MXPA98001174A - Method and apparatus for the generation of duplex pilot signal by tie division - Google Patents

Abstract

A method and apparatus for providing a reliable means for effecting transmission transfer from a code division multiple access (CDMA) system using a pilot signal to an alternative access technique system. A simple pilot box circuitry (350) is added to a set of border base stations (C2A-C2R). Border base stations are base stations (C2A-C2R), which operate only in the alternative access technique and which have coverage areas that are contiguous to the coverage areas of the CDMA operating base stations (C1H-C1S). The mobile unit (10) monitors the pilot signal from the border base stations (C2A-C2R), in the same way as it monitors the pilot signals from the CDMA operating base stations (C1A-C1S). When the mobile unit (10) detects the pilot signal corresponding to a border base station (C2A-C2R), it notifies a system controller (202) according to the standard operation. The system controller (202) is aware that the pilot signal corresponds to a border base station and therefore activates a hard transmission transfer process to the alternative access technique system in response thereto. Border base stations (C2A-C2R), use a time division duplex technique to monitor a synchronization and pilot sequence from a neighboring station of the CDMA operating base stations, to obtain an absolute system time estimate

Description

METHOD AND APPARATUS FOR THE GENERATION OF DUPLEX PILOT SIGNAL BY DIVISION OF TIME BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to communication systems, in particular to a method and apparatus for effecting transmission transfer from a multiple code division access system to an alternative technology system.

II. Description of Related Art In a code division multiple access (CDMA) cellular telephone system or in personal communication systems a common frequency band is used for communication with all base stations in a system. The common frequency band allows simultaneous communication between a mobile unit and more than one base station. The signals occupying the common frequency band are discriminated at the receiving station through the CDMA waveform properties of the spread spectrum based on the use of a high-speed pseudonoise (PN) code. The high-speed PN code is used to modulate transmitted signals P1 0rt 8 / "> MM from base stations and mobile units Transmitting stations using different PN codes or PN codes that are offset in time produce signals that can be received separately at the receiving station. High-speed PN also allows the receiving station to receive a signal coming from a simple transmitting station, where the signal has traveled on several different propagation paths In a CDMA example system, each base station transmits a pilot signal having a common PN extension code that is deviated in the code phase, with respect to a pilot signal from other base stations During the operation of the system, the mobile unit is provided with a list of code phase deviations corresponding to the stations neighboring bases that surround the base station and through which communication is established. with a search receiver or an element that allows the mobile unit to track the intensity of the pilot signal from a group of base stations, including the neighboring base stations. A method and system for providing a communication link with the mobile unit through more than one base station during the transfer process of PIOST OP MX transmission is disclosed in U.S. Patent No. 5,267,261, issued November 30, 1993, entitled "SOFT TRANSMISSION TRANSFER ASSISTED BY MOBILE STATION IN A CDMA CELLULAR COMMUNICATION SYSTEM" assigned to the assignee of this invention. Using this system, communication between the mobile unit and the end user is uninterrupted by the eventual transfer of transmission from a home base station to a subsequent base station. This type of transmission transfer can be considered as a "soft" transfer since communication with the subsequent base station is established before communication with the originating base station is terminated. When the mobile unit is in communication with two base stations, a single signal is created for the end user from the signals of each base station, by means of a cellular or personal communication system controller. The mobile unit-assisted soft transmission transfer operates based on the pilot signal strength of several sets of base stations, as measured by the mobile unit. The Active Set is the set of base stations through which active communication is established. The Neighbor Set is a set of base stations that surround an active base station and that Pl Ortu / 'and X comprises base stations that have a high probability of having a pilot signal strength of sufficient level to establish communication. The Candidate Set is a set of base stations that has a pilot signal strength of sufficient level to establish communication. When the communication is initially established, a mobile unit communicates through a first base station and the Active Set contains only the first base station. The mobile unit monitors the intensity of the pilot signal from the base stations of the Active Set, the Candidate Set and the Neighbor Set. When a pilot signal from a base station is in the Neighbor Set and exceeds a predetermined threshold level, the base station is added to the Candidate Set and removed from the Neighbor Set in the mobile unit. The mobile unit communicates a message to the first base station identifying the new base station. A controller of the personal or cellular communication system decides whether or not to establish communication between the new base station and the mobile unit. If the cellular or personal communication system controller decides to do so, the cellular personal communication system controller sends a message to the new base station with identification information related to the mobile unit and an order to establish I Plied MX communications with it. A message is also transmitted to the mobile unit through the first base station. The message identifies a new Active Set that includes the first and the new base stations. The mobile unit searches for the information signal transmitted by the new base station and communication is established with the new base station, without terminating the communication through the first base station. This process can continue with other base stations. When the mobile unit communicates through many base stations, it continues to monitor the signal strength of the base stations of the Active Set, the Candidate Set and the Neighbor Set. If the signal strength corresponding to an Active Set base station falls below a predetermined threshold for a predetermined period of time, the mobile unit generates and transmits a message to report the event. The controller of the personal or cellular communication system receives this message through at least one of the base stations with which the mobile unit is communicating. The cellular or personal communication system controller may decide to terminate communications through the base station having a weak pilot signal strength. The communication system controller P109S / 98 cellular or personal MX when deciding to terminate communications through a base station, generates a message identifying a new active set of base stations. The new Active Set does not contain the base station through which the communication will be terminated. The base station through which the communication is established sends a message to the mobile unit. The cellular or personal communication system controller also communicates information at the base station to terminate communications with the mobile unit. Communications with the mobile unit are then routed only through base stations identified in the new Active Set. As the mobile unit is in communication at all times with the end user through at least one base station, throughout the smooth transmission transfer process, there is no interruption in communications between the mobile unit and the end user. A soft transmission transfer provides considerable benefits in the inherent "transfer before completion" transfer technique with respect to conventional "terminate before settlement" techniques that are used in other cellular communication systems. The new CDMA systems are deployed P10T8 / 98 MX initially typically in areas with existing FM or other technology systems. The initial deployment of the CDMA system can be gradual and cover only a portion of an operating area covered by the original existing system. In this case, as a mobile unit that is communicating in CDMA mode is transported from the coverage area of the CDMA system to a portion of the system without CDMA coverage, a transmission transfer from the CDMA system to the original system is needed , in order to facilitate continuous communication. The process of soft transmission transfer assisted by mobile unit as described above is not possible between the CDMA system and the original system. The transmission transfer from the CDMA system to the original system must be carried out as a hard transmission transfer of type "terminate before establishing". When a hard transmission transfer is made it is especially important to ensure that the transmission transfer is successful since a failed hard transmission transfer typically results in disconnection of the call. Therefore, an object of this invention is to provide a method and apparatus for effecting transmission transfer from a CDMA system to a system employing a different technology. P1088 / 98 MX Another object of the present invention is to provide a reliable and inexpensive means to detect the entrance to the coverage area of an alternate system.

SUMMARY OF THE INVENTION The present invention defines a method and apparatus for effecting transmission transfer to a second independent system from a code division multiple access (CDMA) system using a pilot signal. A set of base stations forms a boundary between the CDMA operation and the operation in the second system. The border base stations by themselves operate only on the technology of the second system and are unable to receive and demodulate the CDMA signals. A pilot signal is transmitted from the set of border base stations. As a mobile unit operating in the CDMA system approaches a border base station, it receives the pilot signal from the border base station. In the same way that the mobile unit would act upon receiving a pilot signal corresponding to a CDMA base station, the mobile unit reports the reception of the pilot signal from the border base station to the system controller, through the base stations with which is currently in communication. The system controller is aware of P1088 / 9T MX that the pilot signal corresponds to a base station that is not capable of performing the CDMA operation. The system controller can communicate with the system controller of the second system and negotiate the availability of resources for the mobile unit in the second system. The CDMA system controller can send the corresponding source information to the second system for the mobile unit and order the mobile unit to transfer the transmission to the second system. The mobile unit can then effect a rigid transmission transfer to the second system. The pilot signal at the border base station is reproduced in the present system by a simple box that can be installed easily and inexpensively in existing base stations. The pilot box requires only power to operate. The pilot box can also have a connection to a system controller to monitor the operation, to make the configuration and to detect faults. The pilot box can also transmit a synchronization signal. The pilot box uses the pilot signal from the surrounding base station to obtain the system time in a time-division duplex form.

BRIEF DESCRIPTION OF THE DRAWINGS P1088 / 98 MX The features, objects and advantages of the present invention will be more evident from the following detailed description set forth below, taken in conjunction with the drawings, wherein the reference numbers are used consistently in all the drawings, and wherein: Figure 1 illustrates an example base station coverage area structure; Figure 2 illustrates an example base station coverage area structure comprising the present invention; Figure 3 illustrates an example embodiment of the pilot box configuration; Figure 4 is an exemplary block diagram showing the time acquisition circuitry; and Figure 5 is an exemplary block diagram showing the time acquisition circuitry and the message reception circuitry.

DESCRIPCTGM nwrnt.t.aj) A OF THE PREFERRED MODALITIES Figure 1 illustrates an example base station coverage area structure. In this example structure, hexagonal base station coverage areas bump into each other in an array placed symmetrically. Each mobile unit is located within the P1088 / 98 MX coverage area of one of the base stations. For example, the mobile unit 10 is placed within the coverage area of the base station 20. In a personal or cellular communication system by code division multiple access (CDMA), a common frequency band is used to communicate with all base stations in a system that allows simultaneous communication between a mobile unit and more than one base station. The mobile unit 10 is placed very close to the base station 20, therefore, receives a strong signal from the base station 20 and relatively weak signals from the surrounding base stations. However, the mobile unit 30 is located in the coverage area of the base station 40 but is close to the coverage area of the base stations 100 and 110. The mobile unit 30 receives a relatively weak signal from the base station 40 and similarly dimensioned signals from the base stations 100 and 110. If each of these base stations 40, 100 and IO are capable of operating in CDMA, the mobile unit 30 could enter soft transmission transfer with the base stations 40, 100 and 110. The example base station coverage area structures illustrated in Figures 1 and 2 are the most desired. In the personal communication environment P106T / 98 MX or current cellular, base station coverage areas may vary in size and shape. The base station coverage areas may tend to overlap and the coverage area boundaries define coverage area shapes that are different from the ideal hexagonal shape. However, the base stations can also be sectorized, for example in three sectors, as is well known in the art. However, base stations with greater or lesser numbers of sectors are also displayed. In a CDMA system each station or base sector of a sectorized base station transmits a pilot identification signal. The base station 60 of Figure 1 represents an ideal three-sector base station. The base station 60 has three sectors, each of which covers more than 120 degrees of coverage area of the base station. The sector 50, which has a coverage area indicated by interrupted lines 55, overlaps the coverage area of sector 70, which has a coverage area indicated by thick interrupted lines 75. Sector 50 also overlaps sector 80 which has a coverage area indicated by thin interrupted lines 85. For example, location 90 as indicated by X is located both in the coverage area of sector 50 and sector 70.

P1088 / 98 MX In general, the base station is sectorized to reduce the total interference power to and from mobile units located within the coverage area of the base station, while increasing the number of mobile units that can communicate through the base station. For example, sector 80 would not transmit a signal to a mobile unit at location 90 and, therefore, no mobile unit located in sector 80 presents significant interference by the communication of a mobile unit at location 90 with the station base 60. For a mobile unit placed at location 90, sectors 50 and 70 and base stations 20 and 120 contribute to the total interference. A mobile unit at location 90 may simultaneously be in soft transmission transfer with the base stations 20 and 120 and sectors 50 and 70. A method for providing communication with a mobile unit through more than one base station during the transmission transfer process is disclosed in U.S. Patent No. 5,267,261 as mentioned above. . This type of transmission transfer can be considered as "soft" since communication with the subsequent base station is established before communication with the original base station is terminated. New CDMA systems have been developed P1088 / 98 MX initially in areas with existing FM systems or with other technology systems. The initial development of CDMA systems can be gradual and cover only a part of an operating area covered by the original existing system. For example, Figure 2 shows a system in which the C1A-Cls coverage areas have base stations that are capable of operating in the CDMA system. A typical development of a novel CDMA system places coverage areas with superior CDMA capacity in high traffic areas in the C1A-Cls areas, for example in downtown areas. Low traffic areas such as suburban areas, which may have support from the original lower capacity system, may initially be left without capacity in the CDMA system. C2A-C2R coverage areas have original system base stations that are unable to communicate CDMA traffic channel. To fit the CDMA system, a portion of the spectrum used by the original system is reserved for the CDMA operation. The reservation of a portion of the spectrum implies that the base stations that correspond to the C1A - Cls coverage areas do not use the spectrum reserved for communications that use the original technology. In a similar way, the base stations that correspond to border coverage areas C2A - P10T8 / 98 MX C2R can not use the CDMA spectrum reserved for communication using the original technology, since there is mutual interference with the CDMA system. In a typical development, the base stations within the C1A-Cls coverage areas may also be able to communicate using the original technology. In this way, a mobile unit with an established call with an original technology in the C2A - C2R coverage areas can continue communicating as it moves towards the C1A - Cls coverage areas, without changing to the CDMA operation. The base stations within the C1A-Cls coverage areas can support the call in the original technology following a standard transmission transfer procedure used by the original technology system, in the manner controlled by the controller 200 of the original system. (Typically the original technology will use hard or rigid transmission transfer techniques for all transfers made within the system, however, when a mobile unit, for example unit 100 of Figure 2, initiates a CDMA call and during the Calling out of the C1A-Cls coverage area, a hard transmission transfer from the CDMA system to the original technology system will be required to sustain uninterrupted communication P1088 / 98 MX The soft-drive transfer process assisted by mobile unit As described above, it is not possible between the CDMA system and the original system The transfer of transmission from the CDMA system to the original system must be done as a hard transfer transfer of type "interrupt before establishing". of hard transmission, it is especially important to ensure that the transfer of transmission is ex This is because a failed hard transmission transfer typically results in disconnection of the call. The boundary 170, indicated as a thick black line in Figure 2, represents the boundary between the base stations with CDMA capacity corresponding to the C1A - Cls coverage areas and the operation of the original system only in base stations corresponding to the areas of adjacent coverage C2A - C2R. In Figure 2, the mobile unit 100 initiates a CDMA call with the base expression 120 of coverage area C1A and then moves in the direction indicated by the arrow 180. The mobile unit 100 effects a soft transmission transfer between the base station 120 and the base station 150 of the coverage area C1F, as ordered by the system controller 202 CDMA. As the mobile unit 100 enters the coverage area C1P, it is very likely that it is in a P10T8 / 9T MX soft transmission transfer with base station 150, base station 160 for coverage C1P, and base station 140 for coverage area C1Q. As a mobile unit 100 crosses the border 170 and enters the coverage area C2A, a soft transmission transfer is made to the base station 130 and to operate on the original technology. The present invention is a cheap and reliable method to ensure that the mobile unit 100 is secured within the coverage area C2A and within the range of the base station 130 before a hard transmission transfer is made. As described above, a mobile unit participating in an active CDMA call continuously scans the incoming signal in search of pilot signals from neighboring base stations. If the mobile unit finds a pilot signal from a nearby base station with qualification level, the unit sends a message to the CDMA 202 system controller indicating the detection of the signal. The present invention uses this existing process to facilitate the transfer of hard transmission to the original system. In the present invention, it will be added ad «2'0óíá a0 + 24X" pilot "time division duplex in the original technology, only in base stations that will be located in the areas of border coverage, as for example the P1088 / 9T MX adjacent coverage areas C2A-C2R of Figure 2. The pilot box produces a pilot signal which in the preferred embodiment is the same as the pilot signal transmitted from the CDMA-capable base stations, where each base station transmits the pilot signal at a unique time deviation for them. Figure 3 shows a preferred embodiment of the pilot box configuration. The pilot channel does not contain data and, therefore, the input of the pilot data from the pilot box 350 is zero. The Walsh function for the pilot channel is the zero Walsh function which is also always zero. The adder 310 adds the two zero sequences (the function of the adder 310 is exceeding the trivial and is shown in Figure 3 for explanatory purposes.) In a current instrumentation, the adder 310 may not be included and the pilot channel sequence summed with the Walsh function could be instrumented with a simple ground potential or the logical level O1). The output of the pilot sequence of the adder 310 enters the adder 336 so that the short code pseudo noise (PN) sequence of channel I, coming from the short code generator 332 of channel I, is printed on the pilot sequence. The output of the pilot sequence of the adder 310 is also input to the adder 338 so that the pseudonoise (PN) sequence of the short code of channel Q, P1088 / 98 MX from short channel generator 334 of channel Q, is printed on the pilot sequence. As mentioned before, in the preferred embodiment the short codes of channel I and Q are the same for every base station in the system, but they deviate in time from one another. To properly align the time deviation, the pilot box needs the universal time input acquired as described below. The output of the adders 336 and 338 is filtered by the baseband filters 340 and 342 respectively. The baseband filters 340 and 342 can also adjust the gain of the signal path. In typical instrumentation, the pilot signal is transmitted at a higher gain level than another signal. The output of the baseband filter 340 is added to any other optional I-channel signal by the adder 344 as explained in more detail below. Adder 344 is optional and is not needed if other signals are not provided. The output of the adder 344 is then modulated with a cosine wave by the mixer 320. The output of the baseband filter 342 is added with any other optional Q-channel signal by the adder 346 as explained in more detail below. Again, adder 344 is optional and is not needed if other signals are not provided. The output of the adder 346 is then modulated with a sine wave by the P1088 / 98 MX mixer 322. The outputs of mixer 320 and 322 are summed by adder 324. The output of summer 324 is provided to the power amplifier and upconverter 326 when the signal is upconverted to the carrier frequency and amplified. The output of the power amplifier and upconverter 326 is the output of the pilot box 350 which is transmitted from the antenna of the base station into which the pilot box 350 is installed. During the operation of the CDMA system, the mobile unit is provides a list of short code phase deviations corresponding to the neighboring base stations surrounding the base station through which communication is established. This list may include the deviation of the pilot signal from a base station in a border coverage area, if the mobile unit is in close proximity to the boundary between the CDMA operation and the original technology only operation. The search element in the mobile unit tracks the signal strength of the pilot signals coming from the Neighbor Set and in the same way as described above, regardless of the fact that some of the members of the Neighbor Set may be base stations only of original technology. When a pilot signal from a border base station in the Neighbor Set exceeds a level of P1088 / 98 MX qualification, the corresponding base station is added to Candidate Set and removed from the Neighbor Set in the mobile unit. Referring again to Figure 2, the pilot signal of the base station 130 is detected by the mobile unit 100 as it approaches the boundary of the coverage area C2A. The mobile unit 100 communicates a message through the base station or base stations with which it is in communication (most likely the base stations 140 and 160) with the controller of the CDMA system 202 that identifies the base station 130. The controller of the system 202 recognizes that the base station 130 does not have CDMA capability and in this way activates a hard transmission transfer process. The actual hard transmission transfer may result from a variety of stimuli. In other words, once the system controller 202 has received the message that comes from the mobile unit 100, indicating the reception of the pilot signal from the base station 130, the system controller 202 can use any of a variety of methods to be chosen in case of a transmission transfer to the alternative topic. The system controller 202 may use a synchronization method to determine when to effect the transmission transfer. Alternatively, the system controller 202 may base the transfer of P1088 / 98 MX transmission in the measurements of signal strength or in the use of position location techniques. In any case, if resources are available, the original system controller 200 supplies information that is needed for the transmission transfer (e.g., channel information for FM or channel allocation and TDMA interval) to the system controller 202 CDMA. The original system controller 200 also notifies the base station 130 to prepare the transmission transfer of the mobile unit 100. The system controller 202 CDMA sends the channel information to the mobile unit 100 through each base station with which the mobile unit 100 is in communication. The mobile unit 100 receives the message and stops communication through the CDMA base stations and starts the operation in the original system mode with the base station 130. The communication continues in the original system technology not interrupted by the transmission transfer hard. If a mobile unit is located in one of the border coverage areas C2A-C2 it is initially energized, the mobile unit can search first until it finds a CDMA pilot signal. The mobile unit finds the pilot box signal and then tries to find a synchronization channel signal that supports the information P1088 / 98 MX system, ie a signal (sync) in the preferred mode, the pilot box does not transmit a sync signal and the mobile unit is not able to detect the sync signal after certain default actions (default) of time , to operate in the original system mode. The pilot box 350 of Figure 3 can therefore contain a sync signal generation capability (sync). The purpose of the sync channel in the preferred embodiment of a CDMA system is to allow the mobile units within the coverage area of the corresponding base station to acquire initial time synchronization and system information, for example protocol revisions that can be given service by the base station. When energy is first applied to the mobile unit, it seeks to find a pilot signal. When finding the pilot signal, look for a corresponding sync channel. The corresponding sync signal provides information to the mobile unit indicating the minimum protocol revision level supported by the base station. Only mobile units that have the minimum protocol revision level or a higher revision number can access the system. In the second embodiment of the present invention, the pilot box comprises circuitry for producing a sync channel shown as a sync channel option box 300 in the P1088 / 98 MX Figure 3. The bits of the sync channel are first coded convolutionally by the convolutional coder 302 to produce data symbols. The data symbols are repeated in symbol repetition 304. The repeated symbols are interleaved in blocks by the block interleaver 306. The interleaved data is modulated with a Walsh function sequence by the adder 308. In the preferred embodiment 64, the sequences Walsh are available and the sync channel is modulated with the Walsh function 32 which is 32 zeros (0's) followed by 32 ones (l's) the output of the adder 308 enters the adder 312 so that the short channel code I that comes from the generator Short code 328 of channel I is printed on the pilot sequence. The output of the adder pilot sequence 308 is also the input to the adder 314, so that the short code of channel Q that comes from the short code generator of channel Q is printed on the pilot sequence. In the preferred embodiment, the short codes of channel I and Q are the same as the sequences used to modulate the pilot sequence. The output of the adders 312 and 314 are filtered by baseband filters 316 and 318, respectively. The baseband filters 316 and 318 can also adjust the gain of the signal path. The output of the baseband filters 316 and 318 enters the adder 344 and 346 respectively and from P108T / 98 MX there follow in the same trajectory that the pilot sequence towards the transmission antenna. The sync channel option box 300 can be used to avoid a braided mobile unit in case the mobile unit does not automatically switch to the operation of the original system, if it is unable to acquire a sync signal. The sync channel bits in the option box 300 of the sync channel can be adjusted so that the minimum protocol revision level supported is adjusted to the maximum value, so that each and every mobile unit has a lower revision number to the minimum required. In this way, when energized within the coverage area of a base station comprising a pilot box with the sync channel option, the mobile unit acquires the pilot signal first and then acquires the sync channel and then examines the information coming from the channel sync that indicates that the mobile unit is unable to communicate with this base station in CDMA mode, since its protocol revision is too old. The mobile unit then switches to the original technology mode of operation and is capable of initiating or receiving a call in that mode. In yet another embodiment, the pilot box 350 may comprise a connection to either the original system controller 200 or the system controller 202 CDMA P1088 / 98 MX (as shown in dotted lines in Figure 2). The connection would be a minimum data rate connection that monitors the condition of the pilot box 350 of operation and possibly allows the parameters to be adjusted within the pilot box 350. One of the main functions of this connection would be to monitor faults within the the pilot box 350 to facilitate rapid detection and corrections of any fault condition that may arise. The system in Figure 2 assumes that the border base stations correspond to the coverage areas C2A - C2R which are simple sectorized base stations. In a standard situation, generalization happens very likely. Border base stations are typically located in more sub-urban areas where the sectorization of the base station is not needed to adjust the anticipated traffic load. However, as shown in Figure 1, it is common for some base stations within a system to be sectorized. In this case, each original technology sector has only base stations that have a coverage area that meets the boundary, outputting a pilot signal. Those sectors within the border base station that do not have coverage areas that meet the border, would not need to transmit a pilot signal.

P1088 / 98 MX In a very basic instrumentation, each sector of each border base station that meets the boundary or border would have its own pilot box. However, in an alternative preferred embodiment, a single pilot box would be provided for each base station even if the base station has several sectors that hit the limit. In this case, the various sectors of the same base station transmit the same pilot signal. When the mobile unit transmits a message indicating the reception of the common pilot signal, the system must use other methods to determine to which sector of the base station the mobile unit is approaching. For example, the system is aware of the base station or base station sector with which the mobile unit is currently communicating and, therefore, has some idea of the physical location of the mobile unit. Still in another alternative modality, to implement a highly reliable system, two separate pilot boxes could be installed in each station or base sector. Each pilot box would transmit a pilot signal in the nominal deviation assigned to that sector or base station. However, one of the outputs of the pilot box is delayed from the other by a fixed amount. The fixed amount should be small with respect to the standard deviation between the neighboring base station, so that the P108T / 98 MX system correlates delayed and non-delayed deviations with the same base station. The fixed amount must be large enough to avoid interference of the delayed and non-delayed pilot signals due to the multi-path effects of the system. In this way, the reliability of the system increases in case one pilot box fails, the others continue to provide the pilot signal for detection by the mobile unit. It is evident from the above analysis and from Figure 3 that the pilot box requires a universal time sync input to align the short code generators of channel I and Q to the appropriate pilot deviation. As in the preferred embodiment each base station transmits the same pilot sequence to a single deviation and the deviation in the pilot sequence is used to discriminate and identify the pilot signals from the base station, the generation process has no meaning unless it is aligned over time in relation to other base stations in the system. The pilot box of Figure 3 is a low cost item. On the other hand, the circuitry used to produce the universal time input can be expensive and may require an additional antenna in each base station if the Global Positioning System (GPS) is used. However, note that although the sequence P1088 / 98 MX pilot must be aligned in time with respect to other pilot signals transmitted in the system, it is not imperative that the pilot signal is aligned with a final precision. The terrestrial environment provides a natural and unknown path delay as the signal travels from the base station to the mobile units. Therefore, the mobile units look for a window of time deviations surrounding the nominal reception time of a pilot signal, when trying to determine the signal strength of the pilot signals corresponding to the Neighbor Set of the base stations. In this way, the precision with which the pilot signal that comes from the pilot box needs to be aligned, corresponds only to the precision that is required to ensure that the pilot signal reaches a mobile unit within the time window in which the mobile unit looks for the pilot signal. Noting that the pilot signal does not need to be generated as fine precision, it is advantageous to find a way to eliminate expensive and bulky GPS circuitry. One way of doing this is by the instrumentation of a time-tracking, time division duplex circuitry, shown in Figure 4. Note that like a mobile unit that once acquired a pilot signal from the base station is capable of track the pilot signal as the delay changes P1088 / 98 MX between the mobile unit and the base station, a base station can track the pilot signal of the neighboring base stations. For example, in Figure 2 note that the base station 140 transmits a continuous pilot signal that is used in the CDMA system and is equipped with a GPS receiver or with other equipment that provides the base station 140 with an accurate absolute time. The base station 145 is equipped with a time-division duplex pilot (TDD) box of the invention. The distance 135 and the corresponding delay between the base station 140 and the base station 145 are quantities that can be measured and determined in a calibration procedure at the deployment time. Figure 4 illustrates the time division duplex pilot technique of the present invention. As noted above, each base station in a CDMA system transmits a pilot sequence using a frequency band. Therefore, for the base station 145 to track the pilot sequence of the base station 140, in order to acquire system time to use it in the creation of its own pilot signal, the base station 145 must transmit and receive in the same band of frequency. However, the construction equipment that is capable of simultaneously receiving and transmitting in the same band of P1088 / 98 MX frequency with enough insulation to operate, is a difficult task. The process of creating the pilot signal can be simplified by noting certain operating characteristics of the system. Note that when a mobile unit is in search of the pilot signal from the members of the Neighbor Set of base stations, the mobile unit searches sequentially through a set of corresponding pilot sequence deviations. If a pilot sequence at a given deviation is not found, the corresponding base station remains as a member of the Neighbor Set of base stations and another search is made at the corresponding deviation at a later time by the mobile unit. In this way, if a base station were to temporarily terminate the transmission of its pilot signal, for the mobile units that are recently approaching the coverage area of that base station, there could be a delay in the perception of that base station pilot signal . However, finally the pilot signal would be acquired by the mobile units when the base station will continue the transmission of the pilot signal. Also note that as already described, the pilot signal from the base station does not need to be precisely aligned with the system time. In this way, a small error of time deviation in the P1088 / 98 MX pilot signal from a base station is tracked naturally by the same mechanism that the mobile unit uses to track changes in the pilot signal due to trajectory delays in the terrestrial environment. In this way, the pilot generation apparatus and method of the present invention contemplate the use of a time division duplex (TDD) scheme, wherein a border base station comprises a TDD pilot generation box that alternates long transmission periods. of the pilot signal with short periods of reception of the pilot signals from the neighboring base station. Figure 4 illustrates a block diagram according to the present invention. The antenna 400 provides reception of transmission of the CDMA pilot signals. The TDD switch 402 is used to connect the antenna 400 to generator 414 during the transmission moments and to the finder and demodulator 404 during the reception moments. The search and demodulator 404 tracks the pilot signal from at least one neighboring base station. As already mentioned, the search and demodulator 404 needs the PN deviation corresponding to the neighboring base station and needs to know the ground delay so that it can adjust to the delay. The searcher and demodulator 404 outputs a signal indicative of absolute time, to comparator 406. Comparator 406 compares the absolute time measured P1088 / 1T MX with the time sync input that is currently being generated by the stable oscillator 412. During the time in which the TDD switch 402 is connected to the finder to the demodulator 404 and the reception of the pilot signal is being presented, the second TDD switch 408 connects the error signal output of the counter 406 with a control input of the stable oscillator 412. The capacitor 410 maintains the error signal when the second TDD switch 408 is opened during the transmission period. The aligned output of the stable oscillator 412 drives the universal time input of the pilot generator 414. The pilot generator 414 supplies the pilot signal to the antenna 400 through the TDD switch 402. Note also that the base station 145 would easily obtain time by tracking the system time from a plurality of base stations. For example, in the base station 145 of ideal hexagonal configuration, signals similarly sized would be received from both the base station 140 and the base station 155. The base station 145 could easily track the pilot signal received from the base station 155 as well as the base station 140 and filtering together the two absolute time indications to generate the input to the comparator 406. If the TDD pilot box is configured to track only a pilot signal, it must P1088 / 98 MX track the pilot signal it receives with the minimum amount of delay. In some system configurations towards the TDD pilot box it may be necessary to initially or continuously demodulate a synchronization channel from the neighboring base stations to obtain an absolute time indication. Note that in a multisector base station or in a base station in a system where two CDMA frequency bands are assigned, only one sector or one of the frequency bands needs to be used to acquire absolute time which can then be used to drive a plurality of frequencies. different pilot generation circuits. Each sector transmitting to the frequency at which the pilot signal from the neighboring base station is to be received may need to stop transmission during the reception of the neighboring pilot signal. This technique can be especially beneficial in cases where sectors receive only weak pilot signals from neighboring base stations. Note that the ratio of the time elapsed in the transmission of a pilot signal to the time elapsed in the reception of a pilot signal can be high, for example in the order of 50 to l. Note that in the P1088 / 98 MX initial deployment, the TDD pilot box may need to remain in the reception mode for a prolonged period of time to initially acquire the pilot signal. However, once the signal has been acquired, the TDD characteristic can be used to track the pilot signal in the stable state. Note also that it may be advantageous to vibrate randomly or pseudo-randomly over time the reception times in order to prevent any pattern of pulsation from occurring with any periodic operation within the mobile units. It may be possible to align the TDD limits with other limits of system operation to conserve signal processing power. For example, if the TDD limits are aligned with the frame limits within the transmitted signal, a single processor interrupt can be used. In some systems, some mobile units may operate in a slotted or interval mode, wherein the mobile units are intermittently available for communication with the base station. The base stations are aware of slot mode operation or at intervals and only try to contact the mobile unit during those "active time slots or intervals" when the mobile unit is monitoring the mobile units.

P1088 / 98 MX messages. If the TDD pilot box is assigned to a set of active ranges in the same way that a mobile unit is assigned to a set of active ranges, the TDD pilot box can monitor the incoming messages destined thereto during the time intervals. The active time slots can be aligned with the TDD pilot reception times, thus the active time slots serve a dual purpose. The TDD pilot box can use the active time slots as a short message service mechanism to receive messages from the neighboring base station as a forward link from the original system controller or CDMA. Figure 5 shows a TDD pilot box comprising the decoding of the message and the demodulation 416 which monitors incoming messages from the base station supplying the pilot signal. Messages that could be transmitted to the TDD pilot box include operation, administration and maintenance (OA &M) messages. Other information on the slotted or interval mode may be found in U.S. Patent no. 5,293,287, entitled "APPARATUS AND METHOD FOR REDUCING ENERGY CONSUMPTION IN A MOBILE COMMUNICATION RECEIVER" granted on February 21, 1995, assigned to the assignee of the present invention and incorporated herein by reference. P10T8 / 9T MX In the '287 patent, each mobile unit is assigned a mobile unit identification number. When registering with the system, the mobile unit transfers information to the system controller that includes the mobile unit identification number. From the mobile unit identification number and the time of day, both the system controller and the mobile unit can independently determine a set pseudorandom active time interval during which the mobile unit monitors the warnings. The base station only attempts to send messages to the mobile unit during the active time slots. In this case, the TDD pilot box may be assigned an analog mobile identification number on the basis of which an active set of time slots can be determined by both the system controller (or base station) and the TDD pilot box, for example, using a partial function. The active intervals are also used as the pilot reception times. There are many obvious variations in the present invention as presented, including simple changes in architecture such as the replacement of the TDD switch by a simple isolated circuit. The above description of the preferred embodiments is provided to allow any person with skill in the art P1088 / 98 MX make use of the present invention. Various modifications of these modalities will be readily apparent to those with expertise in this field, and the generic principles defined herein may be applied to other modalities without the use of the inventive faculty. Therefore, the present invention is not intended to be limited to the modalities illustrated here, but should be interpreted according to the broadest scope consistent with the novel principles and particularities described herein.

P10T8 / 98 MX

Claims (22)

1. Month. 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. A system for providing communication with at least one mobile unit, the system comprises a first plurality of base stations providing code division multiple access (CDMA) communication, wherein the first plurality of base stations are physically accumulated from In a joint manner, the system further comprises a second plurality of base stations that provide communication using an alternative access communication technique, wherein the second plurality of base stations surrounds the first plurality of base stations, thereby creating a border set of base stations , wherein the border set of base stations is a subset of the second plurality of base stations, wherein each base station in the border set has a coverage area with a contiguous boundary that has a coverage area corresponding to a base station of the first plurality of base stations, a method p to provide the transfer of transmission from the CDMA communication technique to a communication technique of P1088 / 98 MX alternative access, comprising the steps of: transmitting from each base station in the plurality of base stations a pilot identification signal and CDMA call signals in a first frequency band; receiving intermittently at each base station in the border set of base stations a pilot identification signal transmitted by one of the first plurality of base stations; determining from the received identification pilot signal an estimate of the absolute system time; transmit intermittently from each base station in the border set of the base stations a pilot identification signal aligned with the estimate of the absolute time in the first frequency band and call signals in an alternative access communication technique in a different band frequency, wherein each base station in the border set of the base stations receives the pilot identification signal only during that time when the transmission of the identification pilot signal has been paused; measure in a first mobile unit a pilot signal intensity of each of the pilot signals of P1088 / 98 MX that corresponds to a neighboring set of base stations, wherein the neighboring set of base stations comprises base stations having coverage areas in proximity to the first mobile unit; receiving in the first mobile unit a first pilot signal corresponding to a target base station, wherein the target base station is a member of the border set of the base stations and wherein the target base station is a member of the neighboring set of base stations; transmitting a age from the first mobile unit to a CDMA system controller by means of at least one base station in the first plurality of base stations, wherein the age indicates the reception of the first pilot signal; and initiating by the CDMA system controller a transmission transfer procedure for the first mobile unit with an alternative access technique system controller. The method according to claim 1, further comprising the steps of: communicating from the alternative access technique system controller to the CDMA system controller, the information for the operation in the alternative access communication technique for the P1088 / 9T MX first mobile unit; and communicating the information for the information for the operation in the alternative access communication technique to the first mobile unit by means of at least one base station in the first plurality of base stations. 3. The method according to claim 1, which further comprises the step of transmitting from each base station in the border set of the base stations a synchronization channel signal in the first frequency band. The method according to claim 3, wherein the synchronization channel signal comprises an indication of a minimum revision level supported by the base station and wherein the indication denotes a revision level incompatible with the first mobile unit. The method according to claim 1, wherein each base station in the first plurality of base stations comprising multiple sectors, transmits a different identification pilot signal from each of the multiple sectors, and wherein each base station in the border set of the base stations comprising several sectors transmits an identical identification pilot signal in each of the multiple sectors, which has an area limit of P10T8 / 98 MX contiguous coverage with a coverage area corresponding to a base station of the first plurality of base stations. The method according to claim 1, wherein one of the base stations in the border set of the base stations comprising several sectors, has a contiguous boundary with a coverage area corresponding to a base station of the first plurality of stations base, and where one of the base stations in the border set of the base stations determines only an estimate of the absolute system time. The method according to claim 1, wherein the step of receiving intermittently has a random pattern. The method according to claim 1, wherein the step of receiving intermittently has a pseudorandom pattern. The method according to claim 1, wherein the step of determining from the received identification pilot signal an estimate of the absolute system time comprises the steps of: receiving a ground time delay input indicative of a delay of transmission time from the base station corresponding to the received identification pilot signal and to the base station Receiving MX P1088 / 98; demodulating the received identification pilot signal to determine a current estimate of the absolute time; compare the estimate of absolute time with the current estimate of absolute time to generate an error signal; and adjusting the received identification pilot signal according to the error signal. The method according to claim 1, wherein each of the pilot identification signals comprises an identical series of pseudonoise code chips and wherein a time deviation is used to distinguish between each of the pilot identification signals and wherein the absolute time estimate is used to align the identical sets of pseudo noise code chips transmitted from each base station in the border set of base stations with respect to the identical series of pseudonoise code chips transmitted from the first set of seasons. 11. A cellular communication system for providing communication with at least one mobile unit, the system comprising: a first plurality of base stations P1088 / 98 MX physically stacked to provide code division multiple access (CDMA) communication signals, wherein each station of the first plurality of base stations transmits a pilot identification signal; and a border set of base stations, wherein the border set of base stations is a subset of a second plurality of base stations to provide communication using an alternative access communication technique, wherein the second plurality of base stations surrounds the set or stacking of the first plurality of base stations and wherein each base station in the border set has a coverage area with a contiguous boundary having a coverage area corresponding to a base station of the first plurality of base stations, and wherein each base station of the border set comprises: a finder and demodulator circuitry and filter for intermittently demodulating and pausing at least one of the pilot identification signals transmitted by each base station of the first plurality of base stations to obtain an identification of a universal time; and a pilot generator to provide a pilot transmission signal during the time when the P1088 / 98 MX finder and demodulator and filter circuitry, pauses. The cellular communication system according to claim 11, wherein the pilot generator for providing a transmission pilot signal apparatus comprises: a short channel code generating means I for receiving universal time and creating a channel extension sequence I to a deviation of time; a first baseband filter for receiving the channel I extension sequence and providing a filtered channel I extension sequence; a first mixer for modulating the filtered I channel extension sequence and producing a modulated output signal I; a short code generating means of channel Q to receive the universal time and create a channel Q extension sequence at the first time deviation; a second baseband filter for receiving the Q-channel extension sequence and providing a filtered Q-channel extension sequence; a second mixer for modulating the filtered Q-channel extension sequence and producing a modulated Q-output signal; an adder to add the output signal I P1088 / 98 modulated MX and the modulated Q output signal to produce a summed modulated signal; and an upconversion and amplification means for receiving the summed modulated signal and producing the transmission pilot signal. The cellular communication system according to claim 11, wherein at least one base station of the first plurality of base stations comprises several sectors and wherein each sector of the at least one base station transmits a single signal of the signal identification pilot and wherein at least one base station of the border set comprises several sectors, each sector of the at least one base station of the border set transmits an identical signal of the pilot transmission signal. The cellular communication system according to claim 11, wherein at least one base station of the border set comprises a second pilot generator for providing a second pilot transmission signal having a time offset shifted from the time deviation of the generator pilot. The cellular communication system according to claim 11, wherein the finder and demodulator and filter circuitry further comprises: a demodulator to combine a constant of P1088 / 96 MX calibration delay and a measurement of current pilot signal deviation in order to produce a current indication of the absolute time; a comparator to compare the indication of absolute time with universal time in order to produce an error signal; and a variable time generation circuit for adjusting the universal time according to the error signal. 16. In a system for providing communication with at least one mobile unit, the system comprises a first plurality of base stations providing code division multiple access (CDMA) communication, wherein the first plurality of base stations are physically stacked , the system further comprises a second plurality of base stations providing communication, using an alternative access communication technique, wherein the second plurality of base stations surrounds the first plurality of base stations, thus creating a border set of base stations in where the border set of the base stations is a subset of the second plurality of base stations, wherein each base station in the border subset has a coverage area with a contiguous boundary having a coverage area corresponding to a base station of P1088 / 98 MX the first plurality of base stations, a method for providing transmission transfer from the CDMA communication to an alternative access communication technique, comprising the steps of: transmitting from each base station in the plurality of base stations a pilot identification signal and CDMA call signals in a first frequency band; receiving intermittently at each base station in the border set of base stations a pilot identification signal transmitted by one of the first plurality of base stations; determining from the received identification pilot signal an estimate of the absolute system time; and transmitting intermittently from each base station in the border set of base stations a pilot identification signal aligned with the estimate of absolute time in the first frequency band and call signals of alternative access communication technique in a frequency band different, wherein each base station in the border set of the base stations receives the pilot identification signal only during times when the transmission of the identification pilot signal has been paused. P1088 / 98 MX 17. The method according to claim 16, wherein one of the base stations in the border set of the base stations comprising several sectors having a border contiguous with a coverage area corresponding to a base station of the first plurality of base stations, and where one of the base stations in the border set of the base stations determines only an absolute system time estimate. 18. The method according to claim 16, wherein the step of receiving intermittently has a random pattern. The method according to claim 16, wherein the step of receiving intermittently has a pseudorandom pattern. The method according to claim 16, wherein the step of determining from the received identification pilot signal an absolute system time estimate, comprises the steps of: receiving a ground time delay input indicative of a delay of transmission time from the base station corresponding to the received identification pilot signal and to the receiving base station; demodulate the received identification pilot signal to determine a current time estimate P1088 / 98 absolute MX; compare the estimate of absolute time with the current estimate of absolute time to generate an error signal; and adjusting the received identification pilot signal according to the error signal. The method according to claim 16, wherein the step of receiving intermittently has a deterministic pattern based on the absolute time estimate and an identification number assigned to each base station in the border set of base stations. The method according to claim 16, further comprising the step of receiving at least one base station in the border set of base stations a message signal transmitted by one of the first plurality of base stations, while the signal is received identification pilot transmitted by one of the plurality of base stations. P1088 / 98 MX SUMMARY OF THE INVENTION A method and an apparatus for providing a reliable means for effecting transmission transfer from a code division multiple access (CDMA) system using a pilot signal, to a transmission technique system. alternative access. A simple pilot box circuitry (350) is added to a set of border base stations (C2A-C2R). Border base stations are base stations (C2-C2R), which operate only in the alternative access technique and which have coverage areas that are contiguous to the coverage areas of the CDMA operating base stations (C1H-C1S). The mobile unit (10) monitors the pilot signal from the border base stations (C2A-C2R), in the same way as it monitors the pilot signals from the CDMA operating base stations (C1A-C1S). When the mobile unit (10) detects the pilot signal corresponding to a border base station (C2A-C2R), it notifies a system controller (202) according to the standard operation. The system controller (202) is aware that the pilot signal corresponds to a border base station and therefore activates a hard transmission transfer process to the alternative access technique system in response thereto. Border base stations (C2A-C2R) use a time division duplex technique P1088 / 98 MX to monitor a synchronization and pilot sequence from a neighboring station of the CDMA operating base stations, to obtain an absolute system time estimate. P1088 / 98 MX