System and method using adaptive antennas to selectively reuse common physical channel timeslots for dedicated channels

ES 2 289 482 T3

DESCRIPTION

System and method for selective reuse of common physical channel time slots for dedicated channels using adaptive antennas.

Field of invention

The present invention is related to radioelectric digital communication systems. More particularly, the present invention is related to a time division duplex (TDD) autoconfiguration system, which allows selective reuse of certain Common Physical Channel (CPCH) time slots for dedicated channels.

Background

Conventional cellular systems typically use a Broadcast Channel (BCH) to communicate information to a specific mobile user for the Radio Access Network (RAN), as well as for a given call, even before the connection is established. In a TDD system, the BCH is transmitted on the Primary Common Control Physical Channel (PCCPCH). Another example of common channels transmitted in the CPCH time slots is the Direct Access Channel (FACH), which in the TDD system, is transmitted on the Secondary Common Control Physical Channel (SCCPCH). As discussed herein, the term "CPCH time slot" refers to any time slot that is used to transmit the CPCH.

Certain reserved cellular time slots have typically been used through a subsystem of the TDD system, to transmit the CPCH. The subsystem is an assembly of TDD cells that can interfere with each other due to their relatively close proximity, from a path loss point of view to another. For example, a subsystem could understand on a floor of a building deployed using multiple cells if the walls of the building will not provide sufficient insulation (from a path loss point of view). Similarly, an entire building could be considered a subsystem if the floors and ceilings of the building could not provide sufficient insulation (from a path loss point of view) to prevent interference between floors. In an overseas deployment, a subsystem can be anything with respect to a small district, comprising a few cells with respect to a large metropolitan area.

Depending on the performance of the TDD system receivers, as well as the radio frequency (RF) isolation between cells, the TDD system may limit the number of time slots required to transmit the CPCH to one CPCH time slot. Alternatively, the TDD system may have to use more than one time slot, to ensure excellent quality in the CPCH (for example, BCH repetition in the case of PCCPCH, FACH block error rate (BLER) in the case SCCPCH, etc.).

Fig. 1 shows the case where more than one time slot is used in a conventional radio communication system. Each base station (BS) AF in the system would use only one of the time slots 1, 2, 3 for its own CPCH transmission, while refraining from transmitting anything in the other time slots that the system can use for the CPCH . Neighboring base stations would use the other time slots for their CPCH transmissions. A given CPCH time slot would be used only by base stations that are within a certain distance from each other, thus enhancing the signal-to-interference ratio (SIR) of the CPCH for mobile units served by these base stations, and thus ensuring coverage. contiguous of the CPCH. However, this will decrease the capacity of the system, since fewer time slots will be available for traffic on Dedicated Physical Channels (DPCH).

There is a need for a method and a system that can selectively reuse some of the CPCH timeslots in a TDD system, to transmit user data.

DE-19858725-A1 describes a method for transmission on a random access channel in a radiocommunication system, where a plurality of subscriber stations use the channel in an uncoordinated way. The subscriber stations carry out the signal transmissions on the channel with a transmission power corresponding to a predetermined attenuation value, and in a part of the transmissions, the transmission power is increased.

US-2001/026543-A1 describes a method of assigning a channel to user equipment in a CDMA communication system. The physical packet common channel is assigned to a user equipment according to an access preamble signature.

Summary

The present invention uses adaptive antennas in the base stations of a communication system, to monitor the metric parameters associated with the quality of one or more CPCH time slots, to determine if some or all of the CPCH time slots are reused, to transmit the DPCH. If reuse of some or all of the CPCH time slots is determined, a further determination is made to limit the application on the DPCH transmit powers. Adaptive antennas can be used in base stations,

ES 2 289 482 T3 to allow the system to reuse some or all of the CPCH timeslots to transmit DPCH, thus improving the overall capacity of the system, while maintaining CPCH coverage, and quality at a desired level across the entire of the system.

Brief description of the drawings

The objects of the present invention will become apparent upon consideration of the following accompanying description and from the figures, in which:

Figure 1 shows the allocation of CPCH time slots in the cells of a conventional radio communication system;

Figure 2 shows the allocation of CPCH time slots in the cells of a radio communication system operating in accordance with the present invention;

Figure 3 is an exemplary block diagram of a communication system, in accordance with a preferred embodiment of the present invention;

Figure 4 is a flow chart showing the steps of the method for selectively reusing CPCH time slots to transmit user data in the communication system of Figure 3; and Figure 5 shows an exemplary database configuration used in accordance with the present invention.

Detailed description of the preferred embodiments

Currently preferred embodiments are described below with reference to the drawing figures, where like numerals represent like elements in their entirety.

Although the description that follows is specifically explained as applicable to the TDD system and time division synchronized code division multiple access (TD-SCDMA), it will be appreciated that the invention in its broad form is also applicable to other transmission systems without any limitation.

Hereinafter, the radio transmission / reception unit (WTRU) includes, but is not limited to, user equipment, mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in an environment radioelectric. Hereinafter, a base station includes but is not limited to a base station, Node B, site controller, access point, or other interface device in a radio environment.

An exemplary embodiment of a method and system is described below, showing how adaptive antennas can be used in a communication system at base stations, to allow the system to reuse at least some of the slots. of CPCH time, to transmit DPCH, as shown in figure 2, thus improving the overall capacity of the system, meanwhile maintaining the coverage and quality of the CPCH system at a desired level throughout the entire system. However, care should be taken to avoid indiscriminate reuse of CPCH time slots, to transmit the DPCH signal in the same subsystem, which could lead to high interference CPCH signals, and therefore cause CPCH reception problems. for mobile users in some areas. Some consequences resulting from poor CPCH reception could include unacceptable delays for users to access the RAN, and with degradation of key radio resource management functions (for example, such as handoffs and radio control). power), leading to holes or deficiencies in the CPCH service. It will be appreciated that even though the example described refers to a TDD system, the method and system of the invention are equally applicable to other transmission systems, such as the TDS CDMA system.

Figure 3 shows an exemplary communication system 300 operating in accordance with the present invention. Communication system 300 includes a plurality of WTRU units, 305A, 305B, 305C, a Radio Access Network (RAN) 310, and a cellular database 315. RAN 310 includes a plurality of equipped base stations 320A, 320B with adaptive antennas 325, comprising elements 330 of antenna N. The RAN 310 further includes a radio network controller (RNC) 335, comprising a processor 340, in which the channel allocation process 345 is executed. In the context of the present invention dealing with CPCH signals, adaptive antennas 325 are used to identify the direction of arrival of users sending measurements. The RAN 310 is used to collect quality measurement metrics in the CPCH for a large number of mobile positions, as well as for the received power measured by the WTRU, 305A, 205B, 305C units, which will provide internal insights into the loss per path associated with the measured metric parameters of the CPCH system.

Examples of the CPCH quality metric parameters that can be collected by the system include, but are not limited to, the statistics of the BCH read time and the SIR measured in the PCCPCH time intervals, in the case of the PCCPCH or FACH BLER, and the SIR measured at SCCPCH time slots in the case of SCCPCH.

ES 2 289 482 T3

A poor CPCH quality metric is assumed to be caused by the CPCH signal being too low compared to thermal noise, or the CPCH signal being attenuated by interference.

To qualify as a valid CPCH quality metric, the power of the CPCH signal measured in the WTRU unit has to be high enough compared to thermal noise so that the WTRU unit is considered to be within the coverage area of ​​the unit. CPCH. In this regard, the statistics of WTRU units that experience poor CPCH reception due to being too far from the service base station (or in radio shadow area) should not be included in the analysis described below. To this end, the CPCH quality measure for which the received measured power is less than a certain threshold should be discarded.

For each CPCH quality metric that it can collect, the communication system 300 measures the signals received at each element of the antenna 330 from the base stations 320A, 320B. This measurement is used by the communication system 300 to identify, with its array of stacked antennas, the direction of arrival of the WTRU in which the CPCH quality metric is sent.

Channel allocation process 345 running on processor 340 allows base stations 320A, 320B to reuse some or all of the CPCH time slots to transmit the DPCH signals. Referring to FIG. 4, the process 345 used by the communication system 300 allows the dedicated channels to be in the CPCH time slots. Communication system 300 is configured such that more than one CPCH time slot (N_CPCh> 1). In an initial state of the communication system 300, the downlink time slots N are assigned._DL and the uplink time slots N_ul (step 405), where N_DL + N_UL is the total number of time slots per TDD frame. The communication system 300 is also assumed, for example, to use a total of N_CPCh different time slots for transmitting the CPCH signals, where N_CPCh is assigned with a value of one to N_DL (step 410). At this point, none of the CPCH timeslots are used to transmit the DPCH signals.

Still referring to Figure 4, before attempting to reuse the CPCH time slots to transmit the DPCH signals, the communication system 300 has to collect enough series of measurements to provide a relatively stable distribution of quality metrics. CPCH for each angular section of each cell (step 415). Once the communication system 300 is estimated as having adequate CPCH reception, and having a stable distribution of the CPCH metrics, the communication system 300 will initiate a process, in which it will attempt to reuse the CPCH time slots of a station. base on the system, to support DPCH traffic. In the initial stage, an operator using a single CPCH timeslot in its global system, as indicated by the "NO" output of step 420, will label each cell's CPCH timeslot as non-aggressive (step 425). . The operator using more than one CPCH timeslot as indicated by the "YES" output of step 420 would label each cell's CPCH timeslot as aggressive, and would label all other CPCH timeslots N_CPCh-1 as non-aggressive (stage 430).

The aggressive and non-aggressive identifiers are simple binary flags, which provide the ability to remove one or multiple CPCH time slots from a cell from the process described above, once it is estimated that the cell no longer increases the power of the signals. DPCH in said time slot. The term "aggressive" refers to the ability to interfere. If by increasing P_Max__dCh__CPCh For a given time interval in a first cell, it turns out that the CPCH reception of the second cell is degraded, the first cell will be considered aggressive during said time interval.

For each cell that is labeled "non-aggressive" for a given time interval, the value of P_Max__dCh__CPChwill increase in P_i_NCre_Mento Watts, unless P_Max__dCh__CPCh already corresponds to the maximum power (P_max) that the mobile station can allow in a time slot. The value of P_Max__dCh__CPCh is the maximum transmission power that a station is allowed to use to transmit a DPCH signal in a CPCH time slot; P_increment is the dimension of the stage used by the process to iteratively increase the value of P_Max__dCh__CPCh, And p_max is the maximum power that a base station is authorized to transmit regardless of the nature of the signals (ie CPCH or DPCH).

In step 435, a determination is made whether (1) all cells have their CPCH time slots as aggressive, or (2) have their P value_Max__dCh__CPCh set to P_max. In case none of the conditions (1) or (2) exist, in step 440 the value of P_Max__dCh__CPCh increases for each cell in the P _inrTement for CPCH time intervals that (i) are not labeled aggressive, and (ii) that have a value of P_Max__dCh__CPChthat is configured as less than P_max. In step 445, the PCCPCH statistics are collected, and the CPCH quality is monitored for each angular section of each cell. For each angular section of each cell denoting a degradation of CPCH quality, no neighboring cells will be found in the database of cells 315 (step 450). In step 455, the neighboring cells identified in step 450 have their P value_Max__dCh__CPCh reduced by P_increment for the time interval where CPCH degradation was measured. At step 460, neighboring cells identified at step 450 are labeled aggressive for the time interval where CPCH degradation was measured.

Thus, for each angular section of each cell a decision is made as to whether or not the added interference of the DPCH signals is detrimental to the CPCH quality of the time slots. This decision is only initiated when a cell has collected a measure of a CPCH quality sufficient to achieve a certain level.

ES 2 289 482 T3 of reliability in the statistical relevance of the new measures. If unsatisfactory CPCH quality is detected in one or more elements, each of the element's neighbors will be labeled as an aggressive cell. The Pmax_dch_cpch parameter of each aggressive cell will be reduced by the P_ factor_increase Watts There is no minimum power, and it is a variable that can be set to any value. The P factor process_increase continues until all cells are labeled aggressive, or until all cells have P factor_MAX__DCH__CPCH configured for Pmax.

Either of the following two actions, or a combination of the two, can be performed to determine if the added interference is detrimental to CPCH quality:

(1) Compare the newly acquired CCH distributions against the "baseline" distribution. Each angular section has a distribution. For example, if an adaptive antenna has ten antenna elements to allow the definition of ten angular sections, ten distributions should be stored for that base station. This should be done for each angular section N of the cell. Comparison of one distribution with another would be done in several ways, including but not limited to comparing the statistics extracted from the two distributions (for example, mean, median, 5% of the Cumulative Distribution Function, etc.).

(2) Check if the newly acquired CPCH distribution is worse than what is considered to be an acceptable CPCH quality distribution. This criterion differs from the previous criterion in the sense that even in the case where the use of the CPCH time slot transmits DPCH signals that degraded the CPCH quality compared to the baseline, this added degradation could be considered acceptable if the CPCH quality is was still above a certain desired level.

The cell database 315 is used to identify neighboring cells (from a radio frequency (RF) point of view) of any given station. An example of such a database includes the database used by cellular operators with their RF planning tools. Cell database 315 has also been used to associate each antenna element 330 of each base station 320A, 320B, and its associated angle, to one or more of the neighboring cells. The channel allocation process 345 that runs in processor 340 allows base stations 320A, 320B, to reuse some or all of the CPCH time slots to transmit the DPCH signals.

With adaptive antennas made up of N antenna elements, it is possible to identify the direction of arrival of an incoming signal with an angular resolution of (θ / N) where (θ) is the angle covered by the main lobe of a single element of the antenna. The angle (θ) corresponds to the angle spanned by a cell, when the adaptive antenna is used in a cellular context. For example, for a sector in a tri-sectorized display, this angle is 120 degrees, and for an omnidirectional cell this angle will be 360 ​​degrees. Thus, if the cell is divided into N angular sections (covering equal angles), the adaptive antenna allows the determination of which is the angular section of the origin of the incoming signal. From the collection of these measurements for a large number of users, the communication system 300 is able to obtain a distribution of the CPCH quality metrics, for each angular section N of the cell. The CPCH quality distribution could take the form of a histogram in which each set would correspond to a small interval of the CPCH quality metric.

Figure 5 shows an example configuration of a 315 cell database, where C1 ... CN are cell identifiers, and θ_ί_₁ a θί specify a range in terms of the angle from which the interference problem is perceived. It will be noted that the state of whether a cell is labeled aggressive or non-aggressive is not necessarily in the database, but may be in the process itself. For example, once Cell 2 is known to have interference in a certain area (as determined by the angle of arrival provided by adaptive antennas), the database will determine which interfering cell is causing this interference.

The present invention can be implemented in conjunction with a Fast Dynamic Channel Assignment (FDCA) algorithm, which is responsible for assigning DPCH signals to time slots, but only transmitting DPCH signals at a certain power of transmission with P_MAX__DCH__CPCH = 0 Watts (no transmission) in CPCH time intervals. Initially, the FDCA algorithm does not allow the DPCH system to transmit in the CPCH time slots, as indicated by a separate flag, or more simply, by reusing the variable P_MAX__DCH__CPCH, but setting it to zero. The FDCA algorithm is the process by which the RAN assigns channels to mobile users. Typically, the FDCA algorithm receives for each call a list of time slots in which it can use to service the DPCH signals. In conventional systems, the FDCA would receive a list of timeslots that would not include the CPCH timeslots. In the context of the present invention, the FDCA receives, for each cell, a list of time slots including one or more CPCH time slots. In order to control the level at which the CPCH time slots are reused to transmit the DPCH signals, the FDCA will also receive together with each CPCH time slot for each cell, the parameter P_MAX__DCH__CPCH, which explicitly limits the power in a certain base station, allowing to use the power to transmit a DPCH signal during a given CPCH time interval.

In one embodiment of the present invention, the system stores each distribution of the CPCH quality metric, using a histogram where each set of the histogram would correspond to a range of the CPCH quality metric. For example, if the CPCH quality metric were the BCH read time, the histogram might have

ES 2 289 482 T3 sets corresponding to a second duration, that is, the first set of the histogram would be used to store the measurements that reported on a BCH reading time between 0 and 1 second, the second set would be used to store the measurements reporting about BCH read time between 1 and 2 seconds, etc. Every time the WRTU system sends a CPCH quality metric measurement report to the base station, the system will identify the angular section where the WTRU is located, and will associate the CPCH quality metric to the angular section, storing it. in the appropriate set of the histogram associated with the angular section.

After having collected a large number of measurements, the distribution will be considered stable. The exact number of measurements required to obtain a stable distribution depends on the number of sets in the histogram and their capacity. Communication system 800 has to be configured such that CPCH reception is adequate. Proper reception is a general term, which can be implemented in many ways. For example, it could be decided that adequate reception means that no more than 10% of the CPCH quality measures are below a certain desired target value (for example, three seconds if the CPCH quality metric is time to BCH reading). Some of these stable distributions will be referred to as a "baseline" distribution.

In conventional cellular systems, radio operators have a database that contains the different sectors or cells of their systems, and which identify the list of neighboring sectors for each of them. What determines whether sector A is a neighbor of sector B is the amount of power that sector B would receive from sector A, if a base station in sector A transmitted at its maximum power. Software propagation prediction tools and / or performance test measurements are used to populate these databases. The cell database 315 proceeds to a further step to identify its neighboring cells in each corner section, rather than in each sector. Again, this can be accomplished using software propagation prediction tools.

Regarding the execution frequency, the process 345 can be re-executed for a sub-system (or the entire system) after a change in the configuration of the system (for example, addition of cells, modification of the inclination of the antenna, etc.). The re-execution of process 345 consists of resetting P_Max__right__cpch to zero Watts for all CPCH time intervals, reconstruction of the baseline distributions, and execution of the steps outlined above.

The present invention as discussed above reuses CPCH timeslots in a communication system (eg, a TDD system) to transmit user data, thus improving the overall capacity of the system. This is especially important in scenarios where propagation conditions will force the operator to use multiple CPCH time slots to ensure an acceptable level of CPCH quality, a situation where it would prove common when contiguous coverage is desired. Significantly, the invention requires very little operator intervention, and provides efficient utilization of CPCH time slot resources.

Although the present invention has been described in terms of the preferred embodiment, other variations that are within the scope of the invention and are set forth in the claims that follow will become apparent to those skilled in the art.