KR100745276B1 - Blind type adaptive power control method according to ack/nak in arq system - Google Patents

Abstract

The present invention relates to a blind type adaptive power control method using ACK / NAK in a hybrid ARQ system.

According to the present invention, upon initial transmission from a transmitting side (base station) to a receiving side (mobile station) for a given packet, packet transmission is performed by selecting the highest coding rate and the lowest transmitting power. The receiving side receives the packet and compares the reception quality with the target quality. As a result of this comparison, when the reception quality is lower than the target quality, the reception side returns a no acknowledgment (NAK) to the transmitter. The transmitting side receiving the NAK response retransmits the packet of the lowered code rate with increased power while lowering the code rate. When the acknowledgment (ACK) response is received from the receiver as a result of the quality comparison, the transmitter performs packet transmission with a transmission power lowered in encoding rate and initialized to initial power. By repeating the above process, when the probability of bit error is high, the transmission power gradually increases with the number of retransmissions, thereby increasing the reliability (reception probability) of data transmission.

CDMA, Power Control, ARQ

Description

BLIND TYPE ADAPTIVE POWER CONTROL METHOD ACCORDING TO ACK / NAK IN ARQ SYSTEM}

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;

4 illustrates a receiving side (mobile station) control procedure of adaptive power control combined with a hybrid ARQ;

5 is a diagram illustrating a transmitting side (base station) control procedure of adaptive power control combined with a hybrid ARQ;

The present invention relates to a power control method in a hybrid ARQ system (Hybrid Automatic Repeat reQuest System), blind type adaptive using the response information (ACK / NAK) sent to the transmitter according to the result of determining the quality of the received signal at the receiver side It relates to a power control method.                         

More specifically, in the hybrid ARQ system, when there is a packet retransmission request (NAK response) from the receiver to the transmitter, the receiver does not need a separate control signal or control channel in the uplink from the receiver to the base station. The present invention relates to an adaptive power control method for improving performance of a system by controlling a transmitter to perform a predetermined type of power control (gradual increase control of transmission power) according to a transmitted retransmission (NAK) request.

First, a description will be given of a general power control method employed in a CDMA system.

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.

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.

As such, near field / distance problem with large difference in signal power received by the base station according to the distance between the mobile station and the base station occurs, and fading occurs for each mobile station. In order to overcome this environment and maximize subscriber capacity, the operating range is very different in the reverse link. 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.

Such power control can 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.

On the other hand, 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 transmission power of the base station 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.

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 assigns 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 described above as closed loop power control, 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 edge of the cell, away from the base station BS. Maintaining more power than mobile station MS1 blocks a large portion 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.

In FIG. 1, in the 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 measurement SIR is higher than the target SIR, the base station will command the mobile to lower the power, and if it is too low, it will command the power up. 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 view of short-range / far-range problem or maximum capacity, there is an open loop power control method, which is an approximation of path loss using a downlink bit control signal. I think that is somewhat inaccurate.

The reason is that fast fading has no correlation between the uplink and downlink due to the separation of the frequency bands. 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 (open loop power control). External loop power control is to modify the target SIR with the goal of a separate radio link requirement at the base station (BS) and a level of quality defined by BER and FER. The best solution is to operate the target SIR value around the minimum value to meet the required target quality.

3 shows a general external loop power control procedure.

The reception quality is compared with the target quality and the target SIR is decreased or increased depending on the comparison result.

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

Outer loop power control is required for both uplink and downlink links. This is because fast power control is performed on both links.

For reference, external loop power control is only used on the uplink in IS-95 systems. This is because there is no fast power control in the downlink. The frequency of fast power control is 1.5kHz and the frequency of external loop power control is 10-100Hz. Network-based downlink outer loop power control increases the signaling load between the mobile station and the radio network controller (RNC) and causes a time delay in this regard. Therefore, mobile station based external loop power control is used in WCDMA.

Existing 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. In particular, in order to maximize the capacity of the downlink that must support a high data rate in a CDMA system, transmission power control required for each link must be performed.

The present invention proposes a blind power control method using ACK / NAK in a hybrid ARQ system as a power control method combining a hybrid ARQ technique and adaptive power control in a wireless channel.

In the hybrid ARQ system, when there is a packet retransmission request (NAK response) from the receiver to the transmitter, the retransmission request is transmitted without the need for a separate control signal or control channel in an uplink from the receiver to the base station. According to the present invention, an adaptive power control method is proposed to improve performance of a system by controlling a transmitter to perform a predetermined type of power control (gradual increase control of transmission power).

The power control method according to the present invention comprises the steps of: transmitting data at an initial coding rate and an initial transmission power value from a transmitting side to a receiving side in an ARQ system; from the receiving side according to a result of receiving the transmitted data and determining its quality Receiving a retransmission (NAK) request signal to a transmitting side, increasing the transmission power with a decrease in the coding rate in accordance with the retransmission (NAK) request to perform data retransmission at this reduced coding rate and increased transmission power; The adaptive power control method of the blind type using ACK / NAK in an ARQ system characterized in that comprises a.

The power control method of the present invention is characterized in that the transmission power is initialized when an acknowledgment (ACK) signal is received according to the result of determining the reception quality.

In addition, the power control method of the present invention, if the coding rate reduction for the retransmission is supported up to the source coding rate (Source Coding Rate), the retransmission starts from the highest coding rate, at this time initialize or continue the transmission power It is characterized by increasing.

In addition, the power control method of the present invention, if the code rate reduction for the retransmission is supported up to the original code rate, the retransmission is continued at the lowest code rate, at this time, the transmission power is maintained or continuously increased It is done.

In addition, the power control method of the present invention, gradually increasing the target power value of the signal while the data retransmission according to the retransmission (NAK) request and to perform the power control based on the target value according to the outer loop power control It features.

An adaptive power control method in the ARQ system of the present invention made as described above will be described.

First, a hybrid ARQ system to which the adaptive power control scheme of the present invention is applied will be described.

Hybrid ARQ system aims to increase system stability and improve performance by combining general ARQ method that detects error of received signal and requires retransmission to transmitter and error correction channel coding method to overcome channel degradation. System.

The coding rate of the channel code transmitted in the hybrid ARQ system is punched at the source coding rate, and as the retransmission is repeated, the coding rate is decreased to increase the reliability of the signal. The hybrid ARQ scheme, which operates adaptively according to the channel environment, is essential to a system for providing a multimedia service.

This hybrid ARQ scheme is based on an adaptive error correction scheme, in which the number of surplus bits for protecting data bits against channel degradation gradually increases during retransmission. Depending on the ARQ scheme employed, 'stop and wait', 'go back N', and 'selective repeat' protocol schemes may be employed, and the data packet of length L has n information bits, np parity bits, and m '0's. It consists of a tail bit.

In this case, the data packet is denoted by c0, and the original code rate of the encoder is 1 / h. The coded bits are punctured periodically according to an optimal puncturing pattern, and as a result, an RCP code may be obtained. When the coding rate of the RCP code is Rk, k ≥ 1 and Rk> Rk + 1. Incremental code words that can be represented by Ck have code bits included in codewords of Rk code rate without being included in codewords of high code rate. Incremental codewords are interleaved and transmitted over the channel.

In the hybrid ARQ system, signal transmission is initially started at a high coding rate (for example, R1 = 1), and the received signal is decoded at the mobile station and retransmission is required if an error is detected in the decoded signal (NAK response). ).

Upon receiving this retransmission (NAK) response, the sender transmits an incremental codeword at a code rate lower than that previously sent. If even the original code rate fails, it can be resent from the beginning. In other words, if the signal transmission of the 1 / h code rate fails, it can be transmitted again from the beginning, but may also be transmitted at a code rate lower than 1 / h.

In general, convolutional coding or turbo coding may be employed as the channel coding scheme, and type 2 or type 2 may be used depending on whether the code is a RCP code or a complementary coded code. The type is divided by whether or not (type III). Generally, when a transmission signal is retransmission of the same signal, it is defined as type 1 (type I).

Existing 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.

On the other hand, when the hybrid ARQ scheme is employed, an efficient method for power control is required. In particular, in order to maximize the capacity of the downlink that needs to support a high data rate in a CDMA system, transmission power control required for each link is required. Should be performed.

Accordingly, the present invention proposes a power control method having better performance by combining the hybrid ARQ proposed for the multimedia service and the blind type adaptive power control.

Power control is essential in CDMA systems and can increase the reliability of signal transmission or increase throughput. However, power control must operate in accordance with the channel environment and must be insensitive to errors due to time delays in power control loops, errors in power control signaling signals, and SIR estimation errors.

Thus, adaptive power control can be used to compensate for this drawback in poor channel environments. The power control scheme employed in the existing system should perform channel estimation. The proposed scheme is a blind scheme that requires no information on the channel environment by combining the adaptive power control with the hybrid ARQ scheme.

4 and 5 show the power control procedures at the receiving side (mobile station) and transmitting side (base station) according to the present invention, respectively.

In a hybrid ARQ system, one block of data enters the CRC encoder and passes through the next puncture code encoder. Therefore, incremental codewords occur. The codeword selected for transmission is interleaved and forms a channel block of length Lc. The channel block is modulated and then sent to the fading channel. The choice of coding rate and the signal power in each transmission depends on the feedback signal (ACK / NAK). The receiver consists of a decoder and a CRC decoder, and an appropriate feedback signal (ACK / NAK) is determined according to the result of comparing the reception quality with the target quality.

First, data transmission from the transmitting side (base station) to the receiving side (mobile station) initially starts with the highest coding rate and the smallest power. The receiving side determines the quality of the received information and, if the receiving quality is lower than the target quality, makes a retransmission request (NAK) to the transmitting side.

In this way, when an error occurs and a retransmission request (NAK) signal is generated and arrives at the transmission side, the transmission side decreases the coding rate in a predetermined pattern and increases transmission power.

Alternatively, when retransmission is requested, a target power value of a signal may be gradually increased during retransmission, and power control may be performed based on external loop power control as described above.

On the other hand, when increasing the transmission power as described above, the step of power control is fixed to increase the transmission power in this fixed step or to increase the transmission power flexibly.

However, if the reception quality satisfies the target quality, the receiving side generates a corresponding ACK signal and transmits it to the transmitting side. When the receiving side receives the ACK signal, the transmitting side initializes the transmission power and starts the process anew.

Or, if retransmission is performed by gradually decreasing the code rate (increasing the power) according to the request for retransmission (NAK) and supporting all the original code rates, the retransmission is resumed at the highest code rate, or The retransmission can be continued at a low coding rate, and in the former case it can be continuously increased in the fixed or variable steps with or without initializing the transmission power. In the latter case, the transmission power may be maintained as it is, while continuing to retransmit at the lowest coding rate, or continue to increase in the fixed or variable steps.

As described above, the system proposed in the present invention has the basic technical idea that the transmission power simultaneously increases as the coding rate of the hybrid ARQ decreases upon retransmission.

That is, according to the present invention, when the retransmission probability is high, the transmission power gradually increases with the number of retransmissions. This process can be done in a situation where there is no knowledge of the channel at the transmitter, and thus it is possible to solve the overload of the uplink control signal which is a problem in the hybrid ARQ system and the time delay due to the control signal processing. The present invention may bring a great benefit in terms of throughput compared to the existing hybrid ARQ system.

In addition, the generation of the power control signal in the existing system can be estimated by the information on the channel available at the transmitting end, in the present invention, the adaptive power control method to drive in a blind manner without using the information on the channel status, The adaptive determination of power depends on the retransmission request, for the given packet the initial transmission takes the lowest transmit power, and the transmit power gradually increases during the retransmission, which continues until a successful transmission is made. .                     

The power control in the CDMA system described above can reduce the reception capacity due to the increase of the interference when the transmission power is increased, but can increase the reception reliability of the increased signal while taking it. Adaptive power control of the present invention for this purpose can be employed in the IMT-2000 system for providing a multimedia service, adaptive modulation and demodulation, adaptive ARQ can also be considered.

Existing 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.

The present invention combines the hybrid ARQ proposed for the multimedia service with the blind type adaptive power control, thereby reducing the errors and delays mentioned above, and thus improving performance.

In addition, the adaptability to the channel of the hybrid ARQ can be further enhanced by adaptive power control, thereby further improving performance. In addition, overcoming the disadvantages of general power control, channel estimation is unnecessary, reducing uplink control signaling signal load, and processing time delay when ARQ system is processed in node B's MAC (Mdeia Access Control). Can also be significantly reduced.

Claims (8)

In the ARQ system, transmitting data at an initial coding rate and an initial transmission power value from a transmitting side to a receiving side, and a retransmission (NAK) request signal from the receiving side to the transmitting side according to a result of receiving the transmitted data and determining the quality thereof. Receiving the data, and increasing the transmission power with the reduction of the coding rate according to the retransmission (NAK) request to perform data retransmission at the reduced coding rate and the increased transmission power; A blind type adaptive power control method using ACK / NAK in ARQ system. The method of claim 1, wherein the transmission power is initialized when an acknowledgment (ACK) signal is received according to the determination result of the reception quality. The adaptive power control method of the blind type using ACK / NAK in an ARQ system. . 2. The ARQ system according to claim 1, wherein when the code rate reduction for the retransmission is supported up to the original code rate, the retransmission starts with the highest code rate, and at this time initializes or continues to increase the transmit power. Adaptive Power Control Method of Blind Type Using ACK / NAK The ARQ according to claim 1, wherein when the code rate reduction for the retransmission is supported up to the original code rate, the retransmission is continuously performed at the lowest code rate, wherein the ARQ is maintained or continuously increased. Adaptive power control method of blind type using ACK / NAK in system. The method of claim 1, wherein the target power value of the signal is gradually increased while the data retransmission according to the NAK request is continued, and power control based on the target value is performed according to the outer loop power control. A blind type adaptive power control method using ACK / NAK in ARQ system. The ACK / NAK of claim 1, wherein the data retransmission step includes retransmitting data by increasing the transmission power while maintaining the initial coding rate in response to the ARQ system. Adaptive power control method of the blind type using. The method of claim 1, wherein the transmission power control is performed according to the retransmission request without using information on a channel environment . The blind type adaptive power control method of claim 1, wherein a change in a coding rate and a transmission power used in retransmission according to a retransmission request is performed in a predetermined pattern or a variable pattern .

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