Patent Application
20070265026
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.
The present invention provides a method for stably performing an open loop power control in a broadband wireless communication system.
As discussed earlier, in the open loop power control based on Equation (1), the improper transmit power is calculated when the path losses of the uplink and the downlink are not equal to each other. Typically, when Relay Station (RS)(or Repeater)is used between Base Station (BS) and Mobile Station (MS), the simplest method for normally accomplishing the open loop power control is to set the DL gain and the UL gain of the RS to the same value.
The drawbacks of the open loop power control can be addressed by gradually increasing the transmit power in the bandwidth request ranging or the periodic ranging which is carried out before the actual transmission of a UL burst, similar to the initial ranging.
The MS requests a UL bandwidth through the bandwidth request ranging. In the bandwidth request ranging, the transmit power is gradually increased similar to the procedure used during the initial ranging. Specifically, the MS increases the transmit power of the bandwidth request ranging until a BS reception level reaches a proper level. Accordingly, in a later UL burst transmission, the BS reception level can be maintained at the proper level.
The MS also performs the periodic ranging even while no UL packet is transmitted. In this case, like in the initial ranging, the transmit power is gradually raised. Specifically, the MS increases the transmit power of the periodic ranging until the BS reception level reaches a proper level. Accordingly, in a later UL burst transmission, the BS reception level can be maintained at a proper level.
The above methods address the drawbacks of the open loop power control using well-known techniques. Alternatively, a PMC_RSP message can be utilized. In more detail, the Offset_BSperSS value of the PCM_RSP message is set to the difference between the DL gain and the UL gain of the RS. Since every MS connected to the BS and the RS enters the open loop power control mode and transmits signals with high power up to the Offset_BSperss value of the PMC_RSP message, interference on other cells may rise momentarily. However, the MS establishing a link to the BS can lower the transmit power using the constant power control IE, and the MS establishing a link to the RS can maintain a certain reception power level in view of the BS reception.
Besides the above-mentioned methods, the MS can calculate by itself the reliable transmit power in the open loop power control, which is described in detail by referring to the drawings.
The MS of
The MAC layer part 201 serves to receive transmit data from the upper layer (e.g., IP layer part) and to provide the transmit data to the transmit modem 203 by processing the transmit data according to a connection scheme of the transmit modem 203. The MAC layer part 201 receives receive data from the receive modem 205, processes and provides the receive data to the upper layer according to a connection scheme of the upper layer. According to the present invention, the MAC layer part 201 provides information required for the power control to the power controller 209. The information required for the power control can include information received from the BS, and information generated based on the information received from the BS.
The transmit modem 203 includes a channel coding block, a modulation block, a Radio Frequency (RF) transmit block, and so forth. The transmit modem 203 transforms data (burst data) fed from the MAC layer part 201 to a form for the radio section transmission and provides the transformed data to the duplexer 207. The channel encoding block can include a channel encoder, an interleaver, and a modulator. The modulation block can include an Inverse FFT (IFFT) operator for mapping the transmit data to a plurality of orthogonal subcarriers. The RF transmit block can include a filter and an RF front-end unit.
The receive modem 205 includes an RF receive block, a demodulation block, and a channel decoding block. The receive modem 205 restores data from the radio section signals from the duplexer 207 and provides the restored data to the MAC layer part 201. The RF receive block can include a filter and an RF front-end unit. The demodulation block can include an FFT operation for extracting data mapped to the subcarriers. The channel decoding block can include a demodulator, a deinterleaver, and a channel decoder.
The duplexer 207 provides the receive signal (DL signal) from an antenna to the receive modem 205 and provides the transmit signal (UL signal) from the transmit modem 203 to the antenna according to the TDD scheme.
The receive power measurer 211 receives subcarrier values of the preamble received from the BS from the receive modem 205, measures the receive power using the preamble subcarrier values, and provides the measured receive power to the power controller 209. The measured receive power is used to calculate the UL path loss L of Equation (1).
The power controller 209 carries out the closed loop power control or the open loop power control. In the closed loop power control, the power controller 209 determines the UL transmit power according to a power control command received from the BS and provides the UL transmit power to the transmit modem 203. The transmit modem 203 sends the UL signal by adjusting the transmit power of the UL signal according to the transmit power from the power controller 209. The transmit power can be regulated at one of a baseband stage, an Intermediate Frequency (IF) stage, and an RF stage.
In the open loop power control, the power controller 209 determines the UL transmit power based on Equation (1) and provides the determined UL transmit power to the transmit modem 203. When the transmit power is determined based on Equation (1), information relating to the CINR value required by the MCS level of the transmitted UL burst and the average interference and noise power estimation value (NI) per subcarrier at the BS are required, which are supplied from the MAC layer part 201.
When changing from the closed loop power control mode to the open loop power control mode, the power controller 209 computes the MS power compensation value Offset_SSperSS of Equation (1) based on Equation (2) to prevent the abrupt change of the transmit power according to the power control mode switching, and performs the open loop power control by reflecting the computed MS power compensation value into Equation (1).
The parameters in Equation (2) are defined as below.
PTX,CL
PTX,OL
ΔCINRreq: a difference between the required CINR value for the MCS level of the transmitted UL burst and the required CINR value for the last MCS used in the closed loop power control mode, which can be expressed as Equation (4).
Accordingly, Equation (2) can be re-expressed as Equation (5).
The parameters in Equation (5) are defined as follows. PTX,CL
As above, the power controller 209 calculates the MS power compensation value Offset_SSperSS based on Equation (2) or Equation (5), and performs the open loop power control by reflecting the MS power compensation value. As one can see from Equation (2), the MS power compensation value of Equation (1) in the open loop power control is set to the sum of the difference between the last transmit power value in the previous closed loop power control mode and the initial transmit power value estimated by changing to the open loop power control mode, and the difference between the required CINR values based on the MCS difference, rather than to zero.
The MS power compensation value in Equation (2) and Equation (5) is calculated only once when the power control mode is changed from the closed loop power control to the open loop power control, and then is maintained until the power control mode is changed. Under the perfect power control, since the initial power level of the open loop power control is the same as the last power level of the closed loop power control, the MS power compensation value Offset_SSperSS will be zero. However, in the case of a disparity between the UL path loss and the UL path loss, the abrupt change of the transmit power in the mode change is avoided by compensating for the disparity using the MS power compensation value.
In
When entering the open loop power control mode, in step 303 the MS determines the last transmit power value in the closed loop power control mode and the required CINR value for the last MCS level. In step 305, the MS determines the required CINR value for the initial MCS level of the UL burst which will be transmitted after changing to the open loop power control mode.
In step 307, the MS estimates the initial transmit power to be used after changing to the open loop power control mode based on Equation (3). In step 309, the MS calculates the MS power compensation value Offset_SSperSS using the last transmit power value PTX,CL
After computing the MS power compensation value Offset_SSperSS, the MS performs the open loop power control by reflecting the MS power compensation value into Equation (1) in step 311.
As set forth above, in a broadband wireless access communication system such as an OFDMA system, when changing the power control mode to the open loop power control mode, the open loop power control can be stably carried out even with a disparity between the UL path loss and the DL path loss. In other words, by keeping the proper receive power level of the BS for the UL packet transmission, the stable open loop power control can be achieved and the UL performance can be enhanced.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-0042958 | May 2006 | KR | national |
