JP2006517762A - System and method with adaptive antennas for selective reuse of CPCH time slots for dedicated channels - Google Patents

Abstract

An adaptive antenna at the BS to determine whether to reuse some or all of the CPCH time slots for transmitting DPCH by monitoring a metric associated with the quality of one or more CPCH time slots. And communication systems (eg, TDD systems). If it is decided to reuse some or all of the CPCH time slots, additional decisions are made regarding what restrictions apply to the DPCH transmission power. An adaptive antenna that can be used at the BS allows the system to reuse some or all of the CPCH time slots to transmit DPCH, thereby reducing the desired level of CPCH coverage and quality throughout the system. Improve overall system capacity while maintaining.

Description

  The present invention relates to a wireless digital communication system. In particular, the present invention provides a self-configuring TDD (time-division duplex) that allows a specific physical channel (CPCH) time slot to be selectively used in a dedicated channel (DCH). ) Related to the system.

  Conventional cellular systems communicate information to mobile users specific to a RAN (radio access network) before establishing a connection, and similarly communicate information to a predetermined cell, BCH (broadcast channel). Is typically used. In the TDD system, BCH is transmitted to PCCPCH (primary common control physical channel). Another example of a common channel transmitted in a CPCH time slot is a forward access channel (FACH), which is transmitted to a common physical channel (SCCPCH) in TDD. Here, the term “CPCH time slot” refers to any time slot used to transmit a CPCH.

  A reserved timeslot is typically used throughout the subsystems of the TDD system to transmit CPCH. This subsystem is an ensemble of TDD cells that can interfere with each other because they are relatively close in terms of path loss. For example, if the building wall does not provide sufficient isolation (in terms of path loss) to avoid interference from one cell to the other, the subsystem uses multiple cells. It can consist of one floor of a deployed building. Similarly, if the building floor and ceiling do not provide sufficient isolation (in terms of path loss) to avoid interference between floors, the entire building can be considered a subsystem. For outdoor deployment, the subsystem can be anything from a narrow area of small numbers of cells to a large metropolitan area.

  Depending on the performance of the receiver of the TDD system and the radio frequency (RF) isolation between cells, the TDD system determines the number of time slots required to transmit the CPCH to one CPCH time. Can be restricted to slots. Alternatively, the TDD system guarantees good quality on the CPCH (eg, BCH reception in the case of PCCPCH, FACH block error rate in the case of SCCPCH, etc.) Multiple time slots must be used.

  FIG. 1 shows an example where more than one time slot is used in a conventional wireless communication system. Each BS (base station) A-F of the system will use only one of the time slots 1, 2, 3 for its own CPCH transmission, while the system is in the CPCH. In other time slots used for this purpose, the transmission is withheld. Neighboring BSs will use other time slots for CPCH transmission. A given CPCH time slot is only used by BSs some distance apart from each other, which improves the CPCH signal-to-interference ratio (SIR) for mobile units served by these BSs and ensures CPCH. Can be continuously covered. However, this reduces the system capacity because the time slots available for traffic on the dedicated physical channel (DPCH) are reduced.

  There is a need for a method and system that selectively reuses some of the CPCH time slots in a TDD system to transmit user data.

  The present invention uses one or more CPCH time slots to determine whether to reuse some or all of the CPCH time slots for transmitting DPCH using an adaptive antenna at the BS of the communication system. Monitor metrics related to quality. If it is decided to reuse some or all of the CPCH time slots, additional decisions are made regarding restrictions that apply to DPCH transmit power. Adaptive antennas can be used at the BS to allow the system to reuse some or all of the CPCH time slots that transmit DPCHs, so that CPCH coverage and quality is desired throughout the system. The overall capacity of the system can be improved.

  The objects of the invention will become apparent upon review of the accompanying detailed description and drawings.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The same reference signs indicate similar elements.

  In the following description, it will be described as being applicable to TDD and TD-SCDMA (time division synchronous code-division multiple access). However, in a broad sense, the present invention can be applied to other transmission systems in a broad sense. Note that it is applicable without limitation.

  Hereinafter, the WTRU (wireless transmit / receive unit) can operate in the following: user terminal, mobile station, fixed or mobile subscriber unit, pager, or wireless environment Other types of devices are included, but are not limited to these. In the following, BS (base station) is meant to include, but is not limited to, BS, Node-B, site controller, access point, or other interface connection device in a wireless environment. It is not something.

  Hereinafter, in order to allow the communication system to reuse DPCH by reusing at least some of the plurality of CPCH time slots as shown in FIG. An example of a method and system showing how to use the adaptive antenna of the system in the BS will be described. According to this method and system, on the one hand, the coverage and quality of the CPCH is maintained at a desired level throughout the communication system, and on the other hand, the overall capacity of the communication system is improved. . However, the following should be avoided: inadvertent reuse of CPCH time slots to transmit DPCH signals in the same subsystem. Otherwise, the multiple CPCH signals will interfere strongly, causing CPCH reception problems for mobile users in the same region. Poor CPCH reception may result in unacceptable delays in user access to the RAN, major radio resource management functions (eg, handoff and power control) may be degraded, and CPCH service holes may occur. , Will be. Here, although this example is an example of a TDD system, it should be noted that the method and system according to the present invention can be equally applied to other transmission systems, such as TDS CDMA.

  FIG. 3 illustrates an exemplary communication system 300 that operates in accordance with the present invention. The communication system 300 includes a plurality of WTRUs 305A, 305B, and 305C, a RAN (radio access network) 310, and a cell database 315. The RAN 310 includes a plurality of BSs 320 </ b> A and 320 </ b> B including an adaptive antenna 325 including Nae antenna elements 330. The RAN 310 also includes a radio network controller (RNC) 335 that includes a processor 340 that executes a channel assignment process 345. In the context of the present invention dealing with CPCH signals, adaptive antenna 325 is used to identify the direction of arrival of measurements transmitted by the user. Since RAN 310 collects metrics that measure the quality of CPCH at multiple mobile locations, it is also the received power measured by WTRUs 305A, 305B, 305C, and the path associated with this measured CPCH quality metric. Used to collect received power that would allow insight into loss.

  The CPCH quality metric can be collected by the system, but examples of this CPCH quality metric include BCH read time statistics and SIR measurements for PCCPCH time slots in the case of PCCPCH or FACH BLER. , SIR measurements for SCCPCH time slots in the case of SCCPCH are included, but are not limited thereto. Here, it is assumed that the low CPCH quality metric is caused by either a CPCH signal that is less than thermal noise or a CPCH signal that is attenuated by interference.

  In order to qualify as a valid CPCH quality metric, the power of the CPCH signal measured at the WTRU must be greater than thermal noise, and if so, the WTRU is within the coverage of the CPCH. Can be considered. In this regard, statistics from WTRUs that cannot successfully receive CPCH because the WTRU is too far away from the serving BS (or behind the serving BS) are not included in the analysis described below. Better. For this purpose, it is better not to take in a CPCH quality measurement value whose received measurement power is less than a certain threshold.

  For each collected CPCH quality metric, the communication system 300 measures the signals received by the respective antenna elements 330 of the BSs 320A, 320B. This measurement is used by communication system 300 to identify the direction of arrival of the CPCH quality metric transmitted by the WTRU by its antenna array.

According to the channel assignment process 345 running on the processor 340, the BSs 320A, 320B can reuse some or all of the CPCH time slots to transmit DPCH signals. Referring to FIG. 4, process 345 used by communication system 300 grants dedicated channels in CPCH time slots. The communication system 300 is configured to be able to use more than one (N _CPCH > 1) DPCH time slots. In the initial state of the communication system 300, N _dl downlink time slots and N _ul uplink time slots are allocated (step 405). Here, N _dl + N _ul is the total number of time slots per TDD frame. The communication system 300 transmits a CPCH signal using, for example, a total of N _CPCH different time slots. Here, values from 1 to N _dl are assigned to N _CPCH (step 410). At this point, none of the CPCH time slots are used to transmit DPCH signals.

Still referring to FIG. 4, before attempting to reuse CPCH time slots to transmit DPCH signals, the communication system 300 distributes the CPCH quality metric for each cell's angular section relatively stably, Measurements must be collected sufficiently (step 415). Once the communication system 300 is aware that the CPCH reception is good and that the CPCH metrics are stably allocated, the communication system 300 supports the DPCH traffic in the system to support the CPCH of the BS. Initiates a process that attempts to reuse time slots. If “NO” in step 420, in the initial state, an operator using a single CPCH time slot in the entire system tags each cell's CPCH time slot as non-aggressive. (Step 425). If “YES” in step 420, the operator using a CPCH time slot greater than 1 tags each cell's CPCH time slot as active, and N _CPCH −1 all other CPCH time slots. Are tagged as non-aggressive (step 430).

Aggressive and non-aggressive identifiers are simple binary flags that are once in the cell and are believed not to increase the power of the DPCH signal in the time slot. And the function of removing one or more CPCH time slots of the cell from the process described above. The term “aggressive” means to interfere. If P _{max_dch_CPCH} in a given time slot in the first cell has increased and CPCH reception in the second cell has dropped, then this first cell will be aggressive in that time slot. It is regarded.

In the respective cells which are tagging "non-aggressive" in a given time slot, as long as P _{Max_dch_CPCH} is, BS is not in the maximum power (P _max) that can be transmitted in the time slot, P _{Max_dch_CPCH} is P Increased by _{_increment} watts. P _{max_dch_CPCH} is the maximum transmission power that the BS can use to transmit the DPCH signal in the CPCH time slot. _{P_increment} is the step size used by the process to repeatedly increase P _{max_dch_CPCH} . P _max is the maximum power that the BS can transmit regardless of the nature of the signal (ie, CPCH or DPCH).

In step 435, whether (1) the plurality of cells all satisfy the condition that the CPCH time slot is set to aggressive or (2) the condition that P _{max_dch_CPCH} of the cell is set to P _max is satisfied Judging. If neither condition (1) or (2) is satisfied, then in step 440, P _{max_dch_CPCH} for each cell is (i) a CPCH time slot not tagged as aggressive and (ii) ) CPCH timeslot having a set P _{Max_dch_CPCH} less than P _max, is increased by the _P _increment. In step 445, PCCPCH statistics are collected and CPCH quality is monitored for each angular section of each cell. For the angular section of each cell that has been reported to be degraded in CPCH quality, a neighboring cell is found in the cell database 315 (step 450). In step 455, neighboring cells identified in step 450, the time slot reduction of CPCH is measured, to reduce its P _{Max_dch_CPCH} only _P _increment. In step 460, if in the time slot where CPCH degradation was measured and used, the adjacent cells identified in step 450 are tagged as aggressive.

Thus, for each angular section of each cell, it is determined whether additional interference from the DPCH signal adversely affects the time slot CPCH quality. This determination is made only when the cell has collected enough CPCH quality measurements to obtain a certain level of reliability for the statistical validity of this new measurement. If, in one or several elements, the detected CPCH quality is unsatisfactory, each neighbor to that element is tagged with an aggressive cell. The P _{max_dch_CPCH} parameter for each aggressive cell is then reduced by _{P_increment} watts. Although there is no minimum power, _{P_increment} is a variable that can be set to any value. The process continues until all cells are tagged as aggressive, or until all cells have P _{max_dch_CPCH} set to P _max in all cells.

  The following two processes (1) and (2), or a combination of these two processes can be performed to determine whether additional interference adversely affects CPCH quality.

(1) Compare the newly obtained CPCH distribution with the “baseline” distribution. Each angular section has one distribution. For example, if there are 10 antenna elements of an adaptive antenna and 10 angular sections can be defined, 10 distributions should be stored for the BS. Storing such allocation should be performed for N _ae pieces of angular section of the cell. There are various ways of comparing allocations to allocations, which compare statistical values extracted from the two allocations (eg, mean, median, 5% cumulative distribution function, etc.). However, the present invention is not limited to these various methods.

  (2) Verify whether the newly obtained CPCH allocation is worse than what is considered an acceptable CPCH quality allocation. This criterion, in the following sense, in the following sense, i.e., when using CPCH time slots to transmit DPCH signals, will result in reduced CPCH quality compared to baseline: This additional quality degradation is different in the sense that CPCH quality can still be considered acceptable if it is still maintained above some desired level.

  The cell database 315 is used to identify adjacent cells (in terms of radio frequency (RF)) for any given BS. An example of such a database includes a database used by a cellular operator having an RF planning tool. Cell database 315 is also used to associate each antenna element 330 of each BS 320A and 320B and the angle associated with each antenna element 330 with one or more neighboring cells. According to the channel assignment process 345 running on the processor 340, the BSs 320A and 320B can reuse some or all of the CPCH time slots to transmit DPCH signals.

With an adaptive antenna composed of N _ae antenna elements, it is possible to identify the arrival direction of an incoming signal with an angular resolution of (Θ _s / N _ae ). Here, Θ _s is an angle determined by the main lobe of a single antenna element. The angle (Θ _s ) is the angle determined by the cell when the adaptive antenna is used in a cellular context. For example, in the case of three sectors, the angle (Θ _s ) of one sector is 120 degrees, and in an omnidirectional cell, the angle (Θ _s ) is 360 degrees. Accordingly, if, the cell, when it is (conformal to) divided into N _ae pieces of angular section, the adaptive antenna can determine whether sent from any angular section the incoming signal . A collection of such measurements for a number of users, the communication system 300 can acquire the distribution of CPCH quality metrics N _ae pieces of angular section of the cell. This CPCH quality distribution can take the form of a histogram, with each bin corresponding to a small interval of the CPCH quality metric.

FIG. 5 shows an exemplary configuration of the cell database 315. Here, C1... CN are cell identifiers, and Θ _i−1 to Θ _i are angles within a range where interference is known. Note that the status of whether a cell is tagged as aggressive or non-aggressive does not necessarily exist in the database, but can exist in the process itself. For example, once it is known that the cell 2 is interfering in an area, the database determines which interfering cell caused this interference.

The present invention can be implemented in conjunction with an FDCA (Fast Dynamic Channel Allocation) algorithm. This FDCA algorithm is responsible for assigning DPCH signals to time slots. According to this FDCA algorithm, only CPCH signals are transmitted with a certain transmission power, with P _{max_dch_CPCH} = 0 watts (no transmission) in CPCH time slots. be able to. First, even with this FDCA algorithm, the DPCH cannot be transmitted in the CPCH time slot, which is indicated by the individual flags, but simply put, the variable P _{max_dch_CPCH} is reused, but the variable P _{Set max_dch_CPCH} to zero. This FDCA algorithm is a process in which the RAN allocates channels to mobile users. Typically, according to this FDCA algorithm, a time slot list that can be used to serve DPCH signals is received for each cell. In conventional systems, the FDCA algorithm receives a time slot list that will not include CPCH time slots. In the context of the present invention, the FDCA algorithm receives a time slot list containing one or more CPCH time slots for each cell. In order to control the level at which CPCH time slots are reused to transmit DPCH, according to this FDCA algorithm, each cell receives a CPCH time slot for each cell, and a BS can receive a DPCH signal in a given CPCH time slot. _Receives a parameter P _{max_dch_CPCH} that explicitly limits the power that can be used to transmit.

  In one embodiment of the invention, the system uses a histogram to store each CPCH quality metric distribution. Here, each bin of the histogram corresponds to a range of CPCH quality metrics. For example, if the CPCH quality metric is BCH read time, the histogram may have bins corresponding to a duration of 1 second. That is, the first bin of the histogram will be used to store measurements reporting BCH read times between 0 and 1 second, and the second bin will be between 1 and 2 seconds. Will be used to store the measurement value that informs the BCH reading time between, and so on. Each time the WRTU sends a CPCH quality metric measurement notification to the BS, the system identifies the angular section in which the WTRU is located and applies this CPCH quality metric to the appropriate histogram associated with the angular section. And associates the CPCH quality metric with its angular section.

  After a huge number of measurements are collected, the distribution is considered stable. The exact number of measurements required to obtain a stable distribution will vary depending on the number of bins in the histogram and the bin capacity. Communication system 300 must be configured for proper CPCH reception. Proper reception is a general term that can be implemented in many ways. For example, proper reception means that only 10% of the CPCH quality metric is less than some desired target (for example, 3 seconds if the CPCH quality metric is BCH read time). I can decide. These stable allocations are called “baseline” allocations.

  In a conventional cellular system, multiple wireless operators have a database that includes different sectors or cells of the system, and for each identifies a list of adjacent sectors. What determines whether sector A is a sector adjacent to sector B is the amount of power that sector B will receive from sector A when the BS of sector A transmits at maximum power. Software propagation prediction tools and / or drive test measurements are used to fill these databases. Cell database 315 advances one step in identifying adjacent cells in each angular section, not adjacent cells in each sector. This can again be done using a software propagation prediction tool.

For execution frequency, process 345 may be re-executed for a subsystem (or the entire system) after a change in system configuration (eg, cell addition, antenna tilt correction, etc.). To re-execute process 345 is to reset P _{max_dch_CPCH} to 0 watts in all CPCH time slots, rebuild the baseline allocation, and perform the steps described above.

  The present invention reuses CPCH time slots in communication systems (eg, TDD systems) to transmit user data, as described above, thereby improving the overall capacity of the system. This is the case in the following scenario, i.e., where these propagation conditions require the operator to use multiple CPCH time slots to guarantee an acceptable level of CPCH quality, i.e., continuously. This is especially important in situations that often occur when it is desirable to be covered. Importantly, according to the present invention, very little operator intervention is required, and resource utilization of CPCH time slots is performed efficiently.

  While preferred embodiments of the present invention have been described above, it will be apparent to one skilled in the art that other modifications do not depart from the scope of the claims.

FIG. 3 is a diagram illustrating CPCH time slot allocation in a cell of a conventional wireless communication system. FIG. 6 illustrates CPCH time slot assignment in a cell of a wireless communication system operating in accordance with the present invention. 1 is an exemplary block diagram illustrating a communication system operating in accordance with a preferred embodiment of the present invention. 4 is a flowchart illustrating method steps for selectively reusing CPCH time slots for transmitting user data in the communication system of FIG. FIG. 3 illustrates an exemplary cell database configuration used in accordance with the present invention.

Claims (17)

In a wireless communication system, a method of reusing a plurality of CPCH (common physical channel) time slots in order to transmit a dedicated physical channel (DPCH) signal,
(A) tagging the plurality of CPCH time slots as aggressive or non-aggressive, respectively;
(B) limiting the power level for transmitting DPCH signals in the plurality of CPCH time slots to a maximum power level;
(C) tagging the CPCH time slot as non-aggressive if the number of the CPCH time slots does not exceed one;
(D) If the number of CPCH time slots exceeds 1, then CPCH time slots that are reused to transmit DPCH signals in each cell are tagged as aggressive and all other said Tagging CPCH time slots non-aggressively. In claim 1,
(E) increasing the power of the DPCH signal transmitted in each CPCH time slot tagged as non-aggressive and less than a predetermined maximum power level by a predetermined amount;
(F) monitoring a metric associated with the quality of the CPCH time slot;
(G) For each angular section of each cell associated with CPCH quality degradation,
(I) determining each adjacent cell;
(Ii) reducing the maximum power level of the CPCH time slot in the adjacent cell associated with the degradation of the CPCH quality;
(Iii) further comprising aggressively tagging the neighboring cell in the CPCH time slot associated with the CPCH quality degradation. In claim 2,
(H) assigning a predetermined number of downlink time slots;
(I) assigning a predetermined number of uplink time slots;
(J) further comprising allocating a predetermined number of CPCH time slots.   4. The method of claim 3, wherein the number of CPCH time slots is a number between 1 and the number of downlink time slots.   2. The method of claim 1, wherein the communication system is a TDD (time-division duplex) system, and the cell is a TDD cell. In a wireless communication system, a method of reusing the CPCH (common physical channel) time slot to transmit at a power level that does not exceed a maximum power level of a dedicated physical channel (DPCH) signal,
The system includes (i) a plurality of cells, each cell having a plurality of angular sections, (ii) a plurality of wireless transmit / receive units (WTRUs), (iii) the quality of the CPCH time slot, and the WTRU. RAN (radio access network) and (iv) multiple base stations (BSs) that transmit CPCH signals in multiple time slots to collect metrics associated with An adaptive antenna operating in each of the cells, each BS comprising a BS communicating with each of the WTRUs; and (v) a database associating the cell with the adaptive antennas of the BS;
This method
(A) the RAN determines that the communication system has a stable distribution of CPCH metrics for each angular section of the cell;
(B) tagging each CPCH time slot as aggressive or non-aggressive in the database;
(C) increasing the power of the DPCH signal transmitted by the BS by a predetermined amount in each CPCH time slot tagged as non-aggressive, the power being a predetermined maximum power level Steps that are less than,
(D) monitoring the metric associated with the quality of the CPCH time slot;
(E) For each angular section of the cell associated with CPCH quality degradation,
(I) determining each adjacent cell;
(Ii) reducing the maximum power level for the CPCH time slot in the neighboring cell associated with the degradation of the CPCH time slot quality;
(Iii) Aggressively tagging the neighboring cell for the CPCH time slot associated with the degradation of CPCH quality in the database. In claim 6,
(F) assigning a predetermined number of downlink time slots;
(G) assigning a predetermined number of uplink time slots;
(H) further comprising allocating a predetermined number of CPCH time slots.   8. The method of claim 7, wherein the number of CPCH time slots is a number between 1 and the number of downlink time slots.   The steps (c)-(e) according to claim 6, wherein all of the CPCH spreadsheet is tagged as aggressive in the database or designated to transmit DPCH signals at the maximum power level. The method further comprises the step of repeating.   The method according to claim 6, wherein the communication system is a TDD (time-division duplex) system, and the cell is a TDD cell. A wireless communication system that reserves a common physical channel (CPCH) time slot,
Multiple WTRUs (wireless transmit / receive units);
RAN (radio access network) for collecting metrics associated with the quality of the CPCH time slots and the received power measured by the WTRU;
A system comprising a database in which each CPCH time slot is tagged as aggressive or non-aggressive. In claim 11,
A plurality of cells, each cell having a plurality of angular sections;
A plurality of BSs transmitting CPCH signals in a plurality of time slots, each having an adaptive antenna operating in each of the cells, each BS communicating with each of the WTRUs;
A processor in communication with the RAN, the database, the BS, and the WTRU;
A process running on the processor for monitoring the metric associated with the quality of the CPCH time slot, for each angular section of each cell associated with a degradation of CPCH quality,
(I) the respective neighboring cells are determined;
(Ii) the maximum power level is reduced for the CPCH time slot in the neighboring cell associated with the degradation of the CPCH quality;
(Iii) The system further comprising: in the database, the CPCH time slot in the neighboring cell associated with the degradation of CPCH quality is tagged as aggressive.   12. The system according to claim 11, wherein the CPCH time slot is reserved for transmitting a BCH (broadcast channel) signal.   12. The system of claim 11, wherein the CPCH time slot is reused to transmit a DPCH (dedicated physical channel) at a power level that does not exceed a maximum power level. A wireless communication system for reusing a CPCH (common physical channel) to transmit a dedicated physical channel (DPCH),
(A) means for tagging each CPCH time slot as aggressive or non-aggressive;
(B) means for limiting the power level for transmitting DPCH signals in the CPCH time slot to a maximum power level;
(C) means for tagging the CPCH time slots as non-aggressive if the number of the CPCH time slots is not greater than one;
(D) If the CPCH time slot is greater than 1, for each cell to transmit a DPCH signal, tag the CPCH time slot that is reused as aggressive and all other CPCH time slots A system comprising non-aggressive and tagging means. In claim 15,
(E) means for increasing the power of the transmitted DPCH signal by a predetermined amount for each CPCH time slot tagged as non-aggressive, the power being less than a predetermined maximum power level Means,
(F) means for monitoring a metric associated with the quality of the CPCH time slot;
(G) means for determining each adjacent cell for each angular section of each cell associated with CPCH quality degradation;
(H) means for reducing the maximum power level for the CPCH time slots in the neighboring cell associated with the degradation of the CPCH quality;
(I) The system further comprising: means for aggressively tagging the CPCH time slot in the neighboring cell associated with the degradation of the CPCH quality. 16. The system according to claim 15, wherein the system is a TDD (time-division duplex) system, and the cell is a TDD cell.

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