JP2012054996A - Combined open loop/closed loop power control in wireless communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide combined open loop/closed loop power control in a wireless communication system.SOLUTION: There are provided a method, system and apparatus for setting a transmit power control level in a wireless communication system. Aspects of both open loop and closed loop transmit power control schemes are used to determine a transmit power level. A method includes measuring a power level of a received signal, receiving a transmit power control (TPC) command, and calculating a transmit power level based on the path loss and the TPC command.

Description

  The present invention relates to power control in mobile radio systems or radio communication systems, and more particularly to controlling received power levels in a code division multiple access (CDMA) radio system.

  Typically, a radio signal transmitted with increased power causes fewer errors when received than a signal transmitted with reduced power. Unfortunately, signals transmitted with excessive power can interfere with the reception of other signals sharing the wireless link. Wireless communication systems use power control schemes to maintain the target error rate of signals received on the wireless link.

  If the received signal has an error rate that is significantly above the intended error rate, the received signal can have an undesirable effect on the delivery service. For example, excessive errors can result in corrupted voice between voice calls, low throughput on the data link, and glitch in the display video signal. On the other hand, if the received signal has an error rate well below the target error rate, the mobile radio system is not efficiently using that radio resource. A very small error rate may mean that the signal is transmitted at an excessive power level and the user can be provided with a high data rate. Alternatively, additional users can be served if the signal power level is sufficiently reduced. As the data rate increases, the user may receive a higher service level. Therefore, when the target error rate for each user is within an allowable threshold, radio resources can be optimally used.

  Wireless communication systems often use either an open loop scheme or a closed loop scheme to control the uplink transmission power of a mobile radio. The uplink typically refers to the radio link from the mobile radio to the base station, and the downlink typically refers to the link from the base station to the mobile radio. A mobile radio device is not necessarily a mobile body, and may be called a mobile body, a user, a user equipment (UE), a terminal, or a terminal device. The base station may also be referred to as Node-B.

  The error rate is related to a received signal to noise-plus-interference ratio (SNIR). Generally, a high SNIR results in a low error rate, and conversely, a low SNIR generally results in a high error rate. However, the exact relationship between SNIR and error rate, including the radio channel type and the speed at which the mobile moves, is often a function of several factors.

  The target error rate is often reached using a two-stage process. The two-stage process has an outer loop and an inner loop. The first process operates as an outer loop and may serve to adjust the target received SNIR (target SNIR). This first process tracks changes in the relationship between SNIR and error rate. The outer loop generally sets the target SNIR that is used multiple times by the inner loop. Periodically, the outer loop may adjust or update this target SINR used by the inner loop. For example, if the actual error rate exceeds the desired error rate, the outer loop may increase the value of the target SNIR.

  The second process operates as an inner loop and tries to present the target SINR determined by the outer loop on the link. The inner loop may be operated by closed loop or open loop means.

  In the open loop method of inner loop processing, the UE uses the target SNIR value obtained by the network and signaled to the UE. The inner loop running at the UE tries to maintain the target SNIR. The UE uses the information signaled to it to monitor the received strength of the received signal and determine the power level to transmit. Advantageously, this open loop method compensates for fast channel fading by determining the path loss per frame and adjusting the transmit power accordingly. Unfortunately, this open loop method is relatively slow when compensating for changes due to interfering signals from other transmitters.

  In the closed loop method of inner loop processing, the closed loop method operates to match the target SNIR. The received SNIR measurement is performed by the network on the uplink signal. The SNIR measurement is compared with the target SNIR value in the network. The inner loop prompts the system to match the target SNIR by issuing a transmit power control command from the network to the UE. The command instructs the UE to increase or decrease its transmit power by a predetermined amount of dB. Unfortunately, such a closed loop method requires a very high command update rate to adequately compensate for fast channel fading due to the single dB step command used. At low update rates, fast channel fading is not properly tracked because large amounts of interaction and long delays are required to compensate for power changes that are substantially greater than the value in dB steps.

  Both closed-loop and open-loop methods have drawbacks. Accordingly, there is a need for an improved method and system that balances the conflict between the goal of reducing received signal errors and the goal of reducing interference appearing in signals received at other receivers. Improved methods and systems are also needed to successfully reduce the overall residual SNIR variation experienced by each user signal at the receiver.

  According to an aspect of the present invention, there is provided a power control method in a wireless communication system having a first wireless device and a second wireless device, wherein the first wireless device and the second wireless device are provided by the second wireless device. A path loss of a radio channel with the radio is determined, a transmission power control (TPC) command transmitted from the first radio is received, and the second radio is based on the path loss and the TPC command. Setting the transmission power level of the machine and transmitting a signal at the set transmission power level.

  According to another aspect of the present invention, there is provided a power control method in a wireless communication system having a first wireless device and a second wireless device, wherein the first wireless device transmits from the second wireless device. Received signal, measure the SNIR of the received signal, compare the measured SNIR with the target SNIR, and if the measured SNIR is greater than the target SNIR, assign a first value to the step indicator and measure Assigning a second value to the step indicator if the SNIR is less than the target SNIR and transmitting a transmit power control (TPC) command having the step indicator.

  In accordance with another aspect of the present invention, an apparatus having a user equipment is provided, operable to receive a transmission power control (TPC) command transmitted from a base station, and measuring a power level of a received signal A receiver that is operable, a calculation logic coupled to the receiver and operable to determine a path loss of a radio channel between the base station and the user equipment, and a path loss coupled to the calculation logic. Power level setting logic that is operable to set a transmit power level based on a TPC command, and a transmission that is coupled to the power level setting logic and is operable to transmit a signal at the set transmit power level Machine.

  In accordance with another aspect of the present invention, a system having a base station is provided, a receiver operable to measure a SNIR of a received signal, an input for a measured SNIR coupled to the receiver, and A first value is assigned to the step indicator if the measured SNIR is greater than the target SNIR, and a second value is assigned to the step indicator if the measured SNIR is less than the target SNIR. Comparison logic operable to assign, command generation logic coupled to the comparison logic and operable to generate a transmit power control (TPC) command having a step indicator, coupled to the command generation logic, and the TPC And a transmitter operable to send the command.

  Some embodiments provide a power control method in a wireless communication system, determine a path loss of a radio channel between a base station and a remote transceiver, and transmit power control (TPC) commands transmitted to the remote transceiver. Receiving from the base station and calculating a transmit power level of the remote transceiver based on the path loss and the TPC command.

  Some embodiments provide a method for power control in a wireless communication system, wherein a signal transmitted from a first transceiver is received by a second transceiver, a power level of the received signal is measured, and the power is transmitted from the first transceiver. The transmitted power control (TPC) command transmitted is received at the second transceiver and the transmission power level of the second transceiver is calculated based on the power level of the received signal and the TPC command.

  Some embodiments provide an uplink power control method in a CDMA wireless communication system, receive an uplink signal, determine an error metric of the uplink signal, update a target SNIR based on the error metric, and The received SNIR of the link signal is measured, the measured received SNIR is compared with the target SNIR, and if the measured received SNIR is greater than the target SNIR, a first value is assigned to the step indicator, and the measured received SNIR is Assigns a second value to the step indicator if it is less than the target SNIR, sends a transmit power control (TPC) command instructing the transmitter to adjust the uplink transmit power level based on the step indicator, and sets the step indicator to Receive a TPC command, accumulate a step indicator value, and have a downlink power level indication. Broadcast signal, the signal is transmitted at the downlink power level, the received power of the downlink signal is measured, and the transmitted power level based on the received power level and the indication of the downlink power level and the accumulated step indicator value Have to set.

  Certain embodiments provide a method comprising measuring a power level of a received signal, receiving a transmit power control (TPC) command, and calculating a transmit power level based on the received signal power level and the TPC command. To do.

  An embodiment includes a receiver having an output that provides a measured received power level, an accumulator having an input that accepts step increment and decrement instructions, and an output that provides a sum of past step instructions, A power level setting circuit coupled to the output and the output of the receiver and configured to set transmission power based on the output of the accumulator and the measured received power level; and a transmitter for transmitting a signal with the set transmission power; Provided is a wireless device.

Block diagram of wireless communication system Wireless communication system using open loop method Wireless communication system using closed loop system A wireless communication system using both open loop and closed loop elements in accordance with an embodiment of the present invention. Simulation of probability density function of received SNIR in network Simulation of probability density function of received SNIR in network Simulation of probability density function of received SNIR in network

  Other features and aspects of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings. The accompanying drawings show, by way of example, features according to embodiments of the invention. The summary is not intended to limit the scope of the invention, which is defined solely by the claims.

  An embodiment of the present invention will be described with reference to the drawings as an example.

  In the following description, reference is made to the accompanying drawings which show several embodiments of the present invention. It will be appreciated that other embodiments may be used and mechanical, compositional, structural, electrical and operational changes may be made without departing from the spirit and scope of this disclosure. The following detailed description is not to be taken in a limiting sense, and the scope of the embodiments of the present invention is defined by the claims of the issued patent.

  Some portions of the detailed descriptions that follow are presented in terms of procedures, steps, logic blocks, processes, and operational representations of other symbols with data bits executable in computer memory. Here, procedures, computer-executed steps, logic blocks, processes, etc. are considered to be a consistent sequence of steps or instructions that lead to the desired result. The step uses physical manipulation of physical quantities. These quantities may take the form of electrical, magnetic or radio signals capable of being stored, transmitted, combined, compared and manipulated in a computer system. Sometimes these signals are called bits, values, elements, symbols, characters, words, numbers, etc. Each step may be performed in hardware, software, firmware, or a combination thereof.

  FIG. 1 shows a block diagram of a wireless communication system. The network 100 may include one or more base station controllers 120 such as a radio network controller (RNC) and one or more base stations 110 such as Node-B. Each Node-B is connected to the RNC. The network 100 communicates with one or more users 140, 150 through a channel 160 (also called a wireless link) created between the base station and the users.

  Two mechanisms are primarily responsible for the change in SNIR of signals traveling over the radio link.

  First, channel changes affect SNIR. The instantaneous path loss between the base station and the user can change when the user changes location or when the user's environment changes. Rapid changes can result in the transmitted signal being combined constructively and destructively as the signal travels from the base station to the user through multiple paths. In addition, slow changes can occur due to radio wave attenuation with increasing distance between the base station and the user. Also, slow changes can occur due to signal disturbances by buildings, vehicles and hills.

  Second, signals from other transmitters affect SNIR. For example, signals intended for other mobile radios or other base stations can increase radio link interference and thereby reduce the SNIR of the received signal.

  In a Time Division Duplex (TDD) system, both the uplink and the downlink share the same carrier frequency. Due to this interrelationship at the link, path loss measurements made on the downlink by the mobile radio may be used to estimate the path loss on the uplink. That is, the measured downlink path loss may be used to estimate the uplink path loss. Estimated uplink path loss becomes less reliable over time, but may be appropriate within a frame period. Accordingly, the mobile radio may determine a transmit power level for an uplink change that compensates for the estimated uplink path loss, thereby providing a received signal to the base station at an expected input power level.

  Downlink path loss measurement can be facilitated by a beacon channel. The beacon channel is transmitted from the base station at the reference power level. The mobile radio is notified of the actual transmission power level used by the base station for the beacon channel. In addition to recognizing the actual transmission power level of the beacon channel, the mobile radio may measure the received signal power level. By measuring the received signal power level, the mobile radio can calculate the downlink path loss as the difference between the actual transmitted power level and the received signal power level. Accordingly, the mobile radio can estimate the uplink path loss on the channel between the base station and the mobile radio, and preferably can set its uplink transmission power level.

  The path loss calculation may be updated each time a beacon signal is transmitted / received. In the UTRA TDD system compliant with 3GPP (the third generation partnership project), the beacon signal is transmitted once or twice every 10 milliseconds (ms). If the uplink transmission follows the beacon transmission within a relatively short period, the mobile radio can compensate for fast fluctuations (fast fading) in the radio channel. The case where the beacon signal is transmitted once or twice every 10 ms and the uplink transmission occurs in the intervening period is a case where the moving body is moving from a low speed to a medium speed.

  In addition, wireless channels can be adversely affected by changes in interference levels over time. These temporary interference changes can be accommodated by the base station measuring and communicating the level of interference seen in each uplink time slot. In the UTRA TDD system, a table having an interference value measured for each time slot may be broadcast to all users via a broadcast channel (BCH). The broadcast information may be updated about every 16 frames (160 ms) depending on the system configuration. In other embodiments, the mobile radio may receive this interference table as a signaling message intended for individual mobile radios.

  The 3GPP specification describes two separate schemes (open loop scheme and closed loop scheme) for uplink channel power control. For example, in a 3GPP 3.84 megachip per second (Mcps) TDD system, open loop power control is specified for all uplink channels. In the 3GPP 1.28 Mcps TDD system, open-loop power control is specified only for a physical random access channel (PRACH). The implementation of the closed loop power control method is defined by 3GPP. For example, see the 3GPP recommendation for UTRA TDD systems operating at 1.28 Mcps on non-PRACH uplink channels.

  In a wireless communication system using an open loop scheme, the network and the UE use an outer loop to update the target SNIR value and transmit it to the UE. This affects the UE's transmission power. The network updates the target SNIR value signaled based on the error rate observed on the uplink. Upon receipt, the mobile radio considers the signaled target SNIR value when deriving a transmit power level to apply to the next uplink signal to be transmitted.

  In the 3GPP 3.84 Mcps system incorporating the open loop method, the network instructs the UE with the target SNIR value. The network may also communicate its beacon transmit power level and may provide a measure of uplink interference per time slot measured by the network. Typically, the UE receives an input signal that is a composite of the attenuated version of the network signal that has passed through the radio channel, along with interference signals from other transmitters. The UE measures the received power level of the attenuated network signal and determines the path loss of the radio channel. The UE also decodes the signaled target SNIR value from the network signal. The UE calculates the transmission power level based on the target SNIR value, the determined path loss, and the uplink interference measurement if available.

  FIG. 2 shows a wireless communication system using an open loop scheme. The UE transmits user data 200 at a predetermined transmission power level. Uplink signal 202 with user data 204 propagates over the radio link. The network receives an attenuated version of the transmitted signal. The network measures 207 the uplink interference value and determines 206 an error metric for the uplink signal. The network may update 208 the interference measurement table using the measured uplink interference value. The interference measurement table may have an average measured interference level for each uplink time slot.

  The network may also update 210 the target SNIR value using the error metric. The network transmits 212 the target SNIR in a signaling message on the downlink 214. The signaling message on the downlink 214 has the target SNIR 216. The UE receives and stores the target SNIR 220. The network also broadcasts 222 a beacon signal on the downlink 224. Downlink 224 propagates a signal with an indication of beacon power level over the wireless link. The network may also broadcast interference measurements 228. The UE measures 230 the received power level and saves 232 the interference measurement for later processing.

  With the measured power level and the signaled beacon power level, the UE may determine the path loss. The UE may set the transmission power level using the stored reception target SNIR 216, the stored reception interference measurement 228, and the calculated path loss 234. This transmission power level may be used by transmitter 200 to set the power level of transmission user data 204 on uplink 202.

  The 3GPP specification also defines a closed loop method. For example, 3GPP's 1.28 Mcps system uses a closed loop scheme that uses an outer loop and an inner loop. The closed-loop TCP scheme is the main power control mechanism used for all non-PRACH channels in the 1.28 Mcps TDD system. The closed-loop TCP method is not currently used for the uplink of the 3.84 Mcps TDD system.

  The outer loop determines the target SNIR value, and the inner loop uses the target SNIR value. The outer loop has network components that determine an error metric such as bit error rate, block error rate or CRC error number on the uplink from the UE. This error metric is used to set and update the target SNIR value. The inner loop has a network component that uses the target SNIR value calculated and set by the outer loop. The network measures the received SNIR value of the uplink signal.

  The comparator then determines whether the measured SNIR value is greater or less than the target SNIR value. If the measured SNIR value is greater than the target SNIR value, the network communicates a transmit power control (TPC) command on the downlink and instructs the UE to reduce its current transmit power by a step value (eg 1 dB) To do. On the other hand, if the measured SNIR value is less than the target SNIR value, the network conveys the TPC command and instructs the UE to increase its current transmit power by a step dB value.

  In a system that uses only a closed loop power control scheme, multiple TPC commands may be required to properly match the UE transmit power to the target SNIR value. For example, if the path loss from one frame to the next increases by 15 dB, the system requires 15 TPC commands to compensate for 15 dB fading. The UE accumulates increases and decreases in TPC commands and determines an appropriate uplink transmit power level. By increasing and decreasing the uplink power level of each UE, the network ensures that the power of each UE is such that the ratio of the received uplink energy level per transmitted bit to the spectral density of noise and interference signals is a constant value. Try to control the level. This TPC command adjustment process is executed for each UE of the cell. However, the constant value may be non-uniform among UEs depending on the system configuration.

  In the closed loop TPC scheme, the inner loop SNIR is maintained via a closed loop method using binary feedback. The feedback indicates power up or power down. Each time a TPC command is received, the UE integrator is used in the inner loop to update the UE transmit power by a step amount +/− ΔdB. The TPC command itself is guided by the network and signaled to the UE via the downlink channel. When calculating the appropriate TPC command to send, the network measures the received SNIR and compares this measurement with the target SNIR value. If the SNIR is too small, an up command is sent. If the SNIR is too high, a down command is sent. The target SNIR value is updated by the outer loop based on the observed error performance on the link. In this way, the inner and outer feedback loops are closed by TPC signaling.

  FIG. 3 shows a wireless communication system using a closed loop system. The closed loop scheme has a 300 outer loop in which the UE transmits user data over a radio link with an uplink signal 302 having user data 304. The network determines 306 an error metric for the received uplink signal. Using the error metric, the network calculates and updates 308 the target SNIR value.

  The closed loop scheme also has a 310 inner loop where the network measures the received SNIR of the uplink signal 302. The network compares 312 the measured SNIR with the target SNIR determined in the outer loop. The inner loop generates and sends 314 a TPC command based on the comparison 312. Downlink signal 316 carries a TPC command 318 over the radio link. The UE accumulates 320 TPC commands and sets the transmission power of the next uplink transmission 300 using the accumulated TPC commands 322.

  Mobile radio systems using open loop or closed loop schemes have their advantages and disadvantages. Advantageously, the open loop scheme adapts quickly to changes in path loss. If it is observed that the path loss has deteriorated by 15 dB, for example, at 10 ms intervals, the transmit power can be adjusted accordingly. A further advantage is that the open loop may continue to be partially updated when there is no user specific feedback signaling. For example, if the UE has not received an updated target SNIR value, the outer loop is interrupted, but path loss changes may continue to be tracked.

  Unfortunately, the time slot interference level update rate in an open loop system is relatively low. Thus, a system using an open loop scheme is slower to adapt to changes in interference than a system using a closed loop scheme. A further disadvantage of the open loop scheme is that the interference is considered to be the same for all UEs in a particular uplink time slot. That is, each UE assigned a time slot uses the same interference measurement signaled by the base station on the BCH. Commonly used interference measurement tables infer about the statistical nature of the interference and do not consider the individual cross-correlation characteristics of the uplink channelization code. Therefore, it is up to the outer loop to compensate for these effects, but it is unfortunately slowed down.

  Conversely, the closed-loop only scheme cannot adapt well to fast path loss changes because the closed-loop can only move by a step ΔdB between each update. Thus, if the path loss changes by 15 dB during the update and the step ΔdB value is only 1 dB, the closed loop can only move 1 dB during each cycle and cannot adapt quickly. Therefore, at the same update rate (for example, once every 10 ms), the closed-loop TPC scheme cannot track fast fading observed in a general mobile radio channel. Furthermore, the closed loop cannot be updated during the interruption of the transmission of the TPC command.

  Advantageously, the closed loop is relatively quick to respond to changes in uplink interference because both path loss and interference are accommodated by the same loop. The closed loop scheme using TPC commands has a further advantage in that it allows adaptation of interference per user to the open loop scheme. The open loop method broadcasts an average interference table for each time slot.

  In accordance with certain embodiments of the present invention, both aspects of the open loop and closed loop schemes are advantageously combined to form a power control method. Certain embodiments of the present invention advantageously combine elements of both open and closed loop schemes to control power levels, thereby reducing one of the disadvantages associated with one of the separately used schemes. Avoid more than one.

  According to an embodiment of the present invention, the UE incorporates a closed loop TPC structure and an open loop path loss estimation structure. Certain embodiments of the present invention allow for both relatively quick adaptation to fast fading and adaptation of interference per user, partially in the presence of a temporary lack of TPC commands. Holds the function to update the control loop.

  Certain embodiments of the present invention require changes to one or more elements of a standard mobile radio system. For example, some embodiments require changes to the UE only, while some embodiments require changes to the network only. Embodiments that change the UE rather than the network allow the UE of the present invention to operate with a conventional base station. Similarly, embodiments that change the network, not the UE, allow the network of the present invention to operate with a conventional UE. Still other embodiments of the present invention require changes to both the network and the UE. Embodiments that change standard network elements may have changes to only the base station, not the radio network controller (RNC). Other embodiments change both the base station and the RNC.

  Some embodiments of the present invention incorporate a loop with three components (an open loop component located in the UE, a SNIR comparison loop located in the network, and a SNIR update component located in the network as well). .

First, the open loop component may be located at the UE and driven by the measured beacon received power level and path loss calculation. This loop attempts to adapt to all instantaneous path loss changes with every beacon transmission. The partial power calculated by this loop is a function of beacon signal transmission power (P _Tx ) and beacon received signal code power (RSCP), and is denoted by P _open (k). Here, k indicates the current frame number. P _Tx is known to the UE and is derived from the signaled power level of the base station (FIG. 4, 428). The measured power level (RSCP (k)) of frame k may be determined by the UE receiver (FIG. 4, 432). P _open (k) may also be a function of a constant value (C) to ensure that the transmission arrives at an appropriate power level.

P _open (k) = P _Tx -RSCP (k) + C
Second, the SNIR comparison loop is arranged in a network such as Node-B. The SNIR comparison loop is driven by the received SNIR metric. The received SNIR is compared with the target SNIR value set by the outer loop. The comparison result results in signaling a TPC command that is signaled to the UE to change its transmit power. Binary signaling may be used so that the TPC command indicates a change (up or down) by a fixed amount of transmit power. Alternatively, multi-level TPC commands may be used.

  Third, the outer loop is placed in a network such as Node-B or RNC. The outer loop is driven by data error statistics observed in uplink transmission. The outer loop serves to set the target SNIR level of the SNIR comparison loop.

Optional auxiliary processing at the UE is based on (a) γ _SF (spreading factor (SF)) and (b) β _TFC (transport format (TFC)) Adjust the power.

Therefore, in the current frame k, the UE may calculate the transmission power P _Tx (k) as shown below. However, K is an initial frame number determined when the power control process starts. TPC _i is -1 for a down TPC command, +1 for an up TPC command, and 0 when no TPC command is received. step is the size of the amount added to the accumulator when each TPC command is received. The transmission power P _Tx (k) may be updated every frame period. Alternatively, the transmission power P _Tx (k) may be updated each time a new TPC command is received. Alternatively, the transmit power P _Tx (k) may be updated only when a PTC command or a new power level is received from the network.

本発明による電力制御方式の実施例が図４に概略的に示されている。γ_SF及びβ_TPCの調整係数は図面を明瞭にするために示されていない。

An embodiment of a power control scheme according to the present invention is schematically illustrated in FIG. The adjustment factors for γ _SF and β _TPC are not shown for clarity.

  FIG. 4 shows a wireless communication system using both open loop and closed loop elements in accordance with the present invention. The UE transmits 400 user data at the determined transmission power level. Uplink signal 402 with user data 404 propagates over the radio link. The network receives an attenuated version of the transmitted signal.

  The network determines 406 an error metric for the uplink signal 402. Optionally, the network may measure the uplink interference level and may update 422 the interference measurement table. Data measured or calculated from uplink measurements may be entered into an interference measurement table. The interference measurement table may have an average measured interference level for each uplink time slot. Within the network, an error metric may be used to update 408 the target SNIR value.

  The network also transmits 424 a beacon signal. Downlink signal 426 with an indication of beacon transmit power level 428 propagates over the radio link. Optionally, the network may broadcast interference measurement 430. The UE saves 432 the signaled power level, measures the received power level, and saves interference measurements 434 for later processing if available.

  Similar to the closed loop scheme, the UE transmits 400 user data on the radio link with an uplink signal 402 having user data 404. The network determines 406 an error metric for the received uplink signal. Using the error metric, the network calculates and updates 408 the target SNIR value.

  The network also measures 410 the received SNIR of the uplink signal 402. The network compares 412 the measured SNIR with the determined target SNIR. The network generates and transmits 414 a TPC command based on the comparison 412. Downlink signal 416 carries TPC command 418 over the radio link. The UE accumulates 420 TPC commands and partially uses the accumulated TPC commands to set 436 the transmission power level of the next uplink transmission 400.

Similar to the open loop scheme, the UE may determine the path loss P _open (k) based on the measured power level and the signaled beacon power level. The UE may use the stored reception interference measurement I (k) to adjust the transmission power following a transmission interruption or TPC command reception interruption. UE is the accumulated TPC command

と、計算されたパスロスP_open(k)と、調整係数γ_SF及びβ_TFCと、任意選択でI(k)に基づく調整とを使用し、送信電力レベルを設定してもよい436。この送信電力レベルP_Tx(k)は、アップリンク402でユーザデータを送信する400アップリンク電力レベルを設定するために使用されてもよい。 [Outside 1]

And the calculated path loss P _open (k), adjustment factors γ _SF and β _TFC , and optionally an adjustment based on I (k), may be used to set 436 the transmission power level. This transmission power level P _Tx (k) may be used to set a 400 uplink power level for transmitting user data on the uplink 402.

  A downlink signal 426 that has a power level 428 and may have an interference measurement 430 is broadcast in the cell. Previous UEs using a closed loop scheme do not use downlink received power measurements while monitoring the power level signaled in the beacon broadcast to set the uplink transmit power. Similarly, previous UEs using the closed loop scheme do not calculate downlink path loss or use downlink path loss calculation while processing TPC commands. The previous UE simply sets its transmit power level according to the TPC command as instructed. When the network commands a known UE to increase its transmit power by one step amount, the previous UE increases its transmit power by one step amount.

  According to some embodiments of the present invention, the UE may receive a TPC command instructing to change its transmit power by a single step level in a particular direction, but the UE may differ by a different amount or in practice. The transmission power level may actually be changed by an amount in the opposite direction. The UE uses the TPC only as a coefficient for determining whether to increase the transmission power level, decrease the transmission power level, or leave the transmission power level unchanged.

  For example, assume that the UE has transmitted a burst to Node-B at 20 dBm on a radio link with 100 dB path loss. The received power of the Node-B receiver is -90 dBm, which is the difference between 20 dBm and 110 dB loss. Next, assume that Node-B attempts to receive an uplink signal from the UE at -89 dBm. Node-B conveys a TPC command that instructs the UE to increase the uplink transmit power level by 1 dB, which the UE receives. Also assume that the path loss improves by +10 dB from the previous frame to this frame (eg from 110 dB to 100 dB).

  The previous UE transmits the next burst at +21 dBm, which is the sum of the previous level (+20 dBm) and the step increase (1 dB). The transmitted +21 dBm signal will probably reach Node-B at -79 dBm. The signal level of + 10dB is too high because channel improvement was not considered.

  According to an embodiment of the present invention, the UE considers a new path loss. The transmit power level before +20 dBm is reduced by +10 dB to account for the improved channel path loss of +10 dB. The resulting transmit power level is +10 dBm. The UE also takes into account the TPC command by adjusting the transmit power level by the desired step of +1 dB, resulting in a new transmit power level of +11 dBm. This takes into account the improved channel (+10 dB) and also meets Node-B's requirement to have a received signal with a step increase (+1 dB). +11 dBm reaches Node-B at the desired level of -89 dBm if the channel path loss estimate is accurate. As shown in this example, even if the Node-B TPC command commands a 1 dB increase, the transmit power level is reduced by 9 dB (from +20 dBm to +11 dBm). Thus, even if the UE receives a network TPC command that instructs it to step up or down its uplink transmit power by 1 dB, the UE may actually change the transmit power level by a different amount. Indeed, as mentioned above, the UE's transmit power level may change in the opposite direction of the TPC command.

  During uplink 402 inactivity, the TPC command 418 may not be received by the UE. The transmit power level of the UE for the next initial transmission 400 may be determined using the current update of the open loop component. That is, the initial transmit power level may be determined based on the beacon power level 428, the measured 432 received power level, and optionally the interference measurement 430. Since the open loop component does not require feedback, it may continue to be updated with every beacon transmission even during uplink transmission interruptions.

  The history stored in the TPC accumulator may be unchanged. In some situations, the history may be considered useful and is not reset. Alternatively, the accumulated TPC history may be used to set the uplink transmit power level, but some extra power margin may be added to ensure a clean start for the loop. Alternatively, the UE may decide to discard the accumulated TPC history and reset it to an initial set value or an initial value. The initial set value or initial value may optionally be based on the received interference measurement table 430.

  The function of the open loop component to compensate for fast fading is a function of the channel rate and the delay between beacon and uplink time slots. Open-loop control is often effective at walking speeds and higher speeds when the uplink slot is located close to the beacon in time. At high moving speeds, power control performance is likely to improve if beacon RSCP filtering is enabled at the UE. The UE serves to detect whether filtering should be applied to the open loop component. In order to control the effectiveness of RSCP filtering, automatic detection of the channel rate may be performed by the UE. In some embodiments of the present invention, the UE disables the combined open loop / closed loop scheme that operates in accordance with the present invention when the UE passes a threshold indicating the speed of movement.

  Simulations were performed to show the performance benefits of certain embodiments of the present invention. The radio channel simulated here represents the ITU indoor to outdoor pedestrian model B channel described in ITU-R M.1225 Guidelines for Evaluation of Radio Transmission Technologies for IMT-2000. The target SNIR of the outer loop is based on an error rate of 1%. Residual SNIR error terms observed at the base station were monitored.

  5A, 5B and 5C show simulations of the probability density function of the received SNIR in the network, respectively. In each simulation, approximately 10,000 received SNIR values are sampled. The simulation results for each scenario are grouped and collected in a bin. The vertical axis represents the number of occurrences of a specific range (bottle) of received SNIR values. Sampled received SNIR values that fall within the range defined by the bottle are counted as occurrences of that bottle.

  FIG. 5A shows the simulation results of the system using only the open loop method. In this plot, the bottle width is about 0.42 dB. The simulation results show that the system tracks the fast fading in the channel well, but cannot track the interference variations included in the simulation. These values are only updated at the UE via signaling every 160 ms. Thus, the error term represents a significant variation at the receiver.

  FIG. 5B shows a simulation result of the system using only the closed loop method. In this plot, the bottle width is about 0.48 dB. Simulation results show that the system can track interference changes well, but cannot track path loss because it is limited by the +/- 1dB step size of the TPC command.

  FIG. 5C shows a simulation result of a system (shown in FIG. 4) that combines both the open-loop method and the closed-loop method. In this plot, the bottle width is about 0.24 dB. Simulation results show that the system can respond to both path loss and interference changes. Furthermore, the residual SNIR error term shows a small variation. This plot shows that the variation in this distribution is significantly reduced with the combined power control scheme.

  In the above simulation (using the same fading and interference profile for each loop method), the following intermediate transmit power was obtained:

シミュレーションされたチャネル及び干渉のシナリオでは、複合型方式は、開ループ方式より2.17dB小さい電力を使用して、及び閉ループ方式より1.89dB小さい電力を使用して、1%のブロック誤り率（BLER：block error rate）を維持することができる。実際のシステムでは、この電力の節約は、更に広いセル範囲、更に高いアップリンク容量及びスループット、更なる電池寿命と同等になり得る。利得の大きさは、異なるチャネル速度、形式及び干渉プロファイルで変化してもよいが、複合型の性能は、個々に使用されるときの開ループ方式及び閉ループ方式より優れている。

In the simulated channel and interference scenario, the combined scheme uses 1.17 dB less power than the open loop scheme and 1.89 dB less power than the closed loop scheme, and 1% block error rate (BLER: block error rate) can be maintained. In practical systems, this power saving can be equivalent to a wider cell range, higher uplink capacity and throughput, and additional battery life. Although the magnitude of the gain may vary with different channel rates, types and interference profiles, the combined performance is superior to the open loop and closed loop schemes when used individually.

  With respect to signaling overhead, the hybrid scheme helps avoid the need to convey the target SNIR and interference level on the downlink channel and has the same signaling efficiency as the closed loop scheme. In some embodiments, the signaling efficiency is 1 bit per update.

  In systems using complex power control schemes, new physical channels are used in the downlink to convey fast allocation and scheduling information to the user and thereby inform the UE of the uplink resources that may be used. Also good. This new physical channel may also be used as a feedback channel for a hybrid power control scheme. For example, the allocation / scheduling channel may carry a TPC command. Alternatively, the hybrid scheme may be applied to existing channel types (dedicated or shared uplink physical channels) of UTRA TDD and other TDD systems.

  Certain embodiments of the present invention may be incorporated into the UE to control the uplink power level and support the functionality incorporated into the base station. For example, Node-B or RNC may implement new parameters included in signaling commands or broadcast messages. In this case, the new parameter instructs the UE to enable or disable the setting of the uplink transmission power level based on both the path loss estimation and the TPC command. The parameter may also indicate whether the UE uses open loop power control, closed loop power control, or a hybrid scheme.

  Some embodiments of the present invention operate on a downlink signal that includes both a TPC command and an indication of the downlink transmit power level. In these embodiments, the downlink signal provides both downlinks 416 and 430 (FIG. 4) in one signal. The UE may receive one physical channel that decodes the TPC command, decodes the downlink power level indication, and measures the received power level. In these embodiments, the UE measures the power level of the received signal, receives the TPC command, and calculates the transmission power level based on the power level of the received signal and the TPC command.

  Although the present invention has been described with respect to particular embodiments and exemplary drawings, those skilled in the art will recognize that the invention is not limited to the described embodiments or drawings. For example, the composite uplink power control scheme described above may implement the opposite of controlling downlink power. In this case, the function performed by the UE for the composite uplink scheme may be performed by the network. Similarly, the functions performed by the network for the complex uplink scheme may be performed by the UE.

  Furthermore, although individually listed, a plurality of means, aspects or method steps may be implemented by eg a single unit or processor. Furthermore, although individual features may be included in different claims, they may be advantageously combined in some cases and inclusion in different claims indicates that a combination of features is not feasible and / or advantageous. It doesn't mean. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but that this feature can be applied to other claim categories as well, if necessary. Show. Furthermore, the order of the features in the claims does not imply a particular order in which the features must be operated. In particular, the order of the individual steps in the method claims does not mean that the steps have to be performed in this order. The method may be performed in any suitable order.

  The following items are further disclosed with respect to the above embodiments.

(1) A power control method in a wireless communication system having a first wireless device and a second wireless device,
In the second radio,
Determining a path loss of a radio channel between the first radio and the second radio;
Receiving a transmission power control (TPC) command transmitted from the first radio,
Based on the path loss and the TPC command, the transmission power level of the second radio is set,
A power control method comprising transmitting a signal at the set transmission power level.

(2) Determining the path loss
Receiving signaling having a signaled power level, wherein the signaling is transmitted from the first radio at the signaled power level;
The power control method according to (1), further comprising measuring a power level of the received signal.

  (3) The power control method according to (2), wherein determining the path loss further includes calculating a difference between the signaled power level and the measured power level.

(4) The received signaling further includes an interference measurement table;
The power control method according to (2) or (3), wherein the setting of the transmission power level is further based on the interference measurement table.

  (5) The power control method according to any one of (1) to (4), wherein the setting of the transmission power level is further based on an adjustment coefficient.

  (6) The power control method according to (5), wherein the adjustment coefficient incorporates a spreading factor parameter.

  (7) The power control method according to (5) or (6), wherein the adjustment coefficient incorporates a parameter of a selected transport format.

(8) further comprising accumulating a sequence of step indicators;
The power control method according to any one of (1) to (7), wherein the sequence of the step indicator is provided in a sequence corresponding to the received TPC command.

  (9) The power control method according to (8), wherein setting the transmission power level is based on the path loss and the sequence of the accumulated step indicators.

(10) the first radio has a CDMA base station;
The power control method according to any one of (1) to (9), wherein the second wireless device includes a user device.

(11) A power control method in a wireless communication system having a first wireless device and a second wireless device,
In the first radio,
Receiving a signal transmitted from the second radio,
Measure SNIR of the received signal,
Comparing the measured SNIR with the target SNIR;
Assigning a first value to the step indicator if the measured SNIR is greater than the target SNIR, and assigning a second value to the step indicator if the measured SNIR is less than the target SNIR;
A power control method comprising transmitting a transmission power control (TPC) command having the step indicator.

  (12) The power control method according to (11), wherein signaling having a signaled power level is transmitted, and the signaling is transmitted at the signaled power level.

  (13) The power control method according to (12), wherein the transmitted signal further includes an interference measurement table.

  (14) The power control method according to (12) or (13), wherein the transmitted signal is transmitted through a broadcast channel.

  (15) The power control method according to any one of (12) to (14), wherein the transmitted signal is transmitted through a beacon channel.

(16) determining an error metric of the received signal;
The power control method according to any one of (11) to (15), further comprising updating the target SNIR based on the error metric.

(17) measuring an interference value of the received signal;
The power control method according to any one of (11) to (16), further comprising using the measured interference value to update an interference measurement table.

(18) further comprising transmitting signaling having the interference measurement table and the signaled power level;
The power control method according to (17), wherein the signaling is transmitted at the signaled power level.

(19) The first radio has a CDMA base station,
The power control method according to any one of (11) to (19), wherein the second wireless device includes a user device.

(20) A device having a user device,
A receiver operable to receive a transmit power control (TPC) command transmitted from the base station and operable to measure a power level of the received signal;
Computational logic coupled to the receiver and operable to determine a path loss of a radio channel between the base station and the user equipment;
Power level setting logic coupled to the calculation logic and operable to set a transmission power level based on the path loss and the TPC command;
A transmitter coupled to the power level setting logic and operable to transmit a signal at the set transmission power level.

(21) further comprising an accumulator coupled to the power setting logic;
The accumulator is
An input operable to accept a step indicator, wherein the received TPC command provides the step indicator;
Summing logic operable to add past cumulative values and said step indicator to yield a current cumulative value;
A memory operable to hold the current cumulative value;
An output operable to provide the current cumulative value; and
The apparatus of (20), wherein the power level setting logic operable to set the transmit power level is based on the path loss and the current cumulative value.

(22) A system having a base station,
A receiver operable to measure the SNIR of the received signal;
Coupled to the receiver, having an input for the measured SNIR and an input for a target SNIR, and assigning a first value to a step indicator if the measured SNIR is greater than the target SNIR; Comparison logic operable to assign a second value to the step indicator if the measured SNIR is less than the target SNIR;
Command generation logic coupled to the comparison logic and operable to generate a transmit power control (TPC) command having the step indicator;
A transmitter coupled to the command generation logic and operable to transmit the TPC command.

(23) an error metric logic coupled to the receiver and operable to determine an error metric of the received signal;
The system of claim 22, further comprising: update logic coupled to the error metric logic and operable to update the target SNIR.

(24) measurement logic coupled to the receiver and operable to measure interference;
Updating logic coupled to the measurement logic and operable to update an interference measurement table using the measured interference;
The system of (22), wherein the transmitter is further operable to transmit signaling having the interference measurement table and a signaled power level.

Claims (24)

A power control method in a wireless communication system having a base station and a mobile terminal,
In the mobile terminal,
Determining a path loss of a radio channel between the base station and the mobile terminal;
Receiving a scheduled uplink transmission resource allocation in a downlink channel and a transmission power control (TPC) command transmitted from the base station to the mobile terminal in the downlink channel;
Based on the determined path loss and the TPC command, set the transmission power level of the mobile terminal,
A power control method comprising: transmitting a signal on the scheduled uplink transmission resource at the set transmission power level. Determining the path loss is
Receiving signaling having a signaled power level, wherein the signaling is transmitted from the base station at the signaled power level;
The power control method according to claim 1, further comprising measuring a power level of the received signal.   The power control method of claim 2, wherein determining the path loss further comprises calculating a difference between the signaled power level and the measured power level. The received signaling further comprises an interference measurement table;
The power control method according to claim 2 or 3, wherein the setting of the transmission power level is further based on the interference measurement table.   The power control method according to any one of claims 1 to 4, wherein the setting of the transmission power level is further based on an adjustment coefficient.   The power control method according to claim 5, wherein the adjustment coefficient incorporates a spreading factor parameter.   The power control method according to claim 5 or 6, wherein the adjustment coefficient incorporates a parameter of a selected transport format. Further comprising accumulating a sequence of step indicators;
The power control method according to any one of claims 1 to 7, wherein the sequence of step indicators is provided as a corresponding sequence of received TPC commands.   The power control method according to claim 8, wherein setting the transmission power level is based on the path loss and the sequence of the accumulated step indicators. The base station comprises a CDMA base station;
The power control method according to any one of claims 1 to 9, wherein the mobile terminal includes a user apparatus. A power control method in a wireless communication system having a base station and a mobile terminal,
In the base station,
Receiving a signal transmitted from the mobile terminal;
Measure SNIR of the received signal,
Comparing the measured SNIR with the target SNIR;
Assigning a first value to the step indicator if the measured SNIR is greater than the target SNIR, and assigning a second value to the step indicator if the measured SNIR is less than the target SNIR;
A power control method comprising: allocating a scheduled uplink transmission resource in a downlink channel and transmitting a transmission power control (TPC) command having the step indicator to the mobile terminal in the downlink channel.   12. The power control method according to claim 11, comprising transmitting signaling having a signaled power level, wherein the signaling is transmitted at the signaled power level.   The power control method according to claim 12, wherein the transmitted signal further includes an interference measurement table.   The power control method according to claim 12 or 13, wherein the transmitted signal is transmitted through a broadcast channel.   The power control method according to any one of claims 12 to 14, wherein the transmitted signal is transmitted through a beacon channel. Determining an error metric of the received signal;
The power control method according to claim 11, further comprising updating the target SNIR based on the error metric. Measuring the interference value of the received signal;
The power control method according to any one of claims 11 to 16, further comprising using the measured interference value to update an interference measurement table. Further comprising transmitting signaling having the interference measurement table and the signaled power level;
The power control method according to claim 17, wherein the signaling is transmitted at the signaled power level. The base station comprises a CDMA base station;
The power control method according to any one of claims 11 to 19, wherein the mobile terminal includes a user apparatus. A device having a mobile terminal,
Operable to receive a scheduled uplink transmission resource allocation in a downlink channel and a transmit power control (TPC) command transmitted from a base station on the downlink channel, and A receiver operable to measure;
Computational logic coupled to the receiver and operable to determine a path loss of a radio channel between the base station and the mobile terminal;
Power level setting logic coupled to the calculation logic and operable to set a transmission power level based on the determined path loss and the TPC command;
A transmitter coupled to the power level setting logic and operable to transmit a signal on the scheduled uplink transmission resource at the configured transmission power level. Further comprising an accumulator coupled to the power level setting logic;
The accumulator is
An input operable to accept a step indicator, wherein the received TPC command provides the step indicator;
Summing logic operable to add past cumulative values and said step indicator to yield a current cumulative value;
A memory operable to hold the current cumulative value;
An output operable to provide the current cumulative value; and
21. The apparatus of claim 20, wherein the power level setting logic operable to set the transmit power level is based on the path loss and the current cumulative value. A system having a base station,
A receiver operable to measure the SNIR of the received signal;
Coupled to the receiver, having an input for the measured SNIR and an input for a target SNIR, and assigning a first value to a step indicator if the measured SNIR is greater than the target SNIR; Comparison logic operable to assign a second value to the step indicator if the measured SNIR is less than the target SNIR;
Command generation logic coupled to the comparison logic and operable to generate a transmit power control (TPC) command having the step indicator;
A transmitter coupled to the command generation logic and operable to transmit a scheduled uplink transmission resource assignment in a downlink channel and the TPC command to a mobile terminal in the downlink channel system. Error metric logic coupled to the receiver and operable to determine an error metric of the received signal;
23. The system of claim 22, further comprising: update logic coupled to the error metric logic and operable to update the target SNIR. Measurement logic coupled to the receiver and operable to measure interference;
Updating logic coupled to the measurement logic and operable to update an interference measurement table using the measured interference;
23. The system of claim 22, wherein the transmitter is further operable to transmit signaling having the interference measurement table and a signaled power level.

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