KR100665589B1 - A radio communication system, a primary station and a secondary station for use in such a radio communication system, and a method of operating a radio communication system - Google Patents

Abstract

In a wireless communication system having one first station and a plurality of second stations, the power of the uplink and downlink channels between the first station and the second station is controlled by each station that transmits a power control command to the other station. Controlled by closed loop method. In response to this command, the receiving station adjusts its output power step by step. By considering a plurality of received power control commands, the destination station may use a power control step size, for example, a step size less than the minimum or median between the step sizes implemented, rather than the power control step size it implements directly. Emulate ability. This can improve performance under certain channel conditions. In one embodiment, when the required power control step size is less than the minimum step size of the destination station, the destination station processes a group of power control commands to determine whether to adjust its output power by its minimum step size. .

Description

A RADIO COMMUNICATION SYSTEM, A PRIMARY STATION AND A SECONDARY STATION FOR USE IN SUCH A RADIO COMMUNICATION SYSTEM, AND A METHOD OF OPERATING A RADIO COMMUNICATION SYSTEM}

The present invention relates to a wireless communication system, and further relates to a primary station and a secondary station, and a method of operating the system for use in such a system. Although the present disclosure describes a system that is of particular relevance to the recent Universal Mobile Telecommunication System (UMTS), it can be seen that such techniques are equally applicable for use in other mobile wireless systems.

There are two basic types of communication required between a base station (BS) and a mobile station (MS) in a wireless communication system. The first is user traffic, for example voice or packet data. Second is control information necessary to set and monitor various parameters of the transmission channel to enable the BS and MS to exchange the necessary user traffic.

In many communication systems, one of the functions of the control information is to enable power control. Power control of the signal transmitted from the MS to the BS is required in order to minimize the transmit power required by each MS while the BS receives signals from several MSs at approximately the same power level. Power control of the signal transmitted by the BS to the MS is required, in order to reduce interference with other cells and wireless systems, while the MS receives signals from the BS at a low error rate, while minimizing transmission power To do that. In a two-way wireless communication system, power control may be operated in a closed loop or open loop method. In a closed loop system, the MS determines the necessary change in transmit power from the BS, signals this change to the BS, and vice versa. In an open loop system that can be used in a TDD system, the MS measures the signal received from the BS and uses this measurement to determine the necessary change in MS transmit power.

An example of a combined time and frequency division multiple access system using power control is the Global System for Mobile communication (GSM), where the transmit power of both BS and MS transmitters is controlled in 2 dB steps. do. Similarly, power control implementations in systems using Spread Spectrum Code Division Multiple Access (CDMA) technology are disclosed in US patent (US-A-5 056 109).

In considering closed loop power control, it can be seen that for any given channel condition, there is an optimal power control step size that minimizes the required E _b / N _O (energy / noise density per bit). When the channel changes very slowly, the optimal step size may be less than 1 dB, because such a value is sufficient to track the change in the channel while providing minimal tracking error. As the Doppler frequency increases, larger steps provide better performance with the optimum value exceeding 2 dB. However, as the Doppler frequency increases further, the latency (or update rate) of the power control loop becomes so large that the channel cannot be properly tracked, and the point where the optimum step size decreases again, perhaps below 0.5 dB. Leads to The reason is that fast channel changes cannot be tracked, so what is needed is the ability to follow shadowing, which is generally a slow process.

Since the optimal power control step size can vary dynamically, the BS determines the appropriate power control step size for use in the uplink transmission from the MS to the BS and the downlink transmission from the BS to the MS, so that If notified can improve performance. One example of a system that can use such a method is the UMTS Frequency Division Duplex (FDD) standard, where power control is important because of the use of CDMA technology. Although improved performance can be achieved by having a small minimum step size, for example 0.25 dB, this will significantly increase the cost of the station. However, if the station does not need to implement a minimum step size, it may not be able to implement the requested step size.

Additional problems may arise in systems where the implementation of some power control step sizes by the station is optional. For example, in a system operating in accordance with the UMTS specification, a BS may use a plurality of different power control step sizes, e.g., four step sizes 0.5dB, 1dB, 1.5dB, and when varying downlink transmission power. 2dB can be used. However, there may be cases where only 1 dB step size is forcibly implemented. In some circumstances, it may be desirable to ensure that several BSs operate in a similar manner. For example, during a soft handover, the MS communicates with a plurality of BSs (known as the "active set" of the BSs) to determine which BS should transfer even if they switch. To start. Therefore, there is a need to avoid a significant dissipation of the transmit power of the BS in the active set. This is best achieved when the BS in the active set changes the transmit power by using a similar method, eg, a similar power step size in response to a received power control command.

While the two BSs are in smooth handover with the MS moving at the rate at which the 1.5dB step size is optimal, if only one of the BSs supports 1.5dB steps, optimal power control of the two BSs is not possible. . The network instructs the BS to use multiple step sizes so that the optimal step size can be used by BSs that support different step sizes (with the risk of significantly dissipating the transmit power of the two BSs). Or direct the two BSs to use the same non-optimal step size (eg, 1 dB or 2 dB) to avoid excessive dissipation of transmit power. Clearly, no choice is optimal.

It is an object of the present invention to be able to select the optimal power control step size without the need for all stations to implement the same set of step sizes.                 

According to a first aspect of the present invention, there is provided a wireless communication system having a communication channel between a first station and a second station, wherein one of the first station and the second station (transmission station) has its own output to the other station. Means for transmitting a power control command to another station (receiving station) to instruct to adjust the transmit power, the receiving station having an unsupported power control step size by combining at least one supported size power control step; Emulation means for emulating a.

According to a second aspect of the invention, there is provided a first station for use in a wireless communication system having a communication channel between a first station and a second station, the first station comprising: power transmitted by the second station; Means are provided for stepwise adjusting the output transmit power in response to a control command, and emulation means for emulating an unsupported power control step size by combining at least one supported size power control step is provided.

According to a third aspect of the invention, a second station is provided for use in a wireless communication system having a communication channel between a second station and a first station, wherein the second station is configured to transmit power transmitted by the first station. Means for stepwise adjusting its output transmit power in response to a control command, and emulation means for emulating an unsupported power control step size is provided by combining at least one supported size power control step. .

According to a fourth aspect of the present invention, there is provided a method of operating a wireless communication system having a communication channel between a first station and a second station, the system comprising a communication channel between the first station and the second station, The method includes transmitting a power control command to another station (receiving station) to instruct one of the first station and the second station (sending station) to adjust its power in stages, the receiving station being Emulate unsupported power control step size by combining at least one supported size power control step.

The present invention is not provided in the prior art and is based on the recognition that small power control step size emulation by the MS can provide excellent performance.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings.

1 is a schematic block diagram of a wireless communication system.

2 is a flow diagram illustrating a method according to the invention for performing power control at a second station.

3 is a graph of power control step size used in dB for a MS traveling at 300 km per hour versus received E _b / N _o in dB required for a bit error rate of 0.01.

4 is a graph of power control step size used in dB for a MS traveling at 1 km per hour versus received E _b / N _o in dB required for a bit error rate of 0.01.

Referring to FIG. 1, a wireless communication system capable of operating in frequency division duplex mode or time division duplex mode includes one first station (BS) 100 and a plurality of second stations (MS) 110. . BS 100 is a microcontroller (μC) 102, transceiver means (Tx / Rx) 104 connected to wireless transmission means 106, and power control means (PC) 107 for changing the transmitted power level. And connection means 108 for connecting to the PSTN or other suitable network. Each MS 110 includes a microcontroller (μC) 112, a transceiver means (Tx / Rx) 114 connected to a wireless transmission means 116, and a power control means (PC) for changing the transmitted power level. 118; Communication from BS 100 to MS 110 occurs on downlink channel 122, while communication from MS 110 to BS 100 occurs on uplink channel 124.

In a UMTS FDD system, data is transmitted in 10ms frames each having 15 time slots. BS 100 sends one power control command (consisting of two bits) per slot, where bit 11 (hereafter referred to as a value of 1 for simplicity) tells MS 110 to increase power. Bit 00 (hereinafter referred to as 0) requests the MS 110 to reduce power. The required power control step size change is notified individually via the control channel.

In the system according to the invention, this behavior is changed when the MS 110 is requested to implement a power control step size that is smaller than the minimum size that the MS 110 can do. In such a situation, the MS 110 may take no action unless it receives a series of identical power control commands, thereby emulating the performance of the MS 110 with more precise power control.

For example, consider the case where the requested step size is 0.5 dB and the minimum step size implemented by the MS 110 is 1 dB. MS 110 processes the power control commands in pairs and only changes the output power if both commands are identical. Thus, if the received command is 11, the power is increased, if the command is 00, the power is decreased, and if the command is 10 or 01, the power is unchanged. Align the comparison with the transmission of the frame to combine the power control commands sent to slot 1 and slot 2 of the particular frame, then to combine the commands sent to slot 3 and slot 4, and then It may be advantageous to combine in this way.

Similarly, if the requested step size is 0.25 dB and the minimum step size is 1 dB, the MS 110 processes four power control commands at the same time and only changes the output power if all four commands are equal. Thus, power is increased if the received command is 1111, and power is decreased if the received command is 0000, otherwise it does not change. In addition, the comparison is aligned with frame transmission to combine the commands sent to slots 1 through 4 of a particular frame, then to combine the commands sent to slots 5 through 8, and then continue to combine in this manner. It may be advantageous.

Combining commands received in three or five slots is particularly advantageous for the UMTS embodiment under consideration because it maintains alignment with one frame of fifteen slots. However, this method is not limited to such a system. Consider the general case where the minimum step size implemented by the MS 110 is S and the step size requested by the BS 100 is R. In this case, the power control commands can be combined into groups of G, where G = S / R.                 

2 illustrates a method of emulating less power control steps than the minimum of MS 110. The method begins at step 202 with the MS 110 determining the number of commands G to be combined to group, and setting the received power control command counter value from i to zero. In step 204, MS 110 receives the power control command and increments the coefficient value i. Next, in step 206, the value of i is compared with G. If i is less than G, the received command is stored and the MS 110 waits to receive the next command. If i is greater than or equal to G, then the required number of power control commands have been received, and the MS 110 determines in step 208 whether to adjust its power based on the received power control commands. Once this is done, the counter i is reset to 0 (if i is equal to G), or to 1 (if i is greater than G, which will occur if G is not an integer), or MS 110 ) Then waits to receive a power control command.

In an alternative embodiment, instead of combining the power control commands into groups of G, MS 110 maintains a current running total of the requested power changes, once the total requested power changes are at the minimum step size. It changes when you reach it. For example, if the requested step size is 0.25 dB and the minimum step size is 1 dB, then the sequence 11010111 of the received command results in an increase in power by 1 dB. The MS 110 then subtracts the steps actually implemented from the current grand total of the requested power change. However, such a scheme becomes more complex to implement (since this configuration requires maintaining a current total of the requested power change), and it appears to provide only minimal improvements to the performance of the method.

In a variation of this alternative embodiment, the MS 110 uses an easy decision method in maintaining a current total of the requested power change, rather than making a difficult decision through each individual power control command. Each power control command is a function of the amplitude of the signal received for that command, according to a measure of the likelihood that the MS 110 correctly interprets the command before it is added to the current running sum. Weighted by For example, sequence 11010111011, once weighted, corresponds to the sequence 0.8 0.3 -0.3 0.4 -0.1 0.5 0.9 0.8 -0.4 0.7 0.5 (in units of 0.25 dB) of the requested power change. This sequence has a current sum of 4.1, which performs an upwards step of 1 dB and triggers MS 110 to reduce the current sum to 0.1. Such modifications will provide minor improvements in carrying out the method.

Two simulations have been performed to illustrate the effectiveness of the method according to the invention. The simulation examines the performance of the MS 110 with a minimum step size of 1 dB compared to the performance of the MS 110 with a minimum step size of 0.25 dB. Simulation makes a number of ideal assumptions:

There is one slot delay in the power control loop;

No channel coding;

There is complete channel estimation by the receiver;

Equalization at the receiver is performed by a complete RAKE receiver;                 

No control channel overhead is included in the E _b / N _O figures;

A fixed error rate exists in the transmission of the power control command,

The channel is modeled as a simple N-path Rayleigh channel.

The first simulation relates to a rapidly changing channel as the MS 110 moves at 300 km / h in a single path Rayleigh channel with an error rate for a power control command of 0.01. 3 is a graph of power control step size used in dB versus received E _b / N _O in dB required for an uplink bit error rate of 0.01. While the solid line is the result for the MS 110 with a minimum power control step size of 0.25 dB or less, the dashed line controls power in two or four groups to emulate 0.5 dB and 0.25 dB power control step sizes, respectively. Results are shown for MS 110 with a minimum step size of 1 dB combining bits.

In this situation, the best performance is achieved at small step sizes of less than 1 dB. The emulation of the 0.25 dB and 0.5 dB steps results in an implementation loss of almost about 0.05 dB compared to about 0.6 dB when no emulation is performed, demonstrating the effectiveness of the emulation method. By increasing the error rate of the power control command to 0.1, a general reduction of about 0.2 dB occurs in the received E _b / N _O , but the performance of the MS 110 with the emulated small steps directly implements the small steps. It is similar to the performance of the MS (110).

The second simulation relates to a slowly changing channel as the MS 110 moves at 1 km per hour in a six path Rayleigh channel with an error rate of 0.01 for the power control command. 4 is a graph of power control step size used in dB versus received E _b / N _O in dB required for an uplink bit error rate of 0.01. The lines of the graph are identified in the same way as in FIG.

In this situation, there are some advantages to using a power control step of less than 1 dB. By using the first simulation, the results obtained using the emulated small steps are very similar to the results using the direct implementation of the small steps.

In a further application of this method, when considered advantageous for reasons such as reducing the impact of an error in the interpretation of a transmitted power control command (eg by averaging over a longer time period), the value of G is S /. It can be set to a value other than R. Therefore, in some circumstances, the MS 110 may choose to use a step size that is larger than the minimum step size that can be implemented.

A variation of the method described above can be used for emulation of an unsupported power control step size larger than the minimum step size implemented by the station. Consider the case of the BS 100 in a system operating according to the UMTS standard. In one example of such a system, BS 100 may use one of four step sizes, 0.5 dB, 1 dB, 1.5 dB and 2 dB, when adjusting the power of downlink transmission 122, of which only 1 dB is forced. Used as                 

Consider a situation where the BS 100 is instructed through the network infrastructure to use 1.5 dB steps, but implements only 1 dB and 2 dB steps. In the method according to the invention, the BS 100 considers the received power control commands in pairs. For use during smooth handover, it is advantageous for these groups to be aligned with odd or even numbered frame boundaries, since the frame contains odd numbered time slots 15. The definition of an even or odd frame may be determined by a concatenated frame number or a system frame number. Such alignment ensures that different BSs 100 performing emulation algorithms in accordance with the present invention operate in a similar manner in an active set.

In the first time slot of each pair, BS 100 always implements a power step of 1 dB in the direction given by the sign of the received power control command, where the sign is negative if the received command is zero. And is considered positive if the received command is one. In the second time slot, BS 100 implements a power stage of 2 dB if the received power control command is of the same sign as received in the first slot, or if the sign is reversed, a power of 1 dB in magnitude. Implement the steps. If the BS 100 implements only 1 dB steps, more than one 1 dB step may be performed in a single time slot if a larger step size is required by the emulation algorithm. The resulting power change is as follows.

         Command        Power change First slot Second slot First slot Second slot    0    0   -1 dB   -2 dB    0    One   -1 dB   +1 dB    One    0   +1 dB   -1 dB    One    One   +1 dB   +2 dB

The method described above can be generalized to handle the case of emulating a step size equal to (x + 0.5) dB, where BS 100 is suitably equipped with a power step of x dB in the first time slot. And a power step of xdB or (x + 1) dB in the second time slot, thereby implementing steps of xdB and (x + 1) dB.

Other generalizations are also possible. Consider a case of emulating a step size equal to (x + a) ΔdB, where Δ is the smallest step size supported by BS 100 and x is an integer and 0 <a <1. Each time BS 100 receives a power control command, it performs the following calculation.

S _i = S _i-1 + Pa

Where P is -1 when the received command has a value of 0 and +1 when the received command has a value of 1. S _i-1 is initialized to zero in the first time slot, and then becomes the value of S _i in the previous time slot.

If S _i ≦ 0.5, the magnitude of the power step implemented by BS 100 is xΔdB. If S _i > 0.5, the magnitude of the power step implemented by BS 100 is (x + 1) ΔdB, and BS 100 subtracts P from S _i .

Now consider the case of emulating a step size of (x + a / b) ΔdB, where x, a and b are integers and a <b. BS 100 considers the power control commands received in the group of b. For the case of a smooth handover, for the same reason as described above for the basic emulation algorithm, it is preferable that the groups are aligned with odd or even numbered frame boundaries.

BS 100 divides the group of b time slots into sub-groups so that the number difference of time slots in each sub-group is at most one. In all time slots except the last time slot in each sub-group, BS 100 always implements a power step of magnitude xΔ in the direction given by the sign of the power control command received in that slot. In the last slot of each sub-group, BS 100 implements a power step of magnitude (x + 1) ΔdB if the received power control commands to all slots of that sub-group are of the same sign, If they are not the same sign, they implement a power step of magnitude xΔdB. This method ensures that the error in power level is never greater than the larger of a / bdB and (1-a / b) dB.

The method described above may also be further generalized to include emulation of any step size that is intermediate between the two step sizes supported by BS 100 or MS 110.

In the foregoing description, any criterion for emulating the step size by the MS 110 to control the power of the uplink transmission 124 may be based on the BS 100 to control the power of the downlink transmission 122. By the same can be widely used, and vice versa.

Moreover, the foregoing detailed description relates to a system in which a power control command is sent to the station separately from the instructions to set the power control step size of the station. However, the present invention is suitable for use within the scope of other systems. In particular, the present invention can be used in any system where there is a variable power control step size and the station is instructed to use a specific value for this step. It may also be used in a system in which the power control step size is fixed or nearly fixed while the power control step size emulation method is used. The specific step size to be used by the station may be determined by the network infrastructure, BS 100, or MS 110. The specific step size can also be determined by negotiation between any of these individuals.

By reading this specification, other variations will be apparent to those skilled in the art. Such variations may include other features that are already known in the wireless communication system and may be used instead of or in addition to the features already described herein.

In the present specification and claims, although the terminology referred to as a single element is used, this does not exclude the presence of a plurality of such elements. Moreover, the word "comprising" does not exclude the presence of elements or steps other than those described.

The invention is applicable to the scope of wireless communication systems, for example UMTS.

Claims (15)

A wireless communication system having a communication channel between a first station and a second station, wherein the first station is capable of transmitting its transmission power at a short width of a short width required by the second station. 12. A wireless communication system having a transmitter adapted to send a power control command to a second station to instruct coordination, The second station processes the plurality of received commands in response to receiving a command to adjust the transmit power to a short width of an unsupported short width size, and transmit power by the corresponding plurality of steps of at least one supported step size. And a controller adapted to adjust the control. The method of claim 1, wherein the controller adjusts the transmit power to an unsupported step size step of (x + 0.5) ΔdB, where x is an integer and ΔdB is the minimum step size supported by the second station. Upon receipt of the command, the received command is processed in pairs, and if the second command pair has the same sign as the first command pair, a step of size (x + 1) ΔdB, and the first command pair and the second And if the command pair is of opposite sign, a step size of xΔdB is adapted to adjust the transmit power to a step size of xΔdB in response to the subsequent first first command pair. The unsupported short width magnitude (x + a) ΔdB of claim 1, wherein x is an integer, a is between 0 and 1, and ΔdB is the minimum width magnitude supported by the lane-station. Maintains a running sum of the difference between the sum of the widths of the received commands and the sum of the implemented power control widths upon receipt of the command to adjust the transmit power at a short width, and between the sums if If the difference is greater than 0.5Δ, it is adapted to execute a short width size of (x + 1) ΔdB, and if not, a short width size of xΔdB. 4. A wireless communication system according to any one of the preceding claims, wherein the first station is adapted to transmit a plurality of power control commands of a predetermined position in the frame. 5. The system of claim 4 wherein the number of power control commands is accurately separable by the number of power control commands transmitted in a frame. A wireless station for use in a wireless communication system, the wireless station having a controller adapted to adjust its transmit power step by step in accordance with a received power control command, the wireless communication system comprising: The controller processes a plurality of received commands and, upon receiving the command to adjust the transmit power to a short width of an unsupported step size, transmit power to a corresponding plurality of short widths having at least one supported short width size. A wireless station, characterized in that it is adapted to adjust. 7. The controller of claim 6, wherein the controller adjusts the transmit power to a short width of unsupported (x + 0.5) ΔdB, where x is an integer and ΔdB is the minimum step size supported by the lane-station. Upon receipt of the command, process the received command in pairs and, if the second power control command of the pair has the same sign as the first power control command, with a short width of (x + 1) ΔdB, and And if the first and second power control commands have opposite signs, adjust the transmit power to a short width of xΔdB in accordance with the first command of the command pair, followed by a short width of xΔdB. 7. The non-supported short amplitude magnitude of claim 6, wherein x is an integer, a is between 0 and 1, and ΔdB is the minimum step size supported by the lane-station. In response to receiving a command to adjust transmit power at a short width of, maintaining a running sum of the difference between the sum of the short widths of the received commands and the sum of the power control short widths executed, and the sum A step size of (x + 1) ΔdB if the difference is greater than 0.5ΔdB, and a step size of xΔdB otherwise. A method of operating a wireless communication system having a communication channel between a first station and a second station, wherein the first station transmits its own at a short width of the short width required by the second station. 10. A method of operating a wireless communication system comprising transmitting a power control command to instruct to regulate power. The second station processes the plurality of received commands in response to receiving a command to adjust the transmit power to a short width of unsupported short width size, and to a corresponding plurality of short widths having at least one supported short width size. Adjusting the transmit power. 10. The apparatus of claim 9, wherein the second station is configured to transmit transmit power at a short width of unsupported (x + 0.5) ΔdB, where x is an integer and ΔdB is the minimum short amplitude size supported by the second station. Processing the received command in pairs upon receipt of the adjusting command, and if the second command of the pair has the same sign as the first command pair, a short width of magnitude (x + 1) ΔdB, and If the first command and the second command are opposite signs, implementing a step width of xΔdB in response to the first command of the pair following a step of magnitude xΔdB. 11. A method according to claim 10, characterized in that the transmission in the channel occurring in the frame and the pairs of power control commands are aligned with respect to the beginning of the even-numbered frame. 11. The method of claim 10, wherein the step of transmitting in a channel occurring in a frame is characterized in that the pairs of power control commands are aligned with respect to the start of an odd-numbered frame. 10. The unsupported short width size (x + a) of claim 9, wherein x is an integer, a is between 0 and 1, and ΔdB is the minimum step size supported by the sub-station. Maintaining a current running sum of the difference between the sum of the steps of the received command and the sum of the implemented power control steps upon receipt of the command to adjust the transmit power in steps of [Delta] dB; If the difference between the sums is greater than 0.5Δ, executing a step size of (x + 1) ΔdB, otherwise step size of xΔdB. 10. The method of claim 9, characterized by transmitting on the channel occurring in a frame, and wherein the plurality of power control commands have a predetermined position relative to the start of each frame. . 15. The method of claim 14, wherein the number of the plurality of power control commands is accurately separable by the number of power control commands transmitted in a frame.

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