Channel allocation using enhanced pathloss estimates

Channel configuration with enhanced path loss estimation

The present invention can be described with reference to the drawings:

Figure 1 shows the frequency reuse mode applied to a fixed planning cellular system;

Figure 2 is a demonstration of the time-dependent characteristics of cellular system load;

Figure 3 shows a signal measurement result obtained according to a specific embodiment of the present invention;

Figure 4 is a table to illustrate an example matrix of system measurement results;

Figure 5 is a table to illustrate an example matrix of system calculation based on system measurement results;

Figure 6 is a table to illustrate another example matrix, which provides the system operator to determine the frequency configuration;

Figures 7A and 7B show examples of channel assignment based on system calculation results;

Figure 8 shows an exemplary method implemented in a TDMA system according to the present invention;

Figure 9 shows an exemplary method implemented in a CDMA system according to the present invention.

Background of the invention

The present invention relates to a radio communication system. Specifically, the present invention relates to frequency and/or channel selection using enhanced path loss estimation.

In radio communication systems and cellular radio communication systems, a jurisdictional entity usually configures a specific frequency band for its operation. Therefore, the operators of these communication systems all hope to accommodate the largest number of communication users within the configured bandwidth. The traditional method uses frequency reuse to increase the system capacity to the maximum. The frequency reuse technology configures grouped frequencies in a limited geographic coverage area, and this area is the cell. Cell lines containing the same or similar frequency groups are separated by geographic regions, so that callers located in different cells can use the same frequency at the same time without interfering with each other. In this way, thousands of users can be served in a system that uses only hundreds of frequencies.

Link quality is a standard inspection part of any wireless communication system. To provide high-quality voice communication, the required signal in a cellular system must maintain a minimum signal strength higher than all other interferences. The ratio of the required signal to interference is known as the carrier-to-interference ratio (C/I ratio). In addition to ubiquitous noise, basically a designer must deal with two forms of interference. The first type of interference is caused by users operating on the same channel at the same time, which is co-channel interference; the second type of interference source is From the user's use of adjacent channels, this is adjacent channel interference. The control of adjacent channel interference is through the selection of those frequencies with larger frequency increments in a cell. For example, in a standard GSM system, a 200 kHz separation between adjacent channels is used to use three In the cell planning of the section, the frequency configuration of a cell and the use of a steep cut in the channel filter can obtain a higher adjacent channel suppression effect. The way to reduce co-channel interference is to use a frequency reuse mode that geographically separates cells in the same frequency group. Figure 1 shows an ideal seven-cell frequency reuse pattern.

Channel planning is a method of assigning individual channels to cells in the network. At present, most frequency plans are prioritized, which means that a fixed frequency plan will be properly "hard-wired" in the system by each cellular system operator.

This is a fixed channel configuration or FCA. However, because interference and traffic flow change over time, FCA is not the most ideal method. For example, Figure 2 illustrates a highway used to divide a plurality of cell boundaries into two. Since this highway may have significant car traffic in the morning and very little in the afternoon, cellular traffic may vary greatly depending on the location and time of day. Therefore, most fixed frequency plans are not very efficient; many channels in the frequency plan will have better link quality than those required for high-quality voice communications, while many other channels in the same system have only poorer link quality. The quality of the link may cause them to be interrupted or blocked. Through channel configuration forms such as adaptive channel alloca-tion (ACA) schemes, we try to make all links have the same quality and increase capacity.

An important consideration in channel configuration and cell planning is path loss. Path loss is a measurement of the difference between the strength of the transmitted and received signals. There are many factors between the transmitting and receiving stations that affect the path loss, including the influence of terrain, such as hills, trees, mountains, and buildings. In order to enable the receiving station to receive signals of acceptable quality, the greater the path loss between the sending and receiving stations, the higher the transmission power. Traditional systems used to estimate path loss for frequency planning purposes use propagation models to estimate path loss. This propagation model uses information from topographic maps, actual location configurations, and antenna heights to estimate the path loss in the system. Based on this estimated path loss (which may be related to the actual path loss of the system or not), the system determines the average interference in the cell and how much different cells contribute to this interference level. Because in fact this model does not include the combined effect of the actual traffic distribution and the actual radio propagation conditions, there are serious shortcomings in using the propagation model.

This article incorporates another channel configuration solution published by Haartsen, US Patent No. 5,491,837 by way of reference. In Haartsen's invention, the mobile station will be instructed to measure the received signal strength (RSSI) of individual pilot signals sent from surrounding base stations. RSSI measurement can be used to estimate the path loss between the base station where the signal is being measured and the mobile station that performs the measurement. However, the Haartsen system has some limitations. The first limitation is that the RSSI measurement includes signal energy related to different forms of interference, that is, co-channel interference, adjacent channel interference, and non-cellular emissions (including licensed and non-cellular emissions). (Licensed emission source) interference. Similarly, since the source of the interference is unknown, the configuration of the new frequency can eliminate one form of interference, but this configuration may cause interference from other frequencies allocated to other users in other cells, which may be good before the new frequency configuration The quality of the connection. Furthermore, since the Haartsen system must rely on the detector in the mobile station for measurement, the quality of the detector will vary from one mobile station to the next, and the measurement must tolerate errors due to different detectors.

Invention summary

The present invention relates to a method and system for frequency and/or channel configuration using enhanced path loss estimation. According to an exemplary embodiment of the present invention, the available frequency channels (i.e., the frequency and time slot of the TDMA system, the frequency of the CDMA system, the channelization code, and the scrambling code) are configured in a base station to facilitate the connection quality and the time slot. The connection creates the best compromise between the interference of another connection using a specific channel, and provides base station services. Furthermore, the channel selection is based on the actual use of the current channel, the power level of the cell, and the path loss measured between the cell and the mobile station. Exemplary embodiments of the present invention also provide an estimation of actual interference provided by a mobile station in a cell and a base station of another cell for uplink and downlink. With the enhanced path loss estimation method, the system also provides a method to estimate the impact caused by changes in power levels, changes in traffic flow, and changes in mobile station distribution. Furthermore, this system provides an impact assessment of frequency re-planning without causing interference to the system.

By using the measurement results provided by the exemplary embodiments of the present invention, before implementing a frequency plan, it can be used to optimize the frequency plan of an overall cellular communication system. The specific embodiment of the present invention can also use the measurement results to optimize the frequency plan according to different flow conditions during the day. For example, in a region, there are two sets of frequency plans, one for high flow and the other Set for low traffic. In addition, the system uses path loss estimation to determine adjacent cells for handover execution, handover evaluation, and cell reselection.

Schematic description

The present invention can be described with reference to the drawings:

Figure 1 shows the frequency reuse mode applied to a fixed planning cellular system;

Figure 2 is a demonstration of the time-dependent characteristics of cellular system load;

Figure 3 shows a signal measurement result obtained according to a specific embodiment of the present invention;

Figure 4 is a table to illustrate an example matrix of system measurement results;

Figure 5 is a table to illustrate an example matrix of system calculation based on system measurement results;

Figure 6 is a table to illustrate another example matrix, which provides the system operator to determine the frequency configuration;

Figures 7A and 7B show examples of channel assignment based on system calculation results;

Figure 8 shows an exemplary method implemented in a TDMA system according to the present invention;

Figure 9 shows an exemplary method implemented in a CDMA system according to the present invention.

Detailed description of specific embodiments of the invention

The following description is intended to illustrate the needs of the present invention but not to limit it. The proposed specifications, such as specific circuits, circuit elements, methods, etc., are all intended to provide a complete understanding of the present invention. However, a person skilled in the art should understand that the present invention can be implemented in other specific embodiments without departing from these specific detailed descriptions. In other cases, detailed descriptions of known methods, devices, and circuits are omitted so as not to confuse the description of the present invention.

Figure 3 shows the signal measurement results obtained according to an exemplary embodiment of the present invention. The system operation according to the present invention is controlled by a mobile telephone switching office (MTSO) 300, which can be directly or Indirectly connected to base station controllers 310, 320, and 330. According to an exemplary embodiment of the present invention, the mobile station 370 has a call forwarded through the base station 1 (BS1) 350. Therefore, the downlink signal 345 is sending information to the mobile station 370, and the mobile station 370 is sending information to the BS1 350 via the uplink signal 335. Although Figure 3 illustrates the winding signals (305, 315, and 335) sent by the mobile station 370 between the mobile station 370 and different base stations, those skilled in the art can recognize the wind-up signal 370 sent by the mobile station 370. Actually The uplink can propagate in all directions from the mobile station through the air, so each different signal uses a different reference number to illustrate the same uplink signal received by various geographically dispersed base stations. In addition, although the base stations in FIG. 3 are quite close geographically, the cells relative to the base station do not need to be actually adjacent cells. therefore _， BS1350 can be located in cell G in Figure 2, while BS2340 and BS3360 can be located in cell C and cell E, respectively.

When the mobile station 370 is in a call, the MTSO 300 decides whether the base station 2 (BS2) 340 is still using the same channel for transmission and reception. This channel is the mobile station 370 for transmitting and receiving data in the BS1 350. If the BS2340 does not currently use the same frequency to transmit and receive, the MTSO 300 informs the mobile station 370 to lock its transmission power at its current power level. In some systems, when the power is locked, the output power of the mobile station 370 can be adjusted by telling the BS1 350 not to transmit any power control commands. In other systems, for example, the mobile station in this system can independently adjust its transmission power and must send a clear power lock command. Locking the transmission power can make the measurement result more accurate, and will be more accurate than the measurement of a mobile station that has not locked the transmission power. However, if the transmission power is locked for a long period of time, it will cause unwanted signal attenuation between the mobile station and the base station connection. Therefore, although it is better to lock the transmission power during the measurement, if the lock time is too long to cause unwanted signal attenuation, the power lock procedure can be omitted.

Once the transmission power of the mobile station 370 is locked, the MTSO300 informs the BS2340 to identify and measure the uplink transmission 305 of the mobile station 370. According to the traditional time-sharing multiple proximity (TDMA) architecture, the transmission of the mobile station 370 can be identified by frequency, time slot color coding, synchronization characters, and related uplink transmissions. Since this embodiment adopts the TDMA transmission architecture, the mobile station 370 generally does not transmit in all time slots. Therefore, the BS2340 will only be notified to measure the signal 305 during the transmission of the mobile station 370. Therefore, the BS2340 will use information related to the mobile station 370 such as color coding and synchronization characters to identify the mobile station 370's uplink transmission.

According to purely exemplary embodiments, unless the mobile station 370 transmits at high power to avoid synchronization errors, the BS2 340 can limit its measurement function. If the synchronization fails, you can use the lower received signal strength setting preset in BS2 340, because the synchronization failure indicates that the signal strength from the mobile station 370 is very weak. Assuming that the synchronization failure is not due to interference caused by other base stations using the same frequency from surrounding cells, the weaker signal strength indicates that the base station 370 is unlikely to cause interference to the BS2 340.

Once BS2 340 has identified the transmission signal from mobile station 370, BS2340 can measure the time T ₁ The received signal strength of the mobile station 370. BS2340 can record signal 305 intensity measurement results and send this information to MTSO300. At the same time at time T ₁ MTSO 300 informs BS3 360 to identify and synchronize with mobile station 370s on-chain signal 315, and obtain a signal strength measurement result. Whats important is that BS3 360 does not have to be in T at the same time as BS2 340. ₁ The measurement, and the synchronization measurement is only because at time T ₁ Lock the power level of the mobile station. However, the measurement of BS2 340 must be performed at the same time as the measurement of BS1 350. Similarly, the measurement of BS3 360 must be performed at the same time as the measurement of BS1 350. At time t ₁ At this time, the mobile station 370 transmits to the BS1 350, the power level used by the mobile station 370 for transmission, and the power level currently received by the signal 345. If the power level of the mobile station 370 is controlled by the BS2 350, the BS2 350 can know the power level used by the mobile station 370 and does not need the mobile station to transmit its current power level to the BS2 350. Finally, the BS1 350 will report the current power level of the mobile station 370 for transmission, the carrier level of the BS1 350 currently transmitting the downlink signal 345, and the current received signal strength of the uplink signal 335. MTSO 300 collection time T ₁ All measurement results, and calculate the path loss estimation.

FIG. 4 shows an exemplary matrix constructed by the MTSO 300 using the aforementioned measurement results. The first column shows the measurement results reported by the mobile station 370 to the MTSO 300. Therefore, mobile station 370 will report time T ₁ Locked transmission output power at time, MS _TransBS1 , And the received signal strength from BS1 350 at time T1, MS _RSSIBS1 。

The second column in the table in Figure 4 represents the measurement results reported by BS1 350 to MTSO 300. BS1 350 report at time T ₁ The signal strength received from mobile station 370 at time, which is based on BS1 _RsSI335 Express. BS1 350 also reports the received signal strength from mobile station 380 and mobile station 390, and uses BS1 _RSSI365 And BS1 _RsSI375 Express. In addition, BS1 350 reports the power level used by mobile station 370. BS1 _POWER 。

The third column in the table in Figure 4 represents the measurement results reported by BS2340 to MTSO 300. The first column of the third column contains the transmission power from the mobile station 380, in terms of MS _TransBS2 Express. The third column of the third column represents time T ₁ The received signal strength of signal 305 from mobile station 370 at BS2 _RSSI305 Express. The fourth column of the third column contains the estimated value of BS2 340 used power, with BS2 _POWER Express.

The fourth column in the table in Figure 4 represents the measurement results reported by BS33 60 to MTSO 300. The first column of the fourth column contains the transmission power from the mobile station 390, with MS _TransBS3 Express. The third column of the fourth column represents time T ₁ The received signal strength of signal 315 from mobile station 370 at BS2 _RSSI315 Express. The fourth column of the fourth column contains the estimated value of BS3 360's power consumption, with BS3 _POWER Express.

FIG. 5 shows an example of the calculation result table created by the MTSO 300 using the measurement result report in FIG. 4. Therefore, the on-chain signal 335-PL from mobile station 370 to BS1 350 ₃₃₅ -The path loss, which can be used to transmit the power level of mobile station 370, MS _TransBS1 , Minus the power level received by BS1 350 from mobile station 370-BS1 _RSSI335 -Calculated. MTSO 300 also calculates the path loss between mobile station 370 and BS2 340. By adjusting the output power of mobile station 370, MS _TransBS1 , Minus the signal strength received by BS2 340 from mobile station 370-BS2 _RSSI305 . Similarly, for BS3 360, MTSO300 also calculates the path loss between mobile station 370 and BS3 360, by changing the output power of mobile station 370-MS _TranSBSl -Subtract the power level received by BS3 360 from mobile station 370-BS3 _RSSI315 。

In order to estimate the short-term CI value of BS1 350 downlink, MTSO 300 calculates the difference between the predicted power from BS2 340 and the path loss to BS2 340, the predicted power from BS3 360, and the path loss to BS3 360 The gap between and the sum of the two is (BS2 _POWER^－ PL ₃₀₅ )+(BS3 _power^－ PL ₃₁₅ ) ^o Then, the MTSO 300 divides the signal strength received by the mobile station 370 from the BS1 350 by the aforementioned sum, and the MS _RSSIBSl , As shown in the equation in the second column of the first column in Figure 5.

In order to determine the estimated short-term interference level during the uplink connection, MTSO300 uses the base station transmission power in the two cells of BS2 340 and BS3 360, and the relative path loss between the mobile station and BS1 350, that is, MS _Tr a _nsBS2 -PL ₃₆₅ And MS _TransBs3 -PL ₃₇₅^o MTSO 300 then adds the uplink interference measurement results to calculate the estimated short-term interference level of the uplink, that is, MS _TransBS2 -PL ₃₆₅ And MS _TransBS3 -PL ₃₇₅ 。

The estimated long-term average C/I value of the base station connected to the BS1 350 is shown in the fourth column of the first column in Figure 5. MTSO 300 calculates the estimated power used by base stations surrounding BS1350 and the difference between their relative path loss, BS2 _POwer^－ PL ₃₀₅ And BS3 _Power^－ PL ₃₁₅ . The aforementioned gaps are then added up to reach the interference level belonging to the downstream chain of BS1 350 cells. MTSO300 also calculates the carrier power by calculating the difference between the transmission output power of BS1 350 and the path loss of mobile station 370, that is, BS1 _POWer^－ PL ₃₃₅ . Then, the carrier measurement result of the downlink is divided by the interference measurement result of the downlink. MTSO 300 continues to calculate the CI value for a period of time and calculates the average value of CI to obtain the long-term estimated value of CI for the downstream chain.

The long-term estimated value of C/I on the chain of mobile station 370 and BS1350 is the last column in the first column of Figure 5. MTSO300 uses the difference between the transmission power of the base station in the BS2340 and BS3360 cells, and the relative path loss between the base station and BS1350, that is, the MS _TransBS2 -PL ₃₆₅ And MS _TransBS3 -PL ₃₇₅ . MTSO300 then adds the upper chain interference measurement results to calculate the estimated interference level on the chain, that is (MS _TransBS2 -PL ₃₆₅ ) And (MS _TranSBS3 -PL ₃₇₅ ). The carrier level from the mobile station 370 is divided by the estimated interference level to determine the C/I level. MTSO300 continues to calculate the CI value for a period of time and calculates the average value of CI to obtain the long-term estimated value of CI on the chain.

According to an exemplary embodiment, the MTSO 300 issues a measurement operation procedure, instructing the system to measure the typical path loss between two cells at a specified time of the day. The MTSO300 collects the measurement results and calculations of Figures 4 and 5 over a period of time to generate statistical results of the path loss between two cells at a specific time in a day. As described below, these elapsed time calculations can be used to appropriately adjust the frequency planning of the cellular system. It must be noted that the path loss estimation must be performed at the same time as the required signal and the interfered signal, for example: PL ₃₀₅ And PL ₃₃₅ Sampling time and signal strength of signal 345 and MS _TransBS1 , All at the same time. Through these synchronized measurements, an average path loss between different base stations and mobile stations that are interfered is obtained, and the system can determine the average path loss of the required signal, such as signal 345, to a base station. Moreover, when a base station uses a certain power level, the system can also determine the average path loss between the mobile station and different surrounding base stations.

With the path loss value of all cells to other cells, MTSO300 can determine the interference caused by a specific cell to other cells according to the frequency allocated to different cells. For example, Figure 6 shows an example matrix created by MTSO300, which illustrates seven base stations (BS1, BS2, BS1, BS2, BS3, BS4, BS5, BS6, BS7) between the path loss value, the arrangement of these cells, please refer to Figure 2. Therefore, if the path loss from cell A to cell B (that is, the first column in the second column of the table in Figure 6) is large enough, MTSO300 can be configured with the same frequency for cell A and cell B, and the transmission of cell A The co-channel interference of the transmission to cell B is minimal. Conversely, if the path loss from cell A to cell B is small, the system operator can determine adjacent channel interference, that is, cell A uses the first frequency for transmission, and cell B uses the second frequency adjacent to the first frequency for transmission , Such adjacent channel transmission will cause unacceptable voice quality. Because the average estimated path loss from a base station in cell A to a mobile station in cell B is calculated separately from the average estimated path loss from a mobile station in cell A to the base station in cell B. The cellular system operator needs two path loss tables, one for the uplink path loss and one for the downlink path loss, similar to the table in Figure 6, in order to effectively configure the frequency for the cell and adjust the base station and The transmission power level of the mobile station. Because the double distance between the uplink and downlink frequencies of a connection is fixed, when the system configures the uplink and downlink frequencies to be paired with a base station, the path loss table of the uplink and the downlink must be considered at the same time.

Because the path loss between all surrounding cells is known, that is, they have been calculated through the above calculations. The system can determine whether a specific frequency assigned to a cell will cause a third cell to avoid interference with another cell. The interference of individual cells does not require frequency adjustment in the system. For example, if the system determines that a transmission from cell A will interfere with the transmission signal from cell B, the system will automatically configure a new frequency for cell A according to the previously described C/I ratio, so that The interference of cell B is within an acceptable range. Furthermore, this system can calculate before the implementation of the new frequency, and according to the calculated path loss value, decide whether the newly configured frequency in cell A will cause unacceptable interference to any surrounding cells, such as: cell CG.

7A and 7B show examples of channel group assignment before and after channel re-assignment. The channel designation shown in FIG. 7A is that BS1 350 uses channels 5 and 6 for co-channel transmission with BS2 340, and uses channels 1 and 5 for co-channel transmission with BS3360. If after the system performs the aforementioned measurement and calculation, it is found that channel 5 in BS1 350 suffers too much co-channel interference, the system will use a matrix, similar to the matrix shown in Figure 6, to decide to use another one. Channels that cause unacceptable interference. In this way, the system can determine that even if BS3360 is transmitting on channel 11, the co-channel interference of BS3360 will not cause unacceptable interference to BS1350. Therefore, the system can determine whether the channel has an acceptable C/I level before channel assignment.

The present invention can also use the path loss value and the C/I ratio to determine the transmission power level, so as to determine the interference caused by using the transmission power level. For example, the system can determine the unacceptable connection quality caused by using a certain frequency between a mobile station and a base station. However, this system can determine whether to improve the connection quality by increasing the power level of the carrier signal.

Furthermore, this system can determine whether the new power level will cause unacceptable interference between surrounding cell transmissions before implementing the new power level in the cellular system. The system can also determine if the power level used by the first cell is reduced, whether the first cell uses the reduced power level, will reduce the interference to the second cell.

FIG. 8 shows an exemplary method according to this invention, whereby in step 810, the system can determine whether there is a mobile station for transmission in the target cell, such as a cell containing BS1350. If there is a mobile station in transmission, the system will make the mobile station lock its transmission power, report its power level and the measured signal strength received by the base station, and send it to the system in step 820. As mentioned above, if the transmission power is locked for a long time enough to cause unwanted quality degradation, step 820 can be omitted. In addition, when the base station is connected to the mobile station, it starts to collect the measurement results of the received signal from the mobile station. In step 830, surrounding base stations use the aforementioned information to synchronize and identify mobile station transmissions. In step 840, the received signal strength of the base station is measured and reported to the system. The system calculates the path loss in step 850. In step 860, if a base station configures an adjacent or co-channel for transmission to a mobile station, the system uses the current path loss value to estimate the current C/I downlink of a mobile station. It should be noted that for the purpose of non-real-time channel planning, the cumulative average estimated path loss value will be used to estimate the average C/I level of the downlink and uplink, and if the frequency is an interfered base station If used, this C/I level changes the short-term prediction value for the connection.

Although the TDMA system and configuration frequency are used in the above-mentioned specific embodiments, those skilled in the art will understand that this system can also be applied to the CDMA system and its coding configuration in the same way. For example, in a CDMA system, the base station can identify the transmission of the mobile station by the code or combination of codes used to expand the data signal (for example, channel coding and scrambling code). In addition, although some CDMA systems use multiple frequency bands (for example, WCDMA uses a specific 5MHZ band in 60 MHz), when identifying mobile station transmission, it is also necessary to identify the specific frequency band used by the mobile station. Furthermore, because the CDMA system overlaps many transmission signals in the same frequency band, the system according to this invention can be used to determine whether the same coding configuration, such as a scrambling code, will cause one or more surrounding base stations to be unavailable. Acceptable interference level.

In a CDMA system, the mobile station basically measures the common control channel or the pilot channel broadcast by the base station, and the common control channel basically uses a fixed high power. Although different base stations in an area use different scrambling codes, the mobile station can also use the downlink scrambling code to confirm that it is the correct base station for the measurement. Therefore, the mobile station can provide an improved path loss estimate to the system, that is, the source of the signal strength measurement, which can be identified by detecting the scrambling code. Some CDMA systems often change the transmission power level of a mobile station, making it possible to lock the transmission power in these CDMA systems. Therefore, the enhanced path loss estimation procedure in the CDMA system must be able to transmit without locking the mobile station. Operate under power.

FIG. 9 shows a specific embodiment of the present invention in a CDMA system. The channel coding, scrambling code, and power level used in cell A are described in step 905. In step 910, the mobile station in cell B is instructed to search for transmissions using a specific channel and scrambling code. This mobile station synchronizes and recognizes with the base station in step 915. After the mobile station is synchronized with the transmission, in step 920, the mobile station measures and reports the signal strength of the transmission, the average power level during the measurement, and the average signal level received from the cell A. In step 925, the path loss between cell A and cell B is calculated by the mobile station if the mobile station has power level information; if the mobile station does not have the aforementioned information, it can also be calculated by the system itself. In step 930, the C/I value of the downlink can be calculated when the base station uses different power levels, and the C/I value of the uplink can be calculated when the mobile station uses different power levels. calculate.

The above-mentioned procedure can be used in the CDMA system to determine the list of neighboring cells. The adjacent cell list is defined by a cellular system and is used to assist in the execution of handover, handover evaluation and cell reselection. Therefore, the above-mentioned enhanced path loss measurement method and selection technology are used to select specific cells as neighbor cells in the mobile station neighbor cell list, so that the system can easily remove those that may cause unwanted carrier interference from the list. Than the cells. For example, a low path loss value between cells means that a cell must be defined as a neighboring cell, while a high path loss value means that a cell cannot be defined as a neighboring cell. The adjacent cell selection method is also applied in the TDMA system, and the method used is described in the embodiments of the present invention and the TDMA system.

The present invention has been illustrated by specific embodiments, but is not limited thereto. Those skilled in the art can accept amendments and changes without violating the spirit and scope of the scope of the attached patent application.