KR20020074823A - Power control method of checking received data error in tdd system - Google Patents

Abstract

PURPOSE: A method for controlling power according to the existence of a received data error in a TDD(Time Division Duplex) system is provided to execute the power control of a TDD system more efficiently according to the error status of received data. CONSTITUTION: If data, such as an initial coding rate, an initial transmit power value, etc., are transmitted to a receiving side from a transmitting side, a TDD system checks whether an error exists in the transmitted data. In case that an error is contained in the transmitted data, the TDD system varies the transmit power of the receiving side as much as Pa dB. If no error exists in the transmitted data, the TDD system varies the transmit power of the receiving side as much as Pb dB.

Description

Power control method according to receiving data error in TV system {POWER CONTROL METHOD OF CHECKING RECEIVED DATA ERROR IN TDD SYSTEM}

The present invention relates to a time division duplex (TDD) system, and more particularly, to a power control method of a TDD system by checking whether a received data error exists.

More specifically, in order to control the power of the present invention, data is transmitted from a transmitting side (base station or mobile station) to a receiving side (mobile station or base station) at an initial coding rate and an initial transmission power value, and whether or not an error of the transmitted data is detected. Various methods for determining the transmission power of a mobile station or a base station by checking are proposed. 1) A method of varying a transmission power change value according to the presence or absence of a received data error, and 2) a transmission power control (TPC) when there is no error in the received data. 3) A method of determining a transmit power value by checking a bit to raise or lower a power value, 3) A method of performing open loop power control when there is no error in the received data, and 4) All of the above data when there is an error in the received data. A method of determining the transmit power value by checking the TPC bit up or down the power value, respectively; Relates to a method for performing open loop power control does not consider the multiple.

In general, in the case of TDD, since both uplink and downlink share the same frequency, bidirectional channels are regarded as similar. Therefore, when the channel condition in one direction is not good, the other channel condition is also not good at the same time. Therefore, the present invention proposes various power control schemes using the characteristics of the TDD system.

First, the TDD system will be described. A full duplex system for bidirectional communication of uplink (UPLINK) and downlink (DOWNLINK) may be divided into a frequency division duplex (FDD) and a time division duplex (TDD).

In the above, FDD uses different frequencies for uplink and downlink, whereas TDD uses the same frequency for uplink and downlink. In TDD, uplink and downlink are divided into different times. Therefore, in a communication system employing TDD, uplink and downlink experience a relatively similar channel environment.

Second, the general form of power control needs and methods employed in the system will be described.

Close and fast power control is the most important element in a CDMA system, because without close and fast power control, one overpowered mobile station can block the entire cell.

The power control is a technique for adjusting the transmission power of the mobile station and the base station to an appropriate level so that the system performance can be maintained even at the lowest possible power level of radiated radio waves.

There are two types of power control, forward power control and reverse power control. The forward power control is to control the transmission power of the base station for the purpose of reducing interference from neighboring cells.

On the other hand, the reverse power control is to adjust the transmission power of the mobile station to solve the near-far interference problem that occurs because all mobile stations in the cell use the same frequency band.

In general, considering the path loss occurring in the wireless section between the base station and the mobile station in a mobile communication environment, it is known that the magnitude of electromagnetic waves with distance decreases. Therefore, assuming that the output of the mobile station is constant, the received power of the mobile station far away from the base station (mobile station near the cell boundary) is received by the base station in a much smaller size than the mobile station near the base station.

In such a case, the CDMA system is maximized when the channel capacity of the CDMA is the same as the reception power of each mobile station received by the base station. Thus, when the power difference is severe, the capacity of the CDMA is severely reduced. In other words, no matter how far the mobile station is despread due to the interference by the mobile station, demodulation is impossible because a much smaller signal is received than the interference.

This is called the near and far problem.

In order to overcome this short range / distance problem, the transmission power of the mobile station should be adjusted so that the reception power of each mobile station received at the base station is constant. That is, mobile stations near the base station should transmit with low transmission power and remote stations with high power. This is called 'power control', and a very sophisticated power control system must be implemented in a CDMA system.

Therefore, the best solution in terms of maximum capacity is always to make the bit power received from all mobile stations the same.

In this way, the difference between the signal power received by the base station according to the distance between the mobile station and the base station causes a very large short distance / distance problem and fading for each mobile station. In order to overcome this environment and maximize the subscriber capacity, the operating range of the reverse link is very high. Large, sophisticated power control is needed.

In order to maximize the capacity in a CDMA system, the signal of each mobile station should be received at the base station with a minimum signal to interference ratio (SIR). If the transmission power of the mobile station is low, the call quality is low, and if it is high, the call quality of the mobile station is good, but it interferes with other mobile stations using the same channel, resulting in poor call quality of other subscribers. Therefore, in order for all subscribers to maintain good call quality and maximize the capacity, each mobile station should be controlled so that the reception power of each mobile station received by the base station is the same, and the size of the subscriber has the minimum signal-to-interference ratio.

As described above, such power control may be described as reverse link power control and forward link power control.

Reverse link power control includes reverse open loop power control and reverse closed loop power control.

The mobile station cannot accurately predict the path loss of the reverse channel due to mismatch of the transceiver, different fading characteristics due to different frequency bands, and differences between the forward and reverse channels. To correct this error, each mobile station adjusts its output by a slow power control command transmitted from the base station to the forward channel.

The base station monitors the state of the reverse channel to obtain error correction information, compares it with a predetermined value and instructs the mobile station to increase or decrease the output according to the result. In this way, the base station adjusts the power of the reverse channel of all mobile stations to simultaneously satisfy the appropriate call quality and maximize the capacity.

Meanwhile, forward link power control includes forward open loop power control and forward closed loop power control.

If the forward link is bad, increase the transmit power of the base station so that the call quality on this link does not fall below the standard. In this example, if the mobile station is located in a region where the path loss between the current base station and the neighboring base station is similar in a cell boundary region where two or three cells overlap (or the call channel is subject to extreme path loss due to fading and strong interference sources). The mobile station needs to increase base station transmission power due to deterioration in call quality due to interference by other nearby base stations.

On the contrary, when the mobile station is located in a region where the signal-to-interference ratio is very good near the base station, the amount of interference to other mobile stations can be reduced by reducing the transmission power of the base station so that there is no significant effect on the call quality for the call channel.

Each power control is briefly summarized below.

1. Reverse open loop power control

Each mobile station measures the total received power of the total CDMA channel of the designated base station. By monitoring the total power without using the demodulated signal, it is possible to quickly estimate without knowing the synchronization time, base station name, and path loss.

The mobile station transmits the average output calculated in the initial search.

In the subsequent connection discovery procedure, the transmission increments the output until there is a corresponding reply. After initializing the transmission of the reverse communication channel to the average transmission power of the initial reverse communication channel, the process returns to closed loop power control when the output control bit is received from the base station.

2. Reverse closed loop power control

The power control procedure consists of a procedure of measuring an Eb / No prediction value at a base station at a predetermined time interval, and transmitting a command to the mobile station at each time interval in comparison with a predetermined limit Eb / No value.

Here, the variation of the average output for one power control bit is 1dB. The mobile station adjusts the power of the closed loop over a range of ± 24 dB above the open loop measurement, the upper limit being determined by the maximum output.

3.Forward Open Loop Power Control

The forward open loop power control procedure predicts forward loss based on the received power of the mobile station when the base station connects, adjusts the initial digital gain of each talk channel with the predicted value, and the base station initially allocates a reference gain for each channel. .

4.Forward Closed Loop Power Control

In forward closed loop power control, the mobile station measures the quality of the forward call channel frame and reports it periodically to the base station. The base station compares this value with a predetermined value and then adjusts the output of the forward call channel. If this occurs above the specified reference value, this value is automatically reported to the base station, and the base station raises the output allocated to the channel. All mobile stations maintain the call quality of the forward call channel through this procedure, and the base station has a separate function to prevent the power amplification from reaching saturation.

The main power control method in the CDMA system is as closed loop power control described above, and is illustrated in FIG.

Figure 1 shows closed loop power control in CDMA. When mobile station MS1 and another mobile station MS2 operate with different spreading codes at the same frequency, mobile station MS1 at the edge of cell is 70dB more than mobile station MS2 near base station BS. Experience a degree of path loss. If there is no mechanism for power control at the same level at the base station BS for the mobile station MS1 and the mobile station MS2, the mobile station MS2 close to the base station BS is located at the cell edge, away from the base station BS. Maintaining more power than (MS1) to block a large part of the cell. This is called the near and far problem described above.

The short-range / far-range problem occurs because the CDMA system is basically a system whose channel capacity is determined by interference. It is an inherent problem of the CDMA system in which the propagation characteristics of electromagnetic waves affect the channel capacity of the CDMA system.

1, in closed loop power control of the uplink 101, the base station BS frequently measures the received signal-to-interference ratio (SIR) and compares it with the target SIR. If the measured SIR is higher than the target SIR, the base station will instruct the mobile station to lower the power, and if it is too low, it will raise the power. This series of measurements, commands, and responses is performed 1500 times per second (1.5 kHz) for each mobile station, occurring faster than any possible pathloss change and even faster than rapid Rayleigh fading at low to medium speeds. . Thus, the power inequality between all uplink signals received at the base station is eliminated.

In the same manner, it was described above that closed loop power control occurs in the downlink 102. In the downlink, since there is 1: n (n ≧ 2) communication, there is no near / far problem. All signals in one cell are generated from one base station to all mobile stations, with provision of the lowest additional power for the mobile stations at the cell boundary. This is because it increases other cell interference. There is also a need to enhance the signal weakened by Rayleigh fading at low speed in the downlink. This is because interleaving and error correction coding techniques do not work efficiently.

As mentioned earlier, fast closed loop power control is called internal loop power control and is an essential operation due to uplink near / far problems in CDMA systems. Fast closed loop power control performs operations in the uplink and downlink at as fast as 1500 Hz based on one command per slot.

For reference, GSM supports slow power control (2Hz) and IS95 performs fast power control of 800Hz only on the uplink. The default step size for fast power control is 1dB. Additionally, a plurality of step sizes may be used, and smaller step sizes may be modified. A small step size has the same effect as 1dB working every two slots, eventually 0.5dB. In practice, operating below 1dB creates complexity problems. Fast power control gains even more in the following situations. It is the case that there are few multipaths available, such as ITU Pedestrian A Channel, at the required Eb / No rather than the transmission power at a slower moving speed than a fast moving speed.

On the other hand, as described above, in terms of near / far problems or maximum capacity, there is an open loop power control method, which estimates a path loss using a downlink bit control signal. I think that is somewhat inaccurate.

This is because fast fading has no correlation between uplink and downlink due to frequency band spacing. However, open loop power control is used to make an approximate initial power setting of the mobile station at the time the call is opened.

Open loop power control is performed before initiating the RACH or CPCH transmission. It is not very accurate because it is difficult to measure large power movements in the mobile station. The requirement for accuracy is specified to within ± 9dB.

2 shows external loop power control. External loop power control is to modify the target SIR with the goal of a certain level of quality defined by the requirements of individual radio links and the bit error rate (BER) and frame error rate (FER) at the base station (BS). The best solution is to operate the target SIR value around the minimum value to meet the required target quality.

Hereinafter, a power control method in a general mobile communication system considered in the related art of the present invention will be described.

1. General external loop power control (Fig. 3)

External loop power control is necessary to maintain the required communication quality by setting the target value (target SIR) of fast power control.

The flow of external loop power control is as follows.

The receiver periodically measures the average error rate of the received data. The reception quality is compared with the target quality and the target SIR is decreased or increased depending on the comparison result. That is, when the error rate is lower than the error rate required by the system, the target SIR value is lowered. On the other hand, if the error rate is higher than the error rate required by the system, the target SIR value is increased.

For reference, external loop power control is required for both uplink and downlink links. This is because fast power control is performed on both links.

2.open loop power control

Open loop power control is performed through channel estimation according to the characteristics of the received signal. Although the transmission power is adjusted without a feedback command, there is an advantage that it is performed quickly, but it is relatively inaccurate. Useful for shadow fading.

For example, in the 3GPP TDD scheme, a transmission power value of an uplink dedicated channel according to the open loop power control scheme is represented by the following equation.

P _{UL =} aL _P-CCPCH + (1-a) L ₀ + I _BTS + SIR _TARGET + Constant value

In the above, P _UL : transmit power value (dBm) according to each uplink dedicated channel

L _P-CCPCH: Path Loss Measurement (dB)

L ₀ : Long term average path loss (dB)

I _BTS : Interference signal power level in cell receiver (dBm)

a: Weight in consideration of path loss measurement error

SIR _TARGET : Target SIR (dB) controlled by external loop power control

Constant value: The value controlled by the operator.

3. Closed loop power control

Closed loop power control is a method of adjusting the transmit power of the transmitter according to the feedback information transmitted from the receiver. The receiver measures the SIR of the received signal, and transmits a power down command if the measured value is higher than the target SIR, and sends a power up command to the transmitter if the measured value is lower than the target SIR. In 3GPP, the TPC (Transmit Power Control) bit is used as this feedback command.

However, conventional fast closed-loop power control can perform poorly than slow open-loop power control for reasons such as SIR estimation error, power control signaling error, and power control loop time delay.

Accordingly, in the present invention, a method of more efficiently controlling power according to a received data error in transmission power control required for each link in order to maximize the capacity of UPLINK / DOWNLINK that should support a high data rate in a TDD system. Suggest.

1 is a view for explaining a closed loop power control method in a CDMA system

2 is a view for explaining an external loop power control method in a CDMA system;

3 is a diagram illustrating a procedure of a general external loop power control method.

Figure 4 is a first embodiment of a power control method according to the received data error check

5 illustrates a second embodiment of the present invention in which closed loop power control is performed when there is no error in received data.

6 is a third embodiment of the present invention in which open loop power control is performed when there is no error in received data.

7 is a fourth embodiment of the present invention combining closed loop power control with power control according to a data error check.

8 is a fifth embodiment of the present invention combining open loop power control with power control in accordance with a data error check.

In accordance with another aspect of the present invention, a power control method includes transmitting data through an uplink channel or a downlink channel; And checking the transmission error of the transmitted data to change the transmission power of a downlink or uplink channel (ie, a channel in a direction different from the channel in which the data is transmitted).

In addition, the present invention preferably further comprises the step of varying the transmission power by checking the transmission power control (TPC) bit when there is no error in the transmitted data.

Other objects and features of the present invention will become apparent from the detailed description of the embodiments with reference to the accompanying drawings.

Hereinafter, a power control method according to a reception data error in a TDD system according to the present invention will be described with reference to the accompanying drawings.

First, the present invention proposes a power control method according to whether or not a received data error in a TDD system, a method of determining whether the received data error or not, BER (Bit Error Rate), FER (Frame Error Rate) or CRC (Cyclic Redundancy Check) (3Bit) check method can be used.

In general, in the case of TDD, since the uplink and the downlink share the same frequency, bidirectional channels are regarded as similar. Therefore, if the channel condition in one direction is not good, the other channel condition is also not good at the same time. Therefore, the present invention utilizes the characteristics of the TDD system, and thus the error of data transmitted from the transmitting side (base station or mobile station) in bidirectional communication is improved. The transmission power adjusting method of the receiving side (mobile station or base station) in consideration of whether or not will be described.

4 is a first embodiment of a power control method according to a received data error check.

As shown in the figure, data is transmitted from the transmitting side, i.e., the base station or the terminal, to the receiving side, i.e., the mobile station or the base station, at an initial coding rate and an initial transmission power value. Varies the transmit power.

If an error occurs in the received data, the transmit power of the receiving side is changed by PadB, and when no error occurs, the power is changed by Pb dB.

Where Pa and Pb are positive, zero, or negative. Generally Pa is a positive integer and Pb is a negative number.

5 is a second embodiment of the power control method in which closed loop power control is performed when there is no error in the received data.

As shown in the figure, data is transmitted from the transmitting side, i.e., the base station or the terminal, to the receiving side, i.e., the mobile station or the base station, at an initial coding rate and an initial transmission power value. It is different from FIG. 4 in that the transmission power of the transmitter is changed. In particular, when there is no error in the transmitted data, the transmission power is changed by checking the transmission power control (TPC) bit. In more detail, it can be seen that closed loop power control is performed when there is no error in the received data. However, if there is an error in the received data, similar to FIG. 4, the power of the receiver is changed by P0 dB. Where P0, P1, and P2 have positive, zero, or negative numbers. In general, P0 is a positive integer.

6 is a third embodiment of the power control method in which open loop power control is performed when there is no error in the received data.

As shown in the figure, data is transmitted from the transmitting side, i.e., the base station or the terminal, to the receiving side, i.e., the mobile station or the base station, at an initial coding rate and an initial transmission power value. In this case, the open-loop power control is performed when there is no error in the transmitted data.

If an error occurs in the received data, the transmit power of the receiver is changed by P0 dB in the same manner as in FIG. 5, and if the error does not occur in the received data, open-loop power control is performed to improve the transmit power. Decide Where P0 is positive or 0, negative, but generally P0 is a positive integer.

In the open loop power control, the transmission power P for bidirectional transmission at the receiving side is determined in consideration of the following.

The transmit power value on the receiving side is P = a * L _{1 +} (1-a) * L ₀ + I _BTS + b * SIR _TARGET + (1-b) * P _{no_error} + Constant value, where a is a weight value considering the path loss measurement error, L ₁ is the path loss measurement value (dB), L ₀ is the long term average path loss value (dB), and I _BTS is the cell receiver. Interference signal power level in dBm, b is a weight considering the power control method according to the present invention, SIR _TARGET is Target SIR (dB) controlled by external loop power control, P _{no_error} is the value that adjusts the transmission power (dB) when there is no error in the received data, and Constant value is the value that is adjusted by the operator.

7 is a fourth embodiment of a power control method in which closed loop power control is combined with power control according to a data error check.

As shown in the figure, data is transmitted from the transmitting side, i.e., the base station or the terminal, to the receiving side, i.e., the mobile station or the base station, at an initial coding rate and an initial transmission power value. 5 is different from FIG. 5 in that the transmission power is varied by checking the transmission power control (TPC) bit regardless of an error in the transmitted data. In more detail, it can be seen that the closed-loop power control method checks and feeds back the TPC command transmitted from the transmitter regardless of the received data error. Therefore, regardless of the error of the receiver, the TPC bits are checked to change the transmit power by P1, P2, P3, and P4, respectively. Where P1, P2, P3, and P4 have a positive or zero or negative number. Generally P1 is a positive integer.

8 is a fifth embodiment of a power control method in which open loop power control is combined with power control according to a data error check.

As shown in the figure, the data transmitted from the transmitting side is received to check whether there is an error, and the transmit power P of the receiving side is determined as follows.

Open loop power control is performed even if there is an error in the transmitted data, and at this time, the transmit power value of the receiver is P = a * L _{1 +} (1-a) * L ₀ + I _BTS + b * SIR _TARGET + (1-b) * (k _{no_error} * P _{no_error} + k _error * P _error ) + Constant value, where a is a weight considering the path loss measurement error, L ₁ is the path loss measurement value (dB), L ₀ is the long term average path loss value (dB), and I _BTS is the cell Interference signal power level (dBm) in the receiver, b is a weight considering the power control method according to the present invention, SIR _TARGET is Target SIR (dB) controlled by the external loop power control, P _{no_error} is the value to adjust the transmission power when there is no error in the received data (dB), Constant value is the value adjusted by the operator, k _error is 1 if there is an _error in the received data, 0, k if there is no error _{no_error} is 0 if there is an error in the received data, 1, if there is no error. P _error indicates the value (dB) that adjusts the transmit power when there is an _error in the received data.

As described above, the system proposed in the present invention transmits data at an initial encoding rate and an initial transmit power value from a transmitting side (base station or mobile station) to a receiving side (mobile station or base station) for power control of the present invention. Proposed various methods for determining the transmission power of the mobile station or the base station by checking whether the transmitted data is error, 1) a method of changing the transmission power change value according to the presence or absence of the received data error, 2) there is no error in the received data In this case, check the transmission power control (TPC) bit to check the transmission power value by UP or DOWN and 3) open loop power control when there is no error in received data. 4) A method of determining the transmit power value by checking the TPC bit in the presence or absence of a received data error, up or down the power value respectively, and 5) Receive data. The present invention relates to a method for performing open loop power control with or without an error, depending on whether or not a data error exists.

Although the preferred embodiment of the present invention has been described above, the present invention may use various changes, modifications, and equivalents. It is clear that the present invention can be applied in the same manner by appropriately modifying the above embodiments.

Accordingly, the above description does not limit the scope of the invention as defined by the limitations of the following claims.

Existing fast closed loop power control may show worse performance than slow open loop power control for reasons such as SIR estimation error, power control signaling error, and power control loop time delay, but the error after checking the received data error as in the present invention. Power control of the TDD system can be efficiently performed by controlling the transmit power of the receiving side differently depending on the presence or absence.

Claims (5)

In a TDD mobile communication system, Transmitting data in an uplink or downlink channel; Checking the reception error of the transmitted data to vary transmission power of a downlink or uplink channel (i.e., a channel in a direction different from the channel to which the data is transmitted). Power control method according to whether or not. The method of claim 1, further comprising: checking transmission power control (TPC) bits to vary transmission power when there is no error in the transmitted data. 2. The method of claim 1, wherein when there is no error in the transmitted data, open-loop power control is performed, wherein the transmit power value at the receiving end is P = a * L _{1 +} (1-a) * L ₀ + I _BTS + b * SIR _TARGET + (1-b) * P _{no_error} + Constant value, where a is a weight value considering the path loss measurement error, L ₁ is the path loss measurement value (dB), L ₀ is the long term average path loss value (dB), and I _BTS is the cell receiver. Interference signal power level in dBm, b is a weight considering the power control method according to the present invention, SIR _TARGET is Target SIR (dB) controlled by external loop power control, P _{no_error} is a value (dB) for adjusting the transmission power when there is no error in the received data, Constant value is a power control method according to the received data error, characterized in that the value is adjusted by the operator. 3. The method of claim 2, further comprising the step of varying the transmission power by checking a transmission power control (TPC) bit even when there is an error in the transmitted data. 4. The method of claim 3, wherein open loop power control is performed even when there is an error in the transmitted data, wherein the transmit power value at the receiving end is P = a * L _{1 +} (1-a) * L ₀ + I _BTS + b * SIR _TARGET + (1-b) * (k _{no_error} * P _{no_error} + k _error * P _error ) + Constant value, where a is a weight considering the path loss measurement error, L ₁ is the path loss measurement value (dB), L ₀ is the long term average path loss value (dB), and I _BTS is the cell Interference signal power level (dBm) in the receiver, b is a weight considering the power control method according to the present invention, SIR _TARGET is Target SIR (dB) controlled by the external loop power control, P _{no_error} is the value to adjust the transmission power when there is no error in the received data (dB), Constant value is the value adjusted by the operator, k _error is 1 if there is an _error in the received data, 0, k if there is no error _{no_error} is 0 if there is an error in the received data, 1, if there is no error. P _error is a power control method according to the received data error, characterized in that for indicating the value (dB) to adjust the transmission power when there is an error in the received data.