KR100795463B1 - Radio communication system, station for use in such a radio communication system, and method of operating such a radio communication system - Google Patents

Abstract

The wireless communication system has always made power control for transmission between the first station and the second station. The second station sets its transmit power to the first station in response to a power control command received from the first station. The first station determines from the second station when it was synchronized to the transmission and informs the second station about the synchronization. After signaling synchronization, the rate of adjustment of transmit power by the second station is increased (508). The changed rate of power control can be achieved by tailoring the power control step size, otherwise changing the power control command received in response to the second station, or by changing its reception rate for the power control command. These techniques require significant time for synchronization to be established, thus overcoming the problem that transmission power can be increased too much and there is a risk of causing unacceptable interference.

Description

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

The present invention relates to a wireless communication system, and further relates to a first station and a second station for use in such a system, and to a method of operating such a system. It should be understood that such techniques are equally applicable for use in other mobile wireless systems, as long as the system is described with particular reference to the emerging Universal Mobile Telecommunication System (UMTS).

In a wireless communication system, there are two basic types of communication required between a base station (BS) and a mobile station (MS). The first is user traffic, for example voice or packet data. The second is control information, which is required to set and monitor various parameters of the transmission channel so that the BS and MS can exchange the required user traffic.

In many communication systems, one of the functions of the control information is to enable power control. Requiring power control of signals transmitted from the MS to the BS, the BS receives signals from other MSs at approximately the same power level while minimizing the transmit power required by each MS. Power control of the signal transmitted by the BS to the MS is required so that the MS receives the signal from the BS with a low error rate while minimizing the transmit power, thereby reducing interference with other cells and wireless systems. In a two-way wireless communication system, power control operates normally in a closed loop manner, whereby the MS determines the required changes in transmit power from the BS, signals these changes to the BS, and vice versa.

An example of a combined time and frequency division multiple access system employing power control is Global System for Mobile Communication (GSM), where the transmit power of both the BS and MS transmitters is controlled in 2 dB steps. . Similarly, power control implementations in systems that employ spread spectrum code division multiple access (CDMA) techniques are disclosed in US-A-5 056 109.

The problem with these known techniques is that it may take some time for the power control loop to converge satisfactorily at the start of the transmission or after the transmission is interrupted. Until such convergence is made, the data transmission will be received in a corrupted state if its power level is too low and will cause extra interference if its power level is too high.

One known solution to this problem is disclosed in the international patent application WO 00/42716 filed by Koninglike Philips Electronics, which delays the start of data transmission by a sufficient time for power control to ensure that a satisfactory reception of the data transmission is achieved. Converge as much as possible. This period between the start of the control transmission and the start of the data transmission is known as the power control preamble. However, in some systems, part of the power control specialization period is used for synchronization (where the BS derives the received timing of the MS transmission, for example by locking it to the code used by the MS in the CDMA system). Thus, there is a risk of increasing the transmit power of the MS to a level that causes unacceptable interference before the BS is synchronized.

This problem is addressed in part in one UMTS embodiment by the BS transmitting a specific pattern of power control commands before synchronization is achieved, the pattern preventing the MS from making a fast change in transmit power.

It is an object of the present invention to address the problem of proper power control at the beginning of transmission.

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 the second station comprises: receiver means for receiving a power control command from the first station; Means for adjusting its transmit power to the first station in response to a power control command, the first station being in synchronization with the means for determining when the first station is synchronized to a transmission from a second station; Signaling means for signaling to a second station that it has been achieved, the second station changing the operation of the station in response to a notification that synchronization has been achieved so that the rate of change in transmit power is after synchronization is signaled by the first station. Means for making it larger than before.

Signaling by the first station that the first station has achieved synchronization allows the second station to change its operation in a range of ways to increase the rate of change of transmit power of the second station. For example, the second station may increase its power control step size after synchronization. The second station may ignore some power control commands by turning off its receiver before synchronization is achieved.

According to a second aspect of the present invention, a station for use in a wireless communication system having a communication channel between a station and another station is provided, wherein when the station is synchronized to transmissions from other stations, Means for determining whether or not a signal means for signaling another station that synchronization has been achieved.

According to a third aspect of the invention, there is provided a station for use in a wireless communication system having a communication channel between a station and another station, wherein a receiver means for receiving a power control command from another station is provided, A power control means is provided for adapting its transmit power to another station in response to the power control command, and in response to a notification that synchronization has been achieved, change the operation of the station to transmit after synchronization has been signaled by another station previously. Means are provided for allowing the rate of change of power to be greater than before.

According to a fourth aspect of the invention, a method is provided for operating a wireless communication system having a communication channel between a first station and a second station, wherein the second station receives a power control command from the first station. And a power controller that adjusts its transmit power in response to the power control command to the first station, the method determining when the first station is synchronized to a transmission from the second station. Signaling to the second station that it has been achieved; and in response to the notification, the second station changes its operation so that the rate of change in transmit power can be greater than before after synchronization is signaled by the first station. Include.

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

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

2 illustrates a conventional manner of establishing a communication link.

3 illustrates a known manner of establishing a communication link with a delayed start to data transmission.

4 illustrates an improved way of establishing a communication link with a delayed start to data transmission.

5 is a flow diagram illustrating a method in accordance with the present invention for adjusting the rate of change of transmit power during a power control period.

In the figures, like reference numerals have been used to indicate corresponding features.

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

One embodiment of a UMTS frequency division duplex system uses the scheme illustrated in simple form in FIG. 2 to establish a communication link between the MS 110 and the BS 100. The link is initiated by the MS 110 sending a request 202 (REQ) for resources on the uplink channel 124. If BS 100 receives the request and has the resources available, BS 100 sends an acknowledgment 204 (ACK) on downlink channel 122 that provides the information necessary for the communication to be established. . After the grant 204 is sent, two control channels (CON), i.e., uplink control channel 206 and downlink control channel 208, are established, and uplink data channel 210 is set to MS 110. ) Is set for data transmission to BS 100. In some UMTS embodiments, there may be additional signaling between grant 204 and the establishment of control and data channels.

In this manner, separate power control loops can operate on the uplink channel 124 and downlink channel 122, each separate power control loop including an inner and an outer loop. The inner loop matches the received power to match the target power, and the outer loop adjusts the target power to the minimum level that will maintain the required quality of service (eg, bit error rate). However, this approach results in the initial power level and quality target being derived from open loop measurements when transmissions on control channels 206 and 208 and data channel 210 begin, and the measurements differ from the newly initiated channel in which the measurements were made. The problem with this is that it may be inaccurate enough because it will have features. This result indicates that if data is transmitted at too low a power level, data transmission at the start of data channel 210 will be received in a corrupted state, and if data is transmitted at too high a power level, it will cause extra interference. Is the point.

One known solution to this problem is disclosed in patent application WO 00/42716 by Koningleke Philips Electronics and illustrated in FIG. 3, which initiates the uplink data transmission 210, BS (100). Delays by a period 312 which is long enough for the power control to converge sufficiently to allow satisfactory reception of the data transmission. This period 312 is known as a power control preamble (PCP), which typically includes a delay of one or more frames (each 10 ms in length). The delay 312 can be predetermined or alternatively can be dynamically determined by either the MS 110 or the BS 100 (which can detect convergence by monitoring the downlink power control information). The additional overhead in the transmission of redundant control information on control channels 206 and 208 is reduced Eb / No (energy / noise density per bit) for user data received by BS 100 over data channel 210. It is balanced.

The purpose of the power control specialized period 312 is to allow the inner power control loop to converge the transmit power on the uplink channel 124 and the downlink channel 122 above the required level of each of the channels before data transmission begins. To do it. Thus, a larger power control step size than normal can be used for uplink channel 124 during power control telegram 312. One way to implement this is disclosed in the international patent application WO 00/41466 to Koninglike Philips Electronics, in which a large power control step size is used initially, the step size being changed by the required power adjustment. When it is reduced.

However, the use of large power control step sizes creates additional problems. The first part of the uplink power control telegram 312 may be required by the BS 100 to enable it to be synchronized to the uplink control channel transmission 206. Using a larger step size before BS 100 is synchronized may allow MS 110 to increase its transmit power to be sufficient to cause an unacceptable level of interference in the cell.

This problem can be avoided in systems built in accordance with the present invention by delaying the use of larger power control step sizes for some time after the start of the power control telegram 312. This solution is shown in FIG. 4, where the power control telegram 312 is divided into two parts, i.e., the synchronization part S, which enables the BS 100 to be synchronized with the transmission from the MS 110. 414 and the power control convergence portion (C) 416. A small (or even zero) power control step size is used during the synchronization portion 414, while a larger step size is used initially during the power control convergence portion 416. As an alternative to using a smaller power control step size, the rate at which power control commands are issued can be reduced. As a further alternative, the use of smaller power control step sizes has been disclosed in International Patent Application WO 00/74260 (not published on the priority date of this application) by Koninglike Philips Electronics, and in some UMTS implementations. As needed, after receiving a plurality of power control commands from BS 100, it may be emulated by MS 110, which only adjusts its output power. Other technique ranges may also be applied, for example, the MS 110 may use a gated reception technique, in which the MS 110 turns off its receiver for a predetermined period of time.

A common factor in all of the above methods is that the power regulation rate is lower during the synchronization portion 414 of the power control telegram 312 than during the power control convergence portion 416. The length of the synchronization portion 414 may be predetermined. For example, in a UMTS embodiment where the power control telegram 312 is one frame in length (which is subdivided into 15 slots), some simulations may result in six slots of suitable length for the synchronization portion 414. It can be suggested. This charges nine slots for power control convergence to be achieved.

Alternatively, BS 100 may signal MS 110 when BS 100 is synchronized. FIG. 5 is a flow diagram illustrating one embodiment of such a scheme, which is a particularly convenient method of performing the scheme in a UMTS embodiment using a Transport Format Combination Indicator (TFCI) field. The TFCI field is present in most of the slot formats in the transmission on the downlink 122 and includes 2, 4, 8 or 16 bits per slot in the current UMTS specification. The TFCI bits are typically all set to '0' during power control telegram 312.

The method begins at step 502 where the MS 110 sets its power control adjustment rate to a small (or zero) value at the start of the synchronization portion 414. The MS then repeatedly receives the TFCI bit at step 504, and tests at step 506 whether the bit is set to '1'. BS 100 signals that synchronization has been achieved by switching to transmitting the TFCI bit set to '1', thereby signaling the end of synchronization portion 414 and the beginning of power control convergence portion 416. Upon detecting this change, the test at step 506 passes and the MS 110 proceeds to increase its power control adjustment rate at step 508, thereby improving power control convergence. Embodiments of the present invention may operate power control at a lower rate than normal before synchronization is achieved, and / or at a higher rate than normal immediately after synchronization is achieved.

The test at step 506 may require examining the value of each TFCI bit as it is received. Alternatively, test 506 may operate on the value of all of the TFCI bits received in the slit. In this case, the patterns of the TFCI bits in the slots need not all be the same. However, considering the case of four bits per slot, in the presence of noise, the change from 0000 to 1111 is significantly more likely to be detected more accurately than the change from 0101 to 1111, for example. An additional advantage of requiring all bits to be equal is that the test 506 will minimize the length of the synchronization portion of the power control telegram 312 as each TFCI bit is received (this results in a minimum). Or whether it works as an implementation-dependent option for the MS 110 whether or not it operates on a set of bits received during this one slot, thereby improving to be robust to errors upon reception.

The period during which the larger power control adjustment rate is used can be determined by reducing the step size when the downlink power control command first changes sign, in the same way as disclosed in International Patent Application WO 00/41466 by Koninglike Philips Electronics. It may be. Alternatively, larger adjustment rate usage may end after a predetermined number of slots. Thus, it is not necessary for the power control convergence portion 416 to persist until the end of the power control telegram 312.

A further refinement that will overcome the effects of errors in power control commands that may cause the power control adjustment rate to decrease too early may reach the target signal to interference ratio (SIR) from the MS 110. When the BS 100 will signal. One possible way of implementing this improvement is also illustrated in FIG. 5. Once the MS 110 has increased its power control adjustment rate at step 508, at step 510, continue to receive the TFCI bit, and at step 512, the TFCI bit is set to '0'. Test for presence BS 100 signals that convergence has been reached by setting the TFCI bit back to '0' and, in response, passes the test at step 512 and the MS 110 passes its power at step 514. Reduce control adjustment rate. Test 512 may operate on a single TFCI bit or set of bits in the same manner as test 506.

The present invention may be applied to a system without a power control telegram 312, that is to say a system in which control and data transmission begin simultaneously, or a system in which data transmission begins before synchronization is achieved. In such a system, when the BS 100 determines that the BS 100 is synchronized to the transmission from the MS 110, it signals this information to the MS 110. The signal may be in any convenient manner and includes the use of downlink control channel 208, the use of the TFCI bits as described above, or the use of a predetermined pattern of power control commands.

The MS 110 is controlled so that the power control adjustment rate is lower than after that before synchronization is signaled. In addition to changing the power control step size, as described above, such a result may be achieved by the MS 110 ignoring any fraction of the power control command sent by the BS 100. The MS 110 may even turn off the receiver of its transceiver 114 for a predetermined period of time until it receives a signal that synchronization has been achieved. Other corresponding methods will be apparent to those skilled in the art.

Although the above description examined data transmission on the uplink channel 124, the technique is equally applicable to data transmission or bidirectional transmission on the downlink channel 122. Although the present invention has been described in the context of improving power control at the start of transmission between two stations, it may be applicable even in situations where synchronization is temporarily lost.

Embodiments of the present invention have been described using spread spectrum code division multiple access (CDMA) techniques, such as those used in UMTS embodiments, for example. However, it should be understood that the present invention is not limited to use in a CDMA system. Similarly, although embodiments of the invention have been described assuming frequency division duplexes, the invention is not limited to the use of such a system. It can also be applied to other duplexer methods, such as the time division duplex method (although power control rates are normally limited to once per transmission burst in such systems).

Upon reading the present invention, other changes will be apparent to those skilled in the art. Such modifications may involve other known features in the design, manufacture, and use of the wireless communication system and its components, which may be used instead of or in addition to the features already described herein. Although the claims are formed with particular combinations of features in the present application, the disclosure of the present application also includes any novel feature or combination of features disclosed herein which is disclosed, implicitly or in combination with it, which It should be understood that whether or not it relates to the same invention as currently claimed in any claim, whether or not it alleviates some or all of the same technical problems as the invention does. As such, Applicant discloses that new claims may be formed with such features and / or combinations of features while enforcing the present application or any further application derived therefrom.

In this specification and in the claims, the singular forms preceding the elements do not exclude the presence of a plurality of such elements. Furthermore, the word "comprising" does not exclude the presence of elements or steps other than the listed elements or steps.

As mentioned above, the present invention relates to a wireless communication system, and further relates to a first station and a second station for use in such a system, and to a method of operating such a system.

Claims (11)

A wireless communication system comprising a communication channel between a first station and a second station, The second station comprises receiver means for receiving a power control command from the first station, and power control means for adjusting its transmit power to the first station in response to the power control command, The first station comprises means for determining when the first station is synchronized with a transmission from the second station, and signaling means for signaling to the second station that synchronization has been achieved, The second station, in response to the notification that synchronization has been achieved, changes the operation of the second station so that the rate of change in transmit power can be greater than before after synchronization has been signaled by the first station. Means, The communication channel from the second station to the first station includes a control channel for transmitting control information and a data channel for transmitting data, The second station includes means for delaying the start of transmission of the data channel until after the start of transmission of the control channel; Wireless communication system. delete A station for use in a wireless communication system having a communication channel between a station and another station, Means for determining when it is synchronized to transmissions from other stations, and signaling means for signaling to other stations that synchronization has been achieved, said signaling means regularly signaling synchronization achievements by altering the transmitted signal. Station for use in communication systems. delete A station for use in a wireless communication system having a communication channel between a station and another station, Receiver means for receiving a power control command from another station, In response to the power control command, there is provided a power control means for adapting its transmit power to another station, In response to a notification that synchronization has been achieved, a means is provided for changing the operation of the station so that a rate of change in transmit power can be greater than before the synchronization was signaled by another station, Means for modifying the response of the power control means with a power control command received in response to a signal that synchronization has been achieved. delete 6. Station according to claim 5, characterized in that the power control means is operable to use a larger power control step size than before after synchronization has been achieved. 8. Station according to claim 5 or 7, characterized in that the power control means is operable to ignore a portion of the power control command received before synchronization is achieved. 9. A station according to claim 8, wherein said receiver means is turned off when a power control command should be ignored. A method of operating a wireless communication system having a communication channel between a first station and a second station, the method comprising: The second station includes a receiver for receiving a power control command from the first station, and a power controller that adjusts its transmit power to the first station in response to the power control command, The method comprises the steps of the first station determining when the first station is synchronized with a transmission from the second station to signal to the second station that synchronization has been achieved, and the second station in response to the signal. Altering its operation such that the rate of change of transmit power is greater than before after synchronization has been signaled by the first station, The first station changes the signal transmitted regularly to signal the achievement of synchronization, How a wireless communication system works. delete

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