffic channel assigned to it in the new base station without delay. A third particularity of the present invention is that it allows the infrastructure to know which base stations should be in the active set of the mobile station before the mobile station is assigned to the traffic channel. The active set is a set of base stations that are supplying the strongest signals to the mobile station at a given time. This allows the infrastructure to determine, before the mobile station is assigned to the traffic channel, regardless of whether there are sufficient resources to place the mobile station in soft handoff. This is useful, because the mobile station near the cell boundary can immediately request to be placed in P1782 / 98MX smooth transfer after it is assigned to the traffic channel. In addition, this minimizes call losses, due to the rapid changes in the aforementioned signal to noise ratio. Furthermore, attached to the third particularity of the present invention is the inclusion of multiple members of the active set in the channel assignment message, which allows the mobile station to be assigned to a traffic channel in the soft transfer state. Finally, the features presented above provide a special utility in the channel allocation and priority access operation (PACA) that provides users with access to limited communication resources in accordance with the user's designated priorities. While the invention is described in terms of a CDMA system, the invention is applicable to any cellular or satellite communication system.

BRIEF DESCRIPTION OF THE DRAWINGS The features, objects and advantages of the present invention will be more evident from the detailed description set forth below, when considered with the drawings, in which like reference numbers are correspondingly identified.

P1782 / 98MX in the present and, where: FIGURE 1 is a block diagram of a mobile station communicating with a base station of a group of base stations; FIGURE 2 shows an arrangement or distribution of cells corresponding to the base stations; and FIGURE 3 shows the Ec / I0 pilot of a mobile station moving between two base stations.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Referring to FIGURE 1, with the ignition on or energized, the mobile station 2 enters the system determination substate. A system determination processor (not shown) selects a system on which an acquisition attempt is made and provides the necessary frequency information to the receiver (RCVR) 8. Although not shown separately, the system determination processor could be implemented within the control processor 18. The control processor 18 can be implemented in a microprocessor or microcontroller that operates or operates according to the control program stored in memory. In the exemplary embodiment, after selecting a system for determining the system, mobile station 2 moves or moves to the substate Pilot acquisition P1782 / 98MX, in which it attempts to demodulate a pilot signal based on the acquisition parameters retrieved in the system determination substate. In the exemplary embodiment, the mobile station 2 attempts to acquire a CDMA pilot signal in accordance with the acquisition parameters. The signs (if they are present) they are received on antenna 4 and passed through duplexer 6 to receiver 8. Receiver 8 subverts, amplifies the received signal, converts the analog signal into a digital representation and passes the signal to the search engine 10. The search engine 10 tries to acquire a pilot signal when testing the PN displacements. A PN offset is tested by demodulating the signal in accordance with the PN displacement hypothesis and measuring the energy of the demodulated signal. The design and implementation of the search engine hardware for the acquisition of CDMA is known in the art and is described in detail in the aforementioned Patent of the States of America No. 5,109,309. When the searcher 10 detects a pilot signal with power above a predetermined threshold value, the mobile station 2 enters the synchrony channel acquisition substate and attempts the acquisition of the Sync channel. Normally, the Sync channel "as transmitted by the base stations, includes the information P1782 / 98MX basic system such as system identification (SID) and network identification (NID) but, more importantly it provides the timing information to the mobile station 2. The mobile station 2 adjusts its time or timing in accordance with the information of the Sync channel and then enters the free or idle state of the mobile station. With the successful acquisition of the Sincronía channel, the mobile station 2 begins to monitor the radiolocation channel in accordance with a predetermined radiolocation format. The mobile station 2 demodulates a signal based on a predetermined Walsh sequence that is reserved for the transmissions of the radiolocation channel. For example, let's say that the pilot signal that was acquired was transmitted by the base station 26a, then the mobile station 2, monitors the radiolocation channel in accordance with the timing information provided by the Sync channel and using a predetermined Walsh sequence. The base station 26a intermittently transmits supplementary information in the radiolocation channel. In the exemplary mode, the supplementary information includes a list known as the neighbor list. In the IS-95-A, this list is provided to the mobile station 2 by the base stations 26a-26n in the P1782 / 98MX Neighbor List Message. This list is referred to herein as NGHBR_LIST_BASE. The NGHBR_LIST_BASE is a list of base stations in the vicinity of the base station 26a that can supply strong signals to the mobile station 2 and, thus, are candidates for the idle transfer. In the exemplary embodiment, the base stations 26a-26k of FIGURE 1 correspond to the cells 36a-36k of FIGURE 2, respectively. In this way, the base station 26a provides coverage to the cell 36a. Referring to FIGURE 1, in the preferred embodiment, the base stations -26b-26k are in the NGHBR_LIST_BASE transmitted to the mobile station 2. It should be noted that the present invention is equally applicable to the case where some of the base stations in the list of neighbors are not controlled by the same base station controller (BSC). The controller 32 of the base station is responsible for providing the information between the base stations 26a-26o, for selectively supplying the information from a main telephone switching center (MTSO) (not shown) to the base stations 26a-26o and for supplying to the base stations 26a-26o the messages generated internally. If the pilot signal acquired was transmitted by P1782 / 98MX the base station 26a, after receiving the supplementary information, the mobile station 2 can register with the base station 26a when transmitting its mobile identification number (MIN) to the base station 26a. The mobile station 2 then enters the idle state and monitors its assigned radiolocation channel in radiolocation mode with intervals or slots, after successfully registering at the base station 26a. If the registration was not made, the mobile station also enters the free or idle mode and monitors in the radiolocation mode with intervals or slots, its assigned radiolocation channel, which is transmitted by the base station 26a. In the slotted radiolocation mode, the base station 26a transmits any radiolocation or signaling information directed to the mobile station 2 at predetermined time intervals, called time slots. In the exemplary embodiment, the time slots and the radiolocation channel are determined in accordance with the control verification function of the mobile identification number (MIN), which, after registration, is known to the base station 26a and the mobile station 2. In the present invention, the base station 26a transmits to the mobile station 2 a list of stations P1782 / 98MX base to which the mobile station 2 is allowed to perform the unoccupied transfer while in the state of access to the system. This list will be referred to herein as LIST_BASE. The base stations in LIST_BASE are usually a subset of the base stations in NGHBR_LIST_BASE and would normally be using the same base station controller (BSC). Thus, for example, in FIGURE 1, the NGHBR_LIST_BASE may consist of all base stations 26b, 2ßk but, the LIST_BASE may consist of the subset of base stations 26b, 26c (not shown), 26g (not shown) and 26h (not shown). The following description is in terms of a call origin and the discussion focuses on the origin message. The same procedures are applied at the end of the call where the response message to the radiolocation is replaced by the origin message. When the mobile station 2 originates a call, the message generator 20 generates a message of origin and transmits that message in the access channel. The message generator 20 may be implemented in a microprocessor programmed to perform the functions described. Although illustrated as a separate element, the message generator 20 could be implemented within the control processor 18. That message is received and demodulated by the base station 26a, that the mobile station P1782 / 98MX is currently monitoring. In response to receiving the originating message, each of the base stations in LIST_BASE 26a-26i transmits a channel assignment message indicating a traffic channel over which the communications will be conducted. It should be noted that normally the Walsh channel used for communications with a first base station of the LIST_BASE will not be the same Walsh channel used for communications with a second base station in the LIST_BASE. Because a plurality of base stations are sending the channel assignment message, the mobile station 2 is free to effect an unoccupied transfer, while it is in the System Access state and after sending the origin message to any base station that is in the LIST_BASE and can still receive the channel assignment message. In an alternative mode, the mobile station 2 sends the origin message to the base station 26a and then awaits the acknowledgment or acknowledgment of the origin message. Until the mobile station receives the acknowledgment or acknowledgment, the mobile station is not allowed to make a transfer. However, after the mobile station receives the acknowledgment, the mobile station is free to perform an idle transfer to any base station in the LIST_BASE.

P1782 / 98MX In another alternative embodiment, mobile station 2 sends the origin message using the procedures described in IS-95-A as described in detail in the co-pending United States of America Patent Application Serial No. 08 / 412,648, entitled "RANDOM ACCESS CHANNEL", filed on March 12, 1994, assigned to the assignee of the present invention and incorporated herein by reference. If, within a predetermined waiting period, the acknowledgment of the base station 26a is not received, the mobile station increases its transmission power and attempts to send the message again. If the mobile station 2 is unable to receive the acknowledgment from the base station 26a after a certain number of attempts and another base station, for example, the base station 26b is stronger, the mobile station 2 is allowed to perform a unoccupied transfer to the base station 26b and restart transmission of the source message. In one embodiment, each of the base stations in LIST_BASE transmits a channel assignment message indicating only one traffic channel for communication with that particular base station. In an alternative mode, each of the base stations 26a-26i of the LIST_BASE, transmits an identical Channel Assignment Message that indicates not only the traffic channel that will be used for communications with that station P1782 / 98MX particular base but also indicates the traffic channel that will be used for communications with all base stations in the LISTJBASE. This would require the base stations 26a-26i in the LIST_BASE to communicate the available traffic channels through the base station controller 32. By supplying the channel allocation messages from a plurality of base stations, the success rate of the channel allocation process is greatly increased or improved. The above process allows the infrastructure to establish soft transfer and include more than one member of the Active Set the Channel Assignment Message. Instead of first communicating with another base station and then moving towards smooth transfer, it is thus possible for the mobile station 2 to immediately arrive at the soft transfer state and immediately receive traffic communication from two or more base stations. This accelerates the process of moving the mobile station 2 towards soft handoff, which improves system performance and minimizes call loss, due to a low proportion of upward signal to noise. In one mode of this process, the base station establishes smooth transfer with all base stations of the LIST BASE. In a modality P1782 / 98MX alternative to this process, the base station establishes the smooth transfer with a subset of LIST_BASE base stations and sends the necessary information in the channel allocation message so that the mobile station 2 enters the smooth transfer. This information includes the identities of this subset of base stations. In IS-95-A, the pilot PN shift identifies the base station. The radiolocation messages sent by the base stations 2ßa-26i are received in the antenna 4 of the mobile station 2. The received message is then supplied through the duplexer 6 to the receiver 8, where the received signal is subconverted and amplified. The subverted messages are supplied to the demodulators 12a-12j which demodulate the received messages. The control processor 18, in accordance with the information from the search engine 10, selects the radiolocation channel or channels that the mobile station 2 will demodulate the data of the incoming radiolocation channel. In one embodiment, the demodulators 12a-12j monitor only one base station. The searcher 10 together with the control processor 18, determine which other base station is better. Then, the control processor 18 causes the demodulators to begin to demodulate the received signal from the other P1782 / 98MX base station. Because the mobile station 2 will receive an assignment message from more than one base station, the mobile station 2 is free to effect the unoccupied transfer while in the system access state. In another embodiment, the mobile station 2 monitors all the base stations in the LIST_BASE and demodulates the signals identified in the LIST_BASE. In a preferred embodiment, the LIST_BASE is not provided separately from the Neighbor List Message, but rather an indication is provided indicating which of the members of the neighbor list (NGHBR_LIST_BASE) are members of the LIST_BASE together with the Message from the List of Neighbors. In the exemplary mode, one of the reserved values in the supplementary message is used to indicate which of the systems specified in the Message of the Neighbors List are in the LIST_BASE. In the exemplary embodiment of an IS-95-A base station, the reserved values in the supplementary message are used to specify the members of the LIST_BASE are NGHBR_LIST_BASE values of the Neighborhood List Message. In the exemplary embodiment, the Neighbor List Message IS-95-A includes the pilot PN movements of the base stations in the NGHBR_LIST_BASE and an indication of which base stations in the Message of the P1782 / 98MX List of Neighbors are in the LIST_BASE. The pilot PN sequence of the present base station is transmitted to provide a reference to the mobile station 2 that can be used to identify the other PN offsets of the base station. As described above, all base stations in LIST_BASE would be required to send channel assignment messages to mobile station 2. While this would allow mobile station 2 to transfer and thereby increase the success rate of the channel allocation process, requires an additional capacity of the Radiolocation Channel for all calling establishments. A modification of this method that would reduce the impact on the capability of the radiolocation channel is to cause the mobile station 2 to send a list of pilots that are above a predetermined power threshold. This list is referred to herein as LIST_MOBILE. In one embodiment, the searcher 10 demodulates the pilot signals in preference to the PN offsets of the base stations in the LIST_BASE followed by the PN offsets of the base stations in NGHBR_LIST_BASE and, then, in accordance with the rest of the PN offsets. A method for providing an optimized search hierarchy is described in the P1782 / 98MX mentioned above Patent of the United States of America No. 5,267,261. In the exemplary embodiment, the searcher 10 demodulates the received signals in accordance with a pilot PN shift and measures the power of the demodulated pilot. The energy values are supplied to the control processor 18. The control processor 18 compares the energy of the demodulated signal with a threshold value and compiles a list of PN offsets that are above that threshold. This list is referred to as the LIST_MOBILE. Once the LIST_MOBILE has been compiled, it is transmitted over the access channel and is received by the base station 26a which is monitoring the mobile station 2. In the exemplary embodiment, the LIST_MOBILE is included in the origin message. In another embodiment, the LIST_MOBILE is received by more than one of the base stations 26a-26o. The LIST_MOBILE is supplied to the controller 32 of the base station. In the preferred embodiment, the threshold used by the mobile station 2 to determine whether it includes a base station in the T_ADD is sent as part of the supplementary messages by the base stations 26a-26o. In the preferred embodiment, this threshold could be the value T_ADD sent in the System Parameter Message IS-95-A. This value T_ADD is normally used by IS-mobile stations P1782 / 98MX 95-A to determine if the Pilot Intensity Measurement Message IS-95-A is sent on the traffic channel to the base station, indicating that the mobile station has detected a pilot exceeding T_ADD. FIGURE 3 illustrates the Ec / I0 for the pilot channel IS-95-A transmitted by the base stations 26a and 26b as the mobile station 2 moves away from the base station 26a to the base station 26b. When the mobile station 2 is completely within the coverage of the base station 26a, as indicated by the region 38, the pilot channel of the base station 26b is below the level T_ADD. Similarly, when the mobile station 2 is completely within the coverage of the base station 26b, as indicated by the region 41, the pilot channel of the base station 26a is below the level T_ADD. When the mobile station 2 is in the region 38, the base station 26b does not report in the origin message. Similarly, when the mobile station 2 is in the region it is in the region 41, in the origin message it does not report to the base station 26a. When the mobile station 2 is in the region 39, the pilot Ec / I ~ for the base station 26b is above T_ADD and the mobile station reports to 26b in the origin message. Similarly, when the mobile station 2 is in the region 40, the pilot Ec / I0 for the base station 26a is P1782 / 98MX above T_ADD and the mobile station reports to 26a in the origin message. The preferred embodiment uses the Ec / I0 as provided in IS-95-A for these measurements; however, alternative measurements of signal strength or signal-to-noise ratio that are well known in the art are equally applicable. In the preferred embodiment, mobile station 2 would be allowed to perform an idle transfer only to those base stations in both LISTJMOBILE and LIST_BASE. Call the set of base stations in both lists LIST_BOTH. This has two advantages. First, the infrastructure needs to send only the Channel Assignment Message to those base stations identified by the mobile station as possible candidates for an unoccupied transfer and that the mobile station is allowed to transfer. This set of base stations is provided in LIST_B0TH. This will significantly reduce the additional messages that are required. Secondly, LIST_MOBILE provides a list of pilots above T_ADD to controller 32 of the base station, which allows the infrastructure to identify which base stations must be members of the active set of the mobile station. In this way, if the P1782 / 98 X controller 32 of the base station wishes to establish smooth transfer when the mobile station is assigned to a traffic channel, only needs to establish soft transfer with those base stations in the LIST_MOBILE. In an alternative mode, the mobile station 2 sends to the base station in its origin message, those base stations in LIST_BOTH. This reduces the amount of information that needs to be sent from the mobile station 2. Additionally, it allows the infrastructure to establish the smooth transfer and includes more than one member of the Active Set in the Channel Assignment Message. The Channel Assignment Message would include the pilot PN journeys of base stations that are in the Active Set. It is possible that the mobile station 2 immediately appears in the soft transfer state and immediately receives traffic communication from two or more base stations, instead of communicating first with a base station and then moving towards the smooth transfer which may not be possible due to capacity or other limitations. For example, if the mobile station 2 is in the cell 36a near the "boundary with the cell 36b at location 37, as shown in FIGURE 2, then the P1782 / 98MX LIST_MOBILE will identify the pilot PN offsets of the base station 26b. The channel assignment message that will be transmitted by both base stations, 26a and 26b, will identify a traffic channel to be used by the mobile station 2 for dedicated or exclusive communications between the base stations 26a and 26b and the mobile station 2. At least one of the demodulators 12a-12j will be tuned to receive the traffic channel information from the base stations 26a and another one of the demodulators 12a-12j will be tuned to receive the traffic channel information from the base stations 26b. A plurality of demodulators 12a-12j will begin to demodulate the traffic channel signals transmitted by the base stations 26a and 26b. The demodulated signals will be supplied to the diversity combiner 34 which combines the received signals to provide a better estimate of the transmitted data. There are several other elements that are important for the present invention. The first is that the mobile station 2 can not be allowed to make the transfer unoccupied until it receives the acknowledgment of a transmitted message or that the waiting time to receive the acknowledgment has expired. This is to allow the mobile station 2 to receive the acknowledgment P1782 / 98MX in its access channel probes. It also allows the base station 26a to which the mobile station is sending its access channel probes, generate the acknowledgment instead of the acknowledgment being generated by the controller 32 of the base station. This has the advantage of reducing the delay, thus making the call establishment process faster. Additionally, if the mobile station 2 is in the System Access State and makes an unoccupied transfer after the acknowledgment waiting time has expired, the mobile station 2 must restart the transmission procedures of the channel probe. of access. This would be the same as if the mobile station 2 transmitted a new origin message. In an alternative mode, the mobile station 2 can effect the unoccupied transfer to the base stations in the LIST_BASE before receiving the acknowledgment. However, this means that all the base stations in the LIST_BASE would need to send the acknowledgment and, thus, the controller 32 of the base station would need to be involved in the generation of the acknowledgments. In a modification to this alternative mode, the mobile station 2 can perform the unoccupied transfer to the base stations in the LIST MOBILE before receiving the acknowledgment.

P1782 / 98MX Similarly, this means that all base stations in the LIST_M0BILE, would need to send the acknowledgment and, thus, the controller 32 of the mobile station would need to be involved in the generation of the acknowledgments. In a preferred embodiment, the present invention provides for the contingency that the channel assignment message was transmitted by the base station 26a but was not received by the mobile station 2. The base station 26a may have received the Origin Message from the station mobile 2 but, the mobile station 2 may not have received the channel assignment message that acknowledges receipt of the Source Message from the base station 26a. Even in the absence of receipt of the acknowledgment message, the mobile station 2 can effect the unoccupied transfer to, for example, the base station 26b. The base station 2ßb may be sending the Channel Assignment Message to the mobile station 2, while the mobile station 2 is retransmitting the Origin Message. In the exemplary embodiment, when an acknowledgment message is sent, an indication that the message is being recognized accompanies it. Mobile station 2 ignores the Channel Assignment Message, unless the indicator corresponds to the Origin Message that was most recently sent. The present invention P1782 / 98 X presents several ways to correct this problem. An obvious correction is to make the base station 26b use the same acknowledgment indicator as used in the Origin Message received by the base station 26a. This can be done by passing the values of the acknowledgment indicator of the base station 26a to the base station 26b, through the controller 32 of the base station. In an alternative embodiment, the mobile station 2 may stop transmitting an access probe if it receives the Channel Assignment Message and is tuned to the channel specified by the Channel Assignment Message. In an improved embodiment, the configuration of the Radiolocation Channel of all base stations towards which the mobile station 2 is allowed to transfer (base stations in the LIST_BASE) are the same. Base stations that do not support these capabilities would not be included in the LIST_BASE. The above scheme can also be used to support Priority Access and Channel Allocation (PACA). The particularity of PACA is well known in the art and is described in detail in the "TIA / EIA / IS-53-A Cellular Features Description". When the PACA is invoked, the mobile station 2 is given priority over other mobile stations to obtain a Traffic Channel when there is no Traffic Channel available. Specifically, the P1782 / 98MX mobile station 2 sends a Message of Origin that contains the code of the PACA particularity and the dialed number. If a Traffic Channel is immediately available, the Traffic Channel is assigned to mobile station 2. If a Traffic Channel is not immediately available and the mobile station 2 is authorized to use the PACA, the base station monitors the mobile station 2, says the base station 26a, places the request of the mobile station 2 in the formation or row of BALE. Alternatively, this formation or row of PACA can be handled by the controller 32 of the base station. The position in the formation or row depends on the priority of the PACA application and the time of the request. When a Traffic Channel is available, the request at the tip of the formation or PACA row is assigned to the Traffic Channel. When the request from mobile station 2 is In a formation or row of PACA, the mobile station 2 may be sending periodic messages informing the user of the mobile station 2 of the state of the formation or row. One issue with the PACA is that the infrastructure needs to know the cell that is normally using the mobile station 2 in order to determine if the channel is free. With most systems, this implies that mobile station 2 must register or resend the P1782 / 98MX source message each time the mobile station 2 makes an idle transfer. Due to the abruptness of the transitions between CDMA base stations, the mobile station 2 can register or resend the Origin Message several times while crossing the boundaries between base stations. A second consideration with the CDMA is that the mobile station 2 may need to be placed in the soft transfer shortly after it is assigned to a Traffic Channel. Unless resources are available at multiple base stations to support the call, the allocation may not be successful. With the modified Origin Message described above, the mobile station 2 indicates other base stations that must be in the Active Set of the mobile station, the set of base stations from which the mobile station 2 has detected strong pilot signals. In one embodiment, the mobile station 2 sends the LIST_MOBILE and the base station determines the LIST_B0TH. In another embodiment, mobile station 2 sends LIST_B0TH. This allows the infrastructure to determine if resources are free in all the base stations needed for the PACA call. In order to reduce the sending speed of the Source Message, the base stations in the LIST_B0TH are those that the mobile station can move without having to send the Source Message again. When this is invoked P1782 / 98MX particularity, the infrastructure needs to send the training status information or row in all base stations in the LISTJ30TH. If the mobile station 2 moves outside the coverage of the base stations in the LIST_B0TH, the mobile station 2 sends the origin message again. The prior description of the preferred embodiments is provided to allow any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, it is not intended that the present invention be limited to the embodiments shown herein but is in accordance with the broader scope consistent with the novel principles and features disclosed herein.

P1782 / 98MX

Claims (1)

NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property:

1. In a mobile communication system, wherein the first communication device has the ability to communicate with a plurality of second communication devices, the method for providing a channel assignment message for some of the second communication devices, comprises the steps of: transmitting from at least one of the second communication devices to the first communication device, a list of second communication devices to which the first communication device is allowed to transfer; and transmitting a channel assignment message from each of the second communication devices in the list of second communication devices. P1782 / 98MX