KR101395435B1 - Controlling a power level in a wireless communications system with different scrambling codes - Google Patents

Abstract

The power level of the signals transmitted in the wireless communication system under the first or second scrambling code is determined such that the power level of the internal power control loop 51, which is repeatedly estimated and derived from this quality measure 51 and the quality measure reference value 56, And the quality metric reference value 56 is adjusted in accordance with the performance level 52 calculated for signals received during a certain time interval in an external power control loop. The first value 54 is adjusted according to the performance level 52 for the time intervals during which all signals are transmitted under the first scrambling code and is used during these time intervals. The second value 55 is adjusted according to the performance level 52 for at least some of the time intervals during which signals are transmitted under the second scrambling code and is used during at least a portion of this time interval.

Wireless communication system, scrambling code, power control, frame, SIR

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to power level control in a wireless communication system having different scrambling codes. ≪ RTI ID = 0.0 > [0002] <

The present invention relates to a method of controlling the power level of a signal transmitted from a first transceiver to a second transceiver in a wireless communication system, the signal being transmitted using at least one of first and second scrambling codes. The method comprises the steps of iteratively estimating a quality measure of a received signal at a second transceiver in an inner power control loop, repeatedly estimating a quality measure and a quality measure reference value Generating a power control command, transmitting a power control command to the first transceiver, and adjusting the power level in accordance with a power control command in the first transceiver, calculating a performance level of a received signal at a second transceiver during a time interval in an outer power control loop and adjusting the quality metric reference value according to the performance level. The present invention also relates to a method of generating power control commands at a transceiver for receiving signals transmitted from a remote transceiver in a wireless communication system, a transceiver receiving signals from a remote transceiver in a wireless communication system, and a corresponding computer program and computer readable Lt; / RTI > medium.

Background of the Invention In a wireless communications system, the physical channel between a transmitter and a receiver is typically formed by a radio link. By way of example, the transmitter may be a base station, and the receiver may be a mobile station or vice versa. In such a case, the base station typically corresponds to a cell of the system. Since the transmit antenna is not narrowly focused to the receiver side, the transmitted signal can propagate through multiple paths. In addition to the possible direct path from the transmitter to the receiver, there are many other propagation paths that are caused by reflections from nearby objects. Thus, the receiver can receive multiple variants of the same signal at different times, i. E. Different delays, because different parts of the signal are transmitted to the building, moving vehicle or landscape detail Because it reflects from various objects. The wireless link between the base station and the mobile terminal is a bi-directional link, i.e. information is transmitted from the base station to the mobile terminal (downlink) as well as from the mobile terminal to the base station (uplink).

Many transmission systems are attempting to reduce the effect of multipath propagation and fading using a receiver that combines the data symbol energy from all multipath components. In Code Division Multiple Access (CDMA) and Wideband Code Division Multiple Access (WCDMA) systems, the energy of different receiving portions of a signal can be used at the receiver, for example, by using a RAKE receiver.

In these systems, spreading and despreading are used. Data is transmitted from the transmitter side using a spread spectrum modulation technique, where the data is scattered over a wide frequency range. The spreading of each channel consists of a channelization operation followed by a scrambling operation. In a channelization operation, each data symbol is transformed into a number of so-called chips by multiplying it with a channelization code consisting of a binary sequence of ones and zeros. The number of chips per data symbol is called the spreading factor (SF). The channelization code is usually an Orthogonal Variable Spreading Factor (OVSF) with spreading factors of up to 512. The OVSF scheme is a kind of code tree in which each level is a set of mutually orthogonal codes and corresponds to a given spreading factor. In a scrambling operation, the spreading sequence of a chip is then scrambled by multiplying the chip with a complex-valued scrambling code (which is a pseudo noise code). This scrambling code is mainly used to distinguish the base station or cell from each other, while the channelization code is used to distinguish between different physical channels (terminals or users) in each cell. At the receiver, the received signal is despread and demodulated using the same code to recover the transmitted signal.

In a timing structure for a WCDMA system, a chip is transmitted within a TTI (Transmission Time Interval), where each TTI consists of one to eight radio frames. Each radio frame has a duration of 10 ms and is divided into 15 slots. The slot contains 2560 chips. Thus, the TTI may include 15 to 120 slots. The TTI may also be divided into a plurality of transport blocks having a variable duration according to the information to be transmitted.

In the case of downlink transmission, possible scrambling codes are divided into a set of primary scrambling codes and fifteen corresponding secondary scrambling codes. Each cell in the system is assigned one primary scrambling code and the corresponding fifteen secondary scrambling codes. Some physical channels such as CPICH (Common Pilot Channel) of a given link between a transmitter and a receiver within a cell are always transmitted using the primary scrambling code assigned to that cell while other physical channels such as the DPCH (Dedicated Physical Channel) May be transmitted using a primary scrambling code or one of the corresponding secondary scrambling codes, i.e. a secondary scrambling code from that set associated with the cell's primary scrambling code. Thus, for these physical channels, a transition occurs between the primary scrambling code and the one of the secondary scrambling codes because a certain radio frame is transmitted using the primary scrambling code and another radio frame is transmitted using the secondary scrambling code . ≪ / RTI > If the channelization code tree for the primary scrambling code is full, a secondary scrambling code may be used for the DPCH, for example, even though the transmitter still has available transmission capacity.

Another example of a transition between different scrambling codes is when the mobile station enters a so-called compressed mode (in which an alternative scrambling code can be used). Two alternative scrambling codes are associated with each of the primary and secondary scrambling codes, which are designated for use in the compressed mode. There is a compressed mode when some slots of a frame are allocated to a mobile station in order to make the necessary measurements for different carrier frequencies during inter-frequency handover. Thus, in the compressed frame, there are fewer slots available for normal transmission due to the transmission gap used for this measurement. To compensate for this, although the spreading factor can be reduced, the variation of the spreading factor is very likely to require reassignment of some or all of the channelization codes in the code tree to maintain orthogonality. To avoid this reallocation, the sender may instead switch to an alternative scrambling code corresponding to another code tree. Since the correlation of the scrambling codes is similar to noise, the correlation of the channelization codes is still quite low, even if these channelization codes are under different scrambling codes, even if the channelization code is in the same branch of the code tree.

In such a wireless communication system, power control is used to compensate for variations in the channel (such as propagation delay and fading effects) and to ensure satisfactory transmission quality for all users in the system.

Typically, a closed power control loop is used to adjust the transmitted power level to maintain the quality metric for the received signal at a given target value. Whether in an uplink or a downlink, the power control closed loop of WCDMA typically includes components that form a relatively fast inner power control loop and a relatively slow outer power control loop, Lt; RTI ID = 0.0 > a < / RTI > Hereinafter, a downlink transmission, that is, a transmission from a base station to a mobile terminal or user equipment (UE) is referred to, but a similar control loop is also used for uplink transmission.

The inner loop computes the SIR (Signal-to-Interference Ratio) value once per slot and compares this value (or filtered value) with the SIR reference value (target SIR). If the estimated SIR is smaller than the reference value, the user equipment transmits a TPC (Transmit Power Control) through the uplink Dedicated Physical Control Channel (DPCCH) to request the base station to increase the transmission power of the downlink DPCH Power control) command. On the other hand, if the estimated SIR is greater than the reference value, the user equipment will request the base station to reduce the transmit power. Transmit power update can be performed once for every slot or once for every three slots, the default value of the power change step is 1.0dB, and there is an option of 0.5, 1.5 or 2.0dB.

The outer loop power control of the WCDMA receiver uses the relationship between the estimated BLER (Block Error Rate) and the BLER target value to determine the SIR reference value. A cyclic redundancy check (CRC) is performed on each TB (Transport Block) to obtain a flag of 0 or 1 for correctly or incorrectly received blocks, and then a cyclic redundancy check The BLER can be estimated by effectively filtering over the Transmission Time Interval (TTI). The instantaneous BLER for the current TTI can be estimated as the ratio of the number of erroneous transmission blocks to the total transmission block of the TTI. Then, the estimated BLER value is compared with the BLER target value.

Basically speaking, the outer loop power control attempts to adjust the SIR reference value by comparing the estimated BLER with the BLER target value. If the estimated BLER is higher than the predetermined BLER target value, the SIR reference value is increased for the next TTI in order to reduce the block error by obtaining more power from the BS. Likewise, if the estimated BLER is lower than the BLER target value, the SIR reference value is reduced such that the BS does not need to allocate too much power for the targeted user equipment. Thus, at each TTI end, a new SIR reference value is calculated based on the BLER estimated for that TTI, and this new SIR reference value is then used by the inner loop for the next TTI.

As described above, the physical channels of the link between the transmitter and the receiver in a wireless communication system are typically transmitted under the same scrambling code, i.e., the primary scrambling code assigned to the cell, but for certain radio frames, For DPCH, a secondary scrambling code may be used, while a primary scrambling code is used for other radio frames, or an alternative scrambling code is used for a compressed frame, There are situations where a primary or secondary scrambling code is used.

However, this transition between scrambling codes causes problems with power control because the SIR reference value calculated for signals received under one scrambling code is not optimal for signals received under other scrambling codes It is because it has been proven. Thus, by switching between the scrambling codes, the SIR reference value is not optimal for either of the two scrambling codes. Typically, an increase in block error occurs, thus increasing the SIR reference value to a higher level than is actually needed. The end result is a waste of transmit power.

In the case of the above-mentioned compression mode, it is known from WO 00/48335, for example, to increase the transmission power during a compression frame to compensate for the loss of transmission power during transmission nulls. At the same time, the power control threshold at the receiver is increased, and thus the power control loop continues to operate at higher power levels. Although the system improves power control in the compressed mode when the scrambling code is not changed during the compression frame, the system does not consider switching between scrambling codes because the power control threshold is calculated from the length of the transmission gap It is only increased by a fixed value.

US 2003/0036403 proposes to maintain a number of separate outer loops for different transport formats, such as different lengths of transmitted transport blocks. For each transmission format, its associated outer loop attempts to set a target SNIR (Signal-to-Noise-plus-Interference Ratio, signal-to-noise plus interference ratio) such that a defined target BLER is achieved. A plurality of individual outer loops form an entire outer loop that operates in conjunction with the inner loop to derive an appropriate power control command. However, this system also does not consider problems related to different scrambling codes.

It is therefore an object of the present invention to provide a method of improving power control in a wireless communication system in such a situation such that the number of transmission power and / or transmission errors can be reduced when switching between different scrambling codes occurs during transmission have.

SUMMARY OF THE INVENTION [

According to the invention, the method further comprises selectively adjusting the first and second quality metric reference values in the outer loop, the first quality metric reference value being a time interval during which all signals are transmitted using the first scrambling code Wherein the second performance metric reference value is adjusted according to a performance level calculated for at least some of the time intervals over which signals are transmitted using the second scrambling code, Wherein in generating the control command, the quality metric reference value uses the first quality metric reference value during time intervals during which all signals are transmitted using the first scrambling code, and at least some of the signals are transmitted to the second scrambling code During at least a portion of the time intervals transmitted using the second performance metric reference The above object is achieved in that the step of using further comprises.

When two separate quality metric reference values are maintained in the external power control loop and the most appropriate quality metric reference value is used in the internal power control loop at a given time according to the scrambling code being used, And thus the total transmit power can be reduced without sacrificing the required performance level, i. E. Without increasing the amount of transmission errors.

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

In one embodiment of the invention, the signals are transmitted in a WCDMA (Wideband Code Division Multiple Access) system. In that case, the quality measure can be estimated as SIR (Signal-to-Interference Ratio), and the performance level can be calculated as BLER (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. As another alternative, the first scrambling code may be one of a primary and a secondary scrambling code, and the second scrambling code may be an alternative scrambling code.

If the second scrambling code is an alternative scrambling code, and if the time interval is a Transmission Time Interval (TTI) comprising a plurality of frames, then at least some of the TTIs transmitted using the second scrambling code Transmission Time Interval) may include at least one frame in which signals are transmitted in a compressed mode using the alternative scrambling code.

When the second quality metric reference value is used as a quality metric reference value in at least all of the frames of a Transmission Time Interval (TTI) in which some signals are transmitted using the second scrambling code, only one A simple solution is obtained in which a quality metric reference value is used. One quality metric reference value is used for the Transmission Time Interval (TTI) having only the first scrambling code and another quality metric reference value is used for the TTI (Transmission Time Interval) having only the second scrambling code or a mixture of scrambling codes .

In an alternate embodiment, the second quality metric reference value is used as the quality metric reference value in a compressed mode frame of a Transmission Time Interval (TTI) at which certain signals are transmitted using the second scrambling code, The reference value is used as the quality metric reference value in the other frames of this Transmission Time Interval (TTI). As such, additional power can be saved because a first quality metric reference (typically lower) is used in the frames of the mixed TTI (Transmission Time Interval) transmitted using the first scrambling code Because.

The method further comprises adjusting at least one additional quality metric reference value in accordance with a performance level calculated for time intervals in which at least some signals are transmitted using the second scrambling code, in addition to the second quality metric reference value - each of the second quality metric reference value and the additional quality metric reference value is adjusted for different signal amounts transmitted using the second scrambling code, and in the step of generating the power control command, the quality metric reference value For at least a portion of time intervals during which at least some of the signals are transmitted using the second scrambling code, the second quality metric reference value and the additional quality metric, in accordance with the amount of the signal transmitted using the second scrambling code, And using one of the reference values. As such, the method may better adapt to different signal amounts transmitted using the second scrambling code.

As described above, the present invention also relates to a transceiver for receiving signals transmitted from a remote transceiver using at least one of first and second scrambling codes in a wireless communication system, said transceiver comprising a controller Wherein the controller comprises: means for iteratively estimating a quality measure for signals received at the transceiver; means for generating a power control command in accordance with the quality measure and the quality metric reference; Means for transmitting to the transceiver, means for calculating a performance level for signals received at the transceiver during a time interval, and means for adjusting the quality metric reference value according to the performance level.

Wherein the adjusting means selectively adjusts the first and second quality metric reference values so that the first quality metric reference value is adjusted according to a performance level calculated for time intervals during which all signals are transmitted using the first scrambling code Wherein the second performance measure reference is adapted to be adjusted according to a performance level calculated for at least some of the time intervals over which signals are transmitted using the second scrambling code, As a reference, the first quality metric reference value is used during time intervals during which all signals are transmitted using the first scrambling code, and during at least a portion of time intervals during which at least some signals are transmitted using the second scrambling code A second performance measure reference value configured to use the second performance measure reference value; , The transceiver is to be a decrease in the number of transmission power and / or transmission errors in this situation is achieved by increasing the power control in a wireless communication system when each transition between different scrambling codes occurs in the transmission.

In one embodiment of the present invention, the transceiver is configured to receive signals transmitted in a WCDMA (Wideband Code Division Multiple Access) system. In that case, the estimating means may be configured to estimate the quality measure as SIR (Signal-to-Interference Ratio), and the calculating means may calculate the performance level as BLER (Block Error Rate, Block error rate).

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 one of a primary and 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 (TTI) comprising a plurality of frames, the transceiver is configured to receive signals, Each Transmission Time Interval (TTI) transmitted using a second scrambling code includes at least one frame in which the signals are transmitted in a compressed mode using the alternative scrambling code.

And the generating means is configured to use the second quality metric reference value as the quality metric reference value in all frames of a Transmission Time Interval (TTI), at least some of which are transmitted using the second scrambling code, A simple solution is achieved in which only one quality metric reference value is used in the Transmission Time Interval (TTI) of the network. One quality metric reference value is used for a Transmission Time Interval (TTI) having only a first scrambling code, and another quality metric reference value is used for a TTI (Transmission Time Interval) having only a mixture of scrambling codes or only a second scrambling code .

In an alternative embodiment, the generating means is adapted to use the second quality metric reference value as the quality metric reference value in a compressed mode frame of a Transmission Time Interval (TTI), at least some of which signals are transmitted using the second scrambling code And to use the first quality metric reference value as the quality metric reference value in the other frames of this Transmission Time Interval (TTI). Thus, additional power can be saved because the first quality metric reference value (typically lower) is also used in the frames of the mixed TTI (Transmission Time Interval) transmitted using the first scrambling code Because.

The means for adjusting further comprises means for determining, in addition to the second quality metric reference value, at least one additional quality metric reference value according to a performance level calculated over time intervals over which at least some signals are transmitted using the second scrambling code And to adjust each of the second quality metric reference value and the additional quality metric reference value for different signal amounts transmitted using the second scrambling code, Wherein the second scrambling code comprises a second scrambling code and the second scrambling code comprises at least some of the time intervals during which at least some of the signals are transmitted using the second scrambling code, If you are configured to use one of the scale references . As such, the transceiver can better adapt to different signal amounts transmitted using the second scrambling code.

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

The present invention will now be described in more detail with reference to the drawings.

1 is a diagram illustrating communication between two transceivers in a wireless communication system.

2 is a diagram showing a timing structure for a downlink DPCH in a WCDMA system.

Figure 3 is a diagram of a known power control apparatus for the transceiver of the system of Figure 1;

4 is a diagram illustrating spreading operation at the transmitter of the system of FIG.

5 is a diagram illustrating a code tree for an OVSF channelization code of a WCDMA system.

6 is a diagram illustrating the use of the compressed mode in a WCDMA system.

7 is a diagram of a power control apparatus modified to maintain two separate SIR reference values.

8 is a flow chart illustrating the calculations performed in the controller of Fig.

9 is a diagram showing an example of how two SIR reference values are updated and used during a series of TTIs.

10 is a diagram showing the effect of using two separate SIR reference values.

11 is an illustration of an example of an alternative of how two SIR reference values are updated and used during a series of TTIs.

1 shows the communication between two transceivers 11, 12 in a wireless communication system (which may be a WCDMA system, for example), in which two transceivers are connected to a wireless transmission channel 13, and the radio signals transmit different types of information. The two transceivers may be a base station 11 and a mobile terminal or a mobile station 12. The mobile station may also be a designated user equipment (UE). The base station 11 may also communicate with other mobile stations (not shown). Information is transmitted (downlink) from the transmitter 14 in the base station 11 through the channel 13 to the receiver 15 in the mobile station 12 in one direction and transmitted in the transmitter 16 in the mobile station 12 in the opposite direction. To the receiver 17 in the base station 11 via the channel 13 (uplink). The wireless transmission channel 13 affects this transmitted signal in a random unknown manner before the transmitted signal is received by the receivers 15 and 17, respectively. Thus, the receiver may process the received signal by, for example, amplifying, filtering, frequency down converting, sampling, despreading, decoding and de-interleaving the received signal, Forms a received signal and regenerates the transmitted information.

Figure 1 also shows the power control of the downlink transmission. Based on the quality of the signal received at the receiver 15, the power control device 18 (described in more detail below) within the mobile terminal 12 may be used to transmit (Transmit Power Control) command indicating whether the power level of the base station 14 should be increased or decreased. The TPC command is then transmitted from the transmitter 16 via the channel 13 to the receiver 17 in the base station 11 and processed in this receiver 17 to be used to control the power level of the transmitter 14. [ Similarly, in the base station 11, a power control apparatus is used for power control of uplink transmission. However, this apparatus is not shown in Fig. 1 for the sake of clarity.

The signals transmitted in the WCDMA system are transmitted in accordance with a well-defined timing structure (the timing structure for the Dedicated Physical Channel (DPCH) is shown in FIG. 2). The TTI (Transmission Time Interval) consists of one to eight radio frames. Each radio frame has a duration of 10ms and is divided into 15 slots. The slot contains 2560 chips and corresponds to one power control period, which will be described below. Thus, the TTI may include 15 to 120 slots. In DPCH, each slot includes two data fields, Data1 and Data2 (which together form a DPDCH (Dedicated Physical Data Channel)) and three control fields: a Transmit Power Control (TPC) field, a Transport Format Combination Indicator field and Pilot field (which together form a DPCCH (Dedicated Physical Control Channel)). The downlink DPCH can thus be regarded as a time multiplex of the downlink DPDCH and the downlink DPCCH. The TPC field is used to transmit the TPC command, but is used not only for the TPC command transmitted on the downlink DPCH but also for the power control of the uplink transmission, while the TPC command related to the power control of the downlink transmission uses the uplink DPCCH Lt; RTI ID = 0.0 > TPC < / RTI > The chip of the data field (and the pilot field) is despread and decoded at the receiver as a data symbol corresponding to the original data bit spread and encoded in the transmitter. The total number of symbols in a slot is determined by a spreading factor (SF). The TTI may also be divided into a number of transport blocks with a variable duration depending on the information to be transmitted.

Now, the power control device 18 will be described in more detail with reference to Fig. As described above, a power control closed loop is used to adjust the transmit power level to maintain a given received signal quality. The control device 18 includes components for a relatively fast internal power control loop and a relatively slow external power control loop at the receiver of the mobile terminal 12.

In the inner loop, a SIR (Signal-to-Interference Ratio) value 51 is calculated once per slot in the SIR estimator 23. The input to the SIR estimator 23 includes a power estimator 21 that estimates the signal power of the slot from a dedicated pilot symbol and a power estimator 21 that estimates interference from either a common pilot channel (CPICH) (Interference estimator) 22 that estimates the interference signal. From these two inputs, the SIR can be calculated. The estimated SIR value (or its filtered value) in the SIR estimator 23 is then compared to the SIR reference value 53 (the target SIR) in the inner loop regulator 24. If the estimated SIR is smaller than the reference value, the inner loop coordinator 24 transmits the TPC (DPCCH) through the uplink Dedicated Physical Control Channel (DPCCH) to request the base station to increase the transmission power for the downlink DPCH Transmit Power Control) command. On the other hand, if the estimated SIR is larger than the reference value, the inner loop adjuster 24 requests the base station to reduce the transmission power. Transmission power update is performed once for every slot or every three slots, and the default value of the power change step is 1.0 dB and there is an option of 0.5, 1.5, or 2.0 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 BLER (Block Error Rate) for the TTI and the BLER target value. An instantaneous BLER value 52 for the TTI in the BLER estimator 25 by performing a CRC (Cyclic Redundancy Check) on each TB (Transport Block) to obtain a flag of 0 or 1 for the correctly or incorrectly received block, . The instantaneous BLER for the current TTI can then be estimated as the ratio of the number of erroneous transmission blocks for the total transmission block of the TTI. Therefore, if N _err (k) of the UEs are found to be in error by the UE performing the CRC at the k th TTI and N _TB (k) transport blocks transmitted from the base station and at the receiver, The momentary BLER (BLER) is simply:

The instantaneous BLER values (or CRC flags) may be filtered over some TTI to produce an estimated BLER, i. _E. , A BLER _filt value over a long period of time.

The estimated BLER values (instantaneous and / or filtered values) in the outer loop adjuster 26 are then compared to the BLER target value to obtain an updated SIR reference value. The BLER target value BLER _targ is provided by this system. A typical outer loop power control algorithm is based on the generalization of the PI (Proportional Integral) controller, where the integral part is calculated as follows.

Subsequently, the SIR reference value may be updated for the next TTI, i.e., (k + 1) th TTI as follows.

Here, the initial value of the integral part is I (0) and the starting value of the SIR reference value is SIR _ref (0). The constants in the above equations may be different for different BLER target values to accelerate the convergence of power control, especially for low BLER target values.

Therefore, the outer loop power control attempts to adjust the SIR reference value by comparing the estimated BLER with the BLER target value. If the estimated BLER for the TTI is higher than the predetermined BLER target value, the SIR reference value is increased for the next TTI to obtain more power from the base station and thus reduce the block error. Likewise, if the estimated BLER is lower than the BLER target value, the SIR reference value is reduced so that the base station does not need to allocate too much power to the targeted user equipment. Thus, at the end of each TTI, a new SIR reference value is calculated based on the estimated BLER for that TTI, and this new SIR reference value is used by the inner loop for the next TTI.

As described above, the downlink data is spread before being transmitted from the transmitter 14 in the base station 11. The spreading operation in the transmitter is shown in Fig. This figure shows a modulation mapper stage 31 in which an input number is mapped to a real value symbol, that is, a binary value "0" is mapped to a real value +1 and a binary value "1 & ). Then, in the channelization stage 32, data in IQ form (in-phase and quadrature) is multiplied by the real-valued channelization code _{Cch, SF, m} (where SF is a spreading factor) chip rate. The same channelization code is used in Q branch as well as I branch. Thus, the output for each input symbol on the I and Q branches becomes the SF chip sequence corresponding to the channelization code chip sequence multiplied by the real value symbol. The channelization codes will be described in more detail below.

The real value chip sequence in the Q branch is complex multiplied with the imaginary operator j in multiplier 33 and summed with the corresponding real value chip sequence in I branch in IQ combiner 34 so that one complex value chip sequence < RTI ID = 0.0 > . Finally, at the scrambling stage 35, the complex value chip sequence is scrambled (complex chip-wise multiplication) by the complex value scrambling code S _{dl, n} .

The channelization code is an Orthogonal Variable Spreading Factor (OVSF) code that maintains orthogonality between different physical channels. The spreading factor can be up to 512. The OVSF code is defined according to a coding tree as shown in FIG. The code tree is first divided into two branches with SF = 2, then each of which is further divided into two branches with SF = 4. This continues until branches with SF = 512 are reached. 4 and 5, the channelization code is _{Cch , SF , m} (where SF is the spreading factor of the code and m is the code number 0? M? SF-1) Can be expressed uniquely. While the channelization codes under different branches are orthogonal even if they have different spreading factors, this channelization code is not orthogonal to its original code. For _{instance, C ch, 4,0 = (1} , 1, 1, 1) is _{C ch, 4,1 = (1,} 1, -1, -1) as well as C _{ch, 4,2} = (1 , -1, 1, -1), C _{ch, 4,3} = (1, -1, -1, 1) and even C _ch, but _2,1 = (1, -1), the orthogonal transient, C _{ch, 2,0} = (1, 1) is not orthogonal. Therefore, if a channelization code is assigned in a given code tree, not all code under that code with a higher spreading factor should be used to guarantee orthogonality. As a result of orthogonality requirements, the number of channelization codes available in the code tree is fairly limited, especially for high data rates, i.e. small spreading factors.

The scrambling code is a complex value-wise multiply at the scrambling stage 35, as described above, with a complex value code S _{dl, n} , and the complex value chip sequence. A large number of different scrambling codes may be generated, but they are not exhaustive. The scrambling code is divided into 512 sets, each set including one primary scrambling code and 15 secondary scrambling codes. The primary scrambling code consists of a scrambling code n = 16 * i (where i = 0 ... 511). The i-th secondary scrambling code set consists of a scrambling code 16 * i + k (where k = 1 ... 15). There is a one-to-one mapping between each primary scrambling code and fifteen secondary scrambling codes in the set such that the i-th primary scrambling code corresponds to the i-th secondary scrambling code set. Each cell is assigned only one primary scrambling code. Some physical channels, such as the Common Pilot Channel (CPICH), are always transmitted using a primary scrambling code, while other downlink physical channels use a primary scrambling code or a secondary scrambling code in the set associated with the cell's primary scrambling code ≪ / RTI >

Thus, 8191 scrambling codes are used as the primary or secondary scrambling code. In addition, each of the primary and secondary scrambling codes may include two alternative scrambling codes that may be used for the compressed frame: an alternative left scrambling code and an alternative right scrambling code ).

Compressed mode is used in WCDMA when user equipment needs time to make the necessary measurements on different carrier frequencies during inter-frequency handover. To allow the user equipment to perform these measurements, certain slots in the frame - typically one to seven slots per frame - are allocated for this purpose, thus creating transmission gaps in the frame. This frame is called a compressed frame because only the remaining slots of the frame are available for normal transmission of information. Typically, compressed frames occur periodically, but may be requested on demand. The rate and type of compressed frame is variable and depends on the environment and measurement requirements.

6 shows the compression mode. In the figure, a series of TTIs (in this case, each TTI consists of four frames) are transmitted. It can be seen that while some TTIs include four normal frames, other TTIs contain compressed frames. As an example, the second frame of the k-th TTI is compressed and there is a transmission gap in the middle of the frame. As shown, the instantaneous transmit power is increased for the remaining slots of the compressed frame so that the quality (e.g., BLER) is not affected by the reduced number of slots. The amount of power increase depends on the reduction of the transmission time. If, for example, seven slots are used in the transmission space, this means that only about half of the compressed frame is available for transmission of the data. Correspondingly, in FIG. 6, the transmission power of the compressed frame is increased to approximately twice the normal power level.

In addition, in order to maintain the amount of information transmitted even in compressed frames, the spreading factor may be reduced to 2: 1, since this increases the data rate and accordingly the data symbols are transmitted twice faster Because. However, a change in spreading factor may require that the real-location of some or all of the channelization codes in the code tree remain orthogonal. Thus, if a base station must use a channelization code with a spreading factor that is 1/2 of the original spreading factor SF, then some of the codes under the branch with SF / 2 may already be used by another channel have. As an example, if C _{ch, 2,0} should be used in compression mode instead of code C _{ch, 4,0} for normal mode and some code below branch C _{ch, 4,1} is used by another channel, orthogonality Is destroyed. Even if the codes below branch C _{ch, 4,1} are freely used in normal mode, these codes are now blocked due to the compression mode with spread factor reduction.

To avoid this reallocation, the sender could instead switch to an alternative scrambling code for the compressed frame, since other scrambling codes mean that the channel code from another code tree can be used . Since the correlation of the scrambling code is similar to noise, the correlation of the channelization code is still quite low, even if these channelization codes are under different scrambling codes, even if the channelization code is in the same branch of the code tree. Thus, while compressed frames are transmitted using alternative scrambling codes, other frames are transmitted using normal scrambling codes, i.e., primary or secondary scrambling codes. Since the compressed frame is in a pattern determined by the network as shown in Figure 6 (although it is not necessary, typically the compressed frame is at the same frame position in the TTI with the compressed frame) There is a transition between the scrambling code and the alternative scrambling code. Thus, for all TTIs, all frames are transmitted using the same scrambling code, while other TTIs are transmitted using a mixture of different scrambling codes. A similar situation arises when the base station switches between the primary scrambling code and the secondary scrambling code in the normal mode. By using two or more code trees, a base station can provide as many data rates as possible to a large number of users. As discussed above, the base station requires a sufficient amount of channelization code to be available for this purpose. Thus, if necessary, it is advantageous for the base station to use a secondary scrambling code in addition to the primary scrambling code, and a switch between scrambling codes occurs.

The fact that certain TTIs are transmitted using the same scrambling code for every frame, while other TTIs are transmitted using a mixture of different scrambling codes causes the problem of transmission control because the signal received under one scrambling code Lt; RTI ID = 0.0 > SIR < / RTI > reference values for the received signals are not optimal for signals received under different scrambling codes. Thus, by switching between the scrambling codes, the SIR reference value is not optimal for either of the two scrambling codes. Typically, the amount of block error is increased, so that the SIR reference value is increased to a level higher than is actually needed. The end result is a waste of transmit power.

FIG. 7 shows an example of how the power control device 18 can be modified to improve power control in this situation. In the modified power control unit 40, the power control is divided into two types of TTIs: TTIs in which all frames are transmitted using the same scrambling code, and TTIs in which frames are transmitted using different scrambling codes. . In the following description, the modified power control apparatus 40 is described with reference to the above-described compressed mode situation, in which some frames are transmitted under an alternative scrambling code, but the base station does not transmit the primary scrambling code and the secondary scrambling code The same solution can be used.

Compared to the power control device 18 of Fig. 3, the components of the external power control loop are modified in the power control device 40. Fig. The BLER estimator 25 still estimates the BLER value 52 for each TTI while the outer loop adjuster 46 now has two different SIR reference values 54 and 55, SIR _ref1 for the TTI scrambled using the secondary (or secondary) scrambling code and SIR _ref2 for the TTI scrambled using the alternative scrambling code while at least one frame is in the compressed mode. These two SIR reference values are stored in registers 47 and 48, respectively. It determines which SIR reference value the input representing the type of scrambling code used in the current TTI for outer loop adjuster 46 will update. Thus, for example, at the end of a TTI where all frames are in normal mode, SIR _ref1 does not have to be the previous value of the BLER and SIR _ref1 estimated for that TTI (necessarily calculated for the immediately preceding TTI, The reason is that there may be a TTI with a compressed frame between them). Similarly, SIR _ref2 is updated at the end of the TTI where at least one frame is in the compressed mode. Thus, the outer loop power control algorithm (the SIR reference value is updated according to this algorithm) can be created as follows.

In other words, the initial value of the integral part is I (0) and the starting value of the SIR reference value is SIR _ref (O), and m is not necessarily used for the TTI immediately after the SIR reference value calculated at the end of the k-th TTI .

The constants used in equations (4) and (5), i.e., C _I , C _B, and C _S , may be different for the compressed mode and the normal mode under alternative scrambling codes to optimize performance. Alternatively, the same constant may be used for both modes, so the only difference between the normal mode and the compressed mode is that the previous SIR reference value SIR _ref (k) in Equation 5 is different for the two modes and updated The SIR reference value is only applied to the next TTI with the same mode.

In the SIR reference value selector 49, an input indicating the type of scrambling code used in the current / upcoming TTI is used to determine which of the two SIR reference values in the inner loop coordinator 24 for this TTI will be used as the SIR reference value 56 . This input signal is based on information received from the base station.

Figure 8 shows a flow diagram 100 illustrating the calculations performed in the BLER estimator 25, the outer loop adjuster 46 and the SIR reference value selector 49. [ At step 101, an instantaneous and filtered BLER value is calculated from the CRC flag for this TTI at the end of the TTI. In step 102, it is determined whether this TTI contains only a normal frame or a compressed frame. If all the frames of the TTI are in the normal mode, in step 103, the SIR reference value SIR _ref1 is updated. On the other hand, if the compressed frame is included, in step 104, the SIR reference value SIR _ref2 is updated. In step 105, it is determined whether the next TTI includes only normal frames or compressed frames. If all the frames of the next TTI are then in normal mode, then at step 106 the value SIR _ref1 is selected as the SIR reference value. On the other hand, if the compressed frame is included in the next TTI, then in step 107 the value SIR _ref2 is selected as the SIR reference value. Finally, at step 108, the selected SIR reference value is provided to the inner loop adjuster 24. [

Figure 9 shows how two SIR reference values are updated and used during a series of TTIs (some of these TTIs have all frames in normal mode while others contain compressed frames). For the sake of explanation, the TTI is shown as having four frames each in this figure, but the number of frames in the TTI can vary between 1 and 8. [ As an example, TTI _k includes a compressed frame, so during this TTI, the inner loop coordinator 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 SIR _ref2 value is also used at TTI _{k + 2} , which also includes the compressed mode frame, and SIR _ref1 is used during TTI _{k + 1} where all frames are in normal mode.

Figure 10 illustrates the effect of performing power control independently for two types of TTIs. The curves during the power control time when the scramble code of the alternatives used for the DPCH during the compressed frames, i.e. as shown the level of the SIR reference value over a large number of TTI, are constants of the equation 4 and 5 C _I = 0, C _B = 0.25 and C _S = 0.25, and the BLER target value is set to 1%. The upper curve is for a case where only one common SIR reference value is updated for both the normal TTI and the compressed frame, and the lower two curves are for a TTI with all frames in normal mode and a TTI (SIR _ref1 , SIR _ref2 , respectively) are updated for each of the two SIR reference values. In the latter case, it can be seen that the two SIR reference values are automatically distinguished during the power control time. In addition, compared to situations with only one common SIR reference value, the overshoot is reduced and the convergence of the SIR reference value results in less noise. From these curves, if all of the TTIs are transmitted under a primary scrambling code, for example, only one SIR reference value is updated, the known solution has an SIR reference value of about 4 after, for example, 5000 TTIs . However, if there is a switch between scrambling codes, then the solution will instead have an SIR reference value of about 19 under the same channel condition, and the amount of transmit power will increase accordingly. On the other hand, as can be seen from the figure, the solution in which two separate SIR reference values are updated will maintain a SIR reference value of about 4 for TTIs containing only frames transmitted under the original scrambling code, The individual SIR reference value for the TTI including the frames transmitted under the scrambling code of < RTI ID = 0.0 > This means that a significant amount of transmission power can be saved without degrading the BLER. As shown by this simulation, under these conditions, when using two separate SIR reference values instead of one, the average transmit power level could be reduced, and the estimated BLER was also reduced.

As also shown in FIG. 9, in the above solution, one of the two individually updated SIR reference values, SIR _ref1 , is used in the inner loop coordinator 24 during a TTI where all frames are in normal mode, while the other The reference value, SIR _ref2 , is used for the TTI with a mixture of normal and compressed frames. However, it is also possible to switch between the SIR reference value so that during the latter type of frames, SIR _ref1 is used for the normal frames only for a compressed frame, the SIR _ref2. This is shown in FIG. Also, as shown in the figure, two SIR reference values are still updated as described above, i.e., SIR _ref1 is updated at the end of the TTI with only the normal frame, while SIR _ref2 is updated at the end of the TTI with at least one compressed frame Lt; / RTI > As such, the transmit power can be further reduced because a lower SIR _ref1 is used for all normal frames and a higher SIR _ref2 is used for compressed frames only.

In the above example, a two-state model was used in which one state describes an SIR reference value for a TTI that overlaps with a portion of a transmission made via an alternative scrambling code, and the other state uses a primary scrambling code It is used for TTIs that completely overlap with a portion of the transmission being done. However, this modeling can be extended to include three or more states. A number of SIR states may be defined depending on the amount of TTI overlap with the transmission made via the alternative scrambling code. Thus, for example, for the TTI of FIG. 9 (each TTI having four frames), in addition to the SIR reference value for the TTI having only the normal mode frame, one, two, three, or four compressions An SIR reference value for a TTI having a frame can be defined. However, when more states are defined, the statistics of the states are updated less frequently, which may result in a slower system response. Thus, the above two-state model appears to be a good compromise. Since the compressed mode frames are fairly frequent (e.g., every 3 to 7 frames), no data shortage occurs when updating the two-state model.

In the foregoing, the present invention is described in terms of switching between one scrambling code (primary or secondary scrambling code) used in a normal mode frame and an alternative scrambling code used in a compressed frame. However, the above solution is equally suitable in other situations with different scrambling code switching, for example when the base station switches between the primary scrambling code and the corresponding one of the secondary scrambling codes.

Although the preferred embodiments of the present invention have been described and illustrated, the present invention is not limited thereto and can be implemented in other ways within the scope of the present invention as defined in the following claims.

Claims (23)

CLAIMS What is claimed is: 1. A method for controlling the power level of signals transmitted from a first transceiver to a second transceiver in a wireless communication system, the signals being transmitted using at least one of first and second scrambling codes, In the internal power control loop, Repeatedly estimating a quality measure (51) for signals received at the second transceiver, Generating a power control command in accordance with the quality measure (51) and the quality measure reference value (56) Transmitting the power control command to the first transceiver, and Adjusting the power level in accordance with the power control command at the first transceiver; In an external power control loop, Calculating a performance level (52) for signals received at the second transceiver during a TTI (Transmission Time Interval), and Adjusting the quality metric reference value (56) according to the performance level (52) / RTI > The method comprises: Selectively adjusting first and second quality metric reference values in the outer loop, wherein the first quality metric reference value (54) is indicative of a performance measure for TTIs in which all signals are transmitted using the first scrambling code Level 52 and the second performance metric reference value 55 is adjusted according to a performance level 52 calculated for TTIs in which at least some signals are transmitted using the second scrambling code- , And Wherein generating the power control command comprises using the first quality metric reference value (54) as the quality metric reference value (56) during TTIs when all signals are transmitted using the first scrambling code, Using the second performance metric reference value (55) during at least some of the TTIs in which signals are transmitted using the second scrambling code ≪ / RTI > A method for generating a power control command in a transceiver that receives signals transmitted from a remote transceiver using at least one of first and second scrambling codes in a wireless communication system, Repeatedly estimating a quality measure (51) for signals received at the transceiver, Generating a power control command in accordance with the quality measure (51) and the quality measure reference value (56) Transmitting the power control command to a first transceiver, Calculating a performance level (52) for signals received at the transceiver during a TTI (Transmission Time Interval), and Adjusting the quality metric reference value (56) according to the performance level (52) / RTI > The method comprises: Selectively adjusting first and second quality metric reference values, the first quality metric reference value (54) being indicative of a performance level (52) calculated for TTIs in which all signals are transmitted using the first scrambling code, , And the second performance metric reference value (55) is adjusted according to a performance level (52) calculated for TTIs in which at least some signals are transmitted using the second scrambling code; and Wherein generating the power control command comprises using the first quality metric reference value (54) as the quality metric reference value (56) during TTIs when all signals are transmitted using the first scrambling code, Using the second performance metric reference value (55) during at least some of the TTIs in which signals are transmitted using the second scrambling code ≪ / RTI > 3. The method of claim 1 or 2, wherein the signals are transmitted in a Wideband Code Division Multiple Access (WCDMA) system. 4. The method of claim 3, wherein the quality measure is estimated as a Signal-to-Interference Ratio (SIR). 4. The method of claim 3, wherein the performance level is calculated as a BLER (Block Error Rate). 4. The method of claim 3, wherein the first scrambling code is a primary scrambling code and the second scrambling code is a secondary scrambling code. 4. The method of claim 3, wherein the first scrambling code is one of a primary and a secondary scrambling code, and the second scrambling code is an alternative scrambling code. 8. The method of claim 7, wherein the TTI comprises a plurality of frames, and wherein each TTI for which at least some signals are transmitted using the second scrambling code is transmitted in a compressed mode using the alternative scrambling code ≪ / RTI > wherein the frame comprises at least one frame. 9. The method of claim 8, wherein the second quality metric reference value (55) is used as the quality metric reference value in all frames of the TTI in which at least some signals are transmitted using the second scrambling code. 9. The method of claim 8, wherein the second quality metric reference value (55) is used as the quality metric reference value in a compressed mode frame of a TTI in which at least some signals are transmitted using the second scrambling code, 54) is used as the quality metric reference value in different frames of this TTI. 3. The method according to claim 1 or 2, The method comprises: In addition to said second quality metric reference value (55), adjusts at least one additional quality metric reference value according to a performance level (52) calculated over time intervals in which at least some signals are transmitted using said second scrambling code Wherein each of the second quality measure reference value and the additional quality measure reference value is adjusted for different signal amounts transmitted using the second scrambling code, The method of claim 1, wherein generating the power control command further comprises, as the quality metric reference value (56), during a time interval of at least some of the time intervals over which at least some signals are transmitted using the second scrambling code, Using one of the second quality metric reference value and the additional quality metric reference value according to the amount of signal to be transmitted using ≪ / RTI > A transceiver for receiving signals transmitted from a remote transceiver using at least one of first and second scrambling codes in a wireless communication system, the transceiver comprising a controller (40) for generating a power control command, The controller comprising: Means (23) for iteratively estimating a quality measure (51) for signals received at the transceiver, Means (24) for generating a power control command in accordance with the quality measure (51) and the quality measure reference value (56) Means (16) for transmitting the power control command to the remote transceiver, Means (25) for calculating a performance level (52) for signals received at the transceiver during a TTI (Transmission Time Interval), and Means (46) for adjusting said quality metric reference value (56) according to said performance level (52) / RTI > The adjusting means (46) selectively adjusts the first and second quality metric reference values so that the first quality metric reference value (54) is set for each TTI for which all signals are transmitted using the first scrambling code And the second performance measure reference value (55) is adjusted according to the calculated performance level (52) according to a performance level (52) calculated for TTIs in which at least some signals are transmitted using the second scrambling code Is configured to be adjusted, Characterized in that the means for generating (24) uses the first quality metric reference value (54) as the quality metric reference value (56) during TTIs when all signals are transmitted using the first scrambling code, Are configured to use the second performance metric reference value (55) during at least some TTIs of the TTIs transmitted using the second scrambling code. 13. The transceiver of claim 12, wherein the transceiver is configured to receive signals transmitted in a WCDMA system. 14. The transceiver of claim 13, wherein the estimating means (23) is configured to estimate the quality measure as an SIR. 15. A transceiver according to claim 13 or 14, wherein the means for calculating (25) is configured to calculate the performance level as BLER. 15. The transceiver of claim 13 or 14, wherein the first scrambling code is a primary scrambling code and the second scrambling code is a secondary scrambling code. 15. The transceiver of claim 13 or 14, wherein the first scrambling code is one of a primary and a secondary scrambling code, and the second scrambling code is an alternative scrambling code. 18. The method of claim 17, wherein the TTI comprises a plurality of frames, the transceiver is configured to receive signals, and each TTI to which at least some signals are transmitted using the second scrambling code, And at least one frame transmitted in a compressed mode using an alternative scrambling code. 19. The apparatus of claim 18, wherein the means for generating (24) is adapted to use the second quality measure reference value (55) as the quality measure reference value in all frames of the TTI where at least some signals are transmitted using the second scrambling code And a transmission / reception unit. 19. The apparatus of claim 18, wherein the means for generating (24) is adapted to generate the second quality metric reference value (55) as the quality metric reference value in a compressed mode frame of a TTI in which at least some signals are transmitted using the second scrambling code , And to use the first quality measure reference value (54) as the quality measure reference value in other frames of this TTI. 15. The method according to any one of claims 12 to 14, Wherein said adjusting means (46) is operable, in addition to said second quality metric reference value (55), to adjust at least some of the signals according to a performance level (52) calculated over time intervals in which at least some signals are transmitted using said second scrambling code Adjust the at least one additional quality metric reference value and adjust each of the second quality metric reference value and the additional quality metric reference value for different signal amounts transmitted using the second scrambling code, Characterized in that the means for generating (24) is operable, as the quality metric reference value (56), to use the second scrambling code for at least some of the time intervals during which at least some signals are transmitted using the second scrambling code And to use one of the second quality metric reference value and the additional quality metric reference value according to the amount of signal to be transmitted. delete delete

Images