WO2003036837A1 - Procédé de transfert en synchronisation en cdma - Google Patents

Procédé de transfert en synchronisation en cdma Download PDF

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Publication number
WO2003036837A1
WO2003036837A1 PCT/CN2001/001492 CN0101492W WO03036837A1 WO 2003036837 A1 WO2003036837 A1 WO 2003036837A1 CN 0101492 W CN0101492 W CN 0101492W WO 03036837 A1 WO03036837 A1 WO 03036837A1
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WIPO (PCT)
Prior art keywords
cell
downlink
uplink
handover
synchronization pulse
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PCT/CN2001/001492
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English (en)
French (fr)
Inventor
Yongsheng Zhang
Huixia He
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Linkair Communications, Inc.
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Publication date
Application filed by Linkair Communications, Inc. filed Critical Linkair Communications, Inc.
Priority to PCT/CN2001/001492 priority Critical patent/WO2003036837A1/zh
Priority to CNA018228585A priority patent/CN1493125A/zh
Publication of WO2003036837A1 publication Critical patent/WO2003036837A1/zh

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • H04B17/318—Received signal strength
    • 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
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/382—Monitoring; Testing of propagation channels for resource allocation, admission control or handover
    • 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
    • H04W36/0069—Transmission or use of information for re-establishing the radio link in case of dual connectivity, e.g. decoupled uplink/downlink
    • 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
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7073—Synchronisation aspects
    • H04B1/70735—Code identification
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/10—Scheduling measurement reports ; Arrangements for measurement reports
    • 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
    • H04W36/0072—Transmission or use of information for re-establishing the radio link of resource information of target access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/16—Performing reselection for specific purposes
    • H04W36/18—Performing reselection for specific purposes for allowing seamless reselection, e.g. soft reselection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0446—Resources in time domain, e.g. slots or frames
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access, e.g. scheduled or random access
    • H04W74/04—Scheduled or contention-free access
    • H04W74/06—Scheduled or contention-free access using polling

Definitions

  • the present invention relates to the field of wireless communication technologies, and in particular, to a handover method for a synchronous CDMA communication system. Background technique
  • the CDMA system has developed rapidly due to its unique advantages such as large capacity, soft capacity, high voice quality and low transmission power, as well as strong anti-interference and confidentiality, and has become the technology of choice for the third generation of cellular communication systems.
  • both the base station transmitter and the mobile station transmitter use the spreading code to spread the digital information on the transmission spectrum, and the receiving device uses the local spreading code to despread the spread spectrum signal to extract useful information.
  • Synchronization means that the local spreading code and the received spreading code are completely identical in structure, frequency, and phase. Only when the synchronization between the uplink and the downlink is achieved can the relevant characteristics of the spreading code be fully utilized for reliable communication.
  • BSs base stations
  • the user terminal (MS) in a mobile communication system often moves constantly during the communication process from the coverage area of one cell or sector to the coverage area of another cell or sector, and the user terminal is required in this process
  • the communication is not interrupted. This process is called handover.
  • the MS When the MS performs a handover, it can be considered that the carrier synchronization and frequency synchronization of the new and old cells can be maintained.
  • the main problem is the establishment and maintenance of time synchronization in this process.
  • the traditional handover method is "hard handover".
  • the communicating MS detects that the received signal strength is lower than a preset threshold, it indicates that the MS has moved to the boundary of the cell or sector, and the BS will request the MS to search and measure its neighboring cell or sector. Signal strength, and send the measurement results to the BS periodically Verdict of switching. If the signal strength of a cell or sector is higher than a preset threshold value of the cell or sector and the cell or sector has sufficient channel resources, the cell or sector is considered as the target For a cell or sector, a corresponding handover instruction is formed and sent to the MS, and service communication with the MS is interrupted at the same time.
  • the MS After receiving the handover instruction, the MS will interrupt the communication with the original BS, change the channel configuration, and re-establish uplink and downlink synchronization with the new BS. If the synchronization is successfully established, it will start service communication with the new BS.
  • the hard handover technology has the following disadvantages in a synchronous CDMA system: (1) If the handover of the MS to the new BS is unsuccessful, the service will be interrupted and information will be lost. There are many situations that may cause a handover failure; for example, the measurement report sent by the MS or the received handover instruction is wrong, causing it to switch to a cell or sector that cannot maintain its normal communication; and so on. (2) Ping-pong effect. This situation can easily occur when the MS is at the cell or sector boundary.
  • the signal strength fluctuations of neighboring cells or sectors make the MS switch back and forth between the two cells or sectors; it increases the system overhead and the probability of failing to receive signaling correctly, and so on.
  • a time delay for establishing uplink synchronization is introduced during the handover process.
  • each cell or sector sends continuous pilot signals with the same spreading code and different offset PN codes.
  • the MS contains the PN offset information of each adjacent cell or sector, which is stored separately. In different subsets, it is divided into a neighborhood subset and an activation subset, and will be updated as the conditions are updated. After the MS establishes communication with the BS in the active subset, the pilot signal strength of other cells or sectors is periodically measured. Once it exceeds a predetermined threshold, the MS adds the new cell or sector to the candidate.
  • the system controller of the network determines whether to add the cell or sector to the active subset of the MS.
  • the system controller decides that it needs to join, it sends related information to the MS through its associated BS, and it also notifies the corresponding BS to establish communication with the MS.
  • the MS adds the corresponding new cell or sector to the list of active subsets based on the received information.
  • the MS maintains communication with all BSs in the active subset. When the MS keeps in touch with several BSs at the same time, it will continuously monitor its pilot signal strength.
  • the MS will generate a message to notify the network end.
  • the system controller receives this message through at least one BS, determines the interruption, and generates a new list of active subsets. If the BS contains too low strength, it will be sent to the corresponding BS and MS, both of which will interrupt related communication.
  • soft handover When the MS is at the cell or sector boundary, it can maintain communication with several BSs at the same time, and the received signal can perform operations such as maximum ratio combining to achieve diversity gain before demodulation; (1) MS Regardless of handover or not, communication is always maintained with at least one BS, communication will not be interrupted, and information will not be lost.
  • soft handover has the following disadvantages in synchronous CDMA systems: (1) Establish communication with multiple cells or sectors, occupy system resources (such as code channels, etc.), and reduce system capacity; (2) BS and MS need to The received signals are combined at the maximum ratio, which increases the implementation complexity of the hardware. '
  • China Xinwei Communication Technology Co., Ltd. proposed "a method for relay switching in synchronous CDMA communication systems" (application number 98120525), which applies smart antennas to switching and pursues switching between different systems and different frequency bands.
  • the smart antenna of the BS determines the position of the MS with which it is communicating, and the network obtains a list of neighboring cells or sectors where the MS is located, and related information such as the operating frequency, spreading code, and downlink transmission timing deviation. Wait for it to pass to MS. After receiving the MS, it starts to receive the relevant signals of its neighboring cell or sector.
  • the system controller decides whether to perform handover, specifies the target BS, allocates related resources, and transmits the handover information to the MS.
  • the MS uses one set of transceivers to maintain communication with the original cell or sector for a period of time, and the other set ups and downsynchronization with the new BS. If the synchronization is successful, service communication is started. When the system decides that the relay handover has been completed, the MS will interrupt communication with the original BS.
  • relay handover The advantages of relay handover are: (1) it will not interrupt communication and lose information when switching from one cell or sector to another; (2) implement handover between different systems and different frequencies; (3) use intelligence The strength and direction angle of the received signal from the antenna determine the location of the MS.
  • the disadvantage of relay handover is that it only depends on the increasing number of synchronizations, service receivers, and transmitters to implement the handover, which greatly increases the complexity of implementation.
  • the traditional handover decision and handover command formation process is as follows: After receiving the measurement report of the MS, the BS communicating with the MS analyzes and compares the information in it. If N h consecutive times (N h may be 1 or an integer set in advance), at least one neighbor cell has a difference between the downlink synchronization signal strength and the value of the local cell that is greater than the threshold Th e , then The identity of the cell and the neighbor cell that meet the conditions are sent to the base station controller BSC. If the neighbor cell that meets the conditions is within the jurisdiction of another BSC, the message is relayed. Continue to the MSC or higher system controller in the mobile control.
  • the controller will sequentially detect whether the corresponding cell has sufficient wireless resources, such as code channels, time slots, etc., according to the order of the signal strength from high to low. Once the relevant resources are available, the controller will form a corresponding handover.
  • the instruction includes the identity of the local cell and the target cell for handover, and the radio resources allocated by the target cell to the MS.
  • the straight setting of N h and ⁇ can be obtained through the measurement of the field strength in the field.
  • One parameter value can be fixed first to determine another parameter value.
  • Another existing handover decision method is based on the distance from the MS to each cell.
  • the BS selects the cell closest to the MS as the target cell of the MS by measuring the distance from the MS.
  • an object of the present invention is to propose a handover method for a synchronous CDMA system.
  • the invention is achieved by the following methods:
  • the synchronous CDMA system handover method proposed by the present invention enables seamless handover under the condition of using as few hardware and software resources as possible through effective cooperation with uplink and downlink synchronization during the handover process;
  • the combination of signal strength and location information of the user terminal forms a new handover decision criterion, which helps the control center to make a more accurate handover decision, and avoids the influence of factors such as measurement report transmission errors. Therefore, the method of the present invention can be called smooth Switching method.
  • the invention discloses a method for smooth handover of a synchronous code division multiple access communication system, which is characterized by including at least the following steps:
  • a base station in a synchronous code division multiple access communication system sends a downlink synchronization pulse signal
  • the user terminal of the synchronous code division multiple access communication system is provided with a set of radio frequency receivers and transmitters, and a set of service baseband receivers and transmitters; two sets of downlink synchronized baseband receivers and transmitters, and one set for maintaining Synchronize with the downlink of the original cell or sector and continuously measure the signal strength of its downlink synchronization pulse; the other set is used for round To search and measure the signal strength of downlink synchronization pulses in other neighboring cells or sectors;
  • the user terminal When the user terminal measures the strength of the downlink synchronization pulse of a certain cell or sector to a threshold set by the cell, the user terminal sends a customs measurement report to the local base station with which it communicates, and proposes a handover request;
  • the network side performs handover according to the handover information received from the user terminal and the strength of the downlink synchronization pulse signal reported or received by the user terminal and the location distance information measured by the base station to the user terminal, to form a handover instruction;
  • the user terminal When the user terminal receives the handover instruction, it interrupts service communication with the original BS, and uses the time deviation measured by the downlink synchronization pulse, and the code channel and time slot allocated by the neighboring cell directly start to establish up and down with the new cell ⁇ " Business communications;
  • the user terminal After receiving the handover instruction, the user terminal changes the downlink synchronization receiver matching codeword that is continuously measured and synchronized to the "sync pulse spreading code" corresponding to the target base station of the handover to complete downlink synchronization and communication with the target cell. ; And use another downlink synchronization receiver for polling to search and measure other neighboring cells.
  • the step (1) is characterized in that the first subframe in the frame structure of the synchronous code division multiple access communication system is a downlink synchronization subframe, the second subframe is an uplink synchronization subframe, and other subframes
  • the frames are uplink and downlink service sub-frames.
  • the base station uses the pilot symbols in the uplink service to track the uplink synchronization.
  • a fixed access time slot is reserved, and uplink homing pulses are sent in the form of code division.
  • An offset measuring device configured to measure a time deviation between a downlink synchronization pulse of a neighboring cell or sector reaching a first path and a downlink synchronization pulse of a local cell or sector reaching a first path;
  • the user terminal first searches for the nearest ⁇ cell as a measurement target, and then polls and measures the strength of the downlink synchronization pulse signal and the arrival time of this cell, and then uses the uplink dedicated control channel to The cell signal strength value and the strength measurement value of the neighboring cell signal that is greater than or equal to the signal strength value of the cell are sent to the base station of the corresponding cell identifier.
  • the base station completes the handover decision by measuring the position information of the user terminal and assisting the measurement report of the downlink synchronization pulse signal strength.
  • the user terminal sends the measurement report to the base station in the cell, it can simultaneously The uplink synchronization pulse timeslot to the cell and other meeting measurement reports,
  • the requested cell sends an uplink synchronization pulse, and the base station obtains the relative position information of the user terminal and the base station by matching the maximum peak value of the uplink synchronization pulse.
  • the step (5) includes a fast synchronization method, including the following steps:
  • the MS detects the absolute value of the deviation of the downlink synchronization pulse reception time AT d between the target cell and the original cell;
  • the MS directly changes the spreading code and related configuration of transmission and reception time slots for uplink and downlink services, and sends uplink services to the target cell BS and receives its downlink services; c) If AT d > Th d , the MS changes the uplink synchronization spreading code, and sends an uplink synchronization pulse in an access slot allocated by the control center to the MS;
  • the target cell BS receives the uplink synchronization pulse, compares the AT U of the reception time with the standard time, and generates a time delay control command (DCC), which is transmitted to the MS through the downlink dedicated control channel for the next uplink synchronization pulse transmission. Adjust the time until the AT U is less than the threshold T, and complete the uplink synchronization acquisition.
  • DCC time delay control command
  • step d) the MS will change the relevant configuration of the service communication, and establish the upper and lower service communication with the target cell BS.
  • Th d is a threshold value.
  • Th d l / 2Tc may be adopted.
  • the strength of the downlink pulse signal may be the signal strength of the downlink continuous pilot channel or its SINR value.
  • the invention overcomes the shortcomings of traditional hard handover and interrupt service communication, and realizes seamless handover of synchronous CDMA communication system; avoids the complexity of multiple receivers and transmitters required for soft handover and relay handover, and only uses one set of services to send and receive signals Machine and up to two sets of downlink synchronization receivers can achieve smooth handover between cells or sectors; during the handover process, the time delay for establishing uplink synchronization with the new cell is greatly reduced; handover decisions do not depend on the existence of downlink continuous pilot channels;
  • the handover decision criterion combines the signal strength of the downlink synchronization pulse and the distance information between the base station and the user terminal, which can overcome the problems caused by the incorrect transmission of the measurement report and make a more accurate handover decision.
  • Figure 1 Schematic diagram of mobile communication cell structure.
  • Figure 2 Frame structure in TDD mode of synchronous CDMA system.
  • FIG. 3 Schematic of MS measurement report generation.
  • Figure 4 MS downlink synchronization time offset measurer.
  • Figure 5 Time to receive the down pulse of each BS.
  • Figure 6 Determination of the sending time of the uplink service of the target cell.
  • Figure 7 Block diagram of the operation flow of handover decision criterion 1.
  • Figure 8 Block diagram of the operation flow of handover decision criterion 2.
  • Figure 9 Block diagram of the operation flow of handover decision criterion 3.
  • Figure 10 Block diagram of the operation flow of handover decision criterion 4.
  • Figure 11 Flow diagram of MS during smooth handover.
  • Figure 12 Block diagram of MS for fast and smooth handover. detailed description
  • FIG. 1 illustrates a cell structure of a wireless communication system in the prior art.
  • An area is divided into multiple cells, and each cell can be provided with one or more base stations (BSs), respectively corresponding to different sectors.
  • the area shown in the figure includes base stations 101, 102, 103, etc. These BSs work on the same carrier frequency.
  • BSs are connected to the base station controller (BSC) through a wired link.
  • BSC base station controller
  • base stations 101 to 107 are connected to the base station control.
  • Controller 111 some other base stations are connected to the base station controller 112, etc .; several BSCs are connected to the mobile control center (MSC) through a wired link, such as the base station controller 111 and the base station controller 112 are connected to the mobile control center 121.
  • MS mobile control center
  • MS user terminals
  • the MS continuously moves from the coverage area of one cell or sector to the coverage area of another cell or sector.
  • the MS smoothly switches between cells and sectors. In the following special case description, only inter-cell smoothing is considered. Switching, similarity between sectors is available.
  • FIG. 2 is a schematic diagram of a detection structure designed according to the smooth handover method of the present invention in a time division duplex (TDD) synchronous CDMA communication system.
  • TDD time division duplex
  • data transmission is performed in units of frames.
  • the first subframe is defined as a downlink synchronization subframe (or a downlink synchronization pulse).
  • the second subframe is defined as an uplink synchronization subframe (also referred to as an uplink synchronization pulse), and other subframes within one frame are defined as uplink and downlink service subframes, which are used for data and voice transmission.
  • a fixed access slot may be reserved in the uplink synchronization subframe.
  • the MS uses the obtained neighboring
  • the uplink synchronization spreading code of the cell sends the uplink synchronization pulse to the local cell and the neighboring cell by code division in the fixed time slot.
  • the downlink synchronization pulse is sent from the BS to the MS.
  • the MS receives and matches to achieve time synchronization with the system.
  • the MS needs a set of radio frequency receivers and transmitters, and a maximum of two sets of synchronous baseband receivers and transmitters in the downlink logical sense, one of which is used to maintain downlink synchronization with the existing cell and continuously measure its downlink synchronization pulse. Signal strength.
  • the other set is used for polling to search and measure the signal strength of downlink synchronization pulses in other neighboring cells. After completing the search of surrounding cells or sectors, the MS determines the closest N, cell or sector as the target for further synchronization and measurement.
  • the MS opens a set of downlink synchronization receivers and measures the signal strength of the downlink synchronization pulses of the cell being communicated with; another set of downlink synchronization receivers searches for and measures the signal strengths of the downlink synchronization pulses of neighboring cells.
  • the MS opens a set of downlink synchronization receivers to measure the signal strength of the downlink synchronization pulses of the cell being communicated with; when the measured signal strength is less than a predetermined threshold, it opens another set of downlink synchronization receivers and starts searching 2. Measure the signal strength of the downlink synchronization pulse in the neighboring cell.
  • both sets of downlink synchronization receivers are turned on to start searching and measuring signals of downlink synchronization pulses of the cell and its neighboring cells Intensity.
  • the MS compares and measures the downlink synchronization pulse signal strength of each cell, and reports the signal strength value of this cell and the signal strength measurement value of its neighboring cell, and the corresponding cell identifier.
  • the measurement report is transmitted to the BS in the cell through the uplink dedicated control channel.
  • Figure 3 shows a schematic diagram of the measurement report generated by the MS. Assume that the downlink synchronization pulse signal strength of neighboring N cells is measured by polling. 301 is a comparator. Only the value of input port 2 is greater than or equal to the value of input port 1. Device has an output, the maximum value is output.
  • the MS not only needs to measure the strength of the downlink synchronization pulse signal, but also needs to measure the arrival time of the downlink synchronization pulse, which is used as the basis for maintaining the uplink synchronization during the handover process.
  • the condition switch only outputs all the sampled values in a window of a certain size, and the position of the maximum peak is located in the middle of the window.
  • Both 403 and 404 are time delayers, and the delay time is different. 403 needs to delay N d 'N f samples, while 404 only needs to delay ⁇ samples.
  • the function module 405 completes the accumulation of the values in the window, and the accumulation number is N. , The corresponding delay time is N d ⁇ T F (ms), where T F is the time occupied by one frame.
  • the 410 input port value is the inverse 1 / Max of the maximum value among all the window sampling values, and the corresponding output can be obtained when the position of the maximum energy peak is obtained.
  • Figure 5 is the time to receive the downlink pulse of each BS.
  • the base station 101, the base station 103, and the base station Time of arrival of the user terminal 104, respectively, to the downlink user terminal transmits a pulse respectively ⁇ ,, T 3, ⁇ 4 , apparent, the presence of the arrival time of a time difference from each other.
  • FIG. 6 shows a method for determining the uplink service sending time of a target cell.
  • the downlink synchronization reception times of the cells 101, 103, and 104 measured by the downlink synchronization time offset measuring device are: T, L, and T.
  • MS selects the cell 104 as the target cell, and allocates the Kth time slot in a frame. It is the standard relative time for the first transmission of uplink services, and the corresponding start time is T s .
  • the target cell will track the uplink synchronization by receiving the pilot signals in the uplink service, and the uplink synchronization adjustment command will be transmitted to the MS through the downlink dedicated control channel.
  • the BS of the target cell will check the performance of the uplink service for a period of time, such as a CRC check. If the communication requirements are met, it indicates that the handover was successful.
  • the BS completes the handover decision by measuring the position information of the MS and assisting the measurement report of the strength of the downlink synchronization pulse signal. Adding the location information of the MS to the handover criterion is conducive to making a more accurate handover decision, and avoids the influence of factors such as measurement errors and transmission errors.
  • the MS sends a measurement report to the BS in the cell
  • the obtained uplink synchronization pulse idle time slot and the uplink synchronization spreading code of the neighboring cell are used, and at the same time in different idle uplink synchronization pulse time slots, the local cell and other A cell that meets the requirements of the measurement report sends an uplink synchronization pulse, and the BS determines the location of the maximum peak of the uplink synchronization pulse by matching and measures the relative position information with the MS.
  • the MS may also reserve a fixed access slot.
  • the MS uses the obtained uplink synchronization spreading code of the neighboring cell.
  • an uplink synchronization pulse is sent to the local cell and the neighboring cell in a code division manner. Open-loop power control of the uplink synchronization pulse can be introduced here, and the transmit power of the uplink synchronization pulse is determined by the measured signal strength of the downlink synchronization pulse.
  • the handover decision of the system controller combines the signal strength of the downlink synchronization pulse and the distance information of the MS and the BS to form a new handover criterion.
  • it can be divided into the following four points: Let the strength of the downlink synchronization pulse signal of the cell G be S.
  • the downlink synchronization pulse signal strength of other neighboring cells K is Sk , and it can be known from the criteria for generating a measurement report that Sk > S.
  • K l, 2 ... K; Assume that the order of energy from high to low is S ,, S 2 ... S k .
  • R is a preset parameter, such as 0.5, 0.6, etc., indicating that the MS is not at the cell boundary, the signal of the cell may be temporarily blocked by buildings, etc., and the system controller will not generate a handover instruction.
  • r is a preset parameter, such as 0.5, 0.6, etc. It indicates that the MS is not at the cell boundary, the signal of this cell may be temporarily blocked by buildings, etc., and the system controller will not generate a handover command.
  • the corresponding cell is used as the target cell for handover.
  • R is a preset parameter, such as 0.5, 0.6, etc .; indicating that the MS is not at the cell boundary, the signal of this cell may be temporarily blocked by buildings, etc. The device will not generate a switch instruction.
  • the corresponding cell is used as the target cell for handover.
  • Figure 11 shows a flowchart of the MS smooth handover process.
  • the system controller sends a handover instruction to the MS, it also sends the information to the target cell, and the BS of the cell will establish the sending and receiving of uplink and downlink service communication with the MS.
  • the MS When the MS receives the handover instruction, it will interrupt the receiving and sending of the uplink and downlink services with the original cell BS; change the downlink synchronization receiver matching codeword for continuous measurement and synchronization to the downlink synchronization pulse spreading code corresponding to the target BS for handover To complete downlink synchronization with the target cell; use another downlink synchronization receiver to search and measure other neighboring cells or sectors in a polling manner.
  • the service receiver and transmitter change related configurations such as the spreading code, transmission, and reception time, and send the uplink service to the target cell BS, and receive its downlink service.
  • the time for the MS to send the uplink service to the target cell BS is calculated from the measured value of the downlink synchronous reception time and the uplink time slot to be occupied in the target cell.
  • FIG. 12 shows a flowchart of a MS fast synchronous and smooth handover process. This embodiment The handover command needs to include the distance information of the target cell BS to the MS.
  • the MS After the MS receives the corresponding handover instruction, it interrupts the uplink and downlink service communication with the original cell or sector.
  • the method for establishing uplink synchronization and service communication in the target cell is determined by the value of ⁇ T d :
  • the target cell BS does not need to perform uplink synchronization acquisition again, and the MS does not need to adjust the system time.
  • the MS directly changes the related configuration of the spreading code and the sending and receiving time slots of the uplink and downlink services, sends the uplink services to the target cell BS, and receives its sub-sectors.
  • the MS changes the uplink synchronization spreading code, and sends an uplink synchronization pulse in an access slot allocated by the control center to the MS.
  • the specificity of the uplink synchronization pulse in the access slot The sending time is calculated from the distance information between the MS and the BS in the handover command.
  • the target cell BS receives the uplink synchronization pulse, compares the difference between the reception time and the standard time ⁇ T u , and generates a time delay control command (DCC), which is transmitted to the MS through the downlink dedicated control channel for the next uplink synchronization pulse transmission time. Adjustment until ⁇ ! If it is less than the threshold Th u , it indicates that the uplink synchronization acquisition is completed. At this time, the MS will change the related configuration of the service communication, and establish the uplink and downlink service communication with the target cell BS.
  • DCC time delay control command
  • Th d and Th u are time offset thresholds set according to the communication system and the channel environment.
  • the target cell BS will track the uplink synchronization by receiving pilot signals in the uplink service.
  • the time and power adjustment instructions for the uplink synchronization will be transmitted through the downlink dedicated control channel.
  • the BS of the target cell will detect the performance of the uplink service for a period of time, such as a CRC check. If the communication requirements are met, it indicates that the handover is successful.
  • the above highlights the smooth handover between cells.
  • the principle of smooth handover between sectors is the same, and in some specific cases it is even simpler. For example, when the control center requires the MS to switch from one sector to another target sector, if the two sectors belong to the same cell (same BS), the MS directly interrupts the upper and Downlink service communication; without any time adjustment, adjust the spreading code and receive and transmit time slots according to the resources configured by the target sector, and start the uplink and downlink service communication with the target sector.
  • TDD time division duplex mode
  • FDD frequency division duplex mode

Description

同步码分多址通信系统的切换方法
技术领域
本发明涉及无线通信技术领域， 尤其涉及同步 CDMA通信系统的一种切换方 法。 背景技术
近几年来， CDMA系统由于具有大容量、 软容量、 高话音质量和低发射功率 以及抗干扰和保密性强等独特的优势使它得以迅速发展， 并成为第三代蜂窝通 信系统的首选技术。
在通常 CDMA系统中， 实现上、 下行的同步都是非常重要的。 无论是基站发 射机或移动站发射机均用扩频码对传输的数字信息扩展频谱， 而接收设备利用 本地扩频码对扩频信号相关解扩， 解出有用的信息。 同步就是要实现本地扩频 码与接收到的扩频码在结构上、 频率和相位上完全一致。 只有实现了上、 下行 同步才能充分利用扩频码的相关特性进行可靠的通信。
为了实现频率和码的复用， 使在一个有限的区域里为尽可能多的用户提供 服务， 现代无线通信系统一般采用蜂窝小区的技术： 根据用户密度将一个系统 服务的地区分为不同大小的小区和扇区； 在每一小区或扇区设置一个或多个基 站（BS ) , 通过有效的频率和码的分配取得尽可能高的系统容量和频率利用率。
移动通信系统中的用户终端 （MS )在通信过程中往往要不停的移动， 从一 个小区或扇区的覆盖区域移动到另一个小区或扇区的覆盖区域， 而且要求这一 过程中用户终端的通信不被中断， 这个过程就叫做越区切换。
当 MS做越区切换时， 可以认为新老小区间的载波同步和频率同步是能保持 的， 主要的问题是这个过程中时间同步的建立和保持。
传统的切换方法是 "硬切换" 。 当正在通信的 MS检测到收到的信号强度低 于一个事先设定的门限值时， 表明 MS已移动到了小区或扇区的边界处， BS将要 求 MS搜索、 测量其邻近小区或扇区信号的强度， 并把测量结果周期地发给 BS做 切换的判决。 如果有一个小区或扇区的信号强度比本小区或扇区的要高出一个 事先设定的门限值且该小区或扇区有充分的信道资源， 则该小区或扇区被视为 目标小区或扇区， 相应的切换指令形成并被发送给 MS, 同时中断与 MS的业务通 信。 MS在收到切换指令后将中断与原 BS的通信， 改变信道的配置， 重新与新 BS 建立上、 下行同步， 如果同步建立成功， 则开始与新 BS的业务通信。 硬切换技 术在同步 CDMA系统中有如下几个缺点： （1 )如果 MS向新 BS的切换不成功， 业务 将会中断， 会丟失信息。 有很多情况会引起切换的失败； 比如 MS发送的测量报 告或接收到的切换指令有错， 使其切换到了一个不能保持其正常通信的小区或 扇区； 等等。 （2 )乒乓效应。 这种情况在 MS处于小区或扇区的边界处时很容易 发生。 相邻小区或扇区的信号强度波动， 使得 MS将在两个小区或扇区之间来回 的切换； 增加了系统的开销和不能正确接收信令的概率， 等等。 （3 )切换过程 中引入了上行同步建立的时间延迟。
美国高通（ QUALC0MM )公司于二十世纪九十年代发明了软切换技术， 该技 术的详细内容在 US5267261 , 5101501 , 5933787 , 5987326中进行了详细的公开。 在 CDMA通信系统中， 每个小区或扇区发送具有相同扩频码和不同偏移 PN码的连 续导频信号， MS中含有各个相邻小区或扇区的 PN偏移信息， 这些信息分别存储 在不同子集， 分为邻区子集和激活子集, 并将随条件更新而更新。 当 MS与激活 子集中的 BS建立通信后， 周期性的测量其它小区或扇区的导频信号强度， 一旦 高出一个事先确定的门限值， MS将该新小区或扇区加入到候补子集中， 并把有 关信号强度的信息发送给已建立通信的 BS , 由网络端的系统控制器决定是否将 该小区或扇区加入到 MS的激活子集中。 一旦系统控制器决定需要加入， 将相关 的信息通过与之相联的 BS发送给 MS, 同时也会通知对应的 BS与 MS建立通信。 MS 由收到的信息将对应的新小区或扇区加入到激活子集的列表中。 MS与激活子集 中的所有 BS保持通信。 当 MS与几个 BS同时保持联系时， 将不断的监控其导频信 号强度。 如果激活子集中某一个 BS的导频信号强度在一个事先确定的时间内都 低于某个事先确定的门限值时， MS将产生一个消息才艮告给网络端。 系统控制器 通过至少一个 BS收到这一消息， 并确定中断， 生成新的激活子集的列表， 不再 包含强度过低的 BS , 发送给对应的 BS和 MS , 两者都会中断相关的通信。 软切换 的优点在于： （1 ) 当 MS处于小区或扇区边界时， 可同时与几个 BS保持通信， 接 收信号在解调前可做最大比值合并等操作实现分集的增益； （ 1 ) MS不论切换与 否， 始终与至少一个 BS保持通信， 通信不会中断， 信息也不会丢失。 但软切换 在同步 CDMA系统中还有如下的缺点： （1 )与多个小区或扇区建立通信， 占用系 统资源 （如码道等） ， 降低系统的容量； （2 ) BS和 MS需要对接收信号进行最大 比值合并， 增大了硬件的实现复杂度。 '
中国信威通信技术有限公司提出的 "一种应用于同步 CDMA通信系统中的接 力切换的方法" （申请号 98120525 ) , 将智能天线应用到切换中， 追求不同系 统和不同频段间的切换。 由 BS的智能天线测定正在与之通信的 MS的位置， 网络 端获取该 MS所处位置的邻小区或扇区的列表， 将其有关的信息， 如工作频率、 扩频码、 下行发射定时偏差等等传给 MS。 MS收到后开始接收其邻小区或扇区的 有关信号， 如果某个 BS接收信号的信噪比比本地 BS的信噪比高出一个事先确定 的门限值时， 向.同步 CDMA通信系统发出切换要求。 网络端的系统控制器决定是 否进行切换， 指定目标 BS， 分配相关的资源， 并将切换信息传送给 MS。 MS用一 套收发信机在一段时间保持与原小区或扇区的通信， 另一套则与新 BS建立上、 下行同步， 如果同步成功， 则开始业务通信。 当系统决定已完成接力切换后, 该 MS将与原 BS中断通信。 接力切换的优点在于: ( 1 )从一个小区或扇区切换到 另一小区或扇区时不会中断通信和丢失信息； （2 ) 实现不同系统和不同频率间 的切换； （ 3 )用智能天线接收信号的强度和方向角确定 MS的位置。 接力切换的 缺点在于仅仅依靠不断增加的同步、 业务收、 发信机数目来实现切换， 极大的 增加了实现的复杂度。
传统的切换判决和切换命令的形成过程如下： 与 MS正在通信的 BS收到 MS 的测量报告后， 对其中信息进行分析、 比较。 如果连续 Nh次（Nh可以为 1 , 也可 以是事先设定好的一个整数）都至少有一个邻小区的下行同步信号强度与本小 区的值之差大于门限值 The , 则将本小区和满足条件的邻小区的标识发送给基站 控制器 BSC, 如果满足条件的邻小区在另一个 BSC的管辖范围里， 则将该消息继 续发送到移动控制中 MSC或更高层的系统控制器。 控制器将才艮据信号强度从高到 低的排列顺序依次检测其对应小区是否有充足的无线资源， 如码道、 时隙等等， 一旦相关的资源可以获得， 控制器将形成相应的切换指令， 包含本小区和切换 的目标小区的标识， 以及目标小区为该 MS所分配的无线资源。 上述参数 Nh和 The 越高， 网络端就越不易产生切换的命令， 一定程度上减少了乒乓效应； 但过高 的 MS也是不利的， 当 MS业务通信性能已不能保持， 急需切换时将不能及时产生 有效的切换指令。 Nh 、 Ήνί直的设定可通过实地场强测量获得， 可以先固定一个 参数值的选取， 确定另一个参数值。
另一种现有切换判决的方法是以 MS到各个小区的距离为依据， BS通过测量 与 MS的距离, 选择与 MS距离最近的小区作为 MS的目标小区。 发明内容
为解决现有技术中存在的上述问题和缺陷， 本发明的目的在于提出了一种 同步 CDMA系统的切换方法。
本发明通过下述方法来实现：
本发明提出的这种同步 CDMA系统切换方法， 通过在切换过程中与上、 下行 同步的有效配合， 使得在利用尽可能少的硬件、 软件实现资源的条件下实现无 缝切换； 将下行同步脉冲信号强度和用户终端的位置信息结合而成新的切换判 决准则， 有利于控制中心做出更准确的切换判决， 避免了测量报告传输错误等 等因素的影响， 因此又可称本发明方法为平滑切换方法。
本发明公开了一种同步码分多址通信系统的平滑切换的方法， 其特征在于 至少包括如下步骤：
( 1 ) 由同步码分多址通信系统中的基站发送下行同步脉冲信号；
( 2 )在同步码分多址通信系统的用户终端配有一套射频收、 发信机， 一套 业务基带收、 发信机； 两套下行同步的基带收、 发信机， 一套用于保持与原小 区或扇区的下行同步， 持续测量其下行同步脉冲的信号强度； 另一套则用于轮 询地搜索、 测量其他相邻小区或扇区的下行同步脉冲的信号强度；
( 3 )当用户终端测得某个小区或扇区的下行同步脉冲的强度于本小区设定 的门限值， 该用户终端向与之通信的本地基站发关测量报告， 提出切换请求；
( 4 )网络端根据该用户终端发送的测量 4艮告或接收的下行同步脉冲信号强 度和基站测量的与用户终端位置距离信息， 依据切换判决准则进行切换， 形成 切换指令；
( 5 ) 当用户终端收到切换指令时， 中断与原 BS的业务通信， 利用下行同 步脉沖测量的时间偏差， 邻小区分配的码道和时隙， 直接开始与新小区建 立上、 下^"的业务通信；
( 6 ) 用户终端收到切换指令后， 将持续测量、 同步的下行同步接收机匹 配码字改为切换的目标基站对应的下^ "同步脉冲扩频码， 完成与目标小区的下 行同步和通信； 并将另一个下行同步接收机用于轮询地搜索和测量其他相邻小 区。
所述的步骤（1 )中， 其特征在于所述的同步码分多址通信系统帧结构中的 第一个子帧是下行同步子帧, 第二个子帧是上行同步子帧 , 其他的子帧是上、 下行的业务子帧， 基站利用上行业务中的导频符号完成上行同步的跟踪; 在上 行同步子帧中预留固定接入时隙， 采用码分的形式发送上行同命脉冲。 偏差测量器， 用以完成邻小区或扇区下行同步脉冲到达第一径与本小区或扇区 下行同步脉冲到达第一径的时间偏差的测量；
所述的步骤（3 )中， 用户终端首先搜索出最接近的 ^个小区作为测量目标， 然后轮询测量这 个小区的下行同步脉冲信号的强度、及到达时间， 然后通过上 行专用控制信道将本小区信号强度值， 以及大于或等于本小区信号强度值的邻 小区信号的强度测量值， 相应的小区标识发送给本小区的基站。
所述的步骤（4 ) 中， 基站通过测量用户终端的位置信息， 辅助下行同步脉 冲信号强度的测量报告完成切换的判决， 当用户终端向本小区基站发送测量报 告时， 可同时在不同的空闲的上行同步脉冲时隙， 向本小区和其他满足测量报,, 告要求的小区发送上行同步脉冲， 基站通过匹配出上行同步脉冲的最大峰值获 得用户终端与该基站的相对位置信息。
所述的步骤（5 ) 中包含有一快速同步方法， 包括如下步骤：
a ) MS检测目标小区与原小区之间的下行同步脉冲接收时间的偏差绝对 值 ATd ；
b) 如果 ATd Thd， MS直接改变上、 下行业务的扩频码及发送、 接收时隙 等相关配置， 向目标小区 BS发送上行业务， 并接收其下行业务； c) 如果 ATd〉Thd, MS改变上行同步扩频码， 在控制中心为 MS分配的接入 时隙中发送上行同步脉冲；
d ) 目标小区 BS通过接收上行同步脉冲， 比较接收时间与标准时间之 ATU, 生成时间延远控制指令（DCC) , 该指令通过下行专用控制信道传送给 MS, 用于 下一次上行同步脉沖发送时间的调整， 直到 ATU小于门限值 T , 完成上行同步 捕获；
e) 根据步骤 d) MS将改变业务通信的相关配置，与目标小区 BS建立上、 下 行的业务通信。
Thd是一门限值， 在 LAS-CDMA中可取 Thd =l/2Tc。
所述的下行脉冲信号的强度可以是下行连续导频信道的信号强度或其 SINR 值。
本发明克服了传统硬切换中断业务通信的缺点， 实现了同步 CDMA通信系统 的无缝切换； 避免了软切换和接力切换需要多个收、 发信机的复杂度， 仅用一 套业务收发信机和最多两套下行同步接收机就可以实现小区或扇区间的平滑切 换； 切换过程中大大减少了与新小区建立上行同步的时间延时； 切换判决不依 赖于下行连续导频信道的存在； 切换判决准则将下行同步脉冲的信号强度和基 站与用户终端的距离信息相结合， 能克服测量报告错误传送所带来的问题， 做 出更准确的切换判决。 附图说明
下面结合附图， 对本发明的具体实施方式作进一步详细的描述。
图 1: 移动通信蜂窝小区结构示意图。
图 2: 同步 CDMA系统的 TDD模式下的帧结构。
图 3: MS测量报告生成示意图。
图 4: MS下行同步时间偏移测量器。
图 5: 接收各个 BS下行脉冲的时间。
图 6: 目标小区上行业务发送时间的确定。
图 7: 切换判决准则 1的运行流程框图。 - 图 8: 切换判决准则 2的运行流程框图。
图 9: 切换判决准则 3的运行流程框图。
图 10: 切换判决准则 4的运行流程框图。
图 11: MS在平滑切换过程中的流程框图。
图 12: MS实现快速平滑切换的流程框图。 具体实施方式
参考图 1, 图 1示出了现有技术中的无线通信系统的一个蜂窝小区结构。 将一个地区分为多个小区， 每个小区可设置一个或多个基站 （BS) , 分别对应 不同的扇区。 如图所示的区域含基站 101、 102、 103等， 这些 BS工作于相同的载 波频率， 几个 BS通过有线链路连接到基站控制器（BSC) , 如基站 101至基站 107 连接到基站控制器 111, 其他的一些基站连接到基站控制器 112等； 几个 BSC通 过有线链路连接到移动控制中心 （MSC ) , 如基站控制器 111和基站控制器 112连接到移动控制中心 121。 此地区还有很多无线通信系统的用户终端 （MS) 。 通信过程中 MS不断移动， 将从一个小区或扇区的覆盖区域移动到另一小区或扇 区的覆盖区域， 釆用本发明的方法， 在切换过程中与上、 下同步密切结合， 能 实现 MS在小区和扇区间的平滑切换。 在以下的特例说明中只考虑小区间的平滑 切换， 扇区间的类似可得。
图 2示出了时分双工（TDD ) 同步 CDMA通信系统中， 依本发明平滑切换方法 所设计的侦结构示意图。 在时分双工 （TDD )模式下的 CDMA通信系统中， 数据 传送是以帧为单位进行的， 在本发明方法中， 将第一个子帧定义为下行同步子 帧 （或称下行同步脉冲） ， 第二个子帧定义为上行同步子帧 （或称上行同步脉 冲） ， 在一帧以内的其他子帧定义为上、 下行的业务子帧， 用于数据和话音的 传输。 特别的， 在上行同步子帧中可以预留出一个固定的接入时隙， 当需要向 本小区、 相邻小区发送上行同步脉冲以测量 BS与 MS的距离时， MS用所获得的相 邻小区的上行同步扩频码， 在该固定时隙里通过码分的方式向本小区和相邻小 区发送上行同步脉冲。
下行同步脉冲由 BS向 MS发送， MS通过匹配接收， 实现与系统的时间同步。 MS需要一套射频的收、 发信机， 和最多两套下行逻辑意义上的同步的基带收、 发信机， 其中一套用于保持与现有小区的下行同步， 持续测量其下行同步脉冲 的信号强度， 另一套则用于轮询地搜索、 测量其他相邻小区的下行同步脉冲的 信号强度。 MS在完成对周围小区或扇区的搜索后确定出最接近的 N„,个小区或扇区 作为进一步同步和测量的目标。
下行同步接收机不必要一直都处于工作的状态， 有如下的几种处理方式：
1. MS打开一套下行同步接收机， 测量正在通信的小区的下行同步脉冲的信 号强度； 用另一套下行同步接收机， 搜索、 测量相邻小区的下行同步脉冲的信 号强度。
2. MS打开一套下行同步接收机， 测量正在通信的小区的下行同步脉冲的信 号强度； 当测量的信号强度小于一个事先确定的门限值时， 打开另一套下行同 步接收机， 开始搜索、 测量相邻小区的下行同步脉冲的信号强度。
3. MS在完成与初始小区的下行捕获后就关闭下行同步的接收机， 用下行连 续导频信号完成下行同步的跟踪、 多径分离等等功能， 并测量该小区的连续导 频信号强度或信扰比 SINR , 如果低于一个事先确定的门限值时， 将两套下行同 步接收机都打开， 开始搜索、 测量该小区和其相邻小区的下行同步脉冲的信号 强度。
MS比较测量而得的各个小区下行同步脉冲信号强度的大小 , 报告本小区信 号强度值及大于等于它的邻小区的信号强度测量值， 以及相应的小区标识。 测 量才良告通过上行的专用控制信道传送给本小区的 BS。
图 3给出了 MS生成测量报告的示意图， 假设轮询测量相邻 N„,个小区的下行同 步脉冲信号强度。 301为比较器， 只有输入端口 2的值大于等于输入端口 1的值， 比较器才有输出， 输出最大值。 '
MS不仅需要测量下行同步脉冲信号强度， 还需要测量下行同步脉冲的到达 时间， 用于切换过程中上行同步保持的根据。
图 4为 MS下行同步时间偏移测量器。 如果同时测量几个小区下行同步脉冲 的到达时间， 该测量器需要将匹配滤波器的输出分为几路各自按如下的方法处 理。 将匹配滤波器输出值平方相加。 402为条件开关， 由输入的最大峰所在位置 决定打开或关闭。 系统会事先决定下行同步时间偏移测量所需的窗口大小， 即 采样数值的个数 Nr , 比如本特例选择 W^ WJe的窗口， 如果假设采样频率为 Fc, 则 Nf = ' Fe ~ W2 ' Fe。 条件开关只使一定大小的窗口中的所有采样值输出， 最大 峰值所在位置位于该窗口正中处。 403和 404都为时间延迟器， 各个延迟的时间 不一样， 403需要延迟 Nd ' Nf个采样值， 而 404只需延迟^个采样值。 功能模块 405完成对窗口中数值的累积， 累积次数为 N。， 对应延迟时间为 Nd · TF ( ms ) , 其 中 TF为一帧所占时间。 410输入端口值为所有窗口采样值中最大值的倒数 1 /Max , 在获得最大能量峰所在位置时即可对应输出而得。 将窗口中所有采样值与 1/Max相乘， 由最大峰所在位置相应的左右第 k ' F。（k = l , 2... K )个采样值输 入到比较器 406的 1端口中。 406的第 2个输入端口为系统按照实地信道传播环境 测量所得的经验门限值 Thp， 只有 1大于等于 2时， 比较器 406才有输出， 输出其对 应的位置， 其中最前端的位置即为满足条件的第一个位置； 该值为下行同步时 间偏移测量器的输出。
MS下行同步接收第一径的时间测量还有其他一些方法。
图 5为接收各 BS下行脉冲的时间。 如图所示， 由基站 101 , 基站 103和基站 104分别向一用户终端发送的下行脉冲到达该用户终端的时间分别为 Τ, , T3, Τ4, 显而易见， 到达时间彼此存在时间差。
以图 5所示情况为例， 图 6给出了目标小区上行业务发送时间的确定方法。 假设通过下行同步时间偏移测量器测出的小区 101、 103和 104的下行同步接 收时间分别为： Τ, 、 L和 T MS选定小区 104为目标小区， 分配一帧中第 K个 时隙为上行业务第一次发送的标准相对时间， 对应起始时间为 Ts, 则实际 MS 发送给目标小区的第一个时隙的上行业务时间为： 相对原有小区下行业务接 收帧头位置延迟交 ( L - T, ) + TS 。 T。ffsei= 为由下行同步脉冲接收、 测量所调整的时间偏移。
目标小区将通过接收上行业务中的导频信号进行上行同步的跟踪，上行同 步的调整指令将通过下行专用控制信道传送给 MS。 目标小区的 BS将在一段时 间检测上行业务的性能， 如 CRC的检验， 如果满足通信的要求则表明切换是成 功的。
本发明将由 BS通过测量 MS的位置信息， 辅助下行同步脉冲信号强度的测量 报告完成切换的判决。 将 MS的位置信息加入切换的准则， 有利于做出更准确 的切换判决， 避免了测量 4艮告传输错误等等因素的影响。
当 MS向本小区 BS发送测量报告时， 利用所获得的上行同步脉冲空闲时隙、 相邻小区的上行同步扩频码， 同时在不同的空闲的上行同步脉沖时隙， 分别 向本小区和其他满足测量报告要求的小区发送上行同步脉冲， BS通过匹配、 确定出上行同步脉冲的最大峰值所在位置， 测量出与 MS的相对位置信息。
MS也可以预留出一个固定的接入时隙， 当需要向本小区、相邻小区发送上 行同步脉冲以测量 BS与 MS的距离时， MS用所获得的相邻小区的上行同步扩频 码， 在该固定时隙里通过码分的方式向本小区和相邻小区发送上行同步脉冲。 这里可以引入上行同步脉冲的开环功率控制， 由所测量到的下行同步脉冲的 信号强度决定上行同步脉冲的发送功率。
系统控制器的切换判决将下行同步脉冲的信号强度和 MS与 BS的距离信息 相结合， 形成新的切换准则。 按具体实现方法的不同又可分为如下四个分则： 设本小区 G的下行同步脉冲信号强度为 S。 ， 其他邻小区 K的下行同步脉冲信 号强度为 Sk , 由生成测量报告的准则可知 Sk>S。， K=l, 2...Κ; 假设其能量从高 到低的顺序为 S,、 S2...Sk 。 假设各个小区的半径为 Rk， MS与各个小区 BS的测量距 离为 dk, K=0, 1...L 用 ^表示小区 Κ是否有相应的无线资源分配给 MS, 为 1表示 有， 为 0表示无， k- 1, 2...L
( 1 ) 以信号强度为主的判决准则 1, 参考图 7
1 )如果 dD<r - Ro, r为一事先设定的参数， 如 0.5、 0.6等； 表明 MS 不在小区边界处， 本小区的信号可能只是被建筑物等暂时阻档了， 系统控制器将不生成切换指令。
2 )如果 d。 > r · R。； 满足 Ak-1和连续 Nh (KNh<N)次 Sk -S„> The条件 的共有 M个小区， 分别为小区： 、 k2...kH, 选择其中信号强度最大值对
Figure imgf000013_0001
应的小区作为切换的目标小区。 其中， 为 U、 区 Nh次信号强度测量值 Ski的平均值， i= 1, 2...M。
3 ) 如果 d。 > r · R„; 不存在满足连续 Nh ( 1 < Nh < N ) 次 Sk - S。 > The 的 小区， 或即使存在但对应 Ak=0， 没有可分配的无线资源； 系统 控 制器将不产生切换指令。
(2) 以距离为主的判决准则 2, 参考图 8'.
1 ) 如果 d。<r ' R。， r为一事先设定的参数， 如 0.5、 0.6等； 表明 MS不在小区边界处， 本小区的信号可能只是被建筑物等暂时阻挡了， 系统控制器将不生成切换指令。 ·
2) 如果 d。>r ' R。； MS处在小区边界的位置； 满足 Ak=l和连续 Nh ( 1 <Nh N)次31<- S。>The条件的共有 M个小区， 分别为： k2...kM, 选 择其中距离最小值
Figure imgf000013_0002
"' kM }
对应的小区作为切换的目标小区。 其中， ^ 为 ki小区 Nh次距离测量 值 dki的平均值， i = 1， 2... 0
3 ) 如果 d。 > r · R。； 不存在满足连续 Nh ( 1< Nh < N ) 次 Sk -S„> The的 小区， 或即使存在但对应 Ak=0, 没有可分配的无线资源； 系统控制器 将不产生切换指
(3)信号强度和距离共同作用的判决准则 3, 参考图 9:
1) 如果 d。<r -Ro, r为一事先设定的参数， 如 0.5、 0.6等； 表明 MS 不在小区边界处， 本小区的信号可能只是被建筑物等暂时阻挡了， 系 统控制器将不生成切换指令。
2) 如果 d。 > r ' R。； 满足 Ak=l和连续 Nh ( 1 N ) 次 Sk -S0 The条 件的共有 M个小区， 分别为： k,、 k2...kH, 选择其中
Figure imgf000014_0001
对应的小区作为切换的目标小区。 其中， U 小区 Nh次信号强 度测量值 Ski的平均值， ^为 ki小区 Nh次距离测量值 dki的平均值， i = 1, 2.·.Μ。
3 ) 如果 d。 > r · R。； 不存在满足连续 ( 1< Nh < N ) 次 Sk - S0 > The 的小区， 或即使存在但对应 Ak=0, 没有可分配的无线资源； 系统 控制器将不产生切换指令。
(4)信号强度和距离共同作用的判决准则 4, 参考附图 10:
1) 如果 (1。<^11。， r为一事先设定的参数， 如 0.5、 0.6等； 表明 MS 不在小区边界处， 本小区的信号可能只是被建筑物等暂时阻挡了， 系 统控剩器将不生成切换指令。
2 ) ：'如果 d。 > r · R0； .满足 Ak=l和连续 Nh ( 1 Nh N )次 Sk - S0 > The条 件的共有 M个小区， 分别为： k,、 .ΛΜ, 选择其中
Figure imgf000014_0002
对应的小区作为切换的目标小区。 其中， α、 β分别为信号强度、 距 离的权重因子， 0< α, β 1且 α+β=1，具体视网络建设的情况而定； 为 ki小区 次信号强度测量值 Ski的平均值， ^为 M、区 N欠距 离测量值 dki的平均值, i = l, 2〜M。 3 ) 如果 d > r ' R„; 不存在满足连续 Nh ( l Nh N ) 次 Sk - S > The 的小区， 或即使存在但对应 Ak=0， 没有可分配的无线资源； 系统 控制器将不产生切换指令。
本发明公开的平滑切换方法中，若将上述下行同步信号强度换为下行连续导 频信道的信号强度或其 SINR, 相似的准则可以获得。
图 11给出了 MS平滑切换过程的流程框图。系统控制器向 MS发出切换指令 的同时， 也将该信息发送给目标小区， 该小区的 BS将建立与 MS的上、 下行业务 通信的发送和接收。
当 MS收到切换指令， 将中断与原小区 BS的上、 下行业务的收、 发； 将持续测 量、 同步的下行同步接收机匹配码字改为切换的目标 BS对应的下行同步脉冲扩 频码， 完成与目标小区的下行同步； 将另一个下行同步接收机用于轮询地搜索 和测量其他相邻小区或扇区。 业务收、 发信机改变扩频码， 发送、 接收时间等 等相关的配置， 向目标小区 BS发送上行业务， 并接收其下行业务。 MS向目标小 区 BS发送上行业务的时间是由下行同步接收时间测量值及目标小区中将占用的 上行时隙共同计算而得的。
在本发明的另一较佳实施例中， 还公开了一种 '1"夬速同步平滑切换方法。 参 考图 12 。 附图 12给出了 MS快速同步平滑切换过程的流程框图。 该实施例需要切 换命令中包含目标小区 BS到 MS的距离信息。
当 MS接收到相应的切换指令后， 中断与原小区或扇区的上、 下行业务通信， 标小区建立上行同步和业务通信的方法由 Δ Td的值决定：
( 1 ) 如果 A Td < Thd， 目标小区 BS不需要重新做上行同步捕获， MS也不 需要调整系统时间。 MS直接改变上、 下行业务的扩频码及发送、 接 收时隙等相关配置， 向目标小区 BS发送上行业务， 并接收其下行业
( 2 ) 如果 A Td > Thd MS改变上行同步扩频码， 在控制中心为 MS分配的 接入时隙中发送上行同步脉冲。 上行同步脉冲在接入时隙中的具体 发送时间由切换命令中的 MS与 BS的距离信息计算而得。 目标小区 BS 通过接收上行同步脉冲， 比较接收时间与标准时间之差 Δ Tu，生成时 间延迟控制指令 (DCC) , 该指令通过下行专用控制信道传送给 MS , 用 于下一次上行同步脉冲发送时间的调整， 直到 Δ！ 小于门限值 Thu， 表明上行同步捕获完成。 此时 MS将改变业务通信的相关配置， 与目 标小区 BS建立上、 下行的业务通信。
以上 Thd和 Thu均为根据通信系统及信道环境设定的时间偏移门限值。 如对于 LAS- CDMA通信系统, 可选择 Thd-1 /2TC， Thu=l /2TC 。 当 MS已经开始同目标小区 BS 进行上、 下行业务通信时， 目标小区 BS将通过接收上行业务中的导 '频信号进行 上行同步的跟踪， 上行同步的时间和功率调整指令将通过下行专用控制信道传 送给 MS。 目标小区的 BS将在一段时间检测上行业务的性能， 如 CRC的检验， 如杲 满足通信的要求则表明切换是成功的。
以上着重给出了小区间的平滑切换， 扇区间平滑切换的原理也是相同的， 在某些特定情况下又更为简单一些。 比如当控制中心要求 MS由一扇区切换到另 一目标扇区， 如果该两个扇区同属于一个小区 （同一个 BS ) , MS在收到切换指 令时， 直接中断原扇区的上、 下行业务通信； 不做任何时间的调整， 按目标扇 区为其配置的资源调整扩频码和收、 发时隙， 开始与目标扇区的上、 下行业务 通信。
上述发明以时分双工模式（TDD )为特例加以说明的； 任何熟悉该领域的人 都很容易将此方法推广到频分双工模式（FDD ) 。 本发明也可以很容易的推广到 一般的同步通信系统。 其他方面的修改也是很容易作到的。

Claims

权利要求书
1、 一种同步码分多址通信系统的平滑切换的方法； 其特征在于至少包括如 下步骤：
( 1 ) 同步码分多址通信系统中的基站发送下行同步脉冲信号；
( 2 ) 同步码分多址通信系统的用户终端配有一套射频收、 发信机； 一套业 务基带收、 发信机； 两套下行同步的基带收、 发信机， 一套用于保持与原小区 或扇区的下行同步， 持续测量其下行同步脉沖的信号强度； 另一套则用于轮询 地搜索、 测量其他相邻小区的下行同步脉冲信号强度；
( 3 ) 当用户终端测得某个小区的下行同步脉冲信号的强度高于本小区设定 的门限值， 该用户终端向与之通信的本地基站发送测量报告， 提出切换请求； .
( 4 ) 网络端根据该用户终端发送的测量报告或接收的下行同步脉冲信号强 度和基站测量的与用户终端位置距离信息， 依据切换判决准则进行切换， 形成 切换指令；
( 5 ) 当用户终端收到切换指今时， 中断与原 BS的业务通信， 利用下行同步 脉冲测量的时间偏差， 邻小区分配的码道和计隙， 直接开始与新小区建立上、 下行的业务通信；
( 6 ) 用户终端收到切换指令后， 将持续测量、 同步的下行同步接收机匹配 码字改为切换的目标基站对应的下行同步脉冲扩频码， 完成与目标小区的下行 同步和通信； 并将另一个下行同步接收机用于轮询地搜索和测量其他相邻小 E。
2、 如权利要求 1所述的平滑切换方法， 其特征在于： 步骤 （1 ) 中， 所述的 同步码分多址通信系统帧结构中的第一个子帧是下行同步子帧， 第二个子帧是 上行同步子侦， 其他的子帧是上、 下行的业务子帧， 基站利用上行业务中的导 频符号完成上行同步的跟踪； 在上行同步子帧中预留固定接入时隙。 其采用码 分的形式发送上行同步脉冲。
3、 如权利要求 1所述的平滑切换方法， 其特征在于： 步骤 （2 ) 中， 用户终 端在下行同步接收机中使用下行同步脉冲时间偏差测量器， 用以完成邻小区或 扇区下行同步脉冲到达第一径与本小区或扇区下行同步脉冲到达第一径的时间 偏差的测量。
4、 如权利要求 1所述的平滑切换方法， 其特征在于： 步骤（3 ) 中； 用户终 端首先搜索出最接近的 Nm个小区作为测量目标； 然后轮询测量这个 Nm个小区的 下行同步脉冲信号的强度、 及到达时间， 然后通过上行专用控制信道将本小区 信号强度值， 以及大于或等子本小区信号强度值的邻小区信号的强度测量值， 相应的小区标识发送给小区的基站。
5、 如权利要求 1所述的平滑切换方法， 其特征在于： 步骤'（4 ) 中， 基站通 过测量用户终端的位置信息， 辅助下行同步脉冲信号强度的测量报告完成切换 的判决； 当用户终端向本小区基站发送测量报告时， 可同时在不同的空闲的上 行同步脉冲时隙， 向本小区和其他满足测量报告要求的小区发送上行同步脉冲， 基站通过匹配出上行同步脉冲的最大峰值获得用户终端与该基站的相对位置信
6、 如权利要求 1所述的平滑切换方法， 其特征在于： 步骤（5 ) 中包含有一 快速同步方法包括如下步骤'.
a) MS检测目标小区与原小区之间的下行同步脉冲接收时间的偏差绝对 值 Δ
b) 如果 A Td < Thd , MS直接改变上、 下行业务的扩频码及发送、 接 收时隙等相关配置。向目标小区 BS发送上行业务，并接收其下行业 务；
c) 如果 A Td > Thd , MS改变上行同步扩频码， 在控制中心为 MS分配的 接入时隙中发送上行同步脉冲。
d) 目标小区 BS通过接收上行同步脉冲， 比较接收时间与标准时间之差
A TU, 上人。 生成时间延迖控制指令（DCC ) , 该指令通过下行专用 控制信道传送给 MS， 用于下一次上行同步脉冲发送时间的调整， 直 到 A TU小于门限值 Th„, 完成上行同步捕获； e) 根据步骤 d ) MS将改变业务通信的相关配置， 与目标小区 BS建立上、 下行的业务通信。
7、 如权利要求 6所述的平滑切换方法， 其特征在于： Thd是一门限值， 在 LAS-CDMA中可取 Thd = 1 / 2TC 。
8、 如权利要求 1所述的平滑切换方法， 其特征在于： 所述的下行同步脉沖信 号的强度可以是下行连续导频信道的信号强度或其 SINR值。
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