JP5054094B2 - Control of transmit power level in wireless communication systems using different scrambling codes - Google Patents

Description

  The present invention relates to a method for controlling a transmit power level of a signal transmitted from a first transceiver to a second transceiver in a wireless communication system. Here, the signal is transmitted using at least one of a first scrambling code and a second scrambling code. The method comprises the steps of repeatedly estimating a quality measurement value for a signal received by a second transceiver in an inner transmission power control loop (inner loop type transmission power control), the quality measurement value and a reference value for quality measurement, Generating a transmission power control command depending on the step, transmitting the transmission power control command to the first transceiver, and adjusting the transmission power level at the first transceiver depending on the transmission power control command And, in an outer transmission power control loop (outer loop type transmission power control), calculating an operation performance level for a signal received by a second transceiver during a certain time interval, and depending on the operation performance level And adjusting a reference value for the quality measurement. The present invention further provides a method for generating a transmit power control command in a transceiver for receiving a signal transmitted from a remote transceiver in a wireless communication system, and a transceiver for receiving a signal from a remote transceiver in a wireless communication system. And a corresponding computer program and computer-readable storage medium.

  In a wireless communication system, the physical channel between the transmitter and the receiver is typically formed by a radio link. As an example, the transmitter is a base station and the receiver is a mobile station. The reverse is also possible. In that case, the base station typically corresponds to a cell in a wireless communication system. Since the transmitting antenna is not sharply directed toward the receiver, the transmission signal may propagate through a plurality of propagation paths (paths). In addition to the possible direct paths from the transmitter to the receiver, there are many other propagation paths caused by reflections from surrounding objects. Thus, since different parts of the signal are reflected from different objects, such as buildings, moving vehicles, or terrain details, the receiver can receive multiple signals at different times, i.e. with different delays. There is a possibility of receiving the same signal. The radio link between the base station and the mobile terminal is a bidirectional link. That is, the information is transmitted from the base station to the mobile terminal (downlink) and simultaneously from the mobile terminal to the base station (uplink).

  Many transmission systems attempt to reduce the effects of multipath propagation and fading by using a receiver that combines the data symbol energy from all multipath elements. In code division multiple access (CDMA) systems and wideband code division multiple access (WCDMA) systems, the energy of different portions of the received signal can be utilized in the receiver, for example by using a RAKE receiver or the like.

  In these wireless communication systems, spreading and despreading are used. Data is transmitted from the transmitter side using spread spectrum modulation techniques. Here, the data is spread over a wide range of frequencies. Each channel spreading process includes a channelization process followed by a scrambling process. In the channelization process, each data symbol is converted into a number of so-called chips by multiplying a channelization code consisting of a binary sequence of 1s and 0s. The number of chips for one data symbol is called a spreading factor (SF). The channelization code is usually an orthogonal variable spreading factor (OVSF) with a spreading factor of up to 512. The OVSF scheme is a kind of code tree, and each level in the tree is a set of codes orthogonal to each other, corresponding to a given spreading factor. In the scrambling process, the spreading sequence of the chip is scrambled by multiplying the chip by a complex scrambling code that is a pseudo-noise code. While scrambling codes are mainly used to separate base stations or cells from each other, channelization codes are used to separate different physical channels (terminals or users) in each cell. At the receiver, despreading and demodulation are performed using the same code, and the transmitted data is decoded.

  In the timing configuration of the WCDMA system, the chip is transmitted in a transmission time interval (TTI), and each TTI is composed of 1 to 8 radio frames. Each radio frame has a duration of 10 ms and is divided into 15 slots. One slot contains 2560 chips. Thus, one TTI can contain 15 to 120 slots. The TTI is divided into a number of transport blocks (TBs) with variable durations depending on the information to be transmitted.

  For downlink transmission, the usable scrambling codes are divided into several sets of one primary scrambling code and corresponding 15 secondary scrambling codes. Each cell of the system is assigned one primary scrambling code and 15 corresponding secondary scrambling codes. Some physical channels, such as the common pilot channel (CPICH, Common Pilot Channel), on a given link between the transmitter and receiver in a cell are always the primary scrambling code assigned to that cell. Sent using On the other hand, other physical channels such as a dedicated physical channel (DPCH, Dedicated Physical Channel) can be transmitted using a primary scrambling code or one of the corresponding secondary scrambling codes. That is, this secondary scrambling code is one secondary scrambling code included in a set related to the primary scrambling code assigned to the cell. Therefore, in these physical channels, some radio frames are transmitted using the primary scrambling code and other radio frames are transmitted using the secondary scrambling code. There will be a shift between one of the secondary scrambling codes. The secondary scrambling code can be used, for example, for the DPCH when the channelization code tree is full with respect to the primary scrambling code, although the transmitter capacity is still sufficient.

  Another example of shifting between different scrambling codes occurs when the mobile station transitions to a mode called compressed mode, which can use an alternative scrambling code. Two alternative scrambling codes are associated with each of the primary and secondary scrambling codes, which are designated for use in the compressed mode. A compressed mode occurs when performing a handover between frequencies when several slots of a frame are allocated for the mobile station to make the necessary measurements on different carrier frequencies. Therefore, in a compressed frame, only a small number of slots are available for normal transmission due to the transmission gap used for measurement. To compensate for this, the spreading factor can be reduced. However, spreading factor changes are likely to require reassignment of some or all channelization codes in the code tree in order to maintain orthogonality. To avoid this reassignment, the transmitter can instead switch to an alternative scrambling code corresponding to a different code tree. The correlation of scrambling codes is like noise, and the correlation of channelization codes is considerable even if they are under the same branch in the code tree if they are channelization codes with different scrambling codes The value will be low.

  In such a wireless communication system, it is necessary to compensate for fluctuations in the channel (such as propagation delay effect and fading effect) and to maintain acceptable transmission quality for all users in the system. Transmit power control is used to ensure.

  Typically, a closed transmit power control loop (closed loop transmit power control) is used, where the transmit power level is adjusted to maintain the quality measurement for the received signal at a given target value. Closed transmit power control loops for WCDMA typically include a relatively fast inner transmit power control loop and a relatively slow outer transmit power control loop in the receiver of a device in a wireless communication system in the uplink or downlink. With elements to form. In the following, reference is made to downlink transmission. That is, transmission from a base station to a mobile terminal or user equipment (UE), but a similar control loop is also used for uplink transmission.

  The inner loop calculates a signal-to-interference ratio (SIR) value at a rate of once per slot, and compares it with the SIR reference value (target SIR). If the estimated SIR (estimated SIR) is smaller than the reference value, the user equipment transmits transmission power control (TPC, Transmit Power Control) via an uplink dedicated physical control channel (DPCCH, Dedicated Physical Control Channel). A command will be sent and the base station will be requested to increase the transmit power for the downlink dedicated physical channel (DPCH, Dedicated Physical Channel). On the other hand, if the estimated SIR is larger than the reference value, the user equipment will request the base station to reduce the transmission power. The transmission power update can be performed every slot or every 3 slots, and one step of transmission power change is 1.0 dB by default, with 0.5 dB, 1.5 dB, or 2 as the selected value. There is 0.0 dB.

  The outer loop type transmission power control of the WCDMA receiver determines the SIR reference value by using the relationship between the estimated block error rate (BLER, Block Error Rate) and the BLER target value. The BLER performs a cyclic redundancy check (CRC) on each transport block (TB) to obtain a 0 or 1 flag for correctly or incorrectly received blocks, and some number of TTIs. Can be estimated by obtaining effective BLER values through filtering. The instantaneous BLER for the current TTI can be estimated as the ratio of the number of erroneous transfer blocks to the total number of TTI transfer blocks. The estimated BLER (estimated BLER) value is then compared to the BLER target.

Basically, outer loop transmission power control attempts to adjust the SIR reference value by comparing the estimated BLER and the BLER target. If the estimated BLER is higher than the predetermined BLER target, the SIR reference value for the next TTI is increased to obtain higher power from the BS and thereby reduce block errors. Similarly, when the estimated BLER is lower than the BLER target, the SIR reference value is decreased so that excessive transmission power is not sent to the target user apparatus. Therefore, at the end of each TTI, a new SIR reference value is calculated based on the estimated BLER for that TTI. This new SIR reference value is then used by the inner loop during the next TTI.
International Publication WO00 / 48335 US Application Publication US2003 / 0036403 Specification

  As described above, the physical channel of the link between the transmitter and the receiver in a wireless communication system is transmitted using the same scrambling code when normal. That is, the primary scrambling code assigned to the cell. However, the situation is that secondary scrambling codes are used for some radio frames in some channels (eg, in DPCH) and primary scrambling codes are used for other radio frames; Alternatively, a situation occurs in which an alternative scrambling code is used for a compressed frame and an original primary scrambling code or a secondary scrambling code is used for a normal frame.

  However, the SIR reference value calculated for a signal received with a certain scrambling code has proven to be not optimal for a signal received with a different scrambling code. This switching between creates problems for transmit power control. Thus, switching between the scrambling codes results in an SIR reference value that is not optimal for either of the two scrambling codes. Typically, the amount of block errors increases so that the SIR reference value rises to a higher level compared to the level actually required. The net result is wasted transmission power.

  In the case of the compressed mode described above, for example, from International Publication WO 00/48335, it is known that the transmission power is increased while a compressed frame is transmitted in order to compensate for the transmission power loss in the transmission gap. It has been. At the same time, the transmit power control threshold in the receiver is increased so that the transmit power control loop continues to operate even at high transmit power levels. If the scrambling code is not changed while transmitting the compressed frame, this system will improve the transmission power control in the compressed mode, but the transmission power control threshold is determined from the length of the transmission gap. The system does not take into account switching between scrambling codes, since it is only increased by a certain fixed value calculated.

  United States application publication US 2003/0036403 proposes to maintain a plurality of individual outer loops for different transfer formats, such as different lengths of transmission transfer blocks. For each transfer format, the associated outer loop sets the target signal-to-noise plus interference ratio (SNIR) so that the specified target BLER is achieved. Try to do. The plurality of individual outer loops form a total outer loop that operates in cooperation with the inner loop to derive an appropriate transmission power control command. However, this system also does not take into account the problems associated with different scrambling codes.

  Accordingly, it is an object of the present invention to transmit in a wireless communication system so that the transmission power and / or the number of transmission errors in this situation can be reduced if a shift between different scrambling codes occurs in the transmission. It is to provide a way to improve power control.

  According to the present invention, an object is a step of selectively adjusting a reference value of a first quality measurement and a reference value of a second quality measurement in the outer loop, wherein the first quality measurement is performed. The reference value of the second quality measurement is adjusted depending on an operating performance level calculated for a time interval in which all signals are transmitted using the first scrambling code. Is adjusted depending on an operational performance level calculated for a time interval in which at least some signals are transmitted using the second scrambling code, and generates a transmission power control command As a reference value for quality measurement in the step, a reference value for the first quality measurement during a time interval in which all signals are transmitted using the first scrambling code, and at least some No. is achieved by further comprising the method and using the reference value of the second quality measure between at least a portion of the time interval to be transmitted using the second scrambling code.

  Within the outer transmit power control loop, two separate quality measurement reference values are maintained, the most appropriate one of which is the inner transmit power at a given time depending on the scrambling code used. When used in a control loop, it is possible to adapt this transmit power control for shifts between different scrambling codes, thereby sacrificing the required level of operating performance. In other words, the total transmission power can be reduced without increasing the amount of transmission errors.

  As noted above, the present invention also relates to a corresponding method for generating a transmit power control command in a transceiver for receiving a signal transmitted from a remote transceiver in a wireless communication system.

  In an embodiment of the invention, the signal is transmitted in a wideband code division multiple access system. In this case, the quality measurement can be estimated as a signal-to-interference ratio, and the operating performance level can be calculated as a block error rate.

  In one embodiment, the first scrambling code may be a primary scrambling code, and the second scrambling code may be a secondary scrambling code. Alternatively, the first scrambling code may be either a primary scrambling code or a secondary scrambling code, and the second scrambling code may be an alternative scrambling code.

  When the second scrambling code is an alternative scrambling code and the time interval is a transmission time interval including a plurality of frames, at least some signals are transmitted using the second scrambling code. Each of the transmitted transmission time intervals may include at least one frame in which a signal is transmitted in compressed mode using the alternative scrambling code.

  The second quality measurement reference value is used as a quality measurement reference value in all frames of a transmission time interval in which at least some signals are transmitted using the second scrambling code. Provides a simple solution that only one quality measurement reference value is used in each transmission time interval. For a transmission time interval having only the first scrambling code, one of the quality measurement reference values is used, and a transmission having a mix of a plurality of scrambling codes (synthetic code) or only a second scrambling code. The other quality measurement reference value is used for the time interval.

  In an alternative embodiment, the second quality measurement reference value is a quality measurement in a compressed mode frame of a transmission time interval in which at least some signals are transmitted using the second scrambling code. Used as a reference value. On the other hand, the reference value for the first quality measurement is used as the reference value for the quality measurement in other frames in such a transmission time interval. Thus, since the reference value of the first quality measurement, which typically has a lower value, is also used in the transmission time interval of the mix transmitted using the first scrambling code, the additional power is Can be saved.

  In the method, in addition to the reference value of the second quality measurement, the level of operation performance calculated for a time interval in which at least some signals are transmitted using the second scrambling code. A step of adjusting at least one further quality measurement reference value, wherein each of the second quality measurement reference value and the further quality measurement reference value uses the second scrambling code. Adjusting for different amounts of signals transmitted in the second time period, and during the at least part of a time interval during which at least some signals are transmitted using the second scrambling code, One of the quality measurement reference value and the further quality measurement reference value depending on the amount of signal transmitted using the second scrambling code. In the step of generating a command and a step to be used as the quality measure reference value may further include.

  As stated above, the present invention also provides for receiving a signal transmitted from a remote transceiver in a wireless communication system using at least one of a first scrambling code and a second scrambling code. Related to transceivers. Wherein the transceiver comprises a controller for generating a transmit power control command, the controller comprising means for repeatedly estimating a quality measurement for a signal received at the transceiver, the quality measurement, Means for generating a transmit power control command depending on the quality measurement reference value, means for transmitting the transmit power control command to the remote transceiver, and for signals received at the transceiver during the time interval Means for calculating an operating performance level and means for adjusting a reference value of the quality measurement depending on the operating performance level.

  The adjusting means is configured to selectively adjust a reference value for a first quality measurement and a reference value for a second quality measurement, and the reference value for the first quality measurement is the same for all signals. The second quality measurement reference value is adjusted depending on an operating performance level calculated for a time interval transmitted using a first scrambling code, wherein at least some signals are 2 is adjusted depending on the performance level calculated for a time interval transmitted using a scrambling code of 2, and the generating means uses all the signals as the reference values for quality measurement as the reference values for quality measurement. During the time interval transmitted using one scrambling code, the reference value of the first quality measurement is used and at least some signals are transmitted using the second scrambling code. Time interval If configured to use the second quality measurement reference value for at least a portion, the transceiver may be configured in a wireless communication system if a shift occurs between different scrambling codes in transmission. An improvement in transmit power control can be achieved to reduce the transmit power and / or the number of transmission errors in this situation.

  In an embodiment of the invention, the transceiver is configured to receive a signal transmitted in a wideband code division multiple access system. In this case, the estimation means can be configured to estimate the quality measurement value with a signal-to-interference ratio, and the calculation means can be configured to calculate the operation performance level with a block error rate. it can.

  In one embodiment, the first scrambling code is a primary scrambling code and the second scrambling code is a secondary scrambling code. Alternatively, the first scrambling code is either a primary scrambling code or a secondary scrambling code, and the second scrambling code is an alternative scrambling code.

  If the second scrambling code is an alternative scrambling code and the time interval is a transmission time interval including a plurality of frames, the transceiver uses at least some signals for the second scrambling code Each of the transmitted transmission time intervals can be configured to receive such a signal including at least one frame in which the signal is transmitted in compressed mode using the alternative scrambling code. .

  The generating means uses the second quality measurement reference value as a quality measurement reference value for all frames in a transmission time interval in which at least some signals are transmitted using the second scrambling code. The simple solution is that only one quality measurement reference value is used in each transmission time interval. For a transmission time interval having only the first scrambling code, one quality measurement reference value is used, for a mix of a plurality of scrambling codes, or for a transmission time interval having only the second scrambling code. In this case, the reference value of the other quality measurement is used.

  In an alternative embodiment, the generating means uses the second quality measurement reference value as a compressed mode frame in a transmission time interval in which at least some signals are transmitted using the second scrambling code. And the first quality measurement reference value is used as a quality measurement reference value in other frames of such a transmission time interval. In this way, the reference value of the first quality measurement, which typically has a lower value, is also used in the mixed transmission time intervals transmitted using the first scrambling code. The transmission power can be saved.

  In addition to the reference value for the second quality measurement, the adjusting means is adapted to a level of operational performance calculated for a time interval in which at least some signals are transmitted using the second scrambling code. Dependently adjusts at least one further quality measurement reference value and, for different amounts of signal transmitted using the second scrambling code, the second quality measurement reference value and further It can be further configured to adjust each of the quality measurement reference values. In addition, the generating means may use the second scrambling code as a reference value for quality measurement during at least a part of a time interval in which at least some signals are transmitted using the second scrambling code. Depending on the amount of signal transmitted using, the reference value for the second quality measurement and the reference value for the further quality measurement may be used. In this way, the transceiver can be better adapted to different amounts of signals transmitted using the second scrambling code.

  The invention also relates to a computer program and a computer readable medium having program code means for performing the method described above.

  The invention will be described more fully hereinafter with reference to the drawings.

  FIG. 1 shows communication between two transceivers 11 and 12 in a wireless communication system. As an example, the wireless communication system may be a wideband code division multiple access (WCDMA) system. Here, the two transceivers communicate with each other through a wireless transmission channel 13 having radio signals carrying different types of information. The two transceivers are a base station 11 and a mobile terminal or mobile station 12. A mobile station may also be assigned to a user equipment (UE). The base station 11 can also communicate with other mobile stations (not shown). Information is transmitted in one direction (downlink) via a channel 13 from a transmitter 14 in the base station 11 to a receiver 15 in the mobile station 12, and a transmitter 16 in the mobile station 12. To the receiver 17 in the base station 11 via the channel 13 in the opposite direction (uplink). The radio transmission channel 13 has a random and unpredictable effect on the transmission signal before the receivers 15 and 17 receive the transmission signal, respectively. Thus, the receiver can, for example, amplify, filter, frequency downconvert, sample, despread, decode, and deinterleave the signal to form a processed received signal and recover the transmitted information. Etc., the received signal is processed.

  FIG. 1 also shows transmission power control for downlink transmission. The transmission power control unit 18 in the mobile terminal 12 is based on the quality of the signal received by the receiver 15 in order to obtain a sufficient quality of the received signal at the mobile terminal, and the transmitter 14 provided in the base station. One or more transmit power control (TPC) commands are generated that indicate whether the transmit power level of the first to be increased or decreased. The mobile terminal 12 will be described in more detail below. The TPC command is then transmitted from the transmitter 16 via the channel 13 to the receiver 17 in the base station 11, in which the TPC command is processed and controls the transmission power level of the transmitter 14. Used to do. Similarly, the transmission power control unit is used in the base station 11 for transmission power control of uplink transmission. However, for clarity, this unit is not shown in FIG.

  Signals transmitted in WCDMA are transmitted according to a clearly defined timing configuration. This is illustrated in FIG. 2 for the downlink dedicated physical channel (DPCH, Dedicated Physical Channel). One transmission time interval consists of 1 to 8 radio frames. Each radio frame has a duration of 10 ms and is divided into 15 slots. One slot includes 2560 chips and corresponds to one transmit power control period as described below. Thus, one TTI can include 15 to 120 slots. On the DPCH, each slot includes data 1 and data 2 as two data fields and three control fields. Together, the two data fields constitute a dedicated physical data channel (DPDCH, Dedicated Physical Data Channel). The three control fields are a transmission power control (TPC) field, a TFCI (Transport Format Combination Indicator) field, and a pilot field, which together form a dedicated physical control channel (DPCCH, Dedicated Physical Control Channel). . Thus, the downlink DPCH can be viewed as time multiplexed of the downlink DPDCH and the downlink DPCCH. The TPC field is used to transmit the TPC command described above, but the TPC command transmitted in the downlink DPCH is, of course, used for transmission power control of the uplink transmission. The On the other hand, a TPC command related to transmission power control of downlink transmission is transmitted from the transmitter 16 to the receiver 17 in the corresponding TPC field in the uplink DPCCH. The data field (and pilot field) chips are despread and decoded in the receiver to obtain data symbols corresponding to the original data bits spread and encoded in the transmitter. The total number of symbols used for one slot is determined by the spreading factor (SF). Depending on the information to be transmitted, the TTI can be divided into a plurality of transport blocks with variable duration.

  A more detailed description of the transmission power control unit will be given with reference to FIG. As described above, closed-loop transmission power control is used in which the transmission power level is adjusted to maintain a given quality of the received signal. The control unit 18 includes elements for relatively fast inner-loop transmission power control and relatively slow outer-loop transmission power control in the receiver of the mobile terminal 12.

  In the inner loop, a signal-to-interference ratio (SIR) value 51 is calculated for each slot in the SIR estimation device 23. The input to the SIR estimator 23 is from a power estimator 21 that estimates the signal power of a slot from dedicated pilot symbols and an interference estimator 22 that estimates interference from either a common pilot channel (CPICH) or a dedicated pilot symbol. Supplied. The SIR can be calculated from these two inputs. The SIR value estimated by the SIR estimator 23 (or the value obtained through the filter) is then compared with the SIR reference value 53 (target SIR) in the inner loop adjuster 24. If the estimated SIR is less than the reference, the inner loop adjuster 24 transmits a transmit power control (TPC) command over the uplink dedicated physical control channel (DPCCH) and for the downlink dedicated physical channel (DPCH). It will require the base station to increase the transmit power. On the other hand, if the estimated SIR is greater than the reference value, the inner loop adjuster 24 will request the base station to reduce the transmit power. The transmission power is updated every 1 slot or every 3 slots, and one step of the transmission power change width is 1.0 dB by default, and 0.5 dB, 1.5 dB, or 2. There is 0 dB.

The SIR reference value used by the inner loop adjuster 24 is determined by the outer loop adjuster 26 using the relationship between the estimated block error rate (BLER) and the BLER target value for one TTI. The instantaneous BLER value 52 for one TTI is estimated by performing a cyclic redundancy check (CRC) on each transfer block (TB) in the BLER estimator 25, and is received correctly or incorrectly. Get a 0 or 1 flag for the block. The instantaneous BLER for the current TTI can thus be estimated as the ratio of the number of erroneous transfer blocks to the total number of transfer blocks for that TTI. Therefore, if the user equipment is in the kth TTI, N _TB (k) transport blocks are transmitted from the base station in it, and the N _TB (k) of the N _TB (k) by executing CRC at the receiver If N _err (k) turns out to be incorrect, the instantaneous BLER for the current TTI is simply expressed as:
BLER _mom (k) = N _err (k) / N _TB (k) [1]
The instantaneous BLER value (or CRC flag) can be filtered over a certain amount of TTI. From this filtering, it is possible to obtain prolonged estimated BLER, i.e. the value of _{BLER filt.}

The estimated BLER value (instantaneous and / or filtered value) is then compared with the BLER target value in the outer loop adjuster 26 to obtain an updated SIR reference value. BLER target value _{BLER targ} is set by the system. A typical outer loop transmission power control algorithm is based on a generalization of a proportional integral controller (PI Controller, Proportional Integral Controller), and the integral part is calculated as follows.
_{I (k) = C I *} I (k-1) + C B * (BLER filt (k) -BLER targ)
[2]
The SIR reference value can be updated by the following equation for the next TTI, that is, the (k + 1) th TTI.
_{SIR ref (k + 1) =} SIR ref (k) + C S * _[BLER mom _{(k) -BLER targ]} + I (k) [3]
The above equation has an initial value I (0) of the integral part and a starting value SIR _ref (0) of the SIR reference value. The constants in the above equation can be different for different BLER target values, thereby accelerating the convergence of transmit power control, especially for low BLER target values.

  Thus, outer loop type transmission power control attempts to adjust the SIR reference value by comparing the estimated BLER and the BLER target. If the estimated BLER is higher than a predetermined BLER target, the SIR reference value is increased for the next TTI to obtain higher power from the base station and thereby reduce block errors. Similarly, if the estimated BLER is lower than the BLER target, the SIR reference value is decreased so as not to send excessive transmission power to the targeted user equipment. Therefore, at the end of each TTI, a new SIR reference value is calculated based on the estimated BLER for that TTI. This new SIR reference value is then used by the inner loop during the next TTI.

As mentioned above, the downlink data is spread before being transmitted from the transmitter 14 in the base station 11. The spreading process at the transmitter is illustrated in FIG. The spreading process includes a modulation mapper stage 31. Here, the input digits are mapped to real-valued symbols. That is, the binary value 0 is mapped to the real value +1, and the binary value 1 is mapped to the real value -1. Next, in channelization stage 32, the data in IQ format (in-phase and quadrature) is spread to the chip rate by multiplying with real-valued channelization codes C _{ch, SF, m} . Here, SF is a spreading factor. The same channelization code is used for the I branch and the Q branch. Thus, the output for each input symbol on the I branch and Q branch will be a sequence of SF chips corresponding to the channelization code chip sequence multiplied by the real valued symbol. The channelization code is described in more detail below.

The real value chip sequence on the Q branch is complex-multiplied by the imaginary operator j in the multiplier 33 and added to the corresponding real value chip sequence on the I branch in the IQ synthesizer 34. As a result, one complex value chip sequence is obtained. Finally, in the scrambling stage 35, the sequence of complex value chips is scrambled by a complex value scrambling code S _{dl, n} (multiplication in complex number chips).

Channelization codes are orthogonal variable spreading factor (OVSF) codes that preserve orthogonality between different physical channels. The spreading factor can take values up to 512. The OVSF code is defined according to the coding tree illustrated in FIG. The code tree is first divided into two branches with SF = 2, and then each of these is further divided into two branches with SF = 4. This process continues until a branch with SF = 512 is reached. As shown in FIGS. 4 and 5, the channelization code is uniquely represented as C _{ch, SF, m} . Here, SF is a code spreading factor, m is the number of codes, and 0 ≦ m ≦ SF−1. Channelization codes in different branches are orthogonal even though they have different spreading factors. However, channelization codes are not orthogonal to their original codes. For example, C _{ch, 4,0} = (1,1,1,1) is C _{ch, 4,1} = (1,1, -1, -1) and C _{ch, 4,2} = (1 , -1,1, -1), C _{ch, 4,3} = (1, -1, -1, -1), and even C _{ch, 2,1} = (1, -1) is orthogonal Yes. However, it is not orthogonal to C _{ch, 2,0} = (1,1). Thus, if a channelization code is assigned within a given code tree, all codes below that code with a higher spreading factor should be used to ensure orthogonality. Must not. As a result of the requirement for orthogonality, especially for higher data rates, ie smaller spreading factors, the number of channelization codes available in the code tree is quite limited.

As described above, the scrambling code is the complex value code S _{dl, n} , and in the scrambling stage 35, the complex value chip S _{dl, n} is multiplied by the complex value chip sequence. Is done. A great many different scrambling codes can be generated, but not all of them are used. The scrambling codes are divided into 512 sets, and each set includes one primary scrambling code and 15 secondary scrambling codes. The primary scrambling code comprises scrambling code n = 16 * i (where i = 0... 511). The i-th set of secondary scrambling codes consists of scrambling codes n = 16 * i + k (where k = 1... 15). Within a set, there is a one-to-one mapping between each primary scrambling code and its 15 secondary scrambling codes. The i-th primary scrambling code corresponds to the i-th set of 15 secondary scrambling codes. Each cell is assigned only one primary scrambling code. Some physical channels, such as the common pilot channel (CPICH), are always transmitted using the primary scrambling code, while other downlink physical channels are either the primary scrambling code or the primary scrambling of the cell. Transmission can be performed using a secondary scrambling code included in a set associated with the ring code.

  Accordingly, 8191 scrambling codes are used as primary scrambling codes or secondary scrambling codes. Further, each primary and secondary scrambling code is associated with two alternative scrambling codes. That is, a left alternative scrambling code and a right alternative scrambling code, which can be used for a compressed frame.

  The compressed mode is used when the user equipment needs time to make the necessary measurements on different carrier frequencies while performing handover between different frequencies in WCDMA. In order for the user equipment to be able to perform these measurements, several slots in the frame (typically 1 to 7 slots per frame) are allocated for this purpose, and thus the transmission gap in the frame. Will occur. Such a frame is called a compressed frame because only the remaining slots of the frame are used for normal transmission of information. Typically, compressed frames occur periodically, but may be required as needed. Various rates and types of compressed frames can be used, depending on the environment and measurement requirements.

  FIG. 6 illustrates the compression mode. In the figure, a series of TTIs are transmitted, where each TTI consists of four frames. It can be seen that some TTIs contain 4 regular frames, while other TTIs contain compressed frames. As an example, the second frame of the kth TTI is compressed with a transmission gap that occurs in the middle of that frame. As shown, the instantaneous transmit power is increased for the remaining slots of the compressed frame to maintain a quality (eg, BLER) that is unaffected by the reduced number of slots. The amount of increase in transmission power depends on the decrease in transmission time. For example, if 7 slots are used for the transmission gap, it means that only about half of the compressed frame can be used for data transmission. In FIG. 6, the transmission power of the compressed frame is correspondingly increased to about twice the normal transmission power level.

Furthermore, the spreading factor can be reduced by 2: 1 in order to maintain the amount of information transmitted in the compressed frame. This is because reducing the spreading factor by 2: 1 increases the data rate, so that data symbols are transmitted at twice the rate. However, changing the spreading factor is likely to require reassignment of some or all channelization codes in the code tree to maintain orthogonality. Therefore, if the base station has to use a channelization code with a spreading factor equal to half of the original spreading factor SF, the code located under the SF / 2 branch is already It may be used. As an example, instead of the code C _{ch, 4,0} for the normal mode, C _{ch, 2,0} must be used for the compressed mode, and some under the branch C _{ch, 4,1} Is used by other channels, the orthogonality is broken. Even though the codes under branch C _{ch, 4,1} can be used freely for normal mode, they will be blocked for compressed mode with reduced spreading factor.

  To avoid this reassignment, the transmitter can instead switch to an alternative scrambling code for the compressed frame. This is because different scrambling codes mean that channelization codes from different code trees can be used. Since the scrambling code correlation is similar to noise, the channelization code correlation is under the same branch of the code tree, but if they use different scrambling codes, The value is considerably low. Therefore, the compressed frame is transmitted with the alternative scrambling code, while the other frames are transmitted with the normal scrambling code, that is, the primary scrambling code or the secondary scrambling code. As shown in FIG. 6, the compressed frames occur in a pattern determined by the network (typically, but not necessarily, the compressed frames are at the same frame position in the TTI with the compressed frames) There will be a switch between a new scrambling code and an alternative scrambling code. Thus, for some TTIs, all frames will be transmitted with the same scrambling code. Other TTIs are transmitted in a mix of different scrambling codes. A similar situation occurs when the base station in the normal mode switches between the primary scrambling code and one of the secondary scrambling codes. By using two or more code trees, the base station can provide as many data rates as possible to many users. As discussed above, the base station needs a sufficiently large number of channelization codes that can be used for this purpose. Therefore, it is beneficial for the base station to use a secondary scrambling code in addition to the primary scrambling code, if necessary, in which case switching between the scrambling codes will occur.

  The fact that some TTIs are transmitted with the same scrambling code for all frames and other TTIs are transmitted with a mix of different scrambling codes creates a problem for transmit power control. This is because the SIR reference value calculated for a signal received with a certain scrambling code has proven to be not optimal for signals received with a different scrambling code. Thus, switching between the scrambling codes results in an SIR reference value that is not optimal for either of the two scrambling codes. Typically, the amount of block errors increases, so that the SIR reference value rises to a higher level compared to the level actually required. The net result is wasted transmission power.

  FIG. 7 illustrates how the transmit power control unit 18 can be modified to improve the transmit power control function under this circumstance. In the modified transmit power control unit 40, transmit power control is done independently for the two types of TTI. The two types are a type in which all frames are transmitted with the same scrambling code and a type including a frame transmitted with different scrambling codes. In the following description, the modified transmission power control unit 40 is described with reference to the case of the compressed mode described above. Here, some frames are transmitted using alternative scrambling codes. However, the same solution can be applied when the base station switches between the primary scrambling code and one of the secondary scrambling codes.

Compared with the transmission power control unit 18 of FIG. 3, in the transmission power control unit 40, the components for the outer loop type transmission power control are modified. The BLER estimation device 25 estimates the BLER value 52 for each TTI, similar to the previous one. However, the outer loop adjuster 46 now updates two different SIR reference values 54 and 55. SIR reference values 54 and 55 are SIR _ref1 for TTIs in which all frames are in normal mode and scrambled with a primary scrambling code (or secondary scrambling code), and at least one frame is in compressed mode. SIR _ref2 for a TTI scrambled with an alternative scrambling code. These two SIR reference values are stored in registers 47 and 48, respectively. The input to the outer loop adjuster 46, which indicates the type of scrambling code used in the current TTI, determines which SIR reference value to update. Thus, for example, at the end of a TTI where all frames are in normal mode, SIR _ref1 is updated based on the previous values of BLER and SIR _ref1 estimated for that TTI. The previous value of SIR _ref1 is not necessarily a value calculated for the immediately preceding TTI because there is a possibility that a TTI having a compressed frame exists in the middle. Similarly, SIR _ref2 is updated at the end of TTI where at least one frame is in compressed mode. Therefore, the outer loop transmission power control algorithm for updating the SIR reference value can be expressed by the following equation.

_{I (k) = C I *} I (k-1) + C B * (BLER filt (k) -BLER targ)
[4]
and,
_{SIR ref (k + m) =} SIR ref (k) + C S * _[BLER mom _{(k) -BLER targ]} + I (k) [5]
As above, the above equation has the initial value I (0) of the integral part and the starting value SIR _ref (0) of the SIR reference value. Also, m indicates that the SIR reference value calculated at the end of the k-th TTI is not necessarily used for the immediately following TTI.

The constants in Equations [4] and [5], ie, C _I , C _B , and C _S, are used for compression mode and normal mode using alternative scrambling codes in order to optimize operating performance. It may be different. Alternatively, using the same value constant for both modes, the only difference between normal mode and compressed mode is that the old SIR reference value SIR _ref (k) in equation [5] However, the updated SIR reference value may be applied only to the next TTI having the same mode.

  In the SIR reference value selection device 49, an input indicating the type of scrambling code used in the current / next TTI is used as the SIR reference value 56 in the inner loop adjustment device 24, and is selected from It is determined which one to use for this TTI. This input signal is based on information received from the base station.

FIG. 8 is a flowchart 100 showing calculations performed in the BLER estimation device 25, the outer loop adjustment device 46, and the SIR reference value selection device 49. In step 101, the instantaneous BLER value and the filtered BLER value are calculated from the CRC flag for this TTI at the end of the TTI. In step 102, it is determined whether this TTI includes only normal frames or includes compressed frames. If all frames of the TTI are in the normal mode, the SIR reference value SIR _ref1 is updated in step 103. On the other hand, if a compressed frame is included, the SIR reference value SIR _ref2 is updated in step 104. In step 105, it is determined whether the next TTI includes only a normal frame or a compressed frame. If all frames of the next TTI are in normal mode, the value of SIR _ref1 will be selected as the SIR reference value in step 106. On the other hand, if a compressed frame is included in the next TTI, the value of SIR _ref2 will be selected as the SIR reference value in step 107. Finally, in step 108, the selected SIR reference value is supplied to the inner loop adjustment device 24.

FIG. 9 illustrates how these two SIR reference values are updated and used during a series of TTIs. Here, in a series of TTIs, some of the TTIs have all their frames in normal mode, and others have compressed frames. For purposes of illustration, in the figure, each TTI is shown as having four frames. However, the number of frames in one TTI can be any number between 1 and 8. As an example, TTI _k includes one compressed frame, so during this TTI, the inner loop adjuster uses SIR _ref2 as the SIR reference value for the inner loop. At the end of TTI _k , SIR _ref2 is updated based on the BLER value estimated for this TTI. This updated value of SIR _ref2 is used in TTI _{k + 2} which also contains a compressed mode frame. On the other hand, SIR _ref1 is used during TTI _{k + 1} in which all frames are in the normal mode.

FIG. 10 illustrates the effect of performing transmission power control independently for two types of TTIs. The curve shows the level of the SIR reference value during the time of transmission power control, ie over a large number of TTIs, when an alternative scrambling code is used for the DPCH during the compressed frame. In these curves, the constants in equations [4] and [5] were set as C _I = 0, C _B = 0.25, and CS = 0.25, and the BLER target was set at 1%. It is the result of the simulation. The top curve is when the only common SIR reference is updated for both normal TTI and TTI with compressed frames, the bottom two curves are two separate SIR reference values Are updated for TTIs in which all frames are in normal mode (SIR _ref1 ) and updated for TTIs containing compressed frames (SIR _ref2 ), respectively. In the latter case, it can be seen that the two SIR reference values are automatically separated from each other in the course of the transmission power control time. Furthermore, compared to the case where only one common SIR reference value is used, the overshoot is reduced and the converged SIR reference value is less noisy. The curve shows the following. That is, if all TTIs are transmitted with, for example, a primary scrambling code, a known solution that only one SIR reference value is updated is, for example, that the SIR reference value after 5000 TTIs is about 4 It will be. However, if switching between scrambling codes is performed, the SIR reference value of the solution is about 19 instead of 4 under the same channel conditions, and the amount of transmission power is correspondingly increased. Will. On the other hand, in the solution method in which the two SIR reference values are updated, as can be seen from the figure, the SIR reference value is reduced to about 4 for a TTI including only frames transmitted using the original scrambling code. Will keep on. Also, another SIR reference value for a TTI containing a frame transmitted using an alternative scrambling code would be about 16. This means that a very large amount of transmission power can be saved without degrading the BLER. Simulations have shown that, under these conditions, using two separate SIR reference values instead of one can reduce the average transmit power level and simultaneously reduce the BLER estimate.

In the solution shown above, one of the two separately updated SIR reference values, namely SIR _ref1 , is generated in the inner loop adjuster 24 during the TTI when all frames are in normal mode. used. The other, namely SIR _ref2, is used for TTI with a mix of normal and compressed frames. This is also shown in FIG. However, it would be possible to switch the SIR reference value during the latter type of frame to use SIR _ref1 for normal frames and SIR _ref2 only for compressed frames. This is illustrated in FIG. As also shown in the figure, the two SIR reference values are updated here as well, as described above. That is, SIR _ref1 is updated at the end of a TTI having only normal frames. On the other hand, SIR _ref2 is updated at the end of the TTI having at least one compressed frame. In this method, a lower value of SIR _ref1 is used for all normal frames, and a higher value of SIR _ref2 is used only for compressed frames, so the transmission power can be further reduced.

  In the example described above, a two-state model was used. Here, one state represents an SIR reference value for a TTI that covers a portion that transmits using an alternative scrambling code. The other state is used for TTIs that exactly match the part that transmits using the primary scrambling code. However, the model could be extended to include more than two states. Many SIR states could be defined depending on the amount of TTI that covers transmissions made with alternative scrambling codes. Thus, by way of example, for the TTIs of FIG. 9 each having 4 frames, one, two, three, or four compressions in addition to the SIR reference values for TTIs having only normal mode frames. It would be possible to define a SIR reference value for a TTI with a frame. However, if the number of states to be defined increases, the frequency of state statistics is updated, which may result in a slow system response. Therefore, the two-state model described here seems to be a good choice. Since compressed mode frames occur quite often, for example, every 3 to 7 frames, there will be no data shortage when updating the two-state model.

  In the above, the present invention is described in relation to switching between one scrambling code (primary or secondary) used in a normal mode frame and an alternative scrambling code used in a compressed frame. It was done. However, the described solution is not limited to shifting between different scrambling codes, eg when the base station switches between a primary scrambling code and one of the corresponding secondary scrambling codes. It is just as appropriate in this situation.

  While the preferred embodiment of the invention has been described and illustrated, the invention is not so limited, and may otherwise be within the scope of the subject matter defined by the appended claims. It is also possible to implement.

1 is a diagram illustrating communication between two transceivers in a wireless communication system. FIG. It is a figure which shows the timing structure with respect to downlink DPCH of a WCDMA system. FIG. 2 shows a known transmit power control unit for the transceiver of the system of FIG. It is a figure which shows the spreading | diffusion process in the transmitter of the system of FIG. FIG. 3 is a diagram illustrating a code tree for an OVSF channelization code in a WCDMA system. FIG. 3 illustrates the use of compressed mode in a WCDMA system. FIG. 6 shows a transmit power control unit modified to maintain two separate SIR reference values. It is a flowchart which shows the calculation performed in the control unit of FIG. It is a figure which shows an example of how two SIR reference values are updated and used during a series of transmission time intervals. FIG. 6 shows the effect of using two separate SIR reference values. FIG. 6 is an illustration of an alternative example of how two SIR reference values are updated and used during a series of transmission time intervals.

Claims (21)

A method for controlling a transmission power level of a signal transmitted from a first communication device to a second communication device in a wireless communication system, the signal being one of a first scrambling code and a second scrambling code. A signal transmitted using one of
● Inner loop type transmission power control
O repeatedly estimating a quality measurement (51) for a signal received at the second communication device;
Generating a transmission power control command according to the quality measurement value (51) and the quality measurement reference value (56);
Transmitting the transmission power control command to the first communication device;
A step of adjusting the transmission power level in response to the transmission power control command in the first communication device;
● Outer loop type transmission power control
Calculating a performance level (52) for a signal received at the second communication device over a time interval;
Adjusting the quality measurement reference value (56) according to the performance level (52),
The method further comprises:
In the outer loop type transmission power control, a step of selectively adjusting a reference value for the first quality measurement and a reference value for the second quality measurement, the reference value for the first quality measurement (54) is adjusted based on a performance level calculated for a time interval in which all signals are transmitted using the first scrambling code, and the second quality measurement reference value (55) is: Adjusting based on a performance level calculated for a time interval in which at least some signals are transmitted using the second scrambling code;
As a reference value (56) for the quality measurement in the step of generating the transmission power control command, the first quality measurement is performed in a time interval in which all signals are transmitted using the first scrambling code. Using a reference value (54) and using the reference value (55) of the second quality measurement for a time interval during which at least some signals are transmitted using the second scrambling code. A method characterized by comprising. A transmission power control command is generated in a communication device that receives a signal transmitted from a remote communication device using at least one of a first scrambling code and a second scrambling code in a wireless communication system A way to
● repeatedly estimating a quality measurement (51) for a signal received at the communication device;
Generating a transmission power control command according to the quality measurement value (51) and the quality measurement reference value (56);
Transmitting the transmission power control command to the remote communication device;
Calculating a performance level (52) for a signal received at the communication device over a time interval;
Adjusting the quality measurement reference value (56) according to the performance level (52),
The method further comprises:
A step of selectively adjusting the reference value of the first quality measurement and the reference value of the second quality measurement, wherein all the signals of the reference value (54) of the first quality measurement are And adjusting based on a performance level (52) calculated for a time interval transmitted using one scrambling code, wherein the second quality measurement reference value (55) is such that at least some signals are Adjusting based on a performance level (52) calculated for a time interval transmitted using a scrambling code of 2;
As a reference value (56) for the quality measurement in the step of generating the transmission power control command, the first quality measurement is performed in a time interval in which all signals are transmitted using the first scrambling code. Using a reference value (54) and using the reference value (55) of the second quality measurement for a time interval during which at least some signals are transmitted using the second scrambling code. A method characterized by comprising. The method according to claim 1 or 2, wherein the signal is a signal transmitted using a wideband code division multiple access scheme. The method of claim 3, wherein the quality measurement is a value estimated as a signal-to-interference ratio. 5. The method according to claim 3, wherein the performance level is a value calculated as a block error rate. The first scrambling code is a primary scrambling code;
6. The method according to any one of claims 3 to 5, wherein the second scrambling code is a secondary scrambling code. The first scrambling code is either a primary scrambling code or a secondary scrambling code;
The method according to any one of claims 3 to 5, wherein the second scrambling code is an alternative scrambling code. The time interval is a transmission time interval (TTI) including a plurality of frames,
Each of the transmission time intervals (TTIs) is a time interval in which at least some signals are transmitted using the second scrambling code, and the signal is compressed according to a compressed mode using the alternative scrambling code. The method according to claim 7, characterized in that includes at least one frame to be transmitted. The second quality measurement reference value (55) as a quality measurement reference value in all frames included in a transmission time interval (TTI) in which several signals are transmitted using the second scrambling code. The method according to claim 8, characterized in that is used. As a quality metric value in a frame to which a compression mode is applied, included in a transmission time interval (TTI) in which several signals are transmitted using the second scrambling code, the second quality measurement The reference value (55) is used,
9. Method according to claim 8, characterized in that the first quality measurement reference value (54) is used as a quality measurement reference value for other frames included in the transmission time interval (TTI). At least one according to a performance level (52) calculated for a time interval in which at least some signals are transmitted using the second scrambling code in addition to the reference value of the second quality measurement Adjusting two other quality measurement reference values, the second quality measurement reference value and the at least one according to the amount of signal transmitted using the second scrambling code. Adjusting at least one of other quality measurement reference values;
In the step of transmitting the transmission power control command, as a reference value for the quality measurement, the second scrambling is performed in at least a part of a time interval in which at least some signals are transmitted using the second scrambling code. Using one of the second quality measurement reference value and the at least one other quality measurement reference value as a function of the amount of signal transmitted using a plurality of scrambling codes. 11. A method according to any one of the preceding claims, comprising: A communication device that uses at least one of a first scrambling code and a second scrambling code in a wireless communication system to receive a signal transmitted from a remote communication device,
A control device (40) for generating a transmission power control command;
The controller is
An estimation means (23) for repeatedly estimating a quality measurement (51) for a signal received at the communication device;
A generation means (24) for generating a transmission power control command according to the quality measurement value (51) and the quality measurement reference value (56);
A transmission means (16) for transmitting the transmission power control command to the remote communication device;
A calculating means (25) for calculating a performance level (52) for a signal received at the communication device over a time interval;
Adjusting means (46) for adjusting the reference value (56) of the quality measurement according to the performance level (52),
The adjusting means (46) is a means for selectively adjusting a reference value for the first quality measurement and a reference value for the second quality measurement, and the reference value (54 for the first quality measurement). ) Based on the performance level (52) calculated for the time interval in which all signals are transmitted using the first scrambling code, the reference value (55) for the second quality measurement is Means for adjusting based on a performance level (52) calculated for a time interval in which at least some signals are transmitted using the second scrambling code;
The generation means (24) uses the first quality measurement reference value as a reference value (56) for the quality measurement in a time interval in which all signals are transmitted using the first scrambling code. (54), and means for using the reference value (55) of the second quality measurement for a time interval in which at least some signals are transmitted using the second scrambling code. A communication device. The communication device
13. The communication apparatus according to claim 12, wherein the communication apparatus is configured to receive a signal transmitted using a wideband code division multiple access scheme. The estimation means (23)
The communication apparatus according to claim 13, wherein the communication apparatus is configured to estimate the quality measurement value as a signal-to-interference ratio. The calculating means (25)
15. The communication apparatus according to claim 13, wherein the performance level is calculated as a block error rate. The first scrambling code is a primary scrambling code;
The communication apparatus according to claim 13, wherein the second scrambling code is a secondary scrambling code. The first scrambling code is either a primary scrambling code or a secondary scrambling code;
16. The communication apparatus according to claim 13, wherein the second scrambling code is an alternative scrambling code. The time interval is a transmission time interval (TTI) including a plurality of frames,
Each of the transmission time intervals (TTIs) is a time interval in which at least some signals are transmitted using the second scrambling code, and the signal is compressed according to a compressed mode using the alternative scrambling code. The communication device according to claim 17, comprising at least one frame in which is transmitted. The generating means (24)
As a reference value for quality measurement in all frames included in a transmission time interval (TTI) in which several signals are transmitted using the second scrambling code, the reference value for the second quality measurement (55 The communication device according to claim 18, wherein the communication device is configured to use the communication device. The generating means (24)
As a quality metric value in a frame to which a compression mode is applied, included in a transmission time interval (TTI) in which several signals are transmitted using the second scrambling code, the second quality measurement Use the reference value (55)
19. The reference value (54) of the first quality measurement is used as a quality measurement reference value of other frames included in the transmission time interval (TTI). The communication device described. The adjusting means (46) is calculated for a time interval in which at least some signals are transmitted using the second scrambling code in addition to the reference value (55) for the second quality measurement. In accordance with the amount of signal transmitted using the second scrambling code, and configured to adjust at least one other quality measurement reference value according to the performance level (52) Adjusting at least one of the second quality measurement reference value and the at least one other quality measurement reference value,
The generation means (24) is configured to use the second scrambling code as a reference value (56) for the quality measurement in at least a part of a time interval in which at least some signals are transmitted. One of the second quality measurement reference value and the at least one other quality measurement reference value depending on the amount of signals transmitted using two scrambling codes. 21. The communication apparatus according to claim 12, wherein the communication apparatus is configured.

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