Method for a handoff in a broadcast communication system

Field

The present invention relates to broadcast communication, or communication known as one-point to multi-point, in a wireline or wireless communication system. In particular, the present invention relates to systems and methods for handoff in such broadcast communication systems.

background

Communication systems have been developed to allow the transmission of information signals from transmitting stations to physically different destination stations. When transmitting an information signal from a transmitting station through a communication channel, the information signal is first converted into a form suitable for efficient transmission through the communication channel. The conversion, or modulation, of the information signal involves changing the parameters of the carrier according to the information signal in such a way that the spectrum of the resulting modulated carrier is limited within the communication channel bandwidth. At the destination station, the original information signal is replicated from the modulated carrier received through the communication channel. Such replication is commonly made by using the reverse of the modulation process used by the transmitting station.

Modulation also facilitates multiple access, i.e. simultaneous transmission and / or reception of several signals through a common communication channel. A multiple access communication system often includes a plurality of subscriber units that request intermittent services for a relatively short period of time rather than continuously accessing a common communication channel. Several multiple access techniques are technically known, such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and Amplitude Modulated Multiple Access (AM). Another type of multiple access technology is the Code Division Multiple Access (CDMA) Spectral Spread System, which is hereafter referred to as the IS-95 standard, "TIA / EIA / IS-95 Mobile for Dual Mode Wideband Spectral Spread Cellular Systems." Complies with the station-base station compatibility standard. The use of CDMA technology in multiple access communication systems is described in US Pat. No. 4,901,307, entitled "Spectrum Spreading Multiple Access Communication Systems Using Satellites or Terrestrial Repeaters", and "Systems that generate waveforms in CDMA cellular telephone systems and Disclosure in US Pat. No. 5,103,459 entitled "Methods", both US patents have been transferred to the transferee of the invention.

Channel access communication systems are wireless or wireline and carry voice and / or data. An example of a communication system that conveys both voice and data is a system that follows the IS-95 standard, which specifies that voice and data are transmitted through communication channels. The method of transmitting data in a fixed size code channel frame is described in detail in US Pat. No. 5,504,773 entitled "Methods and Devices for Formatting Data for Transmission", which is assigned to the assignee of the invention. Has been done. According to the IS-95 standard, data or voice is divided into code channel frames, which are 20 milliseconds wide and have a data rate of about 14.4 Kbps. Additional examples of communication systems that convey both voice and data include communication systems that comply with the 3G Partnership Project (3GPP), where 3GPP is the document number, 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, And 3G TS It is embodied in a set of documents containing 25.214 (W-CDMA standard) or "TR-45.5 Physical Layer Standard for cdma2000 Spectral Spread System" (IS-2000 Standard).

An example of a data-only communication system is a high data rate (HDR) communication system, which conforms to the TIA / EIA / IS-856 industrial standard, hereafter referred to as the IS-856 standard. This HDR system was filed on November 3, 1997, assigned to the assignee of the invention and disclosed in Simultaneous Continuing Application No. 08 / 963,386 entitled "Methods and Devices for High Rate Packet Data Transmission". It is based on the communication system system that has been used. The HDR communication system defines a set of data rates in the range of 38.4 kbps to 2.4 Mbps, at which the access point (AP) sends data to the subscriber station (access terminal AT). Since APs are similar to base stations, the technology for cells and sectors is the same as for voice systems.

In a multiple access wireless communication system, communication between users takes place through one or more base stations. The first user in one subscriber station communicates with the second user in the second subscriber station by transmitting data over a reverse link to the base station. A base station can receive data and route the data to another base station. The data is transmitted to the second subscriber station on the forward link of the same base station or another base station. The forward link is related to the transmission from the base station to the subscriber station, and the reverse link is related to the transmission from the subscriber station to the base station. Similarly, communication can take place between a first user on one subscriber station and a second user on the ground line station. The base station receives data from the user over the reverse link and routes the data to a second user through the public switched telephone network (PSTN). For example, in many communication systems such as IS-95, W-CDMA, IS-2000, forward and reverse links are assigned to different frequencies.

When a subscriber station moves outside the boundaries of the base station with which the subscriber station is currently communicating, it is desirable to maintain the communication link by moving the call to a different subscriber station. Methods and systems that provide communication with subscriber stations through more than one base station during the soft handoff process are disclosed in US Pat. No. 5,267,261 entitled "Mobile Assisted Soft Handoff in CDMA Cellular Telephone Systems." , This US patent has been transferred to the transferee of the present invention. The methods and systems that provide softer handoffs are described in detail in U.S. Pat. No. 5,933,787 entitled "Methods and Devices for Performing Handoffs Between Sectors of Common Base Stations," which U.S. Pat. No. It has been transferred. By using these methods, communication between subscriber stations is not interrupted by possible handoffs from one base station to the next. This type of handoff is considered a "soft" handoff, and communication with the next base station is established before communication with the original base station ends. When the subscriber unit is communicating with two base stations, the subscriber unit synthesizes the signal received from each base station in the same way that the multipath signal from the common base station is synthesized. ..

According to the invention cited above, each base station transmits a pilot signal of a common PN diffusion code offset in code phase from the pilot signals of other base stations. The subscriber station assist soft handoff operates based on the pilot signal strength detected by the subscriber station. To simplify the pilot search process, four different sets of pilot offsets are specified: active set, candidate set, adjacent set, and remaining set. The active set identifies the base station or sector through which the subscriber station is communicating. Candidate sets identify base stations or sectors for pilots that are received at the subscriber station with sufficient signal strength to be members of the active set, but are not placed in the active set by the base station. Adjacent sets identify potential base stations or sectors for establishing communication with subscriber stations. The remaining set identifies a base station or sector with all other possible pilot offsets in the current system, except for the pilot offsets currently present in the active set, candidate set and adjacent set.

The subscriber station is provided with a list of PN offsets corresponding to the base stations in adjacent cells. In addition, the subscriber station is provided with a message identifying at least one pilot corresponding to the base station through which the subscriber station should communicate. These lists are stored in the subscriber station as adjacent and active sets of pilots and are updated as conditions change.

When communication is first established, the subscriber unit communicates through the first base station and the active set contains only the pilot signal of the first base station. The subscriber unit monitors the pilot signal strength of the active set, candidate set, adjacent set and remaining set base stations. When the pilot signal of the base station in the adjacent set or the remaining set exceeds a predetermined threshold level (T_ADD), the pilot signal identifier is added to the candidate set. The subscriber unit communicates a power strength measurement message (PSMM) identifying the new base station to the first base station. The system controller decides whether to establish communication between the new base station and the subscriber unit and communicates the decision with a handoff instruction message (HDM). The message identifies the active set of pilots that correspond to the base stations with which the subscriber station is communicating. The system controller also communicates information to each subscriber station corresponding to the new pilot in the active set, which commands each of these base stations to establish communication with the subscriber station. Subscriber station communications are routed through all base stations identified by pilots in the subscriber station active set.

As the subscriber unit communicates through multiple base stations, it continues to monitor the signal strength of the active set, candidate set, adjacent set and remaining set of base stations. If the signal strength corresponding to the active set of base stations falls below a predetermined threshold (T_DROP) for a predetermined time period (T_TDROP), the subscriber unit will send a message reporting an event. Generate and send. The system controller receives this message through at least one of the base stations with which the subscriber unit is communicating. The system controller decides to terminate communication through the base station where the pilot signal strength measured at the subscriber station is below T_DROP.

When the system controller decides to terminate communication through the base station, it generates a new message that identifies the active set of pilots through which the subscriber station should communicate. This message, which identifies the pilot of the active set, does not identify the pilot of the base station whose communication with the subscriber station should be terminated. The system controller also communicates information to the base station not identified in the active set and terminates communication with the subscriber station. When the subscriber station receives a message identifying a pilot in the active set, it discontinues signal processing from the base station where the pilot is no longer in the active set. Subscriber station communications are routed only through base stations identified by pilots in the subscriber station active set. Previously there was more than one pilot identified in the active set, but now in the case where there is only one, the subscriber station is the one corresponding to the pilot identified in the subscriber station active set. Communicate only with the base station.

The wireless communication service described above is an example of a one-point to one-point communication service. In contrast, broadcast services provide multipoint communication services from a central station. The basic model of a broadcast system consists of a user's broadcast net handled by one or more central stations. One or more central stations send users information with certain content, such as news, movies, sporting events and the like. The subscriber station of each broadcast net user monitors a common broadcast forward link signal. Since the central station determines the content in a fixed manner, the user generally does not return the communication. Examples of common uses for broadcast service communication systems are TV broadcasts, radio broadcasts, and the like. Such communication systems are generally highly specialized, purpose-built communication systems. Due to recent advances in wireless cellular telephone systems, there is a primary interest in leveraging the existing infrastructure of one-to-one cellular telephone systems for broadcast services. As used herein, the term "cellular" system includes communication systems that utilize both cellular and PCS frequencies.

The described handoff method for a subscriber unit acting as a one-point to one-point unit described above can be applied to a broadcast system, because in a broadcast system a large number of subscribers monitor a common broadcast forward channel. , Base Station-Subscriber Stations Handoffs based on signaling message exchanges result in high signaling loads. In addition, transmissions received simultaneously by the subscriber station during the handoff are synchronized at the transmitting base station, as described in Japanese Patent Nos. 5,267,261 and 5,933,787 cited above. Since broadcast transmissions are directed to many subscriber stations, base stations cannot synchronize transmissions to each subscriber station that wants a handoff. Based on the above, there is a technical need for systems and methods for handoff in such broadcast communication systems.

Overview

The embodiments disclosed herein provide a method for autonomous handoff in a broadcast communication system, where a subscriber station receives a broadcast channel to be transmitted through a first sector and is transmitted by a sector at the subscriber station. The quality metric of the forward link is measured, and the subscriber station identifies and joins at least one sector in which the measured quality metric exceeds the first predetermined threshold, unlike the first sector. The station addresses the above need by synthesizing broadcast channels received from the first sector and at least one identified sector.

In another aspect, the above need is addressed by providing a method for set management in broadcast communication systems, which provides the subscriber station with a first list that identifies the first set of sectors. Provided, the subscriber station measures the quality metric of the forward link transmitted by each identified sector, and the subscriber station gives the identifier of the sector where the measured quality metric exceeds the first predetermined level. Includes removing from the first list and placing the sector identifier on the second list at the subscriber station.

In another aspect, the above need is addressed in a broadcast communication system by a method of migrating a subscriber station from an area covered by a first sector to an area covered by a different sector. At the subscriber station, the configuration of the broadcast channel transmitted by the second sector is determined, and according to the determined configuration of the broadcast channel transmitted by the second sector, from the coverage area covered by the first sector. Including migration.

Detailed explanation

Definition The word "exemplary" is used here to mean "act as an example, case, or example." Any embodiment described herein as "exemplary" need not be construed as favorable or advantageous over other embodiments.

The term one-point to one-point communication is used here to mean communication between two subscriber stations through a dedicated communication channel.

The terms group service, one-point-to-multipoint communication, push-to-talk, or dispatch service are used here to mean communications in which multiple subscriber stations are generally receiving communications from one subscriber station. Will be done.

The term packet is used here to mean a group of bits that contain data (payload) and control elements and are organized in a particular format. Control elements include, for example, preambles, quality metrics, and others known to those of skill in the art. Quality metrics include, for example, Cyclic Redundancy Check (CRC), parity bits, and others known to those of skill in the art.

The term access network is used here to mean a set of base stations (BS) and one or more base station controllers. The access network transmits data packets between multiple subscriber stations. The access network may be further connected to an additional network outside the access network, such as a corporate intranet or the Internet, and data packets may be transmitted between each access terminal and such an external network.

The term base station is used here to mean the hardware with which the subscriber station communicates. The cell relates to the hardware or geographic coverage area, depending on the context in which the term is used. A sector is a cell partition. Since sectors have cell attributes, the teachings described for cells are easily extended to sectors.

The term subscriber station is used here to mean the hardware with which the access network communicates. The subscriber station may be dynamic or static. The subscriber station may be any data device that communicates through a wireless channel or, for example, a wire channel using fiber optics or coaxial cable. Subscriber stations can be any of many types of devices, including but not limited to PC Cards, CompactFlash®, external or internal modems, or wireless or wireline telephones. You may. Subscriber stations in the process of establishing an active traffic channel connection with a base station are said to be in a connection setup state. A subscriber station that has established an active traffic channel connection with a base station is called an active subscriber station and is said to be in a traffic state.

The term physical channel is used here to mean the communication route through which the signal propagates, which is described in terms of modulation characteristics and coding.

The term logical channel is used here to mean a communication route within the protocol layer of a base station or subscriber station.

The term communication channel / link is used here to mean a physical channel or a logical channel depending on the situation.

The term reverse channel / link is used here to mean a communication channel / link in which a subscriber station transmits a signal to a base station.

Forward channel / link is used here to mean a communication channel / link at which a base station transmits a signal to a subscriber station.

The term soft handoff is used here to mean communication between a subscriber station and two or more sectors, where each sector belongs to a different cell. Reverse link communication is received by both sectors, and forward link communication is transmitted simultaneously on the forward links of two or more sectors.

The term softer handoff is used here to mean communication between a subscriber station and two or more sectors, where each sector belongs to the same cell. Reverse link communication is received by both sectors, and forward link communication is transmitted simultaneously on one of the forward links of two or more sectors.

Term elimination is used here to mean failing to recognize a message.

Term-only channels are used herein to mean channels that are modulated by specific information to individual subscriber stations.

The term common channel is used herein to mean a channel that is modulated by information shared between all subscriber stations.

Description As explained, the basic model of a broadcast system is to have a user's broadcast net, which is handled by one or more central stations, one or more central stations having certain content, such as news, movies, sporting events and the like. Send information with to the user. The subscriber station of each broadcast net user monitors a common broadcast forward link signal. FIG. 1 illustrates a conceptual block diagram of a communication system 100, which can perform a high speed broadcast service (HSBS) according to an embodiment of the present invention.

The broadcast content is transmitted on the content server (CS) 102. The content server may be located within the carrier network (not shown) or outside the Internet (IP) 104. The content is delivered to the broadcast packet data serve node (BPDSN) 106 in the form of packets. The BPDSN may be physically co-located or identical to the standard PDSN (not shown), but the term BPDSN can be used because the BPDSN can be logically different from the standard PDSN. used. The BPDSN 106 delivers the packet to the packet control function (PCF) 108 according to the destination of the packet. Since the base station controller is for standard voice services, the PCF is the control entity that controls the functionality of base station 110 for HSBS and any common packet data service. To show the connection between the physical access network and the HSBS high-level concept, Figure 1 shows the PCF as physically co-located or identical to the Base Station Controller (BSC). , Logically different. Those skilled in the art will appreciate that this is for pedagogical purposes only. BSC / PCF108 provides the packet to base station 110. Communication system 100 enables HSBS by introducing a forward broadcast shared channel 112 (F-BSCH) transmitted by base station 110. F-BSCH112 does not have to be transmitted from all base stations 110. F-BSCH has a large number of subscriber stations and is capable of high data rates that can be received. The term forward broadcast shared channel is used.

F-BSCH may be monitored by a large number of subscribers 114. As a result, base station-subscriber signaling message-based handoffs are not efficient at HSBS. The reason is that such a handoff is a high signaling load and may not be feasible because it is a fixed broadcast transmission that is not tuned for a particular subscriber station. On the other hand, due to the high power demand for transmission of common broadcast forward channels, there are only a few common broadcast forward channels on a given CDMA carrier, which is autonomous without base-subscriber signaling message exchanges. Make soft and softer handoffs practical.

Therefore, instead of exchanging messages between the base station and the subscriber station wishing to hand off, information about the broadcast transmission at the adjacent base station is communicated by an overhead message on each channel F-BSCH at each base station. .. Broadcast service parameter messages sent at each base station are part of this sector's soft handoff (SHO) group for each supported F-BSCH, as subscribers soft-synthesize only synchronous transmissions. List the identifiers of. A method and system for signaling, including both of the mentioned embodiments, was filed on August 20, 2001 and is a concurrent US patent application entitled "Methods and Devices for Signaling in Broadcast Communication Systems". Explained in detail in 09 / 933,978, this US patent application has been assigned to the assignee of the invention. As used herein, the SHO group means a group of all base stations that synchronize and transmit a common broadcast forward link. Figure 2 illustrates two SHO groups, with SHO group 1 202 being BS.₁, BS₂And BS₃Including, SHO Group 2 202 is BS₄, BS₅, BS₆And BS₇including.

Referring to FIG. 2, a hard handoff is required when the subscriber station crosses the boundary from the coverage area of SHO group 1 202 to the coverage area of SHO group 2 202. The term hard handoff, as used herein, is used to mean that monitoring of the first channel is stopped (break before make) before monitoring of the second channel begins. On the other hand, the subscriber station is BS₇Monitor transmissions from new base stations such as BS₆When entering the coverage area of, the subscriber is BS because both base stations are in the same SHO group.₇You can monitor the F-BSCH transmission from the base station before you stop listening to the F-BSCH transmission from.

Autonomous soft handoff In one embodiment of the present invention, the subscriber station uses the forward link quality metric to determine which F-BSCH to monitor. Quality metrics include, for example, pilot signal strength, bit error rate, packet error rate, and other quality metrics known to those of skill in the art. To simplify the decision process, several different sets of pilot offsets and transition rules between sets are specified as detailed below. To facilitate the essential concepts of the various embodiments, the following description uses all sets: active set, candidate set, adjacent set and remaining set. When a subscriber station subscribing to the HSBS service captures a sector, it decodes the message and gives the subscriber station a list of sector identifiers that are part of the sector's SHO group for each supported F-BSCH. provide. According to one embodiment, the list is provided in the broadcast service parameter message sent in each sector. According to other embodiments, the list is provided for existing overhead messages. The subscriber station first assigns the identifier of the sector in the provided list to the adjacency set. The subscriber station monitors the signal strength of the sectors in the adjacency set and assigns the pilot signal identifier to the active set, candidate set and adjacency set according to the monitored signal strength. When the subscriber station moves around, the subscriber station is BS₆Update the overhead parameters of at the same time. Broadcast service parameter messages from the new sector indicate additional members and remove some members of the SHO group for information in the old sector broadcast service parameter message. Therefore, BS₆Broadcast service parameter message from (BSPM)₆) Is a member {BS₄, BS₅, BS₇} While containing BS₇Broadcast service parameter message from (BSPM)₇) Is a member {BS₄, BS₆} Only included. The subscriber station puts one sector in the rest of the set.

The advantage of soft handoff is that the subscriber station synthesizes simultaneous transmissions of multiple sectors according to the capabilities of the subscriber station, such as the number of received fingers, processing power, and others known to those skilled in the art. As a result, when the subscriber station decides to monitor the HSBS channel that is modulating F-BSCH, the subscriber station is from the sector, assuming that the active set contains more than one pilot signal identifier. Choosing to synthesize F-BSCH, the pilot signal identifier of this sector belongs to the active set and has the highest signal strength. The subscriber station tunes to a frequency transmitted by the sector and modulated by the selected F-BSCH modulated by the HSBS channel. The subscriber station continues to monitor the pilot signal strength of the sectors in the active set, candidate set, adjacent set and remaining set. When the pilot signal of the second sector in the adjacent set or the remaining set is eligible to move to the active set, the subscriber station adds the pilot signal identifier to the active set. Therefore, the subscriber station monitors the F-BSCH transmitted only by the sector identified by the pilot in the subscriber station active set.

While the subscriber station monitors the F-BSCH transmitted by multiple sectors, the subscriber station continues to measure the signal strength of the active set, candidate set, adjacent set and remaining set of sectors. If the signal strength of the pilot signal corresponding to the sector of the active set disqualifies the pilot signal from the members of the active set, the subscriber station decides to remove the pilot signal identifier from the active set. If the subscriber station is monitoring the F-BSCH transmitted through the sector, the subscriber station will stop monitoring the transmitted F-BSCH. In the case where there is more than one pilot previously identified in the active set and currently only one, the subscriber station monitors only one sector corresponding to the pilot signal and its identifier belongs to the active set. ..

Pilot set management As described above, the autonomous soft handoff of the present invention utilizes the concept of a pilot set, such as the subscriber station assist software and softer handoff described in patents 5,267,261 and 5,933,787 mentioned above. .. According to patents 5,267,261 and 5,933,787 mentioned above, sector-subscriber station signaling is assisted by pilot set management. However, autonomous soft handoffs according to embodiments of the present invention do not utilize such signaling and therefore require different methods of set management. In order to better understand the concept of set management, set management according to Japanese Patent Nos. 5,267,261 and 5,933,787 mentioned above will be reviewed, and embodiments according to the present invention will be described.

Figure 3 illustrates the signaling associated with changes in pilot intensity and various sets of pilot membership embodiments during a subscriber-assisted handoff. In Figure 3, the time t₀Previous, Pilot P_AIs in an adjacent set and has an ascending signal strength measured by the subscriber station searcher receiver. However, the pilot signal strength is below the threshold T_ADD, which qualifies the pilot to enter the candidate set. The subscriber station control processor makes a decision to place an inactive or non-candidate set member in the candidate set when the measured pilot crosses the threshold T_ADD, at which time the subscriber station control processor generates a PSMM. And send.

Time t₀In the pilot P measured by the searcher receiver_AThe signal strength exceeds the value T_ADD. The subscriber station control processor compares the measured value with the T_ADD value and determines that the T_ADD value has been exceeded. The subscriber station control processor generates and transmits the corresponding PSMM.

Searcher is Pilot P_AIt may detect some multipath versions of, and it should be noted that these are only a few chips time-shifted from others. The sum of all available multipath versions of the pilot detected may be used to identify the pilot's intensity.

The decision to place a candidate set member in the active set is made by the system controller. For example, a measured candidate pilot joins the active set when it has a signal strength that exceeds the signal strength of one other active set member pilot by a predetermined value. However, the number of active set members may be limited. If the addition of a pilot to the active set exceeds the active set limit, the weakest active set pilot is moved to another set.

Once the system controller has decided that the pilot should be in the active set, all sectors with the traffic value assigned to the subscriber station will send a handoff instruction message to the subscriber station, which is active. Pilot P on the set_Aincluding. In Figure 3, the time t₁Then, the handoff instruction message is received at the subscriber station, and at the subscriber station, pilot P_AIdentified pilots are used, including pilot P_ADemodulates received signals from the transmitted sector and / or from other sectors. Once the pilot is identified in the handoff instruction message, one version of the information signal or, if present, a multipath version of the information signal corresponding to the identified pilot from the same sector is demodulated. The final demodulated signal is therefore transmitted from one or more sectors into its multipath version. During the soft handoff, the subscriber station diversity-synthesizes the received signal at the symbol level. Therefore, all sectors participating in the soft handoff must transmit the same symbol, except for closed-loop power control subchannel data as described below.

In Figure 3, the time t₁And t₂In between, Pilot P_ASignal strength drops, time t₂The signal strength drops below the predetermined threshold T_DROP. When the pilot's signal strength drops to the value T_DROP for a predetermined time period, the subscriber station control processor again time t.₃PSMM is generated and transmitted in.

In response to this PSMM, the system controller generates a handoff instruction message sent to the subscriber station by all sectors that have a traffic channel assigned to the subscriber station. This is no longer an active set pilot P_ADoes not include. Time t₄In Pilot P_AA handoff instruction message is received at the subscriber station to move the from the active set to, for example, the adjacent set. Once removed from the active set, this pilot is no longer used for signal demodulation.

As is well known to those skilled in the art, spectral diffusion communication systems are interference limited. In the subscriber station assist handoff, the candidate set helps to keep the pilot signal identifier in a convenient location for quick access, and the search frequency for the pilot signal in the candidate set is higher than the search frequency for the pilot signal in the adjacent set. high. Therefore, the effect of delay between PSMM and HDM is minimized. The reason is that when receiving HDM, the subscriber station can quickly put the pilot signal into the active set and start traffic channel synthesis, which improves signal-to-noise ratio (SINR). However, autonomous handoffs allow subscribers to change the search frequency and initiate traffic channel synthesis without delay. As a result, in one embodiment of the invention, the candidate set is removed from the four different sets of pilot offsets. Therefore, the pilot intensity is time t₀In the first threshold T_ADD₁If the number exceeds, the pilot will be upgraded directly from the adjacent set to the active set. Those skilled in the art will recognize that the method of promoting a pilot from an adjacent set is equally applicable to promoting a member from the remaining set.

According to other embodiments of the invention, the candidate set is maintained. With reference to Figure 4, the pilot intensity is the first threshold T_ADD.₁When crossing, the transition from the adjacent set to the candidate set takes time t₀Occurs in. When the pilot signal is observed and according to one embodiment, the pilot intensity is time t₂In the second threshold T_ADD₂When it exceeds, it is promoted from the candidate set to the active set. According to other embodiments, the timer for the pilot is time t₀Starts at. If the pilot remains in the candidate set for the timer interval (T_TADD), the pilot is promoted to the active set. If the pilot is removed from the candidate set before T_TADD, the timer will be stopped. Therefore, the pilot signal is promoted only when the pilot signal strength is increased or stable.

An alternative mode in which the pilot is added to the active set is illustrated with reference to Figure 5. With reference to Figure 5, the strength of the pilot signal rises above the members of the active set. When the signal strength of the pilot signal exceeds the pilot signal strength of the active set pilot by at least T_COMPdB, the subscriber reports the event to the sector. In Figure 5, Pilot P₁, P₂And P₃Is a member of the active set, while pilot P₃Is initially a member of another set, such as an adjacent set.

Generally, the number of active set members corresponds to the number of data receivers available, but the number of active sets may be greater than the number of pilots. Therefore, the subscriber station can select from the active set members the one with the highest signal strength for demodulation of the corresponding data signal. Those skilled in the art will appreciate that one or more pilots in the active set may have multipath propagation in the same sector, i.e. the sector that transmitted the pilot received at the subscriber station. In the case of multipath propagation, the subscriber station reselects the demodulation signal corresponding to the multipath version of the pilot identified by the active set pilot with the highest signal strength. Therefore, the actual sector signal demodulated by the subscriber station may be from different sectors or from the same sector.

Time t₀In, pilot P measured by the searcher receiver and compared to the value T_ADD by the subscriber station control processor.₀Is determined to be greater than the value T_ADD. As described earlier, this event causes the subscriber station control processor to generate a PSMM, which is transmitted by the subscriber station to the sector for relaying to the system control processor. Subscriber station is also Pilot P₀To the candidate set.

Time t₁In Pilot P₀Is a pilot P only for values greater than the value T_COMP₁Beyond. The subscriber station control processor generates another PSMM, which is transmitted by the subscriber station to the sector for relaying to the system control processor. It should be noted that only pilots who are already members of the candidate set are compared to active set members using the T_COMP criteria. Pilot P₀Is the value T_COMP only pilot P₁The system controller begins to set up the modem in another sector or sector communicating with the subscriber station. However, no setup is required if the pilot is not from another sector or sector communicating with the subscriber station. In each case, the system controller communicates a handoff instruction message to the subscriber station, which includes the pilot if it is not already an active set member.

The procedure is pilot P₀Is the same as becoming stronger. Time t₂In Pilot P₀Is only a value greater than the value T_COMP, then the strongest pilot P₂Become stronger than. As a result, the subscriber station control processor spawns another PSMM, which is transmitted by the subscriber station to the sector for relaying to the system control processor. Pilot P₀Is the value T_COMP only pilot P₂If the system controller has not yet been made, the pilot will be added to the active set as described above.

In subscriber-assisted handoffs, adding strong pilots to the active set through the T_COMP method serves the purpose of quickly adding pilots with actually increasing signal strength to the active set. As described, the base station controller has the decision to promote the pilot from the candidate set to the active set. If the sector decides not to promote the pilot to the active set, and the pilot signal strength remains elevated, the sector transmitting the pilot signal becomes an interferer. A new PSMM is generated according to the T_COMP method to facilitate the operation of the base station controller. However, in the autonomous handoff, when the subscriber station identifies a pilot with a fast increasing signal strength, the subscriber station can change the search frequency and start channel synthesis immediately. As a result, according to one embodiment of the invention, the T_COMP method of adding a pilot identifier to the active set is not utilized.

The size of the active set is limited. Therefore, when the active set is already full, the subscriber station may refuse to add the identifier of the pilot signal with sufficient signal strength to the active set. If the pilot signal strength remains rising, the sector sending the pilot signal becomes an interferor, removing the weaker pilot signal identifier from the active set, adding the fast rising pilot identifier, and from the sector. It is effective to start synthesizing the signal of. Therefore, according to other embodiments of the invention, an alternative mode of adding pilots to the active set is maintained. This method must be modified according to the aforementioned embodiments of the present invention.

As a result, according to the embodiment in which the candidate set is deleted, the subscriber station T_COMP the signal strength of the pilot whose identifier is not a member of the active set, and the pilot strength of the pilot whose identifier is a member of the active set._aMonitor whether the value of is exceeded. Upon identifying such a pilot, the subscriber station decides whether to add the pilot's identifier to the active set.

According to the embodiment in which the candidate set is maintained, the method of transitioning to the candidate set has two thresholds T_ADD.₁And T_ADD₂When using, the pilot signal strength is T_ADD, as explained.₂When crossing, the pilot's identifier is added to the candidate set. The subscriber station indicates that the signal strength of the pilot whose identifier is a member of the candidate set is the pilot strength of the pilot whose identifier is a member of the active set, T_COMP._aMonitor whether the value of is exceeded. When such a pilot is identified, the subscriber station decides whether to add the pilot's identifier to the active set.

The transition method to the candidate set is the threshold T_ADD₁And, when using the end of the timer interval T_TADD, once the pilot signal strength exceeds the signal strength of the pilot with the weakest signal strength already in the active set by the value of T_COMP, the timer interval T_TADD ends. Whether or not the subscriber station decides to add the pilot to the active set.

Pilot signal strength is T_DROP_aWhenever it is below, the period is T_TDROP_aBeyond, the pilot is removed from the active set.

Broadcast Service Handoff Control & Signaling Due to the potential mobility of the subscriber station and changing F-BSCH conditions, the subscriber station will need to hand off from the coverage area of the original sector to the coverage area of the second sector. The method of performing the handoff depends on the state of the subscriber station in the coverage area of the original sector and the configuration of the original sector and the second sector.

When the power is turned on, the subscriber station enters the system decision substate and the system that executes the capture attempt is selected. In one embodiment, after selecting a system for system determination, the subscriber station transitions to the pilot acquisition substate and the subscriber station demodulates the pilot signal based on the acquisition parameters retrieved in the system determination substate. Try to do. The subscriber station attempts to capture the CDMA pilot signal according to the capture parameters. When the subscriber station detects a pilot signal with energy above a predetermined threshold, the subscriber station transitions to the synchronous channel capture substate and attempts to capture the synchronous channel. Synchronous channels broadcast by sectors typically contain basic system information such as system identifiers (SIDs) and network identifiers (NIDs), but most importantly, the synchronization channels provide timing information. To provide to the subscriber station. The subscriber station adjusts the subscriber station timing according to the synchronization channel information, and enters the subscriber station idle state. The subscriber station initiates idle processing by receiving the channel provided by the system for the overhead message identified in the synchronous channel message, if the sector captured by the subscriber station supports multiple frequencies. Uses hash functions to determine which frequency both the subscriber station and the sector use for communication. Subscribers and sectors use hash functions to determine which paging channel the subscriber is monitoring. In one embodiment, the hash function receives many entries for hashing, such as frequencies, paging channels, and the like, as well as the International Subscriber Bureau Identifier (IMSI) and outputs one entry.

In the idle state, the subscriber station can receive a message, receive an incoming call, initiate a call, initiate a registration, or initiate a message transmission. In addition, subscribers to the HSBS service monitor the HSBS channel modulation of F-BSCH. The frequency determined by the hash function may or may not be modulated by F-BSCH. As a result, if the subscriber station wishes to monitor an HSBS channel that is modulating F-BSCH on a frequency different from the frequency determined by the hash function, it will re-modulate to the frequency modulated by F-BSCH. Must be in sync.

Based on the above, the subscriber station is in the following state in the original sector: State 1: F-BSCH is not monitored and is tuned to the frequency determined by the hash function; State 2: F-BSCH is not monitored and is tuned to a frequency modulated by F-BSCH that is different from the frequency determined by the hash function; State 3: F-BSCH is being monitored and is therefore tuned to the frequency modulated by F-BSCH.

According to one embodiment, the subscriber station determines the configuration of the second sector according to the value of the HSBS adjacency indicator (NGHBR_CONFIG_HSBS) transmitted by the current sector. Specific values for NGHBR_CONFIG_HSBS include, for example, whether the HSBS configuration of the adjacent sector is known, whether the adjacent sector is transmitting F-BSCH, whether the adjacent sector F-BSCH is transmitting at the same frequency, and so on. Whether the HSBS channels are synchronized, whether the same set of HSBS channels are multiplexed into F-BSCH transmitted in adjacent sectors in the same way, whether autonomous handoffs are allowed, Other configuration information known to those skilled in the art is shown. According to one embodiment, NGHBR_CONFIG_HSBS is included in the broadcast service parameter message sent in the current sector.

When the subscriber station decides to hand off to the second sector, the subscriber station checks NGHBR_CONFIG_HSBS for the second sector. The subscriber station starts working according to the value of NGHBR_CONFIG_HSBS. Here are some scenarios that follow the examples listed above for the NGHBR_CONFIG_HSBS value. Those skilled in the art will recognize that the scenarios described depend on the configuration of the communication system.

When the subscriber station is in state 1 or 2, the subscriber station is not related to the status of F-BSCH. As a result, the subscriber station receives NGHBR_CONFIG_HSBS and determines the configuration parameters for the second sector. The subscriber station executes the idle handoff according to the idle handoff method realized in the communication system. In one embodiment, the idle handoff method uses the hashing method described above to determine the frequency that the subscriber station tunes to and the paging channel that the subscriber station begins to monitor. Instead, if the subscriber station is not currently interested in monitoring the HSBS channel, but sufficient information about the adjacent HSBS channel is available in the broadcast service parameter message for the current sector, the subscriber station is F. -You may choose to tune to the frequency modulated by BSCH.

The NGHBR_CONFIG_HSBS received by the subscriber station in state 1 or 2 may indicate that the configuration of the second subscriber station is unknown. In one embodiment, the subscriber station hands off to the sector indicated by NGHBR_CONFIG_HSBS that the configuration is known. Instead, the subscriber station seeks to discover non-broadcast related adjacencies. For example, communication systems according to the IS-95 and IS-2000 standards provide an adjacency identifier (NGHBR_CONFIG), which indicates adjacency information, such as frequency allocation and the number of paging channels. Those skilled in the art will recognize that other communication systems may provide similar information. As a result, the subscriber station does not need to initiate the complete initialization process as described above, but captures the frequencies and paging channels of the adjacent sectors using the hashing method described above according to the adjacency information. If such information is not found or is not definitive, the subscriber station must enter the initialization process.

When the subscriber station in state 3 receives NGHBR_CONFIG_HSBS indicating that soft handoff by F-BSCH in the second sector is allowed, the subscriber station supports autonomous soft handoff. The station performs an autonomous soft handoff. Both sectors belong to the same SHO group, F-BSCH is transmitted on the same frequency through both sectors, the same set of HSBS channels are similarly multiplexed on F-BSCH, and F-BSCH transmission is synchronized. If so, soft handoff is allowed. Instead, a hard handoff is performed according to the embodiment described by the subscriber station, new sectors are captured, and HSBS channel monitoring is resumed.

When the subscriber station in state 3 receives NGHBR_CONFIG_HSBS indicating that the HSBS channel is available in the second sector but the transmission is not synchronized between sectors, the subscriber station gives a hard handoff. Execute. Since the two broadcast channels are the same, the subscriber station shifts directly to the HSBS channel frequency of the second sector and resumes monitoring the HSBS channel. If the subscriber station fails to capture all the required parameters from NGHBR_CONFIG_HSBS, the subscriber station performs a hard handoff to the second sector and uses the above hashing method according to the adjacency information. It captures the frequency and paging channel of two sectors, determines the information about the HSBS channel from the broadcast service parameter message, tunes to the HSBS channel frequency, and resumes receiving the HSBS channel.

The HSBS channel is available in the second sector, but the configuration parameters of the F-BSCH are different, for example the F-BSCH of the second sector is transmitted on different frequencies and is on the F-BSCH channel. The subscriber station in state 3 receives an NGHBR_CONFIG_HSBS indicating that the set of multiplexed HSBS channels is not identical or not multiplexed in a similar manner. The subscriber station performs a hard handoff to the second sector, captures the frequency and paging channel of the second sector using the hashing method described above according to the adjacency information, and for the HSBS channel from the broadcast service parameter message. Determine the information of, tune to the HSBS channel frequency, and resume receiving the HSBS channel. Alternatively, if the subscriber station can determine that the differences that can be recovered by the operation of the subscriber station, eg, all parameters are the same except for the frequency, then the subscriber station is second. Shifts directly to the HSBS channel frequency of the sector and resumes monitoring the HSBS channel.

In one embodiment, when the subscriber station in state 3 receives an NGHBR_CONFIG_HSBS indicating that the second sector is not transmitting F-BSCH, the subscriber station has a weaker but acceptable pilot signal. Hand off to the sector sending the F-BSCH with. Instead, the subscriber station stops receiving the F-BSCH and performs an idle handoff to the second sector according to the idle handoff realized in the communication system. In one embodiment, the idle handoff method uses the hashing method disclosed above to determine the frequency that the subscriber station tunes to and the paging channel that the subscriber station begins to monitor.

NGHBR_CONFIG_HSBS indicates that the subscriber station is in state 3 and the configuration of the second sector is unknown. In one embodiment, the subscriber station hands off to the sector for NGHBR_CONFIG_HSBS, which indicates that the configuration is known, whether F-BSCH is transmitted or not. Instead, the subscriber station seeks to discover non-broadcast related adjacencies. For example, communication systems according to the IS-95 and IS-2000 standards provide NGHBR_CONFIG, which indicates adjacency information, such as the number of frequency allocations and paging channels. Those skilled in the art will recognize that other communication systems may provide similar information. As a result, the subscriber station does not need to initiate the complete initialization process as described above, but captures the frequencies and paging channels of the adjacent sectors using the hashing method described above according to the adjacency information. If such information is not found or is not definitive, for example the adjacency configuration is unknown, the subscriber station must enter the initialization process. Once the subscriber station captures a new sector, the subscriber station receives a broadcast service parameter message to determine the availability of the HSBS channel in that sector, tune to the appropriate frequency to carry the HSBS channel, and the HSBS channel. Reception can be resumed.

Traffic channel handoff Unlike the embodiment described above, this embodiment is intended to hand off for a subscriber station in a dedicated mode (eg, voice call) on a traffic channel while also monitoring the F-BSCH. According to one embodiment of the invention, the base station-subscriber station signaling assist handoff is performed for calls. Further, the handoff method disclosed in the embodiments of the present invention is carried out for F-BSCH. The base station provides the subscriber station with a new pilot set to hand off on the traffic channel through the handoff instruction message. As described, the subscriber receives information about the pilot set through broadcast service parameter messages according to one embodiment. However, the subscriber station can only receive the broadcast service parameter message when it is idle.

As a result, according to one embodiment, the handoff instruction message indicates a pilot set for both the traffic channel and the F-BSCH. As explained, the SHO group determines the active set for F-BSCH.

According to other embodiments, the information related to F-BSCH is not transmitted in the handoff instruction message. The reason is that F-BSCH is not a dedicated channel. Rather, the F-BSCH SHO group for each sector, which is the equivalent of an overhead message, is sent through a dedicated mode.

Note that whether F-BSCH is soft-synthesized depends on the relevant SHO group (notified by the broadcast service parameter message) and not whether the dedicated traffic channel is soft-synthesized. Should be.

Those skilled in the art will appreciate that although the flow charts are shown in continuous order for understanding, certain steps can be performed in parallel in a real configuration. Moreover, unless otherwise indicated, the method steps are interchangeable without departing from the scope of the invention.

Those skilled in the art will appreciate that information and signals can be represented using any of a variety of different science and technology and technologies. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be mentioned throughout the above description are voltages, currents, electromagnetic waves, magnetic fields or magnetic particles, light fields or light particles, or It may be represented by any combination of these.

Those skilled in the art will appreciate the various exemplary logic blocks, modules, circuits and algorithm steps described in connection with the embodiments disclosed herein as electronic hardware, computer software, or a combination thereof. You will understand further that you may. To clearly illustrate this compatibility of hardware and software, various exemplary components, blocks, modules, circuits, and steps have been described above, generally in terms of functionality. Whether such functionality is realized as hardware or software depends on the design constraints imposed on the particular application and the entire system. Each person skilled in the art may configure the functionality described in various ways for a particular application, but it should be construed that determining such a configuration does not result in a deviation from the scope of the invention. Is.

The various exemplary logic blocks, modules, and circuits described in relation to the embodiments disclosed herein include general purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), and fields. A programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic circuit, discrete hardware component, or any of these designed to perform the functions described herein. May be configured or executed in combination of. The general purpose processor may be a microprocessor, but instead the processor may be any conventional processor, controller, microprocessor, or state machine. The processor can be configured as a combination of computing devices, such as a combination of DSP and microprocessor, multiple microprocessors, one or more microprocessors with DSP cores, or any other such configuration. it can.

The method or algorithmic steps described in relation to the embodiments disclosed herein may be embodied directly in hardware, in software modules executed by a processor, or in combination of the two. Software modules exist in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disks, removable disks, CD-ROMs, or any other form of technically known storage medium. May be. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and write the information to the storage medium. Alternatively, the storage medium may be integrated into the processor. The processor and storage medium may reside in the ASIC. The ASIC may reside in the user terminal. Alternatively, the processor and storage medium may exist as discrete components in the user terminal.

The above description of the disclosed embodiments is provided so that those skilled in the art can make or use the present invention. Various modifications to these embodiments will be readily apparent to those of skill in the art. The general principles set forth herein can be applied to other embodiments without departing from the spirit and scope of the invention. Therefore, the present invention is not intended to be limited to the embodiments presented herein and should follow the broadest scope consistent with the principles and novel features disclosed herein.

The disclosure portion of this patent document contains content that is subject to copyright protection. The copyright holder has no objection to reproduction by anyone when a patent document or patent disclosure appears in a file or record of the Patent and Trademark Office, but otherwise reserves all copyright.

<figref num="1">Figure 1 illustrates a conceptual block diagram of a high-speed broadcast service communication system.</figref><figref num="2">Figure 2 illustrates the concept of soft handoff groups in broadcast communication systems.</figref><figref num="3">Figure 3 illustrates the signaling associated with changes in pilot intensity and various sets of pilot membership embodiments for subscriber assist handoffs.</figref><figref num="4">Figure 3 illustrates the signaling associated with changes in pilot intensity and various sets of pilot membership embodiments in autonomous handoffs.</figref><figref num="5">Figure 5 illustrates an alternative mode in which the pilot is added to the active set for a subscriber assist handoff.</figref>