KR20060129219A - Base station interface control using timeslot resource management - Google Patents

Abstract

A personal base station (PBS 1) configured to connect to the Internet and establish a small area of wireless coverage including means for controlling interference with neighboring personal base stations (PBS 2) using a timeslot management mechanism. Timeslot management mechanisms include timeslot interference detection, timeslot power reduction, timeslot allocation, timeslot offset calibration, and timeslot synchronization management that minimizes the number of frequencies required to control inter-cell interference between neighboring personal base stations.

Description

Base station interface control using timeslot resource management {BASE STATION INTERFACE CONTROL USING TIMESLOT RESOURCE MANAGEMENT}

Related Applications

This application claims the benefit of priority of US Provisional Patent Application No. 60 / 531,419, filed December 19, 2003. This application is part of US Patent Application Serial No. 10 / 280,733, filed October 25,2002.

The present invention relates generally to radio or wireless communications, and more particularly to interface control by the use of timeslot management for pico / personal base stations integrated into conventional wireless networks.

In the roll out of conventional radio carrier networks, one of the major considerations is the process of selecting and assigning frequency channels for all cellular base stations in the system. This process, referred to as frequency reuse or frequency planning, depends on several factors such as available frequency, cell geometry, antenna type, and topography.

An important parameter in determining frequency reuse is the carrier-to-interference (C / I) ratio, which measures the ratio of the power level of the radio frequency carrier to the power level of the interfering signal in the channel. The C / I ratio helps to determine the maximum interference level at which the cellular system configuration will continue to provide acceptable quality of service.

For rollout of a new GSM outdoor macro base station network, assuming a standard 4/12 geometry cell cluster reuse pattern (see FIG. 1), typically at least 12 frequencies are required to maintain quality of service within acceptable limits. . For GSM networks, this means meeting or exceeding the GSM 9 db C / I ratio specification.

In the roll out of a new GSM outdoor micro or pico base station network, one of several frequency planning strategies may be implemented. One strategy is to assign new (unused) frequencies to micro / pico cells, depending on the availability of unused frequencies in the carrier list. Alternatively, the carrier may choose to share the same frequency assigned to an existing macro cell network. In either case, assuming a standard 4/12 geometry cell cluster reuse pattern, typically at least 9 to 12 frequencies are required to meet or exceed the GSM 9 db C / I quality of service specification for a micro / pico cell network. . The reason for the reduction in the number of frequencies is that the micro or pico cells are placed below the clutter height, which means higher signal loss for the farther regions, effectively reducing the interference level.

Considering the roll out of another network of base stations, in particular indoor pico or personal base stations, an excellent frequency planning strategy is a new (unused) approach to avoid interference in stronger outdoor macro stations, especially high rise structures. Is to assign a frequency. When rolling out a new indoor network, assigning a new (unused) frequency is a better (and easier to implement) strategy than sharing frequency with macros and microcells, but for many reasons it is not always feasible.

First, most carriers do not have enough additional frequencies to implement an unused frequency strategy. Typically, the only unused frequencies in the carrier bandwidth list are the two "guard" frequencies at the extreme end of the carrier grant bandwidth. Typically, however, these frequencies are not practically available due to potential interference at frequencies placed and licensed by other carriers. Second, even with these two guard frequencies, they do not allow the carrier to meet or exceed the current GSM 9 db C / I non-quality of service specification described above.

From a carrier perspective, the ideal solution to these frequency planning problems is a method or mechanism that allows rollout of the GSM network of an indoor pico or personal base station that meets the following criteria: a) Only one or two, preferably guard frequencies. Use of two unused frequencies, b) satisfying GSM 9 db C / I non-quality of service specifications, and c) seamless integration with carriers existing in existing outdoor macro / micro networks.

Conventional timeslot allocation management: Conventional networks utilize time slot allocation management to help control mobile terminal interference within a single cell rather than between cells. The base station or base station controller allocates time slots in the cell to all mobile terminals in the cell, ensuring that no two mobile terminals transmit or receive signals within the same time slot, thereby preventing any interference between mobile terminals in a particular cell. It also avoids. In addition, the mobile terminal measures the signal strength or signal quality (based on the bit error rate) and sends the information to the base station controller to finally change the power level or initiate a handover and when to change it. Decide when or when to start.

MS)에 이용되고, 다른 주파수는 업링크(MS

BTS)에 이용된다. 하나의 200 kHz 채널의 쌍은 이중 채널로 지칭된다. Use of Conventional Channel Structures and Timeslots: Since the radio spectrum is a limited resource shared by all users, a method of partitioning bandwidth among as many users as possible must be devised. The method chosen by GSM is a combination of Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA). The FDMA portion requires dividing the frequency of the entire Mhz bandwidth by the assignable carrier frequency of the 200 kHz bandwidth. One or more carrier frequencies are then assigned to each base station. Each carrier frequency consists of two 200 kHz channels separated by a duplex distance (eg 45 MHz in GSM 900). One frequency is downlink (BTS)

MS), other frequencies are uplink (MS)

BTS). One pair of 200 kHz channels is referred to as a dual channel.

Each of these dual channels is then divided into eight time slots using the TDMA scheme. The eight consecutive time slot groups form a TDMA frame, with a time of 4.615 ms each. Each time slot is a burst period (BP) in which the transmission burst of modulated bits is broadcast. One time slot is used for transmission by the mobile terminal (uplink) and the other time slot is used for transmission for reception (downlink). They are separated in time, which simplifies electronics since the mobile terminal unit does not receive and transmit at the same time.

GSM BP lasts 15/26 milliseconds (ms; or approximately 0.577 ms). The eight burst periods are grouped into TDMA frames (120/26 ms, or approximately 4.615 ms) to form the basic unit for the definition of the logical channel, i. E. The constantly repeating period of BP time slot transmission.

A logical channel is defined by its corresponding burst period or number and location of time slots. Logical channels are used to exchange information between mobile terminals and base stations. The logical channel is divided into a dedicated channel assigned to the mobile terminal and a shared channel used by the mobile terminal in idle mode. Within a logical channel, transmission to the mobile terminal (downlink) occurs three timeslots prior to reception from the mobile terminal (uplink).

The first carrier in the cell is referred to as a broadcast control channel (BCCH) carrier. The BCCH carrier transmits BCCH system information on timeslot 0, in addition to Access Grant Channels (AGC), paging channels and most frequently the SDCCH channel. Since the BCCH carrier should be on at any time, the surrounding cell and the mobile terminal in its own cell can identify the BCCH carrier signal on all timeslots. Another characteristic of the BCCH carrier signal is that the base station transmitting the BCCH carrier signal transmits at a constant output power. Even though the traffic channel is in an active utilization state that creates potential interference with the BCCH carrier signal, the BCCH carrier signal continues to be transmitted at a constant output power on all timeslots. If there is no traffic on the carrier / timeslot, all other frequency carriers (TCH carriers) in the cell can be switched off.

Conventional Power Control: To minimize shared channel interference and conserve power, both the mobile terminal and base station transceivers operate at the lowest power level that will maintain acceptable signal quality. The power level can go up or down by 2 dB steps from peak power for class down to at least 13 dBm (20 milliwatts) or 2.5 mW in GSM 1900. Typically, power control is performed on the TCH carrier. The mobile terminal and the base station only need to transmit enough power to establish a connection. No more power is needed, and the use of less power means less interference.

The mobile terminal and the base station measure the signal strength and signal quality (based on the bit error rate) and transmit the information to the base station controller to finally determine when and when to change the power level at the mobile terminal or base station. do. Because of the possibility of instability, power control needs to be handled with care. This occurs because it causes the mobile terminal to increase its power in response to an increase in shared channel interference caused by another mobile terminal that increases its power.

Unlike controlling interference using conventional GSM timeslot allocation management, the present invention uses timeslot allocation management to reduce the number of frequencies needed to control interference between adjacent cells (inter-cell interference control). Mechanisms for this capability are provided for both macro base stations and pico or personal base stations.

Summary of the Invention

US Patent Application No. 10 / 280,733, filed October 25, 2002 and having a common assignee, proposes a portable, low power base station configured to transmit wireless traffic between a mobile base station and a conventional wireless network over the Internet. The base station may be referred to as a "personal" or "pico" base station ("PBS"), is configured to connect to the Internet at a location of the user's choice, and establishes small area wireless coverage within a larger macro network. The user sets the operating parameters of the base station. US Patent Application No. 10 / 280,733 is incorporated by reference, the main content of which is published in the corresponding International Patent Application Publication No. WO 2004/040938.

The present invention provides a method for enabling a network of indoor pico or personal base stations (PBSs) that meet the criteria described in the background section above. More specifically, the method of the present invention, using one or two unused frequencies, allows the network of pico or personal base stations to provide acceptable service levels within the existing carrier network of the macro base station. . This is accomplished by controlling the interference between adjacent pico / personal base stations using several timeslot management mechanisms.

The present invention also provides a method of reducing the number of frequencies required to control interference between adjacent pico or personal base stations (PBSs). The present invention includes one or more of the following GSM TDMA timeslot resource management procedures: timeslot interference detection, timeslot power reduction, timeslot allocation, timeslot offset correction, and timeslot synchronization. One or more of these resource management procedures apply to both BCCH and TCH timeslot resources. There are many configurations (mechanisms and embodiments) to achieve this function.

It is important to note that the present invention benefits carriers that roll out indoor pico / personal base station networks, regardless of whether the carrier chooses to implement a shared or unused frequency planning strategy for the PBS network. It is also important to note that the present invention is not only applicable to inter-cell interference control between PBS cells, but also to PBS and macro base station cells in a sharing strategy.

The principle underlying the PBS interference detection and resource management procedures is simple. 1 shows two adjacent PBS cells with interfering mobile terminal signals. 2 shows a process flow model for initializing, updating, and maintaining two PBS interference detection databases. 3 and 4 show “power off” state and “power on” operation with event “power on” (power on startup procedure) for timeslot interference detection, interference database update, and timeslot resource management. Indicates a procedure.

As shown in Figure 2, each PBS maintains its own interference database. The two PBS databases shown are used to track TCH and BCCH timeslot interference for adjacent PBS units. The BCCH DB is a long-term database (ie week and month) that adjusts its active interference timeslot list indicating the entry and exit of adjacent PBS units. The TCH is a short term database (ie, minutes, hours, and days) that adjusts its active interference timeslot list representing real-time mobile services provided by adjacent PBS units.

The PBS unit operates in one of two modes. During the "power on startup" procedure, the PBS is in mobile mode (i.e., received on the downlink frequency) and in the "power on" state, the PBS is in normal base station mode as needed to detect BCCH interfering signals. (I.e., transmit on the downlink frequency and receive on the uplink frequency) intermittently back and forth from the sampling mode (similar to the mobile mode).

As implemented in the present invention, during the "power on startup" procedure, the PBS detects BCCH signals from adjacent PBS and adds timeslots that interfere with its active list. In the "power on" state, the PBS intermittently switches to sampling mode to detect BCCH signals from adjacent PBSs, add timeslots (if detected) to its BCCH DB active interference list, or (previously detected) If the absence of the signal is recognized for a long time, such as month, for example), the timeslot is deleted from its BCCH DB active interference list. At the same time, as implemented in the present invention, when the PBS is in the " power on " state, the PBS detects a TCH signal from an adjacent mobile terminal and adds or deletes timeslots in real time from the TCH DB active interference list. do.

Whenever there is a state change in the BCCH DB or TCH DB (i.e. the addition or deletion of timeslots interfering with the DB), or whenever several flags or counters indicate that a TCH or BCCH timeslot interfering signal has been detected, the PBS will proceed with several Take appropriate action to manage timeslot resources by appropriately performing one or more of the following: timeslot allocation (select time slots that do not interfere for future mobile service needs), timeslot power control (power on interfering timeslots). Decrease and increase power on non-interfering timeslots, timeslot offset correction (BCCH TDMA timeframe offset to avoid interference with adjacent PBS control signals), and / or timeslot synchronization (related to timeslot frequency deviations). TDMA timeframe synchronization of adjacent PBS units to avoid interference problems).

As implemented in the present invention, timeslot allocation is a procedure for selecting non-interfering timeslots that are not present in the PBS active interference DB list used for future mobile requests in the local PBS cell.

As implemented in the present invention, timeslot power control is a procedure to reduce PBS local cell broadcast strength on interfering timeslots during active use by adjacent PBS cells. The power level is reset to its original level when the local PBS cell is no longer receiving an interfering signal.

As implemented in the present invention, timeslot offset correction is a procedure in which a local PBS cell offsets its BCCH TDMA timeframe to avoid interference by avoiding the use of the same BCCH timeframe used by adjacent PBS cells.

As implemented in the present invention, timeslot synchronization is such that the local PBS cell has a central clock reference, such as the clock, the Internet, or GPS, and its TDMA timeframes of adjacent PBS units in order to avoid interference problems associated with timeslot frequency deviations. This is the procedure to synchronize the clock.

Those skilled in the art can clearly see other systems, methods, features, and advantages of the present invention with reference to the following drawings and detailed description. All such additional systems, methods, features, and advantages are included within this description, are included within the scope of the present invention and protected by this application.

The above and other systems, methods, features, and advantages of the present invention will be readily understood upon consideration of the following detailed description of the present invention, with reference to the accompanying drawings. The elements (components) in the figures are not necessarily drawn to scale, with greater emphasis to clarify the principles and relationships between the elements of the present invention. In addition, in the figures, like (identical) text references or text descriptions correspond to corresponding elements (components) in a number of figures or figures.

1 is a block diagram illustrating interference between mobile terminals located in adjacent PBS cells in adjacent apartments.

2 is a block flow diagram illustrating how PBS TCH and BCCH DBs are used and maintained to manage timeslot resources.

3 is a block flow diagram illustrating a PBS power-on startup procedure.

FIG. 4 is a continuation of the block diagram of FIG. 3, illustrating a PBS operating procedure for continuously updating BCCH / TCH DBs and an ongoing procedure for continuously managing timeslot resources.

5 is a block diagram illustrating logical timeslot allocation and power reduction resource management for controlling interference between adjacent PBS cells.

6 is a block diagram illustrating initial PBS startup with BCCH timeslot offset correction, and subsequent timeslot resource management.

7 is a block diagram showing the effect on field strength when timeslots between base stations become asynchronous.

Introduction

US Patent Application No. 10 / 280,733, filed October 25, 2002 and having a common assignee, proposes a portable, low power base station configured to transmit wireless traffic between a mobile base station and a conventional wireless network over the Internet. The base station may be referred to as a "personal" or "pico" base station ("PBS") and is configured to connect to the Internet at a location of the user's choice and establish a small area of wireless coverage within a larger macrocell network. The user sets the operating parameters of the base station. US Patent Application No. 10 / 280,733 is incorporated by reference, the main content of which is published in the corresponding International Patent Application Publication No. WO 2004/040938.

1.0 implementation

Embodiments of the present invention may be determined as a method consisting of one or more of the following resource management procedures: timeslot interference detection and database update, timeslot power reduction, timeslot allocation, timeslot offset correction, and timeslot synchronization. One or more of these resource management procedures apply to both TCH and BCCH GSM TDMA timeslot resources. Section 2.0 initially detects interference between adjacent PBS cells (FIG. 1), populates the interfering BCCH / TCH DBs (FIG. 2), and then implements timeslot resource startup management (FIGS. 3-7). Explain the PBS startup procedure. Section 3.0 describes the PBS operating procedure, continuing to detect interference, update interfering BCCH / TCH DBs, and continue to manage timeslot resources (FIGS. 2-7).

2.0 PBS Startup  Power-on procedure

If the new PBS is initially activated or the existing PBS comes up after a power outage or some event, such as access to the Internet, the power on startup procedure shown in FIG. 3 is initiated. Embodiments of these power-on startup procedures are described below in Sections 2.1-2.6.

2.1 power on Startup

One embodiment of the power on procedure occurs every time the PBS loses power, either because of a power outage or because its on-off switch was toggled to the off position. After a power outage or a toggle of the on-off switch to the "on" position, the PBS resets itself to the startup mode.

Another embodiment of power on occurs every time the PBS is disconnected from the Internet. When the PBS reconnects to the Internet, the PBS resets itself to startup mode.

Another embodiment of power on occurs whenever the PBS compares the most recent TCH data entry with the current time clock. If the time difference (TD) between the most recent entry and the current time clock is greater than the specified time difference limit (TD-int), such as seven days, the PBS resets itself to startup mode.

2.2 DB  Delete entry

Each PBS maintains its own database (see Figure 2). Two PBS databases are used to track the TCH and BCCH timeslot interference for adjacent PBS units (see FIG. 1). The BCCH DB is a long-term database (ie week and month) that adjusts its active interference timeslot list indicating the entry and exit of adjacent PBS units. The TCH is a short term database (ie, minutes, hours, and days) that adjusts its active interference timeslot list representing real-time mobile services provided by adjacent PBS units.

One embodiment of the DB entry deletion procedure is that when PBS detects that it is in startup mode, based on the embodiment for power-on described above in section 2.1, all of the PBS TCH and BCCH DBs (FIG. 2) are present. To delete the active entry.

2.3 MS In mode PBS  Set

When the PBS is powered on, it initially enters the startup mobile terminal mode rather than the base station mode. When in mobile terminal mode, the PBS, like any other mobile terminal, can receive downlink data sent by another base station. It is important to note that when in mobile terminal mode, the PBS does not transmit any signals.

An exemplary embodiment for setting up PBS in MS mode is similar to the embodiment described above in section 2.2 for the DB entry deletion procedure. One embodiment of a procedure for setting up a PBS in MS mode automatically enters the PBS into startup mobile mode whenever it detects that the PBS is in startup mode, based on the embodiment described above in section 2.1. To do that.

2.4 BCCH  Start detection

When in mobile mode, the PBS does not transmit or provide services to the mobile terminal, but finds another neighboring PBS cell that broadcasts the BCCH signal on the assigned frequency. This is shown in FIG. During the scan in mobile mode, the PBS uses one or more procedures to detect interfering timeslots.

One exemplary embodiment of interference detection is the following procedure. While in mobile mode, the PBS scans the BCCH signal in all timeslots on the assigned frequency. If the PBS can detect any BCCH message in the downlink path, then the timeslot is added to the BCCH DB.

Another exemplary embodiment requires that any detected BCCH timeslot interference signal must exceed a preset FS-BCCH threshold. If the threshold is exceeded, a flag (F-int) or any yes / no binary indicator is set to indicate that an interference condition is occurring for a particular timeslot (e.g., true), and BCCH Indicates detection. For example, if the PBS can receive a BCCH message and the field strength of the received downlink path exceeds FS-BCCH (eg, -80 dBm), BCCH timeslot interference is detected.

Another embodiment for interference detection has nothing to do with absolute field strength. While in the startup mobile mode, the PBS scans the BCCH signal on the assigned frequency. Each time a decoded BCCH signal is detected, interference is occurring and a time slot interference flag or a yes / no binary indicator is set (e.g. true) to indicate BCCH detection.

2.5 BCCH  Offset setting

The BCCH offset setting procedure sets its own BCCH timeslot for the PBS during the power-on procedure where the timeframe is offset by one or more timeslot increments for the interfering BCCH timeslot. An example of a BCCH timeslot offset may be seen in FIG. 6.

One embodiment of the BCCH offset setting procedure is as follows: Before an offset occurs, the PBS uses its time slot (e.g., timeslot 2 in FIG. 6) using one of the BCCH detection embodiment procedures described above in section 2.4. Detect one or more BCCH signals from interfering PBS cell (s) in one or more of the < RTI ID = 0.0 > The PBS then resets (recalibrates) its TDMA framing so that the interfering BCCH signals originally detected in one PBS timeslot (e.g. timeslot 2 in FIG. 6) are different timeslots (e.g., 6, it is still detected in timeslot 6). Note that since the above procedure is performed in "mobile mode", the offset should take into account the BS-MS delay offset. The BCCH offset procedure is determined to be "right" if, after the PBS is switched to base station mode, later, all interfering BCCH timeslots from its neighboring PBS and their own BCCH timeslots do not overlap.

2.6 BCCH DB  replenishment

The BCCH DB is a long term database that adjusts its active interference timeslot list, indicating the entry and exit of adjacent PBS units. An embodiment of the BCCH DB population procedure for PBS in mobile mode may include a timeslot interference flag set to "true" in the BCCH detection start procedure (see section 2.4) to identify and add an active interference timeslot to the BCCH DB. Use any other binary indicator. Even though maintenance of the BCCH DB is a long-term process, the initial filling procedure occurs within seconds.

2.7 BS In mode PBS  Set

After filling the BCCH DB, the PBS switches from MS mode to BS mode. While in BS mode, the PBS receives in the frequency band being transmitted by the mobile terminal and transmits in the frequency band transmitted by another base station. That is, the PBS, like any other standard base station, receives on the uplink and transmits on the downlink.

2.8 Starting another procedure

During the "power on" transition, send several messages to initiate different processes (procedures); Thus, once the "power on" state is reached, these functions are active. Another procedure start includes the following example: "Start TCH detection" to start the TCH detection process and continue monitoring the timeslot. "Start power control", which initiates a power control / power reduction process. Similarly, there are "start of BCCH detection" and "start of synchronization". The details are described in the following paragraphs.

3.0 With "Power On" PBS

Once the PBS is in the "power on" state, more processes become active (see above) and generate the events described in FIG. The procedure in the "power on" state is described below in sections 3.1 to 3.6.

TCH  Start detection TCH  detection/ TCH  Loss)

In order to control inter-cell timeslot interference, the present invention detects interference occurrence (TCH detection) or no occurrence (TCH loss) by monitoring the measured field strength of its idle time slots at the personal base station and counting the occurrence of interference. (See FIG. 5).

One exemplary embodiment of interference generation monitoring and counting begins by defining a field strength threshold interference limit: FS-int (eg, -75 dBm). Using the threshold limit, time slot signal samples are taken (monitored) and the number of timeslot interference occurrences is counted (counted). The time of the timeslot signal monitoring is set (e.g. one time slot, although it may be shorter to handle asynchronous problems), and for each sample signal above or below the threshold limit FS-int, counter N -int is modified (that is, incremented or decremented by some value, as appropriate).

One exemplary embodiment of TCH detection (interference occurrence) is the following procedure. Each time the measured field strength FS of the sampled timeslot exceeds the FS-int threshold, the counter N-int is incremented by a specified number (eg, 1). In contrast, if the FS-int threshold is not reached, the counter N-int is decremented by the specified number (eg, 1). As soon as the counter N-int reaches the limit UP-int (e.g., 3), it satisfies the interference condition, indicating TCH detection. The counter N-int is allowed to increment until the upper limit UPPER-int (eg 5) is reached. If the sample does not reach the FS-int threshold, the counter N-int is decremented by the specified number (eg, 1) until the value 0 is reached. As soon as the counter reaches the value limit LOWER-int (eg 2), the interference condition is no longer valid and indicates TCH loss. Note that the procedure can be reversed, which means that the counter can decrease when the threshold is reached and increase when the threshold is not reached.

Another exemplary embodiment of TCH detection (interference occurrence) is the following procedure. Whenever the measured field strength exceeds the FS-int threshold, a flag (F-int) or binary yes / no indicator is set to indicate that an interference condition has occurred (e.g., true). , TCH detection. Whenever a measurement is taken and the field strength monitored (received) does not exceed the FS-int threshold, a flag (F-int) or binary yes / no indicator is set to indicate that no interference condition has occurred. (Eg, false), indicating TCH loss.

3.2 BCCH  Start detection BCCH  detection/ BCCH  Loss)

BCCH detection while in the “power on” state is similar to BCCH detection during the power on startup procedure (section 2.4). While in base station mode, the PBS may switch to sampling or receiving mode for idle timeslots.

One embodiment of the transition to sampling mode for idle timeslots is as follows. The PBS determines which timeslots are in the idle state, i.e. those timeslots that are not used for BCCH information nor for active calls. For that idle timeslot, the PBS reverses the band it receives by switching off the transmitter and adjusting the receiver to the previous transmission frequency (by switching from downlink to uplink mode). The PBS may then take samples of downlink timeslots from other base stations operating on the same or different frequencies. Note that when doing this, both the transmit and receive timeslots of the PBS should be idle. This means that no timeslots are being transmitted on the downlink and no timeslots are being received on the uplink from active mobile terminals in the cell.

One exemplary embodiment of interference detection is the following procedure. First, scan all timeslots. If the PBS detects any BCCH message in the downlink path and indicates BCCH detection, then this timeslot is added to the BCCH DB. If the PBS does not detect any BCCH message in the downlink path, indicating BCCH loss, this time slot is deleted from the BCCH DB.

In another embodiment, the detected BCCH timeslot interference signal must also exceed the current FS-BCCH threshold. If these conditions are met, the flag (F-int) or any yes / no binary indicator is set to indicate that an interference condition is occurring for a particular timeslot (e.g., true) to enable BCCH detection. Indicates. If these conditions are not met, the flag (F-int) or any yes / no binary indicator is reset (e.g., false) to indicate that no interference condition is occurring for a particular timeslot, BCCH Indicates a loss. For example, if the PBS can receive a BCCH message and the field strength of the received downlink path exceeds the FS-BCCH (eg-80 dBm), BCCH timeslot interference is detected.

Another embodiment performs detection in the uplink mode, such that the PBS does not switch to mobile mode during normal base station operation. Instead, the PBS attempts to measure uplink-BCCH messages, like the SDCCH and RACH messages. In this case, the DB deletion process for BCCH interference signals occurs slowly (requires weeks or months), but the DB addition process for BCCH interference signals occurs quickly (requires minutes or hours). Only after an extended absence of interfering signals from the mobile terminal in the adjacent PBS cell, it can be assumed that the adjacent PBS is always inactive. As in the procedure for adding a DB interference signal, here, too, a counter, such as N-noint, may be implemented. However, to detect a lost BCCH interference signal, the counter can be incremented each time no BCCH message can be received. When the N-noint counter reaches a preset value (e.g., 10,000), a flag (F-noint) or any yes / no binary indicator is set to indicate the absence of a BCCH interference signal for a particular timeslot. (Eg, false), indicating BCCH loss.

Another embodiment of BCCH detection is as follows. If the BCCH message checks the uninterrupted timeslot of the idle state and cannot receive the BCCH message, the counter (N-int) is reset (e.g., zero) and in advance each time a BCCH message is detected. Incremented by a defined value. This may be done irrespective of the measured field strength or with the requirement that the BCCH message also exceed the minimum threshold. When the counter reaches the value N-BCCH-MAX (e.g. 2), the BCCH detection condition is satisfied and the flag (F-int) or any yes / no binary indicator indicates BCCH interference for a particular timeslot. Set to indicate a signal (eg, true) to indicate BCCH detection.

Note also that this procedure is valid even if the increment / decrement procedure on the counter is reversed. For example, when a BCCH message is received, the counter is decremented.

3.3 BCCH  And TCH DBs  Update (add / delete interference signal)

The BCCH DB is a long term database (ie week and month) that adjusts its active interference timeslots indicating the entry and exit of adjacent PBS units. The TCH is a short term database (ie, minutes, hours, and days) that adjusts its active interference timeslot list representing real-time mobile services provided by adjacent PBS units. The PBS database configuration is shown in FIG.

One embodiment of updating BCCH and TCH DBs is as follows. The PBS detects a new TCH or BCCH interference signal on an idle timeslot, using one or more of the procedures implemented in section 3.1 (TCH detection / TCH loss) or section 3.2 (BCCH detection / BCCH loss), or the absence of interference signal. Each time a is detected, the corresponding BCCH DB or TCH DB is appropriately adjusted by adding or deleting from the list of active interference timeslots.

TCH  Start power control (power down)

To control the timeslot intercell interference, the present invention adjusts (reduces) the transmit power of selected timeslots in the PBS, but not in all situations. Typically, a BCCH carrier base station transmits its BCCH signal at a constant power level on all idle timeslots (“regular power”). This may interfere with mobile terminals in other cells. Thus, the present invention changes BCCH carrier timeslot power levels to help reduce interference. The reason is as follows. Unlike macro cells, where base station power reduction may affect hundreds of mobile terminals, in the case of PBS with small cell area and low power output, only a few local adjacent mobile terminals are potentially affected. In addition, the impact of the power change is very advantageous to reduce interference in adjacent cells, even a small change in the mobile terminal location (ie, only a few meters) causes a significant change in field strength. Also, finally, complete output power on all timeslots is only when the mobile terminal is located within the macro-cell close to the PBS cell, which can trigger cell-reselection or handover from the conventional macro cell to the PBS cell. It's just important. However, this rarely occurs. The field strength measured at the mobile terminal is only affected if the mobile terminal measures during the time slot power down. Even when the mobile terminal measures the timeslot, the measured field strength is attenuated in direct proportion to the output power reduction (eg 6 dB).

1 is a block diagram showing two adjacent apartments APT 1 and APT 2 comprising mobile terminals MS 1 and MS 2 and personal base stations PBS 1 and PBS 2. According to the present invention, as soon as PBS 2 detects MS 1 as a potential interference signal in a particular timeslot, PBS 2 proceeds to adjust (decrease) its output power in that timeslot, from PBS 2 to MS 1. It helps to reduce the interference on the downlink. 5 shows the effect on BCCH field strength in timeslot 3 following a decrease in PBS 2 output power. The effective signal-to-noise ratio on the traffic channel in timeslot 3 is significantly reduced, thereby reducing the likelihood of any interference from PBS 2 on MS 1.

An example embodiment of adjusting PBS power is as follows. If the PBS determines from its N-int counter or F-int flag or TCH DB or BCCH DB that it needs to reduce its output power for one of its timeslots, then the constant value Tx-int db (eg For example, 6 db) will reduce power (“interfered timeslot power”). In contrast, when the PBS determines from its N-int counter or F-int flag or TCH DB or BCCH DB that the time slots are not interfering, the output power for the timeslot is set to " normal power. &Quot;

If the PBS determines from its N-int counter or F-int flag or TCH DB or BCCH DB that it is necessary to reduce the PBS output power, another embodiment of the present invention provides a PBS field strength and threshold field strength limit. The power to PBS is reduced by the difference between FS-int. For example, if FS-int = -80 dBm and the field strength of the measured interference signal is -75 dBm, the output power is reduced by 5 db compared to the "normal power" level.

TCH  Start assignment

In order to control inter-timeslot inter-cell interference, the present invention not only reduces the transmit power of selected timeslots used by interfering PBS cells, but in some situations, but also reduces the use of interfering timeslots. It also blocks and assigns (assigns) an unused non-interfering timeslot to any new cell initiated by the mobile terminal in that cell.

PBS 1) 상의 간섭을 회피하는 것을 돕는, 그 셀 내의 이동 단말기(MS 2)에 의해 개시된 임의의 새 호출에 대한 시간슬롯 6인, 단지 미사용된 비간섭 시간슬롯만을 할당도 한다.As can be seen in FIG. 5, according to the present invention, as soon as the personal base station PBS 2 detects a potential mobile terminal MS 1 interference signal in timeslot 3, the interference is detected on the downlinks PBS 2 to MS 1. In addition to reducing the output power in that timeslot, which helps to reduce (see above), PBS 2 not only blocks any new calls in timeslot 3 from the mobile terminal in that cell, but in this example, MS 2

It also assigns only unused uninterrupted timeslots, which are timeslot 6 for any new call initiated by mobile terminal MS 2 in that cell, which helps avoid interference on PBS 1).

An exemplary embodiment for starting TCH allocation of timeslots is as follows. As soon as PBS detects an interference signal at a particular timeslot, from its N-int counter or F-int flag or BCCH DB and TCH DB, the PBS requests a new service (new call) within the detected PBS cell area. Deny (block) the use of the timeslot for any mobile terminal, and b) an uninterrupted timeslot unused for any mobile terminal requesting a new service (new call) within the detected PBS cell (e.g., For example, the timeslot with the lowest measured field strength signal) is assigned (assigned). If all timeslots have constant interference, then the timeslot with the lowest interference level is selected to provide the service.

3.6 Start sync

The present invention provides an additional but optional procedure for implementing BCCH timeslot synchronization to avoid deviations by adjacent PBS units and interference on BCCH timeslots. This is shown in FIG. PBS 2 detects interference from MS 1 in timeslot 3. As shown in Figure 5, PBS 2 proceeds with the procedure of blocking timeslot 3 service for the mobile terminal in its own cell, reducing its own output power during timeslot 3, and Allocates unused timeslots (e.g., 6) that are used by calls from mobile terminals within its own cell. However, as shown in FIG. 2, the problem is that the physical timeslots in two adjacent cells, ie, cell 1 and cell 2, become asynchronous with time, ie the relationship between timeslots in two cells is time dependent. It no longer matches.

If the asynchronous deviation between the two cells is not so severe, no action needs to be taken to correct the situation. Embodiments of the various methods and procedures described herein above will effectively reduce any interference from the detected PBS cell. However, if the asynchronous deviation is severe, an additional procedure is needed to synchronize adjacent PBS cells.

Timeslot synchronization can be achieved by using a universal reference clock that reestablishes global synchronization (via GPS or the Internet) between all PBS cells, or by reestablishing local synchronization (via intercell reception mode) between the nearest PBS cells. By using a carrier signal, it may be achieved.

One embodiment of the present invention is to synchronize all PBS cells to a GPS reference clock. Another, similar embodiment of the present invention is to synchronize all PBS cells to a single signal coming on the Internet.

Another embodiment of the present invention periodically switches all PBS units to receive mode at predetermined time intervals (e.g., every 60 seconds), thereby bringing its own TDMA frame to the BCCH signal from its nearest neighbor. Fit. This is possible because the PBS only needs to transmit in timeslot 0 for the BCCH and, for example, in timeslot 1 if there is an active call. The remaining timeslots can be used to adjust the dual frequency, measure field strength, and detect BCCH framing of adjacent cell (s).

4.0 Applicable Technologies

While many embodiments of the invention described above are based on GMS technology, the invention also supports other technologies, including CDMA, iDEN, and 3G / UMTS.

The scope of the present invention also includes embodiments in which new pico, micro or macro cells are assigned to shared or new frequencies in the current carrier network. The scope of the invention also applies to any situation where a residential home, public space, business, campus, airport, new pico, micro, or macro base station shares frequency. The term timeslot is used in a logical sense. For example, it can be seen that the timeslot exists in the downlink such as ts 0 and the timeslot exists in the uplink such as ts 0 + 3. . The timeslot pairs are referred to as logical timeslots and represent both timeslots in the downlink and uplink, using different frequencies separated for dual frequencies.

5.0 Conclusion

In conclusion, it should be stressed that the above-described embodiments of the invention, in particular any “preferred” embodiments, are only possible implementations and are only described for a clear understanding of the principles of the invention. Many modifications and variations may be made to the above-described embodiments of the invention without departing substantially from the spirit and principles of the invention. Herein, all such modifications and variations are included within the scope of the disclosure and the present invention.

Claims (6)

A personal base station connected to the Internet and configured to establish small area wireless coverage, Means for controlling interference with an adjacent personal base station using a timeslot management mechanism. The method of claim 1, The timeslot management mechanism includes selecting a non-interfering timeslot for the mobile service request. The method of claim 1, The timeslot management mechanism includes reducing power on interfering timeslots and increasing power on timeslots that do not interfere. The method of claim 1, The timeslot management mechanism includes offsetting the broadcast control channel to avoid interference with an adjacent broadcast control channel. The method of claim 1, The timeslot management mechanism includes synchronizing a TDMA timeslot with a timeslot of an adjacent PBS unit to avoid interference problems associated with timeslot frequency deviation. The method of claim 1, And a interference database for tracking TCH and BCCH timeslot interference with adjacent personal base stations.

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