Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/08—Reselecting an access point
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/24—Reselection being triggered by specific parameters
  • H04W36/30—Reselection being triggered by specific parameters by measured or perceived connection quality data
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
  • H04B7/2603—Arrangements for wireless physical layer control
  • H04B7/2606—Arrangements for base station coverage control, e.g. by using relays in tunnels
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0055—Transmission or use of information for re-establishing the radio link
  • H04W36/0079—Transmission or use of information for re-establishing the radio link in case of hand-off failure or rejection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/24—Reselection being triggered by specific parameters
  • H04W36/30—Reselection being triggered by specific parameters by measured or perceived connection quality data
  • H04W36/302—Reselection being triggered by specific parameters by measured or perceived connection quality data due to low signal strength
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
  • H04W16/24—Cell structures
  • H04W16/26—Cell enhancers or enhancement, e.g. for tunnels, building shadow

Definitions

• the present invention relates to communications. More particularly, the present invention relates to a method and apparatus for performing handoff in a CDMA system through the use of repeaters.
• CDMA code division multiple access
• TDM A time division multiple access
• FDMA frequency division multiple access
• AM modulation schemes such as amplitude companded single sideband (ACSSB)
• CDMA has significant advantages over these other techniques.
• TDM A time division multiple access
• FDMA frequency division multiple access
• AM modulation schemes such as amplitude companded single sideband (ACSSB)
• CDMA has significant advantages over these other techniques.
• CDMA techniques in a multiple access communication system is disclosed in U.S. Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” assigned to the assignee of the present invention and incorporated by reference herein.
• CDMA techniques in a multiple access communication system is further disclosed in U.S. Patent No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM", assigned to the assignee of the present invention and incorporated by reference herein.
• the CDMA system can be designed to conform to the "TIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System", hereinafter referred to as the IS-95 standard.
• a base station is the physical hardware through which communications is conducted.
• a cell is the geographical coverage area within which communications with the base station is possible.
• a cell can be partitioned into multiple sectors, and the sectors can be overlapping or non-overlapping.
• each base station can support communications through multiple sectors.
• sector and cell can also refer to the physical hardware through which communication is conducted, depending on the context in which the terms are used.
• a system refers to a set of base stations controlled by a common system controller.
• the conventional FM cellular telephone systems used within the United States is commonly called the Advanced Mobile Phone Service (AMPS), and is detailed in the Electronic Industry Association standard EIA/TIA-553 "Mobile Station - Land Station Compatibility Specification".
• AMPS Advanced Mobile Phone Service
• EIA/TIA-553 Mobile Station - Land Station Compatibility Specification
• the available frequency band is divided into channels typically 30 KHz in bandwidth.
• the system service area is divided geographically into base station coverage areas which may vary in size.
• the available frequency channels are divided into sets.
• the frequency sets are assigned to the coverage areas in such a way as to minimize the possibility of co-channel interference. For example, consider a system in which there are seven frequency sets and the coverage areas are equally sized hexagons. The frequency set used in one coverage area is not used in the six nearest neighboring coverage areas.
• a handoff scheme is used to allow a communication connection to continue when a remote station crosses the boundary between coverage areas of two different base stations.
• the handoff from one base station to another is initiated when the active base station handling the call determines that the received signal strength from the remote station has fallen below a predetermined threshold value.
• a low signal strength indication implies that the remote station is near the coverage area boundary of the base station.
• the active base station asks the system controller to determine whether a neighboring base station receives the remote station signal with better signal strength than the current base station.
• the system controller in response to the active base station inquiry, sends messages to the neighboring base stations with a handoff request.
• Each of the base stations neighboring the active base station employs a special scanning receiver which looks for the signal from the remote station on the channel at which it is operating. Should one of the neighboring base stations reports an adequate signal level to the system controller, a handoff is attempted to that neighboring base station which is now referred to as the target base station. Handoff is then initiated by selecting an idle channel from the channel set used in the target base station. A control message is sent to the remote station directing it to switch from the current channel to the new channel supported by the target base station. At the same time, the system controller switches the call connection from the active base station to the target base station. This process is referred to as hard handoff.
• the term 'hard' is used to characterize the 'break-before-make' characteristic of the handoff.
• a call connection is dropped (i.e. discontinued) if the handoff to the target base station is unsuccessful.
• handoff can fail if there is no idle channel available in the target base station.
• handoff can also fail if one of the neighboring base stations reports receiving a signal from the remote station, when in fact the base station actually receives a signal from a different remote station which is using the same channel to communicate with a distant base station. This reporting error results in the transfer of the call connection to a wrong base station, typically one in which signal strength from the actual remote station is insufficient to maintain communications.
• the handoff fails if the remote station fails to receive the command to switch channels. Actual operating experience indicates that handoff failures occur frequently which significantly lowers the reliability of the system.
• the remote station monitors the signal strength of pilot signals from neighboring base stations.
• the coverage area of the neighboring base stations need not actually abut the coverage area of the base station with which active communication is established.
• the remote station sends a signal strength message to a system controller via the active base station.
• the system controller directs a target base station to establish communication with the remote station and directs the remote station via the active base station to establish contemporaneous communication through the target base station while maintaining communication with the active base station. This process can continue for additional base stations.
• the remote station When the remote station detects that the signal strength of a pilot corresponding to one of the base stations through which the remote station is communicating has fallen below a predetermined drop threshold, the remote station reports the measured signal strength of the corresponding base station to the system controller via the active base stations.
• the system controller sends a command message to the identified base station and to the remote station to terminate communication with the identified base station while maintaining communications with other active base stations.
• interfrequency and /or intersystem handoff One complicating factor in an interfrequency and /or intersystem handoff is the inability to transmit and received signals at two frequencies simultaneously due to hardware limitations. Another complicating factor in the intersystem handoff is that each system is controlled by a different system controller and typically there is no direct link between the base stations of the first system and the system controller of the second system, and vice versa. The two systems are thereby precluded from providing simultaneous communication with the remote station during the handoff process. Even when the existence of an intersystem link between the two systems is available to facilitate intersystem soft handoff, dissimilar characteristics of the two systems often further complicate the soft handoff process.
• interfrequency and/or intersystem soft handoffs When resources are not available to conduct interfrequency and /or intersystem soft handoffs, the execution of a 'hard' handoff of a call connection from one frequency to another frequency and /or from one system to another system becomes critical if uninterrupted service is to be maintained.
• the interfrequency and/or intersystem handoff should be executed at a time and location likely to result in successful transfer of the call connection between systems. The handoff should be attempted only when, for example:
• the remote station is within range of the target base station and the active base station
• the remote station is in a position at which it is assured of receiving the command to switch channels.
• each such interfrequency and /or intersystem hard handoff should be conducted in a manner which minimizes the potential for 'ping-ponging' handoff requests between the base stations of different systems.
• the present invention is a method and apparatus for performing handoff between two communication systems through the use of repeaters.
• the systems can be CDMA systems operating at different frequencies or systems employing different technologies, such as CDMA and AMPS.
• the base station in the first system, is configured to provide coverage to two or more sectors. One or more sectors is associated with the coverage area surrounding the base station, which is also referred to as the cell. The remaining one or more sectors is each associated with a respective repeater which is located at the boundary of the cell. Each repeater provide communications for a coverage area surrounding the respective repeater.
• the coverage area of the repeater overlaps the cell of the first system such that handoff can be performed between the base station and the repeater. In the exemplary embodiment, the coverage area of the repeater also overlaps a cell of the second system such that handoff can be performed between the base station or repeater of the first system and a base station (or a repeater) of the second system.
• the pilot signals of the base station and repeater of the first system are distinguished by different offsets of the common short PN spreading codes which are used to spread the data.
• the pilot signals can be distinguished by different Walsh covers, or other identifying features.
• a remote station located within the cell of the first system communicates with the corresponding active base station. As the remote station moves into the coverage area of the repeater, the pilot signal of the repeater is identified and measured by the remote station and sent to the active base station. If the measured pilot signal is above a predetermined add threshold, the repeater can be added to the active set of the remote station and communications can be established concurrently with the active base station and the repeater.
• the first system can transfer the communications to a base station of the second system using one of at least four embodiments.
• the first system transfers the communications to the base station of the second system upon initiation of a soft handoff by the active base station of the first system with the repeater coverage area.
• This embodiment works well when the coverage area of the repeater is co-located within (a subset of) the cell of the second system.
• the first system is sufficiently assured that communications with the base station of the second system can be reliably established.
• the first system transfers the communications to the base station of the second system if the pilot signal strength of the repeater, as measured by the remote station, exceeds a predetermined handoff threshold.
• the predetermined handoff threshold can be set higher than the predetermined add threshold which is used to add the repeater to the active set of the remote station. This embodiment works well even if the coverage area of the repeater is not co-located within the neighboring cell of the second system.
• the first system transfers the communications to the base station of the second system if the base station of the first system is dropped from the active set of the remote station.
• the remote station periodically measures the pilot signals of the active base station and the repeater and reports the measurements to the first system. If the pilot signal strength of the active base station of the first system, as measured by the remote station, is below a predetermined drop threshold, the base station is removed from the active set of the remote station. When this occurs, the first system can presume that the remote station has traveled sufficiently into the coverage area of the second system to initiate a handoff of the remote station to the second system.
• the first system transfers the communications to the base station of the second system if the repeater of the first system is dropped from the active set of the remote station.
• This embodiment is particularly applicable in system designs wherein the coverage area of the repeater is inclosed within the coverage area of the second system (e.g., an AMP system) and it is desirable to handoff to this second system.
• the first system transfers the communications to the base station of the second system if the active base station and repeater of the first system are both dropped from the active set of the remote station.
• the first system can presume that the remote station has traveled outside the coverage range of the first system. Thus, a handoff of the remote station to the second system is attempted.
• FIG. 1 is a diagram of an exemplary communication system comprising a plurality of base stations and a repeater in communication with a remote station;
• FIG. 2 is a block diagram of an exemplary forward link transmission and receiving subsystem
• FIG. 3 is a block diagram of an exemplary channel element within the base station.
• FIG. 4 is block diagram of an exemplary demodulator within the remote station
• FIGS. 5A-5B are block diagrams of an exemplary repeater communicating through an over-the-air link and a transmission line link, respectively;
• FIGS. 6A-6C are three exemplary diagrams of the coverage provided by a base station and a repeater of two communication systems.
• FIG. 1 represents an exemplary communication system of the present invention which comprises multiple base stations 4 in communication with multiple remote stations 6 (only one remote station 6 is shown for simplicity).
• System controller 2 connects to all base stations 4 in the communication system, the public switched telephone network (PSTN), and system controllers of other communication systems.
• PSTN public switched telephone network
• System controller 2 coordinates the communication between users connected to the PSTN and other systems and users on remote stations 6.
• Each base station 4 can provide communications through zero or more repeater 8 which is used to retransmit or rebroadcast the forward link signal to remote station 6 and to receive the reverse link signal from remote station 6.
• Repeater 8 can be connected to base station 4 through a terrestrial radio link or other transmission links, such as a fiber optic link or transmission lines. Communications from base stations 4 to remote station 6 occurs on the forward link through signal paths 10 and communications from remote station 6 to base stations 4 occurs on the reverse link through signal paths 12.
• FIG. 2 A block diagram of an exemplary forward link transmission and receiving hardware is shown in FIG. 2.
• data source 110 contains the data to be transmitted to remote station 6.
• the data is provided to channel element 112 which partitions the data, CRC encodes the data, and inserts code tail bits as required by the system.
• channel element 112 then convolutionally encodes the data, CRC parity bits, and code tail bits, interleaves the encoded data, scrambles the interleaved data with the user long PN sequence, and covers the scrambled data with a Walsh sequence.
• the traffic channel and pilot channel data corresponding to each sector is combined and provided to a modulator and transmitter (MOD AND TMTR) 114 (only one is shown in FIG. 2 for simplicity).
• MOD AND TMTR modulator and transmitter
• Each modulator and transmitter 114 spreads the covered data with the short PN sequences.
• the offset of the short PN sequences for each modulator and transmitter 114 is selected to be unique from those of neighboring modulators and transmitters.
• the spread data is then modulated with the in-phase and quadrature sinusoids, and the modulated signal is filtered, upconverted, and amplified.
• the forward link signal is transmitted on forward link 10 through antenna 116.
• the forward link signal is received by antenna 132 and provided to receiver (RCVR) 134.
• Receiver 134 filters, amplifies, downconverts, quadrature demodulates, and quantizes the signal.
• the digitized data is provided to demodulator (DEMOD) 136 which despreads the data with the short PN sequences, decovers the despread data with the Walsh sequence, and derotates the decovered data with the recovered pilot signal.
• the derotated data from different correlators within demodulator 136 are combined and descrambled with the user long PN sequence.
• the descrambled (or demodulated) data is provided to decoder 138 which performs the inverse of the encoding performed within channel element 112.
• the decoded data is provided to data sink 140.
• channel element 112 comprises at least one traffic channel 212 and at least one pilot channel 232.
• CRC encoder 214 receives the traffic data, performs CRC encoding, and can insert a set of code tail bits (e.g., in accordance with the IS-95 standard).
• the CRC encoded data is provided to convolutional encoder 216 which encodes the data with a convolutional code.
• the convolutional code is specified by the IS-95 standard.
• the encoded data is provided to interleaver 218 which reorders the code symbols within the encoded data.
• interleaver 218 is a block interleaver which reorders the code symbols within blocks of 20 msec of encoded data.
• the interleaved data is provided to multiplier 220 which scrambles the data with the user long PN sequence.
• the long PN sequence is identical to that assigned to the remote station for which the communications is destined.
• the scrambled data is provided to multiplier 222 which covers the data with the Walsh sequence assigned to this traffic channel.
• the covered data is provided to gain element 224 which scales the data such that the required energy-per-bit-to-noise E ⁇ /Io ratio is maintained at the destination remote station while minimizing transmit power.
• the scaled data is provided to switch 230 which directs the data from the traffic channels 212 to the proper summer 240.
• Each summer 240 sums the signals from all traffic channels 212 and pilot channel 232 designated for that particular sector.
• the resultant signal from each summer 240 is provided modulator and transmitter 114 which functions in the manner described above.
• Channel element 112 comprises at least one pilot channel 232.
• the number of pilot channels 232 required is dependent on system requirements.
• each sector is associated with a pilot signal having the same Walsh cover (e.g., Walsh code 0) but a short PN offset which is unique from those of neighboring sectors.
• each sector can be associated with a pilot signal having the same short PN offset but a Walsh cover which is unique from those of neighboring sectors.
• Other unique identifying features can be used to distinguish the signals of different sectors and are within the scope of the present invention.
• the pilot data is provided to multiplier 234 which covers the data with a pilot Walsh sequence.
• the pilot data for all pilot channels 232 are identical and comprises the all ones sequence.
• the covered pilot data is provided to gain element 236 which scales the pilot data with a scaling factor to maintain the required pilot signal level.
• the scaled pilot data is provided to switch 230 which directs the data from pilot channel 232 to the proper summer 240.
• the spreading with the corresponding short PN sequences is performed within modulator and transmitter 114.
• the hardware as described above is one of many embodiments which can be used by a single base station to provide coverage to multiple sectors.
• Another method and system for adaptive sectorized transmission are disclosed in U.S. Patent Application Serial No. 08/495,382, entitled “DYNAMIC SECTORIZATION IN A SPREAD SPECTRUM COMMUNICATION SYSTEM", filed June 27, 1995, assigned to the assignee of the present invention and incorporated by reference herein.
• Yet another method and system for transmission to particularized areas are described in the aforementioned U.S. Patent Application No. PA446.
• Other hardware architectures can also be designed to perform the functions described herein. These various architectures are within the scope of the present invention.
• FIG. 4 A block diagram of an exemplary demodulator within remote station 6 is shown in FIG. 4.
• the forward link signal is received by antenna 132 and provided to receiver 134 which processes the signal in the manner described above.
• the digitized I and Q data is provided to demodulator 136.
• the data is provided to at least one correlator 310. Each correlator 310 processes a different multipath component of the received signal.
• the data is provided to short PN despreader 320 which despreads the I and Q data with the short PN sequences to obtain the despread I and Q data.
• the short PN despreading is the inverse of the spreading performed by the short PN spreader within modulator and transmitter 114.
• the despread I data is provided to multipliers 322a and pilot correlators 326a and the despread Q data is provided to multipliers 322b and pilot correlators 326b.
• Multipliers 322a and 322b multiply the I and Q data, respectively, with the Walsh sequence (Wx) assigned to that correlator 310.
• the I and Q data from multipliers 322a and 322b is provided to accumulators (ACC) 324a and 324b, respectively.
• accumulators 324 accumulate the data over a 64-chip interval, the length of the Walsh sequence.
• the decovered I and Q data from accumulators 324 is provided to dot product circuit 328.
• Pilot correlators 326a and 326b decover the I and Q data with the pilot Walsh sequence (PWy) assigned to that correlator 310 and filter the decovered pilot signal.
• the filtered pilot is provided to dot product circuit 328 which computes the dot product of the two vectors (the pilot and data) in a manner known in the art.
• An exemplary embodiment of dot product circuit 328 is described in detail in U.S. Patent No. 5,506,865, entitled "PILOT CARRIER DOT PRODUCT CIRCUIT", assigned to the assignee of the present invention and incorporated by reference herein.
• Dot product circuit 328 projects the vector corresponding to the decovered data onto the vector corresponding to the filtered pilot, multiplies the amplitude of the vectors, and provides a signed scalar output to combiner 330.
• Combiner 330 combines the outputs from correlators 310 which have been assigned to demodulate the received signal and routes the combined data to long PN despreader 332.
• Long PN despreader 332 despreads the data with the long PN sequence and provides the demodulated data to decoder 138.
• the pilot signal strength for a particular correlator 310 can be computed from the filtered pilot from pilot correlators 326a and 326b. In addition, the pilot signal strength measurements can be filtered to provide a more reliable measurement.
• repeaters are employed to improve coverage and increase capacity.
• a repeater receives a signal from a source device, amplifies the signal, and retransmits or rebroadcasts the signal to a destination device.
• the repeater provides two-way retransmission or rebroadcast of the forward and reverse link signals between communicating devices.
• the repeater provides signal conditioning (e.g., amplification, filtering, and possibly frequency conversion) but does not provide signal processing or control.
• FIGS. 5A and 5B A block diagram of an exemplary repeater is shown in FIGS. 5A and 5B.
• repeater 8a communicates with the base station through terrestrial or satellite link 410.
• Link 410 can be a terrestrial or microwave link from a source base station, or a satellite link from a communication satellite (such as a GLOBALSTAR communication satellite).
• the forward link signal from the base station is received by donor antenna 412 and provided to duplexer 414.
• Duplexer 414 directs the forward link signal to amplifier (AMP) 416 which amplifies the signal. Filtering and /or frequency conversion can also be provided, although this is not shown in FIG. 5A for simplicity.
• the amplified signal is routed through duplexer 418 and transmitted to the remote stations through server antenna 420.
• Serving antenna 420 also receives the reverse link signal from the remote stations.
• the reverse link signal is routed through duplexer 420 and provided to amplifier (AMP) 422 which amplifies the signal. Again, filtering and /or frequency conversion can also be provided but is not shown in FIG. 5A for simplicity.
• the amplified signal is routed through duplexer 414 and transmitted to the base station from antenna 412.
• Repeater 8b as shown in FIG. 5B operates in the same manner as that of repeater 8a in FIG. 5A. However, repeater 8b interfaces with the base station through transmission line link 424, which can comprise a fiber optic link, a coaxial link, or other links.
• the partition of a cell into multiple sectors provides many benefits in CDMA communication systems.
• capacity can be improved since the traffic channels (e.g., Walsh codes) among the various sectors can be reused.
• Second, reliability can also be improved through the use of soft handoff with two or more sectors.
• the base station can be configured to provide communications through a single sector or multiple sectors.
• the coverage area of the base station (or the cell) can be partitioned into multiple sectors.
• the communications between a remote station and the base station can occur through one or more sectors.
• Each sector has the attributes of a cell (e.g., each sector having its own set of traffic channels and its own pilot signal), except that the communication through the various sectors of the cell are coordinated by a common base station.
• each sector is associated with a different offset of the short PN spreading codes.
• the identity of that sector can be determined.
• the base station is configured to provide coverage to two or more sectors.
• One or more sectors can be associated with the coverage area surrounding the base station.
• the remaining sectors can be associated with repeaters which are placed at the boundary of the cell.
• the cell can be partitioned into two sectors.
• the base station can then be operated to provide coverage to three sectors, two sectors associated with the cell within which the base station is located and one sector associated with a repeater.
• FIG. 6A A first exemplary diagram of the coverage provided by a base station and a repeater of two communication systems is shown in FIG. 6A.
• base station 4 is operated to provided coverage to two sectors. One sector is associated with cell 22.
• the second sector is associated with repeater 8 which provides coverage to coverage area 26.
• both cell 22 and coverage area 26 are operated at the same frequency and overlaps such that a remote station moving along road 30 can be in soft handoff when located within shaded region 30.
• Base station 4 and repeater 8 are part of a first communication system.
• communications in the areas adjacent to cell 22 is provided by a second communication system.
• This second communication system can be another CDMA system operating at a different frequency or a system of an alternative communication technology, such as AMPS.
• Base station 14 of the second system provides coverage to cell 24. Similar to the first system, base station 14 can also be operated in a multi-sector mode to provide coverage to adjoining coverage area 28 through repeater 18. Note, in this example, the coverage area 26 is co-located within cell 24.
• FIG. 6B A second exemplary diagram of the coverage provided by a base station and a repeater is shown in FIG. 6B.
• coverage area 26 overlaps cell 24 but is not completely contained within cell 24 (as is the case in FIG. 6A). Coverage area 26 can be used to bridge the coverage between the first and second systems. Repeater 18 is not shown in FIG. 6B for simplicity.
• FIG. 6C A third exemplary diagram of the coverage provided by a base station and a repeater is shown in FIG. 6C.
• coverage area 26 overlaps cell 24 but is not co-located within cell 24.
• cells 22 and 24 are non- adjoining such that handoff between base station 4 to base station 14 is not possible without an intermediate handoff to repeater 8.
• repeater 18 is not shown in FIG. 6C for simplicity.
• the first system has a priori knowledge that coverage area 26 overlaps cells 22 and 24.
• the first system also has a priori knowledge that base station 14 is controlled by the second system.
• the first system is connected to the second system and can initiate a handoff of a remote station from the first system to the second system.
• repeaters can be used to initiate a handoff of the remote station between the two systems.
• the remote station moves along road 30 from left to right.
• the remote station is located in cell 22 and communicates with base station 4.
• the remote station also receives the pilot signal from repeater 8.
• the remote station demodulates the pilot signal from repeater 8, determines the identity of the new pilot, and reports the pilot signal strength and identity (e.g., the PN offset or the Walsh code of the pilot signal) to base station 4.
• Base station 4 compares the reported pilot signal strength against a predetermined add threshold and can add repeater 8 to the active set of the remote station if the pilot signal strength exceeds the predetermined add threshold.
• the active set comprises the list of base stations (and /or repeaters) through which active communication is established.
• Base station 4 can then direct soft handoff of the remote station in accordance with the method described in the aforementioned U.S. Patent Nos. 5,101,501 and 5,267,261.
• handoff of the communications between the remote station and base station 4 to base station 14 can be accomplished in one of at least four embodiments.
• the first system initiates a handoff of the communications between the remote station and base station 4 to base station 14 upon initiation of a soft handoff with repeater 8.
• coverage area 26 is co-located within cell 24. This can be ensured during the system planning stage and by proper placements of the base stations and repeaters. In this case, the first system is reasonably assured that a remote station which is in soft handoff with repeater 8 is also within the coverage area of base station 14. This information can be used to initiate the handoff to base station 14 when the remote station is within the coverage area of repeater 8.
• the first system initiates a handoff of the communications between the remote station and base station 4 to base station 14 upon measurement of a sufficient pilot signal strength from repeater 8.
• base station 4 initiates handoff with repeater 8 when the reported pilot signal strength of repeater 8, as measured by the remote station, is above the predetermined add threshold as described above.
• the first system does not immediately initiate handoff of the communications from base station 4 to base station 14 upon initiation of a handoff with repeater 8, since doing so may result in disconnection of the communications. Instead, the remote station continues to measure the pilot signal strength from repeater 8 and reports the measurements to base station 4.
• Base station 4 can compare the pilot measurements against a predetermined handoff threshold which is set higher than the predetermined add threshold. The first system initiates the handoff of the communications between the remote station and base station
• the predetermined handoff threshold can be set in accordance with measurements of the pilot signal strength throughout coverage area 26 (e.g., pilot signal strength measurement along road 30) or can be set in accordance with computation of the expected pilot signal strength (e.g., using effective
• the predetermined handoff threshold can be set
• the first system initiates a handoff of the communications between the remote station and base station 4 to base station 14 when base station 4 is dropped from the active set of the remote station.
• the remote station periodically measures the pilot signals of the base stations and repeaters within its active set and reports these measurements to the active base stations.
• the active base stations compare the pilot measurements against a predetermined drop threshold. If a pilot measurement is below the predetermined drop threshold, the base station corresponding to this pilot signal is removed from the active set of the remote station as described in the aforementioned U.S. Patent Nos. 5,101,501 and 5,267,261.
• the first system can presume that the remote station has traveled well within cell 24.
• the first system initiates the handoff of the communications between the remote station and base station 4 to base station 14 when base station 4 is dropped from the active set of the remote station.
• the third embodiment also works well for the coverage illustrated by FIGS. 6A-6B.
• the first system initiates a handoff of the communications between the remote station and base station 4 to base station 14 when repeater 8 is dropped from the active set of the remote station.
• communications between the remote station and repeater 8 is maintained for as long as possible.
• the first system presumes that the remote station is within the coverage area of the second system.
• the first system initiates the handoff of the communications between the remote station and base station 4 to base station 14 when repeater 8 is dropped from the active set of the remote station.
• the fourth embodiment works well for the coverage illustrated by FIG. 6A.
• the first system initiates a handoff of the communications between the remote station and base station 4 to base station 14 when both base station 4 and repeater 8 are dropped from the active set of the remote station.
• communications between the remote station and base station 4 and /or repeater 8 is maintained for as long as possible.
• the first system presumes that the remote station has traveled beyond the coverage area of the first system.
• the first system initiates the handoff of the communications between the remote station and base station 4 to base station 14 when both base station 4 and repeater 8 are dropped from the active set of the remote station.
• the fifth embodiment works well for the coverage illustrated by FIGS. 6A-6C.
• the second, third, and fifth embodiments described above provide hysteresis which minimizes the 'ping-ponging' of handoffs between two systems.
• the hysteresis is provided by the difference between the predetermined add threshold and the predetermined handoff threshold.
• the hysteresis is provided by the difference between the predetermined add threshold and the predetermined drop threshold of the base station and the repeater.
• this handoff to the second system can also occur while the remote station is idle.
• the pilot signal of repeater 8 can be measured.
• the remote station reports the pilot measurements to the first system.
• the first system can direct the handoff to the second system using any one of the embodiments described above.
• the handoff can be accomplished through interface messages which are transmitted between the base stations and the remote station.
• the remote station monitors for a global redirection message which is broadcast over the coverage area of the repeater.
• the global redirection message can direct the remote station to a new frequency or another system (e.g., an AMP system).
• the remote station monitors for an extended neighbor list message which is broadcast over the coverage area of the repeater.
• the extended neighbor list message can indicate that the only neighbors for this remote station are on another frequency or another system.
• the extended neighbor list message is described in the CDMA standard entitled "ANSI J-STD-008 : Personal Station-Base Station Compatibility Requirements for 1.8 to 2.0 GHz Code Division Multiple Access (CDMA) Personal Communications Systems".
• CDMA Code Division Multiple Access
• repeaters can be employed to link non-adjoining coverage areas of the two systems (e.g., repeaters connected in serial manner).
• the system initiating the handoff has a priori knowledge of the particular repeater which overlaps the neighboring system.
• the system uses this information and the report of the identity and/or pilot signal strength of this repeater to initiate the handoff.
• the present invention can also be practiced using a pilot beacon which transmits only the pilot signal (and no traffic channels).
• the use of the pilot beacon can be used in conjunction with the first three embodiments described above.
• the pilot beacon produces minimal interference to the surrounding coverage areas while providing the necessary pilot identification and signal strength measurements.
• any signal transmitted from the repeater or pilot beacon can be used assist with the handoff process.

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• 1998
  • 1998-11-25 KR KR1020007005681A patent/KR20010032440A/ko not_active Application Discontinuation
  • 1998-11-25 ID IDW20001012A patent/ID27894A/id unknown
  • 1998-11-25 BR BR9815435-4A patent/BR9815435A/pt not_active Application Discontinuation
  • 1998-11-25 CN CNB988115603A patent/CN100456872C/zh not_active Expired - Fee Related
  • 1998-11-25 WO PCT/US1998/025219 patent/WO1999027747A1/en not_active Application Discontinuation
  • 1998-11-25 AU AU16073/99A patent/AU759370B2/en not_active Ceased
  • 1998-11-25 JP JP2000522757A patent/JP2001524793A/ja active Pending
  • 1998-11-25 CA CA002311623A patent/CA2311623A1/en not_active Abandoned
  • 1998-11-25 EP EP98960489A patent/EP1034683A1/de not_active Withdrawn
  • 1998-11-25 RU RU2000116264/09A patent/RU2000116264A/ru not_active Application Discontinuation
  • 1998-11-25 IL IL13627398A patent/IL136273A0/xx unknown
• 2000
  • 2000-05-19 FI FI20001211A patent/FI20001211A/fi not_active Application Discontinuation
  • 2000-05-25 NO NO20002671A patent/NO327951B1/no not_active IP Right Cessation

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