Uplink (UL) power control apparatus and method in broadband wireless communication system

Uplink (UL) power control device and method in broadband wireless communication system

Background of the invention

The present invention relates generally to an apparatus and method for controlling uplink power in a wideband wireless communication system, and specifically, to an apparatus and method for regularly changing the power control mode from one mode to another in a wideband wireless communication system.

There is research being conducted to provide users with a different quality of service (QoS) at a high data rate in order to access Fourth Generation communication systems. Specifically, research on accessing high-rate back-up service in order to ensure mobility and QoS in communication systems (4G) such as wireless local area networks (LANs). Urban wireless Metropolitan Area Networks (MAN), which guarantees high data rates, which is currently being researched.

The IEEE 802.16 communication system adopts an orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA) scheme for the broadband transmission network in the physical channels of the wireless MAN system. By applying the OFDM/OFDMA scheme to the wireless MAN system, the IEEE 802.16 communication system enables high-rate data transmission by sending the physical channel signal using a set of plurality of subcarriers.

In an OFDMA communication system, uplink (UL) signals may act as excessive interference to other MSs or adjacent cells depending on transmit power, or may cause a decrease in reception power of the base station (BS).

Accordingly, it is required to provide appropriate power control according to the required Carrier to Interference and Noise Ratio (CINR).

Typically, power control mode can be broadly classified into closed loop power control and open loop power control.

Closed loop power control helps compensate for the Uplink transmission power, especially the MS, under the control of the BS. However, closed loop power control may reduce the accuracy of power control in a packet communication system. The BS determines the power control range by using the CINR value of the information packets received in the uplink. Even when the BS occasionally receives information packets and performs power control for each reception of an information packet, the accuracy of the power control may decrease as there is a difference in the timing of transmitting the Uplink information packet from the BS and the timing of forwarding the power control from the BS.

In open loop power control, assuming that the loss in the path, especially the uplink, is equal to the path loss of the downlink (DL), the station itself adjusts the transmit power of the UL signal. By estimating the path loss of the downlink connection by estimating DL. This means that the station adjusts the amount of uplink signal UL power using using the required CINR received from station BS, information related to interference and noise level for the uplink connection, and path loss for the downlink DL connection. In addition, the BS can direct fine-tuning to the station based on the CINR value of the received information packets.

As discussed above, open loop power control can generally improve the accuracy of power control thanks to the power adjustment by the MS itself and the additional guidance of the power adjustment by the BS, compared to circuit power control. closed loop.

Therefore, the MS station in the OFDMA communication system performs closed loop power control in the initial entry phase of the station, and then performs open loop power control by changing the power control mode from one mode to another.

Figure 1 shows a traditional procedure for changing the mode from closed loop power control to open loop power control in a wide-area wireless communication system.

Upon initial entry, MS 10 shown in Figure 1 receives Downlink Channel Descriptions (UCD/DCD) from BS 20 in step 101, and obtains the information (variables) required for initial entry from the messages. The recipient. In doing so, station 10 can obtain variables related to the initial range determination. Station 10 receives interference and noise level information from BS 20 in step 103.

In step 105, MS 10 sets the band allocation message based on the initial transmit power based on information received from BS 20. In step 107, MS 10 transmits an initial ranging response code to BS 20 using the initial power To send band allocation message. BS 20 sends a ranging response message RNG_RSP to MS 10 in response to the initial ranging response code in step 109. BS 20 sends a CDMA Alloc IE band assignment message based on the range selection request to MS 10 in step 111.

If the RNG_RSP message is not received within a certain time after transmitting the ranging response, MS 10 retransmits the ranging response at a higher transmit power level. When an RNG_RSP message is received within a certain time, MS 10 performs entry procedures to the station (E/N), starting with the initial range determination in step 113. The E/N procedures include the initial range determination of RNG_REQ/RSP, identification of the basic capabilities. SBC_REQ/RSP, and PKM_REQ/RSP documentation.

After the E/N procedures, MS 10 enters a closed loop power control mode that adjusts transmit power according to the IE power control from BS 20 in step 115.

BS 20 checks the open loop power control of MS 10 by performing a basic potential identification procedure. After the E/N actions, BS 20 requests BS 10 to switch to open loop power control mode by sending a power control mode change response message (PMC_RSP) in step 117. Station 10 sends a power control mode change request message (PMC_REQ) to BS 20 in response to its request in step 119, and changes the power control mode to open loop power control. In step 121.

Station 10 calculates transmit power P according to open loop power control based on equation (1).

(1)

The variables mentioned in equation (1) are defined as follows:

- P: transmit power (dBm) per subcarrier per UL burst.

– L: estimated average value of propagation path loss calculated using the total receiving power measured by the effective subcarriers of the first isotropic effective radiation power variable from the BS (BS_EIRP). The variable BS_EIRP is an indication that the transmitting power of the BS has been received using a DCD message.

- N/C: The received CINR value required by the MCS level of the uplink pulse.

– NI: An estimated value of the average interference and noise power (dBm) for each subcarrier measured at the BS, which is provided for each MS network as general information.

- R: number of repetitions according to MCS level.

-: The power compensation value of the MS station that is controlled by the MS station, which is always zero in open loop power control mode, negative.

-: BS power compensation value controlled by the BS. When this value is set using the PMC_RSP message, it is compensated for by the PMC_RSP message value. When the BS routes fine-tuning power using IE power control, the combined power adjustment values ​​in IE power control are used as a value. Alternatively, the aggregate can be used to set the power in the RNG_RSP message received from the BS as a value.

Previous traditional art includes a number of drawbacks. When a relay station (sequel or retransmission station) (RS) is installed in the system, and in particular when the transmit power of the downlink of the RS relay station (MS → RS) differs from the transmit power of the uplink of the RS relay station (MS → RS), it Normally the open circuit power control pattern may not work. This is because the open loop power control pattern intuitively assumes that the loss in the DL propagation path (for the downlink) is equal to the loss in the uplink propagation path (for the uplink).

If the transmission power of the RS DL (relay station downlink) is greater than the transmission power of the Uplink, the MS estimates the loss in the Uplink propagation path by measuring the loss in the DL propagation path. Accordingly, the estimated Uplink propagation path loss is less than the actual path loss. In this case, when open loop power control is carried out on the basis of equation (1), the MS transmits the Uplink information packet with a power much lower than the required transmit power. As a result, the BS may not receive the Uplink signal or the error rate of the Uplink information packet may increase. In particular, when the power control mode is changed (from closed loop power control to open loop power control) and there is a difference in the loss in the propagation path between the downlink and the uplink connection, it is necessary to take into account Its effect is taken into account.

If the set BS_EIRP value is greater than the actual output value from the BS, then when the station calculates the loss in the DL path it is greater than the actual value. In this case, since the unnecessarily large Uplink transmit output may be set in open loop power control, this may have an impact on other MS signals on the receiving BS. In other words, when the BS performs automatic gain control (AGC) before the Fast Fourier Transform (FFT) stage, the AGC operates based on the power set of uplink (UL) signals. Therefore, this may represent interference to the MS signal, which has a relatively weak reception signal.

In contrast, when the BS_EIRP value set for DCD is less than the actual output value from the BS, the DL path loss calculated by the station becomes less than the actual value. In this case, since the Uplink transmitter output may be set lower than necessary in open loop power control, the BS may not receive the BS signal.

As discussed above, since open loop power control can calculate incorrect transmit power due to various external factors, what is required is to find a way to achieve open loop power control in a stable and regular manner. Moreover, such errors can be observed when closed loop power control is changed to open loop power control. Therefore, it is required to properly maintain transmit power when the power control mode is changed.

General description of the invention

One feature of the present invention is to provide a substantial solution to at least the foregoing problems and/or drawbacks and to provide at least the advantages described below. Accordingly, one feature of the present invention is to provide a device and method for regularly changing the power control mode in a wide-area wireless communication system.

Another feature of the present invention is to provide a device and method for systematically changing from a closed loop power control mode to an open loop power control mode in a wide-area wireless communication system.

A further feature of the present invention is to provide an apparatus and method for consistently and regularly performing an open circuit power control procedure in a wide area wireless communication system.

The above-mentioned features have been achieved by providing a mobile station (MS) in a wireless communication system, which includes a power controller whose purpose is to calculate a value to compensate for the power using the last transmit power in a previous power control in a closed loop when the power is changed. Power control mode is used to control open-circuit power, and determine transmit power according to open-circuit power control using the power compensation value. A transmitter whose purpose is to adjust and transmit the transmission power of a signal Uplink under the control of the power controller.

According to one aspect of the present invention, the UL power control method in a wireless communication system includes calculating a power compensation value using the last transmit power in a previous closed loop power control when the power control mode is changed Power control mode depends on open loop power control, and determines the transmission power according to open loop power control using the power compensation value.

According to another aspect of the present invention, the UL power control method in a wireless communication system includes obtaining, when the open-loop power control mode is changed, the last transmit power value in the closed loop power control mode, The path loss value, power compensation value estimated at the MS, the last noise and interference (NI) value received from the base station (BS), and the CINR value required for the last level of the Modulation and Coding scheme. Scheme (MCS) in closed loop power control mode, and the number of repetitions according to the last MCS level; The power compensation value controlled by the MS is calculated using the acquired values ​​based on Eq

Brief explanation of the drawings

The above and other objectives, aspects and features of the present invention will be explained in more detail by means of the following detailed description when submitted with the help of the attached figures and drawings, wherein:

Figure 1: Illustrates a traditional procedure for changing from closed loop power control to open loop power control in a wide-area wireless communication system.

Figure 2: Illustrating a mobile MS in a broadband wireless communication system according to the present invention; And

Figure 3: Illustrates a procedure for controlling the power of an open circuit for an uplink connection in a broadband wireless communication system according to the present invention.

Detailed description

Preferred embodiments of the present invention will be described below with the help of the accompanying figures and drawings. In the following description, well-known functions and compositions will not be described in detail as they may cloud the invention with unnecessary detail.

The present invention provides a method for systematically performing open loop power control in a large-scale wireless communication system.

According to what was previously described, in open circuit power control based on equation (1), incorrect transmit power is calculated when the path loss values ​​for both the uplink and downlink connections are not equal to each other. Typically, when a relay station (RS) is used between a master station (BS) and a mobile station, the easiest way to perform normal open loop power control is to set the DL gain and Uplink gain of the RS to the same value.

The disadvantages of open circuit power control can be identified by gradually increasing transmit power when determining the required bandwidth range or periodically determining the range that is done before the actual transmission of the Uplink pulse, in a manner similar to the initial range determination.

The MS requests the Uplink bandwidth by specifying the required bandwidth range. When determining the required bandwidth range, transmit power is gradually increased in a manner similar to the procedure used during initial range determination. Specifically, the MS increases the transmit power to determine how much bandwidth is required for the BS reception level to reach a suitable level. Accordingly, in any subsequent transmission of the Uplink pulse, the reception level of the BS can be maintained at the appropriate level.

The MS also performs periodic range determinations even when no Uplink information packet is being sent. In this case, as in the initial range determination, the transmission power is gradually increased. Specifically, the MS increases the transmitting power for periodic ranging until the reception level of the BS reaches a suitable level. Accordingly, for any subsequent transmission of the Uplink pulse, the reception level of the BS can be maintained at the appropriate level.

The previous method defines the disadvantages of controlling open circuit power using well-known methods. Alternatively, the PMC_RSP message can be used. In more detail, the value of the PMC_RSP message is set to the value of the difference between the DL gain and the Uplink gain of the RS station. Since each MS network connected to the station BS and station RS enters the open loop power control mode and sends high-power signals up to the value of the PMC_RSP message, interference may arise on other cells instantaneously. However, the MS communicating with the BS can reduce transmit power using fixed IE power control, and the station communicating with the RS can maintain a certain level of power redundancy in view of the BS's receiving light.

In addition to the previously described methods, the MS can itself calculate the transmit power that is relied upon to control the power of an open circuit, and this will be described in detail with the help of figures and drawings.

Figure 2 is a box diagram of an MS network in a broadband wireless communication system according to the present invention. The following explanation describes a time division multiplexing (TDD)-OFDMA system as an example. Note that the present invention can be easily applied to every power control system such as a frequency division duplex (FDD)-OFDMA system and a hybrid system using both TDD and FDD.

The MS shown in Figure 2 includes a MAC layer portion 201 associated with a higher layer, a transmit modem 203, a receive modem 205, a duplex device 207, a power controller 209, and a receive power measurer 211. .

The layer part MAC 201 receives data sent from the upper layer (e.g., layer part IP) and delivers the transmitted data to the transmit modem 203 by processing the transmitted data according to the transmit modem connection scheme 203. Layer part MAC 201 receives the data received from the receive modem 205, and processes the received data and presents it to the upper layer according to the upper layer's connection scheme. According to the present invention, the layer part MAC 201 provides the information required for power control to the power controller 209. The information required for power control may include information received from the BS, and information generated at Based on the information received from the BS.

The transmit modem 203 includes a channel decoding block, a modulation box, a Radio Frequency (RF) transmission box, and so on. The transmit modem 203 converts burst data fed from the MAC layer portion 201 into an image for radio sector transmission and delivers the transformed data to the duplexer 207. A channel decoding block may include a channel encoder, an interleaver, and a modulator. The modulation box may include an inverse FFT (IFFT) operator to map the transmitted data to a group of orthogonal substate waves. The RF transmitter box may include a filter and a front-end unit.

The receive modem 205 includes a receive block RF, a demodulation block, and a channel decoding block. The receive modem 205 recovers data from the radio section signals from the duplexer 207 and presents the restored data to the layer part MAC 201. The receive block RF can include a filter and a front-end RF unit. A demodulation block may include an FFT operator to demodulate the data into subcarriers. The channel decoding block may include a demodulator, a deinterleaver, and a channel encoder

The duplexer 207 provides the receive signal (DL signal) from an antenna to the receive modem 205 and provides the transmit signal (Uplink signal) from the transmit modem 203 to the antenna according to the TDD scheme.

The receive power measurement unit measures the receive power 211 receives the preamble values ​​of the preamble received from the BS of the receiving modem 205, and measures the receive power using the preamble subcarrier values. The measured reception power is sent to the power controller 209. The measured reception power is used to calculate the loss in the Uplink path, L in equation (1).

The power controller 209 implements closed loop power control or open loop power control. In closed loop power control, the power controller 209 determines the transmit power Uplink according to the power control command received from the BS and provides the Uplink transmit power to the transmit modem 203, and the transmit modem 203 sends a signal Uplink by adjusting the transmit power of the Uplink signal according to the transmit power of the power controller 209. Transmission power can be regulated at a mainband stage, an Intermediate Frequency (IF) stage, and an RF stage.

In open loop power control, the power controller 209 determines the Uplink transmission power based on equation (1) and presents the determined Uplink transmission power to the transmit modem 203. When transmit power is determined on the basis of processing (1), information regarding the CINR value required by the MCS level of the transmitted Uplink pulse and the estimated interference and noise power (NI) value of each subcarrier at the BS is required, which is supplied from layer part MAC 201.

When changing from a closed loop power control mode to an open loop power control mode, the power controller 209 calculates the power compensation value for the MS mentioned in Equation (1) on the basis of Equation (2). In order to prevent a sudden change in transmit power according to a change in the power control mode, open circuit power control is implemented by compensating with the MS power compensation value calculated in Equation (1).

(2)

The variables mentioned in equation (2) will be defined as follows.

-: The last value of transmit power in closed loop power control mode.

-: The estimated initial value of the transmission power after changing to the open circuit power control mode, which can be expressed by equation (3).

(3)

-: The difference between the required CINR value for the MCS level of the transmitted Uplink pulse and the required CINR value for the last MCS used in the closed loop power control mode, which can be expressed by equation (4).

(4)

According to this, fairness (2) can be expressed by equation (5).

(5)

The variables mentioned in Process (5) can be defined as follows. It is the last value of transmit power in closed loop power control mode. It is the loss in the path that is estimated by the MS station when changing from closed loop power control to open loop power control. It is the last noise and interference (NI) value received at the BS. It is the CINR value required for the last MCS level (modulation and FEC) in closed loop power control mode. It is the number of repetitions (repetition factor) according to the latest MCS level.

As previously mentioned, the power controller 209 calculates the power compensation value of the MS station on the basis of Equation (2) or Equation (5), and implements open circuit power control by compensating with the MS power compensation value. As one can see from Equation (2), the MS power compensation value mentioned in Equation (1) in open-loop power control mode is set at the sum of the difference between the last power value transmitted in the previous closed-loop power control mode and the power value The initial transmit power value is estimated by changing to an open circuit power control mode, and the difference between the required CINR values ​​is based on the MCS difference, rather than zero.

The MS power compensation value mentioned in Equation (2) and Equation (5) is calculated only once when the power control mode is changed from closed loop power control to open loop power control, and then It is maintained until the power control pattern is changed. Under complete power control, since the initial power level, especially open-loop power control, is the same as the final power level for the closed-loop power control mode, the MS power compensation value will equal zero. However, if there is a difference between the UPLINK path loss and the DL path loss, a sudden change in transmit power when changing the mode is avoided by compensating the difference using the MS power compensation value.

Figure 3 shows a procedure intended to implement open loop power control Uplink in a broadband wireless communication system according to the present invention.

In Figure 3, in step 301, the MS determines whether the power control mode has been changed to open circuit power control. The power control mode is changed using the PMC_RSP message received from the BS as previously described above. Upon receiving the PMC_RSP message from the MS, the MS recognizes the request to change the mode to open circuit power control, sends a PMC_REQ message to the BS as a response to the PMC_RSP message, and then enters open circuit power control.

When entering an open-loop power control mode, in step 303, the MS network determines the transmit power value in the closed loop control mode and the CINR value required for the last MCS level. In step 305, the MS determines the CINR value required for the first MCS level of the Uplink pulse that will be sent after changing to open loop power control mode.

In step 307, the MS estimates the international transmit power that should be used after changing to open circuit power control mode on the basis of equation (3). In step 309, the MS calculates the MS power compensation value using the last transmit power value for the closed loop power control mode, the required CINR value for the last MCS level, the required CINR value for the initial MCS level, and the estimated initial transmit power value . The MS power compensation value can be obtained from Equation (2) or Equation (5).

After calculating the MS power compensation value, the MS performs open circuit power control by substituting the MS power compensation value into equation (1), in step 311.

According to what was mentioned above, in a broadband wireless access and communication system such as the OFDMA system, when the power control mode is changed to an open circuit power control mode, open circuit power control can be implemented stably and regularly even with a difference between Uplink path loss and DL path loss. In other words, by maintaining the correct level of receiving power of the BS in order to transmit the Uplink information packet, regular control of open circuit power can be achieved and the Uplink performance can be enhanced.

While the invention is illustrated and described by reference to some of its preferred embodiments, those skilled in the art will recognize that various changes in form and detail may be made without departing from the substance and scope of the invention as defined by the accompanying claims.